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Denitrification Potential, Root Biomass, and Organic Matter in Degraded and Restored Urban Riparian Zones
GIFT, D. M., P. M. GROFFMAN, S. S. KAUSHAL, AND P. M. MAYER. Denitrification Potential, Root Biomass, and Organic Matter in Degraded and Restored Urban Riparian Zones. RESTORATION ECOLOGY. Blackwell Publishing, Malden, MA, 18(1):113-120, (2010).
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Hydrologic changes associated with urbanization often lead to lower water tables and drier, more aerobic soils in riparian zones. These changes reduce the potential for denitrification, an anaerobic microbial process that converts nitrate, a common water pollutant, into nitrogen gas. In addition to soil saturation, denitrification is also controlled by soil organic matter and nitrate levels. Geomorphic stream restorations are common in urban areas, but their effects on riparian soil conditions and denitrification have not been evaluated. We measured root biomass, soil organic matter and denitrification potential at 0 – 10, 10 – 30, 30 – 70 and 70 – 100 cm depth in duplicate degraded, restored and reference riparian zones in the Baltimore, MD USA metropolitan area. There were three main findings in this study. First, while reference sites were wet and had high levels of organic matter, they had low levels of nitrate relative to degraded and restored sites and therefore there were few differences in denitrification among sites. These results suggest that evaluations of riparian restorations that have denitrification as a goal must consider the complex controls of this process and how they vary between sites. Second, all variables declined markedly with depth in the soil profile. These results suggest that restorations that increase riparian water tables will foster interaction of groundwater nitrate with near-surface soils with higher denitrification potential. Third, we observed strong relationships between root biomass and soil organic matter, and between soil organic matter and denitrification potential that suggest that establishment of deep rooted vegetation may be particularly important for increasing the depth of the active denitrification zone in restored riparian zone soils.