Land-cover Impact on Hydro-chemical Metrics of a Tropical Montane Forest Catchment: a Paired Catchment Assessment between Pristine Conditions and Human Induced Pastures

Abstract:

Many South American headwaters are characterized by land use changes through forest clear-cut and subsequent pasture use. Research on this topic in tropical montane cloud rainforest systems is particularly scarce. Here we present data of a paired-catchment experiment to compare the hydrological functioning of two tropical montane cloud forest catchments, one in pristine conditions and another with a strong dominance of pastures—resulting from slash and burn as well as cattle grazing in the last three decades. The catchments are comparable in size (69 – 123 ha), characteristic steep slopes: 88 and 67% —for forest and pastures catchment respectively—, and similar geology. Both catchments belong to the San Francisco river catchment (79.6 km2), a north-western headwater tributary of the Amazon Basin. Results –based on the comparison of hydrometric and topographic indices, land-cover types, and major chemical element concentrations of stream waters— reveal substantial differences between their hydrological behaviors. The pasture catchment accounts for higher base flows (Base Flow Index, 0.73 versus 0.58), longer mean transit times (4.2 versus 2.2 years) and a larger release of total suspended solids (2.73 versus 0.79 mg/L), among many other contrasting metrics. The present findings indicate that although the variation of some metrics between the study sites could be linked to differences in their physical catchment characteristics (e.g., topography or aquifer size for MTT), others could be associated to human induced shifts in land-cover, pointing out that noticeable changes it the hydrological processes of our study catchments could be traced in a relatively small period of time. Tracking these differences is not a trivial matter if we have in mind the advantages of forests ecosystem services compared to pastures: higher evapotranspiration rates and superior efficiency in soil conservation and carbon capture.