publications > paper > a delicate balance: ecohydrological feedbacks governing landscape morphology in a lotic peatland
A Delicate Balance: Ecohydrological Feedbacks Governing Landscape Morphology in a Lotic Peatland
Laurel G. Larsen,1,3 Judson W. Harvey,2 and John P. Crimaldi1
1428 UCB, University of Colorado, Boulder, Colorado 80309 USA
212201 Sunrise Valley Drive, MS 430, Reston, Virginia 20192 USA
Manuscript received 26 July 2006; revised 9 March 2007; accepted 27 April 2007. Corresponding Editor: J. B. Yavitt.
|©2007 by the Ecological Society of America. Posted here with permission; Ecological Monographs, 77(4), 2007, pp. 591-614.
The Everglades ridge and slough landscape is characterized by elevated sawgrass
ridges regularly interspersed among lower and more open sloughs that are aligned parallel to the
historic flow direction. Landscape degradation, characterized by topographic flattening, has
coincided with a century of drainage, levee construction, nutrient enrichment, and flow
reductions. Here we develop a conceptual model of Everglades landscape dynamics based on a
literature synthesis and supported by the numerical model PeatAccrete. We propose that two
feedback mechanisms govern landscape characteristics. The first, simulated with PeatAccrete,
involves differential peat accretion governed by water level and phosphorus concentration,
leading to the attainment of an equilibrium ridge elevation relative to slough. Differential peat
accretion, however, cannot produce a characteristic ridge width or landscape wavelength.
Instead, we propose that feedback between channel morphology and sediment mass transfer
controls lateral and longitudinal topographic features, consistent with processes in anabranching
rivers. This sediment transport feedback was critical in pattern initiation and evolution, and
sediment redistribution from slough to ridge provides a plausible mechanism for preventing
gradual ridge expansion. However, PeatAccrete model results show that, in the absence of
sediment transport, ridges expand only on the order of meters per century. This result suggests
that a combination of factors has driven the widespread disappearance of sloughs over the past
century, including altered vertical peat accretion rates that lead to slough infilling. Sensitivity tests
indicated that changes in duration and depth of surface water inundation, phosphorus supply,
and redox potential have altered differential peat accretion rates in a way that favors topographic
flattening. These factors are relatively well defined compared with the role of sediment transport,
which requires further quantification. Because both positive and negative feedback processes
interact in the Everglades, the trajectory of landscape evolution in time will depend upon current
conditions, with areas of remnant ridge and slough topography being more likely than areas of
degraded topography to respond to changes in water management in ways that enhance
landscape heterogeneity over human timescales. Dual feedbacks between peat accretion and
sediment transport are likely important controls on landscape evolution in low-gradient
peatlands worldwide with pulsed, unidirectional flow.
Key words: anabranching; Everglades; Florida; geomorphology; landscape ecology; peatland; ridge-slough; wetland; wetland hydrology.
SOFIA Project: Effect of Water Flow on Transport of Solutes, Suspended Particles, and Particle-Associated Nutrients in the Everglades Ridge and Slough Landscape