Dams and ECEs: Sink or Source of Nutrients?

Abstract:

Dams can provide benefits such as flood control, hydropower, irrigation, recreation, and wildlife habitat. However, dams can also be detrimental to fish passage and water quality. Recent work in the Columbia River has shown that dams can also provide resilience against climate impacts like rising water temperatures and changes in streamflow. Can dams also play a role in mitigating extreme storm events by serving as a biogeochemical sink for nutrient rich sediments? In contrast, if a reservoir is filled to capacity before an ECE occurs, nutrient rich sediment may overtop the dam and have a disastrous effect downstream. For example, in 1972 Tropics Storm Agnes, a 200-year storm event, washed millions of tons of sediment over the Conowingo Dam and into the Chesapeake Bay causing major water quality impacts. Nutrient source vs. sink dynamics may change as aging dam infrastructure accumulates sediments. This study explores potential factors (such as age of dam, storm stage, total flood storage capacity, and percentage of flood storage capacity in use before the ECE) that may affect whether dams serve as a sink or source of nutrients during ECEs. These results may have implications for the management of dams for improved resilience to ECEs.