The interaction of physical structure and nutrient loading drives ecosystem change in a large tropical lake over 40 years
The interaction of physical structure and nutrient loading drives ecosystem change in a large tropical lake over 40 years
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DOI：
10.1016/j.scitotenv.2022.154454
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发表时间：
2022-04-07
影响因子：
9.8
通讯作者：
Hall, Ed K.
中科院分区：
文献类型：
--
作者：
Fadum, Jemma M.;Hall, Ed K.
世界各地的许多湖泊弧进入新的状态，并经历了改变地球化学循环，由于当地的生物胁迫。在热带地区，由于缺乏记录的历史条件或缺乏可以区分年内和年际变化的连续监测，理解这些变化的驱动因素可能很困难。在过去的四十年（1980-2020年）中，Yojoa湖（洪都拉斯）经历了流域开发的增加以及引入大型网围栏罗非鱼养殖场，导致季节性水透明度急剧下降，营养状态增加，营养动态改变，将Yojoa湖从贫营养（低生产力）转变为中营养（中等生产力）生态系统。为了评估Yojoa湖发生的变化以及这些变化的假定驱动因素，我们比较了1979年至1983年三年连续半个月间隔的Secchi深度（水透明度），溶解无机氮（DIN）和总磷（TP）浓度，并再次连续16天间隔2018-2020。在这两个时期之间，我们观察到以前在水柱完全混合的月份中发生的清水相的损失。DIN的季节性高峰与混合一致表明，增强积累的铵在下层（分层湖的底层）在分层过程中，并释放到上层（分层湖的顶层）与混合保持高藻类丰度和随后的低Secchi深度在什么是以前的清水相。这种相互作用的营养负荷和湖Yojoa的单胞分层制度说明了一个关键的现象，在物理水柱结构和营养物质相互作用的热带单胞湖泊。这项工作强调需要考虑营养动态的温暖缺氧hypolimnions，而不仅仅是地表水营养浓度，了解这些社会重要的，但研究不足的生态系统的环境变化。
Many lakes across the world arc entering novel states and experiencing altered biogeochemical cycling due to local anthropogcnic stressors. In the tropics, understanding the drivers of these changes can be difficult due to a lack of documented historic conditions or an absence of continuous monitoring that can distinguish between intim- and inter-annual variation. Over the last forty years (1980-2020), Lake Yojoa (Honduras) has experienced increased watershed development as well as the introduction of a large net-pen Tilapia farm, resulting in a dramatic reduction in seasonal water clarity, increased trophic state and altered nutrient dynamics, shifting lake Yojoa from an oligotrophic (low productivity) to mesotrophic (moderate productivity) ecosystem. To assess the changes that have occurred in lake Yojoa as well as putative drivers for those changes, we compared Secchi depth (water clarity), dissolved inorganic nitrogen (DIN), and total phosphorus (TP) concentrations at continuous semi-monthly intervals for the three years between 1979 and 1983 and again at continuous 16-day intervals for 2018-2020. Between those two periods we observed the loss of a clear water phase that previously occurred in the months when the water column was fully mixed. Seasonal peaks in DIN coincident with mixing suggest that an enhanced accumulation of ammonium in the hypolimnion (the bottom layer of a stratified lake) during stratification, and release to the epilimnion (the top layer of a stratified lake) with mixing maintains high algal abundance and subsequently low Secchi depth during what was previously the clear water phase. This interaction of nutrient loading and Lake Yojoa's monomictic stratification regime illustrates a key phenomenon in how physical water column structure and nutrients interact in tropical monomictic lakes. This work highlights the need to consider nutrient dynamics of warm anoxic hypolimnions, not just surface water nutrient concentrations, to understand environmental change in these societally important but understudied ecosystems.