工程水准复测垂直形变分析

利用京沪高铁京津段的八期工程水准复测资料,绘制了2007年3月-2011年3月间的京津地区垂直形变图,并对京津沿线地区近期垂直形变趋势进行了分析研究.研究结果表明,2009年3月至2011年3月期间,不同地点出现了正速率变化,与以往对于这一区域负速率变化的地面沉降规律形成了一个“反向”变化,显示出区域应力场受外部干扰和影响后的变化特征.为分析研究首都圈地区今后一段时间的地壳垂直形变趋势提供依据.     

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Saldanha Bay,South Africa III: new production and carrying capacity for bivalve aquaculture

Measurements of NH₄, NO₃, urea and HCO₃ uptake using 15N and 13C stable isotope tracers were undertaken in Saldanha Bay, South Africa, between January 2012 and January 2013. These studies provide the first direct measurements of N utilisation by the plankton in the bay. Primary production in the bay is driven predominantly by the advection of nutrients from the neighbouring shelf environment during upwelling events, with terrestrial and other sources providing minor inputs. New production (NO₃-based) was calculated from the f-ratio and total primary production and was used to provide estimates of potential carrying capacity for bivalve culture. Despite the apparent light limitation of NO3 uptake in the winter, the availability of NO₃ appeared to exert the major influence on new production throughout the year. In addition, new production was modulated by NH₄ availability as shown by the suppression of NO₃ uptake by concentrations higher than 1?1.5?mmol m^?3. The estimated areal new production of 0.60?g C m^?2 d^?1 yielded a bay-wide annual estimate of 9 811 t C ha^?1 y^?1, slightly higher than previous calculations based on physical models. It is estimated that the total annual production of mussels and oysters, respectively, for a 1 000-ha cultivation area is approximately 40 000–53 000 t y^?1 (mainly Mytilus galloprovincialis) and 4 600–6 000 t y^?1 (Crassotrea gigas). The combined total production figures constitute only 24–31% of the surplus new production. A combined harvestable carrying capacity of 74 000–82 000 t y^?1 can be calculated from this surplus. However, from a management and ecological perspective, bivalve culture should be limited to well below this theoretical maximum. Even with this constraint, there appears to be considerable scope for expansion of bivalve farming over the modest, present levels with little jeopardy to ecological integrity.