Dynamic water storage is the water that remains for enough time in watersheds to influence streamflow generation, chemically weather rock and drive the release of solutes, breakdown organic carbon (C) through microbial activity, and sustain vegetation between periods of precipitation. The amount and connectivity of dynamic water stores control critical zone processes, including evapotranspiration, vegetation productivity and mortality, streamflow, weathering and solute transport. Here, we present recent advances and identify frontiers in the study of dynamic water storage in the critical zone, focusing on observational techniques for quantifying dynamic storage, advances in conceptual and numerical models that capture dynamic storage, and emerging hypotheses that drive dynamic storage evolution. We specifically identify and focus on four primary dynamic water storages: snow, plant‐accessible water, groundwater, and surface water. While we use semi‐arid mountain environments as an exemplar of dynamic storage controls on critical zone processes, this work offers implications for a broad range of geoclimatic settings.

Despite a multitude of small catchment studies, we lack a deep understanding of how variations in critical zone architecture lead to variations in hydrologic states and fluxes. This study characterizes hydrologic dynamics of 15 catchments of the U.S. Critical Zone Observatory (CZO) network where we hypothesized that our understanding of subsurface structure would illuminate patterns of hydrologic partitioning. The CZOs collect data sets that characterize the physical, chemical, and biological architecture of the subsurface, while also monitoring hydrologic fluxes such as streamflow, precipitation, and evapotranspiration. For the first time, we collate time series of hydrologic variables across the CZO network and begin the process of examining hydrologic signatures across sites. We find that catchments with low baseflow indices and high runoff sensitivity to storage receive most of their precipitation as rain and contain clay‐rich regolith profiles, prominent argillic horizons, and/or anthropogenic modifications. In contrast, sites with high baseflow indices and low runoff sensitivity to storage receive the majority of precipitation as snow and have more permeable regolith profiles. The seasonal variability of water balance components is a key control on the dynamic range of hydraulically connected water in the critical zone. These findings lead us to posit that water balance partitioning and streamflow hydraulics are linked through the coevolution of critical zone architecture but that much work remains to parse these controls out quantitatively.

A pipeline, known as Sabal Trail Pipeline, for natural gas transport has been proposed to extend from Alabama to Florida, passing through a very fragile and mostly uncovered karst terrain in Florida. There is considerable concern as to the structural integrity of the pipeline as well as its potential impacts on the environment, particularly on groundwater quality of the Floridan aquifer. Using Geographic Information Systems, this study examines the extent of karst in the proposed trail route and suggest two new alternative routes with significantly less karst development. Mean depression density within 5 km of the proposed Sabal Trail route is 5.2 depressions per km2, with a spatial coverage of 12.2%. Depressions within the alternative route have significantly lower density -2.1 depressions per km2 and much smaller spatial coverage; 5.7%. The routes were also compared with respect to intersected land cover categories.