School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA.
PLoS One. 2013 Aug 13;8(8):e71395. doi: 10.1371/journal.pone.0071395. eCollection 2013.
The Tonle Sap Lake in Cambodia is a dynamic flood-pulsed ecosystem that annually increases its surface area from roughly 2,500 km(2) to over 12,500 km(2) driven by seasonal flooding from the Mekong River. This flooding is thought to structure many of the critical ecological processes, including aquatic primary and secondary productivity. The lake also has a large fishery that supports the livelihoods of nearly 2 million people. We used a state-space oxygen mass balance model and continuous dissolved oxygen measurements from four locations to provide the first estimates of gross primary productivity (GPP) and ecosystem respiration (ER) for the Tonle Sap. GPP averaged 4.1±2.3 g O2 m(-3) d(-1) with minimal differences among sites. There was a negative correlation between monthly GPP and lake level (r = 0.45) and positive correlation with turbidity (r = 0.65). ER averaged 24.9±20.0 g O2 m(-3) d(-1) but had greater than six-fold variation among sites and minimal seasonal change. Repeated hypoxia was observed at most sampling sites along with persistent net heterotrophy (GPP<ER), indicating significant bacterial metabolism of organic matter that is likely incorporated into the larger food web. Using our measurements of GPP, we calibrated a hydrodynamic-productivity model and predicted aquatic net primary production (aNPP) of 2.0±0.2 g C m(-2) d(-1) (2.4±0.2 million tonnes C y(-1)). Considering a range of plausible values for the total fisheries catch, we estimate that fisheries harvest is an equivalent of 7-69% of total aNPP, which is substantially larger than global average for marine and freshwater systems. This is likely due to relatively efficient carbon transfer through the food web and support of fish production from terrestrial NPP. These analyses are an important first-step in quantifying the resource pathways that support this important ecosystem.
柬埔寨的洞里萨湖是一个动态的洪水脉冲生态系统，每年由于湄公河季节性洪水的影响，其表面积从大约 2500 平方公里增加到 12500 平方公里以上。这种洪水被认为是许多关键生态过程的结构因素，包括水生初级和次级生产力。该湖还有一个大型渔业，为近 200 万人的生计提供支持。我们使用状态空间氧质量平衡模型和来自四个地点的连续溶解氧测量值，首次对洞里萨湖的总初级生产力 (GPP) 和生态系统呼吸 (ER) 进行了估算。GPP 的平均值为 4.1±2.3 g O2 m(-3) d(-1)，各地点之间差异最小。每月 GPP 与湖泊水位呈负相关 (r = 0.45)，与浊度呈正相关 (r = 0.65)。ER 的平均值为 24.9±20.0 g O2 m(-3) d(-1)，但各地点之间的差异超过六倍，季节性变化极小。在大多数采样点都观察到反复缺氧，以及持续的净异养 (GPP<ER)，这表明存在大量细菌对有机物的代谢作用，这些有机物可能被纳入更大的食物网中。利用我们对 GPP 的测量值，我们对水动力-生产力模型进行了校准，并预测了水体净初级生产力 (aNPP) 为 2.0±0.2 g C m(-2) d(-1) (2.4±0.2 百万吨 C y(-1))。考虑到总渔业捕捞量的一系列合理值，我们估计渔业捕捞量相当于总 aNPP 的 7-69%，这大大高于海洋和淡水系统的全球平均水平。这可能是由于通过食物网相对有效地转移碳，并支持从陆地净初级生产力 (NPP) 生产鱼类。这些分析是量化支持这一重要生态系统的资源途径的重要第一步。
