Biogeochemical Controls on Strontium Fate at the Sediment–Water Interface of Two Groundwater-Fed Wetlands with Contrasting Hydrologic Regimes

Abstract

Radioactive strontium (Sr) is a common groundwater contaminant at many nuclear sites. Its natural retention in groundwater-fed wetlands is an attractive remediation strategy. However, at present, the biogeochemical mechanisms controlling Sr transport at the sediment-water interface are poorly understood. In this field study, Sr fate was investigated in two wetlands with contrasting vegetation and hydrologic regimes. The marsh was an open-water wetland with constant water table and no emergent vegetation. The swamp was vegetated with fluctuating water levels and a thick mat of submerged cattail litter in the water column. High-resolution porewater Sr concentrations and solid-phase sediment Sr species revealed distinct profiles between the two wetlands. The marsh exhibited a strongly reduced environment and sharp concentration peaks at the sediment-water interface. In contrast, the smaller concentration gradients of the swamp resulted in a reduced flux of Sr to the surface water. The organic fraction of the sediment dominated Sr retention compared to the inorganic iron and manganese oxides. However, the marsh had a significant fraction of recalcitrant Sr presumably due to its incorporation into sulfur and/or carbonate minerals. These results suggest that vegetated wetlands with fluctuating hydrologic regimes could act as efficient sinks for Sr pollution.

Fresh Groundwater Discharge as a Major Source of 90Sr into the Coastal Ocean

“…In this study, we demonstrated that fresh SGD is an important but overlooked source of 90 Sr in the coastal ocean, which may partly address the issue that has remained unanswered in previous studies, namely, surplus 90 Sr has consistently been found in coastal oceans, but no clear evidence of an additional 90 Sr source has been determined. , Notably, the 90 Sr level in fresh groundwater measured in this study is much lower than the drinking water limit of the World Health Organization (WHO) (10 4 Bq m –3 ), and thus, its effect on public health is not of primary concern here. However, due to its high mobility, 90 Sr is a ubiquitous and troublesome anthropogenic radionuclide in groundwater around nuclear facilities. , Extremely high 90 Sr levels have been found in groundwater near nuclear facilities and nuclear test sites worldwide (Table ). For example, the 90 Sr activity in groundwater near the FDNPP reached as high as 5 × 10 9 Bq m –3 .…”

“…There are currently more than 200 nuclear power plants situated along coastlines worldwide . Despite stricter environmental and safety regulations, the expected increase in global nuclear electricity production by 2050 may lead to 90 Sr contamination at more sites. , Thus, we suggest that the subterranean pathway for the release of 90 Sr into the coastal ocean should be considered in the management and risk assessment of coastal areas near nuclear power plants. Furthermore, the implications of our findings could extend beyond 90 Sr to other highly mobile radionuclides (such as 3 H and 129 I).…”

“…The 90 Sr activity in fresh groundwater exhibited high (in XSB and QZB) and low (in DSB) negative correlations with pH, while no clear linear correlations were found between the 90 Sr activity and DO concentration, salinity, and temperature of groundwater (Figure 3). Sr exists as a bivalent ion regardless of the redox potential of natural water on the Earth's surface; 37 thus, it is reasonable that no correlation exists between the 90 Sr activity and DO concentration. Reportedly, the distribution coefficient of 90 Sr between particles and solution varied little (within a range of 3−4 mL g −1 ) between 5 and 30 °C, 38 so the temperature is not the main factor influencing the 90 Sr activity in groundwater, as demonstrated by our results.…”

“…However, due to its high mobility, 90 Sr is a ubiquitous and troublesome anthropogenic radionuclide in groundwater around nuclear facilities. 37,50 Extremely high 90 Sr levels have been found in groundwater near nuclear facilities and nuclear test sites worldwide (Table 1). For example, the 90 Sr activity in groundwater near the FDNPP reached as high as 5 × 10 9 Bq m −3 .…”