Seasonal dynamics of the hepatotoxic microcystins in various organs of four freshwater bivalves from the large eutrophic Lake Taihu of subtropical China and the risk to human consumption

So far, little is known on the distribution of hepatotoxic microcystin (MC) in various organs of bivalves, and there is no study on MC accumulation in bivalves from Chinese waters. Distribution pattern and seasonal dynamics of MC-LR, -YR and -RR in various organs (hepatopancreas, intestine, visceral mass, gill, foot, and rest) of four edible freshwater mussels (Anodonta woodiana, Hyriopsis cumingii, Cristaria plicata, and Lamprotula leai) were studied monthly during Oct. 2003-Sep. 2004 in Lake Taihu with toxic cyanobacterial blooms in the summer. Qualitative and quantitative determinations of MCs in the organs were done by LC-MS and HPLC. The major toxins were present in the hepatopancreas (45.5-55.4%), followed by visceral mass with substantial amount of gonad (27.6-35.5%), whereas gill and foot were the least (1.8-5.1%). The maximum MC contents in the hepatopancreas, intestine, visceral mass, gill, foot, and rest were 38.48, 20.65, 1.70, 0.64, 0.58, and 0.61 mu g/g DW, respectively. There were rather good positive correlation in MC contents between intestines and hepatopancreas of the four bivalves (r = 0.75-0.97, p < 0.05). There appeared to be positive correlations between the maximum MC content in the hepatopancreas and the delta(13)C (r = 0.919) or delta(15)N (r = 0.878) of the foot, indicating that the different MC content in the hepatopancreas might be due to different food ingestion. A glutathione (GSH) conjugate of MC-LR was also detected in the foot sample of C. plicata. Among the foot samples analyzed, 54% were above the provisional WHO tolerable daily intake (TDI) level, and the mean daily intakes from the four bivalves were 8-23.5 times the TDI value when the bivalves are eaten as a whole, suggesting the high risk of consuming bivalves in Lake Taihu. (C) 2005 Wiley Periodicals, Inc.

Seasonal dynamics and distribution of the digenean Phyllodistomum pawlovskii (Trematoda : Gorgoderidae) in the bullhead catfish, Pseudobagrus fulvidraco, in a lake of China

Seasonal population dynamics of the digenean Phyllodistomum pawlovskii in the urinary bladder of the bullhead catfish, Pseudobagrus fulvidraco, were investigated in Liangzi Lake in the flood plain of the Yangtze River in China from February 2001 to July 2002. The overall prevalence of the parasite was high, 41.5% (n = 1,476), while the mean abundance was relatively low, 1.24 +/- 2.11. The parasite exhibited evident seasonality in changes of prevalence and abundance. In brief, prevalence and abundance were very low in midwinter (January), but increased and remained relatively high in other seasons and months. The distribution pattern of this parasite in the fish was overdispersed, with a variance to mean ratio > 1, but its frequency distribution could not be described by the negative binomial model. There were positive correlations between the number of the parasites per fish and the age and length of the fish; a peaked age-parasite abundance curve was not detected in the parasite-host association. It is suggested that the parasite P. pawlovskii has little effect on the population structure of the bullhead catfish.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis, from a large shallow, eutrophic lake of the subtropical China

So far no information is available on microcystin (MC) contents in shrimps, prawns or crayfish from natural freshwaters. Tissue distributions and seasonal dynamics of the hepatotoxic MC-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis were studied monthly (during June-November, 2003) in a Chinese lake containing toxic cyanobacterial blooms. The shrimps P. modestus and M. nipponensis accumulated high MCs not only in the hepatopancreas (mean 4.29 and 0.53 mu g g(-1) DW, respectively) but also in the gonad (mean 1.17 and 0.48 mu g g-1 DW, respectively), and the crayfish Procambarus clarkii accumulated as much as 0.93 mu g g(-1) DW in the gonad. This indicates that gonads of these invertebrates are the second important target organ of MCs. P. modestus apparently accumulated more MCs in their organs than M. nipponensis, which might be a reflection of their difference in trophic niche. Eggs of the shrimps accumulated 8.4% (M. nipponensis, 0.27 mu g g(-1) DW) and 29.0% (P. modestus, 2.34 mu g g(-1) DW) of total toxin burden, indicating that MCs had been transferred into offspring from their adults. Among the shrimp muscle samples analyzed, 31% were above the provisional WHO TDI level, suggesting the risk of consuming shrimps in Lake Chaohu. (c) 2005 Elsevier Ltd. All rights reserved.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) from a large shallow, eutrophic lake of the subtropical China

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) were studied monthly in a large shallow, eutrophic lake of the subtropical China during June-November, 2003. Microcystins (MCs) were quantitatively determined by High-Performance Liquid Chromatography (HPLC) with a qualitative analysis by a Finnigan LC-MS system. On the average of the study period, hepatopancreas was the highest in MC contents (mean 4.14 and range 1.06-7.42 mug g(-1) DW), followed by digestive tracts (mean 1.69 and range 0.8-4.54 mug g(-1) DW) and gonad (mean 0.715 and range 0-2.62 mug g(-1) DW), whereas foot was the least (mean 0.01 and range 0-0.06 mug g(-1) DW). There was a positive correlation in MC contents between digestive tracts and hepatopancreas. A constantly higher MC content in hepatopancreas than in digestive tracts indicates a substantial bioaccumulation of MCs in the hepatopancreas of the snail. The average ratio of MC-LR/MC-RR showed a steady increase from digestive tracts (0.44) to hepatopancreas (0.63) and to gonad (0.96), suggesting that MC-LR was more resistant to degradation in the snail. Since most MCs were present in the hepatopancreas, digestive tracts and gonad with only a very small amount in the edible foot, the risk to human health may not be significant if these toxic parts are removed prior to snail consumption. However, the possible transference of toxins along food chains should not be a negligible concern. (C) 2004 Elsevier Ltd. All rights reserved.

Community structure and seasonal dynamics of planktonic ciliates along salinity gradients

The ciliate community structure and seasonal dynamics in a solar saltern of the Yellow Sea were studied based oil 4 sampling dates and 8 stations with salinities from 27.7 parts per thousand to 311.0 parts per thousand. The effects of the type and concentration of the fixative used (Lugol's and Bouin's) were tested at the first sampling date. Fixative type and fixative concentration had significant effects on ciliate abundance and blovolume, with 1% Lugol's giving the best results. A detailed investigation using live observations and protargol staining techniques revealed a total of 98 morphospecies from 8 sampling stations. There was obvious seasonal variation in species composition at most of the stations, but this tended to be less distinct with increasing salinity, as the dominant ciliate group shifted from oligotrichs to heterotrichs. Ciliate abundance varied from 4.40 x 10(1) to 2.11 x 10(5) cells l(-1) and biomass ranged between 2.39 and 9.87 x 10(3) mu g Cl-1 (at a salinity of 147.6 parts per thousand). Both abundance and biomass decreased abruptly when salinity exceeded 100-150 parts per thousand. Statistical analyses Suggested that the dynamics of ciliate abundance and biomass were regulated by both salinity and by season, but those of diversity and species richness were mainly controlled by salinity and both significantly decreased with increasing salinity. (C) 2009 Elsevier GmbH. All rights reserved.

In situ studies on the distribution patterns and dynamics of microcystins in a biomanipulation fish - bighead carp (Aristichthys nobilis)

The distribution and dynamics of microcystins in various organs of the phytoplanktivorous bighead carp were studied monthly in Lake Taihu, which is dominated by toxic cyanobacteria. There was a good agreement between LC-MS and HPLC-UV determinations. Average recoveries of spiked fish samples were 63% for MC-RR and 71% for MC-LR. The highest MC contents in intestine, liver, kidney and spleen were 85.67, 2.83, 1.70 and 1.57 mu g g(-1) DW, respectively. MCs were much higher in mid-gut walls (1.22 mu g g(-1) DW) than in hind- and fore-gut walls (0.31 and 0.18 mu g g(-1) DW, respectively), suggesting the importance of mid-gut wall as major site for MC absorption. A cysteine conjugate of MC-LR was detected frequently in kidney. Among the muscle samples analyzed, 25% were above the provisional tolerable daily intake level by WHO. Bighead is strongly resistant to microcystins and can be used as biomanipulation fish to counteract cyanotoxin contamination in eutrophic waters. (c) 2006 Elsevier Ltd. All rights reserved.

Biological mechanisms driving the seasonal changes in the internal loading of phosphorus in shallow lakes

Because of the obvious importance of P as a nutrient that often accelerates growth of phytoplankton (including toxic cyanobacteria) and therefore worsens water quality, much interest has been devoted to P exchange across the sediment-water interface. Generally, the release mode of P from the sediment differed greatly between shallow and deep lakes, and much of the effort has been focused on iron and oxygen, and also on the relevant environmental factors, for example, turbulence and decomposition, but a large part of the P variation in shallow lakes remains unexplained. This paper reviews experimental and field studies on the mechanisms of P release from the sediment in the shallow temperate (in Europe) and subtropical (in the middle and lower reaches of the Yangtze River in China) lakes, and it is suggested that pH rather than DO might be more important in driving the seasonal dynamics of internal P loading in these shallow lakes, i.e., intense photosynthesis of phytoplankton increases pH of the lake water and thus may increase pH of the surface sediment, leading to enhanced release of P (especially iron-bound P) from the sediment. Based on the selective pump of P (but not N) from the sediment by algal blooms, it is concluded that photosynthesis which is closely related to eutrophication level is the driving force for the seasonal variation of internal P loading in shallow lakes. This is a new finding. Additionally, the selective pump of P from the sediment by algal blooms not only explains satisfactorily why both TP and PO4-P in the hypereutrophic Lake Donghu declined significantly since the mid-1980s when heavy cyanobacterial blooms were eliminated by the nontraditional biomanipulation (massive stocking of the filter-feeding silver and bighead carps), but also explains why TP in European lakes decreased remarkably in the spring clear-water phase with less phytoplankton during the seasonal succession of aquatic communities or when phytoplankton biomass was decreased by traditional biomanipulation. Compared with deep lakes, wax and wane of phytoplankton due to alternations in the ecosystem structure is also able to exert significant influences on the P exchange at the sediment-water interface in shallow lakes. In other words, biological activities are also able to drive P release from sediments, and such a static P release process is especially more prominent in eutrophic shallow lakes with dense phytoplankton.

Seasonal changes in weight and body composition of yak grazing on alpine-meadow grassland in the Qinghai-Tibetan plateau of China

Forty-five male yaks (born April 2001) were studied to determine how seasonal changes on the Qinghai-Tibetan plateau affected BW and body composition. Thirty yaks were weighed monthly from birth to 26 mo of age to determine seasonal changes in BW. The remaining 15 yaks were allocated randomly to five groups (three yaks per group), designated for slaughter at 13, 15, 18, 22, and 25 mo to measure seasonal effects on body chemical composition. All yaks were grazed on the alpine-meadow grassland of the plateau without any supplementation. All BW and body composition data were calculated on an individual basis. Body weight and body composition data were both compared across seven growth periods spanning 2 yr and defined by season. From April (birth) to December 2001 of the first growing season, yak BW increased (P < 0.01); however, during the subsequent cold season (December 2001 to May 2002), BW decreased (P < 0.01). The second growing season ran from May 2002 (13 mo of age) to October 2002 (18 mo of age), and the second live weight-loss season ran from October 2002 until May 2003. The weight loss experienced by yaks during the first weight loss season was 25.64% of the total weight gain in the first growing season. The weight loss experienced by yaks during the second weight-loss season was 29.73% of the total weight gain in the second growing season. Energy retention in the second growing season was 291.07 MJ, 50.8% of which was consumed during the subsequent cold season. Energy accumulation in the summer (from May to July) and fall (from July to October) of the second growing season did not differ (5.01 and 6.30 MJ/kg of EBW gain, respectively; P = 0.63). The energy mobilized during the second winter (from October 2002 to February 2003) was 16.49 MJ/kg of EBW, and in the second spring (from February to May 2003), it was 9.06 MJ/kg of EBW. These data suggest that the decrease in grazing yak BW during the first cold season is much less than during the second cold season, and that the energy content per unit of BW mobilized is greater (P = 0.02) in winter than in spring. Results from this study demonstrate highly efficient compensatory growth in grazing yaks following the first weight loss period during the first cold season. This benefit could be exploited by herders to improve yak production. Yaks may have developed a type of self-protection mechanism to overcome the long cold seasons in the Qinghai-Tibetan plateau.

家畜放牧对典型草原土壤-植被系统氮素转化的影响

草地生态系统中，放牧对调节物质流动和营养循环起着关键的作用。内蒙古地区已有上千年的游牧历史，放牧是该地区重要的草地利用方式之一。然而，近50年来，由于人口的剧增以及对草原的不合理利用与管理，使得内蒙古草原发生了严重的退化与沙漠化。理解放牧对氮循环的定量影响，对我们更合理地利用草地、防治生态系统的进一步退化以及探求最佳恢复途径都具有重要的意义。中国科学院内蒙古草原生态系统定位站精准设置的5种放牧强度处理（0.00, 1.33, 2.67, 4.00, 5.33 羊/公顷）为我们的研究提供了理想的平台。2005、2006年生长季期间，在经过16年不同放牧强度处理的一个典型草原样地上，我们测定了氮素输入（氮沉降、生物固氮）、转化（净氮矿化）、输出（反硝化及氨气挥发）速率等N循环的重要参量。同时，测定了微生物生物量碳、氮（Cmic，Nmic）及微生物呼吸（Rmic），研究了微生物在氮循环中的作用。另外，还测定了植物、土壤、固氮体中的15N自然丰度值，探讨了其对不同放牧强度的响应格局与机理。 结果表明，干湿混合沉降物全氮浓度最高达11.53 mg N l–1，沉降量最高为1.77 kg N ha–1m–1。月均氮沉降量与浓度正相关，它们与降水量均关系密切，前者更密切。结皮面积所占比例很小，不超过8%。结皮含氮量为1.01-1.43 g N kg–1，受放牧的影响不显著，但随放牧强度的增加有降低的趋势。土壤结皮能固氮，但固氮量不超过土壤氮含量的1倍。地耳的固氮量为结皮的10-20倍，故是主要的固氮体。尽管地耳含氮量受放牧影响不显著，但放牧是不放牧条件下地耳氮含量的1.58倍。 土壤NH4+-N浓度随季节变化范围为1.71-9.45 µg N g–1，它们在各放牧处理之间的差异不显著。土壤NO3–-N浓度变幅为0.27-11.21 µg N g–1。总无机氮浓度在不放牧条件下的变幅为2.69-14.57 µg N g–1，占总氮的0.49-2.6%;放牧条件下的变幅为2.49-8.66 µg N g–1，占总氮的0.35-1.21%。总无机氮浓度随季节和放牧强度的变化趋势与硝态氮相似，表现为2005年夏季期间有逐渐增加的趋势，而在2006年整个生长季期间有逐渐降低的趋势。不放牧比放牧条件下含氮量高，但在4个放牧处理之间的差异不显著。净氮矿化速率的变幅为–0.61-0.27 µg N g–1d–1，峰值通常出现在7月。净氮矿化速率在各处理间没有一致性差异，但中牧（2.67、4.00 羊/公顷）通常比重牧（5.33 羊/公顷）下的值高。净氮硝化速率通常很低，波动在–0.32-0.16 µg N g–1之间，2005年夏季及2006年春秋季的值相对较高。净氮硝化速率在各放牧处理之间差异不显著，但重牧条件下的值通常最低。累积净氮转化量在年际间差异大，2005年总体上遵循正态分布模式，而2006年随着放牧强度的增加有直线下降的趋势，2006年比2005年的累积量高。土壤温度和湿度比放牧强度对净氮矿化的影响更加显著。放牧强度通过调节这两个土壤因子对氮动态而产生间接影响。 反硝化和N2O的释放速率低，前者变幅为0.33-6.21µg N kg–1 d–1，后者为0.42-11.28 µg N kg–1 d–1。释放量夏季较强，春秋较弱。放牧对反硝化释放影响不显著，只在2005年对N2O释放影响显著。尽管如此，反硝化和N2O释放速率整体表现出在不放牧比放牧条件下高的趋势，且比最高放牧强度5.33 羊/公顷下的反硝化速率显著高。然而，它们在4个放牧处理之间的差异始终不显著。累积反硝化和N2O释放存在年际变化，2006年的值显著高。它们随着放牧强度的递增有逐渐降低的趋势，这在2006年表现得尤为明显，这种结果主要归因于土壤总氮量在长期放牧条件下随放牧压力的增加而逐渐降低。 氨气挥发速率变幅为0.88-3.52 g N ha–1d–1，高峰值出现在5月，2005比2006年同期的速率大。两年间放牧强度对氨气挥发的影响都较弱，2005年影响更弱。不放牧条件下的氨气挥发量通常最低，这在生长季的前期表现得更为明显，中牧及重牧条件下通常最高。放牧能影响氨气挥发与氨态氮，硝态氮及总无机氮浓度之间的关系，即不放牧条件下相关性显著，而放牧条件下相关性不显著。年际间氨气挥发速率与无机氮浓度之间的关系趋势相反，2005年负相关，2006年正相关。在水分充足的2006年，所有处理条件下氨气挥发与土壤水分及温度之间显著相关，但在单独每个放牧处理下，相关性不显著。 Cmic变幅大，为13.97-350.45 μg C g–1，占土壤总有机碳的1.58-8.35%。最高和最低值分别出现在夏季和春季。它们在各处理间差异不显著，不放牧下的值相对偏高。Cmic与土壤有机C和全N、前期的立枯、凋落量及含N量、优势种前期的地上生物量、根系生物量、土壤温度以及水分之间关系密切。氮素状态如氨态氮、总无机氮含量、反硝化以及N2O释放速率，氨气挥发速率与Cmic之间关系密切。Nmic占土壤全氮的0.41-2.74%，不受季节和放牧强度的显著影响。Nmic与可溶性N，表土层根系全N，立枯有机C，地上生物量之间关系密切。氮循环过程中氨气挥发速率受Nmic的影响。Rmic随季节而变化，通常5月份值最高。Rmic随着放牧强度的增加有稍降低的趋势。Rmic与土壤可溶性C、有机C，不同土层根系有机C，凋落物、立枯量及其C、N含量、全N，地上生物量，优势种前期的生物量，土壤温度之间关系密切。土壤氮循环动态如氨态氮、硝态氮、总无机氮浓度及反硝化速率与Rmic之间关系密切。 土壤、植物、地耳、生物结皮的δ15N值与放牧强度之间相关关系不显著。然而，放牧有增加表层土和植物的δ15N值而降低表土、地耳、结皮的δ15N值的趋势。表层土δ15N值与前一年生长季末期硝态氮及总无机氮浓度，反硝化速率及累积氨气挥发之间密切相关。 土壤碳含量的变幅为10.44-17.19 g C kg–1，全氮量的变幅为0.54-0.82 g N kg–1。长期的高强度放牧降低了土壤碳、氮储量。根系碳、氮含量分别为土壤碳、氮含量的40-50和10倍。立枯和凋落物有机碳含量变幅为446.94-507.01 g C kg–1，与放牧强度之间关系不密切;氮含量变幅为4.58-7.18 g N kg–1，与放牧强度之间显著负相关。优势种木地肤、冷蒿的含碳量与放牧强度之间相关不显著，但含氮量与之显著相关。 综述以上结果，不同放牧强度对内蒙草地生态系统氮循环中不同过程产生影响的程度各不相同，这种影响主要是通过它与土壤环境因子如温度、水分的联合作用而间接产生。

Bioaccumulation of the hepatotoxic microcystins in various organs of a freshwater snail from a subtropical Chinese lake, Taihu lake, with dense toxic microcystis blooms

In this paper, we describe the seasonal dynamics of three common microcystins (MCs MC-RR, MC-YR, and MC-LR) in the whole body, hepatopancreas, intestine, gonad, foot, remaining tissue, and offspring of a freshwater snail, Bellamya aeruginosa, from Gonghu Bay of Lake Taihu, China, where dense toxic Microcystis blooms occur in the warm seasons. Microcystins were determined by liquid chromatography electrospray ionization mass spectrum. Microcystin (MC-RR + MC-YR + MC-LR) content of the offspring and gonad showed high positive correlation, indicating that microcystins could transfer from adult females to their young with physiological connection. This study is the first to report the presence of microcystins in the offspring of the adult snail. The majority of the toxins were present in the intestine (53.6%) and hepatopancreas (29.9%), whereas other tissues contained only 16.5%. If intestines are excluded, up to 64.3% of the toxin burden was allocated in the hepatopancreas. The microcystin content in the intestine, hepatopancreas, and gonad were correlated with the biomass of Microcystis and intracellular and extracellular toxins. Of the analyzed foot samples, 18.2% were above the tolerable daily microcystin intake recommended by the World Health Organization (WHO) for human consumption. This result indicates that public health warnings regarding human ingestion of snails from Taihu Lake are warranted. In addition, further studies are needed to evaluate the occurrence by Microcystis in relation to spatial and temporal changes in water quality.