Total Nitrogen In The Holocene Loess-paleosol Sequences And Its Environmental Significance In The Middle Reaches Of The Yellow River

The Holocene environmental change bounded up with the development of human beings is one of the most emphasis and hotspots of the globe change study. So, the study of the Holocene environmental change becomes reference to the modern environment. The middle reach of the Yellow River is the main loess-distributing zone. For a long time, many scholar have rebuilt the environmental change's history in virtue of some climate - environment proxy indexes, such as magnetic susceptibility, grain-size analysis, total Fe, organic carbon, CaCO3, silicate body, microelements, etc.The total nitrogen as a climate - environment proxy index is used preferably in lake and ocean sediment, but less in loess-palaeosol sequence. Based on much particular field investigation, three loess-palaeosol profiles along the southern verge of the loess plateau are selected and sampled. The total nitrogen and magnetic susceptibility of the three profiles are measured in the lab. Through the analysis of the total nitrogen in the middle reaches of the Yellow River, the text try to discuss the feasibility as a climate -environment proxy index and climatic significance of the total nitrogen, which not only enrich the method of climate - environment proxy index but also make up for the deficiency of other climate - environment proxy index.The thesis draws the following cognitions:(1) The content of total nitrogen is diversity in different stratigraphy of loess-palaeosol in the Holocene. Obviously, The content of total nitrogen is more in palaeosol than in loess. In LGT, the tiptop of TN appears in the topsoil (0.6630 g/kg), 0.3856 g/kg in palaeosol and 0.2940 g/kg in loess. In PLQ 0.4980 g/kg in the topsoil, 0.2763 g/kg in palaeosol and 0.1761 g/kg in loess. The tiptop of the TN in the topsoil possibly results from human being's influence or demount of organic substance.(2) The change of total nitrogen content is in correspondence with magnetic susceptibility curve and the loess-palaeosol sequence. Because the loess-palaeosol sequence and magnetic susceptibility are regard as good climatic proxy, so total nitrogen can be a climate - environment proxy index. High total nitrogen content shows...