Effects of stream restoration by legacy sediment removal and floodplain reconnection on water quality

Abstract

Stream restoration effects on water quality (WQ) are unknown, and approaches to restoration are diverse. In the mid-Atlantic region of the United States, European land-modifications resulted in the deforestation, erosion, and deposition of sediments into stream valleys – legacy sediments. During the 19th and 20th century, streams incised through legacy sediments (1) creating high banks subject to collapse, (2) removing connection to the floodplain, and (3) lowering water tables promoting adjacent upland soils. Legacy sediment removal (LSR) and floodplain reconnection (FR) projects propose WQ benefits by restoring degraded streams closer to their pre-European hydrologic condition. WQ was investigated at six restored LSR-FR projects and three control/regional sites. Baseflow nitrogen concentrations and fluxes at restored sites were elevated compared to forested controls, particularly in agriculture settings, with little apparent impact of restoration. Nutrient and sediment storm loads may be reduced at the restoration scale; however, regional effects of restoration were not observable.