Macroinvertebrate Resource Utilisation in Upland Streams: Riparian Management Impacts Irish Freshwater Biologists Meeting 2012 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 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 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?

How to assess macroinvertebrate resource utilisation? Natural abundance Carbon and Nitrogen Stable Isotope Analysis 13 C: 12 C 15 N: 14 N 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 (δ 13 C, δ 15 N) 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) Broadleaved Buffer (n=4) Recently Harvested (n=6) 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 25 streams sampled once in summer (50m reach)

Methods: deriving macroinvertebrate dietary reliance δ 13 C (‰) δ 15 N (‰) Stream with an unplanted riparian buffer 5 potential resources / end members

Resource: River conditioned detritus 1. Baetis2. Ecdyonurus3. Elmis4. Simulium 5. Leuctra 6. Gammarus7. Seratella Dietary reliance (%) Methods: deriving macroinvertebrate dietary reliance

1. Baetis2. Ecdyonurus3. Elmis4. Simulium 5. Leuctra 6. Gammarus7. Seratella Resource: Biofilm Dietary reliance (%) Methods: deriving macroinvertebrate dietary reliance

1. Baetis2. Ecdyonurus3. Elmis4. Simulium 5. Leuctra 6. Gammarus7. Seratella Resource: Ulothrix tenuissima (filamentous green alga) Dietary reliance (%) Methods: deriving macroinvertebrate dietary reliance

1. Baetis2. Ecdyonurus3. Elmis4. Simulium 5. Leuctra 6. Gammarus7. Seratella Resource: Seston (suspended fine particulate organic matter) Dietary reliance (%) Methods: deriving macroinvertebrate dietary reliance

1. Baetis2. Ecdyonurus3. Elmis4. Simulium 5. Leuctra 6. Gammarus7. Seratella Resource: Scapania undulata (bryophyte) Dietary reliance (%) Methods: deriving macroinvertebrate dietary reliance

Allochthonous (Terrestrial)% Autochthonous (in situ PP) % Total Invertebrate mass mg m -2 Allochthonous mass mg m -2 Autochthonous mass mg m -2 Baetis Simulium Ecdyonurus Elmis Gammarus Leuctra Seratella Plectrocnemia Total mg m Terrestrial vs. Aquatic Methods: Apportioning macroinvertebrate biomass

CE = No buffer: Conifers to stream edge OB = Open buffer (unplanted) CF = Clear felled B = broadleaved buffer CM = Natural upland (control) Macroinvertebrate Biomass Apportionment by site

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 δ 13 C indicative of methane C ►while terrestrial in origin, the approach regards consumers as utilising an autochthonous resource 100% terrestrial100% aquatic Consumer frequency distributions of reliance on terrestrial C

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.

Results: Isotopic overview