Upper Mississippi River Restoration Program Long Term Resource Monitoring

Time Lag Investigation of Physical Conditions and Submersed Macrophyte Prevalence in Upper Navigation Pool 4, Upper Mississippi River

Lund, E. 2019. Time Lag Investigation of Physical Conditions and Submersed Macrophyte Prevalence in Upper Navigation Pool 4, Upper Mississippi River. A completion report submitted to the U.S. Army Corps of Engineers' Upper Mississippi River Restoration Program from the U.S. Geological Survey. LTRM- 2015A8. 24 pgs.

Abstract

The Long Term Resource Monitoring element (LTRM) of the Upper Mississippi River Restoration program (UMRR) has conducted aquatic vegetation and water quality surveys in several navigation pools since the mid-1990s. Over a 20-year period (1998-2017), the off-channel (i.e. backwater) areas in upper Pool 4 remained chronically turbid and supported a limited submersed macrophyte community with high between-year variability in the proportion of sites where submersed plants were observed. Water surface elevation and discharge rates also fluctuated substantially within- and between-years in the upper pool. Pearson correlation analysis indicated that between-year change in the proportion of sites where submersed macrophytes are observed is correlated to the number of high summer discharge days one year prior (r = -0.48); the number of low summer discharge days during the current year (r =0.46) and one year prior (r = 0.62); minimum discharge (r = 0.52) and the duration that depth at vegetation sample sites was within the estimated photic zone (i.e. a metric that reflects a combination of water clarity and water surface elevation) during the current summer (r = 0.63). Conditions more than one year prior and during the other seasons (winter, spring, fall) exhibited weaker correlations to subsequent fluctuations in the prevalence of submersed macrophytes.

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