Zinc deposition in Acid lakes: the role of diffusion

Steep negative concentration gradients of dissolved zinc are present between the overlying waters and the anoxic pore waters of two acid lakes. In the anoxic pore waters, the low zinc concentrations can be explained as due to the formation of relatively insoluble zinc sulfide minerals. Downward diffusive fluxes of dissolved zinc account for at least 50 to 75 percent of the recent zinc deposition to the sediments of these lakes. This downward diffusion occurs to a depth of 2 to 3 centimeters below the sediment water interface, where pronounced maxima in total zinc are observed. These subsurface peaks in total zinc have been interpreted as an indication of recent lake acidification. The present observations indicate that such subsurface peaks may also result from a diagenetic activity unrelated to recent changes in lake acidity.     

Disruption of the nitrogen cycle in acidified lakes

Experimental acidification of two small soft-water lakes caused nitrification to cease at pH values of 5.4 to 5.7. The resulting blockage of the nitrogen cycle caused a progressive accumulation of amnonium. When the epermental acidification of one of the lakes was ended and the pH was raised to 5.4, nitrification resumed after a time lag of 1 year.     

Long-term ecosystem stress: the effects of years of experimental acidification on a small lake

Experimental acidification of a small lake from an original pH value of 6.8 to 5.0 over an 8-year period caused a number of dramatic changes in the lake's food web. Changes in phytoplankton species, cessation of fish reproduction, disappearance of the benthic crustaceans, and appearance of filamentous algae in the littoral zone were consistent with deductions from synoptic surveys of lakes in regions of high acid deposition. Contrary to what had been expected from synoptic surveys, acidification of Lake 223 did not cause decreases in primary production, rates of decomposition, or nutrient concentrations. Key organisms in the food web leading to lake trout, including Mysis relicta and Pimephales promelas, were eliminated from the lake at pH values as high as 5.8, an indication that irreversible stresses on aquatic ecosystems occur earlier in the acidification process than was heretofore believed. These changes are caused by hydrogen ion alone, and not by the secondary effect of aluminum toxicity. Since no species of fish reproduced at pH values below 5.4, the lake would become fishless within about a decade on the basis of the natural mortalities of the most long-lived species.     

Heat flux anomalies in Antarctica revealed by satellite magnetic data

The geothermal heat flux is an important factor in the dynamics of ice sheets; it affects the occurrence of subglacial lakes, the onset of ice streams, and mass losses from the ice sheet base. Because direct heat flux measurements in ice-covered regions are difficult to obtain, we developed a method that uses satellite magnetic data to estimate the heat flux underneath the Antarctic ice sheet. We found that the heat flux underneath the ice sheet varies from 40 to 185 megawatts per square meter and that areas of high heat flux coincide with known current volcanism and some areas known to have ice streams.     

Radiocarbon dating of East african lake levels

The fluctuations of the key East African lakes discussed are summarized in Fig. 4 which also includes the available evidence from Lake Rukwa (42) and Lake Chad (43) Exceot for Lake Victoria, all of these now lack surface outlets and are situated in much drier climates than the major lakes of the Western Rift Valley, which remain filled to their overflow levels. The apparent differendes among the fluctuations of the lakes are partly due to differendes in the nature of the evidence or the intensity of research or both, although there must also have been important local differences in the histories of the lakes Yet the consistencies are far more striking, most notably the coincidence of early Holocene high stands. Between 10,000 and 8,000 years ago, it seems that lakes in many parts of tropical Africa were greatly enlarged. Where evidence for the previous span of time is well resolved, it appears that transgressions leading to this high stand began about 12,000 years ago, and evidende from three basins (Victoria, Nakuru, and Chad) indicates a pause or minor recession just at or before 10,000 years ago. Wherever information is available for the period preceding 12,000 years ago, it can consistentlybe shown that lakes were much small-er . Several basins (Rudolf, Nakuru, and Chad) also show traces of much earlier phases of lake expansion. which are not yet well dated but which all occurred more then 20,000 years ago. The Holocene record subsequent to the maximum of 10,00 to 8,000 years ago is more complex. Three basins (Rudolf, Nakuru, and Chad) show an apparently concordant, positive oscillation at some point between 6000 and 4000 years ago, but it is uncertain how widely this episode is represented. Although many of these lakes that are now closed filled to overflowing at least once during the late Quaternary, it is evident from Fig. 4 that the periods of expansion were short-lived compared with phases of contraction to levels near those of today. This pattern may be in accord with fragmentary evidence from lower and middle Pleistocene formations, such as those of Olduvai(44)and Paninj (45), within which some relatively short-term lake expansions can be documented, but which lack evidence for any marked long-term departure from a balance of evaporation and precipitation similar to the present one Further, this pattern of brief moist pulsations, with a duration of perhaps 2000 to 5000 years, is also suggested by other late Pleistocene and Holocene sequences (based primarily on geomorphological and palynological evidence) from the Saharan area, Angola, and South Africa (46). In default of radiometric dating, such complex successions of relatively brief moist intervals provide few stratigraphic markers of broad applicability. This, together with the fact that vegetation, weathering processes, montane glaciers, lake size, lake salinity, and so forth are all likely to reflect the diverse aspects of Climatic change differently, underscores the strictures of Cooke (2) and Flint (3) against the use of pluvials and intrlvasas a basis for subdividing Quaternary time in Africa. Positive correlations between high-latitude glacial advances or maxima and intervals of high lake levels have been demonstrated or suggested for many areas of mid-latitude North America and Eurasia (47), and similar patterns have often been regarded as probable for tropical Africa as well. However, the evidence summarized above shows a notable lack of such correlations for the tropical lakes considered here. If glaciation and tropical lake levels were connected at all, then a far more complex-delayed, multiplefactor, or inverse-relationship must be sought for the late Quaternary (48). This renders the introduction of new climato-stratigraphic terms such as hypothermal and interstadial (49) of questionable value in East Africa. Further, whereas the so-called pluvial lakes of higher latitudes were probably due primarily to reduced evaporation (50), our computations for the early Holocene lakes Nakuru and Naivasha, as well as for the oscillations of Lake Rudolf and Lake Victoria in recent decades, suggest that many or most of the high tropical lake levels where associated with a modest but significant increase in precipitation.     

安庆沿江湖泊及长江安庆段沉积物重金属污染特征及生态风险评价

为研究安庆沿江湖泊及长江安庆段重金属污染特征及潜在的生态风险,采集了安庆沿江湖泊及长江安庆段沉积物样品共58个,分析了Cu、Zn、Pb和Cd共4种重金属分布特征,并采用地累积指数法和Hakanson生态危害指数法进行生态风险评价,结果表明:不同水体沉积物重金属含量差异较大,市区湖泊群内各重金属含量普遍高于周边生态湖泊和长江安庆段;与区域对应的沉积物重金属背景值比较,市区湖泊群中各类重金属普遍高于背景值,而其他水体沉积物中的重金属则与背景值相近,表明市区工业生产及生活等人类活动对湖泊沉积物重金属含量有较大影响。地累积指数污染评价表明安庆市区湖泊群受到一定程度的重金属污染,尤其是Cd污染达到了中度污染程度。总的看来,所有安庆沿江湖泊及长江安庆段沉积物中各重金属污染的程度依次为CdPbZnCu。生态风险评价表明市区湖泊群和菜子湖处于中等生态危害状态,其他水体均处于低生态风险状态,各水体潜在生态危害顺序依次为市区湖泊群、菜子湖、长江安庆段、嬉子湖、石门湖、白荡湖;研究区域沉积物中的重金属生态风险以Cd为主。     

浙南地区耕地土壤酸化特点及控治对策

为全面了解浙江南部地区耕地土壤酸化规律,为土壤酸化防治提供依据,利用近期获得的温州和丽水2个市20个县(市、区)4 443个测定数据,统计分析了浙南地区耕地土壤酸碱度现状及其区域分布特点。结果表明,浙南地区耕地主要由酸性(p H值介于4.5～5.5)和微酸性(p H值介于5.5～6.5)土壤组成,地貌与成土母质是控制这一地区耕地土壤酸度的关键因素,人为活动加剧了耕地土壤酸化。丘陵与河谷平原中土壤pH值低于5.5的耕地占比均在83%以上,土壤酸化问题非常严重;滨海平原耕地土壤以中性和微酸性为主。分析认为,浙南地区耕地土壤酸化治理重点是丘陵与河谷平原,需通过施用碱性物质进行降酸;滨海平原与水网平原应做好耕地土壤酸化的预防工作。     

内蒙古沙漠湖泊的特征及保护

湖泊是人类宝贵的自然资源,沙漠湖泊则更为宝贵,它对于维持沙漠生态环境,防止沙漠扩展具有重要作用。内蒙古的沙漠和沙地中分布有大量湖泊,形成了沙漠中独特的自然景观。本文在对内蒙古沙漠湖泊的特征进行论述的基础上,分析了沙漠湖泊所具有的生态功能和在防止沙漠扩展中的作用,希望能引起社会各界对沙漠湖泊的研究和保护给予更多的重视。     

浑善达克沙地淡水养殖试验研究

草原畜牧业是浑善达克地区的主体经济，虽然多年来严重超载过牧，但是经济发展非常缓慢。近年来草场的退化和沙化日趋严重，极大的制约着当地牧民的生产和生活，并且对周边地区的生态安全造成了巨大的威胁。沙漠化程度已发展到了非治不可的地步。在开展浑善达克沙地植被恢复与风沙环境综合治理的同时，有必要引导牧民调整产业结构，因地制宜的培育新产业，进行沙地经济综合开发。因为浑善达克沙地有较多的淡水淖尔，我们在一些地区作了淡水养殖试验及研究，结果表明，浑善达克沙地的水域养鱼是完全可行的，它的水体营养丰富，适宜于不同栖息习性的鱼类生活。有利于多种鱼类混养。小水面季节性养殖，应投放尽可能大的鱼苗，以生长较快的草鱼、鲤鱼和鲢鱼为主；大水面深水越冬养殖的效果较好，应以鲤鱼、鲫鱼、草鱼和鲢鱼为主。因此，应充分利用沙地内较多的淡水淖尔开展多种经营。     

Acid rain on Acid soil: a new perspective

Acid rain is widely believed to be responsible for acidifying soil and water in areas of North America and northern Europe. However, factors commonly considered to make landscapes susceptible to acidification by acid rain are the same factors long known to strongly acidify soils through the natural processes of soil formation. Recovery from extreme and widespread careless land use has also occurred in regions undergoing acidification. There is evidence that acidification by acid rain is superimposed on long-term acidification induced by changes in land use and consequent vegetative succession. Thus, the interactions of acid rain, acid soil, and vegetation need to be carefully examined on a watershed basis in assessing benefits expected from proposed reductions in emissions of oxides of sulfur and nitrogen.     

岩溶区土壤镉生物有效性影响因素研究

为研究岩溶区土壤镉生物有效性的影响机制,以广西碳酸盐岩区土壤垂直剖面、水稻子实与根系土协同样品为基础,讨论了土壤pH、有机质含量、黏土矿物含量、碳酸盐含量对土壤镉生物有效性的影响。结果表明,pH、有机质、黏土矿物主要对镉的吸附产生影响,其对镉生物有效性的影响程度由强到弱依次为pH、黏土矿物、有机质,碳酸盐的作用则主要体现为对土壤酸化的缓冲。总体而言,广西岩溶发育强烈,土壤中不断形成表生条件下稳定的新生黏土矿物,加之岩溶区土壤丰富的碳酸盐与有机质,都对该地区碳酸盐岩母质土壤中镉的固定较为有利,但防止土壤酸化是防控其土壤镉污染风险的首要措施。     

用模拟酸雨淋溶法研究红壤和红色石灰土的盐基迁移状况

用模拟酸雨对红壤和红色石灰土的原状土柱进行连续淋溶,探讨土壤盐基的淋溶强度、容量以及土壤pH和交换性盐基的变化规律。结果指出,酸雨对红色石灰土的盐基淋溶强度和容量大于红壤。交换性盐基的淋溶速率也有同样趋势;土层厚度的增加能大大降低酸雨对盐基的淋溶强度、容量和淋溶速度;红壤的pH对酸雨淋溶较敏感。而红色石灰土的交换性盐基对酸雨的反应较敏感。所以就土壤酸化速率而言,以土壤pH为指标时,则红壤大于红色石灰土;但以盐基淋失量为指标时则相反。     

鄱阳湖小天鹅越冬种群数量与行为学特征

2012年10月-2013年3月,采用直接计数法对鄱阳湖小天鹅Cygnus columbianus种群数量分布进行了5次调查。结果显示,各调查点小天鹅的种群数量均不稳定,可能与食物丰富度、水位等相关。各次调查中以第2次调查观测到的小天鹅数量最多,合计10756 只;调查区域中以鄱阳县白沙洲自然保护区调查到的小天鹅数量最多。5次调查中鄱阳县的小天鹅数量均占每次调查总数的56%以上,平均2239.80 只。小天鹅在各保护区不同湖泊的数量分布存在时间差异,但分布仅局限在几个湖泊中。调查显示,小天鹅的幼体比例为29.04%(n=1150)。采用瞬时扫描法对小天鹅越冬期的行为进行了研究,其用于静止(43.12%)和取食(27.44%)行为的时间较多,用于运动(16.82%)和梳理(11.48%)行为的时间较少,用于社会行为(1.14%)的时间最少。在小天鹅的日间行为节律中,静止行为高峰出现在07:00-08:00和17:00-18:00时段,取食行为高峰出现在16:00-17:00。下午取食强度的增加与冬季夜间长和气温低有关,鸟类必须获得足够的能量以维持其夜间的能量消耗。对小天鹅成幼体行为分配进行检验,发现除社会行为差异显著(Z=-2.310,P=0.021)外,其余行为差异均不显著。但成幼体的行为节律有较大差异,主要体现在静止和取食行为上。     

Gels composed of sodium-aluminium silicate, lake magadi, kenya

Sodium-aluminum silicate gels are found in surficial deposits as thick as 5 centimeters in the Magadi area of Kenya. Chemical data indicate they are formed by the interaction of hot alkaline springwaters (67 degrees to 82 degrees C; pH, about 9) with alkali trachyte flows and their detritus, rather than by direct precipitation. In the process, Na(2)O is added from and silica is released to the saline waters of the springs. Algal mats protect the gels from erosion and act as thermal insulators. The gels are probably yearly accumulates that are washed into the lakes during floods. Crystallization of these gels in the laboratory yields analcite; this fact suggests that some analcite beds in lacustrine deposits may have formed from gels. Textural evidence indicates that cherts of rocks of the Pleistocene chert series in the Magadi area may have formed from soft sodium silicate gels. Similar gels may have acted as substrates for the accumulation and preservation of prebiological organic matter during the Precambrian.     

中国南方水稻土酸化演变特征及影响因素

【目的】明确中国南方水稻土酸化特征及主要影响因素,为防控水稻土酸化提供理论依据。【方法】选择中国南方江苏、湖南、广东、广西、四川和云南6个省份（自治区）的20个水稻土长期定位监测点,统计分析水稻土pH演变特征及阶段性变化规律,并探讨施肥量及土壤氮素含量对水稻土酸化的影响。【结果】1988-2013年25年间中国南方水稻土显著酸化,土壤pH下降0.59个单位,平均每年下降0.023个单位。水稻土酸化具有明显的阶段性特征,起始的14年中水稻土pH急速下降,平均每年可下降0.051个单位;近10年间,土壤pH趋于平稳。增施化肥特别是化学氮肥可导致水稻土酸化,二者与土壤pH均呈显著负相关关系（P＜0.01）,由此推算出化学氮肥每增施100 kg·hm^-2,水稻土pH可下降0.65个单位。减少有机肥的施用也可引起水稻土酸化,有机肥施用量与土壤pH之间呈显著正相关关系,有机肥每减少100 kg·hm^-2,水稻土pH下降0.51个单位。土壤全氮及碱解氮含量与pH间均呈极显著负相关关系,土壤全氮和碱解氮含量每增加100 mg·kg^-1,水稻土pH约下降0.1个单位。【结论】在过去25年间,中国南方水稻土显著酸化,酸化具有明显的阶段性特征,施肥初期土壤pH显著降低。减少化学氮肥的施用和增施有机肥是控制水稻土酸化的重要措施。     

防止和修复湖泊水库富营养化渔业操纵的探讨

为防止和修复湖泊水库富营养化,通过渔业操纵实现营养物质的上岸,找到适合所有水体的生态治理方式,本研究中系统归纳了在不同营养类型、不同水体形态和不同营养物质输入节奏水体的渔业操纵对策。结果表明:对于受面源污染较小,营养物质输入分散的贫、中营养水体,应以保护生物多样性的长食物链的渔业形式为主,即实行以肉食性鱼类为主要对象的渔业操纵;随着水体富营养化程度的提高或营养物质输入集中度的提高,逐渐增加杂食性鱼类的比例,其中滤食性鱼类和底层杂食性鱼类的放养比例应根据水体深度和面积进行调整,不应夸大滤食性鱼类在所有形态水体中的除藻效果,尤其在浅而大的湖泊中,底层杂食性鱼类可通过吞食或刮食被湖盆吸附的藻类,实现除藻作用;对于超富营养水体,除了以杂食性鱼类为主的渔业操纵方式外,还需要增加水体的异质性,以提高水体的生物多样性,以及水中营养物质(鱼产量)被浓缩上岸的速度。本研究中首次提出对大而浅的富营养水体进行围栏分割,将大生态系统分割为互相依托的小生态系统景观集合体的生态修复方法,同时还阐述了渔业操纵效果的评价方法。     

Aboriginal Drained-Field Cultivation in the Americas: Pre-Columbian reclamation of wet lands was widespread in the savannas and highlands of Latin America

The three main types of land reclamation in aboriginal America were irrigation, terracing, and drainage. Of these, drainage techniques have received the least attention, probably because they are no longer important and because the remnants are not conspicuous. Nevertheless, drained-field cultivation was widespread and was practiced in varied environments, including high-land basins, tropical savannas, and temperate flood plains. Sites ranged from seasonally waterlogged or flooded areas to permanent lakes. Ridging, mounding, and ditching were emphasized, rather than diking. Tools were simple, crops varied, and fertilization was accomplished mainly by mulching.     

近20年山东省南四湖大风气候特征分析

根据南四湖畔4个陆面台站近20年的大风记录,对南四湖大风天气的基本气候特征进行了统计分析,结果表明:南四湖地区大风以西北风为主,春季出现大风日数最多,秋季最少。自90年代末大风日数呈逐渐减少趋势,南四湖大风频次逐年减少,造成该结果的原因除了大气环流背景方面的影响因素外,还可能与全球气候变暖、测站周围局地环境改变、人工防护林带面积扩大有关。     

Effects of fish and plankton and lake temperature and mixing depth

A comparative study of small temperate lakes (<20 square kilometers) indicates that the mixing depth or epilimnion is directly related to light penetration measured as Secchi depth. Clearer lakes have deeper mixing depths. This relation is the result of greater penetration of incident solar radiation in lakes and enclosures with high water clarity. Data show that light penetration is largely a function of size distribution and biomass of algae as indicated by a relation between the index of plankton size distribution (slope) and Secchi depth. Larger or steeper slopes (indicative of communities dominated by small plankton) are associated with shallower Secchi depth. In lakes with high abundances of planktivorous fish, water clarity or light penetration is reduced because large zooplankton, which feed on small algae, are reduced by fish predation. The net effect is a shallower mixing depth, lower metalimnetic temperature and lower heat content in the water column. Consequently, the biomass and size distribution of plankton can change the thermal structure and heat content of small lakes by modifying light penetration.     

几种淡水小型鱼类吞食粘性鱼卵的初步观察

通过在室内进行８种淡水小型鱼类吞食鱼卵的试验观察表明：小型鱼吞食鱼卵带有普遍性，吞食强度依次为宽鳍、麦穗鱼、马口鱼、虎鱼、棒花鱼、鱼旁鱼皮、银鱼句、，其中７种鱼具有昼夜摄食节律，高峰期各异，但每天皆有１６ｈ的停食期．由此可见，小型鱼类通过摄食鱼卵，对能够在湖泊水库中自然繁殖的经济鱼类及凶猛鱼类的种群具有一定调控作用，对公鱼等孵化期较长的鱼类移植效果产生不良影响