ABSTRACT

Ecosystem metabolism is an integrative measure of the production and respiration of carbon in aquatic ecosystems. However, under-ice regions and mixing periods are infrequently sampled because of logistical challenges and assumptions of low biological activity, resulting in limited understanding of the contribution of winter epilimnetic metabolism to annual carbon cycling. Aquatic ecosystems can emit up to 76% of the carbon they receive from terrestrial landscapes as carbon dioxide to the atmosphere, making them significant contributors to Earth’s carbon cycle. Consequently, studying metabolism under ice is especially important given that warmer winters have already shortened ice cover and lengthened ice transitional periods, potentially resulting in greater carbon dioxide emissions. Using a continuous year of epilimnetic high-frequency dissolved oxygen data, we found that gross primary production was low but not absent under ice and increased during the end of the under-ice period. Despite cold water temperatures, under-ice respiration was 1.2 times higher than summer respiration, and ice-on and ice-off periods were important contributors to annual metabolism estimates. On average, under-ice net ecosystem production (NEP) was negative, in contrast to positive NEP for the spring and summer periods. Including winter metabolism estimates flipped annual NEP from autotrophy to heterotrophy, demonstrating that year-round sampling is essential for accurately assessing carbon cycling in lakes.

抽象的

生态系统代谢是水生生态系统中碳的产生和呼吸的综合量度。然而，由于后勤方面的挑战和生物活性较低的假设，很少对冰下地区和混合期进行采样，导致对冬季表皮新陈代谢对年度碳循环的贡献的了解有限。水生生态系统最多可将其从陆地景观中吸收的碳的76％作为二氧化碳排放到大气中，从而使其成为地球碳循环的重要贡献者。因此，研究冰块下的新陈代谢尤为重要，因为更温暖的冬天已经缩短了冰盖并延长了冰块的过渡期，从而可能导致更多的二氧化碳排放。使用连续一年的上层高频溶解氧数据，我们发现在冰层下初级总产量较低，但并不缺乏，而在冰末期末则有所增加。尽管水温低，但冰下呼吸仍比夏季呼吸高1.2倍，冰上和冰下时期是每年新陈代谢估计的重要因素。平均而言，与春季和夏季的NEP相比，冰下的净生态系统产量（NEP）为负。包括冬季新陈代谢的估计在内，每年的NEP已从自养变为异养，证明了全年采样对于准确评估湖泊中的碳循环至关重要。尽管水温低，但冰下呼吸仍比夏季呼吸高1.2倍，冰上和冰下时期是每年新陈代谢估计的重要因素。平均而言，与春季和夏季的NEP相比，冰下的净生态系统产量（NEP）为负。包括冬季新陈代谢的估计在内，每年的NEP已从自养变为异养，证明了全年采样对于准确评估湖泊中的碳循环至关重要。尽管水温低，但冰下呼吸仍比夏季呼吸高1.2倍，冰上和冰下时期是每年新陈代谢估计的重要因素。平均而言，与春季和夏季的NEP为正相比，冰下净生态系统产量（NEP）为负。包括冬季新陈代谢的估计在内，每年的NEP已从自养变为异养，表明全年采样对于准确评估湖泊中的碳循环至关重要。