9 pages | [EN] An excess of carbon dioxide is found in the atmosphere due to the burning of fossil carbon. A theoretical calculation of the quantity of this excess that can be dissolved in sea water is made. The calculation is made on the assumption that the CO2 reacts with the calcium carbonate on the sea bed until a balance of the balance of the dissolution of CO3CA is re-established. The quantity which can be eliminated is 91%, but 9% will allways remain in the atmosphere and can only be eliminated if the quantity of organic matter fossilised is equal to the quantity of fossil carbon burn | [ES] Se hace el cálculo teórico de la cantidad de dióxido de carbono que puede disolverse en el agua de mar, del que se encuentra en exceso en la atmósfera procedente de la combustión de carbono fósil. El cálculo se hace en el supuesto que el CO2 reacciona con el carbonato cálcico del lecho marino hasta restablecer el equilibrio de disolución del CO3CA. La cantidad que puede ser eliminada es del 91%, pero siempre quedará en la atmósfera un 9% que solo puede ser eliminado si la cantidad de materia orgánica que se fosiliza es igual ala cantidad de carbono fósil que se quema | Peer reviewed

The City of Manson, Iowa (USA), lies near the center of the Manson Impact Structure (MIS), a 37-km diameter impact crater that formed about 74 million years ago. The MIS is present at the bedrock surface, but it is completely buried by 20–90 m (70–300 ft) of glacial till and displays no surface expression. Groundwater samples were collected from Manson’s municipal well and nearby domestic wells to assess the sustainability of unusually soft water that typifies the central peak of the Manson Impact Structure. Groundwater quality indices from the various aquifer sources were distinctly different, with groundwater from the central peak of the crater exhibiting low Ca (<22 mg/L) and alkalinity (<127 mg/L as CaCO₃), and high concentrations of fluoride (>3.7 mg/L; max = 10.0 mg/L) and certain trace elements (e.g. Li, Mo, W). In contrast, groundwater collected from wells in overlying Quaternary aquifers was very hard (high Ca and Mg), with high alkalinity (>261 mg/L as CaCO₃), sulfate (58–485 mg/L) and occasionally nitrate-N (up to 6 mg/L). Age-dating techniques using³H,¹⁴C, and³⁶Cl suggested water older than 35,000 years to possibly as old as 1,000,000 years within the central peak aquifer, but indicated recent water in overlying aquifers. Pumping of the Manson municipal wells appears to be mining old water of the central peak aquifer and drawing modern water containing elevated hardness and nitrate-N down into the aquifer. The Manson example illustrates a source-water challenge of balancing aquifer quality with sustainability.

Submarine groundwater discharge (SGD) is widely acknowledged as a key driver of environmental change in tropical island coral reefs. Previous work has addressed SGD and groundwater-reef interactions at isolated submarine springs; however, there are still many outstanding questions about the mechanisms and distribution of groundwater discharge to reefs. To understand how groundwater migrates to reefs, a series of offshore ²²²Rn (radon) and submarine electrical resistivity (ER) surveys were performed on the tropical volcanic island of Mo’orea, French Polynesia. These surveys suggest that fresher water underlies the fringing reef, apparently confined by a <1-m-thick low-permeability layer referred to as a reef flat plate. Reef flat plates have been documented elsewhere in tropical reefs as thin, laterally continuous limestone units that form through the super-saturation of calcium carbonate in the overlying marine waters. In other tropical reefs, the reef flat plate is underlain by a highly permeable karstic limestone formation, but the submarine reef geology on Mo’orea is still uncertain. Numerical modeling of two-dimensional reef transects and SGD quantifications, based on water budget and radon/salinity mass balance, support the confining nature of the reef flat plates and indicate important implications for SGD impacts to tropical reefs. Except where incised by streams or local springs, reef flat plates may route SGD to lagoons or to the reef crest 100s of meters offshore. Because groundwater can transport pollutants, nutrients, and low pH waters, the reef flat plate may play an important role in the spatial patterns of reef ecology and coastal acidification.