2005 Progress Report: Ecological Sustainability in Rapidly Urbanizing Watersheds: Evaluating Strategies Designed to Mitigate Impacts on Stream EcosystemsEPA Grant Number: X3832206
Title: Ecological Sustainability in Rapidly Urbanizing Watersheds: Evaluating Strategies Designed to Mitigate Impacts on Stream Ecosystems
Investigators: Palmer, Margaret A. , Curtis, Meosotis , Hennessey, Amy , Kelly, Kevin , VanNess, Keith
Institution: University of Maryland
EPA Project Officer: Hahn, Intaek
Project Period: May 1, 2005 through April 30, 2008 (Extended to April 30, 2009)
Project Period Covered by this Report: May 1, 2005 through April 30, 2006
Project Amount: $278,626
RFA: Collaborative Science & Technology Network for Sustainability (2004) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Urbanization has profound impacts on the hydrology and ecology of streams via alteration in water temperatures, peak and base flows, and nutrient, sediment, and contaminant inputs. Storm water management (SWM) is commonly used to reduce these impacts; however, comprehensive watershed-scale studies to determine the effectiveness of SWM designs in reducing ecological impacts are scarce. With the continuing trend of urbanization, there is an urgent need to more fully understand which SWM designs are most effective and why, so that policymakers are better equipped to address the sustainability of water resources.
In 2000, the state of Maryland adopted new SWM criteria to address the impacts of urbanization on stream ecosystems. Montgomery County (Maryland) Department of Environmental Protection initiated a project in 2002 to evaluate the effectiveness of new SWM practices. Our partnership significantly expands the scientific scope of that project in order to determine the effectiveness of SWM on mitigating the impact of urbanization on receiving streams. Critical questions will be answered using an empirical research design that focuses on multiple stream reaches within three watersheds currently being developed with the most advanced SWM technologies; one watershed developed using older SWM designs; and a largely forested (control) watershed. Our goal is to determine if the new SWM design strategies (post-2k SWM) that combine state of the art treatment technologies, maximize flow dispersion, and maintain watershed topography significantly improve stream ecosystem structure and function through comparison with earlier designs (pre-2k SWM) and a forested watershed. The timing of our study also allows us to collect data during the construction phase of development, prior to the conversion of sediment and erosion control devices to SWM controls. Our three major objectives are outlined below.
Objective 1: Characterize land-use within each of the study watersheds and identify all existing a proposed SWM outfall locations and unique landscape features.
Objective 2: Assess the impact of watershed-scale SWM treatments on six categories of metrics: hydrology, geomorphology, stream temperature, water quality, macroinvertebrate community composition, and stream ecosystem function at regular intervals throughout the period of the study including before, during, and after construction in the post-2k SWM watersheds with simultaneous measurements in the pre-2k SWM and forested watersheds.
Objective 3: Determine relationships between SWM design and response metrics in order to provide recommendations for future management and engineering decisions.
The DEP has identified start dates for construction for the remaining two post-2k SWM watersheds. The DEP is waiting for sediment-trapping devices to be converted to final SWM structures before mapping structure locations, outfalls and compiling installation dates; and they have begun the process of mapping the study watersheds (impervious cover, riparian buffer widths, streamside reforestation projects, BMP locations, etc.), however they cannot complete the process until construction is complete.
Hydrology: Five USGS gauges are in place and operational; discharge data has been collected every 15 minutes for the entire reporting period. Two tipping-bucket rain gauges are also in place and have been collecting data for storms over the entire reporting period. Data indicate that storm hydrographs are attenuated, with longer lag times and lower peak discharges, in watersheds with post-2k SWM compared to the pre-2k SWM treatment; however, the observed trend may be related to total impervious cover (which is currently lower in the post-2k SWM watersheds) and cannot be attributed to SWM treatments since post-2k SWM is not in place; we will continue to monitor these metrics as development progresses. Preliminary work by the Montgomery County Department of Permitting Services using the TR-20 model to assess the hydrological response to post-2k SWM is underway. Wells for monitoring groundwater recharge have been installed by ESA, but monitoring of groundwater-surfacewater exchange has been deprioritized, for now, as attempts to install piezometers and seepage meters (by UMD) have been unsuccessful because of impenetrable streambed sediments (Piedmont physiographic province).
Geomorphology: Geomorphic surveys have been completed for the reporting year by the DEP. Monitoring parameters include cross-section measurements, longitudinal profiles, pebble counts, and sinuosity. Surveys indicate changes in geomorphic metrics in all study watersheds.
Stream temperature: Continuous recording water temperature meters have been installed and downloaded every year of the grant period. Sediment and erosion control devices have not been converted to SWM structures in the post-2K SWM watershed yet so thermal impacts can not be assessed at this time.
Water quality: Grab samples for water quality (N, P, DOC, pH, DO) have been collected monthly during baseflow for the entire reporting year. Data indicates that water quality varies by season; and will be collected seasonally in future reporting years as a result. Trends show the highest N in post-2k watersheds (possibly a result of prior agricultural use), the highest P is found in two of the post-2k watersheds and the pre-2k watershed, and the highest DOC concentrations are found in one of the post-2k watersheds and the pre-2k watershed. The forested watershed consistently has the lowest concentrations of N. P, and DOC. These patterns cannot be attributed to SWM treatment since post-2k SWM is not in place at this time.
Macroinvertebrate community composition: Macroinvertebrate samples were collected at multiple locations within each study watershed this year. Results show marked changes in community composition in the streams draining post-2k SWM watersheds with communities previously dominated by shredders (~48% shredders, ~26% collectors) becoming collector dominated communities (~3% shredders, ~67% collectors); though, this may represent a temporary community shift due to construction activity.
Stream ecosystem function: Nutrient uptake experiments to evaluate the ability of streams in the test watersheds to remove nitrate from the water column were conducted in triplicate at each site during July 2005, November 2005 and March-April 2006. Preliminary data suggest that either nitrate uptake is not occurring in our study watersheds or we are unable to detect removal with current methods; adjustments to our methodology are underway and will be employed for subsequent experiments. Whole stream metabolism metrics (i.e. CR and GPP) were calculated for each watershed for July 2005, November 2005, and March-April 2006. Preliminary data suggest that seasonal variation in metabolism metrics may mask treatment effects; however, we will continue to monitor whole stream metabolism until after post-2k SWM is in place.
Relationships between metrics and SWM have not been determined due to sediment and erosion control devices not being converted to SWM structures. Because the conversion of sediment and erosion control devices to SWM structures has been slower than expected, much of our current data reflects the impacts of the construction phase on receiving streams (including dramatic responses by macroinvertebrate communities and channel morphology). Additionally, some of our results (i.e. nutrient uptake and whole stream metabolism) indicate that ‘treatment’ effects (i.e. SWM) are masked by larger local phenomenon such as local geology and potentially landuse history.
Once SWM is in place and analysis is complete, our work will have implications for the development and maintenance of SWM well beyond our region, since Maryland’s SWM program is used as a model for many states, and will provide feedback regarding the impacts of active development on stream ecosystems.
Monitoring and evaluation will continue, with adjustments to methodologies as needed (i.e. improving detection for nutrient uptake experiments). Because our study relies heavily on watershed-scale treatments that we cannot control, we have begun to recognize that we may need to make some qualifying statements when reporting the final results of our study For example, as mentioned previously, the slow conversion of sediment and erosion control devices to SWM structures has allowed us to thoroughly monitor the response of receiving streams during the active construction pahse, but has thus far prevented us from meeting our original objective of evaluating the most current SWM designs. Also, for the most rapidly developing of the three post-2k SWM watersheds, we may not have adequate ‘before’ data since development was already underway when the first functional measurements were taken. And finally, as development slows, we recognize that we may not adequately capture the true post-construction response in the post-2k SWM watersheds, especially given the short duration of funding relative to the time required for the receiving streams to respond (i.e. there may be a lag between the end of the construction phase/conversion to SWM and the response).