Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea     

Duplisea DE  Jennings S  Malcolm SJ  Parker R  Sivyer DB 《Geochemical transactions》2001,2(1):112

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage.  相似文献   

应用GPS卫星测量建立高程控制     

Zilk.  DB 范思伟 《测绘译丛》1992,(2):1-7

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评GPS和GLONASS兼容机及Ashtech GG24接收机     

郑国忠 《测绘科技通讯》1997,20(3):10-14

在介绍ＧＰＳ和ＧＬＯＮＡＳＳ系统不同点后，论述ＧＰＳ＋ＧＬＯＮＡＳＳ兼容机的技术优势。精度高、抗障碍性好、并有抗美方垄断的可能性，对民用用户十分有利，对我国具有重要意义。Ａｓｈｔｅｃｈ厂ＧＧ２４接收机是世界上第一台较完善的且具有实际应用意义的兼容机。文章评述了它的功用和性能。结论指出兼容机将是未来卫星定位接收机的主要发展方向，将对卫星定位技术应用的发展作出重大贡献。  相似文献   

在砂岩和碳酸盐储层中利用正演模拟作振幅图分析     

Neff  DB 潘秋霞 《海洋地质译丛》1994,(4):45-51

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使用多副天线与单台接收机的GPS方法     

Santer  R 郑国忠 《测绘通报》1995,(3):39-50,38

本文提出将多副天线连接到一台公共接收机的ＧＰＳ测量方法、此法的目的是为了改善几公里基线的高程测定精度，这一技术的优点在于消除两天线之间单差观测值的相对钟参数，因为单差观测值不受钟差影响，对测定基线分量能保持更好的几何强度，只要各电缆之间的偏差能被小心地检验，则这一陈述就是有效的，在这一假定之下，同标准的ＧＰＳ数据处理相比较，总的说高程标准偏差要改善的二倍，使用本文提出的方法，和标准数据处理方法相比  相似文献   

应用数学模型扭曲法对直伸导线的实验研究     

郑国忠 《测绘通报》1983,(5)

随着物理测距仪器以及测边测角结合型仪器的研制和在测绘生产中的应用，使得导线测量的应用范围日益扩大。因此，对导线测量的实验研究，即研究生产上应用的各种具体导线在结构上和精度上与理论分析的符合程度，具有重要意义。  相似文献   

电子速测仪的野外鉴定     

LeoB．Gittings美  郑国忠 《浙江测绘》1986,(2):63-65

国家大地测量局（NGS）完成了三种电子速测仪（ETI）的野外测试，以决定这些仪器是否适合NGS的需要。因此，测试的主要目的是研究做二等控制测量的可能性，而不是去试验ETI的许多其他的测量应用（地籍的、地形的、工程的等等）。被测试的三种ETI是蔡司Elta2，Hewlett Packard 3820A和威特速测仪TC1。在马里兰州Gaithersburg由国家标准局（NBS）所建立的试验场上和弗吉尼亚州Corbin的大地测量局精密基线上，用这些仪器进行了许多观测和量测。作者的意图不在这些仪器的速率上，而是通过展示观测和量测的比较来评价它们，并讨论这些比较实验场地、所使用的仪器和方法以及其他和实验有关的事宜。  相似文献   

谈谈WM101型卫星定位接收机的使用     

郑国忠 《测绘科技通讯》1990,13(1):14-19,13

本文对我国石油、煤炭、地震、军事等部门已购进的大批WM101型大地定位卫星接收机如何使用好，使其作业，充分发挥它们的经济效益以及在使用中的若干问题，进行了初步探讨和评述，以期引起同行们开展这方面的讨论。  相似文献   

用于变形观测的专门测量仪表     

Tesk.  WF 郑国忠 《北京测绘》1989,(3):32-37

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A spreadsheet program for two-well tracer test data analysis     

Tang G  Watson DB  Parker JC  Brooks SC 《Ground water》2012,50(4):614-620

Two-well tracer tests are often conducted to investigate subsurface solute transport in the field. Analyzing breakthrough curves in extraction and monitoring wells using numerical methods is nontrivial due to highly nonuniform flow conditions. We extended approximate analytical solutions for the advection-dispersion equation for an injection-extraction well doublet in a homogeneous confined aquifer under steady-state flow conditions for equal injection and extraction rates with no transverse dispersion and negligible ambient flow, and implemented the solutions in Microsoft Excel using Visual Basic for Application (VBA). Functions were implemented to calculate concentrations in extraction and monitoring wells at any location due to a step or pulse injection. Type curves for a step injection were compared with those calculated by numerically integrating the solution for a pulse injection. The results from the two approaches are similar when the dispersivity is small. As the dispersivity increases, the latter was found to be more accurate but requires more computing time. The code was verified by comparing the results with published-type curves and applied to analyze data from the literature. The method can be used as a first approximation for two-well tracer test design and data analysis, and to check accuracy of numerical solutions. The code and example files are publicly available.  相似文献