ECOHYDROLOGICAL FEEDBACKS CONTROLLING MICROTOPOGRAPHY, VEGETATION DIVERSITY, AND LANDSCAPE PATTERN IN LOW-GRADIENT, LOTIC PEATLANDS

Lotic peatlands, in which flow and sediment transport coexist with organic sediment production, exhibit complex morphologic dynamics that can give rise to topographic and vegetative landscape patterns. We propose that two major classes of feedback mechanisms exert control over landscape dynamics in these systems. The first class involves differential rates of peat accretion for different vegetation assemblages resulting from differential evapotranspiration, concentration of nutrients, constituent organic material, and peat elevation relative to the water table. These peat accretion feedbacks control the vertical dimensionality of the landscape and are similar to those controlling elevation differences between hummocks and hollows in boreal bogs. The second class of feedbacks, similar to those controlling channel morphology in anabranching streams, encompasses interactions between vegetation, flow velocity, and sediment transport. These “anabranching river feedbacks” likely exert lateral and longitudinal control over topographic features. Within a certain region of the biogeochemical/hydrologic/biological parameter space, the combined effects of the differential peat accretion and anabranching river feedback mechanisms can produce topographic and vegetative patterning that is stable over long timescales.

The ridge and slough landscape of the Florida Everglades provides unique insight into the feedback mechanisms controlling landscape dynamics in low-gradient, lotic peatlands. Historically, the landscape exhibited longitudinal patterning in the microtopography and vegetation that remained stable for 2,700 years. Over the past century, anthropogenic perturbations to flow and flooding depth/duration have diminished patterning and heterogeneity. Using the Everglades as a case-study, we combine field data with modeling to explore criteria for the stability of heterogeneity under the proposed suite of hydrologic, biogeochemical, and biological feedbacks.