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Vertical nitrate migration and denitrification zones in a regional recharge area (Lwówek region, Poland)

Dragon Krzysztof, Górski Józef, Burghardt Diana

Geological Quarterly

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2022

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Vol. 66, No. 2

art. no. 15

EN

We examine the influence of groundwater flow patterns and denitrification on nitrate migration in a regional recharge zone. It has been shown that nitrate contamination has a different behaviour in regions where groundwater is exploited (where deep percolation of nitrate takes place) than where natural gradients exist (with no deep aquifer zone contamination). Multicomponent chemical tracers and isotopic methods were used in the investigation. A contaminant plume was discovered in shallow parts of the aquifer which percolated into deeper parts of the flow system in those regions with a downwards gradient induced by groundwater withdrawal, where the influence of denitrification was limited. Local conditions leading to intense denitrification, i.e., local changes in geological conditions (low-permeability silt intercalations), were also documented. Therefore, vertical changes in groundwater chemistry should be examined to ensure groundwater resource management and protection, as these are extremely important in regional recharge zones with a downwards gradient.

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Genetic correlation of source rocks and natural gas in the Polish Outer Carpathians and Paleozoic–Mesozoic basement east of Kraków (southern Poland)

Kotarba M. J., Więcław D., Bilkiewicz E., Dziadzio P., Kowalski A.

Geological Quarterly

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2017

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Vol. 61, No. 4

795--824

EN

Natural gas-source rock correlations in the Polish Outer Carpathians and Paleozoic–Mesozoic basement in the Kraków–Brzesko–Nowy Sącz area (southern Poland) have been established. In the Dukla and Sub-Silesian units, mixed kerogen Type-II/III or III/II occurs. The organic matter is immature or low-mature. The Oligocene Menilite beds of the Silesian Unit are rich in TOC and contain gas-prone Type III kerogen of low maturity. In the Paleozoic–Mesozoic basement, the TOC content and residual hydrocarbon potential vary in the Middle and Upper Devonian strata, Mississippian carbonate and clastic facies and Middle Jurassic strata. The Paleozoic strata are capable of thermogenic hydrocarbon generation, while organic matter in the Middle Jurassic rocks is generally immature. Gaseous hydrocarbons accumulated both in the Silesian and Dukla units of the Polish Outer Carpathians and in the Mesozoic basement are genetically related to thermogenic and microbial processes. The Outer Carpathian natural gas was generated mainly from the Type-II/III kerogen of the Oligocene Menilite beds. The thermogenic gases from the Mesozoic basement were generated from Devonian and Mississippian (carbonate) Type-II and mixed II/III kerogens and probably from Silurian/Ordovician Type-II kerogen and Middle Jurassic Type-III/II kerogen occurring at more than 7 km depth. Microbial methane migrated into the Outer Carpathian flysch succession from the Miocene strata of the Carpathian Foredeep.

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A Better-developed soil profile during biblical times in the western Galilee. 15N evidence in 14C - dated groundwater

Rogojin V., Kronfeld J., Carmi I., Talma A. S.

Geochronometria

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2002

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Vol. 21

79-84

EN

Despite almost a hundred years of reforestation efforts, the recharge area of the Judea Group aquifer in the hills of the western Galilee still shows the signs of the severe soil erosion that transpired in previous centuries. At present the soil profile is thin and basement rock is often exposed. Historical and Biblical sources suggest that the hills in the past were more forested. Therefore, the delta 15N values of dissolved nitrate were measured in radiocarbondated groundwater to see if evidence for past soil conditions could be deduced. Nitrate mineralization processes in soils lead to enrichment in 15 N of the residual nitrate, which being dissolved by rain enters into the groundwater without further isotopic fractionation. Previous studies have shown that there is a trend of increasing delta 15 N in a soil profile from plant, to litter, to the organic material in the soil. In addition, there is a tendency for higher delta 15 N values to be observed in those samples that have been taken at greater depth in a soil profile due to progressive mineralization and subsequent nitrification of soil organic material. As long as the dissolved oxygen is not depleted, denitrification will not occur to alter the isotopic composition of the dissolved nitrate. The nitrate concentrations and delta 15 N values, water chemistry, tritium and radiocarbon activities were measured from the phreatic outcrop recharge region, and onwards into the confined portions of the Judea Group aquifer and its continuation into the juxtaposed Kurdani and Pleistocene aquifers. The radiocarbon activity decreases with flow. Tritium values of above 2 TU are restricted to the recharge region. Using an initial 14 C activity of 64 pMC the radiocarbon ages of the water are found to range from recent to 7800 BP. The delta 15 N values of the dissolved nitrate within the young water recharge area fall in the range of +3.1 to +4.8› (Air), having a mean of +3.9› (n=5). In older water the nitrate concentration increases slightly, while the delta 15 N ranges from +4.7 to +7.2› (Air), having a mean of +6.4› (n=17). The increase in the delta 15 N values in the older water down-dip is not due to denitrification processes; for, the waters are well oxygenated. These older waters infiltrated at the same point of origin in the phreatic portions of the aquifer (non-contaminated) as the recent water. As the earlier infiltrating water flowed down dip they retained the delta 15 N values of the environment at that time. The delta 15 N values present evidence that, compared to the present, the soil and plant cover was better developed in earlier times, including Biblical times.