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The structure, function, and dynamics of Earth's terrestrial ecosystems are profoundly influenced by the frequency and duration that they are inundated with water. A diverse array of natural and human engineered systems experience temporally variable inundation whereby they fluctuate between inundated and non-inundated states. Variable inundation spans from extreme flooding and droughts to predictable sub-daily cycles. Variably inundated ecosystems (VIEs) include hillslopes, non-perennial streams, wetlands, floodplains, temporary ponds, tidal systems, storm-impacted coastal zones, and human engineered systems. VIEs are diverse in terms of inundation regimes, water chemistry and flow velocity, soil and sediment properties, vegetation, and many other properties. The spatial and temporal scales of variable inundation are vast, ranging from sub-meter to whole landscapes and from sub-hourly to multi-decadal. The broad range of system types and scales makes it challenging to predict the hydrology, biogeochemistry, ecology, and physical evolution of VIEs. Despite all experiencing the loss and gain of an overlying water column, VIEs are rarely considered together in conceptual, theoretical, modeling, or measurement frameworks/approaches. Studying VIEs together has the potential to generate mechanistic understanding that is transferable across a much broader range of environmental conditions, relative to knowledge generated by studying any one VIE type. We postulate that enhanced transferability will be important for predicting VIE function under future, potentially non-analog, environmental conditions. Here we aim to catalyze cross-VIE science that studies drivers and impacts of variable inundation across Earth's VIEs. To this end, we complement expert mini-reviews of eight major VIE systems with overviews of VIE-relevant methods and challenges associated with scale. We conclude with perspectives on how cross-VIE science can derive transferable understanding via a 'continuum approach' in which the impacts of variable inundation are studied across multi-dimensional environmental space. [ABSTRACT FROM AUTHOR]

The impact of fines migration on fracture transmissivity reduction was investigated by injecting a brine solution containing a suspension of 0.1 wt.% kaolinite particles with a mean particle size distribution of 9.6 μm through fractured shale core samples. The fractures had apertures estimated to be approximately 100 μm. A mass balance approach was used to determine the quantity of kaolinite that was deposited within the fractures (influent – effluent = amount deposited in fractures). Large fractions (44–90%) of the suspended kaolinite pumped through the fractures were deposited within the fractures. Based on fracture volumes estimated with X‐ray computed tomography, it was determined that approximately 10 to 17% of the fracture volume was filled with kaolinite at the point when flow was completely restricted. These results indicate that 100 μm fractures in CO2 reservoir caprocks could be sealed within hours if the brines passing through the fractures contain a proportional volume of particulates to the tests performed in this laboratory study. © 2021 Battelle Memorial Institute. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Cement samples were reacted with CO2-saturated synthetic groundwater, with or without added H2S (1 wt.%), at 50°C and 10 MPa for up to 13 months (CO2 only) or for up to 3.5 months (CO2 + H2S) under static conditions. After the reaction, X-ray computed tomography (XCT) images revealed that calcium carbonate (CaCO3) precipitation occurred extensively within the fractures in the cement matrix, while micro-fractures with aperture size <∼50 μm at the cement-basalt interface were completely sealed by CaCO3 precipitation. Exposure of a fractured cement sample to CO2-saturated groundwater (50°C and 10 MPa) over a period of 13 months demonstrated progressive healing of cement fractures by CaCO3 precipitation. After reaction with CO2 + H2S-saturated groundwater, CaCO3 precipitation also occurred within the cement fracture as well as along the cement-basalt caprock interfaces. X-ray diffraction analysis showed that major cement carbonation products of the CO2 + H2S-saturated groundwater were calcite, aragonite, and vaterite, all consistent with cement carbonation by CO2-saturated groundwater. While pyrite is thermodynamically favored to form, due to the low H2S concentration it was not identified by XRD in this study. The cement alteration rate into neat Portland cement samples by CO2-saturated groundwater was similar at ∼0.02 mm/d based on XCT images, regardless of the cement-curing pressure and temperature (P-T) conditions, or the presence of H2S in the groundwater. The experimental results imply that wellbore cement with micro-fractures within the cement matrix or along the cement-caprock interface (<∼200 μm aperture under current experimental conditions) is likely to be healed by CaCO3 precipitation during exposure to CO2- or CO2 + H2S-saturated groundwater. Published 2016. This article is a U.S. Government work and is in the public domain in the USA [ABSTRACT FROM AUTHOR]