Baltimore — A new scientific paper warns that saltwater intrusion in tidal rivers poses an emerging global threat to freshwater supplies, driven by climate change and human activities, with potential risks to agriculture and infrastructure in Maryland’s coastal areas. The study, published July 2, 2025, in Environmental Science & Technology Letters, synthesizes worldwide research and calls for enhanced monitoring and modeling to address the issue. Lead author Ming Li, from the University of Maryland Center for Environmental Science, emphasizes that saltwater intrusion in tidal rivers has been understudied beyond local cases, affecting drinking water sources that supply about two-thirds of the world’s population.
The research details how accelerated sea-level rise, prolonged droughts, altered river flows and extreme weather events contribute to saltwater intrusion in tidal rivers. Human factors, including estuary channel deepening, road salt application and watershed chemical weathering, worsen the problem. Examples include threats to drinking water intakes in the Mississippi River in the United States, the Chao Phraya in Thailand and the Rhine in Europe. Broader effects involve corrosion of infrastructure like power plants, bridges and water treatment facilities, plus secondary issues such as worsened hypoxia and mobilization of contaminants including nutrients, metals and radionuclides.
In the Mid-Atlantic region, the paper notes nearly $100 million in agricultural activity at risk from saltwater intrusion in tidal rivers. Nationally, more than $1 trillion in investments are required for drinking and wastewater systems to counter salt contamination. The absence of a federal drinking water standard for salinity in the United States heightens vulnerability. Co-authors from institutions like Pennsylvania State University, Rutgers University and Woods Hole Oceanographic Institution recommend ion-specific measurements, hydrological models and stakeholder-involved decision tools to mitigate risks.
For Maryland, saltwater intrusion in tidal rivers like those feeding the Chesapeake Bay presents direct challenges. The state’s coastal plain, including Southern Maryland counties of Calvert, Charles and St. Mary’s, relies on tidal rivers and aquifers for water supplies. Sea-level rise, projected at 1 to 1.6 feet by 2050 and 2.7 feet by 2100 under current trends, accelerates saltwater intrusion in tidal rivers and salinization of soils and groundwater. In the Chesapeake Bay watershed, sea levels are rising at three times the global average due to land subsidence and climate factors.
Agricultural impacts are evident in areas near Southern Maryland. Visible salt patches on farmland nearly doubled from 2011 to 2017, converting about 20,000 acres into marsh across the Delmarva Peninsula. In Somerset County, adjacent to Southern Maryland, farmer Kevin Anderson lost an acre of corn to tidal flooding, costing $650 per acre with no yield. Dorchester County farmer Wendell Meekins saw a complete loss on 65 acres from a saltwater surge, prompting berm construction as a short-term fix. High salinity levels, up to 35 parts per thousand, reduce crop tolerance for staples like corn and soy. Affected farmland doubled from 18,988 acres in 2011-2013 to 40,120 acres in 2016-2017 across nine Eastern Shore counties, with projections indicating a doubling by 2070 in some areas. A 2022 NASA project identified St. Mary’s County as at risk for agricultural land loss to saltwater intrusion in tidal rivers.
Infrastructure faces corrosion risks from saltwater intrusion in tidal rivers. In Southern Maryland, surficial aquifers used for irrigation and domestic supply are vulnerable, with potential damage to wells, septic systems and roads. The EPA funded a 2023 study on septic failures in coastal Maryland due to sea-level rise and saltwater intrusion. Water supplies in Calvert, Charles and St. Mary’s counties rely on about 210,000 private wells in the coastal plain, with 110 million gallons per day permitted from surficial aquifers. Documented intrusion affects the Patapsco aquifer in Charles County and unknown aquifers in St. Mary’s County.
Ecosystem changes include the proliferation of ghost forests in the Chesapeake Bay region. Aerial surveys from 2016 to July 2024 identified 415,000 acres of salt-affected forests in Maryland’s Delmarva Peninsula, with 27,000 new acres of ghost forest in the latest year. These dead tree stands result from saltwater intrusion in tidal rivers extending up to 6 miles inland via ditches during storms. Forests retreat at 2.7 millimeters per year, lagging behind the 5.5 millimeters annual sea-level rise. In Southern Maryland, this affects timber industries and landowners, with advice to harvest before land becomes inaccessible.
Maryland’s 2019 Plan to Adapt to Saltwater Intrusion and Salinization, updated in 2024, outlines strategies including salt-tolerant crops like sorghum, land transitions to wetlands via easements and enhanced aquifer monitoring. Pilot studies target vulnerable infrastructure, with techniques like reverse osmosis for water treatment. Researchers like Kate Tully from the University of Maryland advocate for drone monitoring to assess soil salinity and guide decisions. As sea levels could rise nearly 3 feet by 2100, farmland may shift to carbon-storing marshes if managed.
The paper underscores the need for collaboration among scientists, engineers, managers and policymakers to protect freshwater from saltwater intrusion in tidal rivers. In Southern Maryland, where communities border the Patuxent and Potomac rivers, these efforts could safeguard local water and farming amid rising threats.
