Complex networks of functional connectivity in a wetland reconnected to its floodplain

Abstract

Disturbances such as fire or flood, in addition to changing the local magnitude of ecological, hydrological, or biogeochemical processes, can also change their functional connectivity—how those processes interact in space. Complex networks offer promise for quantifying functional connectivity in watersheds. The approach resolves connections between nodes in space based on statistical similarities in perturbation signals (derived from solute time series) and is sensitive to a wider range of timescales than traditional mass‐balance modeling. We use this approach to test hypotheses about how fire and flood impact ecological and biogeochemical dynamics in a wetland (Everglades, FL, USA) that was reconnected to its floodplain. Reintroduction of flow pulses after decades of separation by levees fundamentally reconfigured functional connectivity networks. The most pronounced expansion was that of the calcium network, which reflects periphyton dynamics and may represent an indirect influence of elevated nutrients, despite the comparatively smaller observed expansion of phosphorus networks. With respect to several solutes, periphyton acted as a “biotic filter,” shifting perturbations in water‐quality signals to different timescales through slow but persistent transformations of the biotic community. The complex‐networks approach also revealed portions of the landscape that operate in fundamentally different regimes with respect to dissolved oxygen, separated by a threshold in flow velocity of 1.2 cm/s, and suggested that complete removal of canals may be needed to restore connectivity with respect to biogeochemical processes. Fire reconfigured functional connectivity networks in a manner that reflected localized burn severity, but had a larger effect on the magnitude of solute concentrations.

Sheet Flow Effects on Sediment Transport in a Degraded Ridge‐and‐Slough Wetland: Insights Using Molecular Markers

“…Although the direction of flow from the S‐152 was generally radial (as expected from a point source), dye deployed at the S‐152 confirmed findings by Larsen et al (), showing a preferential flow east toward the control sites C1 and Z6‐1 (Eric Cline, SFWMD, personal communication; Sklar & Dreschel, ). The apparent contradiction between greater hydrologic connectivity east of S‐152 (Larsen et al, ) but greater sediment source changes to the south (based on biomarker changes) could potentially be explained by the differential movement of dissolved versus particulate forms in the water column. Hydrologic connectivity quantified by Larsen et al () is based on both dissolved and particulate water column constituents (and only dissolved constituents for dye studies), whereas the change in Paq reflects movement of only particulate, macrophyte‐derived organic matter.…”

“…PC2 may also reflect the long‐term decline in HBI values over the study period, observed in both habitats (Figure S3). The underlying driver for this change remains unclear but may be a response to a fire in June 2011, which burned ridges throughout the study area (described in Larsen et al, ), or by a flow‐mediated change in slough vegetation. The latter, however, seems less likely as such changes were mainly evident in a small subset of high‐flowing sites nearest the S‐152 (Saunders, ).…”

“…The remnant patterning of ridges and sloughs in the DPM study area is oriented approximately north to south (Figure a), whereas water moving south is moving parallel to the orientation of the remnant ridge‐and‐slough pattern, flows moving eastward go against the grain (i.e., perpendicular) of the patterning. Analyzing the spatial and temporal covariance of water quality parameters, Larsen et al () found that S‐152 flows increased hydrologic connectivity between the S‐152, the high‐flow areas, and the control sites directly east of the S‐152. Although the direction of flow from the S‐152 was generally radial (as expected from a point source), dye deployed at the S‐152 confirmed findings by Larsen et al (), showing a preferential flow east toward the control sites C1 and Z6‐1 (Eric Cline, SFWMD, personal communication; Sklar & Dreschel, ).…”

“…Analyzing the spatial and temporal covariance of water quality parameters, Larsen et al () found that S‐152 flows increased hydrologic connectivity between the S‐152, the high‐flow areas, and the control sites directly east of the S‐152. Although the direction of flow from the S‐152 was generally radial (as expected from a point source), dye deployed at the S‐152 confirmed findings by Larsen et al (), showing a preferential flow east toward the control sites C1 and Z6‐1 (Eric Cline, SFWMD, personal communication; Sklar & Dreschel, ). The apparent contradiction between greater hydrologic connectivity east of S‐152 (Larsen et al, ) but greater sediment source changes to the south (based on biomarker changes) could potentially be explained by the differential movement of dissolved versus particulate forms in the water column.…”

“…Range of average ADV‐based measurements from Larsen et al () measured in sloughs at RS1, RS2, C1, and UB2 (latter near Z10‐2) during the 2013 flow event.…”