Seasonal changes in macroinvertebrate
communities in agricultural catchments:
natural variation or anthropogenic impact?
Stephen Davis (UCD/Teagasc)
Mary Kelly-Quinn (UCD), Edel Hannigan (UCD),
Mairead Shore (Teagasc), Per-Erik Mellander (Teagasc), Daire Ó hUallacháin (Teagasc)
Aims
• Describe seasonal variations in macroinvertebrate communities in
agricultural catchments
• Relate changes in communities to antecedent water chemistry
• Identify the main pressures affecting ecology in agri-catchments
Hypothesis
• Changes in macroinvertebrate communities
between seasons are greater than those
which could be expected naturally
• 4 or 5 sites per catchment
Study
Catchments
• 5 catchments
• Three grassland and
two arable
Ecology sites
Snapshot chemistry sites
Ecology
• One 2-minute kick sample taken in both May (spring) and
September (autumn) between 2010 and 2014
Chemistry
• Monthly chemical samples for P and N. All chemical samples
were taken at baseflow
• Monthly mean for Feb, Mar and Apr used to represent spring
antecedent conditions and monthly mean of Jun, Jul and Aug
used to represent summer
Multivariate analysis
• PERMANOVA
• PCA
• Regression modelling
Macroinvertebrate communities
• Seasonal variation in metrics
• Spring values higher than
autumn
• Differences in pollution sensitive
species
Spring
Mean (± standard error)
BMWP
103.9 (± 3.1)
ASPT
5.9 (± 0.06)
SSRS
6.5 (± 0.21)
Total abundance
875 (± 56)
Total richness
19.98 (± 0.47)
A-class abundance
89.5 (± 12)
A-class richness
EPT richness
EPT abundance
% EPT
2.08 (± 0.11)
10.82 (± 0.37)
349.5 (± 20.12)
53.06 (± 0.88)
Autumn
Mean (± standard error)
89.99 (± 2.2)
5.43 (± 0.06)
4.6 (± 0.19)
889.5 (± 71.8)
18.69 (± 0.34)
13.35 (± 2.98)
Z-value
4.19***
6.92***
7.53***
0.04
3.32***
10.86***
0.96 (± 0.1)
8.22 (± 0.29)
182 (± 12.96)
42.85 (± 1)
8.59***
8.72***
8.63***
10.59***
Stream chemistry
• Phosphorus higher in summer than spring
• Nitrogen higher in spring than summer
Total P (mg/l)
TDP (mg/l)
Reactive P (mg/l)
DRP (mg/l)
Nitrate-N (mg/l)
Ammonium-N (mg/l)
Total N (mg/l)
TON (mg/l)
Conductivity (µS/cm)
Spring
Mean (± standard error)
0.069 (± 0.009)
0.05 (± 0.006)
0.05 (± 0.006)
0.04 (± 0.006)
4.65 (± 0.228)
0.08 (± 0.013)
4.82 (± 0.227)
4.68 (± 0.226)
309.39 (± 13.077)
Summer
Mean (± standard error)
0.079 (± 0.006)
0.07 (± 0.005)
0.06 (± 0.005)
0.06 (± 0.005)
3.86 (± 0.226)
0.035 (± 0.009)
3.9 (± 0.203)
3.87 (± 0.227)
320.68 (± 13.781)
Z-value
-1.04
-2.56*
-2.06*
-2.24*
4.62***
2.88**
6.35***
4.73***
-1.24
Ecological community structure
Spring
• Community structure
significantly different
between seasons
Autumn
1.0
PCA
RhithSp
Spring
ChloroSp
AgapetSp
GammarSp
Conducti
PotamoSp
PlecCons
• Rhithrogena and Chloroperlidae
most closely associated with spring
HalesuSp
IsoperSp
DrusAnnu
Ammonium
AmphiSp
TDP
Nitrite
AselluSp
CaenRivo SerrIgni
Nitrate
HydropSp
PotaJenk
OdonAlbi
RhyacoSp
ProtoSp.
LeuctSp
Simuliid
Summer
-0.8
0.8
• Protonemura and Simuliidae most
closely associated with summer
• Pollution tolerant taxa Gammarus
and Asellus associated with TDP
Results highlight significant seasonal differences between
community composition and structure
WHY?
Life history or anthropogenic pressures
•
Can you disentangle natural life history variations from changes caused by
anthropogenic inputs
• Callanan et al. (2008) showed that ecological metrics
varied between seasons in reference systems
• How to assess variation above and beyond that which is
expected naturally?
Community structure
• Difficult to interpret patterns in pollution sensitive taxa without
knowledge of life cycle
All samples
Autumn
Community Structure
Natural Variation?
• Seasonal difference
Spring
Early September samples
Spring
Autumn
• In late September seasonal difference is not
clear
Mid - Late September samples
Conclusions
• Macroinvertebrate communities in
agricultural streams differ significantly
between seasons
• Levels of P are higher during the
summer
• Two types of site
• Sites that change status between
seasons
• Sites that are consistently poor in
both seasons
• Anthropogenic activity may be driving
changes in communities above natural
variation?
Challenges and future research
• Difficult to disentangle natural variation from
anthropogenic impacts in some sites
• Ecological sampling at higher temporal
resolution needed to pinpoint when changes in
community structure occur
Thank you
Acknowledgements
Aquatic Services Unit,
University College Cork for
collecting the macroinvertebrate
data
Research staff, technicians and
farmers of the Agricultural
Catchments Programme
This project is funded through
the Walsh Fellowship
Programme, Teagasc
[email protected]