Conclusions:
The proportion of wetlands in the watershed at different scales affects dissolved organic carbon (DOC) concentrations in downstream lakes and rivers.
Thresholds/Learnings:
Synopsis: This study quantifies how the proportion of wetlands in the watershed at different scales affects dissolved organic carbon (DOC) concentrations in downstream lakes and rivers. Whether the watershed influence varies with season or hydrologic type of lake was also examined. The scaling and modelling approach used offered a useful way to examine heterogeneity of land cover types within the watershed and spatial arrangements, while allowing generality of conclusions with a large sample size. Zones of increasing distance from the lake shore were created around each lake at 25, 50, 100, 200, through to 1500 m until the direct drainage watershed boundary was reached. The concentric scales were overlain with digital wetlands data, and the proportion of wetlands in each zone was calculated. Regression analysis was used to determine which independent variables (proportion of wetlands at different scales) explained the most variability in DOC.
For lakes, the proportion of wetlands in the entire watershed often explained most of the variability in DOC if stepwise regression was used. However, the proportion of wetlands in near-shore riparian areas (25-100 m) was only slightly less powerful in explaining variability in DOC. For rivers, the proportion of wetlands in the watershed always explained considerably more variability in DOC than the proportion of wetlands in the nearshore riparian areas. A summary of the results for rivers is shown in Figure 6 of the paper. The watershed influence also varied seasonally in rivers, as the proportion of the watershed covered by wetlands explained more of the variability in DOC in the fall than in the spring. Overall, the proportion of wetlands in the landscape explained much more of the variability in DOC concentrations in rivers than in lakes. The variability of DOC values was also used to discuss landscape “predictability” as a function of the scale of influence and the type of aquatic system (seepage lakes, drainage lakes, rivers).
