Geothermal waters surface at La Selva Biological Station, Costa Rica: Volcanic processes introduce chemical discontinuities into lowland tropical streams.
Abstract: Dilute geothermal
springs of the sodium-chloride-bicarbonate type modify the chemistry of
receiving streams draining La Selva Biological Reserve in the Caribbean
lowlands of Costa Rica. Streams receiving geothermal waters are solute-rich
and co-occur with solute-poor streams that do not receive geothermal inputs.
Geothermal waters contain significantly greater concentrations of Ca, Fe,
Mg, Na, Si, Cl, SO4, soluble reactive phosphorus (SRP), and total phosphorus
(TP) than waters unmodified by geothermal inputs. Streams that do not receive
geothermal inputs are solute-poor, typically containing < 10 percent
relative concentration of each of the solutes mentioned above. 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 rivers 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 River exhibits a large spatial variability in phosphorous concentration
(5-250 mg L-1 SRP) and conductivity (25-440 mS cm-1) that reflects the
heterogeneous location of geothermal seepages. Geothermal processes
introduce natural chemical discontinuities into stream continua that can
affect nutrient limitation of algal growth and potentially primary production.
In addition, geothermal upwellings represent a source of variation in soil
phosphorous levels that is relatively independent of the composition of
parent material in the surficial catchment and may potentially influence
plant growth and demography.
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.
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