Download or read book Microbial and Geochemical Dynamics in Soils and Their Impact on the Hydraulic Properties : from Laboratory Experiments to Model Development written by Albert Carles Brangarí and published by . This book was released on 2018 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most of the microorganisms on Earth are found in sophisticated colonies called biofilms. Such microbial communities may proliferate everywhere life can exist as long as nutrients are available and surface attachment is possible. Some biofilms can provide valuable services to the society or to the functioning of ecosystems, while others are potentially troublesome and may contribute to health, ecological and economic problems. Particularly, in porous media, a sound characterization of the microbial dynamics is key for the design and management of many technological applications. Literature contains a vast number of experiments and model approaches that have certainly contributed to a better understanding. However, the driving forces behind microbial proliferation in soils are not yet well understood. Difficulties mostly arise from the complex nature of the interactions between microbial pools, porous media and environmental conditions. First, microbes drive the biogeochemical processes, promoting the degradation of organic matter and contaminants. Second, the accumulation of biomass in soils alters their hydraulic properties, changing the capacity to transport and retain water and solutes. Third, organisms may deploy survival mechanisms in response to environmental stresses. On one hand, biofilm matrix helps increasing the hydration status and improving the digestive system efficiency. On the other hand, microbes may be induced into a reversible state of dormancy under unfavorable conditions. The mechanisms by which this microbial habitat is regulated and the resulting impact on the hydraulic properties frame the scope of this contribution. The main outcome of the thesis consists in a new soil microbial model framework that can be used as an explorative tool to elucidate the processes occurring in bio-amended soils. Based on extensive empirical evidence, the model includes: (i) the relevant microbial compartments that permit capturing the complexity of biofilms, (ii) some mechanisms to modulate microbial dynamics according to environmental conditions; and (iii) the feedbacks between biofilms, the soil hydraulic properties and the overall conditions in the vicinities of cells. This document is structured in five chapters. In Chapter 1 the main characteristics of microbial proliferation and its impact on soils are described. In Chapter 2, two laboratory experiments aimed at unraveling the spatiotemporal biogeochemical dynamics in soils under continuous or intermittent ponding conditions are described. Several direct and indirect measurements of biomass and activity reported evidence of microbial adaptation to the environmental circumstances. Chapter 3 presents a mechanistic model to study the impact of biomass accumulation on the variably saturated hydraulic properties of soils. Special emphasis is laid on the mechanisms behind water flow and retention. The biofilm represents bacterial cells and extracellular polymeric substances (EPS), displaying a complex channeled geometry that shrinks/swells with suction. New analytical solutions of the soil-water retention curve and the relative permeability are derived and discussed. In Chapter 4 a model that can simulate the proliferation of multi-compartment biofilms is presented. Such an approach permits unraveling the microbial dynamics in different environments and the underlying mechanisms controlling the response to stress. To achieve this, the model is equipped with indicators to monitor environmental and biological factors and react accordingly. Finally, Chapter 5 comprises a summary of the most important conclusions drawn during the course of the thesis. In general, the model is able to reproduce meaningfully a number of complex experimental processes. The most important mechanisms behind microbial and geochemical dynamics in soils and their impact on the hydraulic properties have been partially elucidated.