Long-term changes of planktonic rotifers in a subtropical Chinese lake dominated by filter-feeding fishes

1. The long-term changes (1956–1998) in density and species composition of planktonic rotifers were studied at two sampling stations (I, II) of Lake Donghu, a shallow eutrophic Chinese Lake densely stocked with filter-feeding fishes. Annual average densities of rotifers increased with an increase in fish yield and eutrophication, whilst species number decreased from 82 in 1962–1963 to 62 in 1994–1998.
2. During 1962–98, some species such as Anuraeopsis fissa , Polyarthra spp. (including P. dolichoptera & P. vulgaris ) , Trichocerca pusilla and Synchaeta oblonga increased their percentage in abundance remarkably, whilst the proportion of Keratella cochlearis decreased at two relatively eutrophic stations from 19 to 4.2% at Station I and from 30 to 3.2% at Station II.
3. The high r _max of A. fissa probably made it more successful than other rotifers under high predation pressure by planktivorous fish. The decrease in the K. cochlearis population might be attributed partly to predation by Cyclops vicinus .
4. Small rotifers were less vulnerable to fish predation than large-sized cladocerans. Decreases in cladocerans coincided with increases in rotifers, suggesting that the indirect effect of fish predation on cladocerans might have partly contributed to the population development of rotifers in Lake Donghu during recent decades.
5. We also conducted surveys (1994–1998) of seasonal dynamics of rotifers at four sampling stations (I–IV) which have varied in trophic status after fragmentation of the lake in the 1960s. A total of 75 species were identified at the four stations. Both densities and biomass of rotifers were considerably higher in the two more eutrophic stations than in the two less eutrophic stations. This indicates that the population increase of rotifers at Stations I and II during recent decades might be partly attributed to eutrophication of the lake water.     

碎石覆盖对河流硬质护坡土壤抗侵蚀性及植物生长的影响

针对河流硬质护坡生态修复中的稳定性和水分平衡等技术难点,提出了一种碎石覆盖技术,并通过抗冲刷实验和盆栽实验分析了不同碎石覆盖对土壤抗冲刷能力、保水性能及植物生长的影响.结果表明：粒径为1.5～2 cm的碎石覆盖处理在增强土壤抗冲刷能力、提高土壤保水性能和植物生物量方面效果明显,但覆盖厚度为5 cm和8 cm的碎石覆盖处理在抗冲刷、保水和促进植物生长方面的作用均无明显差异.厚5 cm、粒径为1.5～2 cm的碎石覆盖技术是硬质护坡生态修复中一种经济有效的技术方法.     

新疆福海底栖动物的研究

本文报道了1985年7月在新疆福海四个湖区的7个断面39个采样点上计采到寡毛类9种,水生昆虫42种,软体动物11种,其它动物7种。在调查湖区中以小海子的种类最多,大海子最少。全湖底栖动物的平均密度为1083个/m2,生物量为18.544g/m2。不同湖区中的现存量有一定差别,密度以中海子为最大,生物量则以“七十三公里”湖区为最高。文中扼要分析了环境条件对底栖动物种类组成和数量分布等方面的影响。       

北京小型湖泊底栖无脊椎动物群落结构特征与营养状况的研究

1987年间逐月调查分析了北京6个小型湖泊底栖无脊椎动物群落结构特征。通过指示种、优势种、种类、数量、生物量、Shannon多样性指数及其与水质的关系分析,前3个湖相当于中营养湖泊,后3个湖相当于中-富营养湖泊。梨形环稜螺(Bellamya purificata)和粗腹摇蚊幼虫(Pelopia sp.)可作为北京6个小湖环境质量的指标生物,前者指示水质较好,后者指示水质较差。Shannon多样性指数值(H′)与湖水BOD、COD、TP、TN含量之间关系比较密切,用该指数并参考指示生物特征评价此类型浅水小湖营养状况是可行的。     

杭州西湖初步治理后的浮游植物现状

本文记录了杭州西湖初步治理后的浮游植物种类组成、相似性、数量分布与环境理化因子的关系,以及根据指示种类评价了西湖水质。在1985年2月至1986年2月周年调查的20个站位中,共鉴定了浮游植物7门92属229种、变种和变型;其中蓝藻门19属39种;绿藻门35属87种8变种1变型;硅藻门24属54种7变种1变型等。西湖浮游植物的数量分布以外湖最高,年均值为529.1×105个/L,三潭内湖最低,仅1.76×105个/L。全湖每升水样含浮游植物细胞密度年均值为614×105个,并且以蓝藻占绝对优势,年均值为423×105个/L,绿藻、硅藻次之,分别为97.3×105个/L和77×105个/L。不同站位浮游植物种类组成的相似性指数值(sorensen 公式)在51.3-85.3范围。       

青海湖地区植被演变趋势的研究

青海湖地区作为祁连山系中段南麓的一个大型山间盆地,是一个独具特色的地区。这里的以草原为基带及其周围山地的高寒灌丛和高寒草甸垂直系列,有其自身的特点和发展趋势。随着整个青藏高原的强烈隆升,本区植被也具有一系列的明显变化。大片森林趋于消退,仅残存有少数适应高寒生境的树种;温性植被类型局限于海拔较低处,而高寒植被类型相对分布较广。分析表明,青海湖地区的整体植被景观有向寒旱生境方向发展的演变趋势。本区植被出现上述演变趋势的主要原因在于该地区生境因抬升而趋于寒旱的过程中,植物种对其生境变化表现出不同的忍耐性和适应性所致。     

A Preliminary investigation on the Vegetational and Climatic Changes Since 11, 000 Years in Qinghai Lake An Analysis Based on Palynology in Core QH85-14C

Qinghai Lake is the largest inland saline lake in China. it is situated in the northeastern part of the Qinghai Xizang Plateau. This paper is based on the information of the sporo-pollen assemblages of 47 samples from the drill core and surface samples. The general treads of vegetational and climatic changes since 11,000 years B. P. may be subdivided in ascending order as follows: In the first stage which corresponds to zone Ⅰ of the sporo-pollen assemlage, the vegetation during the past of 11,000–10,000 years was represented by a temperate shrub, semi-shrub and steppe, consisting of Chenopodiaceae. Artemisia, Nitraria, Ephedra and Gramineae were predominant. At the same time, some subalpine conifers, Pinus, Picea and Betula, would grow by the side of rivers and lakes, the climate was warmer and wetter than that of the Late Pleistocene. Due to the rising temperature in this zone, the Pleistocene-Holocene boundary might be estimated at about 11,000 years B. P.. The vegetation of the first stage belonges to temperate steppe with a few trees: In the second stage (ZoneⅡ of pollen), the vegetation was characterized by a temperate forest steppe during this period of 10,000 to 8,000 years B. P. Forest area apparently increased and some broadleaf deciduous and need leaf evergretn trees, such as Quercus, Betula, Pinus and Picea, grew by lakes and on mountains. At this time, the climate was warmer and wetter than that of the first stage. In the third stage (Zone Ⅲ) between B,000 and 3,500 years B. P, The vegetation was composed of a temperate mixed broad-leaf deciduous and needle-leaf evtrgreen forest. The needle-leaf evergreen forest consisting of Picea, Pinus, Abies, Betula grew in temperate zone mountains. The climate was relatively warm and wet. The fouth stage (zone IV), the vegetation was dominated by shrub semishrub, dwarf semishrubs, steppe and semi-arbors. Some trees consisting of Betula, Picea, and Pinus decreased in number in the lake regions. Some subalpine cold temperature evergreen trees, such as Abies and picea disappeared from the lake region. This indicated that the climate was warmer and drier during the past 3500–1500 years B. P. than the third zone. In the fifth stage (pollen zone V), the vegetation comprised steppe and desert from 1500 years ago to the present time. Some arborealtrus such as Betula and Pinus were less increased about 500 years B. P. at this time the temperate and wet slightly, rose up. From the above analysis, it is clear that the Qinghai lake region has been confronted with the vegetational and climatic changes since ll,000 years B. P. Therefore, the palynoflora of the Qinghai lake has its significance in Geography and vegetational history.     

保安湖沙塘鳢的食性、繁殖、年龄及生长的研究

保安湖沙塘鳢１冬龄成熟,雌雄比１：１．３４,４月初至６月中旬繁殖;个体绝对繁殖力５４０—１９４３ｅｇｇ（１１５４±３１４ｅｇｇ）。渔获物中以体长８．０—１４．０ｃｍ,体重１０．０—４０．０ｇ,２、３龄个体为主。体长－体重关系为Ｗ＝０．０２１２９Ｌ３.０５８５。３龄前生长较快;雄鱼略快于雌鱼。肥满度冬春季较高,最高在３月。体长和体重与年龄的关系可用Ｂｅｒｔａｌａｎｆｆｙ生长方程描述,参数分别为：雌鱼Ｌ∞=１５．２９ｃｍ,ｋ＝０．４０７２,ｔ０＝０．１５９６,Ｗ∞＝８４．９ｇ;雄鱼Ｌ∞＝１６．７１ｃｍ,ｋ＝０．３７３６,ｔ０＝０．１０９５,Ｗ∞＝１１８．５ｇ;体重生长拐点年龄和拐点体重雌鱼分别为２．８６ａ和２５.１ｇ,雄鱼３．１３ａ和３５．４ｇ。     

Food of introduced mosquitofish: ontogenetic diet shift and prey selection

The mosquitofish Gambusia holbrooki of Lake Banyoles, Catalonia, Spain, were strictly littoral. Their population was dominated by females throughout the year, except in spring when males were more common. Their diet was based on littoral cladocerans, particularly Chydorus sphaericus, Scapholeberis ramneri, Ceriodaphnia reticulata , and Pleuroxus laevis , and nematoceran (basically chironomid) adults. There was a large variety of prey of terrestrial (collembolans, ants) or aquatic neustonic origin ( S. ramneri , emerging nematoceran adults), showing the microhabitat of mosquitofish closely linked to the water surface. In contrast to other studies, terrestrial insects were not especially important in summer. In addition to seasonal and between-site variation, there was an ontogenetic diet shift from microcrustaceans, particularly cladocerans (smallest fish also using diatoms and copepod nauplii) to larger prey, namely nematoceran adults. However, there was an unusual, inverse relationship between fish length and the size of two prey ( S. ramneri and the collembolan Sminthurides sp.), paralleling the overall increase in mean prey size.     

Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China

During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1× 10⁴ kg nitrogen and 3.91×10⁴ kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7×10⁴ kg (676 kg/ha) nitrogen and 3.88×10⁴ kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55×10⁴ kg nitrogen and 0.40×10⁴ kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture.The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.