Nitrous oxide in fresh waters of the Great Lakes Basin 1

Evidence presented favors the hypothesis that little N 2 O is transported by rivers into or out of the Great Lakes; rather it is generated or consumed in situ. However transport of nutrients into and out of the lakes probably influences production and consumption within the lakes, i.e. NO 3 − and organic matter in runoff from land and effluent from cities. Exchange values of N 2 O between the atmosphere and the lakes calculated from two models are related to the degree of N 2 O saturation of surface water. The range of fluxes is about 10 times larger than estimates made for the open ocean, i.e. ± 4 pg·cm −2 ·s −1 . Groundwater under a large dairy farm was rich in N 2 O, but once the N 2 O seeped into a headwaters tributary it was lost to the atmosphere.