Evaluating the integrity of forested riparian buffers over a large area using LiDAR data and Google Earth Engine

Abstract

Spatial and temporal changes in land cover have direct impacts on the hydrological cycle and stream quality. Techniques for accurately and efficiently mapping these changes are evolving quickly, and it is important to evaluate how useful these techniques are to address the environmental impact of land cover on riparian buffer areas. The objectives of this study were to: (1) determine the classes and distribution of land cover in the riparian areas of streams; (2) examine the discrepancies within the existing land cover data from National Land Cover Database (NLCD) using high-resolution imagery of the National Agriculture Imagery Program (NAIP) and a LiDAR canopy height model; and (3) develop a technique using LiDAR data to help characterize riparian buffers over large spatial extents. Onemeter canopy height models were constructed in a high-throughput computing environment. The machine learning algorithm Support Vector Machine (SVM) was trained to perform supervised land cover classification at a 1-m resolution on the Google Earth Engine (GEE) platform using NAIP imagery and LiDAR-derived canopy height models. This integrated approach to land cover classification provided a substantial improvement in the resolution and accuracy of classifications with F1 Score of each land cover classification ranging from 64.88 to 95.32%. The resulting 1-m land cover map is a highly detailed representation of land cover in the study area. Forests (evergreen and deciduous) and wetlands are by far the dominant land cover classes in riparian zones of the Lower Savannah River Basin, followed by cultivated crops and pasture/hay. Stress from urbanization in the riparian zones appears to be localized. This study demonstrates a method to create accurate high-resolution riparian buffer maps which can be used to improve water management and provide future prospects for improving buffer zones monitoring to assess stream health. Despite the relatively low spatial extent of riparian buffer areas, they are a major concern for land and water resource managers. Evaluation of the land cover within the riparian buffer areas is critical to protecting water quality 1. The effects of different land cover at the watershed scale can influence the flow of water and nutrients to water bodies, resulting in impacts to stream water quality 2 from increased sedimentation, higher nutrient and contaminant concentrations, and changes to hydrological patterns 3. Land cover mapping is essential to obtain a better understanding of interactions and relationships between human activities and the environment over time. The effect of change in land cover varies by region, geographical location, and spatial scale. Quantifying and assessing land cover is essential to formulating integrated land and water resources management strategies 4,5. Land cover classification can be used as a proxy to the human footprint, which can result in land degradation and a loss of biodiversity 6. Rapid population growth in the Savannah River basin region has had dramatic impacts on the n...

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