Costa Rica Program

Summary of Current NSF - LTREB STREAMS Project (1988-2011):
http://cpringle.myweb.uga.edu/index2.html

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

Location/Duration: Costa Rica (2006-2011)
Current UGA Graduate Students: Chip Small (PhD), Marcia Snyder (PhD)
Previous UGA Graduate Students: Marcello Ardon (PhD), Beth Anderson (PhD), Lindsay
    Stallcup (MS), Alonso Ramirez (PhD), Tina Laidlaw (MS), Scott Pohlman (MS),
    Doug Parsons (MS), & Rodney Vargas (MS)

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.

Chip Small (PhD) - Chip Small's research focuses on integrating food web ecology and biogeochemistry using ecological stoichiometry as a conceptual framework. We have measured the phosphorus content of consumers and basal food resources (algae, leaf litter) in streams ranging widely in dissolved phosphorus. The results show the first evidence of an entire invertebrate consumer assemblage showing deviation from strict homeostasis (i.e. the insects have 2x more P in the high-P streams, where they feed on resources 6x higher in P-content). To understand the physiological implications of feeding on P-enriched food resources, we are measuring how food quality effects the growth rates and RNA content of larval chironomids, a dominant benthic consumer. To understand how the effects of P-enriched invertebrates and basal resources move through the food web, we measured nutrient excretion rates of fishes in high-P and low-P streams, to understand how fish diet, fish nutrient demand, and the degree of P-enrichment in the fish diet combines to control the rate of P-recycling by these consumers. We are also testing the hypothesis that more P is exported to the terrestrial food web in high-P streams through insect emergence.

Marcia Snyder (PhD) - Tropical migratory shrimp populations are well suited to be used as environmental sensors to indicate ecological health of aquatic systems. Marcia Snyder’s dissertation proposes to use field surveys and experiments to: (1) determine if freshwater shrimp populations in relatively pristine upstream forested reaches in the Caribbean lowlands of Costa Rica have changed from historic levels in terms of abundance, size and/or species richness; (2) determine if freshwater shrimp populations, across elevational, discharge, and solute-richness gradients exhibit differences in terms of abundance, species richness, size or fecundity; and (3) use ecological stoichiometry theory to refine shrimps role in the stream food web and (4) determine if shrimp populations directly influenced by agrochemicals exhibit differences in terms of abundance, species richness, size or fecundity from streams in protected old-growth forest. This study will refine our understanding of how macrobenthic consumers respond to anthropogenic alterations of watersheds by monitoring long-term population level changes that could occur through direct or indirect mechanisms and measuring current shrimp abundances across an anthropogenic gradient of water quality. Additionally, this study could fill a much needed gap in our knowledge of how pesticides influence the integrity of neotropical aquatic ecosystems, increase our knowledge as to how native freshwater shrimp respond in situ to chronic exposure to nutrient pulses, a range of pesticides, and a natural pH gradient.

Selected Publications:
Pringle, C. M. 1991. Geothermal waters surface at La Selva Biological Station, Costa Rica:
     Volcanic processes introduce chemical discontinuities into lowland tropical streams.
     Biotropica 23: 523-529.
Pringle, C. M. and F. J. Triska. 1991. Effects of geothermal waters on nutrient dynamics of a
     lowland Costa Rican stream. Ecology 72: 951-965.
Pringle, C. M., G. L. Rowe, F. J. Triska, J. F. Fernandez and J. West. 1993. Landscape
     linkages between   geothermal activity, solute composition and ecological response in
     streams draining Costa Rica's Atlantic Slope. Limnology and Oceanography 38: 753-774.
Pringle, C. M., and T. Hamazaki. 1997. Effects of fishes on algal response to storms in a
     tropical stream. Ecology 78: 2432-2442.
Genereaux, D. and C. M. Pringle. 1997. Chemical mixing model of stream-flow generation at
     La Selva Biological Station, Costa Rica. Journal of Hydrology 199: 319-330.
Pringle, C. M., and T. Hamazaki. 1998. The role of omnivory in structuring a neotropical
     stream: Separating diurnal versus nocturnal effects. Ecology 79: 269-280.
Rosemond, A. D., C. M. Pringle, A. Ramirez, and M. Paul. 2001. A test of top- down and
     bottom-up control in a detritus-based food web. Ecology 82: 2279-2293.
Rosemond, A. D., C. M. Pringle, A. Ramirez, M. J. Paul, and J. L. Meyer. 2002. Landscape
     pattterns in the effects of phosphorus on detritus-based tropical streams. Limnology and
    Oceanography 47: 278-289.
Anderson-Olivas, E. A., M. C. Freeman, and C. M. Pringle. 2006 Ecological consequences
     of hydropower development in Central America: Impacts of small dams and water
     diversion on neotropical stream fish assemblages. River Research and Applications
     22:397-411.
Stallcup, L. A., M. Ardon, and C. M. Pringle. 2006. Does nitrogen become limiting
      under high-P conditions in detritus-based tropical streams? Freshwater Biology.
     51:1515-1526.
Triska, F. J., C. M. Pringle, J. H. Duff, R. J. Avanzino, A. Ramirez, M. Ardon, and
      A. Jackman. 2006. Soluble reactive phosphorus (SRP) transport and retention
      In tropical rainforest streams draining a volcanic landscape in Costa Rica. 1. Long-
      term concentration patterns, pore water environment and response to ENSO events.
      Biogeochemistry. 81: 131-143.
Ramirez, A. and C. M. Pringle. 2006.   Fast growth and turnover of chironomid assemblages
      in response to stream phosphorus levels in a tropical lowland landscape. Limnology and
     Oceanography 51:189-196.
Ramirez, A. , C. M. Pringle, and M. Douglas. 2006. Temporal and spatial patterns in stream
     physicochemistry and insect assemblages in a tropical lowland streams. Journal of the
    North American Benthological Society 25: 108-123.
Ardon, M., and C. M. Pringle. In press. Do secondary compounds inhibit microbial-
      and insect-mediated leaf breakdown in a tropical stream? Oecologia