The correlation between increased urban land cover and watershed salinity has been widely documented and is especially prevalent in northern climates where chloride-based deicing agents are frequently used. There is further evidence deicers can lead to water-quality degradation in urban areas. Urban lakes are also beginning to encounter insurmountable stratification promoted by rising salinity that interrupts normal lake turnover processes and produces permanently redox-stratified hypolimnia. This process may be driving further lake eutrophication through release of previously bound bio-available phosphorus (P). Similar processes may be happening at a smaller scale in urban stormwater ponds. Influx of winter runoff carrying deicer coupled with evaporation, ice formation, and sublimation increases chloride concentration while stagnation and stratification promoted by increased salinity help produce a redox-stratified sediment layer. Internal loading of bio-available P may be flushed downstream along with brackish water during early spring melt and runoff events turning retention ponds in to point sources for P and chloride. The USGS has been measuring the amount of chloride in runoff from both commercial and residential settings to better understand how deicers influence nutrient dynamics in retention ponds. This presentation will highlight preliminary results on the influence of chloride-enriched runoff on nutrient retention in urban stormwater ponds.
