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 greenhousegases (CH4, CO2, N2O) and nutrients(NH4+, NO2−+NO3−, tot-P) were studied in sediment of hyper-eutrophic LakeKevaton, Finland. Undisturbed sediment cores were incubated at 6, 11,16, and 23 °C in a laboratory microcosm using a continuouswater flowtechnique with an oxic or anoxic water flow. The production of CO2increased with increasing temperature in both oxic (Q10 3.2 ±0.6) and anoxic (Q10 2.3 ± 0.4) flows. The release ofCH4 increased with temperature in anoxic conditions (Q102.3 ± 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(Q10 2.4 ± 0.1). There was a net production of NO2−, NO3− and N2O with the oxic flow at temperatures below16 °C. The release of phosphorus was greater from the anoxicsediments and increased with temperature with both the anoxic (Q102.9 ± 0.5) and oxic (Q10 1.9 ± 0.1) flows. It isprobable that the temperature of boreal lakes and the associated oxygendeficiency will increase as the climate becomes warmer. Our experiments showedthat this change would increase the global warming potential of greenhousegasesreleased from sediments of eutrophic lakes predominately attributable to theincrease in the CH4 production. Furthermore, warming would alsoaccelerate the eutrophication of lakes by increasing release of phosphorus andmineral nitrogen from sediments, which further enhance CH4productionin sediments.