Differences in stable isotope compositions of freshwater snails from surface sediments of two Polish shallow lakes

The study reports and discusses the differences in δ¹³C and δ¹⁸O values of shells between several species of freshwater snails. Shells were derived from sediment samples collected from depths of 0.5, 1, 2 and 3 m along transects in two shallow eutrophic lakes located in mid-western Poland. Mean δ¹³C values of the shells ranged between −7.5 and −3.8‰ in Lake Jarosławieckie and between −8.1 and −5.2‰ in Lake Rosnowskie Duże, whereas mean δ¹⁸O values ranged between −2.2 and −0.2‰ and between −2.2 and 0.4‰ respectively in the studied lakes. A similar order of species in terms of shell isotope values, from least to most ¹³C and ¹⁸O-depleted was observed in both lakes and seems to indicate constancy of the factors controlling the stable isotope compositions of snail shells. We postulate that the nearly 4‰ difference in the mean carbon stable isotope values between the species was primarily controlled by the amount of metabolic carbon incorporated into the shells and the δ¹³C values of the snail food. Different growth cessation temperatures and microhabitats of the species studied result in temporally and spatially varied DIC δ¹³C values, water δ¹⁸O values and water temperature of shell precipitation, and may thus differentiate the δ¹³C and δ¹⁸O values of shells. The range of δ¹³C and δ¹⁸O values of individual shells from a sediment sample (mean 2.35 and 2.15‰, respectively) is interpreted as reflecting an intraspecific variability of isotope compositions in shells from a population and changes of the ambient conditions during the accumulation of the sediment layer. The species-specificity and intraspecific variability in C and O isotopic compositions of shells allow concluding that in palaeolimnological studies, stable isotope analyses should be performed on a set of mono-specific shells representing mean isotope compositions of the species for the interval studied rather than single shells or multispecific bulk shell material.     

Stable isotope fractionation of fatty acids of Daphnia fed laboratory cultures of microalgae

We tested a comparatively new method of tracing of natural food webs, compound-specific isotope analysis (CSIA) of fatty acids (FA), using laboratory culture of Daphnia galeata fed Chlorella vulgaris and Cryptomonas sp. In general, Daphnia had significantly lighter carbon stable isotope composition of most fatty acids, including essential, than those of their food, microalgae. Thus, our results did not support the pivotal premise of the FA-CSIA application for food web analysis, i.e., transmitting the isotope ‘signal’ of essential FAs to consumers from their food without any modification. Moreover, the values of isotope fractionation of particular FAs in the consumer relative to its food were not constant, but varied from 1.35‰ to 7.04‰. The different isotope fractionation (depletion) values of diverse FAs in consumer were probably caused by different processes of their synthesis, catabolism and assimilation. More work is evidently to be done for correct interpretation of results of FA-CSIA during field studies for tracing of natural food webs.     

Radiocarbon age anomalies of land snail shells in the Chinese Loess Plateau

In the Chinese Loess Plateau, land snail shells are often the only material available for dating in paleoenvironmental and archaeological research. However, the geochronological suitability of land snail shells is limited because of poor knowledge about their deposition dynamics, particularly with regards to the incorporation of inorganic carbonate and the resulting age anomalies. To evaluate the factors controlling these age anomalies, radiocarbon and stable carbon analyses were carried out on surface soils, as well as the shells and organic bodies of different modern snail species from different ecological habitats. The results showed that all specimens were depleted in ¹⁴C, indicating the influence of inorganic, radiocarbon-free carbonate on the ¹⁴C-activity of the snail shells. The apparent ¹⁴C-deficiencies and the resultant age anomalies of both the Cathaica and the Bradybaena snail shells were within close ranges across the Chinese Loess Plateau, indicating that the shells of these species could, after corrections for radiocarbon anomalies, provide reliable age estimates. The apparent ¹⁴C-deficiencies were closely associated with the ecological habitats of the snails. The shells of the ground-dwelling Bradybaena had the smallest age offsets (533 ± 150 a), followed grass-dwelling Cathaica (1107 ± 138 a) and Cathaica living on trees (1550 ± 345 a). These results suggest that the availability of calcium in the respective ecological habitats is an important factor in explaining the apparent ¹⁴C-deficiencies. The influence of carbonate on the stable carbon isotope composition of shells is overwhelmed by the organic diets of snails, making δ¹³C unsuitable for identifying and correcting shell age anomalies. The radiocarbon activities of surface soils (A_calc) increase with weathering intensity. Thus, a significant uncertainty could be caused by assuming that A_calc is zero when estimating the proportions of different carbon sources in shells, as has been the case in most previous studies.     

Comparison of life-history parameters and effectiveness in competition with Moina macrocopa between two Keratella tropica morphs

Competition and predation are the two major biotic interactions in zooplankton community. Various rotifer species exhibit polymorphism in lorica and spine morphology in the presence of predators and competitors, which effectively increases their defence competition capacity. This study compared life-history parameters between long-spined morph (LSM) and short-spined morph (SSM) of Keratella tropica at three temperatures. The results showed that both morphs showed significantly higher intrinsic rate of population increase at 25 °C than those at 20 °C and 30 °C. The intrinsic rate of population increase was significantly lower in LSM than SSM at 25 °C and 30 °C, and the net reproductive rate was significantly lower in LSM than SSM at 30 °C. These results suggested that K. tropica had cost on development of long spines, which, however, was dependent on temperature. Moreover, the competition outcome of LSM and SSM with Moina macrocopa were investigated at three densities of Scenedesmus obliquus (0.5 × 10⁶, 1.0 × 10⁶ and 2.0 × 10⁶ cells/mL) and three initial densities of M. macrocopa (0.1, 0.3 and 0.9 ind./mL), revealing that both LSM and SSM populations decreased significantly at all tested algal densities and Moina levels. LSM showed higher population growth rate than SSM at lower algal density (0.5 × 10⁶ cells/mL) and higher Moina densities (0.3 and 0.9 ind./mL), which suggested that LSM could be more effective to defend M. macrocopa. Three-way analysis of variance showed no significant effects of algal density on population growth rate of K. tropica, but interaction between algal density and M. macrocopa density significantly affected its population growth rate.     

Species diversity of resident green algae slows the establishment and proliferation of the cyanobacterium Microcystis aeruginosa

As harmful algal blooms (HABs) have expanded in size and become more frequent, there have been increased efforts to predict when and why blooms occur, as well as to identify the ecological factors that limit their formation. Here we report the results of a laboratory experiment in which we examined how the establishment and proliferation of Microcystis aeruginosa, a common HAB species, was influenced by competition with resident green algae. We hypothesized that competition with green algae would reduce the final biomass of M. aeruginosa, and that the effects of competition would be most pronounced in communities of high species richness and when nutrients are scarce. We found that competition with green algae did, in fact, consistently reduce the final biomass of M. aeruginosa. The effects of competition were more pronounced in species-rich than in species-poor communities, but this was only true when nutrients were abundant. When nutrients were scarce, resident diversity did not matter because competition with any resident species was sufficient to limit the growth of M. aeruginosa. Our results confirm that biotic interactions with phytoplankton are important in limiting the establishment and proliferation of HAB species like M. aeruginosa. But our work goes on to suggest that, under some nutrient conditions, diverse communities of resident phytoplankton can be more resistant to proliferation of cyanobacteria that can cause HABs.     

三峡水库澎溪河典型优势藻原位生长速率的初步研究

本文提出了两种原位培养装置(培养笼、培养桶)并采用这两种装置在澎溪河高阳平湖断面进行原位培养实验,旨在研究澎溪河典型优势藻的原位生长速率.研究期间主要生境特征为营养物丰足、光热条件优越、生境条件相对稳定,适宜于藻类生长,为水华形成的敏感期;在此期间代表CR型生长策略的湖北小环藻和兼具C、R、S生长策略的卵形隐藻的原位生长速率总体呈逐渐下降趋势,代表CS型生长策略的水华鱼腥藻和空球藻的原位生长速率则先增加后又有所下降,代表S型生长策略的铜绿微囊藻的原位生长速率虽然前期都为负,但总体呈现逐渐增加的趋势;并测得培养笼和培养桶中各藻种的最大比生长速率分别为湖北小环藻0.31、0.21 d-1;铜绿微囊藻0.09、0.03 d-1;空球藻0.16、0.42 d-1;水华鱼腥藻0.30、0.26 d-1;卵形隐藻0.49、0.95 d-1.本研究中,不同生长策略藻种生长速率的变化在一定程度上体现了不同生长策略藻种的生长趋势.另外,就装置性能实验及原位培养实验结果综合分析,认为两种原位培养装置均能够满足对天然水域藻类原位生长速率的测试要求,但装置的构造对藻类实际生长过程仍存在一定影响.     

Population Growth of Zooplankton (Rotifers and Cladocerans) Fed Chlorella vulgaris and Scenedesmus acutus in Different Proportions

In the present work we tested the effect of Chlorella vulgaris and Scenedesmus acutus in different proportions on the population growth of Brachionus calyciflorus, Brachionus patulus, Ceriodaphnia dubia, and Moina macrocopa. In general, both rotifer species grew well on either type of algae. Regardless of algal mixture, B. calyciflorus had a shorter initial phase, while B. patulus needed more than a week to begin the exponential phase of growth. Both the rotifer species showed consistently better population growth with Chlorella than on Scenedesmus, or the mixture. At any given algal combination, B. patulus had higher peak values than B. calyciflorus. The rate of population increase (r) for both the rotifers varied from 0.18 to 0.48 d^—1 depending on the algal type and combination. Regardless of algal type and combination, B. calyciflorus had a much higher value of r than B. patulus. Both C. dubia and M. macrocopa grew on the algal types, whether offered separately or in mixture. Regardless of the treatment type, C. dubia needed a longer period (about 2 weeks) than M. macrocopa to reach peak abundances. Thus, our study did not support the view that Scenedesmus is consistently superior to Chlorella as a basic diet to the tested species of zooplankton.     

太湖高等水生植物稳定碳、氮同位素特征

高等水生植物的稳定碳、氮同位素能够反映其生理生态学信息.从太湖贡湖湾和梅梁湾采集高等水生植物,分析两湖湾高等水生植物的稳定碳、氮同位素值时空变化和种类差异.结果显示:水生植物的稳定碳、氮同位素值因时间、空间和种类而发生变化,总体上时间变化规律不明显,空间变化有一定规律性:梅梁湾中穗花狐尾藻、马来眼子菜、苦草、凤眼莲的δ~(15)N明显高于贡湖湾,挺水植物芦苇的δ~(15)N差异不显著,反映了梅梁湾较贡湖湾有较高的营养水平;贡湖湾中穗花狐尾藻、苦草的δ~(13)C显著高于梅梁湾,其它种类没有显著差异.从种类特征来看,贡湖湾和梅梁湾浮叶植物与挺水植物芦苇、凤眼莲、菱的δ~(13)C偏低,而微齿眼子菜、金鱼藻、马来眼子菜、苦草、伊乐藻、穗花狐尾藻等沉水植物的δ~(13)C值较高,这与它们所处的环境和碳源有关.     

城市湖泊春季绿藻水华特征及其影响因素——以宁波月湖为例

城市湖泊富营养化问题日趋严峻,以往对水华的研究多集中于大型自然淡水湖库,而对小型城市浅水湖泊的水华动态相对较少.以宁波月湖为研究对象,探讨水华暴发期间浮游植物变化特征及与影响因子之间的关系,以期判别影响城市湖泊水华的主控因子.月湖水华期间营养盐水平处于中富营养至极端富营养之间,此次共检出浮游植物8门61属,藻种组成以绿藻门（51.79%）和硅藻门（21.43%）为主,各点位浮游植物生长主要受水温、光照驱动,经历了隐藻门→硅藻门→绿藻门→蓝藻门的演替.水华种为雷氏衣藻（Chlamydomonas reinhardtii）,总藻密度最高达到1.55×10⁸ cells/L,水华暴发后各点位衣藻属比例升高（最高达到81.10%）,群落结构呈现单一化特征.通过Pearson相关性分析和RDA分析发现衣藻属生长与水温、pH、总磷浓度均呈显著正相关,春季气温回升、天气持续晴好,城市浅水湖泊高营养盐负荷、水体流动性差等特点为带鞭毛的衣藻属提供了适宜的生存条件,在环境条件均适宜的情况下拥有最大生长潜力的衣藻属在营养盐、光照等竞争中生长速率明显优于其他藻种,从而发生绿藻水华.     

基于遥感反射率的太湖优势藻识别方法

我国淡水湖库频发水华,不同类群形成的水华特征、危害及其治理方法差异显著,因此,如何区分不同藻种的遥感反射率特征,获取湖泊优势种信息是一个亟待解决的科学问题。研究基于室内藻种培养实验,培养了富营养化湖泊中的典型蓝藻和绿藻藻种,其中,蓝藻包括铜绿微囊藻（Microcystis aeruginosa）、假鱼腥藻（Pseudanabaenasp．）和束丝藻（Aphanizomenonsp．）,绿藻包括小球藻（Chlorellasp．）以及四尾栅藻（Scenedesmus quadricauda）;基于实测的遥感反射率,经归一化处理后,分析了不同藻种的遥感反射率特征,构建了DI(difference index)指数以及ADI(algae distinguish index)指数,建立了藻种分类模型,利用验证集数据进行检验,整体识别精度达77.55%,Kappa系数为0.7178。将分类方法应用于太湖野外实测遥感反射率数据集中,结果与实测的生物量数据有较好的匹配;将模型应用于太湖OLCI(ocean and land colour instrument)影像数据,获得了2019年12月和2020...     

Stable isotopes as a useful tool for revealing the environmental fate and trophic effect of open-sea-cage fish farm wastes on marine benthic organisms with different feeding guilds

Environmental fate of fish farm wastes (FFW) released from an open-sea-cage farm at Kat O, Hong Kong was examined by measuring carbon and nitrogen stable isotope (SI) ratios in selected benthic organisms collected along a 2000 m transect from the farm. Our results showed that FFW significantly influenced the energy utilization profile of consumers near the fish farm. Although nitrogen enrichment effect on δ¹⁵N was anticipated in biota near the farm, the predicted patterns did not consistently occur in all feeding guilds. Two species of suspension-feeders, which relied on naturally δ¹⁵N-depleted sources, were δ¹⁵N-enriched near the fish farm. In contrast, both species of benthic grazer and deposit-feeder, which relied on naturally δ¹⁵N-enriched algal sources, were δ¹⁵N-depleted under the influence of FFW. The SI signatures of biota can, therefore, serve as feasible biomarkers for FFW discharges only when the trophic structure of the receiving environment is fully elucidated.     

辽河太子河流域藻类植物群落结构及其季节变化

2010年9月到2011年9月分4次对太子河流域的藻类植物群落组成、丰度及优势种进行调查分析.共设置17个采样点,经鉴定共有藻类植物8门120属328种(包括21种变种).藻类植物群落以硅藻最多,有36属144种,占总体的43.77%;其次是绿藻,有49属117种,占总体的35.56%;蓝藻居第3位,有22属38种,占总体的11.85%.调查期间,太子河流域藻类植物细胞丰度在夏、秋季较高,丰度平均值分别为6.80×10⁷和3.29×10⁷cells/L;在春季较低,丰度平均值为1.36×10⁷cells/L.优势度分析显示,太子河流域各季节的藻类植物优势种都在5种以上,主要优势种有巨颤藻(Oscillatoria princeps Vauch.)、链丝藻(Hormidium flaccidum(Kütz.)Br.)、偏生毛枝藻(Stigeoclonium subsecundum(Kütz.)Haz.)等.藻类植物的Jaccard种类相似性指数在0.19~0.46之间.太子河流域藻类植物种类组成及细胞丰度均有明显的季节变化.     

ENVIRONMENTAL RESPONSE OF THE PERMIAN VOLCANISM IN LUCAOGOU FORMATION IN JIMSAR SAG,JUNGGAR BASIN,NORTHWEST CHINA

The lithological features, the types of organic matter and its occurrence and carbon and oxygen isotopic value were clarified by combining core observation, thin slice authentication, X ray diffraction analysis, kerogen type identification and carbon and oxygen isotope analysis. The characteristic of strata, the distribution of volcanoes of Junggar Basin were also taken into consideration. A comprehensive analysis was conducted to evaluate environmental response of volcanism in Lucaogou formation in Jimsar sag. The results show that rocks is a mixed sedimentation of effusive rock and carbonate rocks, volcanic materials is widely developed in Lucaogou formation and origins from the edge of sag or distant source volcano activity. Organic matter is predominantly unstructural algae and asphaltene. The carbon isotopic value of carbonates ranges between 6.8‰ and 9.7‰ with an average of 8.3‰, featured in high positive excursions, while oxygen isotopic value varies from -11.9‰ to -4.3‰ with an average of -6.2‰. During the period of volcanic activity, the volcanic material released high amounts of nutrient to the lake basin, which is beneficial to the algae and other organic organisms. In the poor oxygen and calm water environments, the organic matter is distributed in the laminar algal and the carbon isotope value is high positive drift. During the intermittent period of volcanic activity, the lake level decreased and the lake bottom water changed to the oxygen-enriched environments. The organic matter is locally enriched or dispersed in local layers, and the carbon isotope values decreased slightly. The frequent volcanic activity promoted the organism boom, which lead carbon isotope value to have high positive characteristics and change trends.     

Study of the trophic web of San Simón Bay (Ría de Vigo) by using stable isotopes

Based on the stable isotope composition in ¹⁵N and ¹³C of different potential sources of organic matter and consumers of an intertidal Zostera marina meadow located in San Simón Bay (Ría de Vigo, NW of Spain), a simplified food web of this community was reconstructed. For this purpose, some alternatives in different steps of the most used methodology of stable isotope dietary analysis were developed that cope with some of the limitations associated to the interpretation of isotopic signals for food web analysis, those of uncertainty on the fractionation value, mathematical model to use for the diet resolution and shortage of the isotope number for discriminating many food sources. The application of this protocol to the studied community reported similar results to those from other studies based on similar trophic webs, emphasizing the importance of local primary producers, especially microphytobenthos, which could be available for several primary consumers through resuspension forced by tidal hydrodynamic. The good agreement with previous results suggests that the proposed protocol is a feasible alternative to elucidate the most plausible trophic relationships in complex trophic webs using stable isotopes analysis.     

Land-air boundary environment as recorded by the18O/16O and13C/12C isotope ratios in the shells of land snails

A yearly cycle of carbon and oxygen isotope composition of shells of the Israeli land snailXeropicta vestalis is presented. The¹⁸O/¹⁶O values indicate that the snails use water from the land-air boundary zone. The¹⁸O/¹⁶O ratio of the shells is in isotopic equilibrium with the water condensate from the vapour during the winter months. During the summer months a contribution to the above water from soil water migrating upwards due to evaporation is noticeable. The δ¹³C values indicate that as in marine molluscs, the carbon isotopic composition in land snails is controlled mainly by the aqueous carbonate compound which is in equilibrium with the land-air boundary CO₂.     

Radiocarbon dating of small terrestrial gastropod shells in North America

Fossil shells of small terrestrial gastropods are commonly preserved in wetland, alluvial, loess, and glacial deposits, as well as in sediments at many archeological sites. These shells are composed largely of aragonite (CaCO₃) and potentially could be used for radiocarbon dating, but they must meet two criteria before their ¹⁴C ages can be considered to be reliable: (1) when gastropods are alive, the ¹⁴C activity of their shells must be in equilibrium with the ¹⁴C activity of the atmosphere, and (2) after burial, their shells must behave as closed systems with respect to carbon. To evaluate the first criterion, we conducted a comprehensive examination of the ¹⁴C content of the most common small terrestrial gastropods in North America, including 247 AMS measurements of modern shell material (3749 individual shells) from 46 different species. The modern gastropods that we analyzed were all collected from habitats on carbonate terrain and, therefore, the data presented here represent worst-case scenarios. In sum, ～78% of the shell aliquots that we analyzed did not contain dead carbon from limestone or other carbonate rocks even though it was readily available at all sites, 12% of the aliquots contained between 5 and 10% dead carbon, and a few (3% of the total) contained more than 10%. These results are significantly lower than the 20–30% dead carbon that has been reported previously for larger taxa living in carbonate terrain. For the second criterion, we report a case study from the American Midwest in which we analyzed fossil shells of small terrestrial gastropods (7 taxa; 18 AMS measurements; 173 individual shells) recovered from late-Pleistocene sediments. The fossil shells yielded ¹⁴C ages that were statistically indistinguishable from ¹⁴C ages of well-preserved plant macrofossils from the same stratum. Although just one site, these results suggest that small terrestrial gastropod shells may behave as closed systems with respect to carbon over geologic timescales. More work on this subject is needed, but if our case study site is representative of other sites, then fossil shells of some small terrestrial gastropods, including at least five common genera, Catinella, Columella, Discus, Gastrocopta, and Succinea, should yield reliable ¹⁴C ages, regardless of the local geologic substrate.     

18O and 13C in the shells of freshwater molluscs and their environments

Carbon and oxygen isotope analyses on shells of freshwater molluscs and their habitat are presented. The data obtained reconfirm the usefulness of such ¹⁸O analyses for paleoenvironmental and paleohydrological studies.The ¹³C analyses on freshwater molluscs from lakes in southwestern Ontario, specimens grown under laboratory conditions and a comparison with the ¹³C contents of the dissolved inorganic carbon in their habitat show that the ¹³C contents in mollusc shells are primarily controlled by the aqueous carbonate species. Vital effects and food control appear to have only minor importance. The significance of this observation on the usufulness of mollusc shells for ¹⁴C dating is discussed.     

Nonlinear relationship between preservation of microstructure and geochemical composition of Pleistocene brachiopod shells from the Ryukyu Islands,southwestern Japan

Stable carbon and oxygen isotope composition of fossilized brachiopod shells serves as an important source to delineate Earth's paleoenvironmental evolution in the Phanerozoic. However, the original isotopic composition is potentially modified by various kinds of diagenesis. To evaluate the extent to which the original isotopic composition of fossilized brachiopod shells is modified by meteoric diagenesis, microstructure, cathodoluminescence (CL) images, and carbon and oxygen isotope composition of fossilized Kikaithyris hanzawai (rhynchonellate brachiopod) shells were examined. The shells were collected from Pleistocene shallow marine carbonates exposed on the Ryukyu Islands, southwestern Japan. The extent of diagenetic alteration is quantitatively evaluated here as both the preservation state of the original shell microstructure and the luminescence/non‐luminescence of shells. Although altered fibers were commonly observed in the brachiopod shells, the original isotopic composition was almost retained. There are no significant differences in the isotopic composition between the luminescent and non‐luminescent shells. There is no direct relationship between the preservation state of the original shell microstructure and the luminescence/non‐luminescence of shells at three of four horizons, indicating that CL images are not necessarily useful for the detection of diagenetic alteration of shells or shell portions. Applying multiple criteria to assessing diagenetic alteration and cross‐checking them are required to distinguish between diagenetically altered and unaltered brachiopod shells.     

Spatial distribution of phytoplankton cells in small elongated lakes subject to weak diurnal wind forcing

The horizontal distribution of phytoplankton in a medium-size canyon type reservoir, forced by weak winds of 3–4 ms^?1, is largely driven by the interaction of the large-scale circulation and processes regulating the vertical distribution of algal cells in the water column. These drivers, in turn, are subject to diurnal variations, making our understanding of the horizontal distribution of phytoplankton a challenging task. A three-dimensional physical-–ecological model is used to understand the spatial distribution of algae and the role of diurnal variations in the physical–biological drivers. The model was used to demonstrate that the large-scale circulation induced during the day is more efficient generating patchiness than the circulation existing at night, when convectively driven turbulence homogenizes the upper layers. Different spatial distributions develop for different populations and under different forcing scenarios, characterized in terms of the directionality of wind forcing, wind magnitude and the lags between winds and diel heat fluxes. The time scales needed so that algal biomass in the surface exhibit significant longitudinal gradients—T _P —will vary depending on the algal group, and its ability to regulate its vertical position. These scales are shorter for those species that either migrate actively in the water column or exhibit positive buoyancy (Cryptophytes or Positive buoyant algae). In El Gergal, these scales T _P are on the order of a few days. Synoptic changes in the meteorological forcing, like the passing of a front, could potentially change the longitudinal distribution of algal biomass if they persist for periods of time longer than T _P .