Tracer methods used to verify the hypothesis of Cvijić about the underground connection between Prespa and Ohrid Lake     

Sokrat Amataj  Todor Anovski  Ralf Benischke  Romeo Eftimi  Laurence L. Gourcy  Liliana Kola  Ioannis Leontiadis  Eftim Micevski  Alqiviadis Stamos  Jovan Zoto 《Environmental Geology》2007,51(5):749-753

Prespa Lake and Ohrid Lake constitute a hydraulic system shared between Albania, FYR of Macedonia and Greece. Karst rocks separate both lakes. The elevation of Prespa Lake is about 150 m higher than that of Ohrid Lake. Considering these facts, Cvijić formulated in 1906 the hypothesis that Prespa Lake recharges the St. Naum and Tushemisht springs at Ohrid lakeside. Environmental isotopes demonstrated that Prespa Lake recharges about 37–42 and 52–54% of water emerging in St. Naum, and Tushemisht springs, respectively. An artificial tracer experiment carried out in 2002 physically demonstrated the underground connection between both lakes. This experiment confirmed the supposed underground connection and brought important information about the groundwater velocity, transit time, and karst water conduits development.  相似文献   

Water-extractable and exchangeable phosphate in Martian and carbonaceous chondrite meteorites and in planetary soil analogs     

Michael N. Mautner  Sokrat Sinaj 《Geochimica et cosmochimica acta》2002,66(17):3161-3174

Aqueous extraction contributes to the formation and weathering of planetary materials and renders electrolytes such as phosphate available for biology. In this context, the solubility of phosphate is measured in planetary materials, represented by the Mars meteorites Nakhla, Dar al Gani 476 (DaG 476), Elephant Morraine 79001 (EETA 79001), and terrestrial analogs, and in the Murchison CM2 and Allende CV3 carbonaceous chondrites. The Mars meteorites contain high levels of phosphate that is readily extracted by water, up to 15 mg kg⁻¹ in Nakhla and DaG 476 and 38 mg kg⁻¹ in EETA 79001, while the terrestrial analogs and the carbonaceous chondrites contain 0.5 to 6 mg kg⁻¹. Correspondingly, high phosphate concentrations of 4 to >28 mg L⁻¹ are obtained in extracts of the Mars meteorites at high solid/solution ratios, exceeding the concentrations of 0.4 to 2.0 mg L⁻¹ in the extracts of the terrestrial analogs. A wide range of planetary conditions, including N₂ and CO₂ atmospheres, solid/solution ratios of 0.01 to 1.0 kg L⁻¹, extraction times of 1 to 21 d, and temperatures of 20 to 121°C affect the amounts of extractable phosphate by factors of only 2 to 5 in most materials. Phosphate-fixing capacity and exchangeable phosphate are assessed by the isotopic exchange kinetics (IEK) method, which quantifies the amount of P isotopically exchangeable within 1 min (E_1min) and between 1 min and 3 months (E_1min-3m) and the amount of P that cannot be exchanged within 3 months (E_>3m). The IEK results show that the DaG 476 Mars meteorite and terrestrial analogs have low P-fixing capacities, while the carbonaceous chondrites have high P-fixing capacities. Aqueous processing under early planetary CO₂ atmospheres has large effects on the available phosphate. For example, the fraction of total P that is exchangeable in 3 months increases from 1.6 to 11%, 13 to 51.6%, and 43.9 to 90.4% in the DaG 476 Mars meteorite, Allende, and Murchison, respectively. The results show that solutions with high phosphate concentrations can form in the pores of planetary lava ash and basalts and in carbonaceous asteroids and meteorites. These solutions can help prebiotic synthesis and early microbial nutrition. The Martian and carbonaceous chondrite materials contain sufficient phosphate for space-based agriculture.  相似文献