Understanding Lake Dynamics and Redcedar Encroachment in the Nebraska Sand Hills: A Remote Sensing and Modelling Perspective

The primary objectives of the dissertation were to (1) understand how the hundreds of lakes in the Nebraska Sand Hills (NSH) respond to climatic events such as drought (2) determine if the lakes can be used to monitor groundwater levels to supplement the sparse monitoring network in the NSH and (3) predict the encroachment of Eastern Redcedar in the NSH through 2100. The first chapter assessed the response of lake surface area (size) derived from Landsat satellite images to drought. The results showed a spatial and temporal variation in lake size response to seasonal and long-term droughts. Annual lake size showed greater correlation, R2, and lower mean square error (MSE) towards drought highlighting that lake size can be used to understand and estimate the response to climate effects. The second chapter developed a method to measure and monitor the groundwater level variation using lake water level. Light detection and ranging (LIDAR) combined with the waterline method showed high correspondence of lake water level with the water level of observation wells. The estimated lake groundwater level (LGL) when interpolated with kriging with an external drift (KED) showed a local groundwater level variation while universal kriging (UK) revealed regional groundwater level. The study provides a framework to monitor groundwater level using LIDAR technique. The third chapter explores the potential Redcedar encroachment scenarios that could affect the water balance and hydrology in the NSH. The Landsat images with a deep neural network (DNN) approach were able to estimate the moderate to high Redcedar encroachment at a regional scale. The potential encroachment scenarios, simulated using Markov chain cellular automata model, show the predicted spatial and temporal variation. The results show the Redcedar coverage increases mainly in the natural setting such as riverbanks and loess canyons/hills with few newer pockets of encroachment areas