Characterization of Wetland Scaling and Influence in the Ipswich and Parker River Watersheds of Northeastern Massachusetts

Abstract:

The inclusion of auxiliary surface water features such as wetlands in the study of river channel networks is critical to a complete understanding of watershed dynamics. Due to their proximity to channel networks, fluvial wetlands in particular directly impact the concentrations and flows of nutrients throughout the catchment. Here, we examine how three types of wetlands (fluvial, connected, and isolated) scale with increasing catchment size and river order in the Ipswich and Parker River watersheds. Using the 2005 MassDEP Wetlands layer, weighted flow accumulation methods were employed to determine the rate at which upstream area of each wetland type increases as a function of upstream drainage area. Fluvial wetlands in both watersheds scaled super-linearly (I = 1.19, R² = 0.82; P = 1.23, R² = 0.74) while connected and isolated wetlands tended toward linear scaling, with lower R² values. Additionally, Horton’s Law of Stream Areas was used to compute the Area Ratio (R_A) per wetland type, providing a scaling factor to quantify increases in average wetland area when moving from one river order to the next highest order. Area Ratio values reaffirmed our findings in that fluvial wetlands demonstrated the most rapid growth between orders (R_A = 2.66; 2.64), while connected and isolated wetlands in both watersheds scaled at slower rates (R_A < 2.5). Similar scaling relationships appear to dominate the two adjacent watersheds and emphasize the influence of fluvial wetlands. As these two shallow, coastal watersheds experience increasing urban and suburban development, the use of hydrologic scaling relationships to generate and improve models of biogeochemical flow will remain crucial to future watershed management.