Sources, production and fate of nutrients in Clew Bay, County Mayo and its catchment

Sources, production and fate Sources, production and fate of nutrients in Clew Bay, of nutrients in Clew Bay,

County Mayo and its catchment.County Mayo and its catchment.

Presented to the Clew Bay Forum February 21st 2002

Dr Neil BassWatermarkaqua-environmental

What people say about salmon farms wastes:-What people say about salmon farms wastes:-

Suzuki’s claims have often been cited (Friends of the Earth, WWF) but Suzuki’s claims have often been cited (Friends of the Earth, WWF) but they have never achieved they have never achieved peer-reviewedpeer-reviewed publication in the publication in the scientificscientific presspress . They have been generally regarded as sensationalist and . They have been generally regarded as sensationalist and politically motivated by the scientific community (Hardy 2000). politically motivated by the scientific community (Hardy 2000).

WatermarkWatermarkaqua-environmentalaqua-environmental

HHåkanssen et al (1988):-åkanssen et al (1988):- 1 tonne salmon production ~ 150 people.1 tonne salmon production ~ 150 people.

Invalidated by Ackefors (1990), an environmental scientist.Invalidated by Ackefors (1990), an environmental scientist.

Letters to Mayo News (2001):- Letters to Mayo News (2001):-

David Suzuki Foundation (1988):-David Suzuki Foundation (1988):- 1 tonne salmon production ~ 1,500 people.1 tonne salmon production ~ 1,500 people.

Quoting Quoting Commercial fishing fish farming and fish eatingCommercial fishing fish farming and fish eating; “1 tonne ; “1 tonne of farmed fish produces pollution equal to the untreated sewage of of farmed fish produces pollution equal to the untreated sewage of 2-300 people”.2-300 people”.

Article; Irish Times, Feb 11th 2002; quoted source:- Article; Irish Times, Feb 11th 2002; quoted source:- ““The larger the (salmon farming) industry grows, the more likely it The larger the (salmon farming) industry grows, the more likely it is to burst, (due) to uncontrollable pollution and disease”.is to burst, (due) to uncontrollable pollution and disease”.

Let’s examine the facts.

Desk study of nutrient discharges into Lough Swilly Desk study of nutrient discharges into Lough Swilly (for Lough Swilly (for Lough Swilly CLAMSCLAMS group). group).

Desk study of nutrient discharges into Clew Bay (for Desk study of nutrient discharges into Clew Bay (for Clew Bay Clew Bay CLAMSCLAMS group). group).

EIS and Aquaculture license submission; (in an EIS and Aquaculture license submission; (in an answer to query from the Irish Aquaculture License answer to query from the Irish Aquaculture License Vetting Committee, regarding the “carrying capacity” Vetting Committee, regarding the “carrying capacity” of Kenmare Bay).of Kenmare Bay).


A number of opportunities to do this arose in 2001:-A number of opportunities to do this arose in 2001:-

What’s the plan?What’s the plan?

1.1. We will take a look at the total production of We will take a look at the total production of nutrients by the main inhabitant groups in the nutrients by the main inhabitant groups in the Clew Bay catchment.Clew Bay catchment.

2.2. Next, we will estimate what proportion of all Next, we will estimate what proportion of all nutrients produced in the catchment enter the nutrients produced in the catchment enter the bay.bay.

3.3. Then we will look at what happens to nutrients, Then we will look at what happens to nutrients, once in the bay.once in the bay.

4.4. Finally we will look at their subsequent fate.Finally we will look at their subsequent fate.


A few definitions. NutrientsNutrients are inorganic chemicals, which are required by plants for are inorganic chemicals, which are required by plants for

primary production.primary production. Primary productionPrimary production is the process of plant growth, (phytoplankton is the process of plant growth, (phytoplankton

and algae / seaweed in freshwater / seawater; grass and other and algae / seaweed in freshwater / seawater; grass and other plants on land), by which nutrients, carbon and oxygen (COplants on land), by which nutrients, carbon and oxygen (CO22) are ) are combined into plant matter, with the help of photo-synthesis and combined into plant matter, with the help of photo-synthesis and solar energy. Plant matter is at the bottom of the food chain, solar energy. Plant matter is at the bottom of the food chain, through which all animal nutrition arises.through which all animal nutrition arises.

NitrateNitrate is the first limiting nutrient to primary production in is the first limiting nutrient to primary production in marinemarine systems, where phosphate is plentiful.systems, where phosphate is plentiful.

PhosphatePhosphate is the first limiting nutrient to primary production in is the first limiting nutrient to primary production in freshwaterfreshwater systems, where it is scarce. systems, where it is scarce.

Biochemical oxidation demand (BOD)Biochemical oxidation demand (BOD) is the total amount of oxygen is the total amount of oxygen required to neutralise the environmental impact of a given waste.required to neutralise the environmental impact of a given waste.

Suspended / settleable solids (SS)Suspended / settleable solids (SS) are the insoluble fraction of a are the insoluble fraction of a waste.waste.

Feed conversion ratio (FCR)Feed conversion ratio (FCR) is the ratio of dry feed fed to wet is the ratio of dry feed fed to wet weight gain (example 1.20 : 1).weight gain (example 1.20 : 1).


Fishfarm wastes.

1.1. Develop a growth model.Develop a growth model.

2.2. Select ration type; establish its and protein (nitrogen) Select ration type; establish its and protein (nitrogen) and phosphorus content.and phosphorus content.

3.3. Calculate feed usage and FCR by month.Calculate feed usage and FCR by month.

4.4. Calculate monthly N and P feed intake, from the feed Calculate monthly N and P feed intake, from the feed analysis data.analysis data.

5.5. Use standard formulae to calculate monthly production Use standard formulae to calculate monthly production of BOD, SS, N and P, from the feed intake data.of BOD, SS, N and P, from the feed intake data.


Fishfarm wastes can be easily calculated:-Fishfarm wastes can be easily calculated:-(Not such an easy task for some other sources of waste).(Not such an easy task for some other sources of waste).

Clew Bay salmonid farms; combined nutrient production.Clew Bay salmonid farms; combined nutrient production.(Clare Island Seafarm and Seastream Trout Farm sites) (Clare Island Seafarm and Seastream Trout Farm sites)

Nitrogen and phosphorus production; tonnes per month.Nitrogen and phosphorus production; tonnes per month.

0

5

10

15

20

25

30

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

NO3 N kg

PO3 P kg

Licensed production Licensed production ~ ~ 4,500 tonne pa. 4,500 tonne pa.

September transfer, harvest the following October.September transfer, harvest the following October.

Mean transfer weight = 733gm; mean harvest weight = 4.5kg Mean transfer weight = 733gm; mean harvest weight = 4.5kg

Mean FCR Mean FCR ~~ 1.20 : 1 1.20 : 1

Total inorganic N production = 9.8 - 29.8 tonnes pm = Total inorganic N production = 9.8 - 29.8 tonnes pm = 208.0 tonnes pa.208.0 tonnes pa.

Total inorganic P production = 2.5 – 7.5 tonnes pm = Total inorganic P production = 2.5 – 7.5 tonnes pm = 52.3 tonnes pa52.3 tonnes pa..

Nuttr

ient

pro

dctu

ion

tonn

es


Humans!Data; population from Central Statistics Office ; tourist numbers from Irish Tourist Board;Gross population mean human nutrient production rate data from OSPAR Neut 5/3E 1999;NB; Figures also make allowance for nutrients in domestic and industrial wastewater pc

Clew Bay population statisticsClew Bay population statistics

Permanent residents; 18,000.Permanent residents; 18,000. Tourists; 3,411-11,937 resident Tourists; 3,411-11,937 resident

equivalents per month.equivalents per month. Estimated combined total weight Estimated combined total weight

of humans = 1,054 tonnes.of humans = 1,054 tonnes. Mean human nutrient production Mean human nutrient production

= 9.0gm N and 2.7gm P / day.= 9.0gm N and 2.7gm P / day. Total N production = 5.9 – 8.2 Total N production = 5.9 – 8.2

tonnes pm = tonnes pm = 82 tonnes pa82 tonnes pa.. Total P production = 1.8-2.5 Total P production = 1.8-2.5

tonnes pm = tonnes pm = 24.7 tonnes pa24.7 tonnes pa..


Livestock; cattleData; cattle numbers, types and weights; CSO 1991 data by electoral district (latest data).Excretion rates by type; “Agri-environmental Specifications for the Rural Environmental Protection Scheme (REPS); November 2000” ; Department of Agriculture, Dublin

The total population of cattle of The total population of cattle of all types is 37,838.all types is 37,838.

Their estimated total weight is Their estimated total weight is 15,431 tonnes.15,431 tonnes.

Total N production = 160 Total N production = 160 tonnes pm = tonnes pm = 1.971 tonnes pa1.971 tonnes pa..

Total P production = 24 tonnes Total P production = 24 tonnes pm = pm = 288 tonnes pa288 tonnes pa..


Clew Bay cattle statistics (1991)

Livestock; sheep.Data; sheep numbers, types and weights; CSO 1991 data by electoral district (latest data).Excretion rates by type; “Agri-environmental Specs for REPS 2000” ; DoA Dublin

There are 163,598 sheep in the Swilly catchment.There are 163,598 sheep in the Swilly catchment.

Their estimated total weight is 8,129 tonnes.Their estimated total weight is 8,129 tonnes.

Their total N production is Their total N production is 1,268 tonnes pa1,268 tonnes pa..

Their total P production is Their total P production is 194 tonnes pa194 tonnes pa..


Clew bay sheep statistics (1991)Clew bay sheep statistics (1991)

Let’s do some sums.

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

Humans Cattle Sheep Salmon Trout

020406080100120140160


0

5,000

10,000

15,000

20,000


0

500

1,000

1,500

2,000


Inhabitant populations by number Inhabitant populations by weight

N and P production; tonnes pa. N and P production / inhabitant tonne


Let’s do some more sums.Clew Bay catchment nutrient production by percent.

Annual N production as % of totalAnnual N production as % of total Annual P production as % of totalAnnual P production as % of total


Cattle 55.8%

Humans 2.3%

Trout 1.5%

Sheep 35.9%

Sheep 34.7%

Salmon 7.0%

Humans 4.4%

Cattle 51.5%

Total catchment Total catchment N production N production

3,529 tonnes pa3,529 tonnes pa

Total Total catchment P catchment P

production 560 production 560 tonnes patonnes pa

Salmon 4.4%

Trout 2.4%

What enters Clew Bay from its catchment?What enters Clew Bay from its catchment?All transformation indices from nutrient production to input from OSPAR Neut 5/3E 1999.

The fishfarms are in the bay, thus 100% of The fishfarms are in the bay, thus 100% of solublesoluble nutrient production is input to the water column.nutrient production is input to the water column.

Total = 185.1 tonnes N and 32.4 tonnes P paTotal = 185.1 tonnes N and 32.4 tonnes P pa

Urban dwellers (14,000); after secondary treatment, Urban dwellers (14,000); after secondary treatment, 1.79kg N and 0.46kg P input to the bay pp pa.1.79kg N and 0.46kg P input to the bay pp pa.

Rural dwellers (11,105); from septic tanks, 0.5kg N Rural dwellers (11,105); from septic tanks, 0.5kg N and 0.01kg P is input to the bay pp pa. and 0.01kg P is input to the bay pp pa.


Livestock (cattle and sheep); 20% of all N and 4% Livestock (cattle and sheep); 20% of all N and 4% of all P produced inputs to lough. of all P produced inputs to lough.


Have we Have we missed missed

anything?anything?

Yes!Yes!

Fertilisers; Est. 50% national mean spread rate, Fertilisers; Est. 50% national mean spread rate, 20% of N and 4% of P input to lough pa. 20% of N and 4% of P input to lough pa. Input = 506.3 tonnes N and 16.2 tonnes PInput = 506.3 tonnes N and 16.2 tonnes P

Forestry 135.5kmForestry 135.5km22; input = 73.4T N and 4.5 P pa; input = 73.4T N and 4.5 P pa

Background deposition = 80.9T N and 5.4 T P pa.Background deposition = 80.9T N and 5.4 T P pa.


Here come the sums again.Catchment rainfall and inputs to the bay; % per month.

Rainfall is the controlling factor in inputs that originate on the land. Rainfall is the controlling factor in inputs that originate on the land.

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2

4

6

8

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14

16

Jan Feb Mar Apr May Jun Jul Au Sep Oct Nov Dec

Net freshwater run-off to Clew Bay; % per month Net freshwater run-off to Clew Bay; % per month


Net annual freshwater run-off arising from rainfall in the ClewNet annual freshwater run-off arising from rainfall in the Clew Bay catchment is 1.2 billion mBay catchment is 1.2 billion m33 (=tonnes) pa. (=tonnes) pa.

0

50

100

150

200

250

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Inpu

t ton

nes

Livestock Fertiliser Forestry Background Fishfarming All humans

Nitrogen inputs into Clew Bay; % / month

• Fishfarm nutrients vary with temperature, biomass and feeding.


• Human inputs vary with population change (tourist flux).

• Inputs from land vary in proportion to % monhtly freshwater run-off.

How does that look annually?How does that look annually?Nitrogen inputs from catchment sources by percent.Nitrogen inputs from catchment sources by percent.


Total annual Total annual N input 3,477 N input 3,477

tonnestonnes

Total annual Total annual N input 1,578 N input 1,578

tonnestonnes

Clew Bay Lough Swilly

Fertiliser 32.57%

Fertiliser 26.82%

Forestry1.88%

Forestry4.72% Background

3.91%Background5.20%

Fishfarms11.91%

Fishfarms 2.84%

Humans 3.94%

Humans 1.97%

Livestock 60.61%

Livestock 41.66%

What happens in the Bay?The contribution of the ocean to nutrients in Clew Bay

Mean inorganic N varies monthly from 16-168mgm/tonne water.Mean inorganic N varies monthly from 16-168mgm/tonne water. Mean inorganic P varies monthly from 8.7-18.0mgm/tonne water.Mean inorganic P varies monthly from 8.7-18.0mgm/tonne water. (Source 10 years of 2-weekly sampling data from Clew Bay).(Source 10 years of 2-weekly sampling data from Clew Bay).

The mean low water volume of Clew Bay is 302kmThe mean low water volume of Clew Bay is 302km22 x 20m x 20m = 6,043,221,460 m = 6,043,221,460 m33 (= tonnes weight) (= tonnes weight)

The tidal range is 1.65 m (neap) to 3.75m (spring). The tidal range is 1.65 m (neap) to 3.75m (spring). Using a tidal prism model, we can calculate that Lough Swilly Using a tidal prism model, we can calculate that Lough Swilly

flushes flushes with the tide alonewith the tide alone every 3-6.5 days (spring to neap) every 3-6.5 days (spring to neap) Thus the volume of water flushing into Lough Swilly every month Thus the volume of water flushing into Lough Swilly every month

= 44,750,829,683 tonnes pm = = 44,750,829,683 tonnes pm = almost 540 billion tonnes paalmost 540 billion tonnes pa. . This is equivalent to the weight of 176 x the earth’s human This is equivalent to the weight of 176 x the earth’s human

population marching into Clew Bay every monthpopulation marching into Clew Bay every month..

Since it is the flushing action of tide and current that carries all Since it is the flushing action of tide and current that carries all nutrients into the bay, we can calculate that the total flux of nutrients into the bay, we can calculate that the total flux of nutrients is nutrients is 38,769 tonnes of nitrogen38,769 tonnes of nitrogen and and 7,243 tonnes of 7,243 tonnes of phosphorus per annum phosphorus per annum (windless conditions only).(windless conditions only).


Mean nutrient flux into Clew Bay.

0

1000

2000

3000

4000

5000

6000

7000

8000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

N

P


The “wave form” of the graph reflects the natural, seasonal cycle of nutrient The “wave form” of the graph reflects the natural, seasonal cycle of nutrient uptake, primary production die back and remineralisation in the oceans, uptake, primary production die back and remineralisation in the oceans, hence the term “oceanic flux”.hence the term “oceanic flux”.

Derived by multiplying the monthly tidal flow into Clew Bay by the Derived by multiplying the monthly tidal flow into Clew Bay by the mean monthly ambient nutrient concentration (ten-year database).mean monthly ambient nutrient concentration (ten-year database).

Total nutrient flux in percentagesTotal nutrient flux in percentages% contribitions to total flux from catchment and the ocean.% contribitions to total flux from catchment and the ocean.

Annual N flux as % of totalAnnual N flux as % of total Annual P flux as % of totalAnnual P flux as % of total


Humans 0.07%

Fertiliser 1.31%

Livestock 1.67%

Salmon0.54%

Background0.21%

Forestry0.19%

Oceanic96.02%

Humans 0.07% Livestock

0.27%

Fertiliser 0.22%

Salmon 0.72%

Background0.07%

Forestry0.06%

Oceanic98.59%

Total annual Total annual N flux 14,817 N flux 14,817

tonnestonnes

Total annual P Total annual P flux 2,921 flux 2,921

tonnestonnes

So?


The model tells us that The model tells us that we can infer absolutely no negative impact we can infer absolutely no negative impact from nutrient inputs arising fromfrom nutrient inputs arising from the production of 4,500 tonnes of the production of 4,500 tonnes of salmonidssalmonids in Clew Bay, nor for that matter any other nutrient input. in Clew Bay, nor for that matter any other nutrient input. On the basis of nutrient inputs alone, the bay could support On the basis of nutrient inputs alone, the bay could support considerably more finfish culture. considerably more finfish culture.

Bearing in mind all the allegations made about “pollution from Bearing in mind all the allegations made about “pollution from salmon farming”, should we be surprised that no lobby group salmon farming”, should we be surprised that no lobby group seems to be as bothered about the nutrient impact of agriculture? seems to be as bothered about the nutrient impact of agriculture? As we have seen, agriculture sources account for well over 90% As we have seen, agriculture sources account for well over 90% catchment nitrogen. catchment nitrogen.

In freshwater systems, nutrient inputs from agriculture are now In freshwater systems, nutrient inputs from agriculture are now believed to be Ireland’s biggest single environmental issue, causing believed to be Ireland’s biggest single environmental issue, causing eutrophication and wiping out ame and coarse fish stocks.eutrophication and wiping out ame and coarse fish stocks.

We can see that the power of tide and ocean controls the nutrient We can see that the power of tide and ocean controls the nutrient balance in well-flushed sea areas very effectively. Indeed this is balance in well-flushed sea areas very effectively. Indeed this is the dominant source of their nutrient flux. the dominant source of their nutrient flux.

In case you wondered…


In the case of the Clew Bay model model:-In the case of the Clew Bay model model:-

One tonne of salmon production in Clew Bay produces the same One tonne of salmon production in Clew Bay produces the same nutrient nitrogen waste as about 14 humans (or 1.1 cows!!)nutrient nitrogen waste as about 14 humans (or 1.1 cows!!)

One tonne of salmon production in Clew Bay produces the same One tonne of salmon production in Clew Bay produces the same nutrient phosphorus waste as about 13 humans.nutrient phosphorus waste as about 13 humans.

One tonne of salmon production in Clew produces the same BOD as One tonne of salmon production in Clew produces the same BOD as about 15 adult humans.about 15 adult humans.

Whichever way you look at it, Håkanssen was out by a factor of 10 Whichever way you look at it, Håkanssen was out by a factor of 10 and Suzuki by a factor of 100. The source recently quoted in the and Suzuki by a factor of 100. The source recently quoted in the Mayo News was out by a factor of 15-20. Marine salmon farming is Mayo News was out by a factor of 15-20. Marine salmon farming is notnot a significant polluter in the well flushed waters of the west of a significant polluter in the well flushed waters of the west of Ireland. Anyone who thinks it is is talking a load of ….Ireland. Anyone who thinks it is is talking a load of ….

Bull…!



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Sources, production and fate of nutrients in Clew Bay, County Mayo and its catchment