Spatial variation in basic chemistry of streams draining a volcanic landscape on Costa Rica's Caribbean slope.
Abstract: Spatial
variability
in selected chemical, physical and biological parameters was examined
in
waters draining relatively pristine tropical forests spanning
elevations
from 35 to 2600 meters above sea level in a volcanic landscape on Costa
Rica's Caribbean slope. Waters were sampled within three different
vegetative
life zones and two transition zones. Water temperatures ranged from
24-25
degree C in streams draining lower elevations (35-250 m) in tropical
wet
forest, to 10 degree C in a crater lake at 2600 m in montane forest.
Ambient
phosphorus levels (60-300 mu g SRP/L; 66-405 mg TP/L) were high at
sites
within six pristine drainages at elevations between 35-350 m, while
other
undisturbed streams within and above this range in elevation were low
(typically
<30.0 mg SRP/L). High ambient phosphorus levels within a given
stream
were not diagnostic of riparian swamp forest. Phosphorus levels (but
not
nitrate) were highly correlated with conductivity, Cl, Na, Ca, Mg and SO4.
Results indicate two major stream types: 1) phosphorus-poor streams
characterized
by low levels of dissolved solids reflecting local weathering
processes;
and 2) phosphorus-rich streams characterized by relatively high Cl,
SO4,
Na, Mg, Ca and other dissolved solids, reflecting dissolution of
basaltic
rock at distant sources and/or input of volcanic brines.
Phosphorus-poor
streams were located within the entire elevation range, while
phosphorus-rich
streams were predominately located at the terminus of Pleistocene lava
flows at low elevations. Results indicate that deep groundwater inputs,
rich in phosphorus and other dissolved solids, surface from basaltic
aquifers
at breaks in landform along faults and/or where the foothills of the
central
mountain range merge with the coastal plain.
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.
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