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Watershed Restoration
Contributors: Sujay Kaushal, Todd Lookingbill, and Andrew Elmore, AL/UMCES
Appalachian Laboratory
Restoring watersheds requires an initial understanding of how land cover components (forest, agricultural, and urban land) interact to affect water quality and landscape ecology. To assist in this understanding, Geographical Information Systems (GIS) provide a powerful tool for understanding the spatial relationships among land cover components. Likewise, remote sensing technologies help assess landscape conditions, such as riparian zone tree cover, agricultural land-use, and impervious surface area, for use in models of watershed nutrient budgets and landscape connectivity. These activities supplement restoration efforts to enhance ecosystem structure and function at the watershed scale in order to protect and enhance ecosystem services.
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Among our ongoing research programs, one investigates the effects of restoration of forest patch structure on forest connectivity and another maximizes forest area and restoration of denitrification function in urban floodplains to reduce nitrogen pollution in streams. The effects of these restoration efforts can be modeled in the context of ongoing changes within the watershed, thus providing an understanding of the regional significance of net land-use and land-cover change.
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| Watershed restoration involves prioritizing regions for restoration by balancing the needs for water quality improvements (riparian buffer zone condition) with forest connectivity and moderation of impervious surface area. |
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The wide variety of hydrologic conditions found within the Gunpowder-Patapsco watershed in Maryland is shown by the stream and river network overlying impervious surface area (in red). In some areas, streams pass from restored wetlands to underground sewer pipes to concrete channels on the scale of kilometers (inset). In other areas, riparian buffer zones remain intact and represent significant assets to the capacity of this urbanizing watershed to provide high quality water resources |
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Restoration of Structure of a Historic Landscape
Restoration activities at landscape scales frequently must balance multiple objectives associated with both human and natural resources. For example, Manassas National Battlefield Park was established to preserve the scene of two major Civil War battles. Additionally, the park provides regionally important wildlife habitat. Management practices for these two different types of resources (cultural vs. natural) can sometimes conflict. Park managers were interested in whether a timber harvest proposed to return a portion of the park to historic battlefield conditions would result in isolation of forest patches containing breeding amphibian populations. A landscape-level analysis of the park before and after harvesting used remotely sensed imagery within a geographic information system to model the potential effect of the harvest on connectivity of forest habitat. The analysis indicated that landscape connectivity will likely remain high after the proposed timber harvesting, but important local patches may become isolated. Efforts to mitigate the effect on these local resources have been taken to allow the park to successfully accomplish its multiple management objectives. These efforts include removal of a small swath of land from agriculture to allow a dispersal corridor to develop across the fragmented landscape.
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| Cannon fire along the flank of the attack was instrumental in turning back the Union advance. Battle conditions at the time of the war allowed clear line of sight for these cannons, which now face into an aggrading forest. To recreate these historic conditions, the park is considering a 50-hectare harvest of forest to the north of this position. |
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One consideration in assessing the removal of forest resources is the potential isolation of ephemeral ponds found in forests west of the proposed harvest. These temporary pools of water provide valuable habitat to the park’s amphibian populations. |
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Restoration of Denitrification Function in Coastal Watersheds
Urbanization leads to predictable changes in the hydrologic and geomorphic properties of stream and river channels. One common alteration is incision of banks due to increased storm runoff from impervious surfaces in watersheds. Channel incision and resulting hydrologic “disconnection” between streams and riparian floodplains can decrease the ability of streams and rivers to process and remove nitrogen by promoting transport of nitrate-rich groundwater from pollution sources that enters streams below the roots of plants and “hot spots” of microbial denitrification in the riparian zone.
Our work investigates the effectiveness of restoration techniques fostering hydrologic “connectivity” between streams, rivers, and floodplains on rates of denitrification in urbanizing coastal watersheds. We use state-of-the-art 15N stable isotope tracer techniques in ground water and at the stream reach scale to identify and quantify the effectiveness of new floodplain and river restoration strategies to reduce downstream nitrogen pollution to Chesapeake Bay. Ecosystem functions in restored floodplains and streams are compared to degraded and forest reference watersheds monitored as part of the National Science Foundation funded Baltimore Ecosystem Study.
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| Minebank Run is located outside Baltimore and is influenced by urban and suburban land use activities, which increase concentrations of stream nitrogen. In addition to receiving elevated inputs of nitrogen, Minebank Run also has a reduced ability to process and remove nitrogen because of the bank incision that has occurred as a result of high flow events. Additionally, the vegetation in the riparian zone has been removed, further reducing the stream denitrification rates. |
A number of stream restoration techniques are available. In some cases, the stream is completely rebuilt. Other techniques involve bank reshaping, revegetation, erosion control, and the installation of features that promote denitrification. For urban streams, an optimal restoration should fit in someone’s backyard. |
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A graduate student of the University of Maryland Center for Environmental Science’s Appalachian Laboratory (Ms. Carolyn Klocker) conducting preliminary work on estimating whole stream denitrification rates in Minebank Run. |
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