Subsidence of low moor peat soils in the western Netherlands
Subsidence of low moor peat soils in the western Netherlands
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荷兰西部低沼泽泥炭土的沉降
DOI：
10.1016/0016-7061(77)90089-1
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发表时间：
1977
期刊：
影响因子：
6.1
通讯作者：
C. J. Schothorst
中科院分区：
文献类型：
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作者：
C. J. Schothorst
设计了3个试验场，研究了深排水对沉降过程的影响。研究发现，在沟渠水位下降6年后，沟渠表面下沉了6 - 10厘米。其中，65%是由于地下水位以上岩层有机质的收缩氧化作用，35%是由于地下水位以下岩层的压缩作用。6年后，压缩占沉降量的1 ~ 4 cm。由于深层泥炭只受深层排水的影响很小，因此可以假设，在过去的1000年里，在地下水位高的地区，对深层泥炭的压缩几乎没有造成沉降。通过对地下水位以上和以下各层有机质容重的比较，发现在过去1000年中，约0.30 m（约占2 m总沉降量的15%）可归因于上层的收缩。剩下的85%归因于有机物的氧化。如果假设上层矿物元素含量较高是由于有机物氧化所致，则可以通过比较地下水位以上和以下各层矿物元素的容重来计算氧化速率。通过这种方法，估计了1.75米的氧化，这将解释每年约1.75毫米的地表沉降。有机土壤比矿物土壤为作物提供更多的氮，这一事实支持了这一理论。在有机土壤较深的排水中，这种额外的氮供应大大增加。根据试验田牧草干物质产量的含氮量计算额外的氮供给。以矿质土壤供氮量为参考水平，从额外供氮量计算有机质损失。据此计算，浅排水泥炭土每公顷年有机质损失为4吨，深排水泥炭土每公顷年有机质损失为12吨。表层有机质容重为0.2 g cm−3时，浅层排水时有机质损失率为2 mm /年，深度排水0.5 m后有机质损失率增加到6 mm /年。这些每年2毫米和6毫米的速率与地下水位以上的土壤流失量很好地符合，这些土壤流失量是在沟渠水位下降几年后，通过在剖面中不同深度放置圆盘测量的。这样，就可以对荷兰西部低沼地泥炭土的地表沉降给出一个合理的解释。
Three experimental fields were laid out to study the effects of deeper drainage on the processes of subsidence. It was found that 6 years after ditchwater levels had been lowered, surfaces had subsided 6–10 cm. Of this subsidence, 65% could be ascribed to shrinkage and oxidation of organic matter in the layer above the groundwater level and 35% to compression of the layer below groundwater level. Compression accounted for 1–4 cm of subsidence after 6 years. Because the deep peat is affected only very slightly by deeper drainage, it may be assumed that compression of it caused little or no subsidence over the past 1000 years in areas with high groundwater levels.By comparing the bulk density of organic matter in the layers above and below groundwater level, it was found that about 0.30 m, or approximately 15% of the total subsidence of 2 m in the past 1000 years, could be ascribed to shrinkage of the upper layer. This leaves 85% to be ascribed to the oxidation of organic matter. If it is assumed that higher contents in mineral elements in the upper layer result from oxidation of organic matter, the rate of oxidation can be calculated by comparing the bulk density of mineral elements in the layers above and below groundwater level. In this way oxidation of 1.75 m was estimated which would explain surface subsidence of about 1.75 mm per year.This theory is supported by the fact that organic soils supply more nitrogen to the crop than mineral soils. At deeper drainage of organic soils this additional N-supply increases considerably.The additional N-supply is calculated from the N-content of the dry matter yield of grass of the experimental fields. The loss of organic matter can be calculated from the additional N-supply, taking the N-supply of mineral soils as a reference level. According to this calculation, the annual losses of organic matter per hectare are 4 tons in shallowly drained and 12 tons in more deeply drained (0.5 m more) peat soils.With a bulk density of organic matter of the toplayer of 0.2 g cm−3, the rate of loss of organic matter is 2 mm per year at shallow drainage and it increases to 6 mm per year after 0.5 m deeper drainage. These rates of 2 and 6 mm per year are in good agreement with the soil losses above groundwater level measured by means of disks placed at various depths in the profile, some years after drawdown of the ditchwater levels.In this manner a plausible explanation can be given for the surface subsidence of the low moor peat soils in the western Netherlands.