Salt marshes are one of the most productive areas on the planet and they are disappearing. Salt marshes are wetlands on the coast that have been flooded and drained by tides ebbing and flooding.
In order for them to form they need a source of fresh water which mixes with the ocean tides and creates brackish conditions. These rich ecosystems exist in low energy and relatively flat areas of the coast where salt-tolerant species of herbs, shrubs and grasses are able to grow among the intricate network of channels and pools that protect and nourish many terrestrial and marine species.
Salt marshes provide irreplaceable services to our coast. For example, plant roots reduce erosion of coastlines and trapping nutrients and sediment, which builds organic matter to form peat, and are able the vegetation mutes wave action impacts on the coast. the ecosystem is capable of o grow and keep pace with the rising ocean. The salt marsh acts as a large filter for water entering the ocean.
Only a small amount of the vegetation is directly consumed. Most of the vegetation is broken down by bacteria and small insects. The decaying plants and microbes are then eaten by larger crustaceans, insects, fish, and mussels that reside in the marsh soils. Once the tide comes in, larger fish are able to locate and eat the smaller critters. That is how the salt marsh provides food for aquatic organisms, like salmon, that are valuable to our economy and culture.
Historically, seventy percent of the Fraser River estuary wetlands have been diked, drained, and filled to create land for development. On Vancouver Island, Canada, about half of both the Nanaimo and Cowichan estuary wetlands have been lost. What is unsettling is that the salt marshes seem to be receding and there seems to be no singular reason why. There are many hypotheses. Some suggest declines are due to increases in nitrogen runoff, which diminishes the root growth of plants. Others suggest increases or decreases in sediment starve or overwhelm the system. Climate change and drought are mainly blamed for increased salinity and creating temperatures that salt marsh species cannot tolerate.
Tranquil River's salt marsh, 20km north-east of Tofino, which is located in Vancouver Island, Canada, has also been experiencing noticeable declines in salt marsh habitat over the past few decades. for instance, in 1994, salt marsh was the dominant habitat type in the estuary. By 2012, over half of the estuary was made up of sand and mud flat and the 10.5 hectares of salt marsh was reduced to 7.4 hectares. This reduction is especially concerning as salt marshes are generally dominated by sedges which are critical habitat for at risk juvenile Chinook salmon in Clayoquot Sound. In this circumstance, the loss of habitat may be caused by infilling. This influx of sediment is likely due to material transport from upslope instability caused by historical logging.