Evaluating Impacts of Land-Use Change on Water Quality and Sedimentation in Downstream Estuarine Waters: a Comparative Approach

Watershed land use directly affects the supply of nutrients and sediments to adjacent waters. Higher loads are associated with urban and agricultural land use, often resulting in degraded water quality and increased sedimentation rates. Conservation practices can reduce these loads, but assessing the success of these practices remains challenging. This study evaluates the impacts of land-use conversion from intensive grain agriculture to conservation plantings in Trippe Creek watershed, within the Choptank basin (an estuarine tributary of Chesapeake Bay), compared to those in an adjacent reference watershed (Goldsborough Creek). Changes in both water quality constituents (total nitrogen (N) and phosphorus (P), chlorophyll a ) and bottom sediment characteristics (particulate N and P, organic content, grain size) were compared, as well as seasonal- and decadal-scale sedimentation rates using 7 Be (half-life 53.3 days) and 210 Pb (half-life 22.3 years), respectively. Results provide evidence for improving water quality and reduced sedimentation rates in Trippe Creek, where high concentrations of chlorophyll a decreased to concentrations similar to those in the reference Goldsborough Creek. Sedimentation rates remained fairly steady in Trippe Creek, but increased by ~ 50% in reference Goldsborough Creek. These changes are likely associated with 50% conversion of crop fields to conservation plantings and/or changes in the nature of agriculture over time, offering insight into the effects of land-use change and the difficulties of detecting them in downstream estuarine waters.