The Importance of Hydroscape Complexity in Regional Aquatic Carbon Dynamics

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 of 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. At the regional scale, wetlands exerted a strong influence on watershed dissolved organic carbon (DOC) concentrations. The amount of wetlands in the watershed explained 50% of the variation in watershed DOC concentrations. However, variables that characterized hydroscape complexity appeared to have little or no influence on watershed DOC concentrations. While prior studies have observed that lakes can decrease watershed DOC concentrations, at the regional scale, our results indicate that the presence and location of lakes within the hydrologic networks had not influence on DOC concentrations. Taken together, these results suggest that although aquatic ecosystems are important factors in both lake and global carbon budgets, they do not have a significant influence on aquatic DOC dynamics in the NHLD region. Consequently, we suggest that within this region and potentially at the regional scale, understanding other factors such as wetland composition and hydrologic connectivity are likely more important drivers of aquatic DOC than processes occurring within the hydrologic network.