Effects of temperature and oxygen availability on greenhouse gas and nutrient dynamics in sediment of a eutrophic mid-boreal lake

The effects of oxygen conditions and temperature on dynamics of greenhouse gases (CH4, CO2, N2O) and nutrients (NH4+, NO2-+NO3-,-, tot-P) were studied in sediment of hyper-eutrophic Lake Kevaton, Finland. Undisturbed sediment cores were incubated at 6, 11, 16, and 23 degreesC in a laboratory microcosm using a continuous water flow technique with an oxic or anoxic water flow. The production of CO2 increased with increasing temperature in both oxic (Q(10) 3.2 +/- 0.6) and anoxic (Q(10) 2.3 +/- 0.4) flows. The release of CH4 increased with temperature in anoxic conditions (Q(10) 2.3 +/- 0.2), but was negligible with the oxic flow at all temperatures. The release of NH4+ increased with temperature with the oxic and anoxic flows (Q(10) 2.4 +/- 0.1). There was a net production of NO2-, NO3- and N2O with the oxic flow at temperatures below 16 degreesC. The release of phosphorus was greater from the anoxic sediments and increased with temperature with both the anoxic (Q(10) 2.9 +/- 0.5) and oxic (Q(10) 1.9 +/- 0.1) flows. It is probable that the temperature of boreal lakes and the associated oxygen deficiency will increase as the climate becomes warmer. Our experiments showed that this change would increase the global warming potential of greenhouse gases released from sediments of eutrophic lakes predominately attributable to the increase in the CH4 production. Furthermore, warming would also accelerate the eutrophication of lakes by increasing release of phosphorus and mineral nitrogen from sediments, which further enhance CH4 production in sediments.