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Irish Freshwater Biologists Meeting 2012. Macroinvertebrate Resource Utilisation in Upland Streams: Riparian Management Impacts. C. Barry & Y. McElarney Agri-Environment Branch Newforge Lane, Belfast. Riparian Management Impacts.
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Irish Freshwater Biologists Meeting 2012 Macroinvertebrate Resource Utilisation in Upland Streams: Riparian Management Impacts C. Barry & Y. McElarney Agri-Environment Branch Newforge Lane, Belfast
Riparian Management Impacts RCC – interpretative paradigm for resource utilisation / carbon flow in river food webs But, ● Variation of riparian vegetation at low stream orders – alters resource availability and quality ● Resource utilisation by functional feeding group -feeding mechanisms to determine resource use -opportunism and generalist feeding frequent ●To eat is to assimilate? High terrestrial inputs Low nutrient inputs Low PP low P:R Increasing light and nutrients greater PP P:R increasing High light & nutrients & C inputs from upstream processing P:R decreasing
How to assess macroinvertebrate resource utilisation? Natural abundance Carbon and Nitrogen Stable Isotope Analysis13C:12C 15N:14N Consumer isotopic ratios reflect the isotopic ratios of their diet in a consistent way ► You are what you eat, less what you excrete Fractionation: stuff happens to lighter isotopes more readily ●Physical: evaporation ●Chemical: respiration Ratios unwieldy; reported as signatures- deviation from standards (δ13C, δ15N) Measure stable isotope signatures for ● Macroinvertebrates ● Potential dietary sources Some consumers use several different resources…. Mixing models SIAR in R … Bayesian mixing model
Methods No Buffer (n=6) Natural Upland catchments (n=5) Unplanted Buffer (n=4) Recently Harvested (n=6) Broadleaved Buffer (n=4) 25 streams sampled once in summer (50m reach) Quantitative estimates of biomass and C & N isotopic analysis for ●macroinvertebrates ●biofilm ●biofilm chl a●macrophytes ●macroalgae ●benthic organic matter ●riparian vegetation ●seston ●Light penetration Physico-chemistry sampled seasonally on 3 occasions
Methods: deriving macroinvertebrate dietary reliance Stream with an unplanted riparian buffer 5 potential resources / end members δ15N (‰) δ13C (‰)
Methods: deriving macroinvertebrate dietary reliance 1.0 Resource: River conditioned detritus 0.8 0.6 0.4 Dietary reliance (%) 0.2 0.0 5. Leuctra 1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 6. Gammarus 7. Seratella
Methods: deriving macroinvertebrate dietary reliance 1.0 Resource: Biofilm 0.8 0.6 0.4 Dietary reliance (%) 0.2 0.0 5. Leuctra 1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 6. Gammarus 7. Seratella
Methods: deriving macroinvertebrate dietary reliance 1.0 Resource: Ulothrix tenuissima (filamentous green alga) 0.8 0.6 0.4 Dietary reliance (%) 0.2 0.0 5. Leuctra 1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 6. Gammarus 7. Seratella
Methods: deriving macroinvertebrate dietary reliance 1.0 Resource: Seston (suspended fine particulate organic matter) 0.8 0.6 0.4 Dietary reliance (%) 0.2 0.0 5. Leuctra 1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 6. Gammarus 7. Seratella
Methods: deriving macroinvertebrate dietary reliance 1.0 Resource: Scapania undulata (bryophyte) 0.8 0.6 0.4 Dietary reliance (%) 0.2 0.0 5. Leuctra 1. Baetis 2. Ecdyonurus 3. Elmis 4. Simulium 6. Gammarus 7. Seratella
Methods: Apportioning macroinvertebrate biomass Terrestrial vs. Aquatic
Macroinvertebrate Biomass Apportionment by site CE = No buffer: Conifers to stream edge OB = Open buffer (unplanted) CF = Clear felled B = broadleaved buffer CM = Natural upland (control)
Consumer frequency distributions of reliance on terrestrial C • Un-skewed distributions • - consumers exploiting a wide variety of resources • - greater niche availability / utilisation • ► Clear felled sites, Natural upland sites (control), no buffer sites* • Skewed distributions • consumers exploiting resources of similar origin • Suggests high abundance of such resources and/or resources of the same origin present in different forms…. FPOM, CPOM • ► Broadleaved buffer & Open buffer sites • Caveat • *Depleted consumer δ13C indicative of methane C • ►while terrestrial in origin, the approach regards consumers as utilising an autochthonous resource 100% terrestrial 100% aquatic
Species Specific Resource utilisation Sh = shredder Co = Collector Gr = Grazer Error bars = 1SD
Conclusions • Light reduction, slope & organic biofilm mass most important variables driving resource utilisation among sites • Biomass and species richness greater at buffered compared to un-buffered sites • Invertebrate community structure and resource use at buffered sites show little similarity to unimpacted control sites • Broadleaved buffer sites show high invertebrate biomass but a community largely specialised for an allochthonous diet
Acknowledgements AFBI Staff Lesley Gregg, Rachel Patterson, Alex Higgins Colm McKenna, Kirsty McConnell, Louise Davis, Elaine Hamill, Phil Dinsmore, Brian Stewart Forest Service, NI Ian Irwin, Colin Riley • EPA (Strive) for part funding study (project 2007-W-MS-3-S10): • An Effective Framework For assessing aquatic ECosysTem responses to implementation of the Phosphorus Regulations (EFFECT) • Department of Agriculture and Rural Development (DARD) for remainder of project funding.
