Effects of geothermal waters on nutrient dynamics of a lowland Costa Rican stream.
Abstract: Spatial and temporal
variability of surface and groundwater nutrient chemistry was contrased
between the two tributaries of the Salto River, which drain the terminus
of Pleistocene lava flows in the Atlantic slope foothills of Barva Volcano,
Costa Rica. Some riparian zones along the Salto are saturated by subsurface
inflows of phosphorus rich geothermal groundwater of the sodium-chloride-bicarbonate
type. The heterogeneous pattern of solute-rich groundwater inflows results
in dramatic differences in soluble reactive phosphorus (SRP) concentration
between stream waters of two closely adjacent tributaries. SRP levels also
vary dramatically in the water table and in soils across stream riparian
zones on a scale of metres. The Salto River (SRP 50-200 µg/L) receives
steady phosphorus-rich groundwater inflows that become diluted with increasing
precipitation. The Pantano lacks these inputs and retains a low background
SRP concentration (typically <10 µg/L). SRP levels in waters of
the Salto were strongly negatively correlated with discharge (r=-0.86).
while in the Pantano ther was no correlation.
In situ nutrient bioassays of algal periphyton growth indicated that both nitrate and SRP were at growth saturating levels in the Salto, while , in the Pantano, algal growth was phosphorus limited. The Pantano had a high retention capacity for phosphorus as measured through a whole stream tracer injection experiment. SRP concentration was reduced by 17 and 94% of injected phosphate over 40 and 800 m reaches, respectively. Results indicate the important linkage between geothermal activity and hydrogeochemical features of the volcanic landscape and their role in regulating ecological processes in these streams.
In situ nutrient bioassays of algal periphyton growth indicated that both nitrate and SRP were at growth saturating levels in the Salto, while , in the Pantano, algal growth was phosphorus limited. The Pantano had a high retention capacity for phosphorus as measured through a whole stream tracer injection experiment. SRP concentration was reduced by 17 and 94% of injected phosphate over 40 and 800 m reaches, respectively. Results indicate the important linkage between geothermal activity and hydrogeochemical features of the volcanic landscape and their role in regulating ecological processes in these streams.
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.
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