Hyporheic bacteria - relationships to environmental gradients and invertebrates in a prealpine stream
Brunke, M.; Fischer, H.
published: Oct 11, 1999
ArtNo. ESP141014602003, Price: 29.00 €
Bacterial abundance and production in hyporheic interstices of the Töss River, a gravel-bed stream in Switzerland, were examined focusing on spatial distribution patterns in relationship to potential resources and meio- and macrofaunal consumers. The subsurface flow regime at the study site was characterized by a cross-sectional hydraulic gradient, with ground water exfiltration at the left margin and surface water infiltration at the right margin; in midstream, horizontal advection along the channel flow prevailed. Measurement of biotic and abiotic parameters were performed down to sediment depths of 150 cm within each hydrological exchange type. Bacterial abundances ranged between 1.6 x 105 to 4.8 x 108 cells/ml interstitial volume containing water and fine particles and differed significantly between upper and deeper sediment strata. This change with depth was significantly modulated by the type of hydrological exchange. The bacterial carbon portion of total POC varied between 0.06 % and 5.3 % and tended to decrease with depth. Bacteria were most numerous at sediment depths where inflow of stream water occurred, but had been attenuated. Bacterial production was highest in hyporheic interstices dominated by surface water inflow. Bacterial abundance and production were strongly correlated to interstitial particulate organic matter; the best predictor for both was the content of particulate nitrogen, explaining 75 % and 72 % of the variation, respectively. Inclusion of hyporheic positions, defined by sediment depth and hydrological exchange type, improved the explanatory power of models to 88 % and 84 %, respectively. Hyporheic positions provide information on flowpath connections, which were particularly relevant when one uses dissolved organic carbon and interstitial fine sediment as explanatory variables. Abundance of several hyporheic invertebrate taxa, taxa richness and total invertebrate density were positively correlated to bacterial abundance and production. The hyporheic fauna exhibited a gradient between interstitial positions influenced by surface water and those dominated by phreatic ground water. The coupling of sediment depth and hydrological exchange type revealed flowpath connections as being superimposed vectors in determining hyporheic abiotic and biotic gradients.