Redefining salt marsh research: Are coastal wetlands end members or part of a continuum?

When driving back home to Atlanta recently, my leisurely ride came to a screeching halt when I confronted a huge traffic jam. Two cars had crashed entering a tangled spaghetti junction, backing up vehicles at the intersection and for miles down three of the intersecting highways. Even cars and trucks coming in the opposite direction were stalled – rubber-necking! Frustrated is an understatement. I was upset by the delay, but also by the fact that traffic reporters had not spared me this mess. They had not taken into account the linkages to other traffic in the area. In today’s heavily-traveled highway system, it is irresponsible to think about one interstate without taking into account its connections with other interstates.

Salt marsh near the Cape Fear River mouth, North Carolina. Photo by Anna Braswell.

Traffic reporters are not alone in how they analyze and report on complex connections. In coastal wetland ecology, we also tend to neglect the connections within the larger system. We do our research at the point, plot, platform or site scale (“special snowflake syndrome” as one Duke professor has been known to say). Sometimes if feels as if the only studied connection between these wetland systems and terrestrial uplands are nutrients (i.e. “wetlands are the kidneys of the biome”). In the same way, it seems like we give lip service to coastal wetland’s connections to the marine environment (i.e. “coastal wetlands provide a buffer from tropical storms and nurseries for baby fish”). Let’s face it, these statements are usually the opening sentences of a manuscript or proposal, demonstrating wetland value or why it is relevant to study coastal wetlands. So my questions are: How should we think about coastal wetlands? Are coastal wetlands endmembers or discrete ecosystems? Or are they components of a larger system?

Linkages to both terrestrial and marine environments are implicit in the assumptions we make about inputs to coastal wetlands. For example, we report the nitrogen load, tidal amplitude, suspended sediment concentration or community composition of species present. But, we also can connect the processes that generate these variables to the surrounding terrestrial and marine environments. For instance, suspended sediment concentration and nutrients can be connected to upland land use and to the drainage network. So, my question to coastal wetland scientists as a community is: How can we fundamentally connect these systems in ways that will shed light on the future persistence of coastal wetlands?

Here is where a macrosystem framework can be useful to conceptualize these linkages (Heffernan et al. 2014). What is a macrosystem you say? It is the study of ecology at the scale of regions and continents and of the interactions of such scales with others. By collating data, linking networks of observations and experiments, and using remote sensing data, we can scale up already existing data sets or observe broad scale patterns within a hierarchical structure. These patterns can illuminate the mechanisms and processes that link coastal wetlands to terrestrial and marine ecosystems. And critical to all of this is incorporating humans into the macrosystem. Signals coming from coastal wetlands not only incorporate natural variability, but also human land use, degradation and pressure.

Recently, some excellent researchers have started to illuminate the connections between land and water. Patricia Yager came to the Nicholas School to speak about her very interesting work on the influence of the Amazon River on productivity of the Atlantic ocean and river-ocean linkages. Additionally, Michael Osland has done some enlightening work on the role of freshwater availability and temperature in wetland foundation species and ecological transitions in coastal wetlands.

This research has started conceptualizing the links that create the unique setting within which coastal wetlands form. In order to better understand how coastal wetlands will react to anthropogenic pressures, it is time to stop thinking about coastal wetlands as endmembers, and time to start incorporating them into the broader framework of a macrosystem.