Original paper

The role of river flow dynamics and food availability in structuring hyporheic microcrustacean assemblages: a reach scale study

Mori, Nataša; Simčič, Tatjana; Žibrat, Uroš; Brancelj, Anton

Abstract

The influence of river flow dynamics on the functioning and structure of microcrustacean assemblages (Copepoda, Cladocera, Ostracoda) in the shallow (SHz) and deep (DHz) hyporheic zone were studied in a Sava River (Slovenia) gravel bar over a 3 year period. Temperature, conductivity, dissolved oxygen concentrations, potential food resources (nitrates, dissolved organic carbon - DOC, particulate organic matter - POM, and electron transport system activity of biofilm - ETSA) were measured in the deep hyporheic zone (DHz, 210-240 cm, n = 39) on six sampling occasions (2007-2010) and in the shallow hyporheic zone (SHz, 30-200 cm, n = 10) during the first two sampling dates. Microcrustaceans were collected using the Bou-Rouch pumping method. The physical and chemical properties of the deep hyporheic water, such as conductivity, pH, SO4 and POM varied significantly over time and distance from the river. Less variability was observed in ETSA. Altogether 28 microcrustacean species were recorded within the two distinct habitat types (SHz and DHz). In the latter, mainly stygobiotic species occurred, with Acanthocyclops venustus (Norman and T. Scott, 1906) being the most frequent and abundant. During periods of low flow, patchiness of physical and chemical properties and microcrustacean assemblages increased in comparison to periods of moderate or high flow. Similarly, the patchiness was high after severe flooding with extensive sediment movements and increased clogging of interstitial spaces by fine sediments. Fine sediments and nitrates had the strongest influence on assemblage composition. The study demonstrated a strong connection between river flow dynamics, hyporheic processes and distribution of microcrustaceans, spatially and temporally.

Keywords

subsurface invertebratesbiogeochemical transformationsalluvial aquiferriver flowsava river