My research involves two areas of environmental chemistry: (1) water quality in urbanizing watersheds, and (2) trace metal cycling and speciation.

Urbanizing Watersheds and Green Infrastructure
More than 80% of the US population lives in urban areas (2010 Census), and the move to cities continues.  Dense development puts special stress on urban ecosystems.  Point sources of pollution, especially industry and sewage treatment plants, have been largely curtailed through regulation under the Clean Water Act and its amendments.  But nonpoint sources, caused by how we use urban lands, remain an important challenge in efforts to improve water quality and protect and restore aquatic habitat.  The pollution problem is compounded by alterations we have made to the urban hydrological cycle by installing impervious surfaces and water conveyance infrastructure.  Runoff from urban lands causes extreme high and low flows, degraded water quality, and damaged riparian habitat.

Rather than treating runoff as a waste product that poses risks of disease and flooding, current thinking sees it as a resource.  By retaining and treating water at its source – preferably at the individual lot scale – water can be used for irrigation or other non-potable uses, and downstream impacts can be greatly lessened.  Key tools in this effort are so-called green infrastructure measures, which harness natural purification by vegetation and soils and replace engineered gutters, catch basins, and culverts.

While some benefits of green infrastructure are obvious, there is a dearth of controlled studies that quantitatively document the benefits and limits of these methods, and which could be used as a guide to optimize future installations.  Several projects in my lab are helping to close this knowledge gap.  We also have projects where we continuously monitor discharge and water quality parameters for entire urban watersheds to better understand biogeochemical cycling in these systems.

Trace Metal Speciation and Cycling
For years, metals in water were studied because of the risk posed to humans and aquatic plants and animals.  Today, probably only mercury and sometimes lead and arsenic are likely to pose a health risk to humans from the waters of the US.  Instead, some metals may influence aquatic ecosystems by functioning as micronutrients.  As one example, it has been known for several years that iron is the limiting nutrient in large areas of the global ocean.  Also, we have shown that one step in denitrification in lakes can be limited by manipulating copper speciation to make it less bioavailable.  We hypothesize that Cu and Co speciation in some freshwaters may reduce these metals’ bioavailability down to a level that could limit some biological species and favor others.  While we continue to study toxic metals, increasingly we are using ultra-clean methods and voltammetric techniques to better understand the speciation and behavior of metals that may function as limiting micronutrients.