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

对哥斯达黎加热带溪流的长期研究记录了低地溪流中由冰川驱动的酸化事件。酸化事件是短时间内，从几天到几周，当溪流水变成中等酸性时。 这些事件是由于森林有机物质分解释放二氧化碳，二氧化碳随水进入溪流，在溪流中创造酸性条件。酸化的变化会影响溪流的功能及其生物多样性。 在哥斯达黎加的低地溪流中进行的研究表明，溪流中的无脊椎动物和藻类可以承受中等酸性条件，但在酸性条件极端时会受到负面影响。 本项目调查周期性酸化如何影响低地哥斯达黎加的溪流。 这项研究将在哥斯达黎加加勒比海斜坡上的拉塞尔瓦生物站进行，那里的河流已经被研究了25年多。 这项工作的主要目标是了解机制和后果的变化降水模式的酸度，生物和生态系统功能的热带溪流。 河流酸化是一种普遍现象，了解河流酸化对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iNaturalist移动终端应用程序的公民科学项目提供环境推广。这项研究将进一步推动目前正在进行的关于降水模式变化对哥斯达黎加低地热带溪流的影响的长期研究。 正在进行的LTREB研究描述了间歇性酸化事件的发生。 据推测，流入的土壤来源的CO2通过地下水流路径有助于这些pH值下降，信号降雨，陆地和水生生态系统之间的紧密耦合。酸化驱动的酸化事件更强，更常见的溶质贫乏，缓冲差，流比溶质丰富，缓冲良好，流-研究景观的一个特点。 该项目将通过以下方式评估和进一步发展这一假设：（1）评估溪流水化学中每日、季节、年度和十年期模式与主要气候事件（例如，厄尔尼诺和拉尼娜-厄尔尼诺/南方涛动现象），方法是（2）评估生物对气候驱动的酸化的反应，以及（3）实验性地缓冲低溶质河流，使其免受与厄尔尼诺/南方涛动事件有关的酸化。气候趋势和全球环流模型预测了极端天气频率和强度的变化。对于中美洲，模型预测季节性更强，类似于厄尔尼诺/南方涛动年期间观察到的模式。 在哥斯达黎加的加勒比低地，厄尔尼诺现象导致旱季降水量异常低，而拉尼娜现象则导致降水量高。 因此，该项目将促进我们了解极端天气事件对热带低地河流生态系统的影响。

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.