Influence of hydroscape complexity on watershed biogeochemistry

Background/Question/Methods

While past research has emphasized the importance of watershed composition, very little is known regarding how the configuration of different aquatic elements affects the biogeochemical signatures of surface waters,.  We investigated variation in watershed biogeochemistry in a lake-rich region to determine if relationships existed between hydroscape complexity (i.e., composition and configuration of the aquatic network) and stream biogeochemical signatures.  To address this question,we quantified the biogeochemical attributes 52 streams representing 3 distinct hydroscape categories in the Northern Highlands Lake District, Wisconsin, USA.  Hydroscape categories were based on the presence/absence of lakes and the position of lakes within the watershed.  Headwater stream watersheds (HSW) contained no lakes within the stream network while the other two categories both contained lakes.  Headwater lake watersheds (HLW) contained a single headwater lake (i.e., no stream inlets and a single stream outlet), and drainage lake watersheds (DLW) contained at least one drainage lake (i.e., a lake with a stream inlet and single outlet) at the base of the watershed.

Results/Conclusions

Hydroscape complexity had little influence on nutrients, anions, or cations in this study.  However, it had a significant influence on most carbon related (e.g., DOC, DIC, ANC) variables.  The amount of wetlands in the watershed explained 49% of the variation in watershed DOC concentrations, while the influence of lakes on watershed DOC was less clear.  Watersheds with headwater lakes had significantly lower DOC concentrations that watersheds without lakes, but watersheds with drainage lakes were not significantly different that either HSW or HLW.  A comparison of carbon variables between watersheds with lakes at the top of the watershed (HLW) and the bottom of the watershed (DLW) suggest that configuration plays a role but that role is complicated.  As water moves through these aquatic networks, drainage lakes low in the landscape appear to homogenize the biogeochemical signatures and the resulting signatures are more characteristic of HSW than HLW.  Results from this study suggest that hydroscape composition is dominant factor influencing watershed carbon dynamics, but the location of lakes along these aquatic networks also influences how the chemical signatures evolve as water moves across the landscape.