Relating salt marsh pore water geochemistry patterns to vegetation zones and hydrologic influences

Zhang

Water Resources Research

et al. 2022

Tidal wetlands are connected with coastal estuarine systems and typically have a low-lying intertidal area with a more elevated supratidal zone (Sheaves & Johnston, 2008;Snedden et al., 2012). The low-lying intertidal wetland surface is regularly inundated by saline seawater from tidal creeks and drainage channels within the wetland (Wolanski & Elliott, 2016). This induces complex porewater-seawater mixing in the wetland aquifer. The abundance of salts in the wetland soil creates a brackish-saline environment, which selectively accommodates halophytic (salt-tolerant) species in the intertidal zone (Barbier et al., 2011).A large number of studies have previously been carried out to understand coastal hydrogeological processes in beach settings, including saltwater intrusion, submarine groundwater discharge (SGD), and upper saline plumes (e.g., Evans & Wilson, 2016;Li et al., 1999;Robinson et al., 2007). Similarly, the hydrology and ecology in tidal wetlands are strongly affected by the tide-influenced porewater flow and salt transport in the wetland subsurface (Hughes, 2016;Moffett et al., 2012;Ursino et al., 2004). However, subsurface hydrology in tidal wetlands, particularly the salt transport patterns, is understudied compared to beach environments (Guimond & Tamborski, 2021;Xin et al., 2022). The sand-dominated beach is characterized by receiving fresh groundwater from inland and discharging it through a submarine zone above the seawater wedge (Figure 1b) (e.g.

Section: Discussionmentioning

confidence: 99%

Salt Transport Under Tide and Evaporation in a Subtropical Wetland: Field Monitoring and Numerical Simulation

Zhang

Water Resources Research

et al. 2022

Water Resources Research

“…Root dynamics depend on plant physiological characteristics, groundwater dynamics, and soil types, among other variables (Naumburg et al, 2005;Norby & Jackson, 2000). In addition, recent research (e.g., Moffett & Gorelick, 2016) has highlighted the importance of geochemical contributions to self-organized vegetation zonation, including changes in root distribution shape and density under different salinity stresses (Coppola et al, 2015). Therefore, understanding the combined effects of water and salinity stresses on the redistribution of the root system remains a major challenge for simulations of root water uptake processes (Skaggs et al, 2006).…”

Section: Discussionmentioning

confidence: 99%

Implementing Dynamic Root Optimization in Noah‐MP for Simulating Phreatophytic Root Water Uptake

Wang

Niu

Fang

et al. 2018

Widely distributed in arid and semiarid regions, phreatophytic roots extend into the saturated zone and extract water directly from groundwater. In this paper, we implemented a vegetation optimality model of root dynamics (VOM‐ROOT) in the Noah land surface model with multiparameterization options (Noah‐MP LSM) to model the extraction of groundwater through phreatophytic roots at a riparian site with a hyperarid climate (with precipitation of 35 mm/yr) in northwestern China. VOM‐ROOT numerically describes the natural optimization of the root profile in response to changes in subsurface water conditions. The coupled Noah‐MP/VOM‐ROOT model substantially improves the simulation of surface energy and water fluxes, particularly during the growing season, compared to the prescribed static root profile in the default Noah‐MP. In the coupled model, more roots are required to grow into the saturated zone to meet transpiration demand when the groundwater level declines over the growing season. The modeling results indicate that at the study site, the modeled annual transpiration is 472 mm, accounting for 92.3% of the total evapotranspiration. Direct root water uptake from the capillary fringe and groundwater, which is supplied by lateral groundwater flow, accounts for approximately 84% of the total transpiration. This study demonstrates the importance of implementing a dynamic root scheme in a land surface model for adequately simulating phreatophytic root water uptake and the associated latent heat flux.

“…As tides rise, creek water flows laterally into marsh sediments, and when tides are high enough to overflow natural levees, recharge occurs vertically over the low marsh. During ebb tide, groundwater discharges from the low marsh to creeks, resulting in export of associated solutes . Gradients in tidal flushing and groundwater discharge across morphologic units drive steep gradients in pore water salinity and biogeochemistry .…”

Section: Intertidal Surface Water–groundwater Exchangementioning

confidence: 99%

From soil to sea: the role of groundwater in coastal critical zone processes

2016

Near coasts, surface water–groundwater interactions control many biogeochemical processes associated with the critical zone, which extends from shallow aquifer to vegetative canopy. For example, submarine groundwater discharge delivers a significant fraction of weathering products such as silica and calcium to the world's oceans. Owing to changing fertilizer and land use practices, submarine groundwater discharge is also responsible for high nitrogen loads that drive eutrophication in marine waters. Submarine groundwater discharge is generally unmonitored due to its heterogeneous and diffuse spatial patterns and complex temporal dynamics. Here, we review the physical processes that drive submarine groundwater discharge at various spatial and temporal scales and highlight examples of interdependent critical zone processes. Like the inland critical zone, the coastal critical zone is undergoing rapid change in the Anthropocene. Disturbances include warming air and sea temperatures, sea‐level rise, increasing storm severity, increasing nutrient and contaminant inputs, and ocean acidification. In a changing world, it is more important than ever to understand complex feedbacks between dynamic surface water‐groundwater interaction, rocks, and life through long‐term monitoring efforts that extend beyond inland rivers to coastal groundwater. WIREs Water 2016, 3:706–726. doi: 10.1002/wat2.1157 This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Science of Water > Water and Environmental Change Science of Water > Water Quality