古昆仑湖地区183-90kaBP间的微体古生物与环境变迁

古昆仑湖位于昆仑山垭口昆仑河谷地,大约在200kaBP前已开始沉积,沉积物为一套灰、灰绿、土黄色粉砂质、砂质粘土,厚约7m.在纳赤台西北剖面5.6-2.4m层段产较多微体化石,介形类有8属12种:Ilyocypris biplicata(Koch),I.bradyi Sars,Eucypris crassa(Mller),E.elliptica(Baird),E.rischtanica Schneider,Candona candida(Mller),Stenocypriscf.major(Baird),Cypridopsis obesa Brady Robertson,Prionocypris gansenensis Huang,Potamocypris villosa(Jurine),P.cf.wolfi Brehm和Limnocythere dubiosa Daday等.轮藻类有Chara aliensis Z.Wang,Chara gansenensis S.Wang和Charasp.根据U系法测年,含化石地层的年龄大约为168-90kaBP,属于倒数第二次冰期至末次间冰期早期.按生物组合和沉积物特征分析,古昆仑湖区在183-90kaBP的环境气候变化大致有两个大的期次、6个小期次:(1)183-130kaBP冷湿期,湖区环境较冷湿,湖泊水质较淡,水温不高.早期(约183-170kaBP),湖面较宽,水体较深,环境动荡,化石贫乏;中期(约170-151.3kaBP),湖面有一定收缩,水质含盐度有所提升,水温仍不高,湖区环境湿度较大;晚期(约151.3-130kaBP),化石贫乏,生态环境、水质条件可能与早期类同.(2)130-90kaBP凉湿期,湖内生态环境较好,生物门类中除介形类外,出现沉水性植物轮藻类,且介形类生物量较前期有很大增加,属种分异度较好.早期(约130-105kaBP),偏冷湿;中期(约105-98kaBP),凉湿,为生物大发展大繁盛时期;晚期(约98-90kaBP),偏凉湿,在98-93kaBP,环境不宜生物生息,化石贫乏;约93-90kaBP,生态环境有所改善,有介形类3属5种,但生物量较小.     

Shifts in isotopic signatures of animals with complex life-cycles can complicate conclusions on cross-boundary trophic links

Stable isotopes (¹³C and ¹⁵N) are widely applied in studies of trophic links. We used this method to investigate the contribution of aquatic and terrestrial prey to the diet of riparian predatory arthropods in two mountain headwater streams in Colorado, USA. Aquatic and terrestrial prey and riparian predators were collected during summer 2009. To evaluate the reliability of conclusions based on stable isotope ratios, we compared the isotopic signatures of aquatic larval and terrestrial adult stages of three abundant stream insect species and assessed variation in mixing model estimates for spider diet composition under varying assumptions for trophic fractionation. Adult isotopic signatures of some aquatic prey species were indistinguishable from those of prey species with exclusively terrestrial life histories (stoneflies: ¹³C and ¹⁵N, chironomids: ¹³C). Other prey had distinctly aquatic isotopic signatures as both larvae and adults (a mayfly and a caddisfly). There was no evidence that prey with aquatic isotopic signatures contributed to the diet of the spiders near one stream. For the other stream, mixing model analysis suggested that chironomids were included in the diets of lycosid, linyphiid and liocranid spiders. Reliable estimates of the contributions of prey sources were compromised by the sensitivity of mixing models to assumptions on trophic fractionation and the presence of “isotopically cryptic” prey. This study emphasizes the importance of supporting isotope-based studies on cross-boundary trophic links with data on isotopic shifts in prey with complex life cycles and assessment of fractionation rates specific to the study system.     

Variability of a cyprinid lake ecosystem with special emphasis on the native fish fauna under intensive fisheries management including common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix)

The lake investigated (Lake Heiliger See near the town of Angermünde, North-East Germany) is small (10.2 ha) but deep (z_max = 12 m, ? = 6.5 m). During summer the thermocline is at a depth of 4-5 m, and the hypolimnion is filled with H₂S already by mid-June, making 60-75% of the bottom area inaccessible to fish. The native fish fauna is dominated by planktivorous roach (Rutilus rutilus). A test stocking of silver carp (Hypophthalmichthys molitrix) together with an unplanned and erroneous stocking of common carp (Cyprinus carpio), coupled with an incorrectly calculated strong stocking of eel (Anguilla anguilla), which assumed that the total lake area yielded fish food organisms, brought about a strong depression of the food biomass available to native fish. Both silver carp and common carp showed a pattern of behaviour which only partly agreed with results obtained in experimental ponds prior to lake stocking. At least for 10 years there was a very low zooplankton biomass (mostly below 1 mg/l fresh weight) caused by silver carp and a strongly reduced benthos biomass (frequently below 1 g/m² fresh weight) caused by common carp and eel on H₂S-free bottom areas. Despite this extreme situation, which lasted for 20 years and is rarely found in lakes elsewhere, it was not possible to demonstrate negative effects on the native fish fauna comprising 16 species. Also the dominance pattern seems uninfluenced in the long run. A strong decline of the catchable roach stock was observed for some years, but the stock reappeared soon in comparable quantity. During the time of roach stock depression the individual growth of roach (and common carp) was particularly low. Nevertheless, roach succeeded in reproduction during this time in spite of the reduced zooplankton and detritus concentrations. Fry numbers per year ranged from 500-15 000 individuals/ha. The pike perch (Stizostedion lucioperca) was perhaps the most endangered species of all those living at small population numbers in the lake, since its fry is confined to the limnion where competition from silver carp and adult roach and perhaps predation by roach is highest. However the pike perch stock remained unchanged at the low level of 1950, the time prior of carp and eel stocking. All other rare species of Lake Heiliger See spawn in the littoral zone where fry survival conditions were less impacted. In summary, we present more evidence that the fish fauna of cyprinid lakes is more robust than in salmonid lakes. The regulation capacity of fish communities of eutrophic lakes seems to be able to offset even severe direct and indirect influences of fisheries management.     

The decline of Daphnia hyalina galeata in Lago Maggiore: a comparison of the population dynamics before and after oligotrophication

We reconstruct the impact of different environmental cues on Daphnia seasonal dynamics by means of an analysis of demographic and reproductive parameters, as well as of the size structure of the population. Data from 1996, indicative of the most recent productivity of the lake, with those from 1973, when the lake was meso-eutrophic, allow a discussion of the relevance of the observed changes for the structure of the pelagic food web of Lago Maggiore. Daphnia summer dynamics is mainly controlled by Bythotrephes longimanus. This is quite a different situation from that of the past, when Leptodora kindtii was the prevalent predatory cladocera. The size structure of Daphnia population revealed a depletion of small ovigerous females with increases in the predator. Our data allow a discussion of the idea, recently proposed, of Bythotrephes longimanus as a visual sit- and -wait predator.     

Reduced abundance but increased diversity of chironomid larvae under higher trophic pressure from fish in semi-permanent ponds

Fish may affect macrobenthic communities through trophic interactions and modification of habitat conditions. We compared the density, diversity and taxonomic composition of larval chironomids under low vs high fish impact, created by stocking semi-natural ponds with either young/small common carp Cyprinus carpio at low biomass densities or with high biomass densities of older/large common carp, supplemented by other cyprinids and predatory fish species.Over the study season, May–August, total chironomid abundance was considerably lower in ponds with high fish biomass than in low fish biomass ponds. In July–August larval densities declined significantly, irrespective of the fish status of the ponds. The composition of larval communities diverged between ponds with different fish status. Chironomus riparius and C. plumosus accounted for most of the observed dissimilarity. C. plumosus densities were not affected by the fish status of the pond, constituting on average >38 % of chironomid specimens in both types of ponds. C. riparius was abundant in ponds with low fish biomass (on average 30 %), but rare in ponds with high fish biomass (4 %). Other common taxa were Glyptotendipes pallens (15 % and 13 %, respectively) and Procladius sp. (14 % in ponds with low fish impact). Canonical correspondence analysis showed that fish biomass was more important in determining chironomid community composition than environmental variables indicative of pond eutrophication (total N, P, chlorophyll a and conductivity).Despite adverse effects on total abundance, chironomid diversity was higher under apparently stronger trophic pressure by fish. Fish may have relieved some chironomid species from invertebrate predation and competition with dominant Chironomus larvae. Other important drivers of chironomid assemblage and diversity patterns may include species-specific feeding modes and prey size selectivity of fish, the ability of chironomid larvae to attain size- and depth-refuge from small fish but not larger fish, and differential vulnerability of free-living and tube-dwelling larvae relative to ontogenetic niche shifts of fish.     

Will Astacus leptodactylus displace Astacus astacus and Austropotamobius torrentium in Lake Ägeri, Switzerland?

Lake Ägeri hosts three crayfish species: Austropotamobius torrentium, Astacus astacus and Astacus leptodactylus. To study the interspecific competition and a possible scenario of displacement, we monitored the distribution and relative densities of the different species during the years 1996-1999 by SCUBA diving. We examined the association of the species with different types of substrate and investigated the frequency of limb loss and the life history characteristics of the three species.¶A. leptodactylus was found at more sites than A. astacus and A. torrentium. It was also present in much higher densities than the other two species. A. torrentium preferred areas with hard substrate, whereas A. astacus was more often found at sites with soft substrate and reed vegetation. A. leptodactylus was observed on soft and hard substrate. The frequency of limb loss was highest in A. astacus and more frequent at sites with a high density of A. leptodactylus. Limb loss in A. leptodactylus and A. torrentium was more frequent at sites with high self-densities. Females of the two Astacus species carried more eggs than A. torrentium females. The eggs of A. astacus were larger than the eggs of the other two species. Juveniles of A. leptodactylus grew significantly faster in their first year than juveniles of A. astacus and A. torrentium. During the four years of the study A. leptodactylus expanded its range along the southeastern shore of Lake Ägeri. At the northwestern border of its distribution the portion of A. leptodactylus had slightly increased by the end of the study period. In two areas of the lake the population of A. astacus and A. leptodactylus declined between 1997 and 1999.     

The trophic ecology of arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in Ellidavatn, a small lake in Southwest Iceland

In the lake Ellidavatn, southwest Iceland, fish samples were collected with gillnets of one mesh-size once or twice a month for two years. Stomach samples of 961 Arctic char and 429 brown trout were analysed. The annual diet of char consisted of chironomid larvae (31%), cladocerans Eurycercus lamellatus (19%), bivalves Pisidium spp. (16%), water snails Lymnaea peregra (15%), chironomid pupae (8%) and char eggs (5%) and that of trout consisted of sticklebacks (76%), salmonids (7%) and L. peregra (6%). The average percentage of indigestible plant remains and gravel in the stomach content was much higher for the char (14%) than trout (3%). There were large seasonal changes in the diet of char: char eggs were consumed in autumn, chironomid larvae mostly from autumn to spring, chironomid pupae in summer and E. lamellatus from summer to autumn. No seasonal changes in the diet of trout were seen. The diet overlap of char and trout was very low, usually about 10%, reaching a maximum of about 30% in late summer 1976 when the common diet was mainly E. lamellatus and chironomid pupae. The resource partitioning in Ellidavatn indicates that char are better adapted to preying on small benthic invertebrates than piscivorous trout. The segregation in the diet of the two species indicated competition for restricted food supply, which was also consistent with slow growth and low condition factor of char (0.8–1.0) and trout (1.0) in Ellidavatn. The prey of trout were two orders of magnitude larger than the prey of char which may explain why adult char grew more slowly (2 cm y⁻¹) than adult trout (4 cm y⁻¹) and reached sexual maturity at a smaller size (30 cm) than trout (40 cm).     

Horizontal and seasonal patterns of tropical zooplankton from the eutrophic Prado Reservoir (Colombia)

Zooplankton community analyses can reveal valuable information about the trophic status and secondary production in reservoirs. The zooplankton seasonal distribution and important physical and chemical parameters in Prado Reservoir (Tolima, Central Colombia) were studied in monthly surveys throughout a hydrological cycle (February 2000-January 2001) in order to establish seasonal patterns and the biotic and abiotic relationships for the reservoir. Surface zooplankton collections at 1 m depth were taken at six sampling stations with regard to reservoir morphometry, location of main tributaries and mixing areas of the incoming tributaries. Cladocerans numerically dominated (48.1%) the community throughout the study period followed by Copepoda (32.7%), Rotifera (19.1%), and Diptera larvae (0.01%). Among the cladocerans, there was a greater abundance of Bosmina longirostris (69.8%) than other crustaceans. Among the Rotifera, Brachionus falcatus was the most abundant with 23% and Keratella tropica was least abundant with 8%. The only cyclopoid species found was Thermocyclops decipiens. The phantom midge Chaoborus sp. was also part of the zooplankton community. Based on numbers, cladocerans represented a significant component of the zooplankton in both dry and rainy seasons. Four species (Brachionus spp., K. tropica, Diaphanosoma brachyurum, Ceriodaphnia cornuta, Moina sp., and T. decipiens) had never previously been found in the reservoir, but were recorded for other standing Colombian water bodies. The replacement of B. longirostris instead of Daphnia sp. as dominant species was observed. The results of the comparison of the different studies confirmed that the trophic state of this artificial lake may be classified as eutrophic, and in general, physical, and chemical homogeneity were observed both spatially and temporally.     

青藏高原陆相介形类的分布特征及其对生态环境的响应

统计分析了青藏高原不同区域水体环境表层沉积物陆相介形类的属种分布特征,探讨了介形类在不同水环境下（盐度、pH值及水深）对生态环境的响应.结果显示,青藏高原现生介形类共计21属67种,其中Candona candida、Ilyocypris bradyi、Eucypris inflata、Limnocythere dubiosa、Limnocythere inopinata、Paracypricerus angulata、Leucocytherella sinensis和Leucocythere mirabilis为青藏高原地区的常见种.湖泊、河流、洼地和湿地4类水体环境中,湖泊中介形类最为丰富,达19属62种;青藏高原东北部（祁连山和柴达木盆地）、北部（昆仑山）、西部和南部不同区域的介形类常见种存在较大差异,可能是区域海拔、pH值和盐度综合作用的结果.淡水和微咸水环境介形类属种数量较咸水及盐湖中丰富,分别有17属41种和13属42种,Limnocythere dubiosa （0.52~90.6 g/L）和Leucocythere mirabilis（0.51~174.63 g/L）在淡水、咸水及盐湖中均有出现,适应盐度范围较广;pH值在8.0~10.0范围内介形类属种多样性最丰富,表明大部分介形类具有嗜碱性的特征;青藏高原陆相介形类属种多样性随水深的增加而降低,浅湖（0~15 m）中介形类属种最为丰富,达到17属52种,其中Candona candida（0.2~80 m）和Leucocythere dorsotuberosa（0.3~110 m）从滨湖至深湖区均有分布,二者均具有较大的水深适应范围.     

Contrasting responses of oligochaetes (Annelida) and chironomids (Diptera) to the abatement of eutrophication in Lake Neuchâtel

: Lake Neuchâtel (Switzerland) has been recovering from human-induced eutrophication since 1982. Oligochaetes and chironomid larvae were used to monitor the recovery of sediment at a depth of 40 m. In oligochaete communities, the mean proportion of individuals belonging to species indicative of oligotrophic conditions (mostly Spirosperma velutinus and Stylodrilus heringianus) increased from 16 % in 1984 to 33 % in 1992, but decreased to 11 % in 1997. Based on oligochaetes, benthic conditions deteriorated in 1997 whereas, based on the increase of oligotrophic chironomids (mostly Micropsectra), they improved. This difference was attributed to the impact of large planktonic algae whose sedimentation had altered oxygen concentrations at the water-sediment interface. Oligochaetes were more affected than chironomids because they are less mobile and they depend more on the inner sediment for their food and reproduction than the latter. However, based on the combined response of oligochaetes and chironomids, benthic recovery was stalled in 1997 but was not reversed.     

Determining the photosynthetic productivity of a stratified phytoplankton population

During the summer, a stratified population of the red-coloured cyanobacterium Planktothrix rubescens dominates the phytoplankton of Lake Zürich. The organism hovers in the metalimnion by regulating its buoyancy, provided by gas vesicles. The daily integral of primary production by the organism has been calculated from its P/I curve and measurements of the vertical distributions of Planktothrix sp., irradiance and temperature in the lake, using numerical integration with Excel spreadsheets. The basic methods are described and the particular problems of analysing production by stratified populations are discussed. Daily integrals of primary production based on measured growth/irradiance (7/I) curves of P. rubescens produce a closer correspondence to the changes in the natural population than do integrals based on P/I curves.     

Karpfenintensivbewirtschaftung von Seen und Eutrophierung

In the Galenbeck lake, a shallow lake covering 700 ha and having a nutrient load of 0.23 g/m²a P as well as 4.3 g/m²a N, in 1965 a stock of carp of 500 animals/ha was established and additionally fed with grain. This stock of carp resulted in a considerable whirling-up and redeposition of the soft lime sediments, the rich submersed vegetation disappeared and the phytoplankton reached maxima of 885,420 cells/ml, whereas the zooplanktion reached only 4530 ind./l. The chlorophyll contents increased to 464 mg/m³, the depth of visibility decreased to 10 cm. The total planktonic primary production is estimated at 500 g/m²a C at least. These changes are regarded as eutrophication, its cause being attributed mainly to the internal fertilization by an intensified recirculation of nutrients from the sediment, but also by the fertilization which is connected with feeding. When the fish rearing had ceased and the stock of carp had been fished off, in 1970 a reacreation of the lake began, and in 1974 the lake reached again its original state as a clear-water lake with an abundant contents of macrophytes, supported also by the P-retention in an upstream storage reservoir for spray-irrigation water.     

Simulation of vertical position of buoyancy regulating Microcystis aeruginosa in a shallow eutrophic lake

Vertical distributions of the cyanobacterium Microcystis aeruginosa are examined in a shallow lake in relation to mixing and thermal stratification over three days. A model of buoyancy regulation by Microcystis aeruginosa, applicable for turbulent environments, is coupled with a one-dimensional hydrodynamic model. The coupled model is applied to Thomsons Lake in Western Australia to examine the relationship between buoyancy regulation and the daily stratification/destratification cycle. The vertical distribution of Microcystis aeruginosa in Thomsons Lake depends on the carbohydrate ballast dynamics and the colony size. When thermal stratification occurs, all the simulations show a similar general pattern of diurnal vertical migration of the Microcystis aeruginosa colonies. The colonies accumulate at the surface during the night and in the morning the colonies lose buoyancy, which leads to a reduction by ~ \sim 50% in colony concentration in the top 0.2--0.3 m of the water column. Afternoon winds redistribute the population over the entire water column. When the lake is fully mixed, the vertical migration pattern of the Microcystis aeruginosa colonies may be affected, depending on the colony size and the intensity of the mixing.     

Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling

v--vRegional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller (M < 4.8) seismic events. This path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration (or master) events. This information can be difficult to obtain, especially for smaller events. Generally, explosion or quarry blast generated travel-time data with known locations and origin times are useful for developing the path calibration parameters, but in many regions such data sets are scanty or do not exist. We present a method which is useful for regional path calibration independent of such data, i.e. with earthquakes, which is applicable for events down to M_w = 4 and which has successfully been applied in India, central Asia, western Mediterranean, North Africa, Tibet and the former Soviet Union. These studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events. We find that the error in source depth does not necessarily trade-off only with the origin time for events with poor azimuthal coverage, but with the horizontal location as well, thus resulting in poor epicentral locations. For example, hypocenters for some events in central Asia were found to move from their fixed-depth locations by about 20 km. Such errors in location and depth will propagate into path calibration parameters, particularly with respect to travel times. The modeling of teleseismic depth phases (pP, sP) yields accurate depths for earthquakes down to magnitude M_w = 4.7. This M_w threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth, with the relative amplitude of the P_nl waves to the surface waves and the interaction of regional sPmP and pPmP phases being good indicators of event depths. We also found that for deep events a seismic phase which follows an S-wave path to the surface and becomes critical, developing a head wave by S to P conversion is also indicative of depth. The detailed characteristic of this phase is controlled by the crustal waveguide. The key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms. The regionalization scheme can also incorporate mixed-path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures. We also demonstrate that once depths are established, we need only two-stations travel-time data to obtain reliable epicentral locations using a new adaptive grid-search technique which yields locations similar to those determined using travel-time data from local seismic networks with better azimuthal coverage.     

Earthquake Hazard Parameters in Crete Island and its Surrounding Area Inferred from Bayes Statistics: An Integration of Morphology of the Seismically Active Structures and Seismological Data

-- The study addresses the evaluation of earthquake hazard parameters such as maximum regional magnitude (M_max) and the slope of Gutenberg-Richter law # (where b=# log e) for the Hellenic Wadati-Benioff zone and the overriding lithospheric plate in the area of Crete and its surroundings. The seismicity of the area is divided in a cellular (1.0° 2 1.0°) manner allowing analysis of the localized earthquake hazard parameters and graphical representation of their spatial variation. Our approach incorporates the recently updated earthquake catalogue for Greece and the adjacent areas, the consideration of the morphology of the deep seismically active structures in the studied area and use of a probabilistic procedure for estimating the earthquake hazard parameters.¶One of the main inconsistencies in the earthquake hazard assessment is the estimation of the maximum magnitude and the related uncertaint y. The Bayesian approach, applied in the present, is a straightforward technique for evaluating the earthquake hazard parameters and is based on the following assumptions: Poissonian character of seismic events flow, a frequency-magnitude law of Gutenberg-Richter's type with cutoff maximal value for estimated parameter and a seismic catalogue, having a rather sizeable number of events (i.e., 50 events at least per cell). For five cells in which the number of events is less than 50, an effort is made to produce synthetic data. The re-assessed parameters obtained from the synthetic data show no significant difference and the real data (of the five cells) are finally taken into account although the estimated uncertainty is high.¶For four random cells we constructed hazard curves showing the probabilities that a certain magnitude M will be exceeded in one year and the return periods (in years) that are expected for a given magnitude. These are particularly useful for the mapping of earthquake hazard in regions of either low or high seismic activity, as is Crete and the adjacent area.¶The obtained results show that the W and E parts of both subducting and overriding plates differ in the spatial distribution of all the estimated earthquake hazard parameters. The M_max distribution indicates strong coupling between the western portions of the interacting plates (M_max > 6.3) to the south of 36°N. The smaller values of M_max (M_max < 6.3) estimated in the SE part of the studied area indicate weak coupling between the eastern portions of the subducting and overriding plates.¶Values of b > 1.0 are found to the south and east of Crete for the Wadati-Benioff zone, and over the central part of the island and the area to the northeast of it (cell 11) for the continental wedge, which suggests nonuniform stress field and/or heterogeneous material.     

Macrozoobenthic community structure in a large shallow lake: Disentangling the effect of eutrophication and wind-wave disturbance

Biological communities in shallow lakes are often subject to the combined effects of eutrophication and wind-wave disturbance. However, their relative importance in regulating macrozoobenthic community assembly has not been well addressed. In the present study, a monthly sampling of macrozoobenthos and environmental parameters was conducted at ten sites from December 2012 to November 2013 in Lake Hongze, the fourth largest freshwater lake in China, which has undergone serious water quality deterioration over the past few decades. A total of 30 taxa were recorded during the 12 sampling occasions, including 6 chironomids, 6 bivalves, 4 gastropods, 4 oligochaetes, 4 polychaetes, 4 crustaceans and 2 other aquatic insects. The mean abundance and biomass of total macrozoobenthos varied greatly among the ten sites and presented distinctive taxonomic composition between the protected bays and the offshore zone. Three eutrophication parameters (including permanganate index (COD_Mn), chlorophyll a, and total phosphorus in surficial sediments) and three wind-wave variables (including Secchi depth, turbidity, and mean effective fetch) were highly related to spatial variation of macrozoobenthic assemblages. When eutrophication variables were controlled, there was a significant correlation between community similarity and wind-wave disturbance condition, and vice versa. Variation partitioning showed that wind wave disturbance explained 15.9% of the variation in benthic community composition, slightly lower than that explained by eutrophication (17.9%). These results indicate that wind-wave disturbance is as important as eutrophication in regulating benthic community structure in this large shallow lake. Wind-wave disturbance imposed opposite effects on benthic community relative to eutrophication, and were more prominent in the offshore zone weakening the role of eutrophication.     

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-14 C ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14 C dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction(XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn't change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca((70.12±18.50)×10?5) and ? 18O((1.76±1.03)‰) of ancient lapilli are significantly higher than those of modern lapilli(average Mg/Ca=(3.11±0.41)× 10?5 and ? 18O=(?4.82±0.96)‰). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and ? 18 O ratios than modern Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today's Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ~5% larger than it is today.     

Molecular evidence for species separation in the water mite Hygrobates nigromaculatus Lebert, 1879 (Acari, Hydrachnidia): evolutionary consequences of the loss of larval parasitism

In the present study, we used mitochondrial cytochrome oxidase subunit I (COI) and nuclear D2 region of 28S rDNA sequence data to examine the taxonomic status of the water mite species Hygrobates nigromaculatus from two types of freshwater habitats: lentic (lakes) and lotic (streams). Previous hypotheses about (sub)species status of populations inhabiting lakes and streams based on differences in morphometric data and life-cycle strategy (parasitic vs. non-parasitic larvae) were strongly supported by molecular data. Levels of COI and D2 28S rDNA differentiation between lake and stream populations were much higher (ca. 18 and 7.5%, respectively) than those typically observed for populations of a single species. Both lake and stream populations showed similar high levels of gene diversity (Hd = 0.894 and 0.836, respectively). However, nucleotide within-population polymorphism was more than twice as high in lake populations as that in stream populations (π = 1.33 and 0.60%, respectively). We hypothesize that the ancestral lake-dwelling population originated from a stream form with parasitic larvae (here: H. setosus nov. stat.). For the observed populations, H. nigromaculatus individuals could be separated from H. setosus by distinct morphometric characters. The loss of phoretic parasitic larvae greatly decreased dispersal ability of lake-dwelling mites and consequently also the gene flow between lake populations. Thus, relatively more differentiated genetic structure in lake populations probably results from a stronger isolation between particular lake habitats, but this hypothesis needs further extensive studies.