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Fiscal Year 1999 Findings for the Long Term Resource Monitoring Program

Abstract

This report summarizes monitoring activities of the Long Term Resource Monitoring Program (LTRMP) during 1999 and highlights selected results and accomplishments pertaining to hydrology, water quality, fish, macroinvertebrates, and vegetation.

Mean discharge in 1999 was above average in the Upper Mississippi and Illinois Rivers, but spring flooding was relatively minor. Total nitrogen concentration has declined in the upper reaches of the LTRMP study area (Pools 4 and 8) from highs of about 4 mg/L in 1993 to present levels of about 1.5 mg/L. Mass balance budgets indicate that little nitrogen is lost (denitrified) as water moves through the LTRMP study pools on the Mississippi River. La Grange Pool on the Illinois River also shows little denitrification, but does trap sediments.

Submersed aquatic vegetation was sampled by stratified random sampling in 1999 for the second year. The maximum depth for locating sample sites was changed from 3 to 2.5 m in 1999 because in 1998 little vegetation was found at depths >2.5 m. Vegetation patterns during 1999 were similar to 1998 and no pool-scale changes were detected. Vegetation abundance in 1998 was at or near the highest abundance recorded since 1991. The presence of vegetation was negatively correlated with water depth, current velocity, and wind fetch.

Densities of macroinvertebrates varied among pools in 1999 and showed no systemwide trends. Zebra mussel (Dreissena polymorpha) densities were highest in Pools 13 and 8 with Pool 8 showing a substantial increase from earlier years.

Fish collections in 1999 yielded 66 to 76 species per study area, including 14 state-listed threatened or endangered species. In addition, a new invasive species—rudd (Scardinius erythrophthalmus)—was collected in Pool 13. The abundance of bluegills (Lepomis macrochirus) >150 mm in total length has increased recently in all pools except Pool 26.

Key words: Aquatic vegetation, bluegill, discharge, fish, Illinois River, invertebrates, Mississippi River, nitrogen, water quality

March 4, 2002
Page Last Modified: April 17, 2018