A Riparian Buffer Design for Cropland

Purpose: • Present a general, multi-purpose, riparian buffer design suitable for most cropland situations • Provide some guidelines for adjusting this general design to better fit site-specific conditions or landowner need

The influence of ectomyorrhizae on drought tolerance characteristics of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings

Douglas-fir seedlings were inoculated with different species of ectomycorrhizae-forming fungi in order to test the concept that ectomycorrhizae enhance the drought tolerance of seedlings and to investigate the mechanisms responsible for this effect. Seedlings were transplanted at age 6 to 8 weeks into pots containing pasteurized loam soil and inoculated with either Rhizopogon vinicolor (Rv), Laccaria laccata (L1), or Hebeloma crustuliniforme (Hc), or left uninoculated. Rv and He colonization produced abundant hyphal growth, while Ll produced much less hyphae. After 4 months under well-watered greenhouse conditions, neither Rv- or L1- colonized seedlings had significantly different dry mass and leaf N, P, K, and Ca concentrations compared to nonmycorrhizal controls. Higher nutrient concentrations of Hc-colonized seedlings resulted from suppressed growth, since total amounts of these nutrients were equal to or less than for nonmycorrhizal controls. Seedlings were transferred to a growth room where photosynthesis, stomatal conductance, and plant water potential components were measured under well-watered and soil water-limiting conditions. Drought tolerance, as evaluated by net photosynthesis rate over the soil water potential range of -0.05 to -0.6 MPa, was clearly enhanced by Rv, somewhat enhanced by Hc, and decreased by Ll compared to nonmycorrhizal controls. Stomatal conductances closely followed net photosynthesis rates. Compared to control seedlings, leaf water potentials of mycorrhizal seedlings were lower (Rv by 0.2 to 0.3 MPa) or similar (L1 and Hc) over the entire range of soil water potential. Significantly reduced root lengths (Rv 65% of control; Hc 70% of control; Ll 90% of control) may have counteracted a mycorrhizal benefit of efficient water absorption. It is hypothesized that higher net photosynthesis rate and stomatal conductance despite lower leaf water potential, as observed for Rv-colonized seedlings, can arise from an ectomycorrhizae-altered carbon economy of the plants. According to this hypothesis, net photosynthesis rate and stomatal conductance are correlated with photosynthate sink demand, which here would be increased by export to the mycorrhizal fungus. Strong mycorrhizal demand, which occurs at some cost to plant growth, stimulates photosynthesis, to which the stomata respond by opening in spite of water stress. The degree to which this effect was observed in this study correlated with the visual abundance of hyphal growth which each fungal species developed

A Design Aid for Determining Width of Filter Strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trap¬ping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models

A Design Aid for Determining Width of Filter Strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trap¬ping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models

A design aid for determining width of filter strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trapping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models

Improved indexes for targeting placement of buffers of Hortonian runoff

Targeting specific locations within agricultural watersheds for installing vegetative buffers has been advocated as a way to enhance the impact of buffers and buffer programs on stream water quality. Existing models for targeting buffers of Hortonian, or infiltration-excess, runoff are not well developed. The objective was to improve on an existing soil survey–based approach that would provide finer scale resolution, account for variable size of runoff source area to different locations, and compare locations directly on the basis of pollutant load that could be retained by a buffer. The method couples the Soil Survey Geographic database with topographic information provided by a grid digital elevation model in a geographic information system. Simple empirical equations were developed from soil and topographic variables to generate two indexes, one for deposition of sediment and one for infiltration of dissolved pollutants, and the equations were calibrated to the load of sediment and water, respectively, retained by a buffer under reference conditions using the process-based Vegetative Filter Strip Model. The resulting index equations and analytical procedures were demonstrated on a 67 km2 (25.9 mi2) agricultural watershed in northwestern Missouri, where overland runoff contributes to degraded stream water quality. For both indexes, mapped results clearly mimic spatial patterns of water flow convergence into subdrainages, substantiating the importance of size of source area to a given location on capability to intercept pollutants from surface runoff. A method is described for estimating a range of index values that is appropriate for targeting vegetative buffers. The index for sediment retention is robust. However, the index for water (and dissolved pollutant) retention is much less robust because infiltration is very small, compared to inflow volumes, and is relatively insensitive to the magnitude of inflow from source areas. Consequently, an index of inflow volume may be more useful for planning alternative practices for reducing dissolved pollutant loads to streams. The improved indexes provide a better method than previous indexes for targeting vegetative buffers in watersheds where Hortonian runoff causes significant nonpoint pollution