Clean Water in the News

WILMINGTON - The state Environmental Management Commission recently passed new coastal anti-pollution regulations designed to protect human health and our shellfishing industry. The new rules are strongly based in peer-reviewed science developed in coastal North Carolina, and later repeated and verified in a massive study in coastal South Carolina. The rules, now being challenged in the General Assembly by some legislators, require developers to treat polluted stormwater before discharging it into our tidal creeks, beaches and other waterways.

In North Carolina, shellfishing has been a highly valued commercial and recreational coastal livelihood. Unfortunately, data compiled by the state Division of Marine Fisheries show that over the past 25 years the shellfish catch has decreased dramatically.

In the early 1980s the commercial harvest of clams and oysters in North Carolina yielded over $14 million of revenue (in 2005 dollars) but this income steadily dwindled to less than $4.5 million in 2005, a loss of nearly $10 million a year to coastal communities.

A major reason for the decreases in catch and revenue has been increased closures of shellfishing waters by regulatory agencies because of pollution by fecal bacteria generated by humans and animals. People can be poisoned by fecal microbes either from eating contaminated shellfish or by contacting these microbes while swimming, surfing or water skiing in water polluted by stormwater runoff.

Researchers at UNC-Wilmington and at the state Shellfish Sanitation and Recreational Water Quality Section examined shellfish bed closure data from Carteret, Onslow, Pender, New Hanover and Brunswick counties, and compared those data with human population increases in those same counties for the 20-year period from 1984-2004. The loss in usable shellfishing acreage is strongly related to increased human presence on the coast.

The tidal creeks of New Hanover and Pender counties are normally rich shellfishing beds with extensive oyster reefs. UNC-Wilmington researchers conducted extensive sampling throughout six of these estuarine watersheds and statistically compared the results to watershed population and land uses.

The levels of fecal bacteria pollution in these estuarine creeks were strongly related to the human population of the watersheds and the percent of developed land in the watersheds. The percent of impervious surface coverage (roads, roofs, sidewalks, driveways and parking lots) within the watersheds was directly related to the bacterial pollution levels by a nearly one-to-one relationship.

The study also showed that the only two watersheds with less than 10 percent impervious surface coverage (Futch and Pages creeks) still had areas open to shellfishing, whereas those with greater coverage (Bradley, Hewletts, Howe and Whiskey creeks) were entirely closed to shellfishing because of high fecal bacterial counts.

A later study of 22 tidal creeks by South Carolina researchers verified our studies and showed a similar relationship between impervious surface coverage and fecal bacteria counts, and also noted that the 10 percent impervious coverage percentage is a key level leading to poor coastal water quality and degradation of the fish and shellfish communities.

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STRONG RELATIONSHIPS BETWEEN INCREASED WATERSHED IMPERVIOUS SURFACE COVERAGE AND WATER POLLUTION have also been found by scientists working in freshwater streams in areas as diverse as the mid-Atlantic region, the Midwest, and the Pacific Northwest, with 10 percent watershed impervious cover frequently shown as a point where significant pollution effects occur.

In a naturally vegetated landscape, rainfall is largely removed either by soaking through the soil to the groundwater or by being taken up by trees and other vegetation. Any rainwater not absorbed becomes runoff, which is normally filtered of pollutants by flowing through a vegetated landscape. When the natural landscape is covered with impervious surfaces, rainfall can no longer percolate through the soil, forcing the rain to become stormwater runoff.

Stormwater runoff causes flooding and erosion of the landscape and pollutes the water with eroded and suspended sediments, which adsorb pollutants and carry them downstream. Between rains, the pavement surfaces concentrate pollutants such as nitrogen, phosphorus, metals, toxic chemicals and fecal bacteria. When it rains, parking lots, roads, drives and sidewalks provide rapid and direct flushing of polluted stormwater runoff into ditches and streams, and then into shellfish beds and beach areas.

The science is clear on what factors drive stormwater runoff pollution that leads to pollution of our coastal waters. These waters can be protected by strong efforts to reduce stormwater runoff at the source by reducing impervious surface coverage while increasing green space, using pervious pavement instead of impervious, conservation and enhancement of vegetated streamside buffer zones, and treatment of stormwater runoff by engineered solutions.

The cessation of shellfish bed pollution should be a priority goal to save and revitalize this industry and protect human health, and the new coastal protection regulations are an important step toward reaching that goal.

(Michael A. Mallin is a research professor at UNC-Wilmington's Center for Marine Science.)