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.