The impact of conifer plantation forestry on the Chydoridae communities of blanket bog lakes

The impact of conifer plantation forestry on the Chydoridae communities of blanket bog

lakes

Tom J. Drinan, Conor T. Graham, John O’Halloran and Simon S.C. Harrison

HYDROFOR Project

Background

• Plantation forests cover an estimated 10% of the Irish land surface area. Many of these plantations are on peat soils

• Extensive afforestation of peat soils has taken place since the 1950’s – this crop is now reaching harvestable age

• Previous studies have demonstrated a high risk of plant nutrient and sediment run-off to receiving waters from afforested catchments, particularly on peat soils

• There is a clear risk to the ecological status of high conservation value peatland water bodies from catchment forestry operations

To investigate how conifer plantation forestry operations affect blanket bog lakes in terms of:

1) Their hydrochemical status

2) Their Chydoridae (Cladocera) communities

Aims

Study design

Igneous (Granite) Geology

7 lakes non-forested (‘blanket bog’)

7 lakes afforested:

4 lakes surrounded by mature conifer forests (‘mature plantation’)

3 lakes surrounded by clearfelling (‘clearfell’)

Sedimentary (Sandstone) Geology

6 lakes non-forested (‘blanket bog’)

6 lakes afforested:

3 lakes surrounded by mature conifer forests (‘mature plantation’)

3 lakes surrounded by clearfelling (‘clearfell’)

Study lakes

GB1GB2

GM1GM2

GB3GB4

GM3GM4

GB5 GC1GB6 GC2GB7 GC3

SB3SB4SB5SB6SC1SC2SC3

SB1SB2SM1SM2SM3

• The lakes underlain by granite are located at lower altitude and in closer proximity to the coast than the lakes underlain by sandstone

S = SandstoneG = Granite

B = Blanket bogM = Mature plantation C = Clearfell

Blanket bog lake:catchment containing only undisturbed blanket bog

Mature plantation lake: catchment dominated by closed-canopy conifer plantation

Clearfell lake: catchment containing mature conifer plantation with recently (within 2 – 5 years) clearfelled areas

Water Chemistry

• Dip samples (a single sample from the water column) were taken every two months from each lake, beginning March 2009

• We measured pH, conductivity, temperature, dissolved oxygen, colour, alkalinity, TDOC, TP, SRP, TN, TON, ammonia, SO4, Ca, Na, Cl, Mg, Al, Mn and Fe

Chydoridae

• Semi-quantitative method: slowly sweeping a hand-held sweep net (100 μm mesh, 0.15 m diameter frame) horizontally both inside and outside a stand of vegetation for 30 seconds in the littoral zone of each lake

Methodology

Results – water chemistry

-0.4 0.4

-0.6

0.4

pHConductivity

Temperature

Chlorophyll a

TDOCTP

SRPTN

TON

CaK

MnFe

b)

Water Chemistry PCA

• Higher plant nutrients, TDOC, major ions, heavy metals, and reduced dissolved oxygen concentrations in lakes with forestry

-10 4

-4

4

PC 1

PC 2

a)

Sandstone blanket bog

Granite blanket bog

l Sandstone mature plantation

p Granite mature plantation

l Sandstone clearfell

p Granite clearfell

Blanket bog Mature plan-tation

Clearfell0.00

0.05

0.10

0.15

0.20

(mg

l -1)

Ammonia

Blanket bog Mature plan-tation

Clearfell0.000

0.008

0.016

0.024

(mg

l -1)

Soluble Reactive Phosphorus

Sandstone Granite

Blanket bog Mature plan-tation

Clearfell0

0.4

0.8

1.2

(mg

l -1)

Total Nitrogen

Results – water chemistry

Blanket bog Mature plan-tation

Clearfell0

7

14

21

28

(μg

l -1)

Chlorophyll a

Blanket bog Mature plan-tation

Clearfell6

8

10

12(m

g l -

1)

Dissolved oxygen

Blanket bog Mature plantation

Clearfell0

6

12

18

24

(mg

l -1)

Dissolved organic carbon

Blanket bog Mature plan-tation

Clearfell0

2

4

6

8pH

Blanket bog Mature plan-tation

Clearfell0

60

120

180

240

(μg

l -1)

Total monomeric aluminium

Sandstone Granite

Results – water chemistry

Likely sources of forestry inputs include:

• Decomposition of the clearfell residue (brash, foliage etc.)

• Decomposition of peat soil

• Artificial fertilisers applied during the forest crop cycle

Potential impacts of forestry-mediated hydrochemical change:

• Enhanced autotrophic and heterotrophic production

• Reduced dissolved oxygen concentrations

• Elevated heavy metal concentrations.

Discussion of water chemistry

Chydorid community nMDS

Stress: 0.15

Sandstone blanket bog

Granite blanket bog

l Sandstone mature plantation

p Granite mature plantation

l Sandstone clearfell

p Granite clearfell

Results – chydorids

Sandstone Granite

Alonopsis elongata

Blanket bog Mature plantation Clearfell0

150

300

450

600

750

Mea

n ab

unda

nce

Chydorus sphaericus

Blanket bog Mature plantation Clearfell0

250

500

750

1000

Mea

n ab

unda

nce

Alonella nana

Blanket bog Mature plantation Clearfell0

90

180

270

360

Mea

n ab

unda

nce

Alonella excisa

Blanket bog Mature plantation Clearfell0

50

100

150

200

Mea

n ab

unda

nce

Results – chydorids

• Alonopsis elongata dominant in blanket bog lakes and Chydorus sphaericus, Alonella nana and Alonella excisa dominant in clearfell and mature plantation lakes

• Only two individuals of a single species (Alona guttata) were recorded from a recently clearfelled lake underlain by granite. This lake also contained the highest concentrations of Al & Fe

• Alonella excisa was more abundant in sandsone lakes

Results – chydorids

Discussion of chydorids

• Increased autotrophy and heterotrophy leads to a reduction in size of the dominant food particles available A. elongata feeds on larger food particles, C. sphaericus, A. nana and A. excisa feed on smaller food particles

• C. sphaericus is more tolerant to the general decline in lake water quality

• Toxicity from heavy metals only important following recent extensive catchment clearfelling

• The higher pH and base cation concentration, driven primarily by marine sea-spray deposition, may account for geological effects on chydorids

• Chydorid community change is consistent with conifer plantation forestry exerting a trophic, rather than an acidic or toxic effect on lake ecosystems

Conclusions

• Plantation forestry effect was consistent across geologies and regions, indicating that the anthropogenic effect overrides any effect of catchment geology, altitude and proximity to sea

• This study was funded by the HYDROFOR project which is co-funded by

the Department of Agriculture, Fisheries and Food, and Environmental

Protection Agency (EPA) under the STRIVE Programme 2007–2013

• We thank Dr. Elvira de Eyto for her help with zooplankton identification

and various aspects of the research

Acknowledgements