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

Abstract

Flux estimates show that upward mixing of the deep‐water nitrate pool accounts for more than 85% of the total new nitrogen input to the euphotic zone of Crater Lake. Because measured primary productivity (360 mg C m−2 d−1) is 10–30 times higher than a level supported solely by the input of new nitrogen into the euphotic zone, nitrogen must be recycled in the euphotic zone many times before it is transferred by particles to the deep lake. Nitrogen recycling in the deep lake is also very efficient. Sediment trap measurements of particulate nitrogen fluxes reveal a major imbalance in our estimates of the lake’s internal nitrogen budget. We propose the imbalance reflects an “edge effect,” whereby enhanced biological production occurs near the lake margin and the shallower portions of the lake. Our measurements also reveal that Al, an element carried by refractory phases, is accumulating in basin sediments at a rate 15–30 times higher than the flux we measure with sediment traps. This difference is maintained by the near‐bottom transport of lithogenic particles from the lake margins to the deep basins of the lake. These comparisons of nutrient and refractory element fluxes reflect two important lake processes— enhanced productivity at the lake margin that may be due to greater availability of macro‐ and micronutrients at the lake edges and focusing of particulate material into the deep lake basins.