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Last modified
12/16/2009 7:48:48 AM
Creation date
12/15/2009 4:04:08 PM
Metadata
Fields
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Water Conservation
Project Type
General OWC
Title
Designing Impact Assessments for Evaluating Ecological Effects of Agricultural Conservation Practices on Streams
Date
12/15/2009
Water Conservation - Doc Type
Reports
Supplemental fields
Drought Mitigation - Doc Type
News Article
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SMILEY, SHIELDS, AND KNIGHT <br />impacted stream) management strategies for headwa- <br />ter streams in this region. Some physical and biologi- <br />cal differences are expected to occur between <br />channelized and unchannelized streams. However, <br />this experimental design was developed with the <br />intent of using the control and the minimally <br />impacted stream treatments as opposing reference <br />points for evaluating the effectiveness of the herba- <br />ceous buffers. Specifically, the evaluation criteria that <br />will determine if herbaceous riparian buffers are <br />effective is the prediction that habitat and biological <br />conditions within the buffer treatment should become <br />more similar to the minimally impacted streams than <br />control streams, particularly with increasing time fol- <br />lowing the establishment of the buffers. <br />All sampling sites are located on private land and <br />were selected after conducting site visits to evaluate <br />them based on predetermined habitat criteria: (1) <br />first or second -order headwater ditches or streams, <br />(2) land use within the watershed is predominantly <br />agriculture, (3) accessibility that allowed for estab- <br />lishment of two sites spaced at least 150 m apart. <br />Additional habitat criteria used to create the treat- <br />ment effect were: (1) replicates for the control were to <br />be drainage ditches having narrow riparian zones <br />( <15 m) with mostly herbaceous riparian vegetation, <br />(2) replicates for the buffer treatment were drainage <br />ditches having herbaceous riparian buffers on both <br />streambanks that were established between 2003 and <br />2005 through the Conservation Reserve Enhance- <br />ment Program, and (3) replicates for the minimally <br />impacted streams were required to be unchannelized <br />streams with mature woody vegetation >5 m tall on <br />both streambanks. <br />A replicate in this study is a ditch or a stream. <br />Drainage ditch treatments have three replicates each, <br />but the minimally impacted stream treatment has <br />only two replicates due to the difficulty in finding and <br />obtaining permission to sample another unchannel- <br />ized stream. Two 125 m long sites (subsamples) were <br />established in each replicate and the sites are at least <br />150 m apart to ensure our sampling encompasses a <br />representative range of habitat conditions within <br />each replicate. Habitat and biological data from each <br />site within a ditch/stream during each sampling per- <br />iod will either be composited or averaged to avoid <br />pseudoreplication. <br />Sampling Methods <br />Six permanent transects spaced 25 m apart were <br />established beginning at the downstream border of <br />each site. Permanent transects were established with <br />the use of wooden stakes driven into the ground at <br />the points on both banks that represent estimated <br />bankfull conditions (i.e., the point where the floodwa- <br />ters would begin spilling over into the floodplain) <br />(Figure 2). Riparian vegetation, geomorphology, and <br />instream habitat are measured along each transect. <br />Riparian and geomorphological characteristics are <br />measured once a year (Figure 2). Species composition <br />and density of woody vegetation >1 m tall are mea- <br />sured in twelve 1 m x 10 m quadrats that begin at <br />the water's edge and coincide with permanent tran- <br />sects (Figure 2). The presence and absence of herba- <br />ceous and woody vegetation within four height <br />stratas (0 -0.5 m, 0.5 -2 m, 2 -5 m, and >5 m) are noted <br />in each quadrat. Riparian canopy cover is measured <br />using a convex spherical densiometer while facing <br />upstream in the middle of each quadrat and the wet- <br />ted portion of the channel. Riparian zone widths of <br />the drainage ditches were determined by calculating <br />the straight line distance between coordinate mea- <br />surements obtained at the water's edge and the edge <br />of the agricultural fields (Figure 2) during geomor- <br />phology surveys. Woody vegetation cover and widths <br />of the minimally impacted streams hindered the use <br />of surveying methods for riparian width measure- <br />ments in these sites. Therefore, riparian widths of <br />the minimally :impacted streams were obtained using <br />aerial photos and geographic information systems <br />(ArcGIS). Geomorphological variables including top <br />bank width (i.e., the width of the channel at bankfull <br />capacity), thalweg depth, channel cross - section area, <br />gradient, and sinuosity are calculated from coordi- <br />nate measurements collected from a minimum of nine <br />points along each transect using either a Real Time <br />Kinematic (RTK) system or an electronic total station <br />(Figure 2). Both instruments provide the necessary <br />level of accuracy and the total station is typically only <br />used in the minimally impacted streams because the <br />canopy cover within these streams prevents the use <br />of the RTK system. <br />Measurements of instream habitat characteristics <br />are obtained in the spring (April -May), summer <br />(July - August), and fall (September- November) of each <br />year (Figure 2). One measurement of wet width and <br />four measurements of water velocity, depth, sub- <br />strate, and instream habitat feature are obtained <br />along each transect. Wet width is determined by mea- <br />suring the distance between the left and right water's <br />edge (Figure 2) with a tape measure. Water velocity <br />is measured with an electromagnetic velocity meter. <br />Water depths are measured with a stadia rod. The <br />dominant substrate type and instream habitat fea- <br />tures are visually identified at each point. This <br />method enables the percent of substrate and instream <br />habitat features to be calculated based on the number <br />of times each substrate and instream habitat feature <br />occurred in a site relative to the total number of <br />points sampled. In contrast, qualitative estimates of <br />JAWRA <br />874 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION <br />
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