In this study, we identify the key length and time scales associated with CO2 mineralization in basalt reservoirs. This is achieved through the development and application of a simple yet complete model of the fate and transport of a supersaturated CO2-charged fluid moving unidirectionally through an initially uniform basalt rock. The model consists of three coupled equations describing, (i) the spatiotemporal evolution of porosity with the mineralization reaction, (ii) the resulting temporal and spatially varying fluid discharge, and (iii) the fate and transport of the mineralization reactant(s) in the aqueous phase. A dimensional analysis provides length and time scales that characterize the extent and duration of field-scale carbon mineralization. These scales are applied to a field site to estimate poorly constrained mineralization parameters, notably, the effective first-order reaction rate constant.

Harmful algal blooms (HABs), in particular those consisting of the cyanobacteria \textit{Microcystis}, are becoming increasingly more common across the globe. Despite the growing body of evidence that suggests vertical heterogeneity of \textit{Microcystis} can be a precursor to HAB formation, the abiotic drivers of vertical distribution of \textit{Microcystis} are poorly understood in the field environment. The prediction of subsurface cyanobacteria is also pertinent because subsurface concentrations are not easily recognizable to the public or lake system managers, creating an unnoticed safety hazard. High-frequency temporal and vertical data were collected from an Eulerian research station anchored in a stratified and eutrophic lake for five months. Data show that the magnitude of the subsurface \textit{Microcystis} concentration peak and the center of gravity of the deep cyanobacteria layer are statistically significantly mediated by the thermal structure of the lake. The peak subsurface cyanobacteria biovolume scales linearly with the thermocline depth and temperature, whereas the center of gravity of the subsurface cyanobacteria biovolume scales linearly with the mixed layer depth and temperature. Furthermore, our data suggest there is a seasonal evolution of the subsurface cyanobacteria center of gravity that could potentially indicate timing of HAB onset. Based on easily measured parameters associated with the vertical lake temperature profile and meteorological conditions, we provide evidence of predictable trends in subsurface cyanobacteria variables.

We hypothesize that onshore saline groundwater in delta systems may have resulted from rapid shoreline progradation during the Holocene. To explore this hypothesis, we develop a model for the transport of saline groundwater in a shore-normal longitudinal cross-section of an evolving ocean margin. The transport model uses a control volume finite element model (CVFEM), where the mesh of node points evolves with the changing aquifer geometry while enforcing local mass balance around each node. The progradation of the shoreline and evolution of the aquifer geometry is represented by assuming the shoreline advances at a prescribed speed with fixed top and foreset slopes. The combined model of transport and progradation, is used to predict the transient trapping of saline water under an advancing shore-line across a range of realistic settings for shoreline velocity and aquifer hydraulic properties. For homogeneous aquifers, results indicate that the distance behind the shoreline, over which saline water can be detected, is controlled by the ratio of the shoreline prorogation rate to the aquifer velocity and the Peclet number. The presence of confining units probably had the greatest impact in sequestering onshore seawater behind an advancing shoreline. Further support for the validity of the proposed model is provided by fitting model predictions to data from two field sites (Mississippi River and Bengal Deltas); the results illustrate consistent agreement between predicted and observed locations of fossil seawater.

1. Harmful algal blooms are increasing in both severity and frequency across the globe. Many bloom-forming species are capable of vertical motility and colony formation. The cyanobacterium Microcystis aeruginosa is a common example of such a species, yet current models poorly predict vertical distributions of M. aeruginosa. 2. To couple the hydrodynamics, buoyancy, and the colony dynamics of Microcystis, we present a system of one-dimensional advection-diffusion-aggregation equations with Smoluchowski aggregation terms. 3. Results indicate Smoluchowski aggregation accurately describes the colony dynamics of M. aeruginosa. Further, transport dynamics are strongly dependent on colony size, and aggregation processes are highly sensitive to algal concentration and wind-induced mixing. Both of these findings have direct consequences to harmful algal bloom formation. 4. While the theoretical framework outlined in this manuscript was derived for M. aeruginosa, both motility and colony formation are common among bloom-forming algae. As such, this coupling of vertical transport and colony dynamics is a useful step for improving forecasts of surface harmful algal blooms.