Fluxes of particulates and nutrients during hydrologically defined seasonal periods in an ice-affected great Arctic river, the Mackenzie

摘要

Large circumpolar rivers influence the biogeochemistry of coastal shelf ecosystems and Arctic Ocean circulation. From 2007 to 2010, Mackenzie River nutrients were measured immediately upstream of the Mackenzie Delta. Total suspended sediment (TSS) and the dissolved and particulate fractions of carbon, nitrogen, and phosphorus were measured throughout the water year, stratified by hydrologically defined seasonal periods. Sampling was most frequent during the ice breakup and freshet periods to capture changes in sediment and nutrient concentrations that occurred with rapidly changing discharge. Our 4 year sampling coverage yielded constituent-specific concentration-discharge relationships that differed among seasonal hydrological periods for 6 of 12 constituents. Results revealed that having data from the rising-water freshet, when ice effects drive much higher water levels for a given discharge than during open water, had a surprisingly modest effect on annual flux calculations for most constituents. The rising freshet, however, was dominated by high relative levels of C-rich dissolved organic matter, P-rich particles, and N-rich inorganic nutrients. Comparisons with fluxes based on volume-weighted means of sample concentrations revealed that most, though not all, river fluxes were strongly driven by short-term concentration-discharge dynamics rather than by total annual discharge. Comparisons with fluxes derived for the Mackenzie discharge record, where results from other years are available, suggest that concentration-discharge relations may not be robust beyond the observation period in this system. Constituent fluxes herein differ from previously published fluxes for the Mackenzie (e.g., lower TSS, higher dissolved organic carbon), likely reflecting more frequent measurements, more representative characterization of differing hydrological periods, and possible changes in concentration-discharge relations during the longer-term Mackenzie record.