DOM stratification and characteristics versus thermal stratification – A case study in the Panjiakou Reservoir, China

Panjiakou Reservoir, Hebei province, China Based on our multiple measurements of dissolved organic matter (DOM) and collected published papers, DOM itself stratification has been identified. Then, this stratification is adopted to analyze vertical distribution of DOM and its influencing factors during the thermal stratification period in the Panjiakou Reservoir, a deep and channel type reservoir. It was found that DOM itself was stratified due to thermal stratification and other factors, but its stratification boundaries were not fully consistent with the thermal stratification ones. This strongly indicated that DOM characteristics of different layers should be appropriately and accurately analyzed based on its own stratification rather than the thermal stratification. In the upper layer, DOM characteristics were not only affected by endogenous input, but also affected by an external contribution and photodegradation, resulting in low aromaticity and low molecular weight of DOM. In the middle layer, influenced by runoff, phytoplankton secretion, and microbial activities, DOM quantity first increased and then decreased. Meanwhile, DOM had properties of higher aromaticity, molecular weight, and humification. In the lower layer, endogenous input had the maximum influence on DOM properties, resulting in a decrease in aromaticity and humification of DOM. However, endogenous input produced less DOM because microbial activity and phytoplankton growth were limited by the low temperature and low oxygen environment. [Display omitted] •DOM stratification was inconsistent with the thermal stratification.•Endogenous and exogenous input, and light affected DOM in the upper layer.•Middle layer's DOM was affected by the same as upper layer with weaker light.•Middle layer's DOM quantity first raised then declined, generating a peak.•In the lower layer, endogenous input had the maximum influence in DOM.