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In order to identify the effect of geographic characteristics on the variations of nutrient concentrations and the utilization efficiency of nutrients by phytoplankton, data from 143 lakes, from 2008 to 2010, including three very different types of topography, i.e., the first topography ladder (FTL), second topography ladder (STL), and third topography ladder (TTL), were statistically analyzed. Lakes in the FTL and STL, located at high elevation (above 1000 m) and low longitudes (lower than 105° E), were sporadically oligotrophic, whereas lakes in the TTL were almost all mesotrophic and eutrophic. The trophic level index (TLI) became higher with the rise of longitude. Two turning points (5 and 15℃) on the curve of TLI as function of the average annual temperature (AAT) corresponded with theAAT in different lake regions in the STL and TTL. Because the responses of TLI toAAT differ significantly, there were variations of nutrient and algal biomass concentrations in different lake regions in the same type of topography ladder. According to the differences in utilization efficiency of total nitrogen or total phosphorus by phytoplankton, China could be partitioned into six lake regions. Scientific nutrient criteria for each lake region shall be established considering these differences in China.  相似文献
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The great spatial and temporal variability in hydrological conditions and nitrogen (N) processing introduces large uncertainties to the identification of N sources and quantifying N cycles in plain river network regions. By combining isotopic data with chemical and hydrologic measurements, we determined the relative importance of N sources and biogeochemical N processes in the Taige River in the East Plain Region of China. The river was polluted more seriously by anthropogenic inputs in winter than in summer. Manure and urban sewage effluent were the main nitrate (NO3-) sources, with the nitrification of N-containing organic materials serving as another important source of NO3-. In the downstream, with minor variations in hydrological conditions, nitrification played a more important role than assimilation for the decreasing ammonium (NH4+-N) concentrations. The N isotopic enrichment factors (ε) during NH4 + utilization ranged from -13.88‰in March to -29.00‰in July. The ratio of the increase in δ18O and δ15N of river NO3- in the downstream was 1.04 in January and 0.92 in March. This ratio indicated that NO3- assimilation by phytoplankton was responsible for the increasing δ15N and δ18O values of NO3- in winter. The relationships between δ15N of particulate organic nitrogen and isotopic compositions of dissolved inorganic nitrogen indicated that the phytoplankton in the Taige River probably utilized NH4+ preferentially and mainly in summer, while in winter, NO3- assimilation by phytoplankton was dominant.  相似文献
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