地表覆盖对土壤热参数变化的影响

覆盖条件下土壤热性质的研究对于包气带水热运移及覆盖技术的应用均有重要意义。使用11针热脉冲探头对沙黄土不同深度(6 mm、18 mm、30 mm)的土壤热扩散率、热容量和热导率三个热参数进行测定,并进行地表覆盖(石子覆盖、秸秆覆盖)处理,旨在探究覆盖条件下表层土壤热性质动态变化过程及土壤热参数与水分的内在联系。结果表明:(1)相对于裸土,石子和秸秆覆盖条件下土壤热参数增大,且覆盖对于靠近表层土壤热参数的影响更加明显;(2)随降雨的发生,土壤热参数均增大,在两次降雨期间,土壤热参数逐渐减小,覆盖与裸土热参数差异逐渐增大;(3)三个热参数随降雨的发生,其动态变化过程表现不同,热容量对降雨的响应最为敏感,热导率次之,热扩散率开始减小的时间较热导率和热容量滞后,三个深度滞后时间均在48 h以上,而且覆盖以后热扩散开始减小的时间较裸土推迟(48 h以上)。土壤容重不变的情况下,在频繁干湿交替的过程中土壤水分为土壤热参数变化的最主要影响因素。覆盖条件下土壤热参数与土壤含水量关系研究表明:石子和秸秆覆盖条件下土壤热参数与土壤含水量的变化关系与裸土条件下一致,热导率与含水量呈幂函数增加的趋势,热容量随含水量线性增加,热扩散率随含水量增加先增后减,本研究所用沙黄土热扩散率峰值对应的含水量在0.20 cm3cm-3左右。由以上结果可以发现覆盖对近表层土壤热参数的动态变化有显著的影响,覆盖的保水效应直接影响土壤热参数的变化。     

土壤pH、水分及温度对长期污染土壤中苯并[a]芘动态变化的影响初探

以受多环芳烃长期污染农田土壤中苯并[a]芘(B[a]P)为研究对象,采用室内模拟试验研究了pH、水分和温度对土壤中B[a]P的动态变化的影响。结果表明,供试污染土壤中B[a]P能被土著微生物快速去除,其消减过程受到pH、水分和温度的影响。初始pH为4.6、5.9和7.3的泥浆中B[a]P在7天内的去除率分别为43.8%、37.8%和14.0%。在土壤水分为22%、43%、65%和87%田间持水量,温度为28℃条件下培养80天后土壤中B[a]P的去除率分别为42.5%、96.6%、96.3%和34.3%。在土壤pH为4.5,土壤水分为60%±5%田间持水量,温度为25℃和40℃条件下土壤中B[a]P的半衰期分别为33天和16天。可见,pH、水分和温度等环境条件对土壤中B[a]P的消减过程具有明显的影响,可通过人为调控强化B[a]P污染土壤的生物修复。     

A GIS based approach to modelling the effects of land-use change on soil erosion in New Zealand

Abstract. The problem of soil erosion is particularly evident in New Zealand, given the combination of coarse-textured soils, steep relief, high rainfall, and intensification of agriculture. A study was undertaken to assess the effects of land use change on soil erosion and sediment transport for the Ngongotaha catchment in New Zealand's North Island, using a GIS based decision support and modelling system. Model simulations considered the effect of increased catchment area under deer farming and forestry on the amount of sediment delivered to the catchment outlet, averaged over a period of six years. The simulations predicted that sediment loss from land under deer farming was considerably greater than from land under other livestock or forestry. Further model simulations testing best management practices demonstrated that sediment yield could be halved if deer farming was restricted to slopes under 20%.     

A simplified procedure for terminal restriction fragment length polymorphism analysis of the soil bacterial community to study the effects of pesticides on the soil microflora using 4,6-dinitroorthocresol as a test case

We have studied the structural effects of application to the soil of a potentially detrimental herbicide, 4,6-dinitroorthocresol (DNOC) by analysing amplified ribosomal DNA restriction analysis (ARDRA) and terminal restriction fragment length polymorphism (T-RFLP) signatures of 16S rDNA fragments of culturable bacterial communities isolated from diluted soil suspensions. This approach has the potential to reveal changes induced by stressing the soil microflora with DNOC. This paper shows that, whereas only few changes of the ARDRA and T-RFLP profiles result from ageing of the soil, treatment of the soil with DNOC induces major modifications of these profiles. Therefore, for the practical purpose of pesticide registration, ARDRA and T-RFLP analysis performed on the dominant culturable fraction of the soil bacteria, implemented using conventional gel electrophoresis, offers the means of a routine, simple and meaningful test for detecting some of the changes affecting the structure of the soil microflora in response to pesticide application.     

The effects of mancozeb and lindane on the soil microfauna of a spruce forest: A field study using a completely randomized block design

Summary The effects of mancozeb (fungicide) and lindane (insecticide) were investigated in active soil ciliates, testaceans, rotifers, and nematodes. The effects were evaluated 1, 7, 15, 40, 65, and 90 days after application of a standard and a high (10x) dose. Individual numbers were estimated with a direct counting method. Mancozeb, even at the high dose, had no pronounced acute or long-term effects on absolute numbers of the taxa investigated. The number of ciliate species, which decreased 1 day after treatment with the normal dose (0.05 <P < 0.1), soon recovered. However, the community structure of ciliate species was still slightly altered after 90 days. Testaceans were not reduced before day 15 at the higher dose or before day 40 at the normal one (0.05 <P < 0.1). A normal dose of lindane caused acute toxicity in ciliates and rotifers (P < 0.05) but the latter soon recovered. The number and community structure of ciliate species were still distinctly altered after 90 days (0.05 <P <0.1), indicating the critical influence of lindane. Testaceans were reduced only after day 15, and nematodes only on day 40 (0.05 <P < 0.1). At the high dose of lindane severe long-term effects occurred in soil moisture, total rotifers (P < 0.05), total nematodes (0.05 <P <0.1), and in the structure of the ciliate community. Generally, there were marked differences in the effect of the normal and the high dose of lindane but not with mancozeb. Ciliates showed very pronounced changes after the pesticide applications, indicating their usefulness for testing biocides under field conditions. Testaceans were more resistant than ciliates.