Spatio-temporal trends and change factors of groundwater quality in an arid area with peat rich aquifers: Emergence of water environmental problems in Tanta District, Egypt Alaa A. Masoud a, * , Katsuaki Koike b , Hamdy A. Mashaly c , Fibi Gergis a a Geology Department, Faculty of Science, Tanta University, 31527 Tanta, Egypt b Graduate School of Engineering, Kyoto University, Kyoto 615-8540, Japan c Holding Company for Drinking Water and Wastewater (HCDWW) Headquarter in the Tanta Headquarter, Egypt article info Article history: Received 23 March 2015 Received in revised form 21 August 2015 Accepted 24 August 2015 Available online xxx Keywords: Groundwater quality Non-parametric statistics Spatio-temporal change Trend analysis Tanta abstract An integrated spatio-temporal statistical, P-spline modeling, ManneKendall and ThieleSen trend detection, and factorial analyses techniques were performed on 438 chemical and 274 microbiological data collected from twenty drinking water supply wells over four years (2010e2013) in Tanta District (Egypt). The prime objective was to characterize the spatio-temporal quality trends using indicators of turbidity, pH, TDS, Cl  , SO 4 2 , Na þ , Total Alkalinity, hardness (Total, Mg, and Ca), Fe 2þ , Mn 2þ , Al 3þ , Cu 2þ , Zn 2þ ,F  , NH 4 þ , NO 2  , NO 3  , PO 4 3 , SiO 2, bacterial, and algal contents. Factorial analysis was applied to identify the significant factors loading the quality variation. Out of the 20 wells, notable upward trends were significant (>95% level) for the total hardness (30%), total alkalinity (20%), TDS (15%), Fe 2þ (15%), Mn 2þ (15%), NO 2  (10%), and 10% for the NH 4 þ , PO 4 3 , and SiO 2 . Attenuation rates (mg/l/year) were higher in NH 4 þ (av. 0.023) than Mn 2þ (av. 0.013) and Fe þ2 (av. 0.010), and remarkable average rates were 6.77 (TDS), 3.27 (total alkalinity), 2.12 (total hardness), 0.79 (SiO 2 ), 0.011 (PO 4 3 ), and 0.002 (NO 2  ) in decreasing order. High precision of the trend estimate was confirmed for the Mn 2þ , NH 4 þ , and Fe 2þ data. Five factors were found to explain 78.8% of the total variance of the quality variables and in particular, a significant load of hardness parameters, Total alkalinity, TDS, Mn 2þ , NH 4 þ , and Fe 2þ in decreasing order were identified. The spatio-temporal variation in pollutants originated from organic matter degradation, either naturally from the aquifer peaty sediments or anthropogenic due to improper well head protection in the urban centers or from the agricultural drains in low relief areas. Our findings have important societal implications regarding the management of the limited and valuable water resources in arid and semi-arid lands. The adopted methodologies could be readily applied to similar alluvial aquifers elsewhere. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Pollution control and remediation of groundwater quality is a worldwide essential prerequisite for mitigating water scarcity and sustainable development. Due to the rapid growth of human needs in many sectors, groundwater resources are always sub- jected to significant challenges accommodated by pollution and health hazard risks. Management of these limited resources is paramount in arid and semi-arid regions experiencing rapid urban development (Grimm et al., 2008). Alluvial regions are more accessible to pollution risks due to high population den- sities and intense agricultural and industrial activities. Under- standing of the factors governing variation and detection of groundwater quality trends in these regions are essential for providing an early warning system for quality changes where protection and sound management of the resource can be effi- ciently set. Spatio-temporal trend tests in groundwater quality studies are rare and difficult because the meteorological, hydrological, and anthropological sources of variation can act individually or combined and vary in intensity both in space and time. The joint modeling of both spatial and time elements in a single spatio- * Corresponding author. Geology Department, Faculty of Science, Tanta Univer- sity, 31527 Tanta, Egypt. E-mail address: alaa_masoud@science.tanta.edu.eg (A.A. Masoud). Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv http://dx.doi.org/10.1016/j.jaridenv.2015.08.018 0140-1963/© 2015 Elsevier Ltd. All rights reserved. Journal of Arid Environments 124 (2016) 360e376