Abstract:
Abstract We investigated controls on the water chemistry of a South Ecuadorian cloud
forest catchment which is partly pristine, and partly converted to extensive pasture. From
April 2007 to May 2008 water samples were taken weekly to biweekly at nine different
subcatchments, and were screened for differences in electric conductivity, pH, anion, as
well as element composition. A principal component analysis was conducted to reduce
dimensionality of the data set and define major factors explaining variation in the data.
Three main factors were isolated by a subset of 10 elements (Ca2?, Ce, Gd, K?, Mg2?,
Na?, Nd, Rb, Sr, Y), explaining around 90% of the data variation. Land-use was the major
factor controlling and changing water chemistry of the subcatchments. A second factor was
associated with the concentration of rare earth elements in water, presumably highlighting
other anthropogenic influences such as gravel excavation or road construction. Around
12% of the variation was explained by the third component, which was defined by the
occurrence of Rb and K and represents the influence of vegetation dynamics on element
accumulation and wash-out. Comparison of base- and fast flow concentrations led to the
assumption that a significant portion of soil water from around 30 cm depth contributes to
storm flow, as revealed by increased rare earth element concentrations in fast flow samples.
Our findings demonstrate the utility of multi-tracer principal component analysis to study
tropical headwater streams, and emphasize the need for effective land management in
cloud forest catchments.
