Chemical mixing model of streamflow generation at La Selva Biological Station, Costa Rica.
Abstract: La Selva Biological
Station occupies an area of lowland tropical rainforest in central Costa
Rica. Sodium and chloride data were used to quantify the mixing proportions
of local runoff and geothermal groundwater at several sites throughout
the stream channel system in late April, at the end of the dry season.
The fraction of streamflow accounted for by geothermal groundwater varied
spatially between 0 and 0.85, indicating a significant contribution
to streamflow and to stream solute loads from geothermal groundwater at
some sites. In general, higher inputs of geothermal groundwater were
found at lower elevations. Over half the flow from one basin (the
Salto) was due to geothermal groundwater, suggesting a minimum annual runoff
of about 0.7 m of geothermal groundwater from this basin. A plot
of Na/Cl vs. fraction of geothermal groundwater revealed watershed-scale
chemical differences between the two major drainage systems (the Sura and
the Salto), differences that were note apparent from a traditional two-solute
plot of Cl vs. Na concentration. A small (21 mm) storm produced relatively
little change in mixing proportions, as most throughfall was apparently
retained in the relatively dry soils.
Genereaux, 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.
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