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Streams, Water Quality and Ecology PDF Print E-mail
Greenway corridors and their interconnected local systems and regional networks are important contributors to stream water quality. This results from the width of the naturally vegetated corridors that buffer stormwater runoff and filter standing floodwaters. How important they are is determined by their specific width, as well as their naturalness, and how they are used, managed, and maintained. Beyond water quality, these same characteristics are also the key to whether greenways provide most of the other community benefits that may accrue from this green infrastructure.

Local greenway corridors average about 100 feet of width on each side of streams. This is twice the 50 foot width of the State’s required buffers for water quality protection. On the other hand, it is only a fraction of the 300 foot minimum standard used by the State’s Clean Water Management Trust Fund, Ecosystem Enhancement Program, and Conservation Reserve Enhancement Program for the acquisition of buffers for water quality protection. So the comparison is inconclusive. The only safe rational is that wider is better, and that current greenway widths tend to be more narrow than is appropriate for optimum water quality protection.

Every community with a local greenway system claims that they conserve fish and wildlife, and maintain ecological system functions. While this is generally true of any conservation program, the usual devil is in the detail. Again, there is a direct cause and affect relationship that is based upon corridor width as it impacts specific species. For example, research has shown:

A NC study found that 90% of turtle nesting occurred within 250 feet of wetlands; and another study reached the conclusion that a 400 foot buffer is not sufficient to protect herps and mammals;
  • A Mississippi study found that streamside management zones greater than 160 feet are required to maintain squirrels; while a Washington State study found that 85% of terrestrial vertebrates use wetlands and their buffers;
  • The home ranges [denning, breeding, feeding] for riparian dependent species to maintain a sustainable population have been established for river otter as 100 feed for denning, as less than 300 feet for mink, as 325 feet for beavers, as 800 feet for marsh rabbit, and as up to 1300 feet for muskrat;
  • A Pennsylvania study found that 400 feet is needed to match the natural composition of bird species, although a Southeast study recommended widths of 1600 feet to maintain characteristic bottomland hardwood bird richness and other studies noted wetland dependent birds [e.g. mallard and heron] nest in adjacent uplands; and
  • An Ontario study concluded that removing 20% of forest within 3250 feet of wetland may have the same effect on species as destroying 50% of the wetland.


Is it possible that we are headed to an illogical conclusion where enough land is conserved to protect water quality, but enough adjoining land is not conserved to support the species that live there? Ecological systems exist and continue to function because plant communities and animal home ranges are protected, and food chains are maintained. The existing widths of greenway corridors provide a minimum level of urban environmental quality, but without greater width they are unlikely to guarantee optimum ecological system function.

 
Greenways meet an ever growing need, a need to leave the hectic city (if only for a moment) and to experience earth beneath your feet and fresh air in your lungs – to feel life and to feel alive.
— VICTORIA LOGUE


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