Global climate change models predict increases in both sea-level and severity of droughts and storms. Coastal wetland ecosystems will be subjected to increased salinity due to sea level rise and longer droughts punctuated by more severe storms. In the low lying coastal plain of North Carolina, drought-induced salt water intrusion can provide insights into how wetland ecosystems might function under future scenarios of sea-level rise and an amplified hydrologic regime. We constructed inflow and outflow budgets for water, nitrogen (NO3, and NH4), phosphorus (SRP and TP), and dissolved organic carbon (DOC) for a large-scale (400 ha) restored wetland ecosystem for two years. In the first year there was a severe drought and saltwater intrusion for 4 months. In the second year the site received normal rainfall, but also suffered saltwater intrusion.
Results/Conclusions
Results suggest that changes in the hydrologic regime and ionic strength of surface water led to the site alternating between being a source or sink for both N (DIN: retained 8.3 kg ha-1 yr-1 in year 1 and released 8.2 kg ha-1 yr-1 in year 2) and P (SRP: released 0.23 kg ha-1 yr-1 in year 1 and retained 0.22 kg ha-1 yr-1 in year 2). We observed changes in concentrations of SRP, TP, NH4, and NO3 in the outflow from the site due to increased conductivity caused by salt water intrusion. SRP, TP, and DOC concentrations declined exponentially with increasing conductivity (r2= 0.20, 0.45, and 0.70 respectively). NO3 increased linearly with increasing conductivity (r2= 0.29), while NH4 concentrations depended on both conductivity and pH (r2=0.70). Our results suggest that drought and salt water intrusion can have synergistic and non-linear effects that lead to trade-offs between N and P retention in restored wetland ecosystems.
