Causes and Consequences of Highly Variable CO2 in Aquatic Ecosystems

水生生态系统中二氧化碳高度变化的原因和后果

• 批准号: 9317698
• 负责人: Nina Caraco
• 金额: $ 45万
• 依托单位: Cary Institute of Ecosystem Studies, Inc.
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-03-01 至 1998-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9317698&HistoricalAwards=false
• 关键词: Causes; Consequences; Highly; Variable; CO2

9317698 Caraco Using direct measurements of the partial pressure of CO2, we and others have been finding that the surface waters of lakes are rarely in equilibrium with the atmosphere with respect to CO2. Aqueous carbon dioxide concentrations CO2aq in surface waters vary seasonally and across lakes from less than one-tenth to more than ten-fold of their equilibrium concentration with the atmospheric CO2 of less than 2-fold. Neither the causes nor the consequences of the enormous range in CO2 concentrations in aquatic ecosystems is well understood. %%% Causes. The surface waters of lakes can be under-or over saturated in CO2 with respect to the atmosphere. The causes of severe under saturation are relatively well understood. Excess nutrient inputs (nitrogen and phosphorus) from the watershed allow increased primary production and carbon burial which draws down the CO2 concentration. Although this model is reasonable, it has only been tested in a few experimentally eutrophied lakes and it is not known how generally applicable it is. The causes of CO2 super saturation are much less well investigated and all the more intriguing because the data suggest that a majority of lakes are, in fact, super saturated much of the time. A lake supersaturated in CO2 must be a net source of CO2 to the atmosphere. Our preliminary data and review suggest that most lakes are net CO2 sources over an annual cycle and many are sources even during the summer growing season. This net evasion of CO2 from aquatic systems implies an important and relatively unexplored linkage between the lake and its watershed. These lakes must either import and metabolize significant amounts of terrestrially-derived organic matter or they import CO2 from soil respiration in inflowing ground water. Either way, the flux of CO2 from aquatic systems is a large component of a lake's carbon budgets and warrants further study. We hypothesize that the way a lake is linked to its watershed drives these extreme variations in aquati c CO2. %%% Consequences. Relatively small variations in atmospheric CO2 (2-fold) can have large effects on terrestrial plants, including changes in the rate of productivity, and alteration of the elemental composition of plant material. The effects of the much larger variations in CO2 in aquatic systems are less well known, especially for phytoplankton. We hypothesize that the more than 100-fold range in CO2 concentrations in natural aquatic systems may affect phytoplankton species composition, C:P and C:N ratios of phytoplankton and may alter profoundly the value of phytoplankton as food for consumer organisms. %%% Goals. 1) To determine under what conditions lakes are sources or sinks for atmospheric CO2; 2) To identify the sources of excess CO2 in a single lake(Mirror L) which we know outgasses CO2 during most of the year; and 3) To investigate, using manipulative experiments, the effect this dramatic range in CO2 concentrations has on phytoplankton species composition.

9317698 Caraco 通过直接测量 CO2 分压，我们和其他人发现湖泊的地表水很少与大气中的 CO2 保持平衡。 地表水中的二氧化碳浓度 CO2aq 随季节变化，各湖泊的二氧化碳浓度从其平衡浓度的不到十分之一到十倍以上，而大气中的二氧化碳浓度则不到 2 倍。 水生生态系统中二氧化碳浓度变化巨大的原因和后果尚不清楚。 %%%原因。 相对于大气而言，湖泊地表水的二氧化碳含量可能过饱和或过饱和。 严重欠饱和的原因相对较好。 来自流域的过量养分输入（氮和磷）可以增加初级生产和碳埋藏，从而降低二氧化碳浓度。 虽然这个模型是合理的，但仅在少数实验性富营养化湖泊中进行了测试，尚不清楚其普遍适用性如何。 二氧化碳超饱和的原因还没有得到很好的研究，但更令人感兴趣的是，因为数据表明大多数湖泊实际上在大部分时间都处于超饱和状态。 二氧化碳过饱和的湖泊必定是大气中二氧化碳的净来源。 我们的初步数据和审查表明，大多数湖泊在年度周期内都是二氧化碳净源，许多湖泊甚至在夏季生长季节也是二氧化碳源。 水生系统中二氧化碳的净逃逸意味着湖泊与其流域之间存在着重要且相对未经探索的联系。 这些湖泊要么必须输入并代谢大量来自陆地的有机物，要么从流入的地下水中通过土壤呼吸输入二氧化碳。 不管怎样，来自水生系统的二氧化碳通量是湖泊碳预算的重要组成部分，值得进一步研究。我们假设湖泊与其流域的联系方式导致了水生二氧化碳的极端变化。 ％％％ 结果。大气中二氧化碳相对较小的变化（2倍）可能对陆地植物产生很大影响，包括生产力的变化以及植物材料元素组成的改变。 水生系统中二氧化碳大幅变化的影响鲜为人知，特别是对于浮游植物。 我们假设，天然水生系统中超过 100 倍的二氧化碳浓度范围可能会影响浮游植物的物种组成、浮游植物的 C:P 和 C:N 比率，并可能深刻改变浮游植物作为消费生物体食物的价值。 %%%目标。 1) 确定在什么条件下湖泊成为大气二氧化碳的源或汇； 2) 确定单一湖泊（镜子 L）中过量二氧化碳的来源，我们知道该湖泊在一年中的大部分时间都会释放二氧化碳； 3) 通过操作实验来研究二氧化碳浓度的这种巨大范围对浮游植物物种组成的影响。