Upper Mississippi River Restoration Program Long Term Resource Monitoring

Experimental and comparative approaches to determine factors supporting or limiting submersed aquatic vegetation in the Illinois River and its backwaters

Sass, Greg G., Thad R. Cook, Kevin S. Irons, Michael A. McClelland, Nerissa N. Michaels, and Timothy M. O’Hara.  2017. Experimental and comparative approaches to determine factors supporting or limiting submersed aquatic vegetation in the Illinois River and its backwaters. A completion report submitted to the U.S. Army Corps of Engineers’ Upper Mississippi River Restoration Program from the U.S. Geological Survey, LTRM-2008APE5.  43 pages.

Abstract

Submersed aquatic vegetation (SAV) once flourished throughout the Illinois River but has been severely limited in distribution since the mid-1950s. Submersed aquatic vegetation is important for ecosystem health because its presence may improve water quality and clarity, as well as provide critical habitat for aquatic organisms. We used a comparative and experimental approach to test for factors supporting and limiting SAV in the Illinois River. Specifically, we tested for correlations among abiotic and biotic factors and SAV presence in six reaches of the Illinois River. We also conducted an experimental exclosure study in a backwater lake of the Illinois River to test for factors limiting SAV establishment and growth in the absence of an herbivory effect. The presence of SAV was generally restricted to the uppermost reach of the Illinois River sampled; the Dresden Reach. From downstream to upstream in the Illinois River, the percentage of sites with SAV present were as follows: Alton Reach (0%); La Grange Reach (9.4%); Peoria Reach (0%); Starved Rock Reach (2.8%); Marseilles Reach (8.1%); and Dresden Reach (82.6%). The presence of SAV was positively correlated with water temperature, conductivity, and Secchi disc transparency. In our exclosure study, seed bank viability and herbivory were limiting factors in the north pool of Lake Chautauqua because no SAV was observed in any exclosures and control plots that had not been augmented with sago pondweed (Stuckenia pectinata) or in any of the control plots. Due to a summer draw down of the backwater lake, water level reduction was also identified as a limiting factor for SAV establishment and growth. Water depth, water temperature, and Secchi disc transparency were positively correlated with sago pondweed stem length in the exclosures, whereas turbidity was negatively correlated with stem length. The results of our study presented here and our exclosure study conducted in the Starved Rock Reach of the Illinois River suggest that light, flooding and water level reduction, seed bank viability, and herbivory may be limiting SAV establishment and growth in most portions of the Illinois River. We feel that a systemic management and restoration approach will be required to ameliorate these limiting factors before SAV can be widely restored in the Illinois River.

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