Ambient Background Values of Selected Chemical Substances in Four Groundwater Bodies in the Pannonian Region of Croatia

Abstract

Groundwater quality is a consequence of cumulative effects of natural and anthropogenic processes occurring in unsaturated and saturated zone, which, in certain conditions, can lead to elevated concentrations of chemical substances in groundwater. In this paper, the concept of determining the ambient background value of a chemical substance in groundwater was applied, because the long-term effects of human activity influence the increase in concentrations of substances in the environment. The upper limits of ranges of ambient background values were estimated for targeted chemical substances in four groundwater bodies in the Pannonian region of Croatia, according to the demands of the EU Groundwater Directive. The selected groundwater bodies are typical, according to the aquifer typology, for the Pannonian region of Croatia. Probability plot (PP), the modified Lepeltier method, as well as the simple pre-selection method, were used in this paper, depending on a number of chemical data in analysed data sets and in relation to the proportion of <limit of quantification (LOQ) values in a data set for each groundwater body. Estimates obtained by using PP and the modified Lepeltier method are comparable when data variability is low to moderate, otherwise differences between estimates are notable. These methods should not be used if the proportion of <LOQ values in a data set is higher than 30%; however, the integration of results of both methods can increase the confidence of estimation. If the proportion of <LOQ values is higher than 30%, it is recommended to use the robust pre-selection method with the adequate confidence level. For highly skewed data, the 90th percentile of the pre-selected data set is comparable with other methods and preferable over the 95th percentile. The estimates obtained for inert and mobile substances are comparable on different scales. For highly redox-sensitive substances, estimates may differ by one to two orders of magnitude, in relation to the observed heterogeneity of the aquifer systems. The critical issue in the estimation process is the determination of hydrogeological and geochemical homogeneous units within the heterogeneous aquifer system.

The Health of the Water Planet: Challenges and Opportunities in the Mediterranean Area. An Overview

“…Nitrogen may be present in soil and water mains in four forms (gaseous nitrogen, organic nitrogen, ammonium ion, and nitrates), and it can be introduced into the environment by inorganic fertilizers, human and animal waste, etc. The concentrations of nitrates in Mediterranean waters oscillate between 4 to 496 mg L −1 in MENA Countries and between 3.23 to 50.1 mg L −1 in European Countries [31][32][33]. Balestrini et al (2021) have shown that the increase in nitrate pollution in Mediterranean Countries is often related to the increase in livestock and intensive agriculture, given that the nitrates come from synthetic fertilizers [32].…”

Assessing Natural Background Levels in the Groundwater Bodies of the Apulia Region (Southern Italy)

“…The samples exceeding a fixed value of the chosen markers are eliminated and the NBL is chosen as the 90th, 95th, or 97.7th percentile of the remaining water samples dataset. The main disadvantage of this approach is that the samples are eliminated according to qualitative criteria [17], e. g. the amount of available data and the shape of the related statistical distribution, and that the removal of samples might result in a too scarce data set.…”

Natural Background Levels in Groundwater

“…The main goal of this Special Issue of Water is to bring together and discuss different methodological approaches and tools to improve the assessment of groundwater NBLs. From its first announcement, and after being thoroughly peer reviewed, nine papers have been accepted for publication [3][4][5][6][7][8][9][10][11]. To provide an overview of the experiences collected by this Special Issue, a brief summary of each published paper is reported below.…”

“…To provide an overview of the experiences collected by this Special Issue, a brief summary of each published paper is reported below. A variety of spatial scales is encountered, ranging between national [3,11], regional [3,7,8,10], meso- [6,9] and site-specific [4,5] scales, and different methodologies are applied.…”

“…Another comparison of different methods is presented by Nakić et al [8] for the estimation of the ambient background levels (ANLs) in four groundwater bodies in Croatia. The concept of ABL differs from that of NBL in that it addresses long-term human impacts (e.g., agriculture, urbanization) that have irreversibly altered the natural background hydrochemistry.…”