Assessment Comments
Monitoring by LTRMP staff, Bellevue station.
Basis for Assessment
[NOTE: For the 2002 report, Shrickers Slough was separated from the assessment for Rock Creek. In previous reports, both waterbodies had been assessed as one assessment unit. Thus, the following assessments for Shrickers Slough for the 1996, 1998, and 2000 reports have been developed from the respective assessments originally developed for the combined "Rock Creek/Shrickers Slough" waterbody. In order to make these assessments specific to Shrickers Slough, several deletions and additions were necessary; however, no substantive changes were made. For the unedited original assessments developed for the combined Rock Creek/Shrickers Slough waterbody, see assessment information for lower Rock Creek, segment IA 01-MAQ-0010-1).]
SUMMARY: The aquatic life uses were assessed as "partially supported." EXPLANATION: The assessment of support of the aquatic life uses remains based on occurrence of algae blooms and winterkills related to high levels on nitrogen compounds (nitrate and ammonia) delivered to the Shrickers Slough by Rock Creek. Staff of the Upper Mississippi River "Long Term Resource Monitoring Program" at Bellevue, Iowa, continue to monitor the water quality of Rock Creek (two sites) and Shrickers Slough (one site) every two weeks. Results of this monitoring show general poor water quality at the lower Rock Creek (Highway 67) station (see assessment for Rock Creek, segment IA 01-MAQ-0010-1). Several attempts at correcting the problem of high levels of ammonia and other nitrogen compounds in Rock Creek and Shrickers Slough were made during the 1998-1999 biennial period. Beginning in 1999, hybrid poplar trees were planted along the unnamed tributary of Rock Creek (aka Ammonia Creek) that flows through the PCS property and that delivers high levels of ammonia to Rock Creek. These trees have dense root masses that penetrate deep into the soil profile; research has demonstrated the ability of these trees to remove nitrogen compounds from contaminated groundwater (see Gatliff 1994). A containment trench with a sump system was constructed by PCS Nitrogen to collect and remove the top ten feet of ammonia-rich groundwater feeding Ammonia Creek; this system began operation in April 1999. PCS also plans to convert approximately 120 acres of cropland to native prairie plantings. Through the cooperative efforts of DNR, a private landowner, and PCS Nitrogen, an 80-acre wetland was created in early 2000 through the impoundment of Rock Creek downstream from PCS. This wetland is expected to help process and assimilate high levels of nitrogen compounds leaving the PCS facility and improve the water quality in lower Rock Creek and in Shrickers Slough. In September 1999, PCS Nitrogen announced the closure of its Clinton plant. After closure, the plant was to be dismantled; the site will no longer be used for the storage or production of products produced by PCS Nitrogen. PCS Nitrogen agreed to continue it's activities to recover and remove/treat nitrogen compounds (for example, planting of hybrid poplar trees, conversion of cropland to prairie, and construction/operation of a groundwater recovery system); PCS will continue to monitor groundwater at the PCS site. PCS also assisted with the development of the 80-acre wetland constructed on lower Rock Creek.
