Johanson, Erik

The term "collapse" has become a widely used term that oversimplifies the intricate histories of human-environment interactions. It has contributed to the belief that civilizations in the Americas and the tropics could not endure over time. However, the Manteño civilization of the Ecuadorian coast challenges this notion. Flourishing for a thousand years (ca. 650–1700 CE), the Manteños inhabited the neotropics at the gates of one of the world's most influential climatic forces, the El Niño-Southern Oscillation (ENSO). To thrive, the Manteños needed to navigate the extremes of ENSO during the Medieval Climate Anomaly (MCA, ca. 950–1250 CE) and the Little Ice Age (LIA, ca. 1400–1700 CE) while capitalizing on ENSO's milder phases. This research uses change detection analysis of Normalized Difference Vegetation Index (NDVI) on Landsat satellite imagery under various ENSO conditions from 1986 to 2020 in southern Manabí, where the 16th-century Manteño territory of Salangome was situated. The findings indicate that the cloud forests found in the highest elevations of the Chongón-Colonche Mountains provide the most resilient environment in the region to adapt to a changing climate. Further investigations of the cloud forest of the Bola de Oro Mountain using Uncrewed Aerial Vehicles (UAV) equipped with LiDAR, ground-truthing, and excavation uncovered a landscape shaped by the Manteños.

The Florida Everglades is a vast subtropical wetland that historically spanned over 1,000,000 hectares, but much of the Everglades has changed in the last 100 years due to anthropogenic activity. Collier County was subject to alteration in the form of logging, road building, and canal digging. These actions disrupted the natural sheet flow of water and had large environmental impacts on the region, impacts which are slowly being addressed by Everglades restoration efforts. The aim of this project was to observe the effects of environmental change at a cypress swamp forest in Collier County within the Big Cypress National Preserve. Using sediment core data including charcoal analysis, loss on ignition, and peat humification, as well as remote sensing techniques, this project uses a novel approach to assess local environmental conditions in the modern era. Historical records and contemporary data are used to evaluate change over time, and satellite imagery is used to quantify vegetative health. Modification of the environment related to anthropogenic activity is noted, and evidence of progress from restoration efforts is observed from the last two decades in our study’s data.

This project expands on the 4200-year history of Laguna Los Mangos by adding diatom analysis to existing records of pollen, charcoal, elemental composition, and stable light isotope analysis. Diatoms were counted in peroxide-treated samples, and data were analyzed using cluster analysis, PCA, CCA, and Pearson correlation. Diatom variability was correlated with nitrogen and organic material. Before 3430 cal yr BP, diatoms reflect landscape instability with higher lake levels and macrophyte cover. This period was followed by a period of agriculture-induced nutrient pollution, reduced pH, and increased precipitation until about 2450 cal yr BP. Peaks in A. granulata may indicate periods of increased mixing driven by precipitation. Diatom composition reflects reduced agricultural activity and lake desiccation during the TCD and increased precipitation and agricultural collapse during the LIA. Overall, this record reflects a history of slightly alkaline, eutrophic conditions, increasing salinity, and human disturbance from maize agriculture and deforestation.

Wetlands are an essential part of the water management system in South Florida, providing many ecosystem services. However, the hydrologic connections of many wetlands, including Loxahatchee Slough in Florida, are poorly understood. Loxahatchee Slough is Palm Beach County’s most diverse natural area and a site of ongoing restoration. The primary objective of this research was to characterize the spatial and temporal variability of surface-groundwater exchange at Loxahatchee Slough. The Magnitude of groundwater seepage to the canal varied spatially. Little seasonal variability in exchange was identified in this study. Canal stage had a strong relationship with groundwater levels and slough stage indicating its important influence. This study provides more insight into the heterogeneous nature of wetland-canal exchange and the need for site-specific evaluation at wetlands for successful management.