The toxic mixing zone of neutral and acidic river water: Acute aluminium toxicity in brown trout (Salmo trutta L.)

Mixing of acid river water containing aluminium (pH 5.1, Al 345 g.l^–1) with neutral water of a lake (pH 7.0, Al 73 g.l^–1) resulted in water (pH 6.4, Al 245 g.l^–1) with a pH (6.4) and Al concentration (245 g.l^–1) expected to have low toxicity to fish on the basis of current Al toxicity models. However, under semi-field conditions the freshly mixed water (a few sec. after mixing) proved to be highly toxic to brown trout. The fish were exposed to the water at different places along a 30 m channel. At the beginning of the channel acid and neutral water were continuously mixed; the mixed water left the channel after 340 sec. The cells of the gills showed a highly increased rate of cell death by apoptosis and necrosis. Intercellular spaces were enlarged, and many leucocytes penetrated in these spaces. Mucus release was stimulated to depletion. Plasma chloride levels were hardly affected. There was a clear gradient in the deleterious effects on the fish along the channel. The fish at the beginning of the channel (about 12 sec. after mixing of the water), were severely affected, whereas the fish kept at the end of the channel (340 sec. after mixing) were only mildly affected. In the natural situation fish will relatively quickly pass through a mixing zone. In our study we therefore focused on the effects on fish after a 60 min exposure to a mixing zone (5 sec after mixing), with subsequent recovery in a region downstream of the confluence and in neutral water with low Al. The recovery in the downstream area (at the end of the channel, i.e. 5 min after mixing) was clearly hampered when compared to the recovery in neutral water with low aluminium. Thus, a short exposure to the toxic mixing zone followed by a stay in water downstream of this zone, as may occur in nature, is detrimental to migrating trout. We conclude that freshly mixed acid and neutral water contain toxic components during the first seconds to minutes after mixing, that can not be explained by current models on aluminium toxicity.     

土壤化学中的广义氧化还原反应

 土壤化学中的酸碱反应、沉淀溶解反应、配位反应和氧化还原反应都属于广义氧化还原反应。土壤化学反应中的某些性质可用广义氧化还原理论给出新的解释。     

天津天嘉湖渔业生物学基础调查

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土壤离子扩散系数辨析

引入土壤离子扩散阻滞因子的概念 ,阐述了 3种土壤离子扩散系数表达方式 ,即土壤离子孔隙扩散系数、土壤离子表观扩散系数、土壤离子有效扩散系数及其与离子自扩散系数之间的相互关系 ;明确了利用 Fick第一扩散定律和 Fick第二扩散定律推求的土壤离子扩散系数的类型和运算过程中有关参数的量纲。     

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加强农业院校化学基础教学改革提高人才素质

以农业院校化学基础教育教学改革为对象,针对农业高等教育中化学教学所存在的问题,在教学观念、教学模式及教学方法方面进行了改革,提出应利用现代教学手段培养学生的学习兴趣,加强基础课和综合实验教学,促进学生创新素质的培养。     

先进制造技术在模具制造中的应用及前景

本文介绍了目前模具制造业状况,从不同角度讲述先进制造技术在模具制造业中的应用情况,并且介绍了先进制造技术在模具制造业中的应用前景。     

内浮顶罐浮动出液装置的研制

为了适应民航的用油要求，在内浮顶罐中装浮动出液装置。根据设计原则和要求，设计出一种双回转接头的浮动出液装置。通过对浮动出液装置的受力分析、方案比较，说明了所设计的浮动出液装置对浮盘的作用力小，且能随浮盘一起上下运动，完全符合设计要求。     

杉木混交林土壤微生物及生化特征和肥力

测定了杉木与鹅掌楸，拟赤杨，木荷，檫树和香樟等５个树种的混交林土壤特征，结果表明混交林土壤微生物数量比杉木纯林高７．１９％～４１．３１％，土壤脲酶，转化酶，过氧化氢酶，多酚氧化酶和吸收强度均比纯林高，土壤有机质，全氮，全磷，水解氮，速效磷和速效钾普遍高于纯林。     

高等数学解题中典型错误剖析

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