Metabolisme ecosistèmic de l'Estany de Banyoles

Abstract

The study of the metabolism of a lake ecosystem gives us an estimate of the state of the watershed. In this work, the metabolic rates of production and respiration in the Banyoles Lake were calculated during the annual cycle of 2021, with the aim of quantifying the metabolism of the lake, describing its trophic state and assessing its contribution into the carbon cycle. Sounding lines were placed in the lake to compile high-frequency oxygen, conductivity, and temperature data, which were collected once a month. Rates were calculated from the modification of Bayesian models applied to lentic water bodies. The average annual gross production and respiration is 0.171 and 0.186 mg O2 L-1 day-1, respectively. It is included in the classification of oligo-mesotrophic lakes due to the low concentration of nutrients and phytoplankton biomass, but compared to other systems, it has intermediate metabolic rates between oligotrophic and eutrophic lakes. It should be noted that calculation of the metabolism integrated in the whole water column (mg O2 m-2 day-1) can be underestimated, since the samples are collected only on the surface and light often can penetrate below the mixed layer, so that there is considerable primary production in deeper waters. The production pattern agreed with the model proposed by Legendre (1981), coinciding with an early spring peak of production. However, other high production values can appear during the annual cycle, attributable to external contributions of nutrients, coming from rainfall or the surroundings of the lake. The balance between production and respiration of the system is slightly negative, but given the standard deviation, we cannot conclude it is different from 0. Despite this, the lake certainly behaves more heterotrophically, as these methods do not estimate anaerobic respiration, important in deeper areas