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Analysis of Spatial and Temporal Dynamics of Submersed Aquatic Vegetation and Metaphyton Communities of Pool 4, Upper Mississippi River (1998–2011)

Moore, M.  2015.  Analysis of Spatial and Temporal Dynamics of Submersed Aquatic Vegetation and Metaphyton Communities of Pool 4, Upper Mississippi River (1998–2011).  A completion report submitted to the U.S. Army Corps of Engineers’ Upper Mississippi River Restoration Program from the U.S. Geological Survey, Completion Report LTRM–2012A6, 33 p

Abstract

Contrasting aquatic vegetation communities and environmental conditions exist between the upper and lower reaches of Pool 4, Upper Mississippi River (UMR) due to the presence of Lake Pepin and its role in reducing downstream transport of sediment. This study analyzed the community structure of native submersed aquatic vegetation (SAV) and metaphyton (i.e. duckweed and filamentous algae) in Navigation Pool 4 of the UMR, and tested for differences among reaches (Upper Pool 4 [UP4] and Lower Pool 4 [LP4]), strata (backwater, main and side channels), and time period (UP4 early: 1998‐2006, UP4 late: 2007‐2011, LP4 early: 1998‐2004, LP4 late: 2005‐2011). The assemblages of native SAV communities were significantly different among reaches, strata and time periods. The SAV species of greatest presence in UP4 was sago pondweed (Stuckenia pectinata) followed by coontail (Ceratophyllum demersum), but their frequencies were very low. Nearly all species increased in abundance from early to late time period pool‐wide. In contrast, consistently higher abundances and frequencies of five species distinguished the assemblages found in LP4. The metaphyton communities were significantly different among reaches and time periods, but not all strata comparisons. The metaphyton assemblages increased significantly from early to late time period in both reaches, but were exceedingly sparse in UP4 when present and consisted primarily of filamentous algae. In contrast, metaphyton in LP4 was more prevalent and more evenly divided between filamentous algae and duckweeds. Among the common environmental measures of water quality and hydrology, only spring and summer turbidities were statistically correlated to native SAV and metaphyton communities at the pool reach scale but not time periods. However, within individual reaches, no environmental variables were statistically correlated with the SAV or metaphyton changes. Still, this study demonstrated a community shift over time in which UP4 native SAV increased in overall species richness and plant abundance, resulting in increased similarity to LP4 assemblages during the early time period, and thus reducing the sharp contrast between reaches. The recovery of SAV in UP4 co‐occurred during a period when environmental changes were detected, such as decreases in summer turbidity and summer phosphorus. Aquatic plant community research, such as this study, can benefit the science behind restoration ecology efforts in large floodplain rivers through better understanding of the submersed macrophyte and metaphyton communities and their responses to environmental factors. Management actions aimed at reducing tributary inputs of sediment and nutrients will benefit the aquatic macrophyte communities and the fauna that depend upon them.

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