Following a long-term study on the effects of nutrient enrichment in salt marshes, lead researcher Linda Deegan of Woods Hole Marine Biological Laboratory finds that nutrient loading (adding more nutrients than are naturally there) may actually lead to the decimation of salt marshes along the U.S East Coast. It was previously thought that the marshes could withstand the pressures of increased nitrogen or phosphorous from fertilizers or septic systems, but this study shows that may be a misconception.
What exactly is a salt marsh?
For those that may not know, salt marshes are one of the most productive coastal ecosystems on earth! They can be found on every coast in North America , and in the mid to high latitudes worldwide. They are the northern equivalent of a mangrove ecosystem. Usually located in estuaries, mouths of bays and other low impact coastal wetland areas, they serve as the major intertidal transition zone between the sea and land. These systems are known by their network of channels, and abundance of grasses, mostly cordgrasses (Spartina sp.)
Why should we care?
“Salt marshes have not always been regarded as valuable resources. Over half of our original salt marshes in the United States have been destroyed, many of them between 1950 and the mid-1970s. Most of that destruction was due to filling of marshes to create more land area for homes, industry and agriculture. Other losses were caused by ditching for mosquito control and diking to create impoundments. ” –Dr. Elizabeth Wenner, Marine Resources Research Institute
Salt marshes help humans in ways we don’t often think about.
First of all, they help protect us by acting as a buffer, dampening the blow from bad storms by preventing erosion and reducing flooding. It has been showcased recently what can happen when salt marshes are reduced or removed in the devastation observed from hurricanes Sandy and Katrina. The areas that were hit the hardest from these storms were areas that were marshes but have been long filled in and developed.
Secondly, they act as nurseries, hideouts and refuges for a wide variety of animals including about 75% of pivotal fisheries species. Without salt marshes, there would be a serious decrease in both commercial and recreational fish and crustacean stocks, adding to the already pressured fishing industry.
Lastly, and most important to this study, they act as a filter, removing the toxins and pollutants from runoff before the water reaches the ocean.
This last service that salt marshes provide us as a water treatment plant, may lead to it’s demise according to the study by Linda Deegan and associates. After nine years of studying the direct effects of nutrients on salt marshes by actually introducing them into the system and investigating their effects, it is apparent that the addition of nitrates into the system alters the framework that holds a salt marsh together: the grasses and roots.
In addition to a process known in the agricultural world as lodging, where the plant grows too tall and spindly eventually falling over, the increased nutrients lead to a decrease in root growth. The salt marsh grasses put most of their effort into growth, instead of stabilization and the increased nutrients sped up the decomposition rates below the ground. This eventually (results were seen in about 4 to 5 years) caused the root system to break apart in the areas closest to water, forming “cracks in the marshes” which eventually grew bigger and collapsed into the mud. (seen above)
This study is a reminder that even the most resilient ecosystems are being effected by pollution and runoff. What do you think increased nutrients will do to systems that do not have the resilience of salt marshes? What do you do to decrease your nutrient loads to the environment?
Let us know in the comments below