Influence of sediment characteristics and oxygen demand on winter hypoxia in backwater lakes of the Upper Mississippi River

Abstract

Sediment oxygen demand (SOD), gross primary production, and ecosystem respiration are ecological processes affecting availability of dissolved oxygen (DO), a key feature of overwintering habitat for riverine species. Sediment oxygen demand contributes to oxygen depletion from the water column during ice-covered periods, potentially leading to hypoxic conditions in backwater systems, decreasing the amount of suitable overwintering habitat for riverine fish species in the Upper Mississippi River System (UMRS). Understanding the effect of SOD on habitat during the winter season is critical for management of the UMRS. Winter SOD rates are not well studied in the UMRS and can be costly to sample directly. This study focused on determining winter SOD rates across different winter habitat types within 12 backwater lakes in 3 pools of the UMRS. Additionally, sediment nutrient and physical characteristics were analyzed to identify sediment characteristics as potential drivers of winter SOD rates. Intact sediment cores were collected from backwater lakes of Pool 4, Pool 8, and Pool 13 of the UMRS in January and February 2022 and incubated in the laboratory to determine SOD rates. Measured SOD rates ranged from 0.04 – 0.44 g O2/(m2d) at in situ temperatures, or 0.14 – 1.46 g O2/(m2d) when corrected to 20°C. Results of this study did not show statistically significant relationships between SOD and sediment characteristics, however, DO concentrations were generally lower near the sediment-water interface than near the surface indicating that SOD was influencing winter DO concentrations. This study lends insights into SOD rates and sediment characteristics of backwater lakes of the UMRS that will aid managers in choosing suitable Habitat Restoration and Enhancement Project locations to increase suitable overwintering habitat.