Ecomicrobiology and microbial assimilative capacity of the oligotrophic Andean Lake Laja, Chile

Abstract

A strong socio-economic development pressure in South Chile will more and more cause an impact to the present lakes and rivers. Nevertheless, our knowledge concerning the ecological structure and the microbial self-purifi cation capabilities of these lacustrine water bodies is scant but essential for a future sustainable development of land and water use. We studied Lake Laja, a lake already heavily impacted by water diversions for hydropower generation and irrigation. Typical for the Andean region Lake Laja is an oligotrophic water body, limited by nitrogen nutrients. Only very low chlorophyll a and particulate organic carbon (POC) concentrations and a small abundance and biomass of bacteria (mainly ultramicrobacteria) and heterotrophic fl agellates were encountered. Weak trophic interrelations were derived from a high bacteria-to-heterotrophic fl agellate ratio. For the ten investigated extracellular enzymes (alkaline phosphatase, leucine-, arginine-, glycine-and tyrosine-aminopeptidase, α-, β-D-glucosidase, α-, β-D-galactosidase, N-acetyl-β-D-glucosaminidase), with the exception of α-D-glucosidase, a broad range of organic matter degradation activities was proven. Probably, due to the N-limitation, organic nitrogen hydrolysing extracellular enzymes reached activities on average of 45 % compared to other studies in oligotrophic waters. The possible effect of N-limitation on extracellular enzyme activities was more pronounced by cell specifi c extracellular enzymatic activity rates, which exceeded those of other oligotrophic water bodies on average by factor 2. The overall activities of all microbial extracellular enzymes studied proved to be dominated by the dissolved free external enzymes (up to 98 %) over the ectoenzymes which are associated with particulate organic matter (bacterial cell walls, particles, and aggregates). It is concluded that future socio-economic changes, dealing with watershed human intervention (accelerating inorganic and organic loads) as well as global change (temperature and precipitation changes) could lead to signifi cant changes in the ecology of Lake Laja.Key words: bacterioplankton, extracellular enzymes, heterotrophic fl agellates, N-limitation, phytoplankton. RESUMENLa gran presión generada por el desarrollo socioeconómico del sur de Chile, está causando cada vez más un mayor impacto en los lagos y ríos allí presentes. Sin embargo, el conocimiento de la estructura ecológica y la capacidad microbiana de autodepuración de los cuerpos de agua lacustres es escasa, pero esencial para un futuro uso sostenible de los recursos agua y suelo. Se estudió el lago Laja, por ser un cuerpo de agua muy afectado por la extracción de agua para la generación de energía hidroeléctrica y el riego. Como es característico de la región andina, el lago Laja es oligotrófi co limitado por nutrientes nitrogenados. Se encontraron bajas concentraciones de clorofi la a y carbono orgánico particulado (POC), así como bajas abundancias y biomasa de bacterias (principalmente ultramicrobacteria) y de fl a...

Evidence of Climate Change Based on Lake Surface Temperature Trends in South Central Chile

“…Lakes with a surface area ≥ 10 km 2 were selected based on [6]. The 14 selected lakes present a temperate monomictic circulation pattern, with thermal stratification during summer [34][35][36][37]. At present, 11 of the lakes chosen in this study are oligotrophic, while Villarrica has been classified as meso-oligotrophic, and Vichuquén and Lanalhue, as eutrophic [38].…”