Visualizing and quantifying the spatiotemporal expansion of the Blue Lentic Belt in Alabama and Mississippi

Abstract

The Blue Lentic Belt is a spatial belt of dense lentic habitats formed in the Mobile River Basin since the 1990s, and it is imposing considerable environmental stress on local and downstream aquatic habitats. Depicting the spatiotemporal evolution of the Blue Lentic Belt is essential to understanding its formation and consequential impacts on local environments. However, relevant discussion on it is absent since the Blue Lentic Belt is a new discovery. In this study, we developed a retrospective delineation method to visualize the spatiotemporal evolution of the lentic habitats in the Mobile River Basin and a tesseral model to numerically analyze the spatiotemporal expansion of the Blue Lentic Belt. In the developed method, the baseline inventory of lentic habitats is first delineated from 2019 Sentinel-2 satellite imagery at a spatial resolution of 10 m. The baseline inventory is then used to retrospectively delineate the past lentic habitats in the Mobile River Basin using the National Land Cover Database (NLCD). Kernel density surfaces of lentic habitat image objects are estimated to detect the regions of dense lentic habitats, which sequentially form spatiotemporal objects of dense lentic habitats. The spatiotemporal objects of dense lentic habitats are projected onto planar space and are then structuralized as groups of spatial tesserae, namely α-peaks, β-slopes, and γ-edges. Attributes of these tesserae are numerically derived to quantify the spatiotemporal expansion of the Blue Lentic Belt. The results indicate that the Blue Lentic Belt has 4 α-peaks, 3 β-slopes, and a single γ-edge. It is formed from 4 stable hotspots (α-peaks) of the densest lentic habitats. The expansion of the Blue Lentic Belt ranges about 15.42 km. The expansion distance is about 0.57 of the average range of the β-slopes in the Blue Lentic Belt, indicating a significant change of landscape in the Mobile River Basin. The development of the farm-raised catfish industry is considered the main driving force in the formation of the Blue Lentic Belt. The outcomes of this study have emphasized the rapid expansion of the Blue Lentic Belt and its negative impacts on local and downstream aquatic habitats, which calls for attention to systemic investigations by multiple disciplines.