The influence of terrestrial linkages on small stream habitat and biota

Habitat in small streams is influenced by both longitudinal (upstream) and lateral runoff and allocthonous inputs which differ along the length of a stream.  Our objectives were to: 1) Evaluate associations between lateral contributions to a stream and characteristics of stream habitat and biota, 2) Examine changes in these terrestrial-aquatic linkages following forest harvesting and 3) Develop GIS based techniques to quantify levels of lateral contribution along streams.  Reaches associated with larger areas of lateral contributions, or “Reach Contributing Area” (RCA), had finer substrate and more wood debris, greater thermal variability, a distinct benthic invertebrate community structure, and higher fish abundance compared to reaches with smaller RCAs.  Impacts on terrestrial-aquatic linkages were evaluated by monitoring water and nutrient inputs into a stream before and after experimental harvest. Water yield from RCAs approximately doubled relative to pre-harvest and water flux increased significantly relative to a control.  Concentrations of DOC and some nutrients (e.g. K, N, P) and metals (e.g. Mn, Fe) increased 2 to 3 times in the year after harvest, and the flux rate of mercury approximately double that of reference conditions. Identification of potentially significant RCAs will facilitate planning of forest management activities in order to mitigate adverse impacts.