Human-Generated Nutrient Overloads Can Destroy Coastal Wetlands

A recent study shows that sewage and agricultural runoff causes significant changes in the structure and shape of coastal wetlands, which can lead to catastrophic, rapid loss of salt marshes during sea level rise associated with climate change.

The study by scientists at Boston University and the Marine Biological Laboratory in Massachusetts helps us understand how human-induced nutrient loading of coastal wetlands is harming, rather than helping to retain marsh plants. The result is that coastal wetlands are destroyed and replaced by tidal flats. This can lead to greater coastal erosion, threaten ecosystem viability and also has implications for land management.

While human-induced nutrient loading in coastal ecosystems has been of prime concern for scientists, land managers and the public for decades, impacts on salt marshes and tidal flats have, remarkably, been largely ignored. The study at the Plum Island Long-Term Ecological Research site shows that the increase in carbon, nitrogen, phosphorous, and other nutrients in sewage and agricultural runoff directly and dramatically changes the shape and structure of coastal wetlands, essentially disintegrating the banks of marsh creeks.

More specifically, the researchers found that the increase in nutrients caused salt marsh grasses to grow taller but have shorter root systems. Thus plants fell down and roots did not hold the soil together as well. The resulting changes in the size and shape of the creeks and channels impacts the flow of water in the marsh and changes the exchange of nutrients and sediment between tidal flats, marshes and the coastal ocean. As a result, coastal areas with a lot of runoff will likely quickly lose salt marshes during sea level rise associated with global warming and climate change.