Stable isotope enrichment in muscle,liver,and whole fish tissues of brown-marbled groupers(Epinephelus fuscoguttatus)

Introduction:The purpose of this study was to assess enrichments in stable carbon and nitrogen isotopes(δ^(13)C andδ^(15)N)in brown-marbled groupers(Epinephelus fuscoguttatus),a marine fish that has been widely used in aquaculture.Stable isotope analysis has been used to evaluate dietary sources and the trophic position of fish.There is the need to better understand the pattern of isotope enrichment between consumers and diets under laboratory conditions.Methods:We studied the changes in stable carbon and nitrogen isotopes of juvenile brown-marbled groupers during a feeding experiment in 2009.Fish were grown in aquaria and fed a sole source of protein for 56 days and analyzed forδ^(13)C andδ^(15)N ratios in whole fish,muscle,and liver tissues.Results:At the end of the 56-day feeding experiment,fish grew to an average of 55.6 g from an average of 22.5 g.Compared to the dietary isotope compositions,whole fish and muscle tissues of the juvenile groupers were enriched inδ^(13)C by 1.6 and 0.5%,while the liver was depleted by 1.3%.Theδ^(15)N enrichments were 1.6%for whole fish,1.3%for muscle,and 1.0%for liver.Except for liver,δ^(15)N isotope values increased significantly with time.Conclusions:The small change inδ^(13)C between the diet and fish suggests that little isotope alteration is occurring during the assimilation of dietary carbon.This provides a basis for estimates of the importance of different sources of dietary components when contrasted with the isotope values from a formulated diet with known isotope values of the different components.The smaller than expectedδ^(15)N enrichment in all tissue suggests that isotope values from a wild fish sample may not always reach isotope equilibrium with the current diet,and an inference about recent dietary sources and an estimate of the consumer’s trophic position should be evaluated with caution.

Evaporative enrichment of stable isotopes(δ^(18)O and δD) in lake water and the relation to lake-level change of Lake Qinghai, Northeast Tibetan Plateau of China

Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship be- tween the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions （δ18O, 6D and d-excess） in lake water and pre- cipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and 6D in lake water were higher than those in pre- cipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and 6D in lake water and precipitation showed that the local evaporative line （LEL） in lake water （δD=5.88δ18O-2.41） deviated significantly from the local meteoric water line （LMWL）in precipitation （δD=8.26δ18O＋16.91）, indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quanti- fied the Eli ratio （evaporation-to-input ratio） in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios （ranging from 0.29 to 0.36 between 2009 and 2012） clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleo- lake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.

Geochronology,geochemistry and Hf isotope of monzogranite in Niubiziliang of Qinghai

Zircon U-Pb dating, whole-rock geochemical analyses and Hf isotope are undertaken for the monzogranite in Niubiziliang area with the aim of constraining its formation time,petrogenesis and the regional tectonic setting. The zircons from monzogranite are euhedral-subhedral in shape,and display rhythm growth zoning,indicating a magmatic origin. LA-ICP-MS zircon U-Pb dating indicates the monzogranite formed most probably in the Late Devonian( 359. 0 ± 2. 6 Ma). The monzogranite has Si O2= 74. 69%--76. 11%,Al2O3=12. 07%--12. 81%,Na2 O + K2 O = 8. 24%--8. 70%,Na2 O / K2 O = 0. 60--0. 68,A / CNK > 1,which shows that it belongs to high-Si and high-K weakly peraluminous calc-alkaline series. The monzogranite is enriched in K,Rb,Th( LILEs) and La,Ce,Sm,Nd( LREEs); and depleted in Ba,U( HREEs) and Ta,Nb( HFSEs).Their zircon εHf( t) values range from 1. 21 to 3. 46,in response to their two-stage Hf model ages( TDM2) ranging from 1 034 Ma to 1 159 Ma,respectively,indicating that the primary magma was derived from the young crust in Meso-Neoproterozoic. Combined with the regional geological evolution background,it is considered that the Niubiziliang monzogranite formed the closure of North Qaidam ocean,which was the stretching stage product after the collision between Qaidam block and Qilian block.