Multiyear destratification study of an urban, temperate climate, eutrophic lake

Author: Hanson David  

Publisher: Taylor & Francis Ltd

ISSN: 1040-2381

Source: Lake and Reservoir Management, Vol.28, Iss.2, 2012-06, pp. : 107-119

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Abstract

Hanson D, Austin D. 2012. Multiyear destratification study of an urban, temperate climate, eutrophic lake. Lake Reserv Manage. 28: 107-119. An aeration system for destratification has been in operation since 1973 at Sweeney Lake, an urban, eutrophic lake near Minneapolis, Minnesota, USA. Water quality data are available for 19 of the 39 years, 1972–2010. Growing season (Apr–Oct) aeration was turned off in 2007–2008 to evaluate the effect of destratification on water quality. Aeration never achieved the Lorenzen and Fast (LF) complete destratification airflow criterion of 9.2 m3/min/km2. When aeration was at 51% LF, hypoxia (DO < 2.0="" mg/l)="" occurred="" june–august="" at="" the="" lake="" bottom.="" when="" airflow="" increased="" to="" 65%="" lf,="" bottom="" water="" hypoxia="" was="" restricted="" to="" 4="" weeks="" in="" late="" july–august.="" there="" were="" no="" systematically="" significant="" differences="">p > 0.05) in median Secchi disk depths, chlorophyll a concentrations, or surface total phosphorus (TP) concentrations between destratified and stratified lake conditions, but interannual variability linked to other influences, including partial stratification and stormwater inputs, limits statistical power. The median April–October lake TP mass of 67 kg in 2007–2008 (stratified conditions) was significantly higher (p < 0.0001)="" than="" the="" 44="" kg="" median="" mass="" in1998–2005="" and="" 2009="" (destratified="" conditions).="" destratification="" can="" suppress="" internal="" phosphorus="" loading="" when="" properly="" applied.="">