engleski

The Influence of Hyporheic-Surface Water Exchange on the Spatial Distribution of Benthic Algal Biomass and Community Composition in an Alluvial River.

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 Stigeoclonium or Hydrurus, whereas communities at downwelling sites were dominated by the genus Achnanthidium. 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.

hyporheic-surface water interactions; algal assemblages; periphyton

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