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10 BIOLOGICAL REPoRT 19 Table 2. Mainstem and major tributary sampling stations used in the Minnesota River Assessment Project. Site name River kilometer Mainstem Lac Qui Parle Montevideo Sacred Heart Delhi Morton Fairfax New U1m Courtland Judson Mankato St. Peter Henderson Tributaries& Chippewa River Yellow Medicine River Hawk Creek Redwood River Cottonwood River Watonwan River Le Sueur River Blue Earth River Rush River High Island Creek 463 436 383 352 327 283 243 216 193 172 146 lOB 442 393 381 349 232 183 182 180 109 98 & River kilometer given is at the confluence with the Minnesota River. Level I Level I of land use is an examination of the nonpoint source pollution potential (NPSPP) model and the river continuum concept (Vannote et al. 1980). The model was developed by Peterson (1991) using aquatic ecoregions (Omemik 1987) and water quality data (Fandrei et al. 1988). The model is useful as a plAnning tool for identifying minor wa- tersheds that may be significant contributors of nutrients to the mainstem. The NPSPP model classifies minor watersheds within each ecoregion by percent area of land use, water orientation, soil texture and hydrologic groups, and slope parameters. These variables were correlated with 10 water quality parameters to generate a list of potential nonpoint source pollution indicators. The model assigns each mi- nor watershed to 1 of 10 categories (1-10, 11-20, 21-30, ... 91-100). The 1-10 category has the lowest NPSPP, while 91-100 has the highest. Because the model uses an assigned rank, the overall distribution of categories throughout the basin is uniform. However, within a major water- shed (tributary to the mainstem), there is often considerable variation. A weakness of the model is that it does not take into account current land management practices. A minor watershed with high NPSPP may actu- ally have excellent water quality if BMP's have been applied aggressively. Conversely, a minor watershed with lower. NPSPP may have poorer water quality without BMP's. Level II The objective at Level IT is to identify and recommend the most economical and cost-effec- tive BMP's or resource IJ'IAnagement systems that will alleviate water quality problems caused by agricultural practices. The U.S. Soil Conservation Service is evaluating 10 minor watersheds using AGNPS and GLEAMS, as well as several other computer models. Preliminary data on one of the minor water- sheds indicate the use of BMP's on 80% of the watershed will reduce phosphorus loading by at least 50%. Cost analysis and participation by landowners are being investigated. Level III Local Soil and Water Conservation Districts within the basin have been applying a four-step process to 37 minor watersheds throughout the basin to identify land use characteristics. The proc" ess includes walking each of the minor watersheds to obtain field data, interviewing landowners. within the watershed to determine existing land use practices, developing detailed land use maps, and developing a database. Watersheds were selected in a systematic man- ner. The 10 watersheds studied in Level II were also included in Level III. An attempt was made to select additional minor watersheds that repre- sented a cross section of existing conditions within the watershed. Another factor in choosing minor watersheds for study was the ability of the local soil and water conservation districts to cooperate. This methodology provided accurate maps and an opportunity to inform and educate landowners about the project and the problem of nonpoint source pollution. However, the cost is very high (about $3,500 per watershed). Within the group of watersheds selected for study, there was tremendous variability across the measured characteristics (Table 3). We wanted to study more minor watersheds and to