Impacts of a Regenerative Stormwater Conveyance Restoration on Urban Stream Elemental Chemistry

Abstract:

Stream restoration projects may have unintended consequences on water quality that are not well understood due to a lack of monitoring before and after restoration. Campus Creek in College Park, Maryland was restored during the summer of 2019 using regenerative stormwater conveyance (RSC): an open-channel approach utilizing a series of step pools and sand channels to slow and filter streamwater and retain nutrients such as nitrogen, phosphorus, and heavy metals before they are transported further downstream. However, standing pools that raise water temperatures and decrease dissolved oxygen could potentially release metals that have sorbed onto the streambed as an unintended consequence. Pre-restoration water chemistry data has been collected routinely over the past three years and was compared to post-restoration sampling to identify benefits and trade-offs of RSC restoration. Peaks in magnesium, strontium, sodium, calcium, potassium, manganese, and barium were observed after the restoration occurred, and were 44, 55, 65, 95, 100, 361, and 407 percent larger, respectively, than values for a nearby control reference stream. These peaks reached values comparable to peaks observed during winter road salting events at approximate values of 12.9, 0.146, 64.6, 73.8, 8.01, 0.526, and 0.415 mg/L, respectively. Certain forms of stream restoration may have the potential to mobilize chemical cocktails of metals, and long-term monitoring is important to identifying these changes in water quality following restoration and construction activities. Identifying water quality trade-offs associated with different stream restoration approaches can lead to innovative approaches for reducing contaminants and a comprehensive understanding of the effects of stream restoration on urban water quality.