The Influence of Hyporheic-Surface Water Exchange on the Spatial Distribution of Benthic Algal Biomass and Community Composition in an Alluvial River. <p> HR: <span class="hr"> 14:30h<br></span> AN: <span class="an"> B23A-05 <a href="../absbook/sm05_B23A.html">[Abstracts]</a><br></span> TI: <span class="ti"> The Influence of Hyporheic-Surface Water Exchange on the Spatial Distribution of Benthic Algal Biomass and Community Composition in an Alluvial River. <br></span> AU: <span class="au"> * Wyatt, K H<br></span> EM: <span class="em"> kevin.wyatt@usm.edu<br></span> AF: <span class="af"> Department of Biological Sciences, The University of Southern Mississippi, 118 College Drive Box 5018, Hattiesburg, MS 39406 United States <br></span> AU: <span class="au"> Hauer, F R<br></span> EM: <span class="em"> www.umt.edu/biology/flbs<br></span> AF: <span class="af"> Flathead Lake Biological Station, Division of Biological Sciences, The University of Montana, 311 Bio Station Lane, Polson, MT 59860 United States <br></span> AU: <span class="au"> Pessoney, G F<br></span> EM: <span class="em"> george.pessoney@usm.edu<br></span> AF: <span class="af"> Department of Biological Sciences, The University of Southern Mississippi, 118 College Drive Box 5018, Hattiesburg, MS 39406 United States <br></span> AU: <span class="au"> Gligora, M <br></span> EM: <span class="em"> mgligora@biol.pmf.hr<br></span> AF: <span class="af"> Division of Biology, Faculty of Science, University of Zagreb, Rooseveltov trg 6, Zagreb, Croatia (local name: Hrvatska) <br></span> AB: <span class="ab"> We investigated the influence of hyporheic-surface water interactions on the spatial distribution of benthic algal biomass and community composition in the main-channel of the Middle Fork Flathead River in northwestern Montana. We examined hyporheic-surface water exchange at 120 randomly selected sites by measuring vertical hydraulic gradients (VHG) and hydraulic conductivities using metal piezometers. At each replicate site, we collected algae from a single cobble to analyze chlorophyll a concentration and estimate algal density and community composition. We used Non-metric Multidimensional Scaling (MDS) based on the Bray-Curtis Index of Similarity to evaluate the response of benthic algal communities to hyporheic-surface water exchange. Algal communities at upwelling (+VHG) and downwelling (-VHG) sites occupied discrete regions of ordination space created by the MDS. Algal communities at upwelling sites were dominated by the genus <em>Stigeoclonium</em> or <em>Hydrurus</em>, whereas communities at downwelling sites were dominated by the genus <em>Achnanthidium</em>. There was a statistically significant positive correlation between benthic algal biomass and hyporheic upwelling. The preliminary results of our study suggest that hyporheic-surface water exchange regimes influence the spatial distribution of benthic algal biomass and community composition in large alluvial rivers. <br></span> DE: <span class="de"> 1845 Limnology<br></span> DE: <span class="de"> 9901 NABS Student Award - Basic Research<br></span> SC: <span class="sc"> Biogeosciences [B]<br></span> MN: <span class="mn"> 2005 Joint Assembly<br></span></p></body></html>