Impacts of freshwater salinity levels on crop productivity in agricultural river basins in the United States.
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Freshwater salinisation is an increasing global concern as it is a major factor which contributes to reductions in crop yields. Investigating the impacts of salinisation on crop productivity and monitoring the current levels of salinity in agricultural basins is crucial to ensure the prevention of yield declines. The Great-Plains is one of the most important agricultural regions in the United States and vital to the nation’s economy. In recent years challenging environmental conditions in the Great Plains coupled with land-use change has increased the risk of salinisation and sodification and these patterns have been studied. Few studies have investigated exceedance salinity thresholds for different crop types and estimated loss of crops within the Great Plains of the United States. There can be great insight in synthesising surface water, groundwater and soil salinity data with crop data and conducting analysis on a watershed level. Therefore, the objective of this thesis is to investigate spatiotemporal trends in salinity levels, its relation to crop specific salinity threshold exceedances and potential crop losses in a selection of agricultural watersheds in North Dakota over the last two decades. The results of statistical tests such as Mann-Kendall and Wilcoxon-Sign tests show that surface water salinity tends to increase a considerable amount downstream, even at a watershed scale, and increased from 2001-2020. Furthermore, crop salinity threshold analysis shows that over the past decade, a greater number of crop salt tolerance thresholds have been surpassed. Synthesis of crop acreage data and crop salinity threshold data showed the maximum potential production of dry beans – a saline sensitive crop – is impacted by temporal trend of increasing salinity. This thesis also elaborates on salinity management measures utilised within the study region and possible solutions to the increase in salinity.