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 Autumn Z-value Mean (± standard error) Mean (± standard error) BMWP 103.9 (± 3.1) 89.99 (± 2.2) 4.19*** ASPT 5.9 (± 0.06) 5.43 (± 0.06) 6.92*** SSRS 6.5 (± 0.21) 4.6 (± 0.19) 7.53*** Total abundance 875 (± 56) 889.5 (± 71.8) 0.04 Total richness 19.98 (± 0.47) 18.69 (± 0.34) 3.32*** A-class abundance 89.5 (± 12) 13.35 (± 2.98) 10.86*** A-class richness 2.08 (± 0.11) 0.96 (± 0.1) 8.59*** EPT richness 10.82 (± 0.37) 8.22 (± 0.29) 8.72*** EPT abundance 349.5 (± 20.12) 182 (± 12.96) 8.63*** % EPT 53.06 (± 0.88) 42.85 (± 1) 10.59***
Stream chemistry Phosphorus higher in summer than spring Nitrogen higher in spring than summer Spring Summer Z-value Mean (± standard error) Mean (± standard error) Total P (mg/l) 0.069 (± 0.009) 0.079 (± 0.006) -1.04 TDP (mg/l) 0.05 (± 0.006) 0.07 (± 0.005) -2.56* Reactive P (mg/l) 0.05 (± 0.006) 0.06 (± 0.005) -2.06* DRP (mg/l) 0.04 (± 0.006) 0.06 (± 0.005) -2.24* Nitrate-N (mg/l) 4.65 (± 0.228) 3.86 (± 0.226) 4.62*** Ammonium-N (mg/l) 0.08 (± 0.013) 0.035 (± 0.009) 2.88** Total N (mg/l) 4.82 (± 0.227) 3.9 (± 0.203) 6.35*** TON (mg/l) 4.68 (± 0.226) 3.87 (± 0.227) 4.73*** Conductivity (µs/cm) 309.39 (± 13.077) 320.68 (± 13.781) -1.24
Ecological community structure Spring Community structure significantly different between seasons Autumn
1.0 RhithSp Spring PCA GammarSp Conducti AselluSp TDP AgapetSp PotamoSp PlecCons Nitrite ChloroSp HalesuSp IsoperSp DrusAnnu Ammonium AmphiSp CaenRivo SerrIgni Nitrate HydropSp PotaJenk OdonAlbi RhyacoSp ProtoSp. LeuctSp Simuliid Rhithrogena and Chloroperlidae most closely associated with spring Protonemura and Simuliidae most closely associated with summer Pollution tolerant taxa Gammarus and Asellus associated with TDP Summer -0.8 0.8
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 In late September seasonal difference is not clear Early September samples Mid - Late September samples Spring Autumn
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 Stephen.davis@teagasc.ie