The CO2-equivalent balance of freshwater ecosystems is non-linearly related to productivity
The CO2-equivalent balance of freshwater ecosystems is non-linearly related to productivity
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DOI：
10.1111/gcb.15284
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发表时间：
2020-08-08
影响因子：
11.6
通讯作者：
Tranvik, Lars J.
中科院分区：
文献类型：
--
作者：
Grasset, Charlotte;Sobek, Sebastian;Tranvik, Lars J.
淡水富营养化导致初级生产对CO(2)的吸收增加，但同时增加了向大气排放CH(4)。鉴于CO(2)吸收和CH(4)释放的对比效应，富营养化对淡水co2当量平衡的净影响尚不清楚。我们测量了20种不同营养浓度（总磷浓度范围：中营养型39 μ g/L至高营养型939 μ g/L）的淡水中生态系统的碳通量(CO(2)和CH（4)扩散、CH(4)泡腾）和CH(4)氧化，其中一半为浮游鱼类。我们发现二氧化碳当量平衡与生产力呈u型关系，在过度富营养化系统中达到阈值。二氧化碳当量汇被限制在5 ~ 19 mmol O-2 m(-3) day（-1）的窄幅生态系统净产量（NEP）范围内。我们的研究结果表明，富营养化可以通过增强CO(2)的吸收将淡水从co2当量的来源转变为汇，但持续的富营养化会增加CH(4)的排放，并将淡水生态系统转变为大气co2当量的净来源。营养物的富集以及浮游鱼类的存在提高了生产力，从而调节了产生的二氧化碳当量平衡。浮游鱼类数量的增加往往伴随着富营养化，因此可能会影响淡水的二氧化碳当量平衡。
Eutrophication of fresh waters results in increased CO(2)uptake by primary production, but at the same time increased emissions of CH(4)to the atmosphere. Given the contrasting effects of CO(2)uptake and CH(4)release, the net effect of eutrophication on the CO2-equivalent balance of fresh waters is not clear. We measured carbon fluxes (CO(2)and CH(4)diffusion, CH(4)ebullition) and CH(4)oxidation in 20 freshwater mesocosms with 10 different nutrient concentrations (total phosphorus range: mesotrophic 39 mu g/L until hypereutrophic 939 mu g/L) and planktivorous fish in half of them. We found that the CO2-equivalent balance had a U-shaped relationship with productivity, up to a threshold in hypereutrophic systems. CO2-equivalent sinks were confined to a narrow range of net ecosystem production (NEP) between 5 and 19 mmol O-2 m(-3) day(-1). Our findings indicate that eutrophication can shift fresh waters from sources to sinks of CO2-equivalents due to enhanced CO(2)uptake, but continued eutrophication enhances CH(4)emission and transforms freshwater ecosystems to net sources of CO2-equivalents to the atmosphere. Nutrient enrichment but also planktivorous fish presence increased productivity, thereby regulating the resulting CO2-equivalent balance. Increasing planktivorous fish abundance, often concomitant with eutrophication, will consequently likely affect the CO2-equivalent balance of fresh waters.