Nutrient fluxes in a eutrophic coastal Louisiana freshwater lake

Nitrogen and phosphorus cycling in a eutrophic Louisiana freshwater lake system (Lac des Allemands) was studied. Nutrients from runoff entering the lake, as well as sediment-interstitial and lake water nitrogen and phosphorus fractions, were measured seasonally. Sedimentation rates in the lake were determined using¹³⁷Cs dating.Phosphorus levels in the lake were found to be largely dependent on concentrations in the incoming bayou water from upland drainage. Lake water concentrations appear to respond to fluctuations in incoming waters. Laboratory equilibrium studies showed bottom sediments in the lake are a major sink for the incoming dissolved orthophosphate phosphorus. Total nitrogen concentrations in the lake water generally exceeded incoming runoff concentrations, suggesting fixation by the large blue-green algae population in the lake as being the major source of nitrogen to the system.Sedimentation ranged from 0.44 cm/year to 0.81 cm/year, depending on the proximity to the inlet bayous. Even though the lake is eutrophic the sediment served as a buffer by removing large amounts of carbon, nitrogen, and phosphorus through sedimentation processes. Carbon, nitrogen, and phosphorus were accumulating in the sediment at rates of 60, 7.1, and 1.1 g/m²/year, respectively.The water quality of the lake is likely to continue to decline unless measures are taken to reduce municipal, industrial, and agricultural inputs of phosphorus into the lake.     

释光测年技术在陶器定年研究中的应用进展

陶器释光测年一直是环境考古领域重要的时间界定方法之一。本文通过系统整理释光技术在陶器定年上的主要研究成果，分别从技术方法和应用实践两个方面进行总结和梳理，以阐明其在相应领域的适用性、面临的问题和未来应用潜力。在陶器定年的技术方法上，热释光技术最早应用于陶器测年，但也存在矿物热释光晒退效率较慢、不可重复测试和反映信息较少等问题；光释光测年技术的不断发展拓展了陶器释光测年的技术和方法，近年来相应研究比例也不断提高，但也存在部分年轻样品石英信号较弱、石英光释光信号组分比例影响等效剂量测定等问题。在实践应用上，陶器释光测年技术在世界各地遗址均表现出良好的适用性，能为遗址提供绝对年代测定，以及在多学科交叉的背景下，更多地反映古人地关系演化和文化区域交流。未来需要进一步加强释光技术尤其是光释光技术在陶器测年领域的应用力度，从而更好地服务于环境考古学研究；这对于进一步揭示区域古人地关系演化、文明发展历程和文化区域交流等方面有着重要意义。