Note: A recent issue of Science magazine included a special section called ‘Natural Systems in Changing Climates’ that covered a range of contemporary research about the impact of recent climate behavior on ecosystems and species stability. These articles are a great opportunity to understand the cutting edge knowledge we have about what anthropogenic climate change is doing to our planet. Furthermore, it gives a glimpse into how scientists find and sift through new information to better understand the consequences of climate change. Unfortunately, Science requires a subscription, limiting the range of readership to those outside scientific fields. So, I thought I would spend a few blog posts reviewing the major points from the articles included in the special section. This post will be discussing the article “Can Coastal Marshes Rise Above It All?’ found here.
A Delicate Balance
Wetlands – not the first habitat you would think of putting in the Top 10 Sexiest Earth Ecosystems. But marshes, generally defined as regions of land that are completely saturated with water either all year round or during certain seasons, have been shown to be crucial ecosystems for providing carbon sequestration, storm protection, and water filtering. According to a feature article in Science, these habitats are in extreme danger of drowning due to rapidly increasing sea levels.
Wetlands, like the one pictured above from my current state of residence (Florida), are often typified by this view of clumps of plant life rising up from large pools of water. Much conservation activity in Florida tries to prevent wetland draining aimed at improved irrigation and creating more suitable crop land. However, marshes along the Atlantic coast, such as one in Rhode Island that is the focus of the article, are facing the opposite problem. Rising sea temperatures have melted ice sheets, causing sea levels to rise 1.4-37 millimeters per year in the past half-century. Computer models predict this rise will accelerate to 1 centimeter per year based on the warming trends we are currently seeing.
This may not seem like much, but this is part of the adjustment in perspective we must make in learning more about what we’re doing to the planet: all these ecosystems around us are delicate. Only small perturbations to their current state are required to drastically change their outlook and survivability. In the case of coastal marshes, the ecosystem depends on water saturation levels in a narrow region just above high tide. An increase of a few centimeters in water level will drown most of the plants currently residing there.
Why are these plants so crucial to the ecosystem? The key is in their ability to trap sediment. As current pass through the marshes, the plant leaves catch dirt and convert it into minerals used to accrete sediment in the region. This sediment accretion helps to reduce current velocities and create a transitional region between inland and open ocean. This creates a luscious mix of land and water that is a rich ecosystem for many animals, such as herons, turtles, beavers, dragonflies, and a host of fish. Even if we are only concerned about human needs, coastal marshes are important as a barrier from coastal hazards. It is clear that if plants drown in wetland areas due to increasing sea levels, sediment will no longer be trapped and this distinct ecosystem will no longer be able to survive.
As an example, the image above shows results from a digital elevation model (DEM) done by Larsen and colleagues for the Blackwater National Wildlife Refuge on Chesapeake Bay. The top picture shows current elevation, and the region of tan color around the refuge shows the low marsh areas. The middle and bottom images show model results assuming 3 mm/year and 6 mm/year sea level increase rates – both show a drastic ‘drowning’ of these regions of marsh. The 6 mm/year rise, quite realistic based on sea temperature projections, shows a basic disappearance of the wetlands all together.
What’s a Wetland To Do?
According to geologist Matthew Kirwan, interviewed in the Science article, the marshes have three main options: 1) attempt to build up sediment at a more rapid pace to compensate for the increased sea levels, 2) migrate inland to higher elevation, or 3) die out. Researchers are now trying to understand what factors determine which route a coastal marsh may take.
As far as sediment build-up is concerned, more recent computational studies have given a glimmer of hope for these endangered wetland regions. In particular, a recent study by Kirwan et al shows that if the sea level only rises at a moderate pace, wetlands can survive if enough sediment can survive. This suggests that restoration efforts aimed at pumping mud into at-risk regions could prevent drowning. They also found that plants adapted for higher tide regions are more resistant against drowning – a purposeful expansion of these types of species could also prevent widespread drowning.
Unfortunately, the migration option appears less and less likely, mainly because human development has given the coastal marshes nowhere to go. According to the article, walls to prevent homes near the sea or industrial fences are blocking any possible paths for marshes to move. As one of the only possible solutions, conservationists and government organizations are attempting to protect the few migratory paths left and analyzing soil composition of nearby forests and farmland to see if new paths could be created. These efforts are currently being tested in the Chesapeake Bay region shown above as well as on Long Island.
It’s important to emphasize this impact of our development on the adaptability of natural systems. Our species has expanded exponentially to every nook and cranny sidestepping those ecosystems that are important to us, but this only works if we assume that these ecosystems will continue to function exactly as they have been and exactly where they are. But, in the case of the coastal marshes, this delicate balance of water saturation and sea level requires the marsh to adapt when these variables change. But we have given them no room to adapt, to change, to be flexible and migrate in order to survive. Our expansion assumed nature is static, in a sense, when all evidence shows it is anything but that. Thus it seems a key part of conservation and a vision for a sustainable society is providing space for natural adaptation.
Even Scientists Argue
One last point about the scientific method. Contrary to popular conservative media outlets, scientists are not colluding to propagate the hoax of climate change. We examine the evidence – in this case, the planet and its ecosystems – and make conclusions based on the patterns we see. This can and often leads to arguments between researchers who believe one piece of evidence has very different meanings or interpretations. In the case of the coastal marshes, it surrounds the appearance of shallow pools of water in coastal marshes. Biologist Marci Ekberg, of the conservation group Save the Bay, believes these are warning ‘symptoms’ of marshes close to drowning. Other researchers, namely Mark Bertness of Brown University, claims there is no evidence of correlation between pool formation and sea level rise. Rather, he attributes the pools to winter ice damage, weeds, or some other factor yet to be determined.
But these are the important debates to be had. Instead of entering a situation already believing to understand based on preconceived notions, science allows a cadre of individuals to each research the evidence and claim conclusions. These conclusions can be debated in a public form – peer-reviewed articles, conferences, etc. – that further winnow our understanding closer and closer to the truth. This same process has occurred over the years of understanding climate change, and only after insurmountable evidence has the scientific community concluded that climate change is real and anthroprogenic – not because we all want it to be, but because it is what the world is showing us.
So yes, scientists disagree, and that’s what allows us to get closer to the truth, face reality, and hopefully save some of the wetlands.
Eli Kintisch, Can Coastal Marhes Rise Above It All? Science 2 August 2013: 341 (6145), 480-481. [DOI:10.1126/science.341.6145.480]