Deepwater dissolved oxygen shows little ecological memory between lake phenological seasons

Abstract:Depletion of deepwater dissolved oxygen (DO) in lakes has become increasingly prevalent and severe due to many external stressors, potentially threatening human-derived ecosystem services ranging from drinking water quality to fisheries. Using year-round, high-frequency DO data from 12 dimictic lakes, we compared three measures of deepwater DO depletion during winter and summer: DO depletion rate, DO minimum, and hypoxia duration. Hypoxia (DO < 3 mg L-1) occurred in over half of the lakes and persisted an average of 83% longer in summer than in winter. While we found no difference in DO depletion rates between winter versus summer, these rates were significantly related to lake morphology in winter but trophic state in summer. In assessing cross-seasonal linkages, we found limited evidence for significant legacy effects in deepwater DO availability. Only fall mixing efficacy significantly responded to the previous summer’s minimum DO saturation, but always reached moderate to high DO replenishment levels (> 65%) regardless of the previous summer’s DO depletion severity. This lack of ecological memory in deepwater DO depletion across seasons suggests that deepwater DO largely resets during spring and fall mixing periods in most years in these dimictic lakes. Understanding the patterns and drivers in deepwater DO depletion in both winter and summer is a key step forward for predicting future chemical and biological consequences of seasonal DO depletion and managing lake ecosystem health, as well as the effects that climate change may have on these patterns.Key Words: oxygen depletionlegacy effectslake mixingclimate changeoxygen minimum zoneswater qualityecological memoryDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. Acknowledgements:This work was conceived at the Global Lake Ecological Observatory Network (GLEON), and benefited from continued participation and travel support from GLEON. R.M.P., C.E.W., and E.P.O. were supported by US National Science Foundation grants DEB 1754265, DEB 1754276, and DEB 1950170 and Ohio Eminent Scholar of Ecosystem Ecology funds. K.C.R. was funded by NSF grants 1638704, 1754265, and 1761805. S.A.B., H.P.G., and J.C.N. were supported by the German Federal Ministry of Education and Research (BMBF) within the Collaborative Project “Bridging in Biodiversity Science - BIBS” (01LC1501G) and H.P.G.by the Leibniz Foundation. R.-M. C. was supported by the Sentinel North Research Chair in Aquatic Geochemistry (Sentinel North, a Canada First Research Excellence Fund Program). H.W. received support from the Norwegian Research Council (Lakes in Transition 244558; Climer 243644) and the Nordic Centre of Excellence Biowater (Nordforsk, 82263). The long-term monitoring program of Langtjern is supported by the Norwegian Environment Agency. I.G. and M.T. were funded by the Spanish Ministry of Economy and Competitiveness through the projects PaleoNAO (CGL2010-15767/BTE) and PaleoModes (CGL2016-75281-C2-1-R). Multiprobes in Cimera were provided by Centre for Hydrographic Studies (CEDEX). G.K. was supported by the German Research Foundation (DFG): Projects KI 853-11/1-2, KI 853-13/1; EU Program on International Network for Terrestrial Research and Monitoring in the Arctic (INTERACT): Projects “ConCur”, “LACUNA”, and “IceWave”. A.L. was supported by the Estonian Research Council Grants PSG32 and PRG709. J.R. and H.Y. were supported by the Inter-American Institute for Global Change Research (CRN3038) and the US National Science Foundation Grants GEO-1128040 and EF-1137327. M.S. was partially funded by the Helen V. Froehlich Foundation. Additionally, we thank the Lacawac Sanctuary & Biological Field Station for access to Lake Lacawac and use of research facilities; the Waynewood Lake Association for access to Lake Waynewood; A. Penske for maintaining the measuring devices attached to the IGB-LakeLab in Lake Stechlin, G. Mohr for ice cover observations, and the Lake Stechlin technician team of IGB Department 3 for further data; the Servicio Territorial de Medio Ambiente de Ávila of Regional Government of Castilla y León that granted the permissions for research in Cimera Lake (Regional Park of Sierra de Gredos) and provided the invaluable help of a helicopter flight to transport the heaviest field equipment; the personnel of the Kilpisjärvi Biological Station, whose support made available the long-term lake monitoring in the high Arctic; the staff at the Darrin Fresh Water Institute for assistance in sensor deployment and retrieval; and C. McConnell, T. Field, and R. Ingram for field assistance for Harp Lake.Declaration of Interest Statement:The authors report there are no competing interests to declare.Author Contribution StatementR.M.P., C.E.W., and E.P.O. conceived the manuscript. R.M.P. wrote the manuscript with substantial contributions and feedback from C.E.W., E.P.O., and K.C.R. R.M.P, C.E.W., E.P.O., K.C.R., S.A.B., R.-M.C., H.A.D., I.G., H.-P.F.G., G.B.K., A.L., J.C.N., J.A.R., M.W.S., M.T., and H.Y. contributed to the data acquisition, analysis, and drafting of the manuscript. All authors approved the final submitted manuscript.Data Availability Statement:The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo.7916515 under Creative Commons Attribution 4.0 International (Pilla et al. 2023).