Limnological characteristics of Lake of the Ozarks (Missouri, USA): long-term assessment following formation of a reservoir series

Abstract

Jones JR, Obrecht DV, Thorpe AP. 2022. Limnological characteristics of Lake of the Ozarks (Missouri, USA): long-term assessment following formation of a reservoir series. Lake Reserv Manage. 38:288–303.

Impoundment of Truman Lake in 1980 on the Osage River, above Lake of the Ozarks (LOTO), created a reservoir series. This analysis details the changes and processes over the ensuing 35 yr (1980–2014) in this large impoundment dominated by a longitudinal gradient along the mainstem. Temporal variation was determined by hydrology; seasonal mean total phosphorus (TP) ranged between 12 and 58 µg/L at the near-dam location, and hydrologic flushing during summer explained 82% of this variation. After dam closure, mineral suspended solids, attributed to channel scouring of erodible materials in the tailwater reach, declined over time, with a 50% reduction near the dam. Concurrently, organic suspended solids increased by 1 to 4%/yr in mid-reach locations, which indicates greater autotrophic production. Compared with other Missouri reservoirs, algal chlorophyll (Chl) averaged 1.6 times the value predicted from TP. Ratios of Chl:TP have increased over past decades concurrent with an increase in organic suspended solids and expansion of the ultraplankton (<11 µm) fraction of total Chl. Warm and dry conditions are associated with an increase in Chl in the ultra fraction, suggesting climate influence. A comparison with data collected prior to the closure of Truman Dam (1976–1979) provides incontrovertible evidence that light transmission has improved, and both Chl and Chl:TP have increased in LOTO. Formation of a reservoir series resulted in immediate and long-term changes in this major impoundment.

Keywords:

• Algal chlorophyll
• mineral turbidity
• organic suspended solids
• reservoir series
• reservoirs
• seasonal variation
• ultraplankton

Acknowledgments

This extensive dataset was acquired with support from the Missouri Department of Natural Resources, University of Missouri Agricultural Experiment Station and the J. Michael Dunmire Endowment. We thank scores of undergraduate assistants who collected and processed data over the decades. Specific appreciation is extended to Bruce Perkins, Ruth Ann Obrecht, and Carol Pollard. Drs. Ann St. Amand, Tamar Zohary, Vera Istavanovics, and Judit Padisak provided valuable suggestions regarding ultra phytoplankton. We thank Drs. Ruchi Bhattacharya and Patrick Guinan for assistance with the Palmer Drought Severity Index.