Precipitation has increased discharge in the Maumee River, a major tributary to western Lake Erie (WLE), since the mid-1990s. Given that rivers such as the Maumee River deliver dissolved organic matter (DOM) to WLE, export of DOM may have increased. To address the effect of increasing riverine discharge and export of DOM to WLE, seasonal and annual patterns in DOM (measured as DOC), CDOM, and fluorescent DOM (FDOM) in WLE were assessed from 2014 to 2024. DOC concentration significantly increased from 2015 to 2022 in WLE (p < 0.02). There was no significant increase or decrease in CDOM concentration over time. The proportion of microbially- and terrestrially-derived DOM relative to terrestrially-derived DOM significantly decreased from 2014 to 2024 in WLE (p < 0.05). No significant increase or decrease in aminoacid- like FDOM was observed over the past decade in WLE. DOC concentration was significantly, positively correlated with the proportion of Maumee River discharge relative to Detroit River discharge (p < 0.05). The proportion of microbially- and terrestrially-derived DOM to terrestrially-derived DOM was significantly, inversely correlated with the proportion of Maumee River discharge relative to Detroit River discharge (p < 0.05). If Maumee River discharge continues to result in greater export of DOM to WLE, further shifts in DOM concentration and composition may lead to the browning of WLE.
Emma Johnson (Wed,) studied this question.