19Eutrophication is linked to greenhouse gas emissions from inland waters. Phytoplankton blooms 20 in Lake Erie, one of Earth's largest lakes, have increased with nutrient runoff linked to climate 21 warming, although greenhouse gas emissions from this or other large eutrophic lakes are not well 22 characterized. We measured greenhouse gases around Lake Erie in all four seasons and found 23 that CH 4 and N 2 O emissions have increased 10 times or more with re-eutrophication, especially 24 during and after phytoplankton blooms. Lake Erie is a positive source of CH 4 throughout the 25 entire year and around the entire lake, with the highest emissions in spring and summer near the 26 mouth of the Maumee River. While Lake Erie is an overall N 2 O source, it is an N 2 O sink in 27 winter throughout the lake and in some locations during large phytoplankton blooms. We 28 estimate that Lake Erie emits ~6300 metric tons of CH 4 -C yr -1 (± 19%) and ~600 metric tons 29 N 2 O-N yr -1 (± 37%): almost 500,000 metric tons CO 2 -eq yr -1 total. These results highlight the 30 gravity of eutrophication-related increases in large lake GHG emissions: an overlooked, but 31 potentially major feedback to global climate change. 32 3 40Climate change is implicated in water quality declines, as increased intensity and rates of 41 precipitation increases watershed nutrient and sediment inputs (6). 42 43 Lakes, rivers, and reservoirs play a major role in the global carbon cycle and greenhouse gas 44 emissions budgets (7-11). Inland waters are a major source of CH 4 globally, and anthropogenic 45 construction of reservoirs enhances this flux (12). Eutrophication leads to CH 4 and N 2 O evasion 46 from lakes (13)(14)(10), and eutrophication will increase in lake and coastal ecosystems as 47
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