Dissolved oxygen dynamics in a shallow eutrophic lake: Quantify critical eco-environmental effects

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Dissolved oxygen (DO) serves as a fundamental requirement for aquatic organisms and a key indicator for assessing and managing ecological health of lake ecosystems. Despite substantial research attention on lacustrine DO evolution, systematic investigations focusing on shallow eutrophic lakes remain lacking. This study employs monitoring datasets of water quality and meteorological parameters from a shallow eutrophic lacustrine system, to conduct multidimensional analysis of DO variation characteristics and driving mechanisms. Analytical results demonstrate a 0.034 mg·L −1 increase in DO concentration within the whole lake during the 2012–2021 period. Thermal variation in lake alone proves inadequate to fully elucidate this trend, particularly under lower thermal regimes. Spring and autumn water depth fluctuations significantly modulate DO levels, while reduced Secchi depth correlates with DO decline across multiple lake sectors. Under climate change scenarios, the enhanced oxygen depletion in lacustrine systems induced by prolonged sunshine duration cannot be counterbalanced by the concomitant stimulation of photosynthetic efficiency within the photic zone, while precipitation and wind speed demonstrate dual-phase effects. Critical thresholds occur at monthly precipitation exceeding 20 mm and sustained wind speeds surpassing 3 m·s −1 , where DO transitions from net gain to loss—changes potentially driven by water column mixing dynamics and algal metabolism. Among aquatic environmental, water temperature exerts predominant control over DO variability, with its positive effects under lower temperatures being particularly pronounced. Inversely, chlorophyll-a concentrations exceeding 20 μg·L −1 are prerequisite for net DO increases, whereas subthreshold levels correlate with the decrease of oxygen. Within lacustrine nutrient dynamics, the regulatory influence of total phosphorus on DO is significantly weaker compared to that exerted by total nitrogen, but hypereutrophic total phosphorus concentrations (>0.4 mg·L −1 ) markedly enhance deoxygenation through nutrient-driven eutrophication cascades. Accordingly, targeted phosphorus control emerges as a critical strategy for mitigating hypoxic events in shallow eutrophic lakes.

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