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Saltwater Sportsman Magazine, Feb 2007
THE DISAPPEARING ACT
Why we’re loosing the most important marine ecosystems on earth, and what’s being done about it.
By Capt. John McMurray
Suspended between dry land and open water, salt-marshes are perhaps the most ecologically rich and productive environments in the world. The grasses provide habitat for numerous invertebrate and fish species. The detritus left by dying grasses produce a rich organic substrate that fuels the entire marine food chain. Marshes further serve as important nurseries for bait and juvenile sportfish. Yet their importance stretches quite a bit farther. Salt-marshes serve as massive filters, removing tide-driven silt, sediments and toxins from the water and breaking down pollutants into less harmful forms. They also act as a buffer absorbing large volumes of water associated with a storm surge, thus minimizing the impacts of flooding and erosion. The devastation of last year's Gulf Coast hurricanes serves as a grim reminder of the importance of coastal marshes.
We are drawn to the chartreuse, deep green or soft brown salt-marsh because of the extraordinary angling opportunities it offers. What red-blooded angler hasn’t enjoyed throwing a fly or a plug to a tailing redfish in a mudflat, or worked poppers up against the marsh’s sod banks for ravenous stripers? The abundance of wildlife, the isolation and the serenity such environments provide make the experience of fishing all that much more interesting.
Going, going, gone
During the twentieth century, Atlantic and Gulf coast salt-marshes declined dramatically. Historical wetland surveys suggest that almost half of the marshes that existed in 1900 are gone. Human activities are responsible for most of the loss. Dredging, filling, and draining of salt marshes for mosquito control, and to provide space for industrial sites, housing developments, garbage dumps, highways, airports etc. caused most of the destruction prior to the 1970s, when their importance in ecological systems became understood and laws like the Clean Water Act and the Coastal Zone Management Act were implemented.
However, we are still losing vast expanses of salt-marsh. Even after human activities were halted, or in places where human-related damage never occurred, the marshes continue to shrink. The reasons for the dramatic declines are often complex, and in many cases scientists are still making educated guesses.
The Dynamics of a Marsh and Sea Level Rise.
A coastal marsh is built up slowly. Its plants root into an organic peat created from their own rotting stems and leaves, as well as the accumulated sediment that is brought in on the tide. Coastal salt-marshes are balance between the buildup of peat and sediment anchoring their roots and the depth of the water that washes over them each tide. Once a marsh can no longer construct substrate fast enough to keep up with the level of the sea, it starts to slowly drown.
That would seem to make the sea level rise associated with global climatic change the biggest factor in marsh-loss. However, coastal marshes can, to a large degree, adapt to the changing conditions, and historical records show that, to a remarkable extent, they have. Studies show that that alteration to coastal processes caused by humans is a much greater threat to salt marshes than sea level rise. The many man-made modifications in and around just about every Gulf and East Coast salt marsh are, cumulatively, wreaking havoc with such vital ecosystems.
So what’s happening?
The obstruction of sediment supplies that have historically worked to build up coastal marshes seems to be the biggest factor in most coastal marshes’ retreat. Canalization and dredging in the vicinity of marshes has altered the way in which sediment moves into the system from river systems and the ocean. Hydrodynamics and circulation have been severely altered in some cases by the construction of highways, dredging of navigation channels, and of deep borrow pits to provide fill for various construction projects. This has resulted in a “sediment sink,” that removes a source of sediment formerly available to maintain marsh elevation.
Furthermore, the shorelines around the edges of many coastal marshes have been stabilized and barrier beaches have been developed, effectively limiting over-wash of sands during storms that once contributed sediment to the marshes.
This lack of sedimentation increases water depth and increases wave activity across the tidal flats which slap against the marsh working to break it down over time. The increased numbers of boaters have contributed to the problem as well. Growing traffic and the resulting wakes have been working to erode marsh edges, and as erosion proceeds and marsh islands diminish in size, fetch will increase across the bay, producing more wave action and thus creating even more erosion.
Changes in land use and thus runoff within the watersheds have altered the character and amount of freshwater and sediments delivered to marshes. Both landfills and wastewater treatment plants have contributed excessive amounts of nutrients and contaminants to salt-marshes. The nutrients cause excessive aquatic plant growth. The effects of vigorous sea lettuce growth in some marshes, which is most likely stimulated by high nutrient levels, has smothered other marsh vegetation and limits its growth in some marshes. Furthermore, the excess nutrients often result in blooms of various species that can kill a marsh. Dense banks of mussels along the marsh edge are blocking small marsh drainage channels in several northeast coastal marshes. This causes water to pond on the marsh surface for long periods after high tides, waterlogging the marsh soil and killing marsh vegetation.
There are other causes as well. Over- harvesting of blue crabs may be triggering a die off of salt marshes in the southeastern coast. Without blue crabs to control snail populations, the vegetation that anchors salt marsh habitats is being eaten away. Overabundance of nutria, a rodent which was introduced in Louisiana in the late 1930s for its valuable fur, has also been blamed for some coastal marsh retreat due to its excessive appetite for cord grass.
The Good News:
Tidal wetlands trends analysis has shown that in some areas, the regulatory programs instituted to protect tidal wetlands from the historic "fill and build" damage has been successful. In areas, such as Shinnecock and Moriches Bay on Long Island, there is no detectable loss. In fact, the wetlands have increased over 250 acres in Shinnecock and Moriches Bay due to the natural landward migration of the wetlands.
In areas where marsh loss is particularly bad, state and federal agencies have finally begun to do something about it. Trial remediation projects are being instituted up and down the coast. These include building marsh islands in some areas by placing clean dredged material and planting vegetation, or protecting the remaining marsh islands from wave action by using structures, or by altering the slope of the marsh edge. For example, Jamaica Bay, a 10,000-acrea salt marsh comprising part of Gateway National Park, is loosing an astounding 44 acres/year. The Park Service, The Army Corps, The Port Authority and the NY DEC have embarked on a full-scale restoration project to address the marsh island recession issue.
That is good news for all us anglers…