Tesis Doctoral/PHD

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Browsing Tesis Doctoral/PHD by Author "Crespo Sánchez, Patricio Javier"

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    Bridging the gap between hydrological and biogeochemical processes in a high Andean catchment: a comprehensive tracer-aided model framework
    (Universidad de Cuenca, 2023-09-29) Pesántez Vallejo, Juan Patricio; Crespo Sánchez, Patricio Javier; Birkel, Christian; Célleri Alvear, Rolando Enrique
    The Andean mountains satisfy the vital needs of the Andean population and its lowlands. However, they are projected to experience significant impacts attributed to land-use change and climate change. Despite our understanding of the hydrology in these areas, to date, there has been no modeling framework that incorporates direct data acquisition, simple models, and extends to a distributed modeling framework. Such a framework should be able to elucidate hydrological and biogeochemical processes in a manner comprehensible to decision-makers. Therefore, the primary objective of this thesis is to spatially and temporally assess the production and distribution of water and dissolved organic carbon (DOC) in a páramo catchment using tracer-aided models. To achieve this, we have monitored hydrometeorological and biogeochemical parameters, as well as water stable isotopes. In combination with field observations and perceptual knowledge of these catchments, we evaluated them within a comprehensive hydrological modeling framework. We found that DOC and other solutes can be estimated through in-situ spectrometry. Using these solutes as tracers made it possible to compare different hydrological pathways and was the only way to identify that streamflow response consisted of near-surface rapid flow, more mixed flow through the two main soil types, as well as flow from shallow fractured rock, especially under base flow conditions. Based on the hydrological processes found, a new module was developed to simulate DOC production and incorporate it into a spatially distributed hydrological model at a high spatial (10 x 10 meters) and temporal (1 hour) resolution. This model allowed us to identify DOC hots pots and hot moments. The results showed increased hydrological connectivity between hillslopes and valleys with increasing precipitation. Wetter conditions also favored DOC production, especially in valleys (Histosols), and DOC transport to the river. Our findings suggest that minor changes in meteorological conditions directly affect water dynamics in páramo soils and its biogeochemistry. These conclusions will enable informed decisions to be made regarding water security, taking into account the effect of carbon loss from the soils to the rivers in the páramo.
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    Disentangling water transport and tracer mixing mechanism in mountainous environments influenced by volcanic features
    (Universidad de Cuenca, 2020-06-16) Mosquera Rojas, Giovanny Mauricio; Crespo Sánchez, Patricio Javier
    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.
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    Evaluating electrical conductivity as a surrogate tracer to determine the factors controlling event and pre-event water flow partitioning at a tropical montane Andean ecosystem
    (Universidad de Cuenca, 2024-09-17) Lazo Jara, Patricio Xavier; Crespo Sánchez, Patricio Javier; Segura, Catalina
    The results of this thesis showed that electrical conductivity could be used as an alternative to Oxygen-18 as a tracer for event and pre-event water flow partitioning analyses which highly increases the temporal resolution of tracer concentrations while reducing the uncertainty of the tracer-aided model. The results showed great similarity under a large range of flow conditions, reassuring the consistency of the estimated fractions with 89% of the monitored events showing differences lower than 20% in pre-event water fraction regardless of the antecedent moisture and rainfall conditions. The use of electrical conductivity was possible due to a quasi-conservative behavior related with the presence of organic-rich riparian soils (peat-type) overlying compact bedrock across the catchment. This highlights the potential of electrical conductivity to obtain high temporal frequency data while lowering the costs needed to implement and keep tracer data collection up for long time periods. In addition, results from the comparison of models with different complexities also showed great similarity in their estimations of the event and pre-event water fractions as long as appropriate concentrations of event (Ce) and pre-event (Cp) water for the simpler model are set. In fact, Cp showed to be the most important factor for improving accuracy while Ce had little influence on the results. Hence, the best way to determine Cp was the concentration of a streamflow sample taken before the beginning of each event. These findings will allow to reduce the logistical and economical resources needed to adequately assess hydrograph separation and to carry out quasi-continuous assessments of flow partitioning with high accuracy in high-Andean montane ecosystems. The previous results led to the analysis of several spatial and temporal factors controlling event and pre-event water fractions. This allowed us to obtain tracer and hydrometeorological high-frequency data from a large number of rainfall-runoff events (n=72). The correlations showed that the main temporal controlling factor was rainfall amount with a strong (i.e., r>0.7) and significant (i.e., p<0.05) positive correlation with the event water fraction, whereas, soil type, vegetation cover, and topography were highly correlated when considering the spatial factors. These results suggested an enhanced shallow subsurface hydrological connectivity between hillslopes and riparian wetlands which follow in an increase of event water fraction for events that show higher peak flows while a threshold is exceeded. Overall, our findings suggests that high temporal resolution data is extremely necessary to adequately assess event and pre-event water fraction flow partitioning as it helps to obtain a complete understanding of catchment hydrological behavior at scale event. This improved understanding could aid in the implementation of science-based water management strategies that includes many processes that are often overlooked.