Climate Change

Climate Change & Estuaries


Water in the streets during a high tide event on a storm-free day in Baltimore, MD. Courtesy of NOAA.

Sea level rise: Estuaries are under constant danger of rising sea levels. Sea level rise is often broken into two categories: global and local. Global sea level rise is the increase in the ocean’s average height across the world. Local sea level rise is an increase in the height of the water relative to a specific place on land. Climate change has caused global sea level to rise through a combination of thermal expansion (water expanding as it warms) and the increased melting of land-based ice (such as glaciers). Factors like land subsidence, gravitational forces, and ocean currents can impact the rate of local sea level rise, often resulting in a higher rate when compared to the global average. Many coastal cities are already experiencing the effects of sea level rise, such as flooding and intensified storm surges.

This increase in water levels can severely damage estuaries and wetlands. Plants meant to live above the water line are now being drowned and there is ever-decreasing light availability to submerged aquatic vegetation. Sea level rise also increases the amount of flooding and erosion in coastal areas. If this trend continues, the erosion of beaches will become very severe, destroying dunes that are essential to the prevention of landslides and slumping (when rock and other matter moves a short distance down a slope). Sea level rise can also push native species from the area in search of healthier habitats, allowing invasive species to dominate. 

Saltwater intrusion is the movement of saltwater into freshwater aquifers, which extend beyond the boundaries of an estuary. Excessive groundwater pumping and sea level rise are the main causes of this intrusion. As water levels rise, saltwater stretches further inland, increasing the salinity of water that was once fresh. With less freshwater flowing downstream toward the estuary, the saltwater easily extends beyond the zone of transition (where freshwater and saltwater mix). This can put stress on plants and animals and may even cause the disappearance of certain species when the salinity level reaches above their tolerance.

Changing rainfall patterns also create problems for estuaries. An increase in rain results in more runoff, sedimentation, and erosion, threatening the ecosystems of estuaries. On the other hand, decreased precipitation can raise the salinity of estuaries by reducing the incoming freshwater.

Bleached coral at Lisianski Island in Papahanaumokuakea Marine National Monument. Courtesy of NOAA.

Ocean acidification is currently affecting the entire world’s oceans, including coastal estuaries and waterways. Acidification happens when carbon dioxide in the air is absorbed by the saltwater, turning the water acidic as a result. This causes harm to organisms made from calcium carbonates (like coral) because calcium carbonates dissolve in acidic substances.

For example, coral “bleaching” is caused in part by ocean acidification. When coral are exposed to stressors like acidic oceans, warmer water temperature, or pollution, they expel the algae that live in their tissue. This leaves them completely white, or “bleached.” The bleached coral can recover, but with no source of energy they have an increased vulnerability to disease and death. Healthy coral reefs absorb 97% of a wave’s energy, which buffers shorelines from currents, waves, and storms, helping to prevent loss of life and property damage. Coastlines protected by coral reefs are also more stable in terms of erosion than those without

Eutrophication, a process where excess nutrients in the water lead to the growth of algae on the surface of the water, worsens with climate change. Warm water with high carbon dioxide content provides ideal conditions for algal blooms, while increased nutrient runoff from altered rainfall patterns feeds the algae. Eutrophication is a problem for estuaries because it decreases the light and oxygen for other species.

Algal blooms at the Assateague Island National Seashore, MD. Courtesy of the EPA.

Restore America’s Estuaries Position on Climate Change

Coastal habitats are being subjected to a range of stresses from climate change and many of these stresses are predicted to increase over the next century. The most significant effects are likely to be from sea-level rise, increased storm and wave intensity, temperature increases, ocean acidification, and changes in precipitation that will alter freshwater delivery. These climate change forces are having dramatic effects on coastal habitats and the species dependent on these ecosystems. Addressing the challenges posed by climate change will require a combination of adaptation and mitigation to the changes that are likely to occur and global reductions of greenhouse gas (GHG) emissions from anthropogenic sources. Most importantly, overcoming these challenges will require dissimilar groups and interests being able to have open, and sometimes difficult, conversations that lead to action.

Read our full statement here.


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