Lake effects on outlet stream attributes in Arctic tundra drainages, North Slope, Alaska

Lake-stream networks are common in many regions of the Northern Hemisphere, yet physical, chemical, and biological processes in these systems are poorly understood.  We hypothesized that lakes would act as a physical discontinuity in Arctic lake-stream networks, altering the temperature and hydrographs of outlet streams, thereby affecting the rates of ecosystem processes and macroinvertebrate community compared to inlet streams.  In a longitudinal study (one upstream, three downstream stations) of three lake-stream networks, primary and secondary production differed between watersheds (p<0.01).  Regardless of watershed, rates of leaf litter breakdown increased and primary production decreased in outlet streams compared with inlet streams (p<0.01).  Rates of these processes were positively correlated with substratum stability and nutrient concentrations in streams (p<0.05) but not mean temperature. An ordination of macroinvertebrate communities based on structure and secondary production showed excellent separation between sites (stress=0.05).  This was explained by temperature, nutrient concentrations, and substratum characteristics (BEST, ρ=0.665).  While lakes altered stream community attributes, alterations were not predictable based position relative to lakes in general.  That is, each lake forced its unique signature on the outlet stream.  These results suggest that while lakes influence stream processes in lake-stream networks, a larger set of landscape-scale filters have precedence.