More Like this

1. Dynamics of Saltwater Intrusion Into Coastal Freshwaters in the California Central Coast

   https://doi.org/10.1029/2024WR037141  

   Kim, Lauren N; Meusel, Casey; Barker, Rusty; Lockwood, Brian; Strudley, Mark; Behrens, Dane; Orescanin, Mara M; Merrifield, Mark; Giddings, Sarah N; Levy, Morgan C (March 2025, Water Resources Research)

   Saltwater intrusion (SWI) into coastal freshwater systems is a growing concern in the face of climate change‐driven sea level rise and hydrologic variability. Saltwater contamination of surface freshwater in the coastal California Pajaro Valley exemplifies this concern, where surface water cannot be diverted for agriculture if it is too saline. Closures at the mouth of the Pajaro River Lagoon, a bar‐built estuary in the Pajaro Valley, are associated with SWI. Closures and SWI are driven by a combination of offshore climate, coastal hydrodynamics, estuarine dynamics, inland hydrology, and infrastructure and management. Here, we describe the Pajaro Valley coastal water system and identify the oceanic and inland hydrologic drivers of SWI using available observational data between 2012 and 2020. We use time series and exploratory statistical analyses of coastal total water levels (TWLs), slough stage and salinity, river discharge, and contextual knowledge from local water managers. We observe that wet season lagoon closure and SWI events follow high oceanic TWLs coupled with low stage and discharge in the inland freshwater network, revealing how both wave and inland flow conditions govern lagoon closures and coincident SWI. This study yields novel empirical findings and a methodology for connecting coastal oceanography, estuarine coupled hydro‐ and morpho‐dynamics, inland hydrology, and water management practices relevant to climate change adaptation in human‐modified coastal water systems. 

   more » « less
2. Surface Water‐Groundwater Connections as Pathways for Inland Salinization of Coastal Aquifers

   https://doi.org/10.1111/gwat.13274  

   Hingst, Mary C.; McQuiggan, Rachel W.; Peters, Chelsea N.; He, Changming; Andres, A. Scott; Michael, Holly A. (November 2022, Groundwater)

   Coastal agricultural zones are experiencing salinization due to accelerating rates of sea-level rise, causing reduction in crop yields and abandonment of farmland. Understanding mechanisms and drivers of this seawater intrusion (SWI) is key to mitigating its effects and predicting future vulnerability of groundwater resources to salinization. We implemented a monitoring network of pressure and specific conductivity (SC) sensors in wells and surface waters to target marsh-adjacent agricultural areas in greater Dover, Delaware. Recorded water levels and SC over a period of three years show that the mechanisms and timescales of SWI are controlled by local hydrology, geomorphology, and geology. Monitored wells did not indicate widespread salinization of deep groundwater in the surficial aquifer. However, monitored surface water bodies and shallow (<4m deep) wells did show SC fluctuations due to tides and storm events, in one case leading to salinization of deeper (18m deep) groundwater. Seasonal peaks in SC occurred during late summer months. Seasonal and interannual variation of SC was also influenced by relative sea level. The data collected in this study data highlight the mechanisms by which surface water-groundwater connections lead to salinization of aquifers inland, before SWI is detected in deeper groundwater nearer the coastline. Sharing of our data with stakeholders has led to the implementation of SWI mitigation efforts, illustrating the importance of strategic monitoring and stakeholder engagement to support coastal resilience. 

   more » « less
3. Large‐Scale Moisture Sources and Delivery Pathways Contributing to Winter Floods in the US

   https://doi.org/10.1029/2025WR040353  

   Hwang, Jeongwoo; Sankarasubramanian, A (December 2025, Water Resources Research)

   Abstract Previous seminal studies on US flood hydroclimatology have recognized large‐scale seasonal precipitation water from the lower atmosphere as a significant factor influencing flood patterns and have identified potential moisture delivery pathways associated with seasonal flooding across the conterminous United States (CONUS). Given the changing climate, however, an update of these studies is warranted, leveraging the more extensive and longer series of data sets currently available on floods and exogenous climate drivers. Using a Lagrangian particle tracking model (HYSPLIT), this study explores the large‐scale moisture delivery pathways associated with monthly floods during the winter season across the CONUS. The contributions of various moisture sources (i.e., land, extratropical Pacific, tropical Pacific, extratropical Atlantic, tropical Atlantic, and Arctic) to winter floods are summarized for each hydrologic region (HUC02) based on the moisture delivery pathways identified by the HYSPLIT model. Our results show that major oceanic sources are the primary contributors to winter floods in coastal regions, whereas land remains a significant source for hydrologic regions over the Midwest. Humidity profiles along the trajectories further indicate that air masses from the Pacific lose substantial moisture when crossing western mountain ranges and subsequently gain over east of the Rockies, making land a key contributor to floods over the upper Midwest. We also find substantial variability in moisture source contributions depending on flood severity in specific regions. In addition, the circulation patterns associated with extreme flood trajectories reveal consistent large‐scale features, typically involving a deep low‐pressure system delivering moisture to hydrologic regions. 

   more » « less
4. Freshwater Salinization Syndrome Alters Nitrogen Transport in Urban Watersheds

   https://doi.org/10.3390/w15223956  

   Galella, Joseph G; Kaushal, Sujay S; Mayer, Paul M; Maas, Carly M; Shatkay, Ruth R; Inamdar, Shreeram; Belt, Kenneth T (November 2023, Water)

   Anthropogenic salt inputs have impacted many streams in the U.S. for over a century. Urban stream salinity is often chronically elevated and punctuated by episodic salinization events, which can last hours to days after snowstorms and the application of road salt. Here, we investigated the impacts of freshwater salinization on total dissolved nitrogen (TDN) and NO3−/NO2− concentrations and fluxes across time in urban watersheds in the Baltimore-Washington D.C. metropolitan area of the Chesapeake Bay region. Episodic salinization from road salt applications and snowmelt quickly mobilized TDN in streams likely through soil ion exchange, hydrologic flushing, and other biogeochemical processes. Previous experimental work from other studies has shown that salinization can mobilize nitrogen from sediments, but less work has investigated this phenomenon with high-frequency sensors and targeted monitoring during road salt events. We found that urban streams exhibited elevated concentrations and fluxes of TDN, NO3−/NO2−, and specific conductance that rapidly peaked during and after winter road salt events, and then rapidly declined afterwards. We observed plateaus in TDN concentrations in the ranges of the highest specific conductance values (between 1000 and 2000 μS/cm) caused by road salt events. Plateaus in TDN concentrations beyond a certain threshold of specific conductance values suggested source limitation of TDN in watersheds (at the highest ranges in chloride concentrations and ranges); salts were likely extracting nitrogen from soils and streams through ion exchange in soils and sediments, ion pairing in soils and waters, and sodium dispersion of soils to a certain threshold level. When watershed transport was compared across land use, including a forested reference watershed, there was a positive relationship between Cl− loads and NO3−/NO2− loads. This relationship occurred across all sites regardless of land use, which suggests that the mass transport of Cl− and NO3−/NO2− are likely influenced by similar factors such as soil ion exchange, ion pairing, sodium dispersion of soils, hydrologic flushing, and biogeochemical processes. Freshwater salinization has the potential to alter the magnitude and timing of total dissolved nitrogen delivery to receiving waters during winter months following road salt applications, and further work should investigate the seasonal relationships of N transport with salinization in urban watersheds. 

   more » « less
5. Terrestrial Groundwater Drives Coastal Ecosystem Shifts

   https://doi.org/10.1029/2025GL116251  

   Pratt, D; Guimond, J A; Bacmeister, E S; Fagherazzi, S; Michael, H A (July 2025, Geophysical Research Letters)

   Abstract Saltwater intrusion (SWI) is accelerating along coastlines globally. This process is visually evident in low‐lying regions as conversion of forests and agricultural fields to saltmarsh. Marsh migration is largely attributed to ocean forcings such as sea‐level rise and storm surges. Here we show that terrestrial hydrology may also be a major driver of coastal ecosystem change. Data from the Delmarva Peninsula, USA show that declining upland groundwater head weakens the hydraulic gradient, causing shallow saline groundwater to push inland from coastal marshes. This drives SWI into coastal freshwater forests and farms at magnitudes that can exceed SWI from storms. We show that storm events often contribute to groundwater freshening through rainfall that restores the hydraulic gradient and flushes saline groundwater. Our findings highlight terrestrial groundwater as a primary control on root‐zone saltwater intrusion and suggest that changes in upland head may be a dominant, yet overlooked, driver of marsh migration. 

   more » « less