Spatial evolution and genetic mechanisms of manganese in shallow groundwater of the North Shandong Plain

doi:10.13745/j.esf.sf.2025.10.23

Abstract

Abstract:

Manganese (Mn), a widespread neurotoxic metallic element in groundwater, poses significant health risks when its concentration exceeds the permissible limit (> 0.1 mg·L^-1), potentially inducing Parkinsonian-like neurological disorders. Although previous studies have revealed pronounced spatial heterogeneity of Mn in the shallow groundwater of the lower Yellow River alluvial plain, a systematic understanding of the hydrogeochemical mechanisms controlling its enrichment across different geomorphic units is still lacking. To address this gap, this study investigates the regional distribution of Mn and its controlling factors, complemented by a detailed characterization of representative hydrogeological cross-sections to elucidate the key processes governing high-Mn groundwater. The results indicate that the regional groundwater Mn concentration ranges from below the detection limit to 12.0 mg·L^-1, with a mean of 0.65 mg·L^-1 and an exceedance rate of 96.6%. Along a representative transect, the average Mn concentration increases significantly from the paleochannel highland (0.27 mg·L^-1) to the fluvial plain (0.83 mg·L^-1) and reaches its peak in the coastal plain (2.53 mg·L^-1). This spatial pattern is accompanied by a gradual evolution of hydrochemical facies, from HCO₃-Na-Mg and HCO₃-Cl-Na-Mg types to predominantly Cl-HCO₃-Na-Mg, and finally to the Cl-Na type. The primary sources of Mn are identified as manganese hydroxides and rhodochrosite within the sediments. The regional distribution of Mn is primarily influenced by a series of water-rock interactions, including silicate weathering, dissolution of evaporite minerals, cation exchange, and redox processes. The contributions of these natural sources exhibit significant spatial variations across different hydrogeochemical zones, mirroring the evolution of Mn concentrations. Integrated analysis reveals that the spatial heterogeneity of shallow groundwater Mn is collectively controlled by pH-driven dissolution and adsorption, salinity-driven ion exchange, and the release of Mn from primary sediments under the prevailing depositional background.

Key words: North Shandong Plain, groundwater, manganese (Mn), alluvial plain, hydrogeochemistry

CLC Number:

P641

GUO Jiju, CAO Wengeng, LU Chongsheng, WANG Zhe, ZHU Jingsi, WANG Yanyan, LI Xiangzhi, MA Cuiyan. Spatial evolution and genetic mechanisms of manganese in shallow groundwater of the North Shandong Plain[J]. Earth Science Frontiers, 2026, 33(1): 107-120.

Figures/Tables 14

Fig.1 Study area overview. Geomorphic divisions adapted from[22].

Table 1 Statistical characteristics of the main physicochemical parameters of shallow groundwater sampling points in the typical profile of the study area (n=1 083)

Fig.2 Distribution map of Mn concentration in shallow groundwater within the North Shandong Plain

Table 2 Statistical results for ions exceeding 25% of the total milliequivalents

超过25%毫克当量的离子	HCO₃	HCO₃·SO₄	HCO₃·SO₄·Cl	HCO₃·Cl	SO₄	SO₄·Cl	Cl
Ca	4	0	0	0	0	0	0
Ca·Mg	24	8	0	1	0	8	0
Mg	3	2	0	0	0	0	0
Na·Ca	58	31	9	2	0	9	2
Na·Ca·Mg	118	83	58	0	0	48	2
Na·Mg	84	87	120	14	1	79	43
Na	24	22	24	1	0	19	95

Fig.3 The Piper diagram shows the concentrations of major cations and anions in shallow groundwater of the typical profile in the study area (expressed in units of % meq·L-1)

Table 3 Spearman correlation coefficients between Mn concentration and various hydrochemical parameters in shallow groundwater of the study area

水化学参数	相关系数	水化学参数	相关系数
pH	-0.304^**	${\mathrm{NO}}_{3}^{-}$	0.139^**
Eh	0.196^**	${\mathrm{NO}}_{2}^{-}$	0.133^**
TDS	0.441^**	${\mathrm{NH}}_{4}^{+}$	-0.066^*
Ca²⁺	0.542^**	Fe³⁺	0.128^**
Mg²⁺	0.497^**	Fe²⁺	0.006
K⁺	0.071^*	F^-	-0.211^**
Na⁺	0.322^**	耗氧量	0.213^**
Cl^-	0.494^**	偏硅酸	-0.338^**
${\mathrm{SO}}_{4}^{2-}$	0.426^**	As	-0.176^**
${\mathrm{HCO}}_{3}^{-}$	0.043

Fig.4 Variation characteristics of Mn(a) and related physicochemical factors ((b) Eh、(c) pH、(d)TDS) in shallow groundwater along a representative study area profile

Fig.5 Normalized molar ratio relationships of (a) Mg2+/Na+ and (b) ${\mathrm{HCO}}_{3}^{-}$/Na+ with Ca2+/Na+ in shallow groundwater of the typical profile in the study area

Fig.6 Distribution map of the SI of Mn-bearing minerals in the groundwater of the study area

Fig.7 Gibbs diagram of shallow groundwater of the typical profile in the study area

Fig.8 Ratios of major ions in shallow groundwater of the typical profile in the study area: ${{\mathrm{Ca}}^{2+}}^{}$+ Mg2+ -${{\mathrm{HCO}}_{3}^{-}}^{}$-${\mathrm{SO}}_{4}^{2-}$ to ${{\mathrm{Na}}^{+}}^{}$+ ${{\mathrm{K}}^{+}}^{}$-Cl- ratio; Chloro-alkali index

Fig.9 Relationships related to Mn in the groundwater of the study area: (a) Eh-pH diagram; (b) statistical relationship between Eh and Mn; (c) statistical relationship between pH and Mn

Fig.10 Analysis of the contribution rates of the main controlling factors of groundwater chemistry based on the PMF model

Fig.11 Schematic diagram of the genetic mechanisms for shallow high-Mn groundwater in the North Shandong Plain

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