Effects of flow intermittence on dissolved organic matter quality

• Autores: Verónica Granados Pérez
• Directores de la Tesis: Andrea Butturini (dir. tes.), Biel Obrador Sala (codir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2022
• Idioma: inglés
• Tribunal Calificador de la Tesis: Isabel Muñoz Gràcia (presid.), Anna Maria Romani Cornet (secret.), Núria Catalán García (voc.)
• Programa de doctorado: Programa de Doctorado en Ecología, Ciencias Ambientales y Fisiología Vegetal por la Universidad de Barcelona
• Materias:
  • Química
    • Química analítica
      • Espectroscopia Raman
    • Química inorgánica
      • Química del agua
    • Química orgánica
      • Química de carbonio
  • Ciencias de la tierra y del espacio
    • Hidrología
      • Limnología
• Enlaces
  • Tesis en acceso abierto en: TESEO
• Resumen

  • Water availability is the primary driver of dissolved organic matter (DOM) dynamics in intermittent rivers and ephemeral streams (IRES). Therefore, current research manifests the global influence of flow disruption on organic matter transport and processing, given the wide distribution of intermittent flow watercourses. However, there are still gaps of flow intermittence knowledge, forgetting the continuous and multidimensional nature of the drying disturbance. In this context, in chapter three, we determine the influence of opposite flow conditions, drought and high flow on DOM properties and how the river continuum can cushion the impact of contrary hydrology on DOM and inorganic solutes. Further, in chapter four, we study the evolution of the dry period as a “film frame”, evaluating the diminution of flow daily, especially after the flow disruption. Then, how the hydrological connectivity influences the response timing and shape of the biogeochemical variables analysed and if they are influenced by spatial position, water temperature and volume of the disconnected. Finally, in chapter five, from a multi catchment approach of IRES with a gradient of intermittence from permanent to ephemeral, we investigated how multiple drying components shape dissolved organic matter (DOM) and dissolved organic carbon (DOC). Hence, in the results in chapter three, the DOM quality changed according to hydrology. DOM under high flow conditions was more terrigenous, humified, aromatic, and degraded, and the concentration gradually increased downriver. In contrast, DOM was less degraded and more aliphatic under drought conditions. However, the hydrological variability did not impact the DOM quality uniformly along the river continuum: DOM quality is more sensitive to hydrological changes in headwaters than in downriver reaches. In chapter four, the drying period determined the disruption of the fluvial continuum with a recession of stream continuum at a rate of ~60m/d and the gradual formation of a patched system of isolated pools of different sizes. Our results showed that the time that had elapsed since isolated pool formation (CI-days) was an essential factor for understanding how drying shaped the biogeochemistry of the fluvial system. Overall, drying caused a high DOC concentration and an increase in the humic-like fluorescence signal. Additionally, solutes showed contrasting responses to hydrological disconnection. Thus, we identified three temporal responses on the variables studied: 1) some inorganic solutes reacted before the fragmentation (CI-days<0). Then, DOM optical qualitative parameters replied after the fragmentation (CI-days>0), and 3) BIX and HIX did not show significant differences throughout the dry period. Finally, in chapter five, the sampling was performed during post-drought season and the results showed changes in DOC were driven by annual drying duration, whereas multiple drying components better explained DOM quality. So, we found high DOC concentration and prevalence of terrestrial DOM sources when drying is more extended and more frequent. Furthermore, because of the time of sampling, the DOM quality of the stream reconnection described a catchment “washed” with a terrestrial DOM origin, and it is transported downriver quickly without being processed for the microbial community. The findings of this thesis reveal the role of hydrology as a main driver of DOM dynamics. In particular, the flow disruption does not induce a single biogeochemical response but rather stimulates a set of solute-specific responses that generates a complex biogeochemical mosaic in a single fluvial unit. Furthermore, the necessity of considering multiple drying elements as annual or previous to predict organic matter dynamics on IRES and highlight these systems influence on the global carbon budget.