Estuaries are fragile ecosystems that face immediate pollution from the communities that surround them but also from communities located in the river basins that drain into them. Eastern North Carolina is known for agriculture, an industry that greatly impacts water quality.
Pollution is split into two main categories, point sources and nonpoint sources. In North Carolina Estuaries, point sources make up ⅓ of total pollution. Point sources are permitted to pollute in very small amounts but as more and more parties contribute, it becomes a bigger overall threat. Nonpoint sources make up the remaining ⅔ of total pollution but little is known about their origins.
One main nonpoint source is Concentrated Animal Feeding Operations (CAFOs) for pork and poultry. Pork production is an industry with high amounts of waste, with North Carolina production concentrated in Duplin and Sampson counties. Both counties are in the Cape Fear watershed and drain into the Cape Fear Estuary. Industrial farms use lagoons with anaerobic bacteria to process concentrated animal waste. These lagoons contain nitrogen, phosphorus, and ammonium, which can leak into water systems as lagoons breach or overflow. Most of the waterways in eastern North Carolina are slow moving and have low amounts of dissolved oxygen in the hottest months, making them particularly sensitive to pollution.
In one of the most recent storms in North Carolina, Hurricane Florence (2018) caused 110 lagoons to rupture or be in imminent risk of rupturing. Based on the trajectory of climate change, this will only become more common.
Chemical contaminants also pose a big risk to estuarine systems. 70% of the estuarine system in North Carolina is floored by mud. This mud is made up of organic matter and clay, which together, combine to make a chemically-reactive material. This mud strips toxic chemicals out of the water and acts as important sinks for chemical substances.
As they strip the water of toxins, the toxicity of the mud increases, posing a risk to organisms which breed, eat, and live near the bottom of estuaries. As these chemicals are consumed, they bioaccumulate in the food chain. Residence times vary based on chemical contaminants and some move on into oceanic systems, some pollutants remain in estuarine systems for a long period of time. Overall, the presence of these chemicals impacts the stress and health of organisms.
Resources
Mallin, Micheal A. “Impacts of Industrial Animal Production on Rivers and Estuaries – ProQuest.” American Scientist, vol. 88, no. 1, Feb. 2000, pp. 26–37, https://search.proquest.com/docview/215261309?pq-origsite=gscholar&fromopenview=true.