Peer-Reviewed Publications

Reducing roadside runoff: Tillage and compost improve stormwater mitigation in urban soils

Erin N Rivers, Joshua L Heitman, Richard A McLaughlin, Adam M Howard

https://doi.org/10.1016/j.jenvman.2020.111732

Soils adjacent to urban surfaces are often impaired by construction activities that degrade the natural structure and function of the soil, resulting in altered physical, hydraulic, and vegetative properties that limit the infiltration, storage, and filtration of stormwater runoff. A management approach to enhance the efficacy of vegetated roadside soils for runoff control is the use of compost in conjunction with tillage to improve soil conditions and facilitate improved hydrological function, the establishment of vegetative biomass, and increased nutrient and pollutant attenuation. The purpose of this study was to determine the efficacy of soil improvement measures to reduce runoff volumes and improve water quality along roadsides over time. The effects of tillage with and without compost on 1) bulk density and infiltration rates, 2) runoff volumes, and 3) runoff water quality were evaluated during multiple storm events along two long-established interstate roadsides in North Carolina during 2015 and 2017. Experimental plots were established in the grassed areas adjacent to roads and consisted of an untreated control, tillage only, and tillage amended with compost. Tillage alone did not reduce runoff in roadside soils, however, tillage with compost did improve runoff capture. The patterns in hydrologic performance within and among sites suggests that the incorporation of compost in tilled soils may influence storage potential through different effects on soil properties, such as decreasing bulk density or improving vegetation establishment, thereby increasing evapotranspirative withdrawals, depending on soil texture. Tillage increased sediment concentrations in runoff, however, net export of sediments was reduced with the inclusion of compost due to the reduction of runoff quantities compared to undisturbed areas and tillage alone. Control and treatment plots were equally effective in reducing dissolved nutrient and metal concentrations, however, the improved hydrologic performance in plots with compost decreased net nutrient and metal export in most storms. The results of this study suggest that the incorporation of compost in compacted urban soils may provide significant improvements for biological and physical soil properties that affect stormwater interception and infiltration.

Effects of urban stormwater control measures on denitrification in receiving streams

Erin N Rivers, Sara K McMillan, Colin D Bell, Sandra M Clinton

https://doi.org/10.3390/w10111582

Urban areas are increasingly adopting the use of ecologically-based technologies for stormwater management to mitigate the effects of impervious surface runoff on receiving water bodies. While stormwater control measures (SCMs) reduce runoff, their ability to influence ecosystem function in receiving streams is not well known. To understand the effect of SCMs on net ecosystem function in stream networks, we measured sediment denitrification in four streams across a gradient of urban and suburban residential development in Charlotte, NC. We evaluated the influence of SCM inputs on actual (DNF) and potential (DEA) denitrification activity in stream sediments at the SCM-stream confluence to quantify microbial processes and the environmental factors that control them. DNF was variable across sites, ranging from 0–6.60 mg-N·m−2·h−1 and highly correlated with in-stream nitrate (NO3-N) concentrations. Sites with a greater impervious area showed a pattern of significantly higher DEA rates upstream of the SCM compared to downstream, while sites with less imperviousness showed the opposite trend. We hypothesize that this is because of elevated concentrations of carbon and nitrogen provided by pond and wetland outflows, and stabilization of the benthic habitat by lower peak discharge. These results suggest that SCMs integrated into the watershed have the potential to create cascading positive effects on in-stream nutrient processing and thereby improve water quality; however, at higher levels of imperviousness, the capacity for SCMs to match the scale of the impacts of urbanization likely diminishes.

Sediment chemistry of urban stormwater ponds and controls on denitrification

Joanna R Blaszczak, Meredith K Steele, Brian D Badgley, Jim B Heffernan, Sarah E Hobbie, Jennifer L Morse, Erin N Rivers, Sharon J Hall, Christopher Neill, Diane E Pataki, Peter M Groffman, Emily S Bernhardt

https://doi.org/10.1002/ecs2.2318

Stormwater ponds and retention basins are ubiquitous features throughout urban landscapes. These ponds are potentially important control points for nitrogen (N) removal from surface water bodies via denitrification. However, there are possible trade-offs to this water quality benefit if high N and contaminant concentrations in stormwater pond sediments decrease the complete reduction of nitrous oxide (N2O), a potent greenhouse gas, to dinitrogen (N2) during denitrification. This may occur through decreasing the abundance or efficiency of denitrifiers capable of producing the N2O reductase enzyme. We predicted that ponds draining increasingly urbanized landscapes would have higher N and metal concentrations in their sediments, and thereby greater N2O yields. We measured potential denitrification rates, N2O reductase (nosZ) gene frequencies, as well as sediment and porewater chemistry in 64 ponds distributed across eight U.S. cities. We found almost no correlation between the proportion of urban land cover surrounding ponds and the nutrient and contaminant concentrations in the stormwater pond sediments within or across all cities. Regression analysis revealed that the proportion of potential N2 and N2O production that could be explained was under different environmental controls. Our survey raises many new questions about why N fluxes and transformations vary so widely both within and across urban environments, but also allays the concern that elevated metal concentrations in urban stormwater ponds will increase N2O emissions. Urban stormwater ponds are unlikely to be a problematic source of N2O to the atmosphere, no matter their denitrification potential.