Development of a numerical model for nitrates in groundwater in the reservoir area of the Komesu subsurface dam, Okinawa, Japan

A numerical model consisting of simplified equations was developed to simulate nitrate concentrations in groundwater in a reservoir area of a subsurface dam in a Quaternary limestone region. The model was composed of a water balance sub-model and a nitrogen balance sub-model; the water balance sub-model was built from tank models which can express the quick dilution near caves and the effect of dam construction; and the nitrogen balance sub-model was made to represent changes in nitrogen forms and movement of nitrogen in the soil and aquifer zones. The model was calibrated and verified by observed data before and after the dam construction and then applied to a predictive simulation under a simple assumption that rainfall descends gradually. The model seemed applicable to long-term prediction of changes in NO₃-N in the reservoir area.     

Rhenium and osmium systematics on iron and stony iron meteorites

Abstract— Re and Os abundances and ¹⁸⁷Os/¹⁸⁶Os isotopic ratios in 12 iron meteorites of various groups and five stony iron meteorites have been determined by an inductively coupled plasma mass spectrometry (ICP-MS). The series of iron meteorites studied have Re and Os concentrations ranging from 0.004 to 3.3 ppm and 0.03 to 41 ppm, respectively. The ¹⁸⁷Re/¹⁸⁶Os ratios in these meteorites fall between 3.0 and 6.1 and the ¹⁸⁷Os/¹⁸⁶Os between 1.0 and 1.2, giving an initial ¹⁸⁷Os/¹⁸⁶Os isotopic ratio of 0.790 and a Re-Os age of iron meteorites of 4.30 ± 0.28 Ga when employing the decay constant of 1.64 × 10^?11 yr^?1. The observed Re-Os age for iron meteorites appears somewhat younger than that for chondrites. The resultant younger age might be due either to a very slow cooling of the parental planetesimals or due to a secondary “shock” event. However, for definite conclusions about the Re-Os age, higher precisions of the Re and Os isotopic measurements and of the decay constant of ¹⁸⁷Re are required. Furthermore, the clear elucidation of the mechanisms for the fractionation of the Re/Os abundance ratios are related to the understanding of the meaning of the Re-Os age. The Re and Os abundances in pallasite stony iron meteorites are extremely low compared with those for most iron meteorites. On the other hand, the Re and Os abundances in mesosiderite stony iron meteorites show values comparable with those observed in most iron meteorites. The difference in Re and Os abundances in pallasite and mesosiderite stony iron meteorites strongly suggests that these stony iron meteorites are different in origin or history of chemical evolution. Re and Os abundances in the series of iron and stony iron meteorites were found to have a wide variation covering nearly four orders of magnitude, with a very high correlation coefficient (0.996), and a slope very slightly less than unity. The regression line observed here covers various groups of iron meteorites, stony iron meteorites and also chondrites. Masuda and Hirata (1991) suggested the possible direct mixing process of particles of most refractory metallic elements with gaseous clouds of less refractory matrix elements, since the Re and Os were predicted theoretically to be the first elements to condense as a solid phase from the high temperature solar nebula. The aims of this paper are to present a reliable technique for the Re-Os chronology and to study the cosmochemical sequences of the meteoritic metals.     

Trace elements and stable isotope ratios (δC and δN) in fish from deep-waters of the Sulu Sea and the Celebes Sea

Trace elements (TEs) and stable isotope ratios (δ¹⁵N and δ¹³C) were analyzed in fish from deep-water of the Sulu Sea, the Celebes Sea and the Philippine Sea. Concentrations of V and Pb in pelagic fish from the Sulu Sea were higher than those from the Celebes Sea, whereas the opposite trend was observed for δ¹³C. High concentrations of Zn, Cu and Ag were found in non-migrant fish in deep-water, while Rb level was high in fish which migrate up to the epipelagic zone, probably resulting from differences in background levels of these TEs in each water environment or function of adaptation to deep-water by migrant and non-migrant species. Arsenic level in the Sulu Sea fish was positively correlated with δ¹⁵N, indicating biomagnification of arsenic. To our knowledge, this is the first study on relationship between diel vertical migration and TE accumulation in deep-water fish.