Quantifying hydrologic controls on local- and landscape-scale indicators of coastal wetland loss

Annals of Botany
By: , and 

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Abstract

Background and Aims

Coastal wetlands have evolved to withstand stressful abiotic conditions through the maintenance of hydrologic feedbacks among vegetation production and flooding. However, disruption of these feedbacks can lead to ecosystem collapse, or a regime shift from vegetated wetland to open water. To prevent the loss of critical coastal wetland habitat, we must improve understanding of the abiotic-biotic linkages among flooding and wetland stability. The aim of this research was to identify characteristic landscape patterns and thresholds of wetland degradation that can be used to identify areas of vulnerability, reduce flooding threats, and improve habitat quality.

Methods

We measured local- and landscape-scale responses of coastal wetland vegetation to flooding stress in healthy and degrading coastal wetlands. We hypothesized that conversion of Spartina patens wetlands to open water could be defined by a distinct change in landscape configuration pattern, and that this change would occur at a discrete elevation threshold.

Key Results

Despite similarities in total land and water cover, we observed differences in the landscape configuration of vegetated and open water pixels in healthy and degrading wetlands. Healthy wetlands were more aggregated, and degrading wetlands were more fragmented. Generally, greater aggregation was associated with higher wetland elevation and better drainage, compared to fragmented wetlands, which had lower elevation and poor drainage. The relationship between vegetation cover and elevation was non-linear, and the conversion from vegetated wetland to open water occurred beyond an elevation threshold of hydrologic stress.

Conclusions

The elevation threshold defined a transition zone where healthy, aggregated, wetland converted to a degrading, fragmented, wetland beyond an elevation threshold of 0.09 m NAVD88 (0.27 m MSL), and complete conversion to open water occurred beyond 0.03 m NAVD88 (0.21 m MSL). This work illustrates that changes in landscape configuration can be used as an indicator of wetland loss, with specific elevation thresholds to inform restoration and conservation planning to maximize wetland stability in anticipation of flooding threats.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Quantifying hydrologic controls on local- and landscape-scale indicators of coastal wetland loss
Series title Annals of Botany
DOI 10.1093/aob/mcz144
Edition Online First
Year Published 2019
Language English
Publisher Oxford Academic Press
Contributing office(s) Wetland and Aquatic Research Center
Country United States
State Louisiana, Texas
Other Geospatial Chenier Plain, Gulf of Mexico, McFaddin National Wildlife Refuge, J.D. Murphree Wildlife Management Area