## 1 Introduction  
Throughout the last decades, trace elements have become one of the greatest environmental concerns all over the world because of their ubiquitous character, persistence, non-degradability, availability, bioaccumulation, and high toxicity [1, 2, 3, 4, 5, 6, 7, 8]. Apart from natural sources, which are insignificant, trace elements' release, distribution, and contamination of different environmental compartments are due to anthropogenic activities such as industrialization, transport, mining, urbanization, agriculture, etc., [2, 4, 5, 9]. These anthropogenic activities are intensified due to the rapid increase in the world population, with more than 60% living in coastal regions within 60 km from the seashore, with a projection of 75% by 2050 [10, 11]. This situation exerts strong pressure on wetlands, resulting in an increase in all kinds of pollution loads [11], including those caused by trace elements. Among the environments contaminated by trace elements, aquatic ecosystems, particularly coastal ones, are more vulnerable because of their great ecological and socio-economic importance [12; 13]. Coastal aquatic ecosystems and estuaries, particularly, are breeding grounds for several aquatic species such as fish, and for the development of the larval and juvenile stages of many species due to the high nutrient inputs [13; 14]. The monitoring of aquatic ecosystems' pollution by trace elements has become increasingly important in recent years and is a very important subject of global concern. Some of these trace elements (Fe, Cu, Zn, Ni, Mn, Cr, As, etc.) are essential and required for biological functions, but can be toxic when their threshold concentrations are exceeded. However, others such as Pb, Hg, Cd, Sb, etc., have no metabolic function and are toxic to living organisms even at low concentrations [8; 15; 16; 17; 18]. Thus, toxic trace elements' contamination of the aquatic environment poses a serious ecological and public health concern [19; 20; 21; 22]. A better study of environmental quality must necessarily use geostatistical methods. These methods are able to provide spatial models that can identify sources of contamination and pollution risk areas, enhance decision-making processes, and better guide management strategies. This spatial information is neglected by univariate and multivariate statistical methods. Thereby, it is important to always consider geostatistical techniques or combine them with multivariate analyses to better explain the behavior of environmental quality parameters. For that, significant advancement has been noticed in the environmental assessment regarding spatiotemporal variabilities [23; 24]. Multivariate statistical methods such as PCA, CHA, and correlation matrix allow one to reveal the possible origins, entry routes of the parameters, and processes which affect the quality of the environment [25; 26]. The spatial variability of pollutant concentrations, such as trace elements in an environment, has often been used to understand and explain their possible sources and determine the most polluted and critical areas [27; 28; 29]. The spatial variation can be performed using methods of geostatistics and spatial analysis such as interpolation technique, [29; 30; 31] as described by [PERSON] and [PERSON] [32]. A better study of water quality must necessarily use geostatistical methods. These methods are capable of providing spatial models that can identify sources of contamination, risk areas, and better guide management strategies [29; 30; 31]. For more than a half-century, the coastal zone of Togo, which is also the watershed of Lake Togo, has been the place of phosphoric mining. This activity releases a lot of different kinds of mining waste into the watershed without their treatment or appropriate management [33; 34]. However, high concentrations of trace elements were detected in these phosphorites by some studies [35; 36; 37; 38; 39; 40].