Abstract
Hyperspectral reflectance sensing provides a rapid and cost-effective technique for assessing the suitability of groundwater for irrigation by monitoring real-time changes in its quality at a large scale. In this study, we assessed the quality of 15 groundwater samples from El Fayoum depression in the Western Desert (WD) and 25 groundwater samples from the Central Nile Delta (CND) in Egypt using a traditional approach of the physiochemical parameters, irrigation water quality indicators (IWQIs), and hydrochemical facies. The spectral reflectance data of the water surface was used to build new simple reflectance indices (SRIs), and the performance of these indices for assessing IWQIs was compared with those by partial least square regression (PLSR) that was based on all SRIs or the full-spectrum ranges. Generally, the groundwater of the CND was fresher and more suitable for irrigation purposes than those of the WD. Based on the six IWQIs, ~6.7–60.0% and 85.0–100.0% of the groundwater samples of the WD and CND, respectively, were categorized as highly suitable for irrigation purposes. Based on hydrochemical facies, Na-Cl and Ca-HCO3 were dominant in the WD and CND, respectively, as well as the alkali earth metals (Na+ + K+), which significantly exceeded the alkaline earth metals (Ca2+ + Mg2+) in the WD, with the reverse for the CND. Most developed SRIs had a moderate, weak, and moderate to strong relationship with physiochemical parameters and IWQIs in the WD, CND, and across both regions, respectively. The PLSR models based on all SRIs provided a more accurate estimation of IWQIs in calibration and validation datasets than those based on full-spectrum ranges, and both PLSR models provided better estimation than the individual SRIs. These findings support the feasibility of using ground reflectance measurements as a fast and low-cost tool for the assessment and management of groundwater for irrigation in arid and semiarid regions.
Highlights
Water shortages, especially for agriculture, are prevalent in countries in arid and semiarid regions and they have become more and more severe in these regions in recent years due to a lack of waterWater 2020, 12, 2169; doi:10.3390/w12082169 www.mdpi.com/journal/waterWater 2020, 12, 2169 resources and abrupt climatic changes [1]
During the summer of 2019, 40 groundwater samples were collected from depths of 5–100 m from the Quaternary aquifer to assess groundwater quality for irrigation purposes: 15 samples were collected from the Western Desert (WD) and 25 samples were collected from the Central Nile Delta (CND) (Figure 1)
These results indicate that most of the groundwater samples from both regions of this study are suitable for irrigation purposes and human consumption, as long as the water is treated, in the WD
Summary
Especially for agriculture, are prevalent in countries in arid and semiarid regions and they have become more and more severe in these regions in recent years due to a lack of waterWater 2020, 12, 2169; doi:10.3390/w12082169 www.mdpi.com/journal/waterWater 2020, 12, 2169 resources and abrupt climatic changes [1]. Regular assessment of groundwater quality is necessary to identify its suitability for irrigation purposes where the productivity and quality of crops depend highly on soil characteristics and quality of irrigation water. The irrigation water quality indicators (IWQIs), namely percentage sodium (%Na), sodium absorption ratio (SAR), soluble sodium percentage (SSP), total dissolved solids (TDS), potential salinity (PS), total hardness, and Kelly’s index (KI), which are based on the major cations (K+ , Ca2+ , and Mg2+ ) and ions (Na+ , Cl− , and SO4 2− ), are frequently used to assess the suitability of water for irrigation purposes [4,5,6,7,8]. Accurate and efficient assessment of these indicators can improve the management and effective use of groundwater
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