A Multi-Tracer Study of Fresh Water Sources for a Temperate Urbanized Coastal Bay (Southern Baltic Sea)

Terrestrial surface waters and submarine ground water discharge (SGD) act as a source of dissolved substances for coastal systems. Solute fluxes of SGD depend on the ground water composition and the water-solid-microbe interactions close to the sediment-water interface. Thus, this study aims to characterize and evaluate the hydrogeochemical gradients developing in the fresh-salt water mixing zone of the Wismar Bay (WB), southern Baltic Sea, Germany. Sampling campaigns covering the WB, the fresh-salt water mixing zone at the beach of the WB shoreline, terrestrial surface and ground waters near the WB as well sediments pore water were carried out. In these different waters, the distribution of dissolved inorganic carbon, nutrients, major ions, trace elements, stable isotopes (H, O, C, S), and radium isotopes have been investigated. Enhanced concentrations of radium isotopes together with dissolved manganese, barium in the surface waters of the eastern WB indicated benthic-pelagic coupling via the exchange between pore water and the water column. Salinity, stable isotopes, and major ions in sediment pore water profiles identified the presence of fresh ground water below about 40 cmbsf in the central part of the bay. Geophysical acoustic techniques revealed the local impact of anthropogenic sediment excavation, which reduced the thickness of a sediment layer between the coastal aquifer and the bottom water, causing, therefore, a ground water upward flow close to the top sediments. The fresh impacted pore water stable isotope composition (δ18O, δ2H) plot close to the regional meteoric water line indicating a relatively modern ground water source. The calculated organic matter mineralization rates and the dissolved inorganic carbon sediment-water fluxes were much higher at the fresh impacted site when compared to other unimpacted sediments. Therefore, this study reveals that different fresh water sources contribute to the water balance of WB including a SGD source.

Using a delayed coincidence counting system to determine ²²³Ra, ²²⁴Ra in seawater sample

A Radium Delayed Coincidence Counter (RaDeCC) includes 3 channels (223Ra channel,224Ra channel, and total channel). It has been newly designed and assembled at Nuclear Research Institute. To determine 223Ra and 224Ra in seawater samples, the system efficiency at all 3 channels were investigated and calibrated. The research results showed that the RaDeCC operates stably and reliably with high efficiency of 26%. In this project, a procedure for measuring short half-life radium isotopes was established with a low detection limit (LOD (223Ra) = 0.002 Bq; LOD (224Ra) = 0.01 Bq), good reproducibility, and high precision. The technique is suitable for qualitative analysis of 223Ra, 224Ra in seawater samples at low concentration. The 11 coastal water samples were collected in a coastal of Ninh Thuan province. The analytical data of short-lived radium isotopes concentration in seawater at Ninh Thuan coastal area are 11.2 × 10-3 ÷ 45.5 × 10-3 mBq/L for 223Ra, and 34.7 × 10-2 ÷ 21.9 × 10-1 mBq/L for 224Ra.

The role of seagrass leaf litter in the SGD-derived nutrient fluxes in Cala Pudent (Menorca, western Mediterranean)

<div> <p>The assessment of the biogeochemical cycles in coastal environments often relies on riverine inputs as the main source of nutrients and other dissolved compounds from land to the ocean. However, the discharge of groundwater through continental margins, commonly known as Submarine Groundwater Discharge (SGD), is also recognized as relevant sources of nutrients to the coastal ocean, particularly in oligotrophic and semi-arid environments, such as the Mediterranean Sea. In this study, we use radioactive tracers (radium isotopes and radon) to i) quantify the magnitude of SGD-driven nutrient fluxes to a Mediterranean cove (Cala Pudent, Menorca, Balearic Islands) and ii) characterize the nutrient transformations occurring in the beach before groundwater discharges to the sea. Cala Pudent is a limestone coastal cove with a restricted connection to the open sea. In this system, groundwater from a permanent spring infiltrates through an organic substrate dominated by thick deposits of seagrass (Posidonia oceanica) leaf litter and flows into the sea. This substrate, together with the dynamic groundwater-seawater mixing, are chiefly influencing the nutrient enrichment and transformation occurring in the beach and thus modulating the SGD-derived nutrient input to the sea. The ecological implications of these inputs are also assessed, particularly for the Posidonia oceanica and Cymodocea nodosa meadows located near the study site.  </p> </div><div> <p> </p> </div>

Elevated radium levels in Nubian Aquifer groundwater of Northeastern Africa

The Nubian Sandstone Aquifer System in Northeast Africa and the Middle East is a huge water resource of inestimable value to the population. However, natural radioactivity impairs groundwater quality throughout the aquifer posing a radiological health risk to millions of people. Here we present measurements of radium isotopes in Nubian Aquifer groundwater from population centers in the Western Desert of Egypt. Groundwater has 226Ra and 228Ra activities ranging from 0.01 to 2.11 and 0.03 to 2.31 Bq/L, respectively. Most activities (combined 226Ra + 228Ra) exceed U.S. EPA drinking water standards. The estimated annual radiation doses associated with ingestion of water having the highest measured Ra activities are up to 138 and 14 times the WHO-recommended maxima for infants and adults, respectively. Dissolved Ra activities are positively correlated with barium and negatively correlated with sulfate, while barite is approximately saturated. In contrast, Ra is uncorrelated with salinity. These observations indicate the dominant geochemical mechanisms controlling dissolved Ra activity may be barite precipitation and sulfate reduction, along with input from alpha-recoil and dissolution of aquifer minerals and loss by radioactive decay. Radium mitigation measures should be adopted for water quality management where Nubian Aquifer groundwater is produced for agricultural and domestic consumption.