Scale‐Dependent Patterning of Wetland Depressions in a Low‐Relief Karst Landscape

Abstract

Thousands of small wetland depression features (cypress domes) dot the low‐relief karst of Big Cypress National Preserve (BICY) in South Florida, USA. We hypothesized that these wetland depressions are organized in a regular pattern, which is atypical of wetlandscapes elsewhere. Regular patterning implies the existence of coupled feedbacks operating at different spatial scales, with local wetland depression expansion (facilitation via karst dissolution) limited by competition among adjacent depressions for finite water resources (inhibition). We sought to test the hypothesis that wetlands in BICY exhibit regular patterning, and to quantify pattern properties to evaluate competing genesis mechanisms. We tested four predictions about landscape structure and geometry using high‐resolution Light Detection and Ranging elevation data from six 2.25‐km2 domains across BICY. Specifically, we predicted (1) feature overdispersion resulting from competition between adjacent basins; (2) truncated wetland area distributions due to growth inhibition feedbacks; (3) periodicity in surface elevation indicating a characteristic pattern wavelength; and (4) elevation bimodality indicating distinct upland and wetland states. All four predictions were strongly supported. Depressions were significantly overdispersed and efficiently fill the landscape, generating hexagonal patterning. Wetland areas followed truncated power law scaling, indicating incremental constraints on basin expansion, in contrast to depression areas elsewhere. Variogram and radial spectrum analyses revealed clear periodicity (~150‐ to 250‐m wavelength) in surface elevations. Finally, surface elevations were consistently bimodal with elevation divergence of 10 to 40 cm. Regular patterning of wetland depressions across BICY is clear, implying long‐term biogeomorphic control on landform structure in this karst landscape.

Local Storage Dynamics of Individual Wetlands Predict Wetlandscape Discharge

“…The landscape is characterized by bedrock depressions with a regular pattern spacing of approximately 200 m (Figure 1; insets) (Quintero & Cohen, 2019). The depressions contain deeper soils than the surrounding pine uplands (Watts et al, 2014).…”

“…The coefficient r ET is an effective value over the whole wetlandscape, that is, including inundated and noninundated areas. The inundated fraction A r [−] of the total area was determined as a function of the detrended stage at monitoring locations TR1, TR2, TR3, BCA16, and BCNPA14 (Figure 4) based on circles of 500 m radius in order to capture multiple wetlands (pattern period ≈ 200 m; Quintero & Cohen, 2019). The function A r ( h ) is simply the hypsometric curve, that is, the cumulative distribution function of ground surface elevation in each circle.…”

Pathways for Methane Emissions and Oxidation that Influence the Net Carbon Balance of a Subtropical Cypress Swamp

“…The combination of low relief and a humid subtropical climate with mean annual precipitation of 1.33 m (McPherson, 1974;Shoemaker et al, 2011) results in significant water storage on the landscape. Thousands of small (< 2 ha) karst depressions dot the landscape in a remarkable regularly patterned landscape of distributed water storage (Quintero and Cohen, 2019). These depressions have far thicker soils (Watts et al, 2014) with far higher OC content (Zhang et al, 2019) than the surrounding uplands because they hold water for much of the year, thereby supporting hydrophytic vegetation such as pond cypress (Taxodium ascendens) and a variety of wetland taxa (e.g., Salix caroliniana, Cladium jamaicense).…”

“…Barometric pressure correction was performed using data collected from barometric pressure transducers (Solinst Barologger) deployed in a dry well adjacent to each water level recorder. LIDAR digital elevation models were provided by the National Center for Airborne Laser Mapping, processing of the LIDAR digital elevation models are described in detail in Quintero and Cohen (2019). Elevations are reported with an estimated mean accuracy of 5 cm across each domain, and with a spatial resolution of 5 m. The surface area of the center, intermediate, and edge sections of each wetland were determined based on elevation thresholds that aligned with shifts in vegetation coverage and inundation extent.…”

“…The cypress domes in BICY are thought to form via feedback between water storage and carbonate rock dissolution, mediated and accelerated by organic matter cycling (Cohen et al, 2011;Dong et al, 2019). The resulting regular pattern of wetland sizes and arrangement (Quintero and Cohen, 2019) illustrates the importance of these feedbacks in creating geomorphic structure, a process thought to have occurred over the last 10,000 years (Chamberlin et al, 2018;Zhang et al, 2019).…”