Quantifying solute input, export, and budgets in a tropical Andean páramo ecosystem comparing different methods with high-resolution data

Abstract

Monitoring solute fluxes in water quality studies can reveal ecosystem disturbances, which can be particularly useful in Andean headwater catchments as they are the main water providers for downstream populations. However, such studies have mainly focused on organic matter and nutrients, disregarding other solutes that can threaten water quality (e.g. arsenic, lead, calcium, magnesium). Additionally, low-resolution (weekly or monthly) routine sampling schemes, may overlook important solute dynamics. Therefore, we collected water samples every four hours for analysis of twenty-four solutes in a pristine tropical Andean páramo catchment. Solute fluxes were calculated with five different methods. The 4-hourly data set was filtered to test for an optimum sampling frequency without compromising the export rates. The results showed that the interpolation export method of the available 4-hourly data was the best suited due to a weakly correlation with discharge. From the twenty-four solutes analyzed, DOC, TNb, Si, Ca, Mg, K, and Na presented the highest input (i.e., DOC = 4.167E+08 mEq km-2 yr-1 and Si = 1.729E+07 mEq km-2 yr-1 ) and export rates (i.e., DOC = 2.686E+08 mEq km-2 yr-1 and Si = 2.953E+08 mEq km-2 yr-1 ). DOC, TNb, NH4, NO2, NO3, PO4, Al, B, Cu, Fe, Zn. As, Cd, Cr, Pb, and V presented more input than export, while Ca, K, Mg, Na, Rb, Si, Sr, and Ba presented more export than input (geogenic sources). Filtered sampling frequencies demonstrated that a minimum of daily grab samples would be required to obtain reliable export rates with errors consistently below 10% compared to the 4-hourly solute export. These findings can be particularly useful for the implementation of long-term monitoring programs at low costs and maintenance and provide for the first time high-quality information about biogeochemical budgets in a pristine páramo catchment.