Full ecoregional plan - Conservation Gateway

Size 2 Watershed: Landscape Context Non-Relative RankingA “Non-System Relative” analysis was run to investigate the range of Landscape Context of size2 watersheds in the entire analysis area (Figure 10). By measuring the watersheds on a single“ruler” or scale across the entire analysis area, it provided a template to compare size 2watershed examples across different system types. A simplified set of condition variables wereused to explore the range in quality within the analysis area. Percent developed land cover,percent agriculture land cover, total road density per watershed area were chosen because thesevariables were considered to summarize distinct and important classes of impacts to aquaticsystems.The following class breaks were used to integrate the input variables into an overall LandscapeContext rank of watersheds into classes 1-5 (Table 9). These categories were developed inconsultation with Mark Anderson after review of the population distribution for each variable.The lowest class of the percent developed category, greater than 15%, is well supported in theliterature as a threshold beyond that streams show clear signs of degradation and fair to poorIndices of Biotic Integrity (IBIs) (Jones and Clark 1987, Steedman 1988, Couch et al. 1997,Dreher 1997, Wang et al. 1997, Yoder et al. 1999, Gordon and Majumder 2000, Schueler 1994).This category was choosen to stand alone as a “maximum threshold category”/ unique rank 5category due to its known biological relevance. The remaining percent developed distributionwas broken into 4 categories. A narrow very good (1) class to represent the best 10% ofwatersheds, followed by a rank 2 and 3 class that each represented 25% of the watersheds, and acategory 4 that represented 20% of the watersheds. For the percent agriculture and road densityvariables, no thresholds have been uniformly identified in the literature (Fitzhugh 2000). Forthese variables, 4 categories were used due to the imprecision of identifying a biologicallysignificant category 5 or maximum threshold category. The following class breaks were made byexamining the range and distribution of data. A narrow best (1) category was used to representthe top 10% of watersheds, followed by another rather narrow rank 2 category representing about20% of the watersheds, a rank 3 category representing 35% of the watersheds, and a category 4representing 35-40% of the watersheds (similar to combining the categories 4 and 5 from thepercent developed rank that also held 40% of the watersheds together). The overall LandscapeContext watershed rank was determined by worst individual category score.Table 9: Size 2 Watershed Landscape Context Ranking CriteriaLandscape Context RankingsRank %Developed % Agriculture Road Density (mi rd/sq.mi.watershed)1 15%REVISED 6/2003AQUA-RESULTS-28