RESEARCH ARTICLE ‘‘Dead Zone’’ dynamics in Lake Erie: the importance of weather and sampling intensity for calculated hypolimnetic oxygen depletion rates Joseph D. Conroy • Leon Boegman • Hongyan Zhang • William J. Edwards • David A. Culver Received: 20 October 2009 / Accepted: 16 November 2010 / Published online: 7 December 2010 Ó Springer Basel AG 2010 Abstract Calculated hypolimnetic oxygen depletion (HOD) rates depend not only on environmental factors but also logistical ones. In particular, lack of understanding of the effects of weather in addition to how sampling effort determines calculated HOD rates complicates ecological understanding and environmental management of lake ecosystems. To better determine the roles of weather and sampling effort, we combined (1) weekly measurements of temperature and dissolved oxygen (DO) concentrations from seven stations in the Sandusky subbasin of Lake Erie’s central basin during 2005, (2) contemporaneous measures of storm activity and tributary discharge, and (3) a two-dimensional coupled hydrodynamic, chemical, and biological model of Lake Erie to investigate (1) how increased storm activity and tributary discharge affected short- (daily) and long-term (seasonal) dynamics of hypo- limnetic hypoxia, and (2) how spatial (number of sites sampled) and temporal (sampling frequency) sampling effort affected calculated HOD rates. Our model closely replicated field-observed DO dynamics. When comparing baseline modeled dynamics to those in a second simulation with twice the number of days with high winds, however, we found that with more storm activity (1) periods of entrainment became more frequent, (2) the hypolimnion was warmer, (3) thermal stratification occurred 1 month later, whereas autumnal turnover occurred at least 1 week earlier shortening the duration of stratification by 1–2 months, and (4) HOD rates increased 12%. Further, spatial and temporal sampling intensity also affected calculated HOD rates. Consequently, adequately quantifying actual HOD rates requires sufficient sampling effort and the particular role of weather should be assessed with rigorous field and simulation studies, especially if HOD rates are used to indicate management success. Keywords Storm-induced mixing  Hypoxia  Anoxia  CE-QUAL-W2 Introduction Recurring seasonal zones of hypolimnetic hypoxia (dis- solved oxygen concentrations, DO \ 4 mg O 2 L -1 ) and anoxia (DO \ 1 mg L -1 ), so called ‘‘Dead Zones,’’ con- tinue as a current, relevant problem in many aquatic J. D. Conroy (&) Aquatic Ecology Laboratory, Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 1314 Kinnear Road, Columbus, OH 43212, USA e-mail: joseph.conroy@dnr.state.oh.us L. Boegman Department of Civil Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada H. Zhang Cooperative Institute for Limnology and Ecosystems Research, University of Michigan, 4840 South State Road, Ann Arbor, MI 48108, USA W. J. Edwards Department of Biology, Niagara University, NY 14109 Lewiston, USA D. A. Culver Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, 1315 Kinnear Road, Columbus, OH 43212, USA Present Address: J. D. Conroy Inland Fisheries Research Unit, Division of Wildlife, Ohio Department of Natural Resources, 10517 Canal Road, Hebron, OH 43025, USA Aquat Sci (2011) 73:289–304 DOI 10.1007/s00027-010-0176-1 Aquatic Sciences 123