Unbalanced particle flux budgets in Crater Lake, Oregon : Implications for edge effects and sediment focusing in lakes

In a study of nutrient cycles and particle fluxes in the 590 m deep Crater lake, Oregon, the nitrate budget was determined by evaluating allochthonous fluxes and estimating settling particulate and sediment accumulation fluxes from an 8-year record of sediment trap data. Modelled relationships between deep-water residence time and the particulate nitrogen settling flux indicated that upward mixing of deep-water nitrate accounted for more than 85 per cent of the total new nitrogen input to the upper lake (less than 200 m deep). Annual nitrogen fluxes to the euphotic zone were 5-9 times greater than the sum of burial and seepage removals and the estimated total new nitrogen would support only 3-9 per cent of measured primary productivity (approximately 360 mg carbon per m2.d) in the euphotic zone. These results demonstrated the efficiency of nitrogen recycling in both the euphotic zone and the deep lake. Major discrepancies in the estimated internal nitrogen balance together with a factor of 30 for the mismatch between trap and burial fluxes of aluminium were explained by a proposed edge effect with enhanced productivity at lake margins not collected by sediment traps and subsequent focusing of particulate matter into the deep lake basins. There are 47 references.