As natural wetland acreage continues to decline worldwide, concerns of freshwater salinization present increasingly unique challenges in the urban environment. Stormwater ponds have been continually installed in urban areas to reduce excess run-off and pollutants, such as road salts, despite concerns of their true ability to minimize local stream degradation. While these man-made ponds are not intended to serve as freshwater ecosystems, it is becoming clear that they do provide an aquatic habitat for many organisms. From April – June 2009, we surveyed 8 seasonally flooded stormwater ponds in the Red Run Watershed, Baltimore County, MD to quantify shifts in salt loading and associated food web patterns. Periphyton and phytoplankton samples were collected from each pond every 4-6 weeks and analyzed for chlorophyll a concentration. Zooplankton samples were taken simultaneously, then sorted and counted as adult copepods, copepod nauplii, rotifers, ostracods and daphnia.
Results/Conclusions
Specific conductance values among the 8 ponds varied widely throughout the survey, ranging from 99 µS to 19,320 µS. Some pulsing patterns in salt loading emerged. Periphyton and phytoplankton biomass were greater in stormwater ponds with elevated specific conductance. Low conductance ponds had a greater abundance and diversity of zooplankton taxa relative to high conductance ponds, which were largely devoid of all zooplankton taxa through the end of May. Our research suggests that road salts directly reduce zooplankton grazers, thus algal resources are freed from grazing pressure resulting in algae laden urban ponds. Road salt inputs into freshwater habitats are likely to alter the trophic relationships of unique urban communities.
