Using remote sensing to detect indicator species of tidal influence along the lower Apalachicola River, Florida

Abstract

Wetlands are an important part of coastal ecosystems for the multiple services they provide, including erosion control, water quality, and wildlife habitat. With the threat of rising sea levels, it is important to understand the potential shifts in these ecosystems for the services they provided and for the overall health of the environment. Apalachicola Bay is one of the most productive coastal systems in the southeastern United States (U.S.). Important shifts in freshwater input to the bay and lower Apalachicola River have been caused by managed flows in the watershed, recent and significant droughts, and climate change. Studying wetlands along the Apalachicola River, the primary objectives of this work were to: (1) understand the range of the tidal freshwater forested wetlands along the lower Apalachicola River based on the detection of cabbage palm (Sabal palmetto) using image classification of National Agriculture Imagery Program (NAIP) imagery, and (2) analyze shifts in tidal herbaceous vegetation through a time series image analysis using black needlerush (Juncus roemerianus). Both species are understood to be important indicator species of tidal conditions along the lower river. Though the extent of cabbage palm within the study area was greater than expected, the detection of this species showed patterns of occurrence primarily along river ways and along the transitional zone between forest and marshland, Results suggest tidal influence may occur further inland that expected. Based on a 14-year change detection of Juncus marsh, 2008-2014 experienced more gain (596.3 hectares) than loss (114.7 hectares), but the opposite was found in the years between 2014-2022 (157.8 hectares of gain, 371.4 hectares of loss). These results indicate that relative river flow and its control of the lower river salinity may play a role in the distribution of cabbage palm and changes in marsh composition. By better understanding the range of tidal influence along the Apalachicola River, findings from this study will aid resources managers in identifying and mitigating current and future wetland composition shifts.