Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
PHOSPHORUS LOSSES THROUGH TRANSFER, SOIL
EROSION AND RUNOFF:
PROCESSES AND IMPLICATIONS
Ward, J.e. Talbot, J.M. Denne, T. and
Abrahamson, 1>1.
December 1985
Information Paper No.3
Centre for Resource Management
Lincoln College and University of Canterbury
TABLE OF CONTENTS
FOREWARD
1. INTRODUCTION
1.1 The nature and scope of the problem
1.2 Specific objectives
2. PHOSPHORUS LOSS PROCESSES
2.1 Stock transfer
2.2 Management of transfer loss
Page
i
1
1
1
1
2
4
2.3 Water runoff and soil erosion 5
2.4 Management of losses caused by runoff and erosion 15
2.5 Riparian zones and wetlands 16
3. IMPLICATIONS OF PHOSPHORUS IN WATER RESOURCES
3.1 Sources of phosphorus loading
3.2 Effects of phosphorus ·additions on primary
productivity and sediments
3.3 The trophic status of New Zealand lakes
4. CONCLUSIONS AND POLICY IMPLICATIONS
4.1 Future risks
4.2 Management needs and approaches
ACKNOWLEDGEMENTS
REFERENCES
19
19
20
24
29
30
31
33
34
FOREWORD
Phosphate rock is a strategic material upon which pastoral agriculture
and all New Zealanders depend. Phosphate fertilizer has no close
substitute, and is, therefore an important limiting factor to agricultural
productivity. The future wellbeing of the country depends on its
efficient acquisition, manufacture, distribution and use.
This report is part of a larger cross-disciplinary study carried out
by Centre staff on the multiple dimensions of phosphate management in
New Zealand. The report presents an examination of phosphorus losses
from the production system and the attendant consequences on environ
mental quality. Special emphasis is given to hill country loss
mechanism, where it is known that significant amounts of phosphate
fertilizer are picked up in surface runoff and/or are displaced by
grazing animals. The longer term consequences of nutrient loading
on downstream water bodies are discussed, and the policy and management
implications for maintaining current water quality levels are highlighted.
K.L. Leathers
Study Team Leader
1
1. INTRODUCTION
Phosphorus is added to New Zealand soils to increase plant growth
but is lost from the pasture system by stock transfer, soil erosion
and water runoff. When this nutrient reaches waterways, growth of
aquatic plants is promoted; excessive growth results in changes to
water quality and potential uses of the water. Phosphorus is
retained by lake sediments so additions have long term consequences
on lake and downstream water quality. While phosphorus losses to
the farmer may be small, the costs borne by society may be large
because of the long term effects and the expense of any remedial
measures.
1.1 The nature and scope of the problem
The amount of phosphate fertiliser applied annually to New Zealand
pastures has been approximately two million tonnes in recent years.
To sustain growth of agricultural exports in coming decades, greater
levels of fertiliser phosphorus may be required. Since a significant
proportion of the applied fertiliser is lost to the production system,
efficiency in on-farm use if becoming an important concern for farm
managers and policy makers. On-farm losses raise production costs
and lower farm incomes, while phosphorus enrichment of freshwater
bodies has implications for environmental quality.
1.2 Specific objectives
This paper examines what is currently known about fertiliser phosphorus
losses in New Zealand pastoral systems. It focuses on the potential
above ground losses (and costs) to the farmer, management options
for conserving phosphorus, and on the ecological effects and potential
social costs of fertiliser phosphorus additions to waterways and
approaches to avoiding or managing these unintended impacts. Our
understanding of the issues, and factual evidence which underlines
these two main theses, is explored in some detail.
2. PHOSPHORUS LOSS PROCESSES
Fertiliser phosphorus losses result from four basic mechanisms:
1. below ground phosphorus cycling processes (discussed by
Scott, 1985);
2
2. embodied phosphorus in animal carcases and products
removed from the farm;
3. 'animal transfer' or the displacement of dung phosphorus
to locations on the farm which effectively removes this resource
from entering into subsequent production cycles; and,
4. phosphorus lost via water runoff and soil erosion.
The relative order of magnitude of these losses is not known at present,
nor are the potential savings that might be realised in their control
the value of phosphorus conservation. Because the first two mechanisms
of loss are largely uncontrollable this paper considers only the nature
of stock transfer, soil and runoff losses and their potential for
control through improved farm management.
2.1 Stock transfer
Phosphorus cycles in ecological systems through the action of organisms
at different trophic levels. Herbivores have an important role in
cycling. Because of cultural practices, sheep and cattle are the
dominant herbivores of New Zealand pastoral agricultural systems
(although other herbivores such as horses and deer may be locally
dominant), and management aims to maximise their production. Phosphorus (P)
is applied to pastoral systems to increase plant production to provide
food for livestock. Phosphorus is consumed with the plants; some is
retained by the animal and some is returned rapidly to the soil-plant system
via excretion. Although the amount returned may be quite large,
phosphorus is concentrated largely in dung and deposits may be dis-
tributed in such a way that the phosphorus is unavailable to much
of that system.
The distribution of cattle dung is more or less random. However,
O'Connor (1981) found that the annual return of dung at 3 cows ha- l would
cover only 5.5% of the grazed area. This would leave appreciable
areas of the paddock without phosphate from that source for several
years.
3
Sheep dung tends to be clumped on small areas. This is related to
a behavioural characteristic of sheep in which they tend to collect
together at night. Gillingham and During (1973) found a net gain
of 28.6 kg P ha- l on a sheep camp occupying 6.4% of a block and an
average net loss of 5 kg P ha- l on the other areas. Gillingham (1980)
found more than 88% of the dung on campsites in two paddocks of north
and south aspects, these sites occupying 20.1% and 12.2% of the total
pasture respectively.
Areas grazed heavily can be depleted of phosphorus if fertiliser is
not applied (Hilder, 1966). Sheep tend to camp and excrete at high
points, so there is a transference of phosphorus in dung to higher
areas as shown in Figure 1. However, greater movement of phosphorus
in runoff means complete depletion would not occur on steep slopes.
E8~
.s::.-6 g'(1)
4 ~CtI...
C)
10
12
-2
....... No.of faeces
11-. Grass length
o
~
.. \. /---/ "".:::><:~ /.--.
··1........ ...•.......•.... .....•
-E,-12(1)0-'-(1)10-(1)
E~ 8"0
Eo 6
('II
1\en(1) 4o(1)~_ 2ooz O ..........-....-......- .........,-....-..,--po-...,.-..,-... 0
6 12 18 24Distance downslope (m)
FIGURE 1: Mean number of faeces> 2 cm diameter per m2
at 3 m intervals down the Wool shed Paddock,Taita, for Enclosure 1 (18 Sept 1975) andEnclosure 2 (20 Oct 1975). Faeces were countedafter grazing; grass lengths were measuredbefore grazing.
(McColl and Gibson, 1979)
4
Overall estimates of phosphorus loss through animal transfer are not
available.
2.2 Management of transfer loss
Reduction of phosphorus loss caused by stock transfer through direct
stock management (shepherding) is not presently practised in New zealand.
Current management practices such as fencing, rotational and controlled
grazing may help.
Gillingham and During (1973) suggest it is possible to avoid topdressing
10% of a block (i.e. stock camps and ridges) without affecting pasture
yields in high country development. However, the economic viability
of this practice has not been demonstrated (Saunders et al., 1981).
In the high country, fencing steep slopes from gentle slopes would
theoretically reduce transfer losses, as sheep would not be able to
move to and camp on the easier slopes. In practice, the complexity
of land topography limits this.
Planting trees in pasture is a potential source of phosphorus conservation.
Recent experiments by M. Belton and K.F. O'Connor (in prep.) show
that Olsen P levels (plant available P) in soils of different types
are three times higher under exotic forest than under unimproved or
improved pasture. By spacing the trees, sheep would be kept dispersed
when they seek shade or shelter and slope stability would be enhanced.
Systems of management may affect the distribution of dung. While
neither Gillingham (1982) nor Thorrold et al. (1985) could find discernible
differences between continuous and rotational grazing on dung distribution,
stocking rates may influence dung distribution. Thorrold et al.,
(1985) have found that a more even distribution of dung was obtained
on slopes by high stocking rates. Daytime dung frequency was found
to be more closely related to grazing distribution than to resting
or total animal distribution. Correlations between soil Olsen P levels
and dung frequency were low even when night camp areas were included,
but Olsen P levels were consistently higher in paddocks with higher
stocking rates. It is suggested (ibid) that at high stocking rates,
pasture consumption is high and a more even distribution of phosphorus
5
is returned to the soil as dung, perhaps in more quickly released
forms. At low stocking rates, pasture consumption is low and much
of the phosphorus is retained in the herbage or in the litter from
which it is released more slowly.
There are no quantitative studies on the relative turnover rates of
dung and litter in New Zealand pastures. Microorganisms, earthworms,
temperature and moisture are some of the factors involved in this
process. Addition of earthworms is an effective and increasingly
practiced method of increasing litter and dung turnover rates (Stockdill
and Cossens, 1984), especially in the earthworm deficient yellow brown
earths of otago and Southland.
The economic viability of many indirect methods of stock management
to reduce transfer loss of phosphorus are not known. Increased use
of some methods, such as silvipastoralism and selective topdressing,
appear warranted for the other benefits that accrue.
2.3 Water runoff and soil erosion
Phosphorus is present in soils in various forms which vary in solubility,
and consequently in susceptibility to movement by water. Phosphorus
can be lost from soil by dissolution when contact is made with water
or by erosion of soil particles containing phosphorus. Erosion may
occur by wind or by water. Lost phosphorus may be transported to
waterways and aquatic biological systems in runoff water and attached
to soil.
Phosphorus losses through soil erosion by wind and water are variable
in New Zealand and are related to the land form, soil type, intensity
of land use and climate. In the high country, losses through soil
erosion may be high due to slope instability and heavy rainfall.
In Central Otago and the Canterbury plains wind erosion causes signifi
cant phosphorus losses. The few rates of both wind and water soil
erosion that have been measured point to very high soil losses by
overseas standards on many New Zealand farms (Painter, 1978). Phosphorus
losses through wind erosion have not been quantified but, as with
runoff, may be high on cultivated or recently fertilized land.
6
On well-managed pastoral land phosphorus losses in runoff are usually small.
Because of the reactivity of phosphorus in soils these amounts are
generally regarded as insignificant from an agricultural perspective.
But as phosphorus is often a limiting nutrient for aquatic biological
systems, small additions of phosphorus may have a considerable effect
on the biological productivity of rivers and lakes.
Runoff may be categorised as surface, subsurface or groundwater as
defined by Langbein and Iseri (1960 in Ryden et al, 1973). These
different types of runoff transport different forms of phosphorus.
Surface runoff transports particulate and dissolved phosphorus, sub
surface runoff transports dissolved and some colloidal phosphorus,
and groundwater transports dissolved phosphorus (Ryden and Syers,
1973).
There have been some differences of opinion in the New Zealand literature
regarding the quantitative importance of different runoff types for
the transport of phosphorus. It is widely recognised that phosphorus
is strongly held by most soils, and that losses in subsurface and
groundwater runoff are insignificant in comparison with losses in
surface runoff (Baker et al., 1975). But some workers have suggested
that fluctuations in available phosphorus in subsurface runoff may
often be similar and in some cases higher than those in surface flows
(Ryden et al., 1973; Syers, 1974). While it can be argued that the
soils tested by these authors are prone to leaching, it is still apparent
that there is uncertainty regarding the importance of different runoff
types to water enrichment.
Table 1 presents various data on the amount of phosphorus (loading)
in different forms of runoff from pasture systems. The largest amounts
of all forms of phosphorus appear to be carried in surface runoff.
Particulate phosphorus (PP) incorporated in soil particles comprises
the major portion of total phosphorus (TP) carried. Thus Burwell
et al., (1975) found 96% of TP was transported in the form of PP over
a variety of soil cover treatments. Owing to the low energy of surface
runoff there tends to be preferential transportation of small sized
particles (clay and silt sized colloids). Small soil particles tend
7
to contain higher amounts of phosphorus than large particles. Thus
eroded material has higher concentrations of phosphorus than the soil
from which it is derived (Stoltenberg and White, 1953).
TABLE 1: Phosphorus loadings in runoff
Runoff Form P 10a?-ing1
P Fertiliser ReferenceComponent ofP* kg ha yr- applied
N. AmericaGroundwater TP 0.1 + Minshall et a1.
(1969 )
Subsurface TDP 0.01 Bolton et a1.0.12 + (1970)
Surface and TP 0.7 § + Witzel et a1.subsurface (1969)
Surface Soluble P 0.22 + Schuman et a1.TP 0.28 + (1973)
Surface Available Stoltenberg &
P 0.2 + White (1953)
New ZealandAccelerated DIP 0.07 - 0.44 + Sharpley and
subsurface TDP 0.10 - 0.52 + Syers (1979c)TP 0.18 - 0.89
Surface DIP 0.28 - 0.50 Sharpley & Syers1.66 - 2.80 + (1979c)
TDP 0.31 - 0.611.66 - 2.89 +
TP 0.85 - 1.283.67 - 5.63 +
Surface TP 0.7 - 1.0 + Lambert et a1.(1986)
*TP = Total Phosphorus; DIP = Dissolved Inorganic Phosphorus;TDP = Total Dissolved Phosphorus
~Based on extrapolation assuming direct relationship betweenrunoff and nutrient loss.
As additions of phosphorus to waterways via surface runoff generally
occur in large events, phosphorus concentrations in receiving waters
8
may be greatly increased over the short period of time. However,
the immediate effects on the receiving streams may be minimal as amounts
of phosphorus available may be greater than that which can be used
in primary production (McColl et al., 1977). Groundwater and subsurface
runoff provide a more constant supply of phosphorus to waterways.
The effects of phosphorus from these sources on water quality may
be greater than their smaller phosphorus loading suggests when compared
to the effects of phosphorus from surface runoff.
The effects of inputs of phosphorus on receiving waters may be limited
by the absorptive capacities of the sediments. Much of that arriving
in runoff may quickly react or become absorbed. Conversely a very
large proportion of the phosphorus concentration of waterways derives
from stream-bank erosion and the release of inorganic phosphorus (IP)
from suspended and in situ particulate material (Sharpley and Syers,
1979c). Sharpley and Syers (ibid.) present data which indicate
that the major proportion of PP (83%) and TP (71%) transported annually
in stream flow is derived from stream-bank and stream-bed material.
The contribution of dissolved inorganic phosphorus (DIP) and total
dissolved phosphorus (TDP) from these sources were 27% and 42% respectively.
Stream sediments appear to function collectively as a slow-release
pool of phosphorus. Phosphorus which is rapidly absorbed when it
enters the stream is made available over time. Thus the immediate
effects of additions of phosphorus to streams are reduced, but the
effects extend over longer periods of time.
Absorption-desorption processes mean phosphorus loadings can be quite
different at different locations in a waterway or catchment. Measurements
of high phosphorus losses from small plots may not be evidence for pro
portionally large losses from whole catchments. For example, McColl·
(1978b) measured concentrations of reactive phosphorus in a stream3
as high as 13.4 g m- after the application of fertiliser: losses
of reactive phosphorus from the subcatchment were up to 1 kg ha- l
in a single storm: however, losses of reactive phosphorus from the
whole basin averaged 0.004 kg ha- l .
9
Effects of fertiliser on loading
Different types of phosphorus fertiliser probably produce different
effects in terms of additions of phosphorus to waterways. Sharpley
et al., (1978) conducted experiments with dicalcium phosphate (DCP)
as a less soluble alternative to monocalcium phosphate (MCP, as
superphosphate). Both were applied at levels of 50 kg P ha-l . Although
in the short term greater amounts of phosphorus were transported in
surface runoff from MCP applications, the annual TP loss from areas
with DCP applied was 7.09 kg ha-lvs. 5.63 kg ha- l from MCP, equivalent
to 11.5% and 8.8% of fertilizer phosphorus respectively. To our
knowledge, other fertilisers have not been examined for their runoff
effects.
Applications of fertiliser clearly increase the loss of phosphorus
from agricultural land. But some of the dramatic increases in phosphorus
concentrations are measured immediately after fertiliser applications
and are the result of fertiliser falling directly into streams. The
physical and biological effects of these additions depend on sorption
reactions within those streams and dilution within the whole catchment.
In experiments by Sharpley and Syers (1979c) 50 kg P ha- l yr- l was
applied to one of duplicate plots in June of three consective years
and phosphorus losses were measured over the whole study period.
Comparison of phosphorus losses in surface runoff from undrained,
fertilized and unfertilized plots indicate that between 2.9 and 4.8%
TDP and 5.7 and 8.8% TP was lost annually. These losses of fertilizer
phosphorus were greater than observed in overseas studies (Table 2)
although shorter time periods were measured in the latter. Large
losses of phosphorus (6%) were also recorded in runoff from fertilized
pakihi soils on the West Coast of the South Island (Lee et al., 1979).
McColl (1978b) recorded fertilizer phosphorus losses from 0.02 to
1.9% (Table 2). It is suggested (ibid.) that this range in losses and the
low values may be due to chemical adsorption during downstream transport
and hydrological differences in the stream channel regime due to
riparian vegetation. A conservative estimate of 1-2% of applied fertiliser
phosphorus lost in runoff (Table 2) would represent a total of approximately
1600-3200 tonnes P y-l (assuming 1-2% of 2 million tonnes superphosphate
y-l with 8% P).
10
TABLE 2: Percentage losses of P forms from agricultural landafter fertiliser applications
Form of P % fert.P lost
Soluble P 1.01.2
Soluble P 1.3
Soluble P 0.6TP 0.7
DIP 2.0PP 2.9TP 5.3
TDP 2.9 - 4.8TP 5.7 - 8.8
TP 6.0
TP 0.02 - 1.9
TP 2.9
Fertiliser Length Sourcerate 1 of study(kg P ha- ) period
U.S.A.56 Nelson and Romkens
112 (1970 in Burwellet al. 1975)--
50 3 mths Nelson and Romkens(1971 in Sharpleyand Syers, 1979c)
39 6 mths Schumann et a1.(1973)
New Zealand30 4 mths Sharpley and Syers
(1979b)
50 3 yrs Sharpley and Syers(1979c)
42 5 mths Lee et al (1979 )
60 - 76 2~yrs McColl (1978b)
38 4 yrs Lambert et a1. (1985)
Although the percentage of fertiliser lost in runoff (Table 2) is
usually insignificant to the agricultural system (McColl, 1978b),
the change in phosphorus concentrations in receiving waters may be
considerable. For example, the Waingaehe stream which flows into
Lake Rotorua, normally has an orthophosphate concentration of around
Topdressing of adjacent land caused a four-week pulse of
orthophosphate which peaked at 890 mg m- (Fish, 1969), one hundred
times the natural level. Similar trends in change in orthophosphate
concentrations were recorded by Mitchell (1971), Sharpley and Syers
(1979b, 1979c) and Turner et al., (1979).
Effects of animals on loading
Animals can be responsible for large additions of phosphorus to runoff
waters. They exert three major effects on the soil-grass system (Cooke,
1981): by eating the grass short the soil surface is more susceptible
to erosion; closely grazed grass cannot sieve particulate matter in
11
the manner that long grass can; and animal trampling lowers the
infiltration capacity of the soil and increases the likelihood of
surface runoff. In addition, grazing animals are more directly
responsible for additions of phosphorus through dung. Data relating
to the increased concentration of phosphorus in runoff attributable
to grazing are presented by Lambert et al., (1985) and by McColl and
Gibson (1979), Sharpley and Syers (1976a, 1979a) and Turner et al.,
(1979).
Sheep
Scott (1985) has shown that the amount of P returned as sheep dung
(for an 18 stock unit ha-l grazing system) was about 26 kg ha- l yr- l
or equivalent to 0.33 t of superphosphate. Transfer of some of this
dung to waterways is a potential source of phosphorus loading. McColl
(1978a) estimated that dung provided a greater amount of total P to
Lake Tutira than any other source (Table 3).
TABLE 3: Estimated phosphorus loading on Lake Tutira (catchmentsources)
Input
Fertiliser runoff (assuming 1% loss)
Dung/urine runoff
Subsurface runoff
Soil erosion
Other sources
TOTAL
Source: after McColl (1978a)
Cattle
Phosphorus
700 kg y-l
300-1600 kg y-l
300 kg y-l
1000 kg y-l
100 kg y-l
2400-3700 kg y-l {14-21 kg ha- l y
In contrast to sheep who tend to remain on the margins of waterways
and wetlands, cattle are often observed wading in bogs, ponds and
12
streams. In dry seasons cattle are often grazed on swamplands. This
may result in stream channel widening and a change in water column
structure (Skovlin, 1984) and modification of the land drainage system
by interrupting stream flow (Hughes et al., 1971). The cumulative
impact on the catchment of fluctuating stream levels may be considerable,
particularly in downstream locations. Cattle access to these areas
should be strictly controlled to maintain drainage. The advantages
of an intact riparian zone in reducing nutrient losses (see p.16)
and drain clearance costs need to be made clearer. Controlled grazing
by livestock need not affect the ability of the riparian zone to
filter nutrients (Skovlin, 1984). However, the physical conditions
of this zone must be understood and matched to the grazing regime.
The grazing of cattle can have a large effect on phosphorus levels
in stream flows. Sharpley and Syers (1976a) found the loss of total
phosphorus (principally DIP and PP) in surface runoff due to animals
alone, in the weeks following a 24 hour period of grazing by dairy
cattle (25 ha-l ) to be 0.77 kg P ha- l . (This is 27% of that lost
as a result of fertilizer addition alone.) With two or three grazing
events during the period when runoff occurs in the study area (June-1
to September) a maximum of 5.1 kg P ha could have been lost in surface
flow as a result of both cattle grazing and fertilizer addition (10%
of that added). In a later study, Sharpley and Syers (1979b) found
that ten hours of grazing at a pressure of 25 cattle ha- l resulted
in a 100-fold increase in both PP and sediment in a nearby stream.
The effect was short-lived, however, and concentrations decreased
to the pre-grazing levels within two days. The observed increases
could be attributed to the movement of cattle in the stream channel
stirring up bottom sediments and depositing dung in the stream.
Lambort et al., (1985) report runoff losses of 1.5 kg P ha-l y-l
from catchments with rotationally grazed cattle as opposed to losses
of 0.7 kg P ha-l y-l from sheep grazed catchments.
Earthworms
In addition to the effects of grazing animals, earthworms can exert
some influence on phosphorus losses in runoff. Surface casts of
earthworms contain a higher proportion of fine particles than underlying
13
soil and appreciably greater concentrations of inorganic and organic
P. Casts have been found to be more readily transportable in surface
runoff than soil (Sharpley and Syers, 1976b). These authors estimated
for one study area that approximately 14 kg ha- l of inorganic P and
11 kg ha-l of organic P were accumulated in casts during one year.
They also found that casts released considerable quantities of inorganic
and organic P to solution.
Effects of land use on loading
Different land uses produce different levels of runoff. Ryden et
ale (1973) present data relating to runoff from land under different
crops; highest nutrient losses occurred from vegetables, corn, soybeans
and wheat. Losses of phosphorus from intact forest watersheds are
generally much smaller than from agricultural land (Berg, 1980; Cooke,
1979, 1981; McColl et al., 1977; Ryden, et al., 1973; Syers and Ryden,
1973). Cooke (1981) suggests that typical exports of phosphorus from
forest catchments are approximately one tenth of those from pasture catch
ments. Ryden et al., (1973) found runoff from unfertilised forest
land contained concentrations of P lower than that of incident rainfall.
Therefore forests conserve phosphorus. Surface runoff from forests
is also low owing to the protection provided by both canopy and forest
floor vegetation, and the high infiltration capacity usually found
at the ground surface.
Owing to the major contribution to runoff made by phosphorus carried
by eroded sediments, together with the value of vegetation in reducing
runoff and sediment movement, losses from bare ground may be consider
able under any circumstances. Several workers cited by McColl and
Syers (1981) found significant correlations between percent bare ground
and quantities of surface runoff.
Phosphorus in urban runoff originates from sewage, stormwater, industrial
effluents and other waste discharges. Total discharges of phosphorus
in sewage effluent from urban areas in New Zealand have been estimated
at approximately 9000 tonnes y-l (Syers, 1974). Polyphosphates, which
are very soluble and biologically active ingredients of many detergents
(especially in the dairy industry), are significant sources of phosphorus
to waterways (OECD, 1981). Since most urban areas in New Zealand
14
are coastal, total discharges of phosphates to freshwater systems
are probably smaller than those to the sea. McColl (1982) estimated
that 1500 tonnes y-l phosphorus from sewage is discharged to freshwaters.
Preliminary estimates of phosphorus contributions to freshwater systems
from various sources are reported in Table 4. Point source discharges
are apparently only slightly greater than diffuse sources: 18 and
15 tonnes of phosphorus per day respectively. However, fertiliser
phosphorus ranks along with the dairy industry as the highest source
of phosphorus input. Diffuse source dung is next in relative importance.
TABLE 4: Estimates of total phosphorus entering New Zealandfreshwaters
Type of Discharge
POINT SOURCES
Dairy industry
Meat industry
Human sewage
Cowsheds
Piggeries
TOTAL
DIFFUSE SOURCES
Dung
Fertiliser
TOTAL
Source: McColl (1982)
Amount of P (tonnes day-I)
9
0.3
4
1
3.5
18
6
9
15
Point source discharges tend to be localized in certain areas of
the country, particularly in the North Island and near urban centres.
Diffuse sources of phosphorus are more widespread, although they
too are higher in regions of intensive land use. North Island soils
receive two thirds of the applied fertiliser in New Zealand. In 1981-82
approximately 2,000,000 tonnes of phosphate fertiliser was produced.
15
1,347,000 tonnes (68%) was used in the North Island and 624,000 tonnes
(32%) was used in the South Island (New Zealand Meat and Wool Board,
1985). Table 5 shows the breakdown of phosphatic fertiliser into
upland and lowland regions during 1981-82.
TABLE 5: Distribution of phosphatic fertiliser use in New Zealand,1981-82
Location tonnesfertiliser
%
North Island
South Island
Upland
Lowland
Upland
Lowland
457,000
890,000
102,000
522,000
23.2
45.1
5.2
26.5
Source: data from N.Z. Meat and Wood Board (1984)
The consequence of this discrepancy between the islands is clearly
seen in lake trophic levels in the North and South Islands (Figures
3a & b, P 25 & 26).
2.4 Management of losses caused by runoff and erosion
Farm management practices leading to improved water quality,
by reducing fertiliser losses in runoff and erosion, can also reduce
fertiliser requirements without appreciable loss in production or
profit. Such practices include:
- well-engineered roads and tracks, including use of vegetated
buffer strips on downhill slopes;
- the use of well-constructed shelter belts to reduce wind erosion
transport of soil to water bodies;
- improvement in the application of fertiliser - applying the
correct amount at the right time to the land types capable of
generating the highest relative return to the farmer;
- reducing stocking rates in areas prone to significant runoff
problems;
16
- avoiding direct application of fertiliser to stream channels,
seepage zones, land adjacent to lakes and streams, stock camps
and well-defined ridge tops;
- maintaining longer grass at the time of fertiliser application;
- practising conservation tillage, especially overdrilling in
hill and high country development;
- utilising trees more fully, e.g. planting fast-growing thin
crowned species such as poplars in gullies and on steep hillsides
to control erosion or use as cattle fodder, growing a tree
crop in conjunction with pastoralism (silvipastoralism);
- improving overall grazing management, e.g. fencing or correct
stock rotation; and
- improved drainage of land e.g. mole drains (Sharpley and Syers,
1976).
The relative and absolute value of each of these practices in specific
situations is at present not known. More research is needed on these
to enable the best choice of management options to be applied in a
given situation.
2.5 Riparian zones and wetlands
Riparian zone management offers the last chance to filter out nutrients
and sediment before they enter waterways (Pittmans (unpublished),
1979; McColl and Hughes, 1981; Williams and Brickell, 1983). Wetlands,
and areas away from waterways but prone to surface runoff because
of the poor soil infiltration capacity, may also be managed similarly
(Williams and Brickell, 1983; McColl, 1983).
As water passes through the riparian zone suspended matter is filtered
by the soil (McColl and Syers, 1981) or, in wetlands, the particles
settle out, trapping absorbed and organically bound phosphorus in
the sediment (Klopatek, 1978). Dissolved inorganic phosphorus (DIP)
remaining in the water, in solution in the soil or sediment (interstitial
water), or released from the sediments if conditions become anaerobic
(Richardson et al., 1978) is taken up by micro-organisms and plants.
For rooting plants the depth of the rooting zone and thus the species
composition influences the effectiveness of interstitial
17
phosphorus utilization (Williams and Brickell, 1983). Species composition
is also important for year-round uptake of phosphorus. Few overseas
studies have looked at these two aspects (Von Oertzen, 1981), and
no studies have been undertaken in New Zealand.
The efficiency of the riparian zone as a phosphorus trap is affected
by the hydrological regime which may vary from year to year (Sloey
et al., 1978; van de Valk et al., 1978), the biological productivity
of the system and the concentration of phosphorus (Klopatek, 1978).
Under conditions of high phosphorus loading the DIP uptake capacity
of plants soon becomes saturated (Richardson, 1985), and although
particulate phorphorus is still trapped the efficiency of the zone
is reduced. Further, riparian vegetation usually has only limited
possibilities for phosphorus storage unless periodic harvesting is
undertaken (Richardson, 1985; Young et al., 1980). Richardson (1985)
found that 35-75% of the phosphorus taken up by plants was released
during winter dieback. Although this may be partly retained in the
soil or sediments, net retention is dictated by precipitation events
during the time of maximum senescence and nutrient release in late
autumn and winter (Prentki et al., 1978).
Adequate water quality management should be able to be achieved by
responsible land management. Management practices include:
- limited or lax grazing of riparian land and exclusion of
stock when runoff risks are high (Yates, 1971; McColl,
1983);
- using riparian land only for meadow hay production or for
growing specialised trees, especially fodder trees which
are periodically harvested;
- leaving a grass border between tilled land and water
(Burwell et al., 1975);
- protecting and encouraging vegetation of stream and lake
sides, especially thick ground cover e.g. leaving a zone of
native vegetation; and
- prevention of stock entry to streams and wetlands
(permanent stock exclusion fencing would be essential only
in sensitive areas).
18
In all cases where harvesting takes place by grazing or mechanical
means, care must be taken to maintain soil permeability by avoiding
compactation and pugging.
Research to test the operation of the natural water treatment process
ascribed to the riparian zone is only just beginning in New Zealand
(Williams and Brickell, 1983). Nevertheless, the limited evidence
available indicates that riparian zones justify more care than most
other parts of a catchment (McColl, 1978b).
19
3. IMPLICATIONS OF PHOSPHORUS IN WATER RESOURCES
Phosphorus is an essential element for plant growth. In water it
is required by phytoplankton, benthic algae and rooted plants which
are basic living components of aquatic ecosystems. When a large amount
of phosphorus is present in the system, excessive plant growth may
occur. This is acceptable in some countries and in some circumstances.
For example, in China green shallow lakes are an asset for fish farming.
In developed countries, eutrophic lakes (meaning those with 'good
food') are often considered unacceptable because their high biological
production conflicts with scenic and recreational values. Large sums
of money have often been spent cleaning up eutrophic lakes.
The purpose of this section is to review the implications of phosphorus
in water, and to discuss the options for managing the use of phosphate
fertiliser with respect to water quality objectives.
3.1 Sources of phosphorus loading
Phosphorus enters freshwater systems in many ways. Firstly, phosphorus
may be carried into rivers and lakes by way of the following:
- water from springs, streams (including transported
sediment), surface runoff and ground water movements;
- air, such as from rainfall, wind-blown soil, fertiliser,
leaves and dung;
- direct contact with the soil along stream and river
banks and areas of swamp or flooded land;
- plant and animal biomass through natural decay and direct
deposition by animals;
- direct discharge from urban and agricultural sources; and
- release from sediment during periods of anoxia or by
catastrophic events.
Secondly, phosphorus loading may be considered as a point source
diffuse source continuum. Point sources include, for example, discharges
from dairy and meat industries and treated sewage effluent. Diffuse
sources, on the other hand, include such sources as runoff from agric
ultural land. Between these classifications exist cases which may
20
fall into either category, such as stockyard runoff or tip leachates.
A similar situation applies to dung movement. Point sources are much
easier to quantify than diffuse sources.
Phosphorus loading may also be viewed from its temporal aspect. Sources
of phosphorus loading may be continuous or periodic. Continuous sources
of phosphorus typically come from such sources as springs, while
urban discharge, stream inflow and surface runoff sources may come
in pulses according to human decisions or climate. Catastrophic events
such as freak storms, major floods and earthquakes are hard to predict
and equally hard to measure. By contrast, continuous sources are
more easily quantified.
3.2 Effects of phosphorus additions on primary productivity and sediments
Primary productivity changes
Any effect that phosphorus has on a water body will depend on the
form it is in when it reaches the water. If it is present as dissolved
inorganic phosphorus it is immediately available for plant growth.
Phytoplankton and floating plants obtain their phosphorus requirements
from the water column, while submerged rooted plants obtain theirs
from the sediments and the water column (Bristow and Whitcombe, 1971;
Denny, 1972). Phosphorus may be locked up in plant biomass both in
streams (Vincent and Downes, 1980) and lakes (Mitchell, 1975) and
released again during algal and macrophyte decay. It is released
more slowly from macrophytes than from phytoplankton, but the annual
decay of macrophytes results in the liberation of significant amounts
of phosphorus. In Lake Rotorua, 7 tonnes of phosphorus are (potentially)
released from macrophytes each year (Richmond, 1978).
Where phosphorus is limittrrg' the effect of fertiliser phosphorus on a
water body is to increase primary productivity. In lakes, this
increase is usually reflected in high phytoplankton numbers (Golterman,
1973; Mitchell, 1975). However, in some lakes increased phosphorus
in the water results in increased biomass of macrophytes (Mitchell,
1971; Haumann and Waite, 1978) or of filamentous algae (Howard-Williams,
1981). The reasons why either phytoplankton or macrophytes show a
dominant response to phosphorus additions in a given situation are
21
unclear but appear to be releated to the availability of light and
the nutrient balance in the water (Mitchell, 1971; Spence, 1982).
Patterson and Brown (1979) suggest that increased phytoplankton prod
uctivity results in more suspended material in the water. This is
filtered by the macrophyte beds and accumulates as sediment with high
nutrient content (Brown and Dromgoole, 1977). The sediment then
stimulates further weed growth. In this way eutrophication may
accelerate the growth and spread of weed by enabling suitable sub
strates to be formed more quickly than under low nutrient conditions.
The problems caused by increasing productivity are of several types.
Algal blooms cause loss of water clarity and unsightly scums may result.
Concentrations of oxygen may drop in deeper waters during plankton
blooms due to increased bacterial activity resulting from sedimentation
of dying plant cells. Decreased oxygen levels may in turn affect
fish such as trout living in the deeper lake waters. Blue-green algae
periodically become the dominant algal type under high nutrient
conditions. Some of these are nitrogen fixers which may produce
substances toxic to mammals. The nuisance value of excess macrophytes
in lakes and reservoirs is well known both for clogging drains, streams
and water filters and for interfering with boating, swimming and fishing.
Sediments
The sediments in a water body are a sink for phosphorus. They may
also be a source of phosphorus under some circumstances and are an
active centre for phosphorus cycling. Knowledge of ~hether the sediments
act as a source or sink for phosphorus is essential for predicting
the effects of different phosphorus loadings and for planning lake
restoration (Bostrom et al., 1982).
When phosphorus enters an oligotrophic lake the sediments provide
a sink for a major portion of the inflow (up to 96%, Twinch and Breen,
1978), either by direct binding by the bottom sediments or by sedi
mentation of suspended material. In lakes with higher nutrient levels,
phosphorus may be released from the sediments and transported to the
water column. This internal loading of phosphorus into lake water
may exceed deposition for certain periods of the year, often increasing
22
the primary productivity of the lake. A detailed discussion of the
phosphorus interactions between the water and sediments is given by
Syers et al., (1973) and Bostrom et al., (1982). Since dissolved
inorganic phosphorus is required for primary productivity, the influence
of other phosphorus compartments in both sediment and water on the
dissolved inorganic phosphorus is important. Figure 2 illustrates
the major phosphorus compartments and the interactions between them.
/Dissolved / Dissolved ,p. P
~ 0
I 1"M~1Particulate "- Particulatep. P~ 0
EX'i'ERNAL 1\ SETTLING, MIXING A INTERNALHOSPHORUS .J SEDJ:.lENT DIFFUSION V PHOSPHORUS
Sediment: SedimentParticulate Particulate
p. p~ 0
~ v;YSediment SedimentDissolved / Dissolved
p. P~ 0
FIGURE 2: Interchange between water and sediment P compartments
(p.= inorganic Pi P = organic Pl.~ 0
(Syers et al., 1973)
Nutrient exchange with the overlying water may occur from up to 20 cm
deep in the sediment. This is also the zone of greatest fungal and
bacterial activity. The phosphorus concentrations near the sediment
surface are very variable and likely to be influenced by many factors
including shape of the lake basin, water movement, water depth and
trophic state. This variability suggests care should be taken when
comparing lakes (McColl, 1977). The deeper sediments may reflect
23
more accurately the sediment characteristics of the lake (Fish and
Andrew, 1980). Sediment cores from Lake Rotorua show total phosphorus
decreases from about 1.5 mg g-l dry sediment at the sediment surface
to an approximately constant rate of about 0.8 mg g-l 20 cm below
the surface (Fish and Andrew, 1980).
The interstitial water between the sediment particles contains less
than 1% of the total phosphorus in the sediments but it is important
because it is the phosphorus directly exchangeable with the lake
water (Syers et al., 1973). The concentration of total dissolved
phosphorus in the interstitial water is much higher (usually 5-20
times) than in the lake water (Bostrom et al., 1982). There is also
a large difference in phosphorus concentration in interstitial water
between oligo- and eutrophic lakes. Unlike the total phosphorus content
of the lake sediments, the interstitial water concentration reflects
the trophic state of a lake (Bostrom et al., 1982).
Once phosphorus has entered the sediments of a lake system, it becomes
a major problem from the point of view of eutrophication control.
Sediments release inorganic phosphorus to the overlying water during
periods of anoxia. The more eutrophic the lake becomes, the more
frequent and severe will be the anoxic conditions of the lake bottom,
and consequently the more phosphorus will be liberated. Phosphate
release from temporarily deoxygenated sediments of eutrophic Lake
Rotorua during a period of summer stratification was estimated as
20-40 mg m-2
d- l . In contrast, the rate at which phosphorus returned
to lake sediments during oxygenated conditions was measured at about
0.5 mg m-2
d- l (White et al., 1978). More recent experiments (Vant,
1985) estimate that 35 tonnes of phosphorus were released from the
sediments of this lake over the 1984-85 summer.
Once eutrophic, lakes will probably remain in that condition for some
time even after all external sources of phosphorus are removed, because
of phosphorus release from the sediments (Syers et al., 1973).
Dredging the lake may reduce the problem, but equally, dredging may
expose lower sediments which then become new sources of phosphorus.
24
Activities that stir up the sediments such as storms or harvesting
of macrophytes may also promote phosphorus release. Reversal of
eutrophication through control of phosphorus input is possible
although a return to the oligotrophic condition would be slow and
costly.
For waters that have become eutrophic, various treatment possibilities
exist:
- mechanical removal of sediments from shallow lakes
or bottom sealing;
- diversion of phosphorus rich waters entering lakes
or reduction in input concentration;
- selective discharge of nutrient enriched bottom water;
- artificial circulation or aeration to maintain oxygenated
bottom water;
- reduction of water retention time or flushing with water
of low nutrient content;
- chemical treatment with Iron or Aluminium compounds to remove
dissolved and particulate phosphorus and increase
phosphorus retention by the sediments (Syers et al., 1973); and
- harvesting of aquatic weeds.
Most of these management techniques have been used in New Zealand.
For example, dredging of sediments has been used in Tomahawk Lagoon
(Mitchell, 1971). In Lake Tutira some inflow water has been diverted
and the lake water has been artificially circulated by air from
October to March to maintain oxygenated bottom water (Tierney, 1980).
3.3 The trophic status of New Zealand lakes
It is useful to classify lakes according to the amount of primary
productivity. The productivity of a lake depends on the nutrient
input, the size of the lake basin, the residence time of the water
in the lake and phosphorus retention by the sediments. Oligotrophic
lakes have low nutrient levels and relatively low primary productivity
Most lowland lakes in New Zealand are classified as eutrophic and
most upland North Island lakes are also tending towards eutrophic
status (Figure 3a & 3b). Upland South Island lakes so far have
25
//
Legend
o 01 igotrophic
() Mesotrophic
• Eutrophic
FIGURE 3a: Trophic status of North Island lakes
o
o..0
oo0o
oo
~
o
8eo
9<:
27
relatively low trophic status, with a few exceptions such as Lake
Hayes, Lake Johnson and Lake Alexandrina (Figure 3b). Apart from
a few urban catchments, the trophic state of New Zealand lakes
reflects the intensity of agricultural development in the relevant
catchments (White, 1982). In the South Island, further development
of irrigation and concommitant increase in land use intensity in many
areas is likely to promote greater movement of nutrients into water
bodies. There is accumulating evidence to suggest that the trophic
status of many upland South Island lakes is changing as greater
development occurs in the high country (Stout 1981, Malthus 1985).
In the Lake Mahinerangi catchment, 30% development over 16 years has
resulted in nine times greater phytoplankton production along with
increased total nitrogen and total phosphorus (Table 7) (Malthus,
1985).
TABLE 7: The relationship between catchment development andphytoplankton production in Lake Mahinerangi andinflow stream nutrient concentration
% lake Phytoplankton % stream Inflow Inflowcatchment production catchment stream streamdevelopment mg C m-
2d- l development Total N Total P
- 3 - 3mg m ~m
1964-66 0 76 0 132 13
1968-70 3 210
1976-78 380
1980-82 30 630
100 451 86
Source: Mitchell and Galland (1981), Malthus (1985)
Phosphorus concentration in water is a commonly measured indicator
of trophic status. However, other factors can also be used to dist
inguish one trophic state from another. These include water transparency,
chlorophyll a, oxygen and total nitrogen (McColl, 1972, 1977; White,
1983). It is now generally agreed that no single quantitative parameter
can be used to distinguish between trophic states. Table 8 shows
the average total phosphorus concentration in lakes of different trophic
28
status in New Zealand. Data obtained from the OECD programme for
eutrophication research is also reported (White, 1982). The large
range for each category clearly illustrates that total phosphorus
alone is not sufficient to categorise each lake.
Several nutrient loading models have been developed in the USA and
Europe (as part of the OECD programme on eutrophication) to describe
the relationships between nutrient load and trophic condition.
Phosphorus loading curves have been used to estimate the specific
phosphorus loading on a lake necessary to produce a particular trophic
state (Vollenweider and Dillon, 1975). However, some New Zealand
lakes do not fit well on these curves, such as Lake Taupo (White, 1982).
This is because New Zealand lakes exhibit low levels of nitrogen,
compared with lakes sampled in the OECD study, and may be nitrogen
limited at times. Caution is therefore necessary in the use of OECD
predictive equations (White, 1983).
TABLE 8: Average total phosphorus concentration in lakesof different trophic status
MESOTROPHIC EUTROPHIC- mg m-
mg m
Rotoaira 13.7 Ohakuri 29.1
Okareka 14.1 Rotorua 26.0
Rotoiti 21.1 Rerewhakaaitu 15.9
Mahinerangi 23.8 Okaro 56.0
Ngapouri 51.6
Tutira 60.3
Rotongaio 231
Horowhenua 501
OLIGOTROPHIC
Taupo 5.5
Aratiatia 1l.5
Tikitapu 6.4
Rotorua 11.0
Okataina 17.6
Waikaremoana 4.2
Ahaura 8.7
Brunner 16.5
Haupiri 21.5
Hochstetter 10.4
Kangaroo 14.0
Kaniere 13 .0
Lady 8.8
Poerua 14.0
N. Z. lakes 11. 7 mean
OECD study
4.2-21. 5 range
8.6 mean
3.0-16.1 range
20.8 mean
13.7-31. 3 range
25.1 mean
5.6-80.0 range
115
15.9-501
113
8.1-386
Source: after White (1982)
29
Another approach to assessing primary productivity assumes a direct
relationship between phosphorus and chlorophyll concentration in the
water. However, lakes with high levels of phosphorus do not fit this
relationship (Stans, 1983). Studies by Vant and Pridmore (1981)
suggest that ATP (adenosine triphosphate) concentration may be a more
useful indicator of algal biomass. This is because when phytoplankton
numbers are high, chlorophyll increases faster than ATP in order to
compensate for increasing light limitation by self shading.
The phosphorus content of water is a function of inflow concentration,
residence time and loss to sediments. Estimates of phosphorus transfer
between Lake Taupo and the Waikato River suggest that 80-90% of phosphorus
inputs to the lake are retained in the lake (White and Downes, 1977).
Hoare (1982) has related the nutrient concentration in a lake to both
the nutrient concentration of the inflow and the 'retention coefficient'
of the lake. He has applied these concepts to lakes Rotorua, Tutira
and Alexandrina (Hoare, 1980; 1982; 1983). His results indicate that
mass balance phosphorus models can be very useful in predicting the
results of changes in nutrient loading or water retention time.
Potential sources of nutrients can be compared using simple calculations
before decisions on the treatment of eutrophication problems are made
(e.g. McColl, 1978a).
4. CONCLUSIONS AND POLICY IMPLICATIONS
The New Zealand agricultural industry is based to a considerable extent
on a ryegrass-clover system which requires substantial inputs of phosphate
to maintain productivity. Each year large quantities of phosphate
are applied to agricultural land in the form of superphosphate and
each year a proportion of this is lost via stock transfer, soil erosion
and water runoff.
Available data suggest that on farmland in many parts of New Zealand
losses through runoff and soil erosion can reach over 10% of the
maintenance fertiliser phosphorus additions.' The total value of phos
phorus lost from agricultural land in runoff waters alone is conservatively
estimated as being $3-$6 million per year, while loss of phosphorus
30
through erosion of the topsoil by wind is likely to be equally
significant where farming practices expose dry silty and sandy soils
such as on the Canterbury plains and in Central Otago. Furthermore,
although overall estimates of phosphorus losses through animal
transfer are not known the few studies suggest that in hill country
at least an additional 5% per year can be lost in this way. Losses
of this kind are agriculturally very significant, costing in the order
of 15-25% of annual fertiliser expenditure. However, they may, with
appropriate management techniques, be partly avoidable.
Even when loss of phosphorus from agricultural land is less than 5%
of maintenance phosphorus additions, a level insignificant to farmers,
the effects of phosphorus on water quality of the receiving rivers
and lakes may be considerable. Water is the common property of the
people of New Zealand and hence adverse effects on water quality result
in losses that are shared by the community as a whole.
4.1 Future risks
Increased use of fertilizer in the future also implies increased losses
to the farmer via stock transfer, wind erosion and water runoff if
improved fertilizer management is not practised. If a 'do-nothing'
policy is adopted, the water quality of many New Zealand waterways
will continue to decrease from increased phosphorus loading.
Currently unaffected water bodies could also change in the future.
For lakes in agriculturally developed catchments, the expense and
effort of lowering trophic levels may be too great for society to bear.
However, lakes and their catchments can be managed to maintain the
present water quality so that they may continue to be used for recreation
and/or as a wildlife habitat •. Prevention is almost always less costly
than rehabilitation. It is therefore important to identify the potential
lake management problems in terms of the aspirations of people and
the technical and economic feasibility of fulfilling these aspirations.
The future risks and management needs are poorly understood in New
Zealand at the present time.
31
4.2 Management needs and approaches
If the surface runoff and wind erosion losses of fertiliser phosphate
could be controlled, using one or more of the methods put forward
in this paper, a significant reduction in the social costs associated
with water quality degradation could be achieved. For animal transfer
losses however, alternative grazing management approaches at present
are limited to significantly reducing overall fertiliser phosphorus
waste (inefficient use). Successful and economic fertiliser phosphorus
conservation methods would appear to involve increased diversification
rather than extremely intensive management currently precluded by
very high costs. Management options based on economic criteria from
the viewpoint of the individual farmer include "targeting" fertiliser
applications to those areas of hill country where stock transfer of
phosphorus is relatively less severe; silvipastoralism, which has
the added advantages, if well planned, of reducing runoff and erosion
and enhancing soil nutrient levels; and diversification e.g. running
goats or deer with, or rather than, sheep. However, while the techniques
for control of phosphorus losses listed in the second section of this
paper are all viable options few, if any, have been tested and
evaluated technically or economically in New Zealand and their relative
usefulness is unkown. This applies equally to the catchment develop
ment phase (preventioro and the developed catchment phase (rehabilitation).
The economic benefit to the individual farmer of controlling losses
may not by themselves be sufficient to encourage farm phosphorus
conservation practices. But farm management may be the most
efficient way to avoid the social costs associated with reduced water
quality. Clearly, then, there is the important question of how to
encourage individuals to behave in such a way that contributes to
the larger interests of society. To achieve this end, the main
task will be to demonstrate to the farmer that wider land and water
management objectives are important and that various management options
are available to achieve them.
32
The environmental costs of farming are not generallyappreciated, particularly in the case of riparianwetlands. But it is certain that a positive, constructive response would eventuate from the farmingcommunity, given encouragement and advice fromlocal authorities, water boards, and agriculturaladvisors. Regional and local government and theMinistry of Agriculture and Fisheries have especiallyimportant responsibilities in this respect.
Williams and Brickell, 1983.
Studies of the options from the viewpoints of efficient nutrient
control and agricultural management need to be undertaken by research
organisations so that authorities will have a basis on which to base
their recommendations to farmers.
33
ACKNOWLEDGEMENTS
The authors are very grateful to Dr R.H.S. McColl, T.J. Malthus
and Dr S.F. Mitchell for their criticism of the manuscript. We
also thank those who attended the phosphate workshop in February,
1984 and staff at the Centre for Resource Management for their
helpful discussions on phosphorus losses.
34
REFERENCES
Baker, J.L., Campbell, K.L., Johnson, H.P. and Hanway, J.J. 1975.
Nitrate, phosphorus and sulphate in subsurface drainage water.
Journal of Environmental Quality 4: 406-12.
Berg, N.A. 1980. Control of phosphorus from agricultural land in the
Great Lakes Basin. In: Phosphorus Management Strategies for
Lakes. Loehr, R.C., Martin, C.S. and Rast, W. (Eds.). Ann
Arbor Science, Michigan. 459-485.
Bolton, E.F., Aylesworth, J.W. and Hare, F.R. 1970. Nutrient losses
through tile drains under three cropping systems and two
fertility levels on Brookston clay soil. Canadian Journal of
Soil Science 50: 275-279.
Bostrom, B., Jansson, M. and Forsberg, C. 1982. Phosphorus release
from lake sediments. Archiv fur Hydrobiologie Beihefte
Ergebnisse der Limnologie 18: 5-59.
Bristow, J.M. and Whitcombe, M. 1971. The role of roots in the nutrition
of aquatic vascular plants. American Journal of Botany 58:
8-13.
Brown, J.M.A. and Dromgoole, F.I. 1977. The ecophysiology of
Lagarosiphon in Rotorua Lakes. Proceedings of the 30th New
Zealand Weed and Pest Conference 1977. 130-134.
Burwell, R.E., Timmons, D.R. and Holt, R.F. 1975. Nutrient transport
in surface runoff as influenced by soil cover and seasonal
periods. Proceedings of the Soil Science Society of America
39: 523-528.
Cooke, J.G. 1979. The effect of land use on water quality in New
Zealand. In: Proceedings of a seminar on land use in relation
to water quantity and quality, Nelson, November 7-8, 1979.
Nelson Catchment Board and Regional Water Board. 40-60.
1981. Pollution from our pastures. Soil and Water 17(5): 13-15.
35
Denny, P. 1972. Sites of nutrient absorption in aquatic macrophytes.
Journal of Ecology 60: 819-829.
Fish, G.R. 1969. Lakes: the value of recent research to measure
eutrophication and to indicate possible causes. Journal of Hydrology
(New Zealand) 8: 77-85.
and Andrew, I.A. 1980. Nitrogen and phosphorus in the
sediments of Lake Rotorua. New Zealand Journal of Marine and
Freshwater Research 14: 121-128.
Gillingham, A.G. 1980. Phosphorus uptake and return in grazed, steep
hill pastures. New Zealand Journal of Agricultural Research
23: 313-21.
and During, C. 1973. Pasture production and transfer
of fertility within a long-established hill pasture. New
Zealand Journal of Experimental Agriculture 1: 227-32.
Goltermann, H.L. 1973. Natural phosphate sources in relation to
phosphate budgets: a contribution to the understanding of
eutrophication. Progress in Water Technology 2: 3-17.
Haumann, D. and Waite, T.D. 1978. The kinetics of phosphate removal
in small alkaline lakes by natural and artificial processes.
Water, Air and Soil Pollution 19: 291-313.
Hilder, E.J. 1966. Rate of turnover of elements in soils: the effects
of stocking rate. Wool Technology Sheep Breeding, C.S.I.R.O.
13(2): 11-16.
Hoare, R.A. 1980. The sensitivity of phosphorus and nitrogen loads,
of Lake Rotorua, New Zealand. Progress in Water Technology 12:
897-904.
1982. Lake nutrient load calculations: A management tool.-------Soil and Water 18(3): 14-17.
1983. Review of water and soil conservation research.-------1981. Water and Soil Miscellaneous Publication No.53: 47-48.
36
Howard-Williams, C. 1981. Studies on the ability of a Potamogeton
pectinatus community to remove dissolved nitrogen and
phosphorus compounds from lake water. Journal of Applied Ecology
18: 619-637.
Hughes, J.G., McClatchy, D. and Hayward J.A. 1971. Beef cattle on
tussock country. Lincoln papers in Resource Management No.1.
Lincoln College. 270p.
Klopatek, J.M. 1978. Nutrient dynamics of freshwater riverine marshes
and the role of emergent macrophytes. In: Freshwater Wetlands:
ecological processes and management potential. Good, R.E., Whigham,
D.P., Simpson, R.L. (Eds.) Academic Press, New York. 195-216.
~Lambert, M.G., Devantier, B.P., Nes, P. and Penny, P.E. 1985. Losses
of nitrogen, phosphorus and sediment in runoff from hill country
under different fertilizer and grazing management regimes.
New Zealand Journal of Agricultural Research 28: 371-379.
Lee, E.S., Powell, H.K.J., Taylor, M.C. and Tsao, N.Y. 1979. Concentratiol
of nutrients in runoff from agley podzol soil in South Island,
New Zealand. New Zealand Journal of Science 22: 35-8.
McColl, R.H.S., 1972. Chemistry and trophic status of seven New Zealand
lakes. New Zealand Journal of Marine and Freshwater Research
6: 399-447.
1977. Chemistry of sediments in relation to trophic
condition of eight Rotorua lakes. New Zealand Journal of Marine
and Freshwater Research 11: 509-523.
1978a. Lake Tutira: the use of phosphorus loadings
in a management study. New Zealand Journal of Marine and
Freshwater Research 12: 251-6.
1978b. Chemical runoff from pasture: the influence
of fertiliser and riparian zones. New Zealand Journal of Marine
and Freshwater Research 12: 371-380.
37
MCColl, R.H.S. 1982. Water quality in agricultural areas - the prospects
for management of diffuse pollution sources. In: Water in New
Zealand's future. Proceedings of the 4th National Water
Conference 1982. Auckland. 153-160.
1983. Farm runoff - the mechanisms and moderating
factors. Soil and Water 19(3): 31-35.
and Gibson, A.R. 1979. Downslope movement of nutrients
in hill pasture, Taita, New Zealand. II. Effects of season,
sheep grazing and fertilizer. New Zealand Journal of Agricultural
Research 22: 151-161.
and Hughes, H.R. (Comp.) 1981. The effects of land
use on water quality - a review. Water and Soil Miscellaneous
Publication No. 23: 59p.
and Syers, J.K. 1981. The effects of agriculture.
Grassland and cropland. In: The effects of land use on water
quality - a review. McColl, R.H.S. and Hughes, H.R. (Comp.).
Water and Soil Miscellaneous Publication No. 23: 21-23.
_______________ ; White, E. and Gibson, A.R. 1977. Phosphorus and
nitrate runoff in hill pasture and forest catchments, Taita,
New Zealand. New Zealand Journal of Marine and Freshwater
Research 11: 729-744.
Malthus, T.J. 1985. Long term eutrophication of Lake Mahinerangi.
Ph.D. thesis in Zoology, University of Otago.
Minshall, N., Nichols, M.S. and Witzel, S.A. 1969. Plant nutrients
in base flow of streams in south western Wisconsin. Water
Resources Research 5: 706-713.
Mitchell, S.F. 1971. Phytoplankton productivity in Tomahawk Lagoon,
Lake Waipori, and Lake Mahinerangi. Fisheries Research Bulletin
No.3 (New Zealand Marine Department, Fisheries Divisionk 87p.
38
Mitchell, S.F. 1975. Phosphate, nitrate, chloride in a eutrophic
coastal lake in New Zealand. New Zealand Journal of Marine and
Freshwater Research 9: 193-198.
and Galland, A.N. 1981. Phytoplankton photosynthesis,
eutrophication and vertical migration of dinoflagellates in
a New Zealand reservoir. Verhandlungen Internationale Vereinigung
fUr Theoretische und Angewandte Limnologie 21: 1017-1020.
N.Z. Meat and Wool Boards' Economic Service, 1984. Supplement to
the sheep and beef farm survey 1981-82. Publication No. 1893,
Wellington.
of the sheep and beef industry 1984-85.
Wellington.
1985. Annual review
Publication No. 1918,
O'Connor, K.F. 1981. Comments on Dr Floate's paper on grazing
effect by large herbivores. In: Terrestrial nitrogen cycles.
Clark, F.E. and Rosswall, T. (eds.). Ecology Bulletin
(Stockholm) 33: 707-714.
O.E.C.D. 1981. Environmental policies in New Zealand: a review.
Government printer, Wellington.
Painter, D.J. 1978. The pastoral scene. Soil erosion rates on New
Zealand farm land. Proceedings of the Conference on Erosion
Assessment and Control. New Zealand Association of Soil
Conservators 1978, 25-42.
Patterson, K.J. and Brown, J.M.A. 1979. Growth and elemental composition
of the aquatic macrophyte, Lagarosiphon major, in response to
water and substrate nutrients. Progress in Water Technology
11: 231-246.
39
Pittams, R.J. 1979. Riparian strip studies - a review. Hamilton
Science Centre unpublished internal report.
Prentki, R.T., Gustafson, T.D., and Adams, M.S. 1978. Nutrient
movements in lakeshore marshes. In: Freshwater wetlands: ecological
processes and management potential. Good, R.E., Whigham, D.F.,
Simpson, R.L. (Eds.). Academic Press, New York. 169-194.
Richardson, C.J. 1985. Mechanisms controlling phosphorus retention
capacity in freshwater wetlands. Science 228: 1424-6.
__________________ , Tilton, D.L., Kadlec, J.A., Chamie, J.P.M. and
Wentz, W.A. 1978. Nutrient dynamics of northern wetland ecosystems.
In: Freshwater wetlands: ecological processes and management
potential. Good, R.E., Whigham, D.F., Simpson, R.L. (Eds.)
Academic Press, New York. 217-241.
Richmond, C.J. 1978. Lake Rotorua macrophytes: standing crop and
nutrient content in late February 1978. Unpublished report to
Conservator of Wildlife, Rotorua .
~RYden,J.C. and Syers, J.K. 1973. Evaluation of the potential of
soils for the phosphorus enrichment of streams. Proceedings
of the Pollution Research Conference, Wairakei, New Zealand,
20-21 June, 1973. 481-493
and Harris, R.F. 1973. Phosphorus in
runoff and streams. Advance in Agronomy 25: 1-45.
Saunders, W.H.H., Koller, B.G., Gillingham, A.G. and Hill, L.J. 1981.
Getting better value from fertiliser from pasture. Ruakura
Farmers Conference 33: 39-44.
_~Schuman~ G.E., Spomer, R.G. and Piest, R.F. 1973. Phosphorus loss:;r",
from four agricultural watersheds on Missouri Valley loess.
Proceedings of the Soil Science Society of America 37: 424-427.
40
Scott, G. 1985. Phosphorus cycling in New Zealand pastoral systems:
A conceptual framework for improved understanding and management
of phosphorus resources. Centre for Resource Management
Discussion Paper. Lincoln College. (In press).
Skovlin, J.M. 1984. Impacts of grazing on wetlands and riparian
habitat: a review of our knowledge. In: Developing strategies
for rangeland management. National Research Council/National
Academy of Sciences. Westview Press Inc. Colorado, U.S.A. 1000-1103.
~ Sharpley, A.N. and Syers, J.K. 1976a. Phosphorus transport in surface
runoff as influenced by fertiliser and grazing cattle. New Zealand
Journal of Science 19: 277-282.
1976b. Potential role of earthworm
casts for the phosphorus enrichment of runoff waters. Soil
Biology and Biochemistry 8: 341-346.
1979a. Loss of nitrogen and phosphorus
in tile drainage as influenced by urea application and grazing
animals. New Zealand Journal of Agricultural Research 22: 127-131.
1979b. Effect of aerial topdressing
with superphosphate on the loss of phosphate from a pasture
catchment. New Zealand Journal of Agricultural Research 22: 273-277.
~~ 1979c. Phosphorus inputs into a stream
draining an agricultural watershed. II. Amounts contributed
and relative significance of runoff types. Water, Air and Soil
Pollution 11: 417-428.
and Gregg, P.E.H. 1978. Transport
in surface runoff of phosphorus derived from dicalcium phosphate
and superphosphate. New Zealand Journal of Science 21: 307-310.
Sloey, W.E., Spangler, F.L. and Fetter, C.W. Jr. 1978. Management
of freshwater wetlands for nutrient assimilation. In: Freshwater
Wetlands: ecological processes and management potential. Good, R.E.,
Whingham, D.F., Simpson, R.L. (Eds.) Academic Press, New York. 321-340
41
Spence, D.H.N. 1982. The zonation of plants in freshwater lakes.
Advances in Ecological Research 12: 37-125.
Stans, J.C. 1983. The contribution of predictive methods to the
scientific approach in EIA. Delft Hydraulics Laboratory,
Publication No. 308. 26p.
Stockdill, S.M.J. and Cossens, G.G. 1984. Soil earthworm introduction
methods and effects on production. AGLINK FPP 211, Ministry of Agricuj
and Fisheries, New Zealand. 2p.
Stoltenberg, N.L. and White, J.L. 1953. Selective loss of plant nutrients
by erosion. Proceedings of the Soil Science Society of America 17:
406-410.
Stout, V.M. 1981. Lake Alexandrina. Freshwater Catch No.ll: 12-13.
Syers, J.K. 1974. Effect of phosphate fertilisers on agriculture
and the environment. New Zealand Agricultural Science 8: 149-164.
Harris, R.F. and Armstrong, D.E. 1973. Phoshpate chemistry
in lake sediments. Journal of Environmental Quality 2: 1-14.
and Ryden, J.C. 1973. Losses of phosphorus from forest
watersheds. Fertilising Forests Workshop. University of
Waikato, Hamilton. 65-79.
Teirney, L. 1980. Tutira, a lake worth restoring. Soil and Water 16(1):
10-13.
Thorrol~ B.S.,O'Connor, K.F., White, J.G.H. 1985. Management influences
on sheep behaviour, dung distribution and soil phosphate.
Proceedings of the New Zealand Grasslands Association 46:
127-134.
Turner, M.A., Tillman, R.W. and Syers, J.K. 1979. Losses of phosphorus
and nitrogen forms in subsurface drainage water as influenced
by phosphate fertiliser, grazing animals, and irrigation
treatments. Progress in Water Technology 11: 287-294.
42
Twinch, A.J. and Breen, C.M. 1978. Enrichment studies using isolation
columns. II. The effects of phosphorus enrichment. Aquatic
Botany 4: 161-168.
Young, R.A., Huntrods, R. and Anderson, W. 1980. Effectiveness of
vegetated buffer strips in controlling pollution from feedlot
runoff. Journal of Environmental Quality 9: 483-487.
van der Valk, A.G., Davis, C.B., Baker, J.L. and Beer, C.E. 1978.
Natural fresh water wetlands as nitrogen and phosphorus traps
for land runoff. In: Wetland Functions and values: the state
of our understanding. Greeson, P.E., Clark, J.R., Clark, J.E.
(Eds.) American Water Resources Association, Minneapolis. 457-476.
Vant, W.N. 1985. Lake Rotorua: nutrients regenerated from anoxic
bottom sediments. Paper presented to New Zealand Limnological
Society Conference, Auckland, 1985.
and Pridmore, R.D. 1981. Nutrients and phytoplankton in
four Waikato lakes. In: Waters of the Waikato. Campi C
and Ridell, G. (Eds.). Proceedings of Seminar, University
of Waikato, 1981. 115-133.
Vincent, W.F. and Downes, M.T. 1980. Variation in nutrient removal
from a stream by watercress (Nasturtium officinale R.Br.)
Aquatic Botany 9: 221-235.
Vollenweider, R.A. and Dillon, P.J. 1974. The application of the
phosphorus loading concept to eutrophication research.
National Research Council of Canada No.13690. 42p.
Von Oertzen, I.A.M.L. 1981. Use of different water plants in biological
filter systems for the treatment of agricultural wastewaters.
B.Ag.Sc. thesis. Rheinische Friedrich-Willhelms Universitat,
Bonn, West Germany.
43
White, E. 1982. Eutrophication in New Zealand Lakes. In: Water in
New Zealand's Future. Proceedings of the 4th National Water
Conference, 1982, Auckland. 129-136:
1983. Lake eutrophication in New Zealand - a comparison
with other countries of the Organisation for Economic Co-operation
and Development. New Zealand Journal of Marine and Freshwater
Research 17: 437-444.
__________ , Don, B.J., Downs, M.T., Kemp, K.J., Mackenzie, A.L. and
Payne, B.W. 1978. Sediments of Lake Rotorua as sources and sinks
for plant nutrients. New Zealand Journal of Marine and Freshwater
Research 12: 121-130.
__________ , Downes, M.T. 1977. Preliminary assessment of nutrient
loads on Lake Taupo, New Zealand. New Zealand Journal of Marine
and Freshwater Research 11: 341-356.
Williams, P. and Brickell, D. 1983. Guideline Riparian zone management.
Upper Waitemata Harbour Catchment Study. Auckland Regional Authority. I!
Witzel, S.A., Minshall, N, Nichols, M.S. and Wilke, J. 1969. Surface
runoff and nutrient losses of Fennimore watersheds. Transactions
of the American Society of Agricultural Engineering 12: 338-341.
Yates, M.E. 1971. Effects of cultural changes on Makara experimental
basin: Hydrological and agricultural production effects of
two levels of grazing on unimproved and improved small catchments.
Journal of Hydrology (New Zealand) 10: 59-84.