April 5, 2007
Albemarle County Planning Department
Charlottesville, VA 22902
Dear Ms. McDowell,
It is my understanding that Albemarle is seeking advice from StreamWatch regarding stream buffering. StreamWatch is a partnership of the entities listed in the margin, and our mission is to provide data and information about local stream conditions and the factors driving those conditions. StreamWatch does not typically give management recommendations. However, when the science is clear, and if all StreamWatch partners are in agreement, we can participate in management discussions upon request. This is such a case.
StreamWatch has not performed a study of buffer effectiveness in Albemarle, and we do not believe such a study is needed in order for the County to make a well-informed decision about improving buffer protection. Buffering is perhaps the most intensively scrutinized aspect of stream management. Literally hundreds of peer-reviewed studies document the importance and effectiveness of buffers. Though this letter is not a comprehensive academic-style review of the literature, I, a number of StreamWatch technical advisors, and a number of StreamWatch steering committee members are sufficiently familiar with the literature to give us strong confidence in the comments that follow. The statements we make in this letter are supported by several representative papers and publications, including the Chesapeake Bay Riparian Handbook and an exhaustive review of buffer studies conducted by the University of Georgia’s Institute of Ecology. (Please see the list of references below).
A buffer, as you know, is a vegetated strip alongside the stream. The streamside zone, also called the riparian zone, exercises very strong controls over stream conditions. Our region’s natural vegetative condition is forest. Riparian forests serve to stabilize stream banks, control stream temperature, supply food (tree leaves) to aquatic organisms, facilitate reproduction for aquatic organisms that need forest habitat to complete their lifecycles, and filter runoff. Since local stream ecosystems are by nature“geared” to forested riparian zones, streams inevitably degrade when the forest is removed.
We base our recommendations on the assumption that Albemarle’s goal is to protect water quality and stream health throughout the County. We use the term water quality to refer to the physiochemical quality of stream water, where “better water” means water that carries fewer human-generated toxic, nutrient, and sediment pollutants and is less burdened by human-caused temperature increase than “poorer water.” We use the term stream health to refer to the ecological robustness of the stream, where “better health” connotes better water quality, better habitat, and richer biological diversity than “poorer health”. Water quality and stream health are interdependent. For instance, streams with poor biological diversity almost invariably have poor water quality.
Our recommendations are as follows:
1) Extend buffer protection to intermittent streams throughout the County. (Presently, intermittent streams are protected only in drinking water supply areas).
The protection of intermittent streams confers enormous water quality and stream health benefits to the entire stream system—not simply the intermittent streams themselves. Intermittent streams constitute the majority of stream miles in the stream network. Research shows that during stormflow, these streams can contribute large volumes of sediment and other pollutants to the system. Generally, the goal of good water quality and stream health cannot be met if intermittent streams are unprotected.
Most research indicates that a 100-foot buffer on either side of the stream is usually sufficient for water quality and stream health protection in non-hilly areas.
2) Increase buffer widths on sloping land, and in hilly and mountainous areas. As slope and runoff water velocity increase, buffer widths need to be increased. Formulae are available for calculating ideal buffer widths on sloping land. Minimally, a 200-foot buffer may provide an acceptable level of protection in most hilly settings, but on very steep land, buffers may need to be extended beyond 200 feet. Much research suggests that the target width of the buffer should not include land with greater than 25 percent slope. In other words, steeply sloping land does not provide buffering service, and these steep slopes should be subtracted when calculating the functioning width of the buffer.
3) Promote livestock exclusion. When given direct access to the riparian corridor, cattle and other livestock profoundly affect water quality and stream health. They do this by:
a) consuming buffer vegetation (thus diminishing the vegetation’s effectiveness as a pollution filter).
b) destabilizing stream banks, leading to erosion and sediment pollution.
c) wallowing in the stream and damaging stream habitat.
d) introducing excessive nutrient pollution by defecating in and near streams.
Livestock can undo most of the gains achieved by buffers, and a strategy that does not exclude livestock from the buffer will fail to meet many stream protection objectives.
4) Promote native forest in the buffer. Currently, a large portion of buffers in Albemarle is unforested, even in water supply areas. Grass buffers can help protect water quality by filtering runoff. But the natural condition of the Albemarle landscape is forest, and local stream ecosystems are adapted to this forested condition. Thus, buffers composed of native forest are essential for achieving overall stream health. Riparian forests maintain stream health by:
a) stabilizing stream banks with tree roots, thereby reducing erosion and associated sediment loading.
b) supplying essential food (i.e. the leaves of deciduous trees) for invertebrates. These invertebrates, in turn, support fish and other higher organisms.
c) serving as essential habitat for the aquatic invertebrates that need forested terrestrial habitat to complete their life cycles. Again, higher organisms depend on these invertebrates.
d) providing complex habitat for fish and other organisms in the form of woody debris (fallen trunks and limbs).
e) maintaining stream water temperature within the natural range of variation to which native organisms are evolutionarily adapted.
Buffers are not bullet-proof. Water quality and stream health are functions of conditions throughout the entirety of a stream’s watershed, and are also profoundly affected by flow alteration (e.g. impoundments and withdrawals for water supply; high stormflows caused by impervious surfaces). Effective watershed management incorporates many tools. Buffering is essential among these, and though buffers cannot solve all problems in all settings, the great majority of Albemarle streams would benefit tremendously if protected with a continuous, adequately-sized buffer of intact native forest.
On behalf of the StreamWatch partnership, I thank you for inviting these comments.
John Murphy, Director
List of References:
Allan, JD, Erickson, DL and Fay, J. 1997. The Influence of Catchment Land Use on Stream Integrity Across Multiple Spatial Scales. Freshwater Biology 37: 149–161.
Correll, DL. 2003. Vegetated Stream Riparian Zones: Their Effects on Stream Nutrients, Sediments, and Toxic Substances. An annotated and indexed bibliography of the world literature, including buffer strips and interactions with hyporheic zones and floodplains. Thirteenth Edition, April 2003.
Correll, DL. 2005. Principles of Planning and Establishment of Buffer Zones. Ecological Engineering. 24(5): 433-439.
Wenger, S. 1999. A Review of the Scientific Literature on Riparian Buffer Width, Extent, and Vegetation. Revised Version, March 5, 1999. Office of Public Service & Outreach, Institute of Ecology, University of Georgia.
Palone, RS, Todd, AH (editors). 1997. Chesapeake Bay riparian handbook: a guide for establishing and maintaining riparian forest buffers. Revised June 1998. USDA Forest Service. NA-TP-02-97. Radnor, PA.
Schueler, TR. 2003. Impacts of Impervious Cover on Aquatic Systems. Center for Watershed Protection. Ellicott City, MD.
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