Hydrologic and biogeochemical controls on the spatial and temporal patterns of nitrogen and phosphorus in the Kuparuk River, arctic Alaska

Nitrogen (N) and phosphorus (P) dynamics ill the Kuparuk River in arctic Alaska were characterized in a 3-year study using routine samples near the mouth of the river at the Arctic Ocean, synoptic whole-river surveys, and temporally intense sampling during storms in three headwater basins. The Lower Kuparuk River has low nitrate concentrations (mean [NO(3)(-)-N] = 17 mu g 1-1 +/- 1.6 SE) and dissolved inorganic N (DIN, mean [N] = 31 mu g 1(-1) +/- 1.2 SE) compared with rivers in more temperate environments. Organic forms constituted on average 90% of the N exported to the Arctic Ocean, and high ratios of dissolved organic N (DON) to total dissolved N (TDN) concentrations (mean 0.92) likely result from waterlogged soils formed by reduced infiltration due to permafrost and low hydrologic gradients. Annual export of TDN, DON, and particulate N averaged 52 kg km(-2) 48 kg km(-2) and 4.1 kg km(-2) respectively. During snowmelt, the high volume of runoff typically results in the highest nutrient loads of the year, although high discharge during summer storms can result in substantial nutrient loading over short periods of time. Differences in seasonal flow regime (snowmelt versus rain) and storm-driven variation in discharge appear to be more important for determining nutrient concentrations than is the spatial variation in processes along the transect from headwaters towards the ocean. Both the temporal variation in nitrate: DIN ratios of headwater streams and the spatial variation in nitrate: DIN between larger sub-basins and smaller headwater catchments is likely controlled by shifts in nitrification and soil anoxia. Copyright (C) 2008 John Wiley & Sons, Ltd.