Anthropogenic alteration of the nitrogen (N) cycle through the addition of excess nutrients has had substantial effects on ecosystems across the globe. In urban and agricultural landscapes constructed wetlands are often used to mitigate the effects of excess nutrient input loads. Although constructed systems are becoming commonplace for waste-water treatment, there is a paucity of comprehensive research addressing the detailed functioning of these systems. Our research focused on N dynamics in Lake Lieberman, an urban constructed wetland located on the State University of New York, Binghamton campus. We measured seasonal input, output and retention of N in the wetland to determine the efficiency of the system at removing inorganic N waste. We hypothesized that: (1) seasonal variation of wetland processes (plant growth and microbial denitrification) will affect available N concentrations in surface water and N retention in the ecosystem (i.e. surface water concentrations of NH4+ and NO3- in the spring and summer will be lower than those in the fall and winter months), (2) plant biomass and plant N accumulation (change in N from May to September) will be highest near the input source, (3) there will be a greater retention of N in the sediment near the input source (sediment organic matter (SOM) and N mineralization will have the highest values in those areas).
Results/Conclusions
We found that on average, surface water N concentration (NH4+ and NO3-) was lower in the growing season and decreased more substantially between the input and output of the wetland than during the non-growing season. On average, plant biomass was the highest closest to the input and decreased linearly as proximity to the output increased. However, percent sediment organic matter and N mineralization rates followed no clear pattern across sampling areas and seasons.
