Nitrous oxide in fresh waters of the Great Lakes Basin1

Evidence presented favors the hypothesis that little N2O 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. NO3− and organic matter in runoff from land and effluent from cities. Exchange values of N2O between the atmosphere and the lakes calculated from two models are related to the degree of N2O 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 N2O, but once the N2O seeped into a headwaters tributary it was lost to the atmosphere.