Sources and Fates of Nutrients in the Tidal, Freshwater James River

• Main Author: Isenberg, William
• Format: Others
• Published: VCU Scholars Compass 2012
• Subjects: Nutrient retention; Mass Balance; Tidal Freshwater; James River; Nitrogen; Phosphorus; Point Source; Environmental Sciences; Physical Sciences and Mathematics
• Online Access: http://scholarscompass.vcu.edu/etd/2686; http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=3685&context=etd

Tidal freshwater reaches of estuaries may play an important role in mitigating nutrient fluxes from watersheds to the coastal zone due to their location at the interface between riverine and estuarine systems. We developed annual N and P budgets for the tidal, freshwater James River over 4 calendar years (2007-2010) taking into account riverine inputs at the Fall Line, local points sources (including CSO events), ungagued inputs, riverine outputs, and tidal exchange. The tidal freshwater James River experiences high areal loading rates of TN (383 mg/m2/d) and TP (70 mg/m2/d) due to the combined effects of large watershed area and local point source discharges. On an annual basis, riverine sources dominated TN and TP inputs (59% and 84%, respectively), whereas during low discharge summer months (May-Oct) point sources were more important. Proportional retention of TP inputs (59±7%) was greater than TN retention (27±4%) with annual absolute retention being 1,800±350 kg TP/d, and 5,900±2,700 kg TN/d. Proportional retention of TN and dissolved inorganic fractions of N and P was highest during the low discharge summer months due to reduced loading rates and increased residence times and biotic activity. TP retention was greatest during high discharge winter months (Nov-Apr) when loading rates were highest. High retention during this period of low biotic activity suggests that trapping of riverine derived particulate-bound P via sedimentation was an important mechanism of P retention. Understanding this seasonal variation in nutrient inputs and retention can help to inform management decisions regarding reducing nutrient inputs to the Chesapeake Bay and improving local water quality.