An evaluation of the factors determining the effectiveness of water quality buffer zones

doi:10.1016/0022-1694(89)90054-1

Journal of Hydrology

Volume 107, Issues 1–4, 30 May 1989, Pages 133-145

https://doi.org/10.1016/0022-1694(89)90054-1 Get rights and content

Abstract

This study examines the relative role of slope length, slope gradient, surface roughness, and soil hydrologic properties on determining the pollution control effectiveness of vegetated buffer zones. Two models describing buffer conveyance capacity are introduced. The first assumes that pollutant transport through the buffer depends on the energy of overland flow and is based on Bagnold's stream power concept. The second assumes that the buffer effectiveness is a function of total contact time of both surface runoff and throughflow and is based on Darcy's law and the Manning equation. The hydraulic and detention models, respectively, are applied to the problem of estuarine shoreline buffer zone delineation in Carteret County, North Carolina. Results show that where solid-phase pollutants transported as suspended or bedload in overland flow are the major concern, slope gradient is the most critical factor, followed by soil hydraulic conductivity. Where dissolved pollutants that are transported by both surface and subsurface flow are of concern, buffer width is by far the most important factor, with soil moisture storage capacity also playing a role. Methods developed here may be applied to any water quality buffer delineation problem to determine the relative influence of soil properties, geomorphology, and surface conditions.

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Using plan and ordinance quality to evaluate the implementation of riparian buffer policies
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Given the plethora of ecological benefits associated with buffer areas, an assessment of width, vegetative content, and impervious surface encroachment provides information about policy implementation but is not a measure of their effectiveness as these characteristics do not capture whether riparian buffers protect and improve water resources. Studies do, however, identify buffer width in conjunction with topography, hydrogeology, and stream morphology as important factors affecting a buffer’s potential role in pollutant removal (Lowrance et al., 1997; Phillips, 1989). There are no single recommendation for optimum buffer width although a meta-analysis of studies suggests wider buffers are more effective in nutrient removal (Mayer, Reynolds, Mccutchen, & Canfield, 2007).
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Landscape metrics are often used to model nonpoint source pollution from agricultural and urban surface runoff. By considering topography and the spatial arrangement of land cover, landscape metrics can better account for hydrologic connectivity, loading quantity, and vegetated buffer filtering between nutrient loading sources and streams. For this study we develop a surface runoff nutrient loading metric that considers source (i.e. cropland or developed) loading and buffer filtering along hydrologic transport vectors, or flow paths. We use General Additive Modeling to evaluate the relationship between this metric and in-stream nitrogen (N) and phosphorus (P) concentrations in the Saginaw Bay watershed in Michigan, US and compare the relative predictive power between this metric and other landscape metrics that do not consider hydrologic connectivity. The flow path-based cropland loading metric was a stronger predictor of in-stream NO₃ concentrations than alternative metrics. In-stream P concentrations were best predicted by models that included 48-h antecedent precipitation and catchment-wide proportion of developed landcover. Metric maps reveal high nutrient loading areas where only a small proportion of loading reaches streams via surface runoff, highlighting the need to consider nutrient loading via drainage tiles and other subsurface pathways in efforts to quantify nonpoint source loading to surface waters. The flow path-based loading metric is represented spatially as a gridded dataset showing estimates of nutrient loading adjacent to streams, and with higher resolution stream delineation data it could be used by land managers to target locations for precision buffer placement to intercept surface runoff and reduce nutrient loading.
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Establishing perennial vegetation adjacent to a stream is considered to be an effective best management practice (BMP) to buffer aquatic ecosystems against nutrient losses from groundwater (Phillips, 1989; Schultz et al., 1995; Spruill, 2000).
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The model ordinance developed by US EPA recommended that the required width for all forest buffers (i.e., the base width) shall be a minimum of 100 feet, but the width chosen by a jurisdiction varies and usually depends on the sensitivity and characteristics of the resource being protected and the political environment in the community (Heraty, 1993). Some studies call for variable-width riparian buffers which involve designing riparian buffers with variable width along the streams based on the site-specific natural resource conditions to improve buffers’ effectiveness (Basnyat, Teeter, Flynn, & Lockaby, 1999; Herron & Hairsine, 1998; Phillips, 1989; Xiang, 1993). Alternative conservation buffer strategies take the whole watershed or area approach and consider the topographic, soil and land use conditions within and beyond the riparian areas in watersheds to identify the potential sites for conservation buffers.
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Research paperAn evaluation of the factors determining the effectiveness of water quality buffer zones

Abstract

Overland flow wastewater treatment at Easley

S.C.J. Water Pollut. Contr. Fed.

An approach to the sediment transport problem from general physics

U.S. Geol. Surv., Prof. Pap.

Bedload transport by natural rivers

Water Resour. Res.

Stream corridor management in the Pacific Northwest

Environ. Manage.

Development of ecological criteria for natural freshwater wetlands wastewater management: The risks of hydrological impacts on vegetation

Environ. Sci. Eng. Fellowship Rep., Am. Assoc. Adv. Sci., Washington, D.C.

Roughness coefficients for routing surface runoff

J. Irrig. Drain. Eng.

Urban runoff: Pollution sources, control, and treatment

Water Resour. Bull.

Soil Survey of Carteret County, North Carolina

U.S. Soil Conserv. Ser.

Water resources and the land-water interface

Science

Hillslope hydrology

Managing riparian ecosystems to control nonpoint pollution

J. Soil Water Conserv.

Long term sediment deposition in the riparian zone of a coastal plain watershed

J. Soil Water Conserv.

Riparian forests as nutrient filters in agricultural watersheds

BioScience

Research paper
An evaluation of the factors determining the effectiveness of water quality buffer zones