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
Aims
To investigate how conifer plantation forestry operations affect
blanket bog lakes in terms of:
1) Their hydrochemical status
2) Their Chydoridae (Cladocera) communities
Study design
Sedimentary (Sandstone) Geology
Igneous (Granite) Geology
6 lakes non-forested (‘blanket bog’)
7 lakes non-forested (‘blanket bog’)
6 lakes afforested:
7 lakes afforested:
3 lakes surrounded by mature
conifer forests (‘mature
plantation’)
4 lakes surrounded by mature
conifer forests (‘mature
plantation’)
3 lakes surrounded by
clearfelling (‘clearfell’)
3 lakes surrounded by
clearfelling (‘clearfell’)
Study lakes
• The lakes underlain by
granite are located at lower
altitude and in closer
proximity to the coast than
the lakes underlain by
sandstone
GB1
GB2
GB3
GB4
GB5
GB6
GB7
SB3
SB4
SB5
SB6
SC1
SC2
SC3
S = Sandstone
G = Granite
B = Blanket bog
M = Mature plantation
C = Clearfell
GM1
GM2
GM3
GM4
GC1
GC2
GC3
SB1
SB2
SM1
SM2
SM3
Blanket bog lake:
catchment containing only
undisturbed blanket bog
Mature plantation lake:
catchment dominated by closedcanopy conifer plantation
Clearfell lake:
catchment containing mature conifer
plantation with recently (within 2 – 5
years) clearfelled areas
Methodology
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
Results – water chemistry
Water Chemistry PCA
• Higher plant nutrients, TDOC,
major ions, heavy metals, and
reduced dissolved oxygen
concentrations in lakes with
forestry
4
a)
PC 1
-10
4
PC 2
-4
 Sandstone blanket bog
 Granite blanket bog
l Sandstone mature plantation
p Granite mature plantation
l Sandstone clearfell
0.4
b)
Chlorophyll a
TP
tot. Al
TDOC
TN
SRP
-0.4
Fe
Ammonia
Mn
0.4
TON
Ca
K
Temperature
Conductivity
pH
p Granite clearfell
-0.6
Dissolved
oxygen
Results – water chemistry
Soluble Reactive Phosphorus
(mg l -1)
0.008
0.8
0.4
0
0.000
Blanket bog
28
Total Nitrogen
1.2
0.016
Mature
plantation
Blanket bog
Clearfell
Chlorophyll a
(mg l -1)
14
0.10
0.05
0
0.00
Mature
plantation
Clearfell
Sandstone
Clearfell
0.15
7
Blanket bog
Mature
plantation
Ammonia
0.20
21
(μg l -1)
(mg l -1)
0.024
Blanket bog
Granite
Mature
plantation
Clearfell
Results – water chemistry
Dissolved oxygen
240
Total monomeric aluminium
180
10
(μg l -1)
(mg l -1)
12
8
120
60
0
6
Blanket bog
Mature
plantation
Blanket bog
Clearfell
(mg l -1)
Dissolved organic carbon
8
18
6
12
4
6
2
0
0
Mature
plantation
Clearfell
Sandstone
Clearfell
pH
24
Blanket bog
Mature
plantation
Blanket bog
Granite
Mature
plantation
Clearfell
Discussion of 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.
Results – chydorids
Chydorid community nMDS
 Sandstone blanket bog
 Granite blanket bog
l Sandstone mature plantation
p Granite mature plantation
l Sandstone clearfell
p Granite clearfell
Stress: 0.15
Results – chydorids
Chydorus sphaericus
Alonopsis elongata
1000
Mean abundance
Mean abundance
750
600
450
300
150
750
500
250
0
0
Blanket bog
Mature
plantation
Blanket bog
Clearfell
Clearfell
Alonella excisa
Alonella nana
200
Mean abundance
360
Mean abundance
Mature
plantation
270
180
90
150
100
50
0
0
Blanket bog
Mature
plantation
Clearfell
Sandstone
Blanket bog
Granite
Mature
plantation
Clearfell
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
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
Conclusions
• Chydorid community change is consistent with conifer plantation forestry
exerting a trophic, rather than an acidic or toxic effect on lake ecosystems
• 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
Acknowledgements
• 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