In urban landscapes constructed wetlands are often used to treat wastewater. These systems have been
shown to decrease inorganic nitrogen (N) pollution and improve water quality. However, many studies
focus just on N removal under base-flow conditions. With climate change altering precipitation patterns,
itis becoming increasingly criticalto understand how these systems function during storm events in addition
to base-flow conditions. Our research focused on N dynamics in an urban constructed wetland located
on the State University of New York, Binghamton campus. We conducted a multi-year field research
project to examine seasonal and yearly variations in dissolved inorganic nitrogen (DIN) export under
naturally variable hydrologic conditions. From 2007 to 2011, during base-flow conditions, we collected
weekly to monthly grab samples at the inlet and the outlet of the wetland, except some winter months;
corresponding discharge measurements were also recorded. From July 2010 through March 2011, during
storm events, we used two ISCO automated samplers to collect water samples and stage measurements
at the inlet and outlet weirs. Water samples were analyzed for DIN (NO3–N and NH4–N). Mass balance
input and output budgets were calculated by multiplying concentration and discharge values for each
sampling event and averaging them to calculate mean monthly fluxes. Under base-flow conditions, DIN
concentrations in the wetland were significantly lower at the outlet than the inlet in all sampling years
and for the spring, summer, and autumn seasons, but not during the winter. Over the entire 4-year sampling
period, 38% of the DIN entering the wetland was removed during base-flow. In contrast, the wetland
removed DIN in only two ofthe seven storm events sampled and overall, DIN-export was 34% greater than
the input. Our results show that during base-flow, the constructed wetland was capable of decreasing
N loads from urban sources. However, it had a limited ability to lower N during storm events. Thus, if
the number of rainfall events increase as expected under future climate change scenarios, the N removal
capacity of urban constructed wetlands could be compromised