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Hydrology and Nitrogen Biogeochemistry in the Hyporheic Zone of a Geomorphically Degraded Urban Stream
Citation:
MAYER, P. M., E. A. STRIZ, P. M. Groffman, AND S. S. Kaushal. Hydrology and Nitrogen Biogeochemistry in the Hyporheic Zone of a Geomorphically Degraded Urban Stream. Presented at The 2nd Symposium on Urbanization and Stream Ecology, Salt Lake City, UT, May 23 - 24, 2008.
Impact/Purpose:
To present information at the 2nd Symposium on Urbanization and Stream Ecology.
Description:
Few studies have investigated the relationship between hydrology and nitrogen biogeochemistry in hyporheic zones of degraded urban streams despite significant national efforts to restore such streams. We examined relationships between hydrology and biogeochemistry in Minebank Run, a geomorphically degraded urban stream near Baltimore, Maryland, that exhibited “urban stream syndrome” characteristics including steep bank incision and flashy hydrology stemming from altered runoff from surrounding impervious surfaces. Hyporheic NO3¯ was inversely related to DOC (R2 = 0.64, P = 0.01) but not to any other chemical variable. The redox environment of the subsurface was closely linked to ground water elevation (R2 = 0.96, P = 0.004). Hyporeheic NO3¯ was positively related to mean water table elevation (R2 = 0.69, P = 0.01), DOC was inversely related to water table elevation (R2 = 0.5, P = 0.05), whereas Cl, a conservative natural tracer in this system, was not related to ground water level. Thus, NO3¯ concentrations in the hyporheic zone of this degraded stream were strongly influenced by both DOC availability and ground water topography. Stream restoration efforts that increase DOC availability and which address flashy hydrology (e.g. reduce stream flow velocities and/or increase ground water residence) are likely to improve the nutrient uptake capacity of urban streams.