Long Term (1998–2019) Changes in Water Quality Parameters as a Function of Freshwater Inflow in a River–Bay Continuum

Abstract

Freshwater inflow is important in transporting nutrients to a bay. We hypothesized that freshwater inflow was transporting dissolved nitrogen and phosphorus to the Inland Bays. We analyzed long term (1998–2019) water quality data collected from Indian River, Indian River Bay, Lewes-Rehoboth Canal, Little Assawoman Bay, and Rehoboth Bay watersheds. Freshwater inflow altered nitrite+nitrate (N-NO2_3) concentrations in all but Lewes-Rehoboth Canal watershed, whereas phosphate (P-PO4) concentrations in all watersheds were altered by freshwater inflow and metabolic processes in the water. The average N-NO2_3 and P-PO4 were higher than the standard (0.14 and 0.01 mg/L for N-NO2_3+N-NH3 and P-PO4, respectively) for growing seasons (March–October) i.e., 0.83 + 0.14 and 0.09 mg/L in Indian River; 0.79 + 0.10 and 0.06 mg/L in Indian River Bay; 0.21 + 0.15 and 0.09 mg/L in Lewes-Rehoboth Canal; 0.49 + 0.10 and 0.11 mg/L in Little Assawoman Bay; 1.0 + 0.08 and 0.06 mg/L in Rehoboth Bay. Average total suspended solids in the Indian River (33), Indian River Bay (22), and Lewes-Rehoboth Canal (31) were higher than the standard concentrations, i.e., 20 mg/L for the Inland Bays. With the evidence of higher dissolved nutrients and low dissolved oxygen concentrations, need for nutrient load reduction and water quality monitoring are paramount for the sustainable management of Inland Bays.