Multi-phase and multi-scale modeling of environmental flow : from magma dynamics to pollutant transport
Keywords: Sustainability.
Geophysics.

Environmental flows dynamically change the solid earth, form a key part of various ecosystems, and deeply shape our society. Pursuing sustainability requires advancing our understanding of various environmental flow systems, because they are associated with resources, environmental health, and natural hazards. However, establishing a comprehensive understanding of these systems is usually challenging because of the complexity of earth systems and the difficulty in directly observing the dynamically evolving flows. Numerical modeling have been an important approach in studying environmental flows, because it can both patch together available data to form a consistent picture of unobservable processes and decode the information in observations to help improving our interpretation of the valuable data. In this dissertation we present model frameworks that bridge numerical models with data for two types of environmental flows, magmatic flow in volcanic systems and pollution of surface water. The motivation of focusing on these two systems is to provide insights for tackling challenges in natural hazard and environmental enforcement. In Chapter 1, we introduce the context and challenges of studying environmental flows and provide an overview of each chapter. In Chapter 2, we present a model framework for quantifying the magma mixing in the conduit flow of persistently degassing volcanoes. This model framework consists of a conduit-flow model that simulates the dynamics of bubble-bearing magma in volcanic conduits, and a volatile-concentration model that bridges magma mixing with melt and gas composition. By quantifying how different rates of magma mixing in conduit flow alters the volatile concentrations of melt at depth and the compositions of volcanic gas, this study demonstrates that the observed compositions of melt inclusion and surface gas flux support the bidirectional conduit flow in persistently degassing volcanoes. In Chapter 3, we investigate the formation mechanism of quartz-hosted embayments and melt inclusions during the crystallization of silicic magma using direct numerical simulations. By integrating crystal growth, the evolution of water concentrations, and the flow of surrounding melt, this chapter proposes a formation mechanism of embayments and melt inclusions and provides new insights for interpreting their compositions. We find that water is more enriched in the interior of defects on crystal surface compared to the exterior because the removal of water from the interior is less efficient. The resultant lower disequilibrium in the defect interior causes lower growth rate than in the exterior, elongating the defect into an embayment. The melt entrapped by both embayments and melt inclusions may be enriched in incompatible components, such as water and carbon dioxide. The degree of enrichment depends on inclusion size, component abundance, the crystal growth regime, and the post-formation equilibration with surrounding melt. In Chapter 4, we propose a model framework for attributing agricultural phosphorus pollution in a river network at high spatiotemporal resolutions and to specific source types. This model framework consists of a forward model of nutrient transport and an inverse model with statistical inferences. We construct the prior distributions of source contributions by integrating data of nutrient input, nutrient uptake, and land use. We develop the nutrient transport model based on the river network and stream flow data. With the water-quality data, we update the prior distribution using the Approximate Bayesian Computation method to generate the posterior distributions of source contributions. Our attribution results reveal significant variability in subwatershed-scale phosphorus release. Phosphorus release is higher during spring planting than the growing period, with fertilizer contributing more SRP than manure and manure contributing most of the UP. The results also suggest locations for additional water-quality monitors by identifying regions with high contributions but ambiguous attribution results due to the lack of water-quality measurements and disagreements between existing datasets of nutrient input