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

对哥斯达黎加热带河流的长期研究记录了降雨导致的低地河流酸化事件的发生。酸化事件是指在短时间内，从几天到几周，当水流变得中等酸性时。这些事件是由于森林有机物质分解释放出的二氧化碳随着水进入溪流，在溪流中形成酸性环境造成的。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。这个项目调查了周期性酸化如何影响哥斯达黎加低地的溪流。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，那里的溪流已经被研究了25年多。这项工作的主要目的是了解降水模式变化对热带河流酸度、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的普遍现象，因此了解它对于保护和维持河流生态系统非常重要。该研究(1)将有助于了解降雨模式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iNaturalist移动设备应用程序的公民科学项目提供环境宣传。这项研究将进一步推动目前正在进行的关于哥斯达黎加低地热带河流降水模式变化的后果的长期研究。正在进行的LTREB研究描述了间歇性酸化事件的发生。据推测，来自土壤的二氧化碳通过地下流动路径流入导致了这些pH值的下降，这表明降雨、陆地和水生生态系统之间存在紧密耦合。降水驱动的酸化事件在贫溶质、缓冲较差的河流中比富溶质、缓冲良好的河流中更强烈、更常见——这是研究景观的一个特征。该项目将通过以下方式评估并进一步发展这一假设：(1)评估河流水化学的日、季、年和年代际模式与主要气候事件（如El Niño和La Niña - ENSO）之间的关系；(2)评估生物对气候驱动酸化的反应；(3)通过实验缓冲与ENSO事件相关的低溶质河流酸化。气候趋势和全球环流模式预测了极端天气发生频率和强度的变化。对于中美洲，模式预测的季节性更强，与ENSO年观测到的模式类似。在哥斯达黎加的加勒比海低地，El Niño事件导致旱季降水异常少，而La Niña事件导致降水异常多。因此，该项目将促进我们了解极端天气事件对热带低地溪流生态系统的影响。

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.