Nitrous oxide emission and its influencing factors at the cyanobacteria-dominated lake

Abstract

湖泊等内陆水体是大气N₂O潜在的重要排放源,也是全球N₂O收支估算的重要组成部分。目前全球湖泊普遍面临富营养化和蓝藻暴发等问题,明晰藻型湖泊N₂O排放强度及其环境影响因子对准确估算湖泊N₂O排放和预测其未来变化至关重要。本研究选择太湖藻型湖区为研究对象,同时选取人为活动影响较小的湖心区作为对比区域,基于2011年8月至2013年8月为期2年的逐月连续观测,探讨藻型湖区N₂O排放特征及其影响因素。结果表明,藻型湖区呈现极强的N₂O排放,其排放通量为(4.88±3.05) mmol/(m²·d),是参考区域(湖心: (2.10±4.31) mmol/(m²·d))的2倍多。此外,在藻型湖区中不同点位N₂O排放差异显著,受河流外源输入影响,近岸区是N₂O的热点排放区,其年均排放通量高达10.93 mmol/(m²·d)。连续观测表明N₂O排放具有显著的季节变化模式,但在不同区域调控N₂O排放时间变化的因子有所不同。其中,近岸区N₂O排放主要受氮负荷影响,其他区域N₂O排放变化受水温和氮负荷等多因子影响。氮素富集是藻型湖区N₂O高排放的直接原因,水体氮负荷可以作为N₂O排放热点的重要指示因子。但藻型湖泊N₂O排放极其显著的时空变异等在未来研究中应得到更多关注。;Inland lakes potential emit large nitrous oxide (N₂O) to atmosphere and play significant role in global N₂O budget estimation. Widespread global increase in lake phytoplankton blooms have been found, identifying the N₂O flux and its influencing factors at the cyanobacteria-dominated lake is essential to being able to accurate estimate the N₂O emissions from lakes and predict future change. In order to identify N₂O flux characteristics and its influencing factors in the cyanobacteria-dominated zone of Lake Taihu, the N₂O emission was observed based on the two-year field measurements. Results showed the annual mean N₂O flux from the cyanobacteria-dominated zone ((4.88±3.05) mmol/(m²·d)) was about twice higher than that in the central zone with less cyanobacteria blooms ((2.10±4.31) mmol/(m²·d)). Meanwhile, the N₂O emissions varies spatially within the cyanobacteria-dominated zone, peak N₂O emission (10.93 mmol/(m²·d)) occurred in littoral zone due to the large external loadings input via river discharge. Continuous filed measurement showed that the N₂O emission varied seasonally, but the factors influencing the seasonal patterns varied among sub-zones. Generally, the temporal variation of N₂O emission were regulated by N loadings in littoral zone, and were regulated by multiple environment variables, such as temperature and N loadings, in Meiliang Bay and the central zone. High nitrogen loadings contributed to large N₂O emission from cyanobacteria-dominated zone, indicating that N loadings can be used as proxy of N₂O emission from lakes. Considering significant temporal and spatial variation of N₂O emission from cyanobacteria-dominated zones, more attention should be paid in future research.