Seagrasses and other underwater plants, known as submerged aquatic vegetation (SAV), grow only in shallow estuarine waters rather than in deep water. Like plants on land, these marine flora—which provide critical habitat for economically important fish species and help protect coastlines and communities from shoreline erosion—need sunlight to grow.
In recent years, however, scientists and managers focused on the health of North Carolina’s coastal ecosystems have increasingly found that much of the 298 square miles of SAV in the state’s coastal rivers, creeks, and sounds aren’t getting enough light to thrive. Though the waters are shallow, they simply are not clear enough for the sun’s rays to penetrate. So, state leaders are now considering setting standards for water clarity to help restore and protect the health of SAV and the diverse ecosystems these plants support.
Last year, as part of its updated Coastal Habitat Protection Plan, North Carolina identified restoring and maintaining the state’s historical expanses of SAV as a key goal. State managers prioritized SAV because it supports abundant and diverse coastal fisheries that are essential to many of North Carolina’s economic sectors and, together with salt marsh, protect the state’s coast against rising sea levels and strong storms by anchoring barrier islands, absorbing wave energy, reducing erosion, and safeguarding human life and property.
For all these reasons, creating a standard to maintain water clarity and help SAV grow should be a priority for everyone who loves North Carolina’s vibrant and beautiful coast and who relies on it for their livelihood.
The color shows the cause
Clear water allows ample light to reach plants
When a coastal body of water is healthy and the substances that float or flow in it are balanced at natural levels, the water is typically visibly clear, allowing plenty of light to reach seagrasses and other underwater plants and supporting a robust ecosystem. However, changes to the usual color of a water body can indicate that certain substances—most often natural ones—are too abundant and are blocking light from reaching SAV.
When water is bright green, it’s usually a sign of an overgrowth of algae
Although some algae belong in a healthy ecosystem, high algae concentrations, known as a “bloom,” can block so much sunlight that underwater plants cannot survive. Algae blooms often result from an overabundance of two key nutrients—nitrogen and phosphorous—getting into the estuary when stormwater causes fertilizers used on farms, golf courses, residential lawns, and other landscaped areas to wash into streams, rivers, and sounds.
A brown or gray color, like waves on a rough day at the beach, often means too many fine particles are suspended in the water
Like algae, sediment also is a normal feature in flowing bodies of water. But an eroding shoreline, water stirred up from a boat wake, or runoff from fast-moving stormwater can add and churn up sediment that blocks light from reaching seagrass—at least until the water calms down enough for suspended sediment to settle to the bottom.
Water can turn dark brown or even black from the slow decay of organic material
The darkening of water from decomposing organic matter—such as leaves, plants, and wildlife droppings—can be normal and healthy, but when excessive quantities of dark water surge into estuaries or sounds, such as during heavy rains or flooding, they can block the light that plants need.
What is a water clarity standard?
Most people understand that “clean water” means water that is healthy for humans and wildlife because it is low enough in pollutants to be generally safe for wading and swimming or eating fish from—though not necessarily for drinking. Many people also understand that good water quality is important for ecosystem health, local economies, and ways of life. State regulators set standards—often called “water quality standards”—for clean water, periodically check that bodies of water are meeting those standards, and take action when they do not. The Clean Water Act allows the federal government to step in and set standards if a state is not effectively ensuring that its waters are clean enough for residents and the natural environment.
A water clarity standard—a newer, related concept aimed at keeping underwater plants healthy—differs from many water quality standards that focus on human health, and instead sets baselines for the amount of light that should be able to penetrate to various depths in different types or bodies of water. For example, Delaware, Maryland, Virginia, and the District of Columbia have all adopted consistent sets of water clarity standards for the Chesapeake Bay and its tidal rivers based on a scientific consensus about the minimum clarity needed to support healthy seagrasses in the bay. Each state’s standard requires that of the sunlight at the surface of shallow waters, 22% should be able to reach the bottom in salty areas and 13% should reach the bottom in waters with lower salinity. These salinity-specific standards help ensure that underwater plants have the light they need to thrive and to reach each state’s target restoration acreage.
In addition, water clarity standards not only define a goal, but they also provide maximum flexibility in how to reach it. For instance, if a water body is not meeting the standard because of suspended sediment and too many nutrients—as evidenced by an algae bloom—officials are not obligated to address both issues right away. They could instead choose to tackle the most feasible measures first, such as reducing erosion in the area, which might be enough by itself to meet the standard.
November meeting could advance recommendation
In July of this year—and again in September—the Science Advisory Council for the North Carolina Nutrient Criteria Development Plan discussed the state’s need to adopt the same water clarity standard used in the Chesapeake Bay. And our organizations, The Pew Charitable Trusts and the North Carolina Coastal Federation, along with our partners, have already taken steps to convene stakeholders from up and down the coast to identify voluntary, nonregulatory actions that could help achieve this standard for North Carolina.
At its next meeting on Nov. 9, the Water Quality Subcommittee of the state’s Environmental Management Commission could ask the North Carolina Division of Water Resources to initiate a rule-making process to make this standard official. The benefits of a standard are undeniable—and we urge the commission to act.
Leda Cunningham is an officer and Joseph Gordon is a project director with The Pew Charitable Trusts’ conserving marine life in the United States project. Todd Miller is the executive director of the North Carolina Coastal Federation.
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