B51F-01 INVITED
Sediment Flux in First Order Basins in the Mid-Atlantic Piedmont
The flux of sediment within and from headwater basins in the Piedmont of the Mid-Atlantic has historically been poorly documented. Most available sediment data have been obtained from alluvial channels at the outlets from third order or higher watersheds. This has hindered prediction of sediment yield in large basins, such as the Chesapeake Bay watershed. Three years of flow and suspended sediment monitoring in the headwaters of the Upper Patuxent River watershed in Maryland have provided a new dataset that allows for the investigation of the relative roles of hillslopes and first order gullies in producing sediment yield from first order watersheds. Measurements from three primary settings, including cropped land, forest, and suburban land cover conditions with similar lithologies and slopes, provides a new opportunity to evaluate mass flux of sediment within a region undergoing rapid land use transitions. The results have implications to watershed management strategies including storm water management, erosion control, and water quality modeling in the suburbanizing region between Washington D.C. and Baltimore.
B51F-02
Geomorphology of Urban and Suburban Riparian Zones
The geomorphic pattern of riparian zones in urban and suburban watersheds is affected by several prominent trends that vary in their expression depending on the age of development and the dominant management regime: (1) truncation of headwater portions of the drainage network and replacement by storm drains; (2) incision and widening of channels in response to altered storm hydrographs and sediment supply; (3) fragmentation or longitudinal segmentation of the riparian corridor by frequent bridges, culverts, and road embankments or other kinds of artificial fill acting as either barriers or conduits; (4) introduction of detention ponds designed for temporary storage of storm runoff and associated constituents. The resulting mosaic of landforms includes a combination of natural features and elements of the built environment, but an understanding of its hydrologic, geomorphic and biogeochemical behavior requires that we treat it as an integrated system. The availability of high-resolution topographic data derived from airborne LiDAR allows us to capture the morphology of the entire drainage network and to describe and quantify longitudinal trends influencing propagation of flood waves and transient patterns of storage associated with floodplain inundation. Trends in the hydraulic geometry of stream channels and in the longitudinal sequencing of fluvial landforms may be compared among suburban watersheds developed during different time periods in order to assess the impact of management regime on geomorphic expression and on hydrologic and hydraulic function. The time-transgressive pattern of urban development in the Gwynns Falls watershed, the primary study site of the Baltimore Ecosystem Study, together with extensive recent development in adjacent Howard County, Maryland, offers a test case well suited for comparative analysis of drainage networks, channels and floodplains.
B51F-03
Dissolved Organic Matter Dynamics in two Suburban Catchments in NE England
Recent advances in fluorescence spectrophotometry enable rapid and optically precise analysis of river dissolved organic matter (DOM). In this study we investigate the potential of detecting river pollution associated with urban expansion (cross connected sewerage; overloading of combined sewer overflows (CSOs), land use change) using fluorescence and absorbance spectrophotometry, paired with conventional geochemistry, microbiological analyses and 14C/13C isotope fingerprinting of dissolved organic matter, in two small, rural-Urban fringe catchments in NE England over the period 2002-present. In the United Kingdom, 'suburbia' (post 1945AD) is distinguished by separate sewerage systems and associated issues of cross connections. Results indicate: (1) suburban catchments have a seasonal trend in DOM fluorescence, with a maximum of tryptophan-like fluorescence in summer low flow, indicative of an increased proportion of cross connected sewer inputs, with a statistically significant inverse relationship with discharge. Older 'urban' catchments with CSOs exhibit an opposite seasonality, with combined sewerage overflows occurring in winter at high flow due to CSO discharge. (2) Sampling cross connected storm drains for both Escherichia coli. and fluorescence demonstrates a statistically significant relationship. This finding matches laboratory microbial cultures, which have demonstrated that a wide range of environmentally relevant microbes exhibit tryptophan-like fluorescence, and suggests that when coliforms dominate a river or wastewater microbial community then fluorescence intensity could potentially be employed to monitor faecal coliforms in urban waters. (3) 14C/13C fingerprinting of DOM in three contrasting sub-catchments separates urban and industrial DOM sources through positive 13C and 'old' 14C.
B51F-04
Carbon and Nitrogen Dynamics in a Chronosequence of Suburban Lawns
Given the rate of suburban and exurban expansion in the US, conversion of land to residential use is likely to be an important contributor to regional ecosystem dynamics, but little is known about how suburban lands cycle C and N. In this study, we quantified turfgrass productivity, soil respiration, and soil C and N along a chronosequence of suburban lawns in South Burlington, VT ranging in age from 1 to 20 years. All lawns in the study were located in the same suburban development and established using identical home building and lawn seeding procedures; site preparation and topsoil origin were removed as potential sources of variability among lawns. Turfgrass productivity was not correlated with lawn age, and varied with lawn management practices as reported by homeowners. Soil N stocks in the upper soil layers increased linearly with lawn age up to 6 years. Soil C stocks were roughly constant with time in both the 0-10 cm and 10-20 cm soil layers, and soil C:N decreased linearly with lawn age up to ~10 years. These results contribute to our growing understanding of nutrient dynamics in turfgrass-dominated systems, and suggest that - all else equal - housing age and land management are especially important drivers of C and N dynamics in suburban landscapes.
B51F-05
Nutrient fluxes from coastal California catchments with suburban development
Numerous streams originate in the mountains fringing California's coast and transport nutrients into coastal waters. In central California, these streams traverse catchments with land covers including chaparral, grazed grasslands, orchards, industrial agriculture and suburban and urban development. Fluvial nutrient concentrations and fluxes vary as a function of these land covers and as a function of considerable fluctuations in rainfall. As part of a long-term investigation of mobilization and fluvial transport of nutrients in catchments bordering the Santa Barbara Channel we have intensively sampled nutrient concentrations and measured discharge during storm and base flows in multiple catchments and subcatchments. Volume-weighted mean concentrations of nitrate generally ranged from 5 to 25 micromolar in undeveloped areas, increased to about 100 micromolar for suburban and most agricultural catchments, and were in excess of 1000 micromolar in catchments with greenhouse-based agriculture. Phosphate concentrations ranged from 2 to 20 micromolar among the catchments. These data are used to examine the premise that the suburbanized portion of the catchments is the primary source of nutrients to the streams.
B51F-06
Nitrogen inputs, ouptut, and retention in a coastal suburban basin
Understanding the biogeochemistry of suburban basins is becoming increasingly important due to the rapidly accelerating suburban sprawl in many parts of the US. In southeastern New Hampshire, population density is expected to increase by 50% over 20 years, and most of the development will occur as low-density suburban home lots with wells and on-site waste disposal. We measured the N inputs, outputs, and loss/storage in a 470 sq km basin, the Lamprey River of coastal New Hampshire. Atmospheric deposition and food imported into the basin were both significant inputs, and totaled 13 kg/ha/yr. Output was 0.6 kg/ha/yr, for a net loss/retention of 95% of inputs. Net retention among various sub-watersheds of the Lamprey ranged from 50 to 98%. Because the Lamprey river basin contains a high proportion of wetlands (14% wetlands and open water), has some water courses that undergo periodic oxygen depletion, and has high levels of dissolved organic carbon in surface waters (6 mg/l), in-stream and wetland denitrification may be a major loss pathway for N in the basin. Results from a study of riparian zone biogeochemistry suggest that riparian denitrification may also be a significant loss pathway. Accelerating suburbanization may greatly increase N delivery to the coast if it shortens hydrologic flow paths and decreases wetland coverage while increasing N inputs.
B51F-07 INVITED
Integrating Hydrology, Ecology, and Biogeochemistry in Stormwater Management: the Vermont Experience
Although Vermont has had a stormwater management program since the 1970's, support for the program languished during a period intense suburban development in several counties in the state, most notably Chittenden County next to Lake Champlain. Beginning in 2000, the state renewed efforts to address concerns that stormwater runoff from suburban developments had significantly degraded streams in the area and threatened the health of the Lake. The state employs an extensive, EPA-approved biomonitoring program (based on macroinvertebrates and fish) to assess the health of streams. However, it is difficult to translate these data into targets for stormwater management or to predict how and especially when they will change as a result of future management practices. The challenge of managing stormwater in this area is further compounded by a complete lack of historical hydrologic monitoring data. Ultimately a stakeholder-driven process developed that has lead to an innovative partnership among state agencies, resource managers, NGO's, the US-EPA and scientists. Through this partnership a unique consensus evolved that management for hydrologic targets by themselves would address most of the stakeholders' concerns. The new regulations that are emerging are based on two components. The first component relies on flow-duration curves (FDC's) derived from a simple, widely-Used stormwater model (P-8) for which adequate input data are available. The model was calibrated for streams in other areas for which long-term hydrologic data were available and then used to generate 'synthetic' FDC's for the stormwater impaired and a suite of 'attainment' (developing, but currently un-impaired) watersheds in Vermont. Statistical (cluster) analyses of synthetic FDC's provide watershed-wide targets for hydrologic reduction. Sub-watershed mapping linked to further multivariate analysis of the flow data identify specific locations to implement best management practices (BMP's) that will achieve these targets. This approach is firmly grounded in first principles of stormwater hydrology and recognition of the impacts of altered hydrology on stream ecology and biogeochemistry. Stakeholders have accepted the approach because it is objective, defensible, and subject to future, quantitative analysis and adjustment (adaptive management). This approach is not specific to Vermont and could be employed in any region.
B51F-08 INVITED
Coupling of Hydrologic and Ecosystem Nutrient Cycling in Forest and Suburban Catchments
This paper discusses the coupling of hydrologic and biogeochemical cycles in forested and suburban catchments of the Baltimore Ecosystem Study. Suburban development produces important changes in land cover, surface and subsurface hydrologic flowpaths and the water and nutrient balances of watersheds. The built environment is characterized by increased spatial heterogeneity of surface cover and more rapid convergence of surface flowpaths. This results in alterations of stream channel geomorphology and the characteristics and coupling of riparian areas with drainage lines. The presence of sanitary infrastructure (sanitary sewers and septic systems) in the moderate and low density suburban catchments introduces new nutrient sources and altered subsurface flowpaths. We combine detailed sampling of distributed soil water, stream discharge and water quality, with high resolution digital land cover, lidar derived elevation data and household surveys of lawn management practices to develop a spatial dataset characterizing hydrologic and ecosystem dynamics of suburban and control forest catchments. A conceptual model is developed based on hydrologic controls of nitrogen transformations and transport within forested catchments, augmented by anthropogenic sources of nitrogen and altered flowpaths within developed sites. The altered geomorphic structure and built drainage systems of the watershed produces significant modification of catchment scale soil moisture and potential nutrient retention. We also modify and apply an ecohydrologic catchment model that simulates the interaction of spatially distributed water, carbon and nutrient cycling. Numerical experiments with the simulation model are used to explore coupling and nonlinear response of water and nutrient cycling within each catchment. Opposite trends are seen in the response of nutrient export to a major drought in our forest and low density suburban catchments, that appears to be explained by spatial location of nutrient sources and the interaction between hillslope and riparian flowpaths.