|Lead PI||Catherine Pringle|
|Co-PIs||Alonso Ramirez, John Duff|
|Past Co-PI||Frank Triska (Emiritus USGS)|
|Graduate Students||Beth Anderson (PhD), Marcelo Ardon (PhD), Tina Laidlaw (MS), Carissa Ganong (PhD), Doug Parsons (MS), Scott Pohlman (MS), Alonso Ramirez (PhD), Marcia Snyder (PhD), Chip Small (PhD), Lindsay Stallcup (MS), Rodney Vargas (MS)|
|Post-Doctoral Fellows||Rebecca Bixby, Toshihide Hamazaki, Amy Rosemond|
Emergent Landscape Patterns in Stream Ecosystem Processes Resulting from Groundwater-surface Water Interactions
Initiated by Pringle, as a postdoc in 1986, the STREAMS Long-Term Research in Environmental Biology (LTREB) Project examines how ground- and surface-water interactions affect stream ecosystem ecology. This project has resulted in over 60 publications on tropical stream ecology and biogeochemistry. Emergent patterns in our long-term (25+ years) stream chemistry data have led us to our current focus on ecological effects of climate-driven acidification. The STREAMS Project is located in lowland Coata Rica at La Selva Biological Station (owned and operated by the Organization for Tropical Studies, OTS) Before this program, little was known about the biogeochemistry, structure, and function of Central American streams. Scientific understanding of Neotropical streams has been primarily based on research conducted in South America on the Amazon (and to a lesser extent, the Orinoco). Results of the STREAMS Project comprise one of the few long-term datasets on stream solute chemistry and ecology in primary lowland rainforests of Central America. Our current objective is to understand how groundwater-surface water interactions determine short- and long-term (>25 years) responses of solute chemistry and ecosystem processes in response to hydroclimatic variability. In tectonically active regions of Central America, solute-rich regional groundwater (i.e. from outside of the immediate watershed) commonly emerges at gradient breaks in lowlands where mountains merge with the coastal plain. These regional groundwaters contain high levels of phosphorus (up to 400 μg SRP L-1) and other solutes (HCO3, Ca, Cl, Mg, SO4). Our research is focused at La Selva Biological Station in Costa Rica. where we have shown that high levels of phosphorus in regional groundwaters stimulate microbial activity and alter stoichiometric relationships throughout stream food webs. Moreover, landscape patterns in stream chemistry, resulting from variation in inputs of regional groundwater, reflect patterns in stream ecosystem processes on landscape scales, such as decomposition rates of organic matter and growth rates of insect consumers. Our current research shifts from identifying and validating stream solute patterns at multiple temporal and spatial scales to investigating underlying mechanisms and their ecological consequences for ecosystem function.
Current research is extending our record of stream solute chemistry to a total of 28 years. This long-term data set is the only one that we are aware of for lowland primary rainforest of Central America. Distinctive patterns have emerged that appear to be related to seasonal and episodic climatic phenomena (i.e. El Nino-Southern Oscillation (ENSO) events) which differentially affect poorly-buffered solute- poor streams versus solute-rich streams. We hypothesize that prolonged acidification events (in poorly-buffered streams following ENSO events) are an amplification of normal seasonal trends. To complete our decadal plan we are examining the following:
- Mechanisms causing observed seasonal and inter-annual patterns in stream solute chemistry and pH that have emerged from our long-term data set
- Effects of seasonal variation in solute levels on in-stream carbon processing
- Impact of acidification on stream ecosystem functioning.
In addition, ongoing research is testing the ecological effects of acidification on aquatic organisms and quantifying the resistance and resilience of benthic communities to pH shifts. We are currently analyzing data from a long-term quarterly sampling effort of algae and benthic macroinvertebrates, as well as conducting mesocosm experiments to determine the effects of acidification on survival and growth of dominant stream macroinvertebrate taxa. Our focus on mechanisms driving annual and inter-annual changes in stream chemistry is critical, given climate model predictions of decreased dry- season rainfall and ENSO-like conditions in Central America. Our findings suggest that such changes in climate could increase the magnitude of seasonal acidification in poorly- buffered Neotropical streams.