Our paper on the landscape pattern of cypress dome wetlands in Big Cypress National Preserve, led by Adam Watts, is available online at Earth Surface Processes and Landforms. Using a variety of lines of evidence, we show that cypress domes are regularly distributed, and that this pattern is more strongly reflected in the bedrock and vegetation than in soil elevations. We also expand on and refine our conceptual model of how this pattern arises. In brief, we propose that cypress domes are drilling into the limestone bedrock via the acidity of organic matter and CO2 production by vegetation. This local positive feedback expands wetland basins vertically and laterally. As wetlands expand, they essentially come into competition for runoff from the adjacent uplands, which ultimately limits the size and density of wetlands on the landscape. Patterns of soil phosphorus suggest that P mobilization by this dissolution may amplify this biogeomorphic feedback. This paper lays the foundation for our new NSF grant, which will support more mechanistic study of the processes that create these wetland basins and control their distribution on the landscape.
We've just heard from NSF that our proposal to study the wetlands of Big Cypress National Preserve will be funded! The Big Cypress landscape is a mosaic of isolated wetlands, grasslands, and pine forests. The core observation that motivates our proposal is that the Cypress wetlands appear to be regularly spaced. This sort of regular pattern occurs in dryland vegetation, in peatlands (including the nearby Everglades) and elsewhere, and is thought to arise from feedbacks that are spatially-dependent. Basically, organisms improve the environment in their immediate vicinity, but that has the effect of making more distant locations unsuitable. In Big Cypress, we think that cypress trees essentially capture water from the surrounding landscape by dissolving the limestone bedrock and creating wetland depressions. Pretty smart! Testing this core hypothesis, and all of its pieces, requires an interdisciplinary team. My colleagues at UF, who are going to do most of the field work, include ecohydrologists, soil scientists, and organic and inorganic geochemists. Brad Murray and I are in charge of developing a model of this landscape. It's gonna be fun.
Meredith Steele's paper (with a long list of co-authors) on the surface water characteristics of US cities has been accepted at Ecosystems! Congratulations Meredith!
Abstract: Earth’s surface is rapidly urbanizing, resulting in dramatic changes in the abundance, distribution and character of surface water features in urban landscapes. However, the scope and consequences of surface water redistribution at broad spatial scales are not well understood. We hypothesized that urbanization will lead to convergent surface water abundance and distribution: in other words, cities will gain or lose water such that they become more similar to each other than are their surrounding natural landscapes. Using a database of more than 1 million water bodies and 1 million km of streams, we compared the surface water of 100 US cities with their surrounding undeveloped land. We evaluated differences in areal (AWB) and numeric densities (NWB) of water bodies (lakes, wetlands, etc.), the morphological characteristics of water bodies (size), and the density (DC ) of surface flow channels (i.e. streams and rivers). The variance of urban AWB, NWB, and DC across the 100 MSAs decreased, by 89%, 25%, and 71% respectively, compared to undeveloped land. These data show that many cities are surface-water poor relative to undeveloped land; however, in drier landscapes urbanization increases the occurrence of surface water. This convergence pattern strengthened with development intensity, such that high intensity urban development had an areal water body density 98% less than undeveloped lands. Urbanization appears to drive the convergence of hydrological features across the US, such that surface water distributions of cities are more similar to each other than to their surrounding landscapes.
New paper on hydrologic feedbacks in the Everglades has been published in PLoS One. In this study, we develop a mathematical model of interactions between peat accumulation, vegetation productivity, soil elevation, and water flow. We show that the resulting feedbacks can cause spontaneous divergence of ridges and sloughs, and that these feedbacks act differentially with direction. The model provides a range of predictions that we are hoping to test with data from our Everglades monitoring project. You can download the paper here.
Our paper on ecohydrologic feedbacks and pattern formation has just been accepted for publication in PLoS One. This paper uses a simple quasi-spatial model to show that the need to route water through the Everglades landscape, in conjunction with local positive feedbacks on peat accretion, can produce directional feedbacks that generate flow-perpendicular pattern. The model also makes a number of predictions about relationships between water flow and microtopographic variation that we hope to test with our large-scale Everglades field sampling. Will post a link to the paper as soon as it is in press.
Anna Braswell, PhD student in the lab, has received a grant from the Garden Club of America to support her research on land use history and the structure and resilience of coastal wetlands. Way to go Anna!
This is the homepage of the Heffernan Lab at Duke University. Here you can find all sorts of information about our research, teaching, and outreach. If you have any questions, contact Dr. Heffernan.
Dr. Jim Heffernan
I am an Assistant Professor in the Nicholas School of the Environment at Duke University. My research is focused on the causes and consequences of major changes in ecosystem structure, mostly in streams and wetlands.
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