Major factors influencing the efficacy of vegetated buffers on sediment trapping: a review and analysis

Sediment is a major agricultural pollutant threatening water quality. Vegetated buffers, including vegetative filter strips, riparian buffers, and grassed waterways, are best management practices (BMPs) installed in many areas to filter sediments from tailwaters, and deter sediment transport to water bodies. Along with reducing sediment transport, the filters also help trap sediment bound nutrients and pesticides. The objectives of this study were: (i) to review vegetated buffer efficacy on sediment trapping, and (ii) to develop statistical models to investigate the major factors influencing sediment trapping. A range of sediment trapping efficacies was found in a review of over 80 representative BMP experiments. A synthesis of the literature regarding the effects of vegetated buffers on sediment trapping is needed. The meta-analysis results based on the limited data showed that buffer width and slope are two major factors influencing BMPs efficacy of vegetated buffers on sediment trapping. Regardless of the area ratio of buffer to agricultural field, a 10 m buffer and a 9% slope optimized the sediment trapping capability of vegetated buffers.     

Meta-analysis of nitrogen removal in riparian buffers

Riparian buffers, the vegetated region adjacent to streams and wetlands, are thought to be effective at intercepting and reducing nitrogen loads entering water bodies. Riparian buffer width is thought to be positively related to nitrogen removal effectiveness by influencing nitrogen retention or removal. We surveyed the scientific literature containing data on riparian buffers and nitrogen concentration in streams and groundwater to identify trends between nitrogen removal effectiveness and buffer width, hydrological flow path, and vegetative cover. Nitrogen removal effectiveness varied widely. Wide buffers (>50 m) more consistently removed significant portions of nitrogen entering a riparian zone than narrow buffers (0-25 m). Buffers of various vegetation types were equally effective at removing nitrogen but buffers composed of herbaceous and forest/herbaceous vegetation were more effective when wider. Subsurface removal of nitrogen was efficient, but did not appear to be related to buffer width, while surface removal of nitrogen was partly related to buffer width. The mass of nitrate nitrogen removed per unit length of buffer did not differ by buffer width, flow path, or buffer vegetation type. Our meta-analysis suggests that buffer width is an important consideration in managing nitrogen in watersheds. However, the inconsistent effects of buffer width and vegetation on nitrogen removal suggest that soil type, subsurface hydrology (e.g., soil saturation, groundwater flow paths), and subsurface biogeochemistry (organic carbon supply, nitrate inputs) also are important factors governing nitrogen removal in buffers.     

Reduction of stream sediment concentration by a riparian buffer: filtering of road runoff in disturbed headwater basins of montane mainland southeast Asia

We determined the extent that a riparian buffer reduces stream suspended sediment concentrations by filtering road runoff during 18 rain events in a 2.5-ha, multi-use watershed in northern Thailand. The dominant buffer species was the perennial sedge Fimbristylis aphylla Zoll. ex Steud. (Cyperaceae). We monitored stream sediment concentration for situations where road runoff either flowed into the riparian buffer or was diverted directly into the stream (buffer and no buffer scenarios). These data were used to develop the following relationships between instantaneous stream sediment concentration (Ci) and discharge (Qi): Ci= 28.329Qi(0.851) (buffer scenario) and Ci= 22.265Qi(1.579) (no buffer scenario). Using these functions to calculate total event suspended concentrations, we determined that the buffer reduced suspended sediment concentration by 34 to 87%, for the range of events monitored. Removal of sediment from runoff generated on a 2.4-m-wide, 165-m-long unpaved road section was achieved principally via ponding, which reduced the transport capacity as flow entered the relatively flat, saturated buffer. Sediment deposition occurred primarily within the first 10 m of the buffer. Some sediment was also deposited on the fillslope leading to the buffer. Maximum road sediment concentration during the largest buffer event approached 100,000 mg L(-1). Meanwhile, the corresponding maximum stream suspended sediment concentration was <4000 mg L(-1). In contrast, maximum stream concentrations when flow bypassed the buffer during smaller events were commonly 4000 to 7000 mg L(-1). Naturally occurring buffers represent an economical means of mitigating road-related impacts in upland basins in Southeast Asia, particularly if combined with measures limiting sediment and runoff production on contributing road sections.     

INTEGRATED MANAGEMENT OF IN‐FIELD,EDGE‐OF‐FIELD,AND AFTER‐FIELD BUFFERS1

This review summarizes how conservation benefits are maximized when in‐field and edge‐of‐field buffers are integrated with each other and with other conservation practices such as residue management and grade control structures. Buffers improve both surface and subsurface water quality. Soils under permanent buffer vegetation generally have higher organic carbon concentrations, higher infiltration capacities, and more active microbial populations than similar soils under annual cropping. Sediment can be trapped with rather narrow buffers, but extensive buffers are better at transforming dissolved pollutants. Buffers improve surface runoff water quality most efficiently when flows through them are slow, shallow, and diffuse. Vegetative barriers ‐ narrow strips of dense, erect grass ‐ can slow and spread concentrated runoff. Subsurface processing is best on shallow soils that provide increased hydrologic contact between the ground water plume and buffer vegetation. Vegetated ditches and constructed wetlands can act as “after‐field” conservation buffers, processing pollutants that escape from fields. For these buffers to function efficiently, it is critical that in‐field and edge‐of‐field practices limit peak runoff rate and sediment yield in order to maximize contact time with buffer vegetation and minimize the need for cleanout excavation that destroys vegetation and its processing capacity.     

Classification and spatial mapping of riparian habitat with applications toward management of streams impacted by nonpoint source pollution

Management of riparian habitats has been recognized for its importance in reducing instream effects of agricultural nonpoint source pollution. By serving as a buffer, well structured riparian habitats can reduce nonpoint source impacts by filtering surface runoff from field to stream. A system has been developed where key characteristics of riparian habitat, vegetation type, height, width, riparian and shoreline bank slope, and land use are classified as discrete categorical units. This classification system recognizes seven riparian vegetation types, which are determined by dominant plant type. Riparian and shoreline bank slope, in addition to riparian width and height, each consist of five categories. Classification by discrete units allows for ready digitizing of information for production of spatial maps using a geographic information system (GIS). The classification system was tested for field efficiency on Tom Beall Creek watershed, an agriculturally impacted third-order stream in the Clearwater River drainage, Nez Perce County, Idaho, USA. The classification system was simple to use during field applications and provided a good inventory of riparian habitat. After successful field tests, spatial maps were produced for each component using the Professional Map Analysis Package (pMAP), a GIS program. With pMAP, a map describing general riparian habitat condition was produced by combining the maps of components of riparian habitat, and the condition map was integrated with a map of soil erosion potential in order to determine areas along the stream that are susceptible to nonpoint source pollution inputs. Integration of spatial maps of riparian classification and watershed characteristics has great potential as a tool for aiding in making management decisions for mitigating off-site impacts of agricultural nonpoint source pollution.     

Significant Escherichia coli attenuation by vegetative buffers on annual grasslands

A study was conducted to estimate the retention efficiency of vegetative buffers for Escherichia coli deposited on grasslands in cattle fecal deposits and subject to natural rainfall-runoff conditions. The study was conducted on annual grasslands in California's northern Sierra Nevada foothills, a region with a distinct wet-dry season Mediterranean climate. We used 48, 2.0- by 3.0-m runoff plots to examine the efficacy of 0.1-, 1.1-, and 2.1-m buffers at three land slopes (5, 20, and 35%) and four dry vegetation matter levels (225, 560, 900, and 4500 kg/ha) across 27 rainfall-runoff events during two rainfall seasons. Buffer width treatments were implemented by placement of cattle fecal material containing known loads of E. coli 0.1, 1.1, or 2.1 m upslope of the plot runoff collector. Mean total runoff to total rainfall ratio per plot ranged from 0.014:1 to 0.019:1 and reflected the high infiltration capacity of these soils. Approximately 94.8 to 99.995% of total E. coli load applied to each plot appears to be either retained in the fecal pat and/or attenuated within 0.1 m downslope of the fecal pat, irrespective of the presence of a wider vegetated buffer. Relative to a 0.1-m buffer, we found 0.3 to 3.1 log10 reduction in E. coli discharge per additional meter of vegetative buffer across the range of residual dry vegetation matter levels, land slope, and rainfall and runoff conditions experienced during this project. Buffer efficiency was significantly reduced as runoff increased. These results support the assertion that grassland buffers are an effective method for reducing animal agricultural inputs of waterborne E. coli into surface waters.     

Effectiveness of Constructed Overland Flow Areas in Decreasing Diffuse Pollution from Forest Drainages

Forestry is the largest scale human impact affecting catchments in Finland and a prominent source of diffuse pollution in many water courses. Among the forestry activities, draining of wetlands had the most pronounced impacts on sediment, nutrient, and metal loading in the past. At present, renovation of old ditches and fertilization of peatlands constitute the major risk of forestry-induced diffuse pollution. Contemporary forestry aims at decreasing this risk with various riparian buffer strip designs. Among such designs, creation of overland flow areas by plugging the outlet ditches is increasingly used. Our objectives were to evaluate the potential of constructed overland flow areas to function as riparian buffers and estimate the quality and quantity of diffuse pollution from old versus recent forest drainages. We studied retention and release of pollutants from 20 constructed, 2- to 10-m-wide overland flow areas receiving drainage water from forested peatlands. Drainage waters were sampled above and below the plugged ditches three times per year from 1998 to 1999. Chemical oxygen demand and nutrient and metal loads and concentrations varied strongly between seasons, years, and drainage areas. Areas subjected to recent ditch renovations and fertilizations had clearly elevated seasonal loads and concentrations of total phosphorus (TP), PO₄, Fe, and Al in comparison to old treatment areas. Especially TP loads were high above the national average values measured for forestry-induced diffuse pollution. In general, water quality above and below the buffer strips did not differ significantly. Our results indicate that plugged outlet ditches and associated narrow overland flow areas do not function as proper buffers in peatland areas. We suggest that wider buffers with extensive overland flow areas are needed in order to control diffuse pollution from forested and drained peatlands.     

GRAZED STUBBLE HEIGHT AS A CRITERION FOR CONTROLLING SEDIMENT PRODUCTION FROM GRAZING LANDS1

ABSTRACT: Efforts by state and federal agencies to develop standards and guidelines for protecting and enhancing water quality on grazing lands have led to suggestions that grazed stubble height criteria could be used to determine when cattle should be removed from a specific pasture or grazing area. Until recently only indirect scientific evidence from agronomy and laboratory studies gave support to the stubble height concept. Consequently, a grazing study was initiated on a Montana ranch in 1997 to determine the reduction in overland sediment achieved by grazing a pasture to a predetermined stubble height. Treatments consisted of 7 cm (3 in) grazed, 7 cm (3 in) clipped or mowed, 15 cm (6 in) grazed; 15 cm (6 in) clipped and untreated or natural forage plant height. The five treatments were used in a two‐year trial spanning 1997 to 1999. At the conclusion of this study the magnitude of sediment production was related to the number of intense rain events during the March through June period rather than total precipitation. There was a significant year effect in terms of sediment accumulation (P < 0.01) but no year by treatment effect (P = 0.11). Even though a significant difference in sediment accumulation was detected between the shorter and taller stubble heights (P = 0.04) in both 1998 and 1999, the difference could not be explained by grazed stubble height alone. Close grazing (7 cm stubble) consistently ranked lowest in sediment production (P < 0.01) among all treatments, including the ungrazed control. These results suggest that changes in plant community structure and microtopographic caused by grazing influence sediment entrapment (retention) on hillslopes more than those caused by plant height.     

Efficacy of vegetated buffer strips for retaining Cryptosporidium parvum

Overland and shallow subsurface hydrologic transport of pathogenic Cryptosporidium parvum oocysts from cattle feces into surface drinking water supplies is a major concern on annual grasslands in California's central and southern Sierra Nevada foothills. Soil boxes (0.5 m wide x 1.1 m long x 0.3 m deep) were used to evaluate the ability of grass vegetated buffer strips to retain 2 x 10(8) spiked C. parvum oocysts in 200-g fecal deposits during simulated rainfall intensities of 30 to 47.5 mm/h over 2 h. Buffers were comprised of Ahwahnee sandy loam (coarse-loamy, mixed, active, thermic Mollic Haploxeralfs; 78:18:4 sand to silt to clay ratio; dry bulk density = 1.4 g/cm(3)) set at 5 to 20% land slope, and >/=95% grass cover (grass stubble height = 10 cm; biomass = 900 kg/ha dry weight). Total number of oocysts discharged from each soil box (combined overland and subsurface flow) during the 120-min simulation ranged from 1.5 x 10(6) to 23.9 x 10(6) oocysts. Observed overall mean log(10) reduction of total C. parvum flux per meter of vegetated buffer was 1.44, 1.19, and 1.18 for buffers at 5, 12, and 20% land slope, respectively. Rainfall application rate (mm/h) was strongly associated with oocyst flux from these vegetated buffers, resulting in a decrease of 2 to 4% in the log(10) reduction per meter buffer for every additional mm/h applied to the soil box. These results support the use of strategically placed vegetated buffers as one of several management strategies that can reduce the risk of waterborne C. parvum attributable to extensive cattle grazing on annual grassland watersheds.     

WATERSHED SCALE INVENTORY OF EXISTING RIPARIAN BUFFERS IN NORTHEAST MISSOURI USING GIS1

An observational study was conducted at the watershed scale using land cover (vegetation) data to assess the absence or presence of riparian buffers in three northeastern Missouri watersheds. Forests and grasslands lying within a 61 m (200 ft) parallel band directly adjacent to streams were considered “buffers” for improving or protecting water quality and were characterized according to their length, width, and vegetation type. Results indicated that riparian buffers were abundant throughout the watersheds but were typically narrow along first‐order and second‐order streams; in many cases they may not have been wide enough to provide adequate stream protection. At least 90 percent of all streams had buffer vegetation immediately adjacent to the streambanks, but as few as 31 percent of first‐order streams had buffers extending to 61 m from the stream on at least one side. On‐site evaluations are needed to determine the condition of these forests and grasslands and their ability to process nonpoint source pollutants. The results will be useful for providing natural resource managers with knowledge of current watershed conditions as well as in identifying specific locations for future conservation efforts within each watershed.     

Surface runoff water quality in a managed three zone riparian buffer

Managed riparian forest buffers are an important conservation practice but there are little data on the water quality effects of buffer management. We measured surface runoff volumes and nutrient concentrations and loads in a riparian buffer system consisting of (moving down slope from the field) a grass strip, a managed forest, and an unmanaged forest. The managed forest consisted of sections of clear-cut, thinned, and mature forest. The mature forest had significantly lower flow-weighted concentrations of nitrate, ammonium, total Kjeldahl N (TKN), sediment TKN, total N (nitrate + TKN), dissolved molybdate reactive P (DMRP), total P, and chloride. The average buffer represented the conditions along a stream reach with a buffer system in different stages of growth. Compared with the field output, flow-weighted concentrations of nitrate, ammonium, DMRP, and total P decreased significantly within the buffer and flow-weighted concentrations of TKN, total N, and chloride increased significantly within the buffer. All loads decreased significantly from the field to the middle of the buffer, but most loads increased from the middle of the buffer to the sampling point nearest the stream because surface runoff volume increased near the stream. The largest percentage reduction of the incoming nutrient load (at least 65% for all nutrient forms) took place in the grass buffer zone because of the large decrease (68%) in flow. The average buffer reduced loadings for all nutrient species, from 27% for TKN to 63% for sediment P. The managed forest and grass buffer combined was an effective buffer system.     

STRATIFICATION OF VARIABILITY IN RUNOFF AND SEDIMENT YIELD BASED ON VEGETATION CHARACTERISTICS1

ABSTRACT: Runoff and sediment yield were collected from 100 plots during simulated rainfalls (100 mm/hr for 15 minutes) at antecedent soil moisture conditions. A clustering technique was used to stratify the variability of a single data set within a sagebrush‐grass community into four groups based on vegetation life form and amount of cover. The four cluster groups were grass, grass/shrub, shrub, and forb/grass and were found to be significantly different in plant height, surface roughness, soil bulk density, and soil organic matter. Stepwise multiple regression analyses were performed on the single data set and each cluster group. Results for individual groups resulted in more robust predictive equations for runoff (r²= 0.65–0.73) and sediment yield (r²= 0.37–0.91) than for equations developed from the single data set (r²= 0.56 for runoff and r²= 0.27 for sediment yield). The standard errors of the cluster group regression equations were also improved in three of the four group equations for both runoff and sediment yield compared to the single data set. Runoff was found to be significantly less (p >0.01) in the forb/grass group compared with other vegetation cluster groups, but this was influenced by four plots that produced little or no runoff. Sediment yield was not found to be significantly different among any cluster groups. Discriminant analysis was then used to identify important variables and develop a model to classify plots into one of the four cluster groups. The discriminant model could be incorporated into rangeland hydrology and erosion models. The percentage cover of grasses, shrubs, litter, and bare ground effectively stratified about 12 percent of the variation observed in runoff and 26 percent of the variability for sediment yield as determined by r².     

Grass‐Shrub Riparian Buffer Removal of Sediment,Phosphorus, and Nitrogen From Simulated Runoff1

Abstract: Riparian buffer forests and vegetative filter strips are widely recommended for improving surface water quality, but grass‐shrub riparian buffer system (RBSs) are less well studied. The objective of this study was to assess the influence of buffer width and vegetation type on the key processes and overall reductions of total suspended solids (TSS), phosphorus (P), and nitrogen (N) from simulated runoff passed through established (7‐year old) RBSs. Nine 1‐m RBS plots, with three replicates of three vegetation types (all natural selection grasses, two‐segment buffer with native grasses and plum shrub, and two‐segment buffer with natural selection grasses and plum shrub) and widths ranging from 8.3 to 16.1 m, received simulated runoff having 4,433 mg/l TSS from on‐site soil, 1.6 mg/l total P, and 20 mg/l total N. Flow‐weighted samples were collected by using Runoff Sampling System (ROSS) units. The buffers were very efficient in removal of sediments, N, and P, with removal efficiencies strongly linked to infiltration. Mass and concentration reductions averaged 99.7% and 97.9% for TSS, 91.8% and 42.9% for total P, and 92.1% and 44.4% for total N. Infiltration alone could account for >75% of TSS removal, >90% of total P removal, and >90% of total N removal. Vegetation type induced significant differences in removal of TSS, total P, and total N. These results demonstrate that adequately designed and implemented grass‐shrub buffers with widths of only 8 m provide for water quality improvement, particularly if adequate infiltration is achieved.     

EFFECTS OF A NORTH CENTRAL WASHINGTON WILDFIRE ON RUNOFF AND SEDIMENT PRODUCTION1

ABSTRACT: Runoff was measured from a 564-ha catchment located on the Entiat Experimental Forest for nine years before a severe wild-fire in 1970 destroyed the mixed conifer vegetation. Runoff records from the Chelan River (2 393 km²) were used as control data for determining changes in water yield during the seven years following the fire. The first post-fire year was a period of transition in which the soil profile retained more water than in previous years and measured runoff was 8.9 cm greater than the predicted value based on pre-fire conditions. Runoff from the burned catchment during subsequent years was much greater than measured values before the fire. Measured minus predicted runoff, based on the pre-fire calibration equation, varied from 10.7 cm during the dry year of 1977 to 47.2 cm during the abnormally wet year of 1972. Flow duration curves indicated that runoff at each percent value after the fire was at least double the comparable pre-fire value. Sediment production increased dramatically after the fire because of increased flow rates, increased overland flow caused by reduced infiltration capacity, and mass soil movement. Sediment yield is beginning to decrease as stream channels become stabilized and vegetation on upper slopes improves infiltration capacity.     

Effects of Local Land Use on Physical Habitat, Benthic Macroinvertebrates, and Fish in the Whitewater River, Minnesota, USA

Best management practices (BMPs) have been developed to address soil loss and the resulting sedimentation of streams, but information is lacking regarding their benefits to stream biota. We compared instream physical habitat and invertebrate and fish assemblages from farms with BMP to those from farms with conventional agricultural practices within the Whitewater River watershed of southeastern Minnesota, USA, in 1996 and 1997. Invertebrate assemblages were assessed using the US EPA's rapid bioassessment protocol (RBP), and fish assemblages were assessed with two indices of biotic integrity (IBIs). Sites were classified by upland land use (BMP or conventional practices) and riparian management (grass, grazed, or wooded buffer). Physical habitat characteristics differed across buffer types, but not upland land use, using an analysis of covariance, with buffer width and stream as covariates. Percent fines and embeddedness were negatively correlated with buffer width. Stream sites along grass buffers generally had significantly lower percent fines, embeddedness, and exposed streambank soil, but higher percent cover and overhanging vegetation when compared with sites that had grazed or wooded buffers. RBP and IBI scores were not significantly different across upland land use or riparian buffer type but did show several correlations with instream physical habitat variables. RBP and IBI scores were both negatively correlated with percent fines and embeddedness and positively correlated with width-to-depth ratio. The lack of difference in RBP or IBI scores across buffer types suggests that biotic indicators may not respond to local changes, that other factors not measured may be important, or that greater improvements in watershed condition are necessary for changes in biota to be apparent. Grass buffers may be a viable alternative for riparian management, especially if sedimentation and streambank stability are primary concerns.     

Effects of riparian forest buffers on in-stream nutrient retention in agricultural catchments

In northeastern Austria, marshlands have been turned into the most productive arable land of the country. As a result, most headwater streams show structurally degraded channels, lacking riparian buffer zones, which are heavily loaded with nutrients from the surrounding crop fields. The present study examines whether longitudinally restricted riparian forest buffers can enhance the in-stream nutrient retention in nutrient-enriched headwater streams. We estimated nutrient uptake from pairwise, short-term addition experiments with NH, NH, PO, and NaCl within reaches with riparian forest buffers (RFB) and degraded reaches (DEG) of the same streams. Riparian forest buffers originated from the conservation of the pristine vegetation or from restoration measures. Hydrologic retention was calculated with the model OTIS-P on the basis of conductivity break-through curves from the salt injections. A significant increase in surface transient storage was revealed in pristine and restored RFB reaches compared with DEG reaches due to the longitudinal step-pool pattern and the frequent occurrence of woody debris on the channel bed. Ammonium uptake lengths were significantly shorter in RFB reaches than in DEG reaches, resulting from the higher hydrologic retention. Uptake velocities did not differ significantly between RFB and DEG reaches, indicating that riparian forest buffers did not affect the biochemical nutrient demand. Uptake of NH was mainly driven by autotrophs. Net PO uptake was not affected by riparian forest buffers. The study shows that the physical and biogeochemical effects of riparian forest buffers on the in-stream nutrient retention are limited in the case of highly eutrophic streams.     

Vegetative Buffer Strips for Reducing Herbicide Transport in Runoff: Effects of Buffer Width,Vegetation, and Season

The effectiveness of vegetative buffer strips (VBS) for reducing herbicide transport has not been well documented for runoff prone soils. A multi‐year plot‐scale study was conducted on an eroded claypan soil with the following objectives: (1) assess the effects of buffer width, vegetation, and season on runoff transport of atrazine (ATR), metolachlor (MET), and glyphosate; (2) develop VBS design criteria for herbicides; and (3) compare differences in soil quality among vegetation treatments. Rainfall simulation was used to create uniform antecedent soil water content and to generate runoff. Vegetation treatment and buffer width impacted herbicide loads much more than season. Grass treatments reduced herbicide loads by 19‐28% and sediment loads by 67% compared to the control. Grass treatments increased retention of dissolved‐phase herbicides by both infiltration and adsorption, but adsorption accounted for the greatest proportion of retained herbicide load. This latter finding indicated VBS can be effective on poorly drained soils or when the source to buffer area ratio is high. Grass treatments modestly improved surface soil quality 8‐13 years after establishment, with significant increases in organic C, total N, and ATR and MET sorption compared to continuously tilled control. Herbicide loads as a function of buffer width were well described by first‐order decay models which indicated VBS can provide significant load reductions under anticipated field conditions.     

COMPARISON OF 1-D AND 2-D MODELING OF OVERLAND RUNOFF AND SEDIMENT TRANSPORT1

ABSTRACT: One-dimensional and two-dimensional modeling approaches were compared for their abilities in predicting overland runoff and sediment transport. Both 1-D and 2-D models were developed to test the hypothesis that the 2-D modeling approach could improve the model predictions over the 1-P approach, based on the same mathematical representations of physical processes for runoff and sediment transport. The models developed in this study were applied to overland areas with cross slopes. A hypothetical case and an experimental study reported by Storm (1991) were used. Based on the simulation results from the selected hypothetical case and experimental study, the 2-D model provided better representation of spatial distribution of flow depths and sediment concentrations than the 1-D model. However, no significant differences in predictions of total runoff volume and sediment yield at the outlet area were found between the 1-D and 2-D models.     

METHOD TO IDENTIFY EFFECTWE RIPARIAN BUFFER WIDTHS FOR ATLANTIC SALMON HABITAT PROTECTION1

ABSTRACT: Successful restoration of declining anadromous species is dependent upon effective riparian buffer zone management. Natural resource managers, policy developers and local conservation groups require science‐based information concerning the width at which a given buffer will be effective for its stated purpose. This paper summarizes a method developed in 1999 to determine effective riparian buffer widths for Atlantic salmon habitat protection as part of the Atlantic Salmon Conservation Plan for Seven Maine Rivers. A major assumption of the method is that no two buffers are alike with respect to their effectiveness and that various buffer characteristics dictate the required width for a given level of effectiveness. The method uses a predictive model that generates suggested riparian buffer widths as a function of specific, measurable buffer characteristics (such as slope, soil characteristics, and plant community structure and density) that affect buffer function. The method utilizes a variable‐width, two‐zone approach and specifies land uses that are consistent with desired buffer function within the two zones.     

Effect of Watershed Subdivision and Filter Width on SWAT Simulation of a Coastal Plain Watershed1

Cho, Jaepil, Richard R. Lowrance, David D. Bosch, Timothy C. Strickland, Younggu Her, and George Vellidis, 2010. Effect of Watershed Subdivision and Filter Width on SWAT Simulation of a Coastal Plain Watershed. Journal of the American Water Resources Association (JAWRA) 46(3):586-602. DOI: 10.1111/j.1752-1688.2010.00436.x Abstract: The Soil and Water Assessment Tool (SWAT) does not fully simulate riparian buffers, but has a simple filter function that is responsive to filter strip width (FILTERW). The objectives of this study were to (1) evaluate SWAT hydrology and water quality response to changes in watershed subdivision levels and different FILTERW configurations and (2) provide guidance for selecting appropriate watershed subdivision for model runs that include the riparian buffer feature through the FILTERW parameter. Watershed subdivision level is controlled by the critical source area (CSA) which defines the minimum drainage area required to form the origin of a stream. SWAT was calibrated on a 15.7 km² subdrainage within the Little River Experimental Watershed, Georgia. The calibrated parameter set was applied to 32 watershed configurations consisting of four FILTERW representations for each of eight CSA levels. Streamflow predictions were stable regardless of watershed subdivision and FILTERW configuration. Predicted sediment and nutrient loads from upland areas decreased as CSA increased when spatial variations of riparian buffers are considered. Sediment and nutrient yield at the watershed outlet was responsive to different combinations of CSA and FILTERW depending on selected in-stream processes. CSA ranges which provide stable sediment and nutrient yields at the watershed outlet was suggested for avoiding significant modifications in selected parameter set.