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BES Long Term Stream and Watershed Study Update – Overview
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Activities
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Figure 1. BES Stream Sampling sites.
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The watershed approach, i.e. monitoring inputs and hydrologic outputs of nutrients, has long been fundamental in ecosystem ecology, and is an important component of many sites in the National Science Foundation (NSF) Long Term Ecological Research (LTER) network. The BES long-term stream sampling network includes four longitudinal sampling sites along the Gwynns Falls as well as four small (40 – 100 ha) watersheds located within or near to the Gwynns Falls (Figure 1). The longitudinal sites provide data on water and nutrient fluxes in the different land use zones of the watershed (rural/suburban, rapidly suburbanizing, old suburban, urban core) and the small watersheds provide more focused data on specific land use areas (forest, agriculture, rural/suburban, urban). Each of the gaging sites is continuously monitored for discharge by the USGS and is sampled weekly for chemistry. Water quality analysis includes major nutrients (inorganic and organic forms), total suspended solids, temperature and dissolved oxygen. Data are used to compute input-output budgets. All streamflow and chemistry data are posted on the BES website under the heading "Products".
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Findings
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Figure 2. Six years of weekly stream nitrate concentrations in forested, suburban and agricultural streams.
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Figure 3. Nitrogen Budgets from 1999 - 2001. From Groffman et al. 2004
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- Urban and suburban watersheds consistently have nitrate concentrations that are higher than forested watersheds, but lower than agricultural watersheds (Figure 2). This result is of great interest as the mix of land use changes in the region.
- Suburban watershed input/output budgets for nitrogen (Figure 3) have shown surprisingly high retention which has led to detailed analysis of sources and sinks in these watersheds:
- Home lawns, thought to be major sources of N in suburban watersheds, have more complex coupled carbon and N dynamics than previously thought, and are likely the site of much N retention.
- Riparian zones, thought to be an important sink for N in many watersheds, have turned out be N sources in urban watersheds due to hydrologic changes that disconnect streams from their surrounding landscape.
- In-stream retention, thought to be an important sink for N in forested watersheds is reduced by structural degradation caused by urban runoff.
- Urban and suburban streams are strongly affected by road salting activities, leading to high levels of chloride in streams (Figure 4).
- Improvements to sanitary sewer infrastructure appear to result in major improvements in water quality (Figure 5). The City of Baltimore is spending $900 million on improvements of this sort.
Figure 4. Mean annual chloride concentrations versus impervious surface in BES watersheds. From Kaushal et al. 2005.
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Figure 5. Sanitary sewer improvements result in reductions in total nitrogen in tributaries to Gwynns Falls. Source: Peter Groffman.
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Publications
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Band, L.E., C. Tague and P. Groffman. 2001. Forest ecosystem processes at the watershed scale: Hydrological and ecological controls of nitrogen export. Hydrological Processes 15:2013-2028.
Bushey, J.T., P.M. Groffman, C.T. Driscoll and G.T. Fisher. Mercury patterns and flux in an urban watershed ecosystem. Submitted to Environmental Science and Technology.
Findlay, S. and R.L. Sinsabaugh. 2006. Large-scale variation in subsurface stream biofilms: A cross-regional comparison of metabolic function and community similarity. Microbial Ecology. In press. DOI: 10.1007/s00248-006-9095-
Groffman, P.M., A.M. Dorsey and P.M. Mayer. 2005. Nitrogen processing within geomorphic features in urban streams. Journal of the North American Benthological Society 24:613-625.
Groffman, P.M., N.L. Law, K.T. Belt, L.E. Band and G.T. Fisher. 2004. Nitrogen fluxes and retention in urban watershed ecosystems. Ecosystems 7:393-403.
Groffman, P.M., D.J. Bain, L.E. Band, K. T. Belt, G.S. Brush, J.M. Grove, R. V. Pouyat, I.C. Yesilonis and W. C. Zipperer. 2003. Down by the riverside: Urban riparian ecology. Frontiers in Ecology and Environment 6:315-321.
Groffman, P.M. and M.K. Crawford. 2003. Denitrification potential in urban riparian zones. Journal of Environmental Quality 32:1144-1149.
Groffman, P.M., N.J. Boulware, W.C. Zipperer, R.V. Pouyat, L.E. Band, M.F. Colosimo. 2002. Soil nitrogen cycling processes in urban riparian zones. Environmental Science & Technology 36:4547-4552.
Hale, R. and P.M. Groffman. Chloride effects on nitrogen dynamics in forested and suburban stream debris dams. Journal of Environmental Quality. In press.
Higgins, J.A., K.T. Belt, J.S. Karns, J. Russell-Anelli and D.R. Shelton. 2005. tir- and stx-Positive Escherichia coli in stream waters in a metropolitan Area. Applied and Environmental Microbiology 71:2511-2519.
Kaushal, S.S. P.M. Groffman, G. E. Likens, K. T. Belt, W. P. Stack, V. R. Kelly, L. E. Band and G. T. Fisher. 2005. Increased salinization of fresh water in the northeastern U.S. Proceedings of the National Academies of Science of the United States of America 102:13517-13520.
Smith, J.A., M.L. Baeck, K.L. Meierdiercks, P.A. Nelson, A.J. Miller and E.J. Holland. 2005. Field studies of the storm event hydrologic response in an urbanizing watershed. Water Resources Research 41, W10413, DOIi:10.1029/2004WR003712.
Walsh, C.J., A.H. Roy, J.W. Feminella, P.E. Cottingham and P.M. Groffman. 2005. The urban stream syndrome: current knowledge and the search for a cure. Journal of the North American Benthological Society 24:706-723.
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