Saltwater Intrusion: A Unique Water Pollution Challenge

Saltwater intrusion is a growing concern for coastal communities, threatening their access to clean drinking water. The movement of saline water into freshwater aquifers degrades water quality and endangers future water exploitation, with climate change and human activities such as groundwater pumping and navigation channels contributing to this issue. This has led to a slow poison of drinking water sources, with potential health risks for coastal populations, including high blood pressure. As saltwater creeps inland, communities are faced with costly adaptation measures, such as treatment plants and water pipelines, or the alternative of relying on bottled water, which brings financial burdens and plastic pollution. With sea-level rise and extreme weather events predicted to worsen, the impact of saltwater intrusion on water quality and the environment is a pressing issue that requires urgent attention and effective management strategies.

Is Saltwater Intrusion Considered Water Pollution?

Saltwater intrusion is considered water pollution

The primary cause of saltwater intrusion is groundwater extraction, which has increased over time as groundwater is the main source of drinking water in many coastal regions of the United States. This extraction lowers the level of the freshwater table, reducing the pressure exerted by the freshwater column and allowing denser saltwater to move inland. In Cape May, New Jersey, water withdrawals since the 1940s have lowered groundwater levels by up to 30 meters, causing widespread contamination of water supply wells.

Other human activities that contribute to saltwater intrusion include the construction of canals and drainage networks, which provide pathways for saltwater to move inland. Additionally, navigation channels, agricultural channels, and drainage channels can also worsen saltwater intrusion. Climate change, including rising sea levels and extreme weather events like hurricane storm surges, further exacerbates the problem.

The consequences of saltwater intrusion are significant. It degrades groundwater quality by raising salinity levels beyond acceptable standards for drinking water and irrigation. This endangers the future exploitation of coastal aquifers and poses health risks to coastal populations, such as an increased risk of high blood pressure. Preventing and managing saltwater intrusion can be costly, requiring treatment plants, water pipelines, and storage facilities that can incur millions of dollars in expenses for cities and towns.

Overall, saltwater intrusion is a pressing issue that threatens water security and requires proactive measures to safeguard freshwater resources and protect the health of vulnerable communities.

Climate change and sea level rise

Saltwater intrusion is a growing concern for coastal communities, and climate change is a key driver of this issue. As sea levels rise due to the warming planet, saltwater is encroaching further inland, threatening drinking water sources and ecosystems. This phenomenon is known as saltwater intrusion, and it poses significant challenges to water security and public health.

The impacts of saltwater intrusion are already being felt along the East Coast of the United States, from Maine to Georgia, with southeastern states experiencing the fastest rates of intrusion. In these areas, saltwater is migrating inland at a rate of 400 feet per year, contaminating groundwater reserves and rendering wells unusable. For example, on Hilton Head Island, a popular tourist destination, saltwater has overtaken six of the island's original drinking water wells, and more are at risk.

Climate change-induced sea-level rise is a primary factor contributing to saltwater intrusion. As sea levels rise, the "salt front," or the boundary between freshwater and saltwater, moves further upstream. This encroachment is exacerbated by factors such as drought, reduced rainfall, and changes in water use and demand. The increasing salinity of groundwater and surface water sources poses risks to both the environment and human health.

Several studies have modelled the impacts of saltwater intrusion under future climate scenarios. These studies predict that by 2050, 41 nations across all continents, except Antarctica, will experience inland saltwater intrusion of at least 1 km. The maximum distance of inland saltwater intrusion is projected to reach up to 53.9 km in Vietnam under certain climate scenarios. These intrusions will have significant implications for water security and public health, particularly in low- and middle-income countries.

The consequences of saltwater intrusion are far-reaching. Affected communities may need to invest in costly treatment plants, water pipelines, and storage facilities to maintain access to safe drinking water. In some cases, alternative sources of freshwater may need to be developed, incurring additional expenses. These adaptations can be particularly challenging for low-income communities, who may not have the financial resources to implement these solutions.

To address saltwater intrusion, a combination of prevention, adaptation, and mitigation strategies is necessary. Preventative measures include reducing freshwater usage, particularly for non-essential purposes like irrigating lawns and golf courses, which can account for a significant proportion of freshwater consumption in coastal towns. Adaptation strategies involve implementing solutions like desalination plants and alternative water sources. Additionally, further research is needed to improve understanding of local geological nuances and develop contextually appropriate solutions to secure equitable access to clean drinking water.

Human activities and groundwater extraction

Saltwater intrusion is a growing problem for coastal communities around the world, and human activities and groundwater extraction are major contributors.

Groundwater extraction is the primary cause of saltwater intrusion. As coastal communities extract more groundwater for drinking water, irrigation, and industry, they lower the level of the freshwater table. This reduction in the freshwater column's pressure allows denser saltwater to move inland laterally, a process known as "saltwater intrusion." The construction of canals and drainage networks further aids the inland movement of saltwater. Canals, drainage channels, and the deepening of navigation channels provide conduits for saltwater to infiltrate inland areas.

In the United States, saltwater intrusion has affected many coastal aquifers, with states like New Jersey, Washington, and Florida experiencing significant contamination of water supply wells. In Cape May, New Jersey, groundwater extraction has lowered water tables by up to 30 meters, leading to the closure of over 120 water supply wells since the 1940s. Similarly, in Hilton Head, a popular tourist destination, saltwater intrusion has rendered six of the island's original 12 drinking water wells unusable, with five more at risk of the same fate by 2024.

Human activities, such as the construction of sewers, roads, parking lots, and buildings, further contribute to saltwater intrusion. These structures replace permeable surfaces with impermeable ones, reducing the recharge of groundwater and accelerating saltwater intrusion. Additionally, pier and bridge construction, as well as harbor dredging, can breach confining layers above coastal aquifers, providing pathways for seawater to invade.

The impacts of saltwater intrusion are far-reaching. It affects drinking water supplies, agriculture, and industry. As saltwater intrudes into freshwater aquifers, it alters the ionic strength and oxidative capacity of these systems, leading to elevated concentrations of certain chemical species in the groundwater. This, in turn, affects the subterranean estuaries and the ocean, as the contaminated groundwater is discharged.

With rising sea levels due to climate change, the problem of saltwater intrusion is expected to intensify. Preventative measures, such as the construction of treatment plants, water pipelines, and storage facilities, can be costly for communities. Therefore, it is essential to implement effective groundwater management plans that consider potential changes in water quality due to saltwater intrusion and to develop strategies to secure access to clean drinking water for vulnerable populations.

Health risks and environmental impacts

Saltwater intrusion, a natural process, involves the movement of saline water into freshwater aquifers, leading to groundwater quality degradation, including drinking water sources. This can have significant ecological and morphological impacts on coastal freshwater environments, threatening conservation efforts for wetlands, flora, and fauna.

Health Risks

Saltwater intrusion poses health risks to human populations, particularly those consuming saline drinking water. Increased sodium consumption from saline water can elevate the risk of high blood pressure and other adverse health outcomes. A study identified 41 nations across all continents (except Antarctica) that are vulnerable to health impacts from saltwater intrusion by 2050. These countries are projected to have inland saltwater intrusion of at least 1 km, with populations relying on groundwater for drinking water. The maximum distance of inland saltwater intrusion was modelled to reach up to 53.9 km in Vietnam under specific climate change scenarios.

Access to treated water varies across these vulnerable countries, with Myanmar having the lowest access (15%) and Egypt the highest (99%). Urinary sodium excretion levels, a marker of sodium consumption, also differ, ranging from 2.1 g/day in Turkey to 7.0 g/day in China. The health impacts are expected to be more significant in low- and middle-income countries, with seven such nations identified as highly vulnerable, all located in South/Southeast Asia.

Environmental Impacts

The environmental consequences of saltwater intrusion are significant and far-reaching. Firstly, it affects water quality by "unlocking" nutrients from fertilizers in farm fields. The unique chemistry of saltwater allows it to interact with the soil and mobilize nutrients, which then travel through agricultural ditches into coastal water bodies. This excess nutrient runoff causes excessive algae growth, and when the algae die and are broken down by bacteria, oxygen levels in the water deplete. This depletion of oxygen can lead to fish kills, loss of animal habitat, and other harmful effects on coastal ecosystems and wildlife.

Secondly, saltwater intrusion poses a threat to coastal agriculture. As saltwater moves inland, it renders previously farmable land unusable due to the high salt content in the soil. This intrusion can occur through natural processes, such as sea-level rise caused by climate change, and human activities, such as groundwater pumping, the construction of navigation channels, and drainage networks. Farmers can employ strategies to manage saltwater intrusion, such as removing excess salt from the soil through irrigation, using gypsum, or planting cover crops. However, in the long term, fields affected by saltwater intrusion may need to be converted into marsh habitats, impacting agricultural productivity.

Additionally, saltwater intrusion has economic implications for coastal communities. Adapting to and mitigating the effects of saltwater intrusion can be costly, with treatment plants, water pipelines, and storage facilities requiring significant investments. For example, Hilton Head Island in the United States has spent over $129 million to address saltwater intrusion and expects to spend an additional $80 million in the coming decades.

Prevention, treatment, and management strategies

Saltwater intrusion is a growing issue that poses a significant threat to water sources and the environment. While it may not be traditionally viewed as a contaminant, saltwater intrusion can have detrimental effects on freshwater ecosystems and human communities that rely on these water sources. As such, it is essential to implement effective prevention, treatment, and management strategies to mitigate this issue.

Prevention Strategies

• Allow Coastal Wetlands to Migrate Inward: By implementing measures such as setbacks, density restrictions, and land purchases, coastal wetlands can be allowed to migrate inland, helping to prevent saltwater intrusion.
• Adaptive Stormwater Management: Promoting natural buffers, adequate culvert sizing, and removing impervious surfaces can help manage stormwater and reduce the risk of saltwater intrusion.
• Protect Critical Areas: Identify and protect ecologically significant areas, such as nursery grounds, spawning grounds, and areas with high species diversity, to maintain biodiversity and ecosystem resilience.
• Incorporate Wetland Protection in Infrastructure Planning: Consider wetland protection in transportation planning, sewer utilities, and other infrastructure developments to minimize their impact on wetlands and prevent saltwater intrusion.
• Land Acquisition and Exchange Programs: Governments can purchase coastal lands prone to damage and use them for conservation, while also offering land exchange programs to move properties out of flood-prone areas.
• Remove Shoreline Hardening Structures: Replace bulkheads, dikes, and other engineered structures with living shorelines, such as beach nourishment and vegetation planting, to allow for natural shoreline migration.
• Restrict Development in Erosion Zones: Prohibit or restrict development in areas susceptible to erosion to reduce the impact of human activities on the environment and prevent the disruption of natural processes.

Treatment and Management Strategies

• Use Containment Areas: Establish or expand "use containment areas" to control and limit water withdrawal, ensuring a balanced and sustainable water supply.
• Incorporate Sea Level Rise in Infrastructure Planning: Consider sea level rise when planning and designing new infrastructure, such as sewage systems, to ensure they can withstand and adapt to changing water levels.
• Integrate Climate Change Scenarios in Water Supply Systems: Anticipate and plan for the impacts of climate change on water supply systems, including the increased salinity of water sources.
• Manage Water Demand: Implement measures such as water reuse, recycling, rainwater harvesting, and desalination to optimize water usage and reduce the extraction of freshwater, which can help slow down saltwater intrusion.
• Incorporate Coastal Management in Land Use Planning: Integrate coastal management strategies into land use planning to ensure a comprehensive and sustainable approach to land and water resource management.
• Create Permitting Rules for Hazardous Waste Facilities: Establish permitting rules to constrain the locations of landfills, hazardous waste dumps, mine tailings, and toxic chemical facilities, reducing their environmental impact and potential contribution to saltwater intrusion.

Frequently asked questions