Short-term impacts of urban landscape conversion on surface runoff quality

Given the rapid pace of urbanization and resulting pressures on water supplies in many regions, landscape water conservation has become increasingly important for many communities. To achieve this goal, programs incentivizing partial or complete removal of turfgrass lawns have been developed by many municipalities. While prior studies have been published examining effects of urban land change on stormwater runoff, few have addressed how the transition from traditional home lawns to alternative water-efficient landscapes alters runoff water quality. The objective of this 13-month study was to compare differences in stormwater runoff quality attributes among five commonly used urban residential mesocosms including established St. Augustinegrass lawn and four alternative residential mesocosms including xeriscaping, mulch, artificial turf, and sand-capped lawn. Runoff quality parameters including pH, electrical conductivity, nitrate–N, ammonium-N, dissolved organic N, total dissolved N, orthophosphate-P, total suspended solids, and dissolved organic carbon were monitored. Results demonstrated that export of nutrients via runoff, specifically N and P, were influenced by mesocosm type. In particular, artificial turf showed elevated runoff nitrate–N relative to other mesocosms, possibly due to minimal plant absorption of inorganic N coming onto plots as dry and wet deposition. However, an additional layer of compacted decomposed granite used for xeriscapes and artificial turf seems to have protected legacy soil P from leaving the system as runoff. Collectively, the findings of this study demonstrate that there is no one specific landscape that is best suited for mitigating runoff quality, but rather, alternative mesocosms should be selected based on local climate and environmental concerns.