Limnology,although showing progress overall,still has many handicaps:there is a lack of understanding of process and functions,of animal and plant diversity,of taxonomy in some climatic regions like the tropics-subtropics,and the teaching of the discipline is lagging so far behind that in many countries that span several climatic zones,the temperate zone is still used as a standard.On the other hand,water problems all over the world are becoming more and more acute,both as regards quantity as quality.China is no exception to this rule.Stretching from a cool continental climate in the north to a tropical climate in the south,it faces severe problems of pollution and eutrophication,including almost perennial blooms of toxic blue-green algae.

The zooplankton,defined a the assemblage of animals and animal-like creatures that lives in the water column of small to big waterbodies,has primarily been studied in the temperate zone,so most "received" concepts about it derive from the temperate,not the tropical belt of this planet.

Clean safe water is increasingly valuable everywhere.Everyone lives in a watershed and desires high quality water.However,many activities lower water quality by way of increased productivity and pollution.Traditional limnological knowledge has been successfully applied to improve temperate zone lakes and streams.Research in the tropics will develop strategies to reduce productivity and control toxic chemicals related to biomagnification and endocrine disruption.

Phytoplankton is a polyphyletic group of photosynthetic,oxygen producing protoctists and bacteria adapted topersist in suspension and liable to passive movement by wind and current (Reynolds,2006)^[1].They inhabit almost all the aquatic ecosystems of the biosphere and show an enormously wide variability of shape,size,evolutionary and phylogenctic position,as well as energy and nutrient demands.Their amazing diversity in an apparently homogeneous medium,as the pelagic environment can be perceived at a first sight,caused concern a few decades ago and puzzled aquatic biologists for years.Actually, the contemporary occurrence of many species competing for the same few resources (apparently) violated the Competitive Exclusion Principles (Hutchinson,1961).

Sensor networks are playing an increasingly important role in ecology.Continual advances in affordable sensors and wireless communication are making the development of automated sensing systems with remote communication (i.e.,sensor networks) affordable for many ecological research programs (Porter et al.2005)^[1].These in situ instruments provide high-frequency data of key variables that previously were measured intermittently and by hand.A number of federal research organizations have realized the potential of environmental sensor networks, and large-scale initiatives are under development.Independent of these initiatives,small sensor networks have emerged to meet the needs of the individual or small teams of ecologists.Ecologists are entering (or already have entered,in some cases) an era in which high temporal and spatial resolution in situ measurements are generating data at unprecedented rates.The use of sensor networks will dramatically increase the volume of ecological data generated in the next decade.

Phytoplankton are classfied into three groups based on size: microphytoplankton (>20 μm),nanophytoplankton (2-20 μm),and picophytoplankton(＜2 μm) (Sieburth et al.1978)^[1].Picophytoplanktonare composed of three groups:Prochlorococcus,Synechococcus,and picophytoeukaryotes.The former two are unicellular cyanobacteria.

Shallow water bodies can exist in alternative stable states,a clear water state with high coverage of maerophytes or a turbid state with high phytoplankton biomass.The alternative equilibria hypothesis has been proposed to explain the occurrence of the alternative stable states (Scheffer et al.,1993)^[1],which assumes that:1),turbidity increases with the nutrient level; 2),macrophyte reduces turbidity; and 3),macrophyte disappears when a critical turbidity is exceeded.At low nutrient levels,the water should be clear,with low phytoplanlaon biomass and extensive macrophyte coverage.At high nutrient levels,the water should be turbid,with high phytoplankton biomass and a lack of macrophytes.

Submerged macrophyte coverage, percentage of Vallisneria natans and Hydrilla verticillata, and concentrations of total nitrogen (TN)、total phosphorus (TP) and Chl a, were studied in a shallow eutrophic lake. The results showed that: 1) Percentage of Vallisneria natans increased from 30% to 95%, while Hydrilla verticillata decreased from 60% to 5% before May, respectively ; 2) Content of nutrients and chl a reduced quickly with the stabilization of ecosystem after rapid increasing period in the process of transition, concentrations of TN、TP and Chl a reduced to about 0.840 mg·L^-1、0.028 mg·L and 2.562μg·L^-1, respectively, Secchi depth (SD) increased to 120cm, water quality improved obviously; 3) Our results indicated that ecosystem of Nan Lake was at a clear water state dominated by Vallisneria natans which shifted from turbid state dominated by phytoplankton, after a short interim state dominated by Hydrilla verticillata, gradually.

Lobose Testate Amoeba Difflugia, a worldwide distributed genus with its remarkable size and prey species, are critical plankters which link the classic food chain to the microral loop in the water column. To recognise its prey species and its predation mechanism, a field study, including statistical study and direct live observation was carried from May, 2006 to December, 2007 in Liuxihe Reservoir, Guangdong Province, with several coexisting Difflugia, and D. tuberspinifera as the dominant species in the water column. Both live observation and fixed samples from fields indicated that soft body rotifers, such as Collotheca sp. and Conochilus dossuarius are preferred food for D. tuberspinifera, but C. dossuariu might not be captured easily by D. tuberspinifera because of the colonying behavior. Keratella cochlearis can also be successfully handled by D. tuberspinifera by tearing up the strong lorica. However, the handling time was much longer than the soft body rotifers which might prevent it from been frequently caught. D. tuberspinifera might have direct trophic cascade effect toward Collotheca in the water body.

In reservoirs or lakes, mixing depth affects growth and loss rates of phytoplankton. Based on data collected from Zeya Reservoir, China, we investigated the influence on phytoplankton dynamics using cluster analysis of the scaled mixing depth. According to the scaled mixing depth, a year could be divided into three different periods, including the thermally stratified period, the isothermally mixed period, and the transition period. Mixing depth had a significant correlation with phytoplankton biovolume. According to steady state assumption, a unimodal curve (mixing depth-phytoplankton biovolume) with a significant peak at the mixing depth of 2 m was observed, which is largely consistent with Diehl'prediction.

Life history characteristics of three sibling species including sibling HE1, HE3 and LE9 in Brachionus calyciflorus species complex collected from Lake Liantang and Pond Hehuatang in Wuhu City and cultured at 13℃, 18℃, 23℃ and 28℃ with 2.0×10⁶ cells/mL of Scenedesmus obliquus was compared by means of life table demographic approach. The results showed that the differences in life table parameters among the three sibling species differed with temperatures. At 13℃, sibling species LE9 had longer life expectancy at hatching, average lifespan and generation time than sibling species HE3, and the highest net reproductive rate and intrinsic rate of population growth among the three sibling species. The percentage of mictic females in all produced offspring was similar among the three sibling species. At 18℃, sibling species LE9 had longer life expectancy at hatching and average lifespan than sibling species HE3, and longer generation time than sibling species HE1 and HE3. Sibling species HE3 had higher intrinsic rate of population growth than sibling species LE9, and produced the most mictic daughters among the three sibling species. However, the net reproductive rates were similar among the three sibling species. At 23℃, sibling species HE1 had the longest life expectancy at hatching, average lifespan and generation time among the three sibling species. Sibling species HE1 produced less mictic daughters than sibling species HE3. Both net reproductive rate and intrinsic rate of population growth was similar among the three sibling species. At 28℃ and among the three sibling species, life expectancy at hatching, average lifespan, generation time and intrinsic rate of population growth were all similar, sibling species HE1 had the lowest net reproductive rate, sibling species HE3 produced the most mictic daughters. The responses in life table parameters to increasing temperatures were different among the three sibling species. Temperature, sibling species and their interactions all significantly influenced generation time, average lifespan, life expectancy at hatching and percentage of mictic females in the produced offspring. Both temperature and sibling species affected markedly the net reproductive rate and intrinsic rate of population growth, but their interactions did not appear to be significant.

We used a spectrophotometry method with 1, 10-phenanthroline-Fe (Ⅲ) to determine the contents of total polyphenol in two species of leaf litter, Dracontomelon duperreanum and Syzygium jambos. The effects of remaining polyphenolics concentration on decomposition rates, colonization of macroinvertibrates and microbial respiration in a subtropical stream were examined. Results showed that total polyphenol was significantly higher in S. jambos (19%) when compared to D. duperreanum (6%), and breakdown rate of S. jambos (k=0.01 day^–1) was slower than that of D. duperreanum (k=0.04 day^–1). The results also indicated that the average microbial respiration rates (0.2 mg O₂ h^-1 g DM^-1) of S. jambos litters was significantly lower than those of D. duperreanum ( 0.4 mg O₂ h^-1 g DM^-1), and its taxa richness and total density in shredders of macroinvertebrate was significantly less than in those of D. duperreanum (P<0.05). The low breakdown rate of S. jambos leaves in the early period is mainly as a result of inhibition of microbial activity as well as less palatable to shredders of macroinvertebrates due to high contents of polyphenols, which showed that the leaf polyphenol had a strong negative effect on leaf litter decomposition.

In China, the most diverse molluscan fauna occurs in the Yangtze basin. The molluscan fauna in this region are highly imperiled due to increasing human activities. Aiming at effective conservation of the deteriorating molluscan fauna, intensive field investigations of freshwater molluscs on the mid-lower Yangtze Lakes were conducted between June, 2003 and May, 2005. Altogether 69 species were identified during the collection, including 29 gastropod species belonging to 9 families, 40 bivalve species belonging to 5 families, and 42 endemic species. Among them, Unionidae and Viviparidae are the two families with the highest species numbers, accounting for 50.7% and 14.5% of the total, respectively. The diversity variesgreatly from lake to lake. River-connected lakes contain the most diverse fauna, especially those adapted to lotic habitat, such as Rivularia spp, Semisulcospira spp and some species of Unionidae. In the two large river-connected lakes, Poyang·Lake and Dongting·Lake, there are 66 species and 40 endemic species, accounting for 95.7% of the total species number and 95.2% of the total endemic species number, respectively. In contrast,the historical records, it is found that total species number and endemic species number decreased greatly, with a loss of about 50% of the historical records. Meanwhile, the distribution ranges of most taxa were also shrunk. Habitat loss and hydrological alteration in the Yangtze Potamo-lacustrine Complex Ecosystem caused by river-lake isolation should be the primary factor causing the decline of molluscan fauna. Other human activities, such as overharvesting, reclamation and pollution, may be also the important factors.