Collaborative LTREB: Acidification in lowland Neotropical streams: building on a 25-year study of groundwater-surface water interactions

哥斯达黎加热带溪流的长期研究记录了低地溪流中由降雨引起的酸化事件的发生。酸化事件是指溪水变得中等酸性的短时间段，从几天到几周不等。这些事件是森林有机物质分解的结果，释放的二氧化碳随着水进入溪流，在溪流中造成酸性条件。酸化的变化会影响溪流的功能及其生物多样性。对哥斯达黎加低地溪流的研究表明，溪流中的无脊椎动物和藻类可以承受中等酸性条件，但在极端酸性条件下会受到负面影响。该项目调查周期性酸化如何影响哥斯达黎加低地的河流。这项研究将在哥斯达黎加加勒比海斜坡上的La Selva生物站进行，那里的溪流已经研究了25年以上。这项工作的主要目的是了解变化的降水模式对热带河流的酸度、生物和生态系统功能的机制和后果。酸化是世界范围内河流普遍存在的现象，因此了解它对于保护和维持河流生态系统具有重要意义。这项研究(1)将有助于了解降雨模式的变化如何影响河流生物多样性和生态系统功能，(2)为研究生和本科生提供研究培训，(3)通过使用iNaturist移动设备应用程序的公民科学项目提供环境推广。这项研究将进一步对哥斯达黎加低地热带溪流降水模式变化的后果进行长期研究。正在进行的LTREB研究描述了间歇性酸化事件的发生。据推测，土壤来源的二氧化碳通过地下径流的流入导致了pH值的下降，表明降雨、陆地和水生生态系统之间存在紧密的耦合。降水驱动的酸化事件在溶质贫乏、缓冲较差的溪流中比在溶质丰富、缓冲良好的溪流中更强烈和更常见--这是研究景观的一个特征。该项目将评估和进一步发展这一假设，方法是：(1)评估溪水化学的日、季、年和年代际模式与主要气候事件(例如，厄尔尼诺和拉尼娜-ENSO)之间的关系；(2)评估生物对气候驱动的酸化的响应；以及(3)通过实验缓冲与ENSO事件有关的低溶质溪流的酸化。气候趋势和全球环流模型预测了极端天气的频率和强度的变化。对于中美洲，模型预测了更大的季节性，类似于在ENSO年观察到的模式。在哥斯达黎加的加勒比海低地，厄尔尼诺事件导致旱季降水量异常低，而拉尼娜事件导致降水量高。因此，该项目将促进我们对极端天气事件对热带低地河流生态系统的影响的理解。

Long-term studies in tropical streams in Costa Rica have documented the occurrence of rainfall-driven acidification events in lowland streams. Acidification events are short periods of time, from a few days to weeks, when the stream water becomes moderately acidic. These events result from the breakdown of forest organic material releasing carbon dioxide that moves with the water into streams, creating acid conditions in streams. Changes in acidification can affect the way streams function and their biodiversity. Research in lowland streams in Costa Rica suggest that stream invertebrates and algae, can withstand moderately acid conditions, but are negatively affected when acid conditions are extreme. This project investigates how periodic acidification affect streams in lowland Costa Rica. The research will take place at La Selva Biological Station, on the Caribbean slope of Costa Rica, where streams have been under study for more than 25 years. The main objective of this work is to understand the mechanisms and consequences of changing precipitation patterns on the acidity, biology and ecosystem functions of tropical streams. Acidification is a common phenomenon in streams wordwide, thus it is important to understand it in order to protect and sustain stream ecosystems. The research (1) will contribute to understanding how changing patterns of rainfall affect stream biodiversity and ecosystem function, (2) provide research training for graduate and undergraduate students, and (3) provide environmental outreach through a citizen science project using the iNaturalist mobile device application. The study will further ongoing long-term research on the consequences of changing patterns of precipitation on lowland tropical streams in Costa Rica. Ongoing LTREB research described the occurrence of episodic acidification events. It was hypothesized that an influx of soil-derived CO2 via subsurface flow paths contributes to those pH declines, signaling a tight coupling among rainfall, terrestrial, and aquatic ecosystems. Precipitation-driven acidification events are stronger and more common in solute-poor, poorly-buffered, streams than in solute-rich, well-buffered, streams - a characteristic of the study landscape. This project will evaluate and further develop this hypothesis by (1) assessing the relation among daily, seasonal, annual, and decadal patterns in stream water chemistry with major climate events (e.g., El Niño and La Niña - ENSO), by (2) assessing biotic responses to climate-driven acidification, and by (3) experimentally buffering a low-solute stream against acidification related to ENSO events. Climate trends and global circulation models predict changes in the frequency and intensity of weather extremes. For Central America, models predict greater seasonality, similar to patterns observed during ENSO years. In the Caribbean lowlands of Costa Rica, El Niño events result in abnormally low precipitation during the dry season, while La Niña results is high precipitation. Thus, the project will advance our understanding the consequences of extreme weather events on tropical lowland stream ecosystems.