Temporal variations in the salinity of shallow groundwater from the periphery of some North Dakota wetlands (USA)

• Published in: Journal of Hydrology (Amsterdam) [J. HYDROL.]. Vol. 141, no. 1-3. 1993 Vol. 141; no. 1; pp. 75 - 105
• Main Authors: Arndt, J.L, Richardson, J.L
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 1993; Elsevier Science
• Subjects: Brackish; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Geochemistry; Hydrology; Hydrology. Hydrogeology; Lakes; Q1; Midwest; United States; North America; North Dakota; USA, North Dakota; salinity; salt; mobilization; accumulation; ground water; calcite; gypsum; wetlands; grasslands; hydrochemistry; recharge; soil profiles; discharge; ions; electrical conductivity
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/0022-1694(93)90045-B

Several studies have shown the important role of groundwater recharge and discharge on the geochemical development of salinity in prairie wetlands and hydric soils; however, none have focused on the effects of transient groundwater mounding on the accumulation and mobilization of salts within, and between, wetlands. The present study examines temporal variations in the salinity of pondwaters, and near-surface groundwaters collected from hydric soil profiles in brackish to subsaline semipermanent North Dakota wetlands, and places these variations in a geo-hydrological context. Groundwater samples were collected periodically from extractor nests in the peripheral, shallow-marsh zone of the wetlands. Pondwaters were collected from locations near each extractor nest. Standard methods were used to characterize salinity soil, and the saturation status of calcite and gypsum in pondwater and groundwate. All extractor locations had coarse-textured surface sediment overlying finer textured subsurface sediments. The electrical conductivity of groundwaters collected from extractors in coarse-textured surface sediments was usually highest after drawdown and steadily declined after recharge events. Groundwaters collected from fine-textured subsurface sediments were much less variable in EC compared with coarse-textured surface sediments. The greatest variation in the saturation status of calcite and gypsum was associated with pondwater and groundwater from coarse-textured surface sediments that contained little or nor observable amounts of these minerals. Zones containing identifiable calcite and gypsum were usually saturated with respect to these minerals. Zones of gypsum accumulation in particular were fine textured and below the level associated with normal seasonal water fluctuations. Our results indicate that temporal and spatial salinization patterns in near-surface groundwaters and pondwaters are dynamic in semipermanent prairie wetlands, and are closely related to transient recharge events. Electrical conductivity and gypsum distribution patterns in groundwaters and sediments at the extractor locations indicate that salt mobilization from the pond edge can be rapid and is primarily by lateral groundwater flow through coarse-textured surface sediments. Salt accumulation and removal is particularly sensitive to the intensity and location of recharge and drawdown episodes.