Landscape patterns

Patterns at La Selva

Long-term Monitoring

Experimental Phosphorus Erichment

Publications

Landscape patterns in stream chemistry in Costa Rica

    Surface waters draining three different volcanoes in Costa Rica, ranging from dormant to moderately active to explosive, have a wide range of solute compositions that partly reflect the contribution of different types of solute-rich, geothermal waters. Three major physical transport vectors affect flows of geothermally-derived solutes:  thermally driven convection of volcanic gases and geothermal fluids;  lateral and gravity-driven downward transport of geothermal fluids;  and wind dispersion of ash, gases, and acid rain. Specific vector combinations interact to determine landscape patterns in solute chemistry and biota:  indicator taxa of algae and bacteria reflect factors such as high temperature, wind-driven or hydrologically transported acidity, high concentration of various solutes, and chemical precipitation reactions. Many streams receiving geothermally-derived solutes have high levels of soluble reactive phosphorus (up to 400 mg L^-1), a nutrient that is typically not measured in geochemical studies of geothermal waters.  Geothermal activity along the volcanic spine of Costa Rica provides a natural source of phosphorus, silica, and other solutes and plays an important role in determining emergent landscape patterns in the solute chemistry of surface waters and aquatic biota (Pringle et al. 1993).
 

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    Geothermal groundwater springs of the sodium-chloride-bicarbonate type modify the chemistry of streams that drain La Selva Biological Station. These springs are NOT elevated in temperature and the waters have long since cooled during lateral transport. Streams receiving geothermalwaters are solute-rich and co-occur with solute-poor streams that do not receive geothermal inputs.  Geothermal waters contain high concentrations of Ca, Fe, Mg, Na, Si, Cl, SO₄, soluble reactive phosphorus, and total phosphorus.  Most geothermal waters that have been identified to date issue near the terminus of the youngest lava flow known for La Selva.  The two major streams of La Selva, the Salto and Sura, are both modified by inputs of geothermal waters and their main channels follow the lateral margins of the youngest lava flow, where it overlies older flows. Discharge points of geothermal seepages appear to be determined by the shape and hydrogeological properties of the lava flows and possible faulting.  The lower watershed of the Salto exhibits a large spatial variability in phosphorous concentration (5-250 mg L^-1) and conductivity (25-440 mS cm^-1) that reflects the heterogeneous location of  geothermal seepages.  Spatial and temporal pattern in nutrient limitation of algal growth in light gaps are controlled by the presence / absence of geothermally- introduced phosphorus and / or physical / hydrologic characteristics of the stream channel that influence surface-subsurface exchange rates (Pringle 1991).
 

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    In 1996 we began long-term monitoring of stream solute chemistry that incorporates important geomorphic features associated with local watershed runoff and geothermal inputs along the two major stream drainages at La Selva (Salto and Sura streams).  Spatial and temporal patterns in the solute chemistry of surface- and ground-water appear to be related to three major geomorphic features of the volcanic landscape: (1) upland Pleistocene lavas drained by high-gradient streams that are phosphorus-poor, (2) a "gradient break" at or near where phosphorus-rich springs emerge, and (3) lowland alluvial areas drained by low-gradient streams that are often phosphorus-rich.  Process-oriented studies in the Salto stream have allowed us to link solute chemistry and transport data in representative geomorphic sub-features of the landscape to ecosystem-level processes. (Map of La Selva) (Triska et. al. a, b submitted) (see Ecology and Natural History)
 

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    Although phosphorus is a main component of geothermally modified groundwater entering La Selva streams, it is not the only solute.  Groundwater inputs are also rich in Si, Ca, Mg, SO4 and other solutes (Pringle 1991).  In order to isolate the influence of phosphorus in the absence of these other solutes, we are evaluating the long-term (began in 1998) in situ effects of a whole-stream phosphorus enrichment.
    In July 1998 we began a long-term phosphorus-enrichment experiment in a 2nd -order phosphorus-poor stream (Carapa) to evaluate phosphorus-effects on insect assemblages.

    We have found that:

• Experimental phosphorus enrichment of a phosphorus-poor stream will increase microbial respiration rates, leaf decomposition rates, bacterial and fungal biomass accrual rates, insect growth rates, and insect secondary production below the point of enrichment. (Ramirez et. al. 2003)
• Experimental phosphorus enrichment affects breakdown rates of high quality leaves more than low quality eaves (Ardon, in progress)
• Nitrogen does not become secondary limiting under phosphorus-rich conditions (Stall cup 2004)

Duff, J. H., C. M. Pringle and F. J. Triska. 1996. Denitrification in sediments of a lowland tropical stream draining swamp forest. Biogeochemistry 33: 179-196.

Eklund, T. J., W. McDowell, and C. M. Pringle. 1997.  Seasonal patterns in tropical precipitation chemistry: La Selva, Costa Rica.  Atmospheric Environment. 31: 3903-3910.

Genereux, D. and C. M. Pringle. 1997. Chemical mixing model of streamflow generation at La Selva Biological Station, Costa Rica. Journal of Hydrology 199: 319-330.

Genereux, D., S. Wood, and C.M. Pringle. 2002. Chemical tracing of interbasin groundwater transfer in the lowland rainforest of Costa Rica. Journal of Hydrology. 258: 163-178.

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., 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 F. J. Triska.  1991.  Effects of geothermal waters on nutrient dynamics of a lowland Costa Rican stream. Ecology 72: 951-965.

Pringle, C. M. and F. J. Triska. 1991.  Variation in phosphate concentrations of small order streams draining volcanic landscapes in Costa Rica: Sources and implications for nutrient cycling, pp 70-83. In: H. Tiessen, D. Lopez-Hernandez and I. H. Salcedo (eds.) Phosphorus cycles in terrestrial and aquatic ecosystems. Regional Workshop 3: South and Central America. Organized by the Scientific Committee on Problems of the Environment (SCOPE) and the United Nations Environmental Program (UNEP), Maracay, Venezuela, l989. Turner-Warwick Communications, Saskatoon, Canada, 257 p.

Pringle, C. M., and F. J. Triska.   2000.  Emergent biological patterns in streams and surface-subsurface water interactions at landscape scales, Chapter 7,  pp. 167-193. In: J. B. Jones and P. J. Mulholland  (eds.) Streams and Groundwaters. Academic Press.

Pringle, C. M., F. J. Triska, and G. J. Browder  1990.  Spatial variation in basic chemistry of streams draining a volcanic landscape on Costa Rica's Caribbean slope. Hydrobiologia 206: 73-86.

Small, G. E., and C. M. Pringle ,et al.  2008.   Phosphorus uptake dynamicsuring an eight-year P-addition in a Neotropical headwater stream.  Verhandlungen  Internationale Verein.  Limnol.  30: 1-4.

Triska, F. J., C. M. Pringle, G. Zellweger, J. H. Duff and R. J. Avanzino. 1993. Dissolved inorganic nitrogen composition, transformation, retention and transport in naturally phosphate-enriched and unenriched tropical streams. Canadian Journal of Fisheries and Aquatic Sciences 50: 665-675.

Triska et al. 2006. Soluble reactive phosphorus (SRP) transport and retention in tropical, rain forest streams draining a volcanic and geothermally active landscape in Costa Rica.1: Long-term concentration and pore water environment.  to Biogeochemistry 00:00-00.

Dissertations

Ramírez, A. 2001. Control of benthic assemblages in detritus-based tropical streams. University of Georgia, Athens, GA.

Ardon, M. 2006. Exogenous versus endogenous control of microbially-mediated decomposition in lowland neotropical streams. University of Georgia, Athens, GA.

Small, G. In Progress. Resource-consumer stoichiometry along a natural phosphorus gradient in Neotropical stream food webs.  University of Georgia, Athens, GA.

Master's Theses

Stallcup, L. 2004. Effects of water chemistry and leaf species on leaf breakdown in neotropical headwater streams. University of Georgia, Athens, GA.

Ramírez, A. 1997. Structure, function and production of benthic macroinvertebrate communities in lowland tropical streams, Costa Rica. University of Georgia, Athens, GA.
 
 
 

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