STREAMS Project: Emergent landscape patterns in stream ecosystem processes resulting from groundwater/surface water interactions

This Data Set is hosted by the Luquillo LTER Program (LUQ) and owned by a LUQ's investigator.
Our primary objective is to understand the linkage between surface-subsurface water interactions and ecosystem processes in neotropical lowland streams over an extended time frame (>25 yrs). Proposed research will occur at La Selva Biological Reserve in Costa Rica, which is owned and operated by the Organization for Tropical Studies
In tectonically active regions of Central America, it is common for solute-rich groundwater to emerge at gradient breaks within the complex volcanic topography of mountains and foothills which intergrade with the coastal plain. These groundwaters can significantly influence solute chemistry and related ecological and ecosystem-level processes in receiving surface waters. Many solute-rich groundwaters are associated with underlying volcanic activity which has altered the chemistry of receiving streams throughout Central America. Geothermally-modified groundwaters, surfacing at the gradient break between the Central Mountain range and the coastal plain at La Selva Biological Station, have high levels of P (up to 400 mg SRP L-1) and other solutes (Ca, Cl, Mg, SO4) but are not elevated in temperature. Spatial patterns in stream solute chemistry are determined by geomorphic features of the volcanic landscape that include: upland lavas drained by P-poor streams; a gradient break (~50 m.a.s.l.), at or near where P-rich springs emerge; and lowland alluvial areas drained by streams that are both P-rich and P-poor depending on whether they receive the input of solute-rich springs.
Our project is the first to determine long-term effects of nutrient enrichment in a detrital-based stream within the wet tropics. We will continue to build upon our long-term(1988-present) data set on stream solute chemistry, which is the only one that we are aware of for lowland primary rainforest of Central America. The proposed project will build on 18 years of past research which has shown that landscape patterns in stream solute chemistry (resulting from variation in solute-rich groundwater inputs) reflect ecosystem processes such as rates of primary production and decomposition of organic material. Specifically, we are: (1) continuing our evaluation of long-term trends in the solute chemistry of these lowland tropical streams as related to large scale climatic phenomena (e.g., El Nino Southern Oscillation Events); (2) examining how stream segments draining three major geomorphic subfeatures of the lowland tropical landscape respond to temporal (wet versus dry season) changes in precipitation; (3) examining stoichiometric mechanisms behind elevated levels of insect growth and biomass turnover rates in phosphorus-rich streams; and finally (4) concluding (and build upon) an ongoing long-term whole-stream phosphorus enrichment by determining the storage, fate and transport of the artificially-introduced phosphorus (that has been injected over an 8 year period) and examining related effects on detrital foodwebs.
Stream solute chemistry and ecosystem process-oriented data are of fundamental importance to our understanding and management of tropical forests and in predicting effects of regional (and potentially global) environmental change on these threatened ecosystems. Our long-term program will provide new insights into how large scale climatic phenomena interact with subsurface hydrologic factors and geothermal activity to influence stream solute chemistry and related ecosystem processes. We will continue to link the data sets generated from our LTREB Project to those from other long term sites for both tropical (e.g., Luquillo LTER site in Puerto Rico) and temperate research (Coweeta LTER site in North Carolina USA). Finally, the project will contribute to our ongoing environmental outreach program Water for Life, which includes local outreach in communities near La Selva Biological Station and an internationally accessible web page equipped with teaching tools on river conservation and water quality and quantity issues at the high school- level in both Spanish and English. Support for this work was provided by grants BSR-8811902, DEB-9411973, DEB-9705814 , DEB-0080538, DEB-0218039 , DEB-0620910 , DEB-1239764, DEB-1546686, and DEB-1831952 from the National Science Foundation to the University of Puerto Rico as part of the Luquillo Long-Term Ecological Research Program. Additional support was provided by the USDA Forest Service International Institute of Tropical Forestry and the University of Puerto Rico.

本数据集由卢奎略长期生态研究计划（Luquillo LTER Program, LUQ）托管，归属LUQ的一名研究者所有。

本研究的核心目标为，在超过25年的长期时间尺度下，解析新热带低地溪流中地表水与地下水交互作用和生态系统过程之间的关联。拟建研究将在哥斯达黎加拉塞尔瓦生物保护区开展，该保护区由热带研究组织（Organization for Tropical Studies）所有并运营。

中美洲构造活动区域内，山地与山麓复杂的火山地貌与沿海平原过渡地带，常于坡度转折处出露富含溶质的地下水。此类地下水可显著改变受纳地表水的溶质化学特征，并进而影响相关生态及生态系统尺度过程。诸多富含溶质的地下水与地下火山活动相关，这类活动已改变了中美洲全境受纳溪流的水体化学组成。在拉塞尔瓦生物站，中央山脉与沿海平原的坡度转折处出露的地热改造地下水，可溶性活性磷（SRP, Soluble Reactive Phosphorus）含量高达400 mg·L⁻¹，同时富含钙、氯、镁、硫酸盐等溶质，但水温并无异常升高。溪流溶质化学的空间格局由火山地貌的地貌特征决定：包括由贫磷溪流汇水的高地熔岩区；约海拔50米处的坡度转折带——富磷泉群的出露位置即位于该带或其附近；以及低地冲积区，该区域溪流的磷含量随是否接受富溶质泉水补给而呈现富磷或贫磷的差异。

本项目是首个针对湿热带碎屑依托型溪流开展养分富集长期效应研究的项目。我们将持续完善自1988年至今的溪流溶质化学长期数据集——据我们所知，这是中美洲低地原始热带雨林领域唯一的同类长期数据集。本拟建项目将基于此前18年的研究基础，此前研究已证实：溪流溶质化学的景观格局（由富溶质地下水输入的差异所导致）可反映生态系统过程，如初级生产速率与有机质分解速率。

具体而言，本研究将开展以下四项工作：（1）持续评估这些低地热带溪流的溶质化学长期趋势，及其与厄尔尼诺-南方涛动事件等大尺度气候现象的关联；（2）探究汇水于低地热带景观三大主要地貌亚单元的溪流片段，如何响应降水的季节变化（湿季与干季）；（3）解析富磷溪流中昆虫生长速率与生物量周转速率升高的化学计量学机制；以及（4）收尾并拓展一项持续开展的全溪流长期磷富集实验：通过量化8年间人工注入磷的储存、归趋与迁移过程，探究其对碎屑食物网的相关影响。

溪流溶质化学与以生态系统过程为导向的数据集，对于我们理解和管理热带森林，以及预测区域乃至全球环境变化对这些受威胁生态系统的影响，具有基础性重要意义。本长期研究计划将深入解析大尺度气候现象如何与地下水文因子、地热活动交互作用，进而影响溪流溶质化学及相关生态系统过程。我们将持续将本LTREB项目生成的数据集，与其他热带（如波多黎各的卢奎略LTER站点）及温带（如美国北卡罗来纳州的科韦塔LTER站点）长期研究站点的数据集进行关联整合。

本项目还将助力我们正在推进的“生命之水”（Water for Life）环境外展项目，该项目包括在拉塞尔瓦生物站周边社区开展本地外展活动，以及搭建国际可访问的网页，提供西班牙语、英语双语的高中阶段河流保护、水质与水量问题教学工具。

本研究得到了美国国家科学基金会授予波多黎各大学的多项拨款支持（BSR-8811902、DEB-9411973、DEB-9705814、DEB-0080538、DEB-0218039、DEB-0620910、DEB-1239764、DEB-1546686、DEB-1831952），作为卢奎略长期生态研究计划的组成部分。额外资助来自美国农业部林务局国际热带森林研究所与波多黎各大学。