Walnut Creek IA 04-LDM-1069

Assessment Comments

Assessment is based on results of chemical and biological monitoring conducted as part of the Walnut Creek Watershed Resoration project from 1995-1997.

Basis for Assessment

This stream is located on the Walnut Creek Wildlife Refuge in Jasper County near Prairie City.   This primarily agricultural area was designated in 1990 by the U.S.  Congress for restoration and development to presettlement conditions.   This stream was sampled in 1991 by the U.S.  Fish and Wildlife Service and in 1994-1995 as part of the U.S.  EPA-sponsored Tri-State Ecoregion study.   The Walnut Creek Watershed Restoration and Water Quality Monitoring Project, conducted by the DNR Geological Survey Bureau in cooperation with the University of Iowa Hygienic Laboratory, began in April 1995 and is to end in 1998.   The goal of the project is to evaluate water quality changes related to watershed habitat restortation and agricultural management changes as the watershed is restored from row crop agriculture to native prairie by the U.S.  Fish & Wildlife Service.  

This assessment is based on results of the DNR GSB/UHL monitoring from 1995 through 1997.   Monitoring thus far has shown that (1) atrazine is the most frequently detected pesticide, with most levels below the MCL of 3.0 ug/l, (2) levels of nitrate are high but typical for streams in Iowa, with average levels at or above the 10 mg/l MCL [this stream is not designated for Class C (drinking water) uses; thus, the 10 mg/l MCL does not apply when developing Section 305(b) water quality assessments], (3) the macroinvertebrate community has low diversity that compares unfavorably with other streams that have been evaluated in the same ecoregion (47f), and (4) the fish community is dominated by the expected taxa that are tolerant of a wide range of environmental conditions with from 10 to 15 species captured in sampling years 1995, 1996 and 1997.   Based on the above results of DNR-GSB/UHL sampling, & based on results of the August 1992 DNR stream use assessments at three locations that showed aquatic habitats and flow conditions were not capable of supporting the Class B(LR) aquatic life use designation, this stream appears to support the environmentally tolerant types of aquatic life typical of Iowa streams classified only for general uses.   Thus, the general use aquatic life uses of this stream were assessed as "fully supported" for the 1998 Section 305(b) report.