UNBALANCED PARTICLE-FLUX BUDGETS IN CRATER LAKE, OREGON - IMPLICATIONS FOR EDGE EFFECTS AND SEDIMENT FOCUSING IN LAKES

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 euph otic zone of Crater Lake. Because measured primary productivity (360 m g C m(-2) d(-1)) is 10-30 times higher than a level supported solely b y the input of new nitrogen into the euphotic zone, nitrogen must be r ecycled in the euphotic zone many times before it is transferred by pa rticles to The deep lake. Nitrogen recycling in the deep lake is also very efficient. Sediment trap measurements of particulate nitrogen flu xes reveal a major imbalance in our estimates of the lake's internal n itrogen 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 reference is maintained by the near-bottom transp ort of lithogenic particles from the lake margins to the deep basins o f the lake. These comparisons of nutrient and refractory element fluxe s reflect two important lake processes-enhanced productivity at the la ke margin that may be due to greater availability of macro- and micron utrients at the lake edges and focusing of particulate material into t he deep lake basins.