Postulated responses of phytoplankton and bacteria to predicted increases of inorganic suspended sediments in oligotrophic lakes

Abstract

We establish the relationships between concentrations of inorganic suspended sediments (ISS) on light, nutrients, phytoplankton, and bacteria in three oligotrophic lakes (four sites) and we use these relationships to predict the impacts of increasing concentrations of ISS on the biomass and productivity of phytoplankton and bacteria in the lakes. Increased concentrations of ISS contributed little available nutrient to the lakes. The relationships between ISS and underwater light attenuation differed among lakes because of variation in sediment size-structure, and composition. Only at the site with the highest ISS concentrations and a relatively deep mixing depth, were phytoplankton apparently lightlimited and, thus, predicted to decline with increased ISS concentrations. In contrast to previously published studies, bacterial abundance and production were not highly correlated to suspended sediment concentrations in these lakes. However, bacterial biomass, productivity, and specific productivity were more strongly correlated to phytoplankton production. As a result of light limitation and stimulation of bacterial production, increases in ISS concentrations are not predicted to significantly shift the metabolic balance in the planktonic ecosystem of three † Author for correspondence. M00077 Received 2 November 2000; accepted 20 February 2001of the sites towards greater heterotrophy. Where light limits phytoplankton production, increases in ISS are predicted to reduce the productivity of both phytoplankton and bacteria by direct inhibition of phytoplankton production, again without a large shift towards greater importance of the microbial loop. By reducing phytoplankton production and inhibiting larger cladoceran grazers, we predict that high concentrations of ISS will reduce available energy and its flow up the food chain.

Spectromicroscopy Mapping of Colloidal/Particulate Organic Matter in Lake Brienz, Switzerland

“…Recent publications have shown that the properties of the catchment have a clear impact on the macroinvertebrate communities in these lakes, while the influence of geographical patterns is minor (14). Large inputs of suspended sediments and glacial silt/colloids may also limit the spring phytoplankton peak in alpine lakes, which occurs in a number of other temperate lakes (15,16). As part of a large project focused on understanding the severe productivity limitation conditions existing in a peri-alpine lake (17)sLake Brienz, Switzerlands,submicrometer natural organic matter (NOM), in particular, refractory organic matter (ROM) (18), and inorganic colloids (19,20) have been studied for over a year in the lake and its two main tributaries, the Aare and Lu ¨tschine Rivers.…”