Nitrogen Cycling Within Stormwater Basins: Microbial Ecology, Process Performance, and Seasonal Variations

In recent years, stormwater management has evolved to address the detrimental impacts of urbanization on stormwater runoff quantity and quality. Various stormwater control measures have been implemented in order to reduce stormwater pollution and discharges. In this regard, the use of stormwater detention basins has gained increasing traction among practitioners due to their straightforward design and reliable function. Stormwater detention basins serve to prevent flooding as well as trap pollutants by infiltrating stormwater runoff into basins and slowly releasing the water through outlets. In this dissertation, influent and effluent stormwater samples were collected over a long-term period from three detention basins in order to determine their impact on water quality treatment, particularly nitrogen treatment. Moreover, the characteristics, distribution, heterogeneity, and diversity of microbial communities in basin soils were examined in relation to their potential impacts on basin performance and nitrogen cycling. In the first study, the performance of a detention basin in mitigating nitrogen pollution was examined and the abundance of N-cycling genes (amoA, nirK, nosZ, hzsB and Ntsp-amoA) present in the soil media of the basin was measured using quantitative PCR. A net export of nitrogen was found to occur from the basin; however, the differences between inflows and outflows did not differ significantly. Additionally, the quantitative PCR indicated that the nirK gene (denitrification gene) is more abundant during the winter season, whereas the amoA gene (nitrification gene) is more abundant during the summer season. Furthermore, 16S rRNA gene sequencing revealed that Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, and Planctomycetes accounted for over 80% of relative abundance. In the second study, soil physiochemical properties surrounding two distinct basins were examined to determine their impact on soil microbial communities. Soil samples were collected from these basins during two different seasons and soil physiochemical properties including organic matter, carbon, nitrogen, phosphorus, and soil particle size were measured. 16S rRNA gene sequencing analysis on the soil samples revealed different microbial community structure between sites. Further, differences in organic matter and pH between two sites explained the differing abundance of taxa discovered in the studyIn the third study, the performance of the basins in the second study were evaluated in terms of reducing water quality pollutants, including nitrogen (nitrate, nitrite, ammonia, and total dissolved nitrogen), solids (dissolved and suspended), carbon (total and organic) and chemical oxygen demand. During a one-year period between January 2021 and December 2021, samples of influent and effluent were collected at each site using automatic sampling equipment. In both basins, TSS and COD concentrations in the outflow were effectively reduced. In spite of higher nitrate concentrations in the effluent during the sampling period, the total net exported load in the basins was not significantly different from the influent load due to the volume reduction in the basins. Overall, these studies have provided some new insights into the performance, microbial community structure, and nitrogen cycling in stormwater basins, providing some clues toward improving the efficiency of these systems.