Urban Hydrology, Biogeochemistry, and Water Quality
I am interested in studying the intersection of hydrology, biogeochemistry, and water quality in urban settings, including sociological influences, such as how people interact with water in cities. As the percent of the world population that lives in cities continues to grow, the importance of balancing basic human needs for food and water with ecosystem services provided by rivers and streams increases. Contamination from cities to receiving water bodies not only impacts the population living in the city, but also the livelihoods of people living downstream. Understanding what controls urban water pollution, relaying this knowledge to the public, and having the public join with researchers to influence policy change is the only way we will improve urban water quality in a changing world.
Along with the projects listed below, I am also part of CSAW: Community-Soil-Air-Water, the NSF-funded project to integrate justice, equity, diversity, and inclusion principles and programming with community collaborators to solve socio-environmental issues.
Along with the projects listed below, I am also part of CSAW: Community-Soil-Air-Water, the NSF-funded project to integrate justice, equity, diversity, and inclusion principles and programming with community collaborators to solve socio-environmental issues.
Hydrologic and nitrogen retention around urban beaver dams and beaver dam analogues: Current graduate students are conducting field work to quantify the hydrologic and nitrogen retention around beaver dams in Atlanta. Overall ecosystem retention of solutes, plus stormwater issues, mean cities need to understand fully where their water is going and what biogeochemical cycling is happening. Beaver are ubiquitous across the southeastern United States but are considered a nuisance species. Their ponding may help retain stormwater and induced hyporheic exchange may result in denitrification. Quantifying their impact on cities will allow us to understand these unanticipated retention sites and their role in the landscape.
Landscape controls on urban baseflow and water quality: The original Urban Stream Syndrome hypothesis assumed urbanization would reduce baseflow in streams due to decreased infiltration, incision of streams, and decreased groundwater table elevations. Continued observation of baseflow in streams shows this is not always the case, and understanding the sources and sinks of groundwater in cities is a growing topic. In particular, leaking drinking water pipes are potentially a large source of groundwater, with cities reporting 30%+ water losses across their systems. In addition, sewer pipes can be sources of baseflow when the groundwater table is low, but water can infiltrate into these pipes with the groundwater table is high. Finally, wastewater treatment plant discharges create artificial sources of baseflow throughout the year. This all drives potentially heterogeneous patterns in water quality, as well, including major ions and E. coli.
Working with watershed advocacy groups to monitor sewer spills: Since 2019, we have worked closely with the South River Watershed Alliance to monitor 20 sites across the City of Atlanta and DeKalb county for E. coli, looking for sewer spills. This work is driven by the environmental justice issues around flooding and sewage in the Upper South River, a predominately Black watershed that suffers a disproportionate environmental burden.
Previous Research
Biogeochemical cycling: Many questions remain about how urban streams cycle nitrogen, phosphorus, and carbon, and if/how we can improve these cycles to reduce nutrient pollution in streams, improve in-steam habitat, and reduce eutrophication. Sources of these nutrients have been well identified, but pools and processing rates not well understood. I study biogeochemical cycling in urban streams and the heterogeneity of pools and processing rates among streams in different climates, geologies, and levels of urbanization. I am also interested in seasonal changes in cycling, especially when looking at the interaction between carbon dynamics and nitrogen and phosphorus removal. Questions I aim to answer include: What is the importance of riparian vegetation as a carbon source during the fall to nutrient cycling and what are the potential impacts of this on restoration strategies? We know denitrification requires organic carbon and a favorable suite of electron acceptors, so how do we promote the creation of ‘hot spots’ and ‘hot moments’ in urban watersheds? How do these processes change when the stream is controlled by wastewater effluent discharge instead of groundwater base flow? I approach these questions with intense field campaigns, collecting high-temporal nutrient data, either through grab samples (ISCOs) or nutrient and DO loggers (SUNA V2, SeaBird Coastal Cycle PO4, Onset HOBO DO).
Microbial communities as indicators of biogeochemical cycling: During my post-doctoral research, I have worked with faculty and students at Drexel University to look at using surface water microbial communities as indicators of biogeochemical cycling in urban streams. We used quantitative polymerase chain reaction (qPCR) and 16s rDNA amplicon sequencing of stream water samples to look at how microbial communities shift above and below wastewater treatment plant effluent discharges. We hope to use changes in microbial communities to tease out changes in biogeochemical cycling. Our preliminary research shows that there is a decrease in the order flavobacteriales below wastewater treatment plants. Flavobacterials thrive in areas with high dissolved oxygen and organic carbon, so decreases in their importance to the microbial community may be indicative of changes in DO and OC dynamics.
Modeling: As we continue to learn about the processes controlling nutrient pollution in urban streams, how do we build the best possible models of urban systems, knowing that the heterogeneity cannot fully be captured? Many models offered to stream managers that I have encountered use a ‘black box’ approach, where the loads and calculations of pollutants from different categories are unclear in origin. These models are often different from the models researchers use, and so it should not be a surprise when model answers disagree. I think this creates a large gap between academics and practitioners that needs to be overcome by continuing to evaluate different urban biogeochemical models used by academics and policy makers, such as the US EPA’s Storm Water Management Model (SWMM), and comparing them to the models that stream managers use, such as the Spreadsheet Tool for Estimating Pollutant Loads (STEPL), to evaluate similarities and differences.
Road Salt: I am also interested in continuing to study groundwater storage of chloride in urban systems and the impact this has on baseflow chloride concentrations in urban streams year-round. Increased baseflow chloride concentrations are indicative of groundwater storage, even in areas with low impervious surface cover, and thus minimal salt application. Modeling movement of road salt from surface to groundwater and subsequent residence times of chloride are vital to understanding this emerging contaminant. Issues are also beginning to arise from TDS limits on WWTP discharge and the inability of treatment plants to remove chloride from stormwater runoff.
Modeling: As we continue to learn about the processes controlling nutrient pollution in urban streams, how do we build the best possible models of urban systems, knowing that the heterogeneity cannot fully be captured? Many models offered to stream managers that I have encountered use a ‘black box’ approach, where the loads and calculations of pollutants from different categories are unclear in origin. These models are often different from the models researchers use, and so it should not be a surprise when model answers disagree. I think this creates a large gap between academics and practitioners that needs to be overcome by continuing to evaluate different urban biogeochemical models used by academics and policy makers, such as the US EPA’s Storm Water Management Model (SWMM), and comparing them to the models that stream managers use, such as the Spreadsheet Tool for Estimating Pollutant Loads (STEPL), to evaluate similarities and differences.
Road Salt: I am also interested in continuing to study groundwater storage of chloride in urban systems and the impact this has on baseflow chloride concentrations in urban streams year-round. Increased baseflow chloride concentrations are indicative of groundwater storage, even in areas with low impervious surface cover, and thus minimal salt application. Modeling movement of road salt from surface to groundwater and subsequent residence times of chloride are vital to understanding this emerging contaminant. Issues are also beginning to arise from TDS limits on WWTP discharge and the inability of treatment plants to remove chloride from stormwater runoff.