Abstract
Stormwater infiltration basins (SIBs) are vegetated depressions that collect stormwater and allow it to infiltrate to underlying groundwater. Their pollutant removal efficiency is affected by the properties of the soils in which they are constructed. We assessed the soil nitrogen (N) cycle processes that produce and remove inorganic N in two urban SIBs, with the goal of further understanding the mechanisms that control N removal efficiency. We measured net N mineralization, nitrification, and potential denitrification in wet and dry seasons along a sedimentation gradient in two SIBs in the subtropical Tampa, Florida urban area. Net N mineralization was higher in the wet season than in the dry season; however, nitrification was higher in the dry season, providing a pool of highly mobile nitrate that would be susceptible to leaching during periodic dry season storms or with the onset of the following wet season. Denitrification decreased along the sediment gradient from the runoff inlet zone (up to 5.2 μg N/g h) to the outermost zone (up to 3.5 μg N/g h), providing significant spatial variation in inorganic N removal for the SIBs. Sediment accumulating around the inflow areas likely provided a carbon source, as well as maintained stable anaerobic conditions, which would enhance N removal.
Highlights
The effects of stormwater runoff on receiving waterbodies have attracted more attention as urban expansion and development increase globally and as impervious surfaces have taken the place of watershed vegetation and soils
As stormwater runoff washes over impervious surfaces, it can cause flooding and erosion, as well as mobilize and transport various pollutants that diminish the quality of downstream waterbodies [1,2,3]
The nutrient loads of stormwater runoff can be especially problematic since excess nitrogen (N) and phosphorus (P) loading to aquatic ecosystems can cause eutrophication and algal proliferation in surface waters and has detrimental effects in groundwater and groundwater-fed ecosystems such as natural springs [4,5,6]
Summary
The effects of stormwater runoff on receiving waterbodies have attracted more attention as urban expansion and development increase globally and as impervious surfaces have taken the place of watershed vegetation and soils. Stormwater infiltration basins (SIB) are one of the best management practices (BMPs) for controlling both stormwater volumes and stormwater pollutant loads [12,13]. They are designed as dry, excavated basins that hold and release the stormwater runoff through infiltration to underlying soils over a short time period (several days) [12].
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