Riparian Buffer Function

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This page was developed to organize increasing materials related to how the riparian zone at a watershed scale provides services such as water supply, and salmonid habitat.

"To buffer" is an verb. A "buffer" is a regulatory designation of an area were management is changed near a stream to reduce the potential negative impacts of proximate land uses like forestry, agriculture or residential development. On the other hand, "riparian functions" are those dynamics observed in historical systems (i.e. evolved over long periods of time, and to which biota are adapted) that support biota directly or indirectly--many of these functions involve environmental buffering. Buffering functions are varied and complex, and could be divided into two general groups:

Geomorphic and bioenergetic processes:

  • Habitat islands or corridors for riparian dependent species
  • Habitat corridors for terrestrial species
  • Shading effects on microclimate and stream temperature
  • Organic litter inputs to stream ecosystems
  • Large wood and rootwad effects of stream structure

Biochemical and water quality processes:

  • Nutrient and sedimentparticles of clay, silt, sand, gravel, or cobble, transported by water, are called sediment. removal and sequestration (in soils and biomass, with harvest providing removal)
  • Denitrification (as a nitrogen removal pathway) particularly in anaerobic soils.
  • Pathogen removal (livestock and pet waste).
  • Toxin decomposition and sequestration (pesticides, transportation runoff?)

The size and character of stream-side land necessary for buffing reflects a combination of the social consensus that these functions have value, and the degree to which proximate land uses create a threat that demands buffering.

All buffer functions are often lumped in political discussions of buffer regulation. Buffer width is the most commonly debated factor (File:Johnson & Ryba 1992 king county recommendations for buffer width.pdf; Knutson & Naef 1997; GEI 2002; Varanasi 2003).

Buffer function management has implications for forest management most commonly in headwater valleys. This management is defined in the Forest Practices Act as implemented by WDNR in consultation with Tribes and WDFW, strongly affected by the Timber Fish and Wildlife Agreement.

Agricultural landscapes often associated with floodplains, are a current (2014) focus of buffer management conflict, as agricultural land preservation and property rights interest groups compete legally and politically with salmon recovery and water quality interest groups over who has the authority and responsibility to manage buffer conditions.

In urbanizing landscapes often associated with lowland watersheds, issues around riparian buffer functions are often eclipsed by impervious surface effects, which drive stream condition through modification of stream flow. Any analysis of buffer function in a given system is likely to be dependent on analysis of watershed hydrology, such that deforestation, impervious surfaces and groundwater withdrawal has effects on stream conditions that cannot be offset by increasing buffer function.

Buffer management debate in the Salish Sea has been driven by Endangered Species Act and the effects of riparian conditions on salmon, and pathogen impacts on shellfish harvest, and water quality designation under the Clean Water Act.


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