doctoralThesis
Disentangling water transport and tracer mixing mechanism in mountainous environments influenced by volcanic features
Autor
Mosquera Rojas, Giovanny Mauricio
Institución
Resumen
Landscape features of volcanic origin influence the transport of water and solutes
across high-elevation environments. Nevertheless, knowledge regarding how these
features affect subsurface hydrological behavior at different spatial scales (from
plot to catchment) is scarce. The effect of the soils originated from volcanic ash,
such as Andosols (or Andisols), and the influence of highly fractured geology of
volcanic origin on subsurface hydrological behavior and water flow path delineation
are poorly understood. To fill this knowledge gap, I took as the main objective in
the doctoral project the analysis of how Andosols and fractured volcanic geology
influence flow transport and tracer mixing mechanisms. Laboratory, experimental,
and field measurements of the water retention curve (WRC) of Andosols in
combination with data extracted from the published literature shows that standard
laboratory methods resemble well a small portion of the wet range of the WRC,
specifically, from saturation to the matric potentials 3 to 5 kPa (pF 1.5-1.7). For
higher matric potentials, standard laboratory methods substantially overestimate
the water content of the soils in comparison to experimental and field
measurements. Further, a unique set of hydrometric, stable isotope, and soil
hydraulic properties data were evaluated to investigate how Andosols influence
water transport and tracer mixing mechanisms at a steep tropical hillslope. The
results from this analysis point to the dominance of vertical flow paths within the
soil matrix, despite the formation of a perched water layer below the root zone,
which mimics the hydraulic behavior of a wet, layered sloping sponge. Last, I used
a tracer-aided hydrological model (TraSPAN) calibrated for the stable isotopes of
water and electrical conductivity (or specific conductance) during a rainstorm event
for the analysis of the role of the fractured volcanic geology on flow transport and
tracer mixing at the catchment scale. The model structure that best simulated the
streamflow hydrograph and the tracers concentrations during a rainfall event
consisted of two water reservoirs representing the soils with high infiltration
capacity and the groundwater system formed in the fractured bedrock. During the
monitored event, only 13% of total precipitation was converted into runoff, with a
major proportion (75-81%) corresponding to pre-event water stored in the
catchment prior to the event. These findings indicate a large water storage capacity
of the system in the fractured volcanic geology.