Seston flux in a tropical saline lake

Abstract

The dynamies of seston fluxes has been assoeiated with phytoplankton blooms in marine and freshwater systems (VINERMozziNI et al. 2003). The fate of these blooms is erucial to the understanding of earbon flow, nutrient eycling and eeosystem funetions. As a eonsequenee, it is important to unravel the meehanisms of particle sedimentation as well as the quantity and quality of settling particles. Eeosystem proeesses are important determinants o f the biogeoehemistry o f the oeean that ean be profoundly affeeted by ehanges in elimate (LE QuÉRÉ et al. 2005). The different routes that the particles take in the aquatie eeosystem (transfer in food-web, respiration, sedimentation, and burial) will define the availability of earbon to organisms and the time of return of earbon moleeules in the earbon eycle. The transfer in the food web and its proeesses are important eontrols of aquatie biogenie earbon flux and water-atmosphere earbon dioxide exehange (LEGENDRE 1999). Rapid inereases in phytoplankton biomass have a high potential for exporting partieulate organie matter from the euphotie layer, providing important information for the study of global fluxes of earbon in the inland water systems; however, if a larger fraetion of assimilated earbon is respired at low than at high latitudes, a smaller proportion o f produetion ean be exported in tropieal regions. The explieit inelusion of eeosystem proeesses in models will permit eeologieal ehanges to be taken into aeeount, allow us to understand how the uptake o f C02 in inland water systems is likely to ehange in the future, and improve our understanding o f the loeal and regional climate systems. The main losses forbloom biomasses are grazing, deeomposition in the mixing layer, and sedimentation to the bottom of lakes (ZoHARY et al. 1998). The dominant size fraetion o f phytoplankton defines the principal transfer path ofbiogenie earbon in the eeosystem. When the small fraetion (<2 f..Lm) dominates, the main route will be nutrient reeycling through the mierobialloop in the euphotie zone. In eontrast, when the large fraetion (>2 f..Lm) dominates, new produetion will either be exported to the bottom o f the lake or eonsumed by herbivores and eventually exported as feeal pellets (LEGENDRE 1999). The aim ofthis study was to evaluate the vertieal and temporai variation ofseston fluxes inLake Alchiehiea to betterunderstand the earbon dynamies of a tropieal, oligotrophie lake where the large size fraetion ofphytoplankton dominates.