The impact of climate change and brownification on primary and bacterial production

Sammanfattning: Climatic condition is what ultimately frames all ecosystems and is now undergoing dramatic change. IPCC models predict, in 100 years, a temperature increase between 2-5 ˚C and, as a consequence of warmer and wetter conditions, increased humic content in northern temperate freshwater systems. To study the impact of increasing temperature and humic content on shallow freshwaters a long-term outdoor mesocosm experiment was performed. Five different treatments were used, where temperature and water colour was gradually increased simultaneously to correspond to a future scenario of 100 years. This resulted in +5 ˚C and 250% increase in absorbance (as a proxy for humic content) at the highest treatment compared to the control. No consistent significant difference in either primary or bacterial production between the treatments was observed. There was a steady increase of PP during spring and a tendency in total cumulative PP, summarized for the whole experimental period, until intermediate treatment effect. Further, a tendency for increasing heterotrophy was found during June and July. The condition of fish was highest at intermediate treatment effect. Several factors can possibly control PP and BP, such as nutrient limitation and predation as well as different stable states. Since increasing heterotrophy has been suggested, due to climate change, it is of great importance to further investigate the question of how the basal production will be affected and how this shapes freshwater systems, considering both ecosystem and societal values.