2007 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, 2007 through April 30,2008
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.
Currently, only one sediment and erosion control structure within the post-2k SWM watersheds has been converted to SWM. The DEP is waiting for all of the sediment-trapping devices to be converted to final SWM structures before mapping structure locations, outfalls and compiling installation dates; 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; currently two of the gauges are ‘real-time’ and the gauge at the pre-2k SWM site will be relocated and upgraded to ‘real-time’ in June 2007. Data continue to 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 cannot be attributed to SWM treatments since post-2k SWM is not fully in place. The Montgomery County Department of Permitting Services has completed modeled of the hydrological response to post-2k SWM using the TR-20 model.
Geomorphology: Geomorphic surveys have been completed for the reporting year by the DEP. Monitoring parameters include cross-section measurements, longitudinal profiles, pebble counts, and sinuousity. 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. Most of the 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) were collected during baseflow in all five study watersheds during July 2006 and November 2006. Plans are in place to collect additional samples in June 2007 to assess nitrogen saturation and possible nutrient limitation.
Macroinvertebrate community composition: Macroinvertebrate samples were collected at multiple locations within each study watershed this year. Results show continued changes in community composition in the streams draining post-2k SWM watersheds resulting from 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 2006 and November 2006. Previous methods to detect uptake were modified to increase our chances of observing a reduction in nitrate over the study reach. Additional injection experiments (ammonium, phosphate and DOC) are planned for Summer 2007 to determine if either nitrification or nutrient limitation is preventing us from observing nitrate removal. Whole stream metabolism metrics (i.e. CR and GPP) were calculated for each watershed for July 2006 and November 2006. Metabolism metrics cannot be evaluated with respect to SWM treatment until after post-2k SWM is in place.
Relationships between metrics and SWM have not been determined due to the slow conversion of sediment and erosion control devices 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 of response metrics will continue during the construction phase and through the post-construction phase as planned. Despite the fact that it does not directly address our original objectives, data collected during the active construction phase (especially with respect to macroinvertebrate community composition) is quite interesting and publishable. Again, while our approach to measuring nutrient uptake will be modified this summer as a result of the metrics responding to larger-regional patterns rather than watershed scale patterns, information about possible N saturation and nutrient limitation (especially in our forested watershed) is quite interesting and not well reported in the literature. While the watershed-scale treatments are not fully in place, we are hopeful that the sediment and erosion control devices are converted within the next year for at least one of our post-2k watersheds so that we may provide some feedback to managers and engineers regarding these SWM designs, recognizing that we are unlikely to adequately capture the true post-construction response in the post-2k SWM watersheds over the course of one year. And finally, the state of Maryland passed new SWM regulations this year, and so, while these approaches have yet to be implemented, our study is no longer assessing the most advanced SWM designs.