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Waste stabilisation ponds (WSPs) are highly enriched environments that may emit large quantities of greenhouse gases (GHG), including CO 2 , CH 4 and N 2 O. However, few studies provide detailed reports on these emissions. In the present study, we investigated GHG emissions from WSPs in Western Australia and Quebec, Canada, and compared emissions to WSPs from other climatic regions and to other types of aquatic ecosystems. Surface water GHG concentrations were related to phytoplankton biomass and nutrients. The CO 2 was either emitted or absorbed by WSPs, largely as a function of phytoplankton dynamics and strong stratification in these shallow systems, whereas efflux of CH 4 and N 2 O to the atmosphere was always observed albeit with highly variable emission rates, dependent on treatment phase and time of the day. The total global warming potential index (GWP index, calculated as CO 2 equivalent) of emitted GHG from WSPs in Western Australia averaged 12.8 mmol m −2 d −1 (median), with CO 2 , CH 4 and N 2 O respectively contributing 0%, 96.7% and 3.3% of the total emissions, while in Quebec WSPs this index was 194 mmol m −2 d −1 , with a relative contribution of 93.8, 3.0 and 3.2% respectively. The CO 2 fluxes from WSPs were of the same order of magnitude as those reported in hydroelectric reservoirs and constructed wetlands in tropical climates, whereas CH 4 fluxes were considerably higher compared to other aquatic ecosystems. N 2 O fluxes were in the same range of values reported for WSPs in subtropical climate. [ABSTRACT FROM AUTHOR]

Abstract: Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L−1), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L−1, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m−2 d−1 in the hypoxic western LSLE to 100 μmol m−2 d−1 in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m−2 d−1, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 106 t N, yielding an almost balanced N budget for the SL marine system. [ABSTRACT FROM AUTHOR]