Alonso Ramirez

The proposed research is for continuing our unique long-term study of the consequences of climate change on lowland tropical streams in Costa Rica. We now have over 30 years of data that shows the occurrence of climate-driven acidification events in lowland streams. Our previous LTREB research indicates 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. Climate-driven acidification events are stronger and more common in solute-poor, poorly-buffered, streams than in solute-rich, well-buffered, streams - another characteristic of the study landscape. Here we propose to continue working towards testing 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 Ni????????o and La Ni????????a - ENSO), by (2) assessing biotic responses to climate-driven acidification, and by (3) experimentally buffering a low-solute stream against climate-driven 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 Ni????????o events result in abnormally low precipitation during the dry season, while La Ni????????a results is high precipitation. Our own dataset from lowland Costa Rican rainforest streams, combined with additional long-term data from our terrestrial ecology colleagues, has shown that decreased precipitation during the dry season can decrease carbon sequestration and increase the acidity of streams. Our studies suggest that despite showing the capacity to withstand low pH, both macroinvertebrates and algal assemblages are shaped by climate driven acidification. In this proposal, we build on continuous stream water chemistry and benthic insect data to examine the mechanisms and consequences of changing precipitation regimes on the acidity and biotic response of tropical streams.

LUQ VI: UNDERSTANDING ECOSYSTEM CHANGE IN NORTHEASTERN PUERTO RICO The Luquillo Long Term Ecological Research Program (LUQ) combines long-term measurements, experimental manipulations, and models to determine the effects of changes in climate and disturbance frequency on wet tropical forest and stream ecosystems. The overarching goal of the Luquillo LTER program is to determine how changing climate and disturbance regime, alone or in concert, drive changes in the biota and biogeochemistry. An enhanced mechanistic understanding of change in natural and human-modified landscapes will improve our theoretical understanding and inform management of tropical forest ecosystems globally. Global climate change will lead to an increase in the frequency of intense hurricanes and droughts in the Caribbean as well as other tropical regions. We hypothesize that changing climate and disturbance regimes interacting with the effects of past disturbance events will result in new combinations of species and biogeochemical conditions that have the potential to create ecosystems with no prior analog. These new ecosystem states will arise from material and information legacies of multiple disturbances, as well as immigration of species adapted to drier and more open conditions. We rely on a dynamic conceptual framework to guide our research and explore these altered ecosystems as they develop from the combined effects of increased hurricane frequency and/or drought. Within this large research program, we will address the following question: How do large-scale factors such as climate change interact with hurricanes and drought to shape tropical forest ecosystems of the future? The cumulative effects of increasing frequency of intense hurricanes, more frequent droughts, and climate change are likely to result in fundamental shifts in population, community, and ecosystem characteristics, akin to a state change.

This REU Site award would support the training of eight students for 10 weeks during the summers of 2021- 2025. Research is conducted at El Verde Field Station, located at El Yunque National Forest in Puerto Rico. The program focuses on Tropical Ecology and Evolution ?????????????????? the study of plant population biology, stream ecology and aquatic insect dynamics, forest ecology, arthropod biology, and coevolution in tropical rainforest. Students develop independent projects under the advice of faculty mentors, spending most of their time conducting research and attending seminars and workshops on scientific data analysis and techniques to study tropical systems. The program also provides workshops on relevant topics, such as graduate school application process. Student selection is based on their research interest, academic record, and potential for outstanding research in biological sciences.

The impacts of environmental degradation and climatic variation on the biosphere and its inhabitants remain poorly understood. As a major interface between organisms and their surroundings, the nervous system can provide sensitive and reliable measures of biological responses to environmental perturbations. In this project, we will work with the Puerto Rico Center for Environmental Neuroscience (PRCEN) to understand how environmental stressors affect the nervous system of insects. We will focus on two anthropogenic stressors: the elevated temperature and a by-product of the plastic industry, the phthalates. Insects, because they do not thermoregulate are particularly sensitive to changes in temperature. This project aims at unveiling their effects on the nervous system ranging from gene regulation to the behavior of the entire animal. A particular attention will be given to the possible synergistic effects of these two stressors.

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 water becomes moderately acid (low pH values). These events are natural and related to changes in precipitation between dry and wet seasons. Their occurrence is the result of interactions between the stream and the surrounding forest. During the dry season organic matter accumulates on the forest floor, then precipitation during the following rainy season facilitates the breakdown of that material releasing CO2 that moves with the water into streams, creating acid conditions in streams (or lowering the water pH). Acidification events become more extreme during El Ni????????o years, which in Central America increases seasonality creating drier and wetter season than normal. Changes in acidification can affect the way aquatic ecosystems function and also their biodiversity. Research in lowland streams in Costa Rica suggest that aquatic organisms, both invertebrates and algae, can withstand moderately acid conditions, but are affected when conditions are extreme. This project investigates how periodic acidification affect stream ecosystems in lowland Costa Rica. Research will take place at La Selva Biological Station, on the Caribbean slope of Costa Rica, where streams have been under study for >25 years. The main objective is to understand the mechanisms and consequences of changing precipitation patterns on the acidity and biotic response of tropical streams. Acidification is a common phenomenon in streams word wide, thus it is important to understand it to protect and sustain tropical stream ecosystems. The study will further ongoing long-term research on the consequences of climate change 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. Climate-driven acidification events are stronger and more common in solute-poor, poorly-buffered, streams than in solute-rich, well-buffered, streams - another characteristic of the study landscape. The 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 Ni????????o and La Ni????????a - ENSO), by (2) assessing biotic responses to climate-driven acidification, and by (3) experimentally buffering a low-solute stream against climate-driven 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 Ni????????o events result in abnormally low precipitation during the dry season, while La Ni????????a results is high precipitation. Thus, the project will advance our understanding the consequences of extreme climate events on tropical lowland stream ecosystems.

This REU Site award to the University of Puerto Rico, San Juan, Puerto Rico, will support the training of eight students for 10 weeks during the summers of 2016- 2020. Research is conducted at El Verde Field Station, located at El Yunque National Forest in Puerto Rico. The program focuses on Tropical Ecology and Evolution ?????????????????? the study of plant population biology, stream ecology and aquatic insect dynamics, forest ecology, arthropod biology, and coevolution in tropical rainforest. El Verde is the base of operations of the program and of many tropical researchers and the Luquillo LTER program. Students develop independent projects under the advice of faculty mentors, spending most of their time conducting research and attending seminars and workshops on scientific data analysis and techniques to study tropical systems. The program also provides workshops on relevant topics, such as graduate school application process. A responsible conduct in science component is also provided to discuss issues commonly encountered by students during their careers. Student selection is based on their research interest, academic record, and potential for outstanding research in biological sciences. The project PI makes a short list and mentors are in charge of making final selections. It is anticipated that a total of 40 students, primarily from schools with limited research opportunities, will be trained in the program. Our program focuses on students with interest in ecological research and in pursuing graduate studies. Students will learn how research is conducted, many will present the results of their work at scientific conferences, and some will publish their work in peer-reviewed journals. A common web-based assessment tool used by all REU programs funded by the Division of Biological Infrastructure (Directorate for Biological Sciences) will be used to determine the effectiveness of the training program. Students will be tracked after the program in order to determine student career paths. Students will be asked to respond to an automatic email sent via the NSF reporting system. Applications are accepted starting in December every year. More information is available by visiting http://reu.ites.upr.edu/ or by contacting the PI.

The flow regime (i.e., the rate and timing of water flow) is a central physical factor regulating the dynamics of biotic communities in stream and river ecosystems. The determination of optimal flow regimes that meet societal demands for water resources while sustaining and enhancing aquatic life is especially applicable to tropical island aquatic ecosystems, and the Caribbean island of Puerto Rico is an ideal landscape upon which to empirically research such dynamics. Recent destructive tropical storms in the Caribbean further compel and facilitate study of extreme disturbance, both as flooding and drought, and the need to plan adaptation strategies is critical. In response to critical information and research needs, we propose research to address specific objectives, with an ultimate goal of understanding how stream flow dynamics affect aquatic communities, as an initial step toward ultimately developing environmental flow prescriptions to sustain and enhance aquatic life in Caribbean streams and rivers. The proposed research is multidisciplinary, including aspects of ecology, fishery science, hydrology, and climate science, and spans multiple spatial, temporal, and organizational scales. The objectives will be addressed via empirical data analyses of physical and biotic parameters on the island of Puerto Rico, but the findings may be applicable and informative to other tropical Caribbean islands and nations.