Impacts of vegetation and landscape management practices in suburban watersheds on runoff water quality
Bachman, Matthew James
University of Delaware
Steadily increasing rates of urbanization over recent years have raised concerns about the negative impacts of urban runoff on receiving surface water quality. These concerns have been further amplified by the current landscaping paradigm in urban/suburban ecosystems that encourages high input, intensive management and larger and more homogenous lawn areas. This study attempts to quantify the water quality benefits that could be attained by managing urban/suburban landscapes, including lawns, less intensively and using more diverse, native vegetation. Our main hypothesis was that stream water in native meadows and forests would exhibit healthier water quality characteristics than in their intensively managed lawn counterparts. The study was conducted at Winterthur Museum and Garden where six different watershed treatments were present including - turf, meadow, two forests, urban and mixed. The watershed sizes ranged from 7.2 -36.1 hectares (ha). Synoptic water quality sampling was performed for baseflow and stormflow from June 2012 through December 2013. Nutrient concentrations in stream baseflow from the turf watershed, representative of a traditional suburban lawn, were lower than expected and were comparable to those measured in the surrounding meadow and forests. Total nitrogen, total phosphorus, nitrate and phosphate numbers were all generally lower than EPA or state standards, suggesting minimal risk to surrounding surface waters. Runoff and leaching losses may have been minimal due to the superior quality of the management received at Winterthur compared to that of a traditional homeowner's lawn. Total nitrogen concentrations were significantly higher in the turf stream during the first storm following fertilization, suggesting that despite optimal management there exists a risk for nutrient runoff directly following fertilization. pH values in the turf stream were consistently lower than other watersheds. Similar studies have suggested that long-term fertilization may increase acidity in soil and subsequently lower the pH of affected water. Dissolved organic carbon (DOC) concentrations were significantly higher during stormflow in the turf watershed compared to its native counterparts. These results are consistent with previous studies' findings regarding turf landscape's effect on carbon sequestration. Dissolved organic matter (DOM) was also significantly more humic (decomposed) than counterparts' DOM. Higher humic proportions in turf DOM may have been a result of increased nitrogen from fertilizer indirectly increasing DOM decomposition rates in soil or simply a result of the turf stream's unique location within the landscape lending itself to wetting-drying cycles that have been shown to increase humic DOM. Overall, this study suggests that turf lawns, when managed properly, typically pose minimal environmental risk to surrounding surface waters. Even under optimal conditions, however, lawns exhibit nutrient leaching/runoff potential directly following fertilization. Based on the results of this study, providing homeowners with increased information regarding best management practices for lawn maintenance may serve as a cost-efficient method for reducing suburban runoff pollution, as current literature suggests that the risks posed from improper lawn maintenance are not well understood by homeowners.