Hatchability of zooplankton egg in water after irradiation with pulsed intense relativistic electron beam

Hatchability of zooplankton (Artemia Salina ) eggs in water irradiated with pulsed intense relativistic electron beam (PIREB) was studied. The PIREB with a kinetic energy of up to 6 MeV, a peak current of −500 A and pulse duration of 80 ns (FWHM) is generated by using the intense pulsed power generator “ETIGO‐III.” The hatchability after PIREB irradiations reduced up to almost 0% in the higher‐dose region. Also, the hatchability on the outside of the penetration depth of PIREB reduced in comparison to one without PIREB irradiation.     

Underestimation of microzooplankton is a macro problem: One size fits all zooplankton sampling needs alterations

Microzooplankton (rotifers, copepod nauplii, and dreissenid veligers) are an important but overlooked part of zooplankton communities and aquatic food webs, particularly in the Great Lakes. Most studies that do include microzooplankton data are not describing the full picture due to inappropriate sampling methodology. We compared the traditional macrozooplankton sampling method (64-μm mesh plankton net) to a microzooplankton method using a 20-μm mesh screen in various habitats in Lake Michigan. The macrozooplankton method significantly underestimated total rotifer density by an order of magnitude, veliger density by nearly an order of magnitude, and copepod nauplii density by threefold. Combining macrozooplankton method estimates for cladocerans and copepods with estimates of rotifer, nauplii, and veligers from the microzooplankton method samples showed rotifers contributed 51% of total mean zooplankton biomass, refuting the past notion that rotifers contribute little to overall zooplankton biomass. Our study demonstrates that the traditional one-size fits all sampling approach used in the majority of zooplankton monitoring studies in the Great Lakes significantly underestimates microzooplankton abundance and its relative importance. Biassed information on Great Lakes zooplankton community composition has ramifications beyond a basic understanding of Great Lakes food webs. The lack of accurate data on microzooplankton abundance suggests that prey resources available to Asian carp in Lake Michigan have been greatly underestimated along with the likelihood these invasive species could become established. The dual sampling approach must become the norm rather than the exception for zooplankton research in the Great Lakes and other freshwater systems.     

净水厂水蚤类浮游动物的生物风险及影响因素研究

针对净水厂水蚤类浮游动物带来的感官问题及潜在的生物安全风险,考察了净水厂沉淀池出水中水蚤类浮游动物死体溶出物的微生物含量和有机物浓度、超声时间和频率对水蚤类浮游动物的影响,以及不同预氧化剂投加量和排泥周期时对水蚤类浮游动物的控制效果。结果表明,净水厂沉淀池出水中水蚤类浮游动物体内携带细菌,超声破体后溶出,使水中的细菌总数增多;水蚤类浮游动物死体的溶出物导致水样中有机物浓度增大;超声处理使水蚤类浮游动物的活跃性显著降低,且随着超声时间的增加,水蚤类浮游动物活跃性下降;相同超声时间下,随着超声频率的增加,水蚤类浮游动物活跃性降低;夏季和冬季时,投加预氧化剂和缩短排泥周期都可以有效控制水蚤类浮游动物的丰度,且随着预氧化剂投加量的增加,浮游动物去除率增大,当预氧化剂投加量达到1.5 mg/L后,去除率趋于稳定,约为92%。     

Seasonal periodicity of plankton and benthic fauna community structure and diversity in a small North African reservoir

Aquatic biota in terms of phytoplankton, zooplankton and benthic fauna were qualitatively and quantitatively followed seasonally during 2007 in a North African small reservoir, Aswan Reservoir. Simultaneously, seasonal variations in water quality were investigated in order to determine how far the aquatic biota could be altered by physicochemical and biotic factors. In phytoplankton of the investigated reservoir, 75 species belonging to four systematic groups were recorded, comprising 11 Cyanoprokaryota, 24 Bacillariophyceae, 2 Dinophyceae and 38 Chlorophyceae. Most numerous zooplankton were Rotifera (23 species). Cladocera and Copepoda were less numerous, with only seven and three species, respectively. Early development stages of copepods, nauplii and copepodites were sometimes recorded in considerable numbers. Twenty‐two invertebrate species related to five animal groups were exclusively benthic fauna: three Oligochaeta, nine Mollusca, seven larvae of Chironomidae, one Platyhelminthes, one Hirudinea and one Decapoda. Generally, the estimated values of phytoplankton species richness were relatively higher than those of zooplankton or benthic fauna. In particular, phytoplankton was influenced by physicochemical factors – water transparency, salinity and soluble reactive silica contents – as well as biotic factors – zooplankton and benthic fauna. Levels of pH value, Mg⁺², NO₃‐N and chlorophyll‐a contents appeared to be the most influential parameters dictating the pattern of seasonal periodicity of benthic fauna. Numerically, the phytoplankton was somewhat more abundant in winter and autumn than in spring or summer. The peak of zooplankton population densities was observed in spring season. Benthic fauna tended to be abundant in summer and autumn seasons, showing a reverse seasonal trend from that of zooplankton. Cyanoprokaryota and Bacillariophyceae were the most important groups that determined the seasonal fluctuation pattern of phytoplankton. Rotifera and Copepoda were the most predominant groups influencing the seasonal periodicity of zooplankton. Oligochaeta and Mollusca alternated the dominancy of benthic fauna community in Aswan Reservoir.     

Top‐down biological controls on tropical lake productivity

Although productivity is primarily controlled by bottom‐up factors (nutrient levels), there are secondary effects caused by biological factors such as zooplankton grazing and algal self‐shading. The measurement of grazing effects and determination of the contributions of different nutrient pools should elucidate the roles of nutrient levels and biotic effects and also infer the relative importance of classical and microbial food webs. To produce a series of grazing intensity, after initial screening to remove macrozooplankton, lake water was filtered to remove remaining zooplankton. This was used to dilute whole lake water in a filtered : unfiltered ratios from 0:1 to 1:0, which was then incubated with nutrient enrichment. Results show an increase of up to 20% in productivity for surface midlake waters. To investigate grazing by nutrient dilution/deletion, grazing dilutions were again prepared; however, nutrients were added to produce three different conditions,+N +P (all nutrients), –N (nitrogen omitted) and –P (phosphorus omitted). From productivity measurements, the contributions of internal, external and recycled nitrogen and phosphorus nutrient pools were calculated. Sites at Hippo Point (HP) (midlake) and Malewa River inflow (MR) (near the mouth of the River Malewa) show little difference in the contribution of external nutrients, but remaining productivity is mostly fuelled by recycled nutrients at the MR site. Little difference was found between nitrogen and phosphorus‐limited conditions.     

Trophic evolution of Lake Lugano related to external load reduction: Changes in phosphorus and nitrogen as well as oxygen balance and biological parameters

Lake Lugano is located at the border between Italy and Switzerland and is divided into three basins by two narrowings. The geomorphologic characteristics of these basins are very different. The catchment area is characterized by calcareous rock, gneiss and porphyry; the population amounts to approximately 290 000 equivalent inhabitants. The external nutrient load derives from anthropogenic (85%), industrial (10%) and agricultural (5%) sources. The limnological studies carried out by Baldi et al. (1949) and EAWAG (1964) revealed early signs of eutrophication, with a phosphorous concentration of about 30–40 mg m^–3 and an oxygen concentration of less than 4 g m^–3 in the deepest hypolimnion. Subsequently Vollenweider et al. (1964) confirmed these data and was the first to point out the presence of a meromictic layer in the hypolimnion of the northern basin. From the 1960s, as a result of an increase in the population and internal migration, the lake became strongly eutrophic with the P concentration reaching 140 mg m^–3 and the oxygen in the hypolimnion reduced to zero. Fifty‐five per cent of the P was from metabolic sources and 45% from detergents and cleaning products. In 1976, a partial diversion of waste water from the northern to the southern basin was begun, and gradually eight waste water treatment plants came into operation using mechanical, chemical and biological treatments. In 1986, Italy and Switzerland began to eliminate the P in detergents and cleaning products. Since 1995, the main sewage treatment plants have improved their efficiency by introducing P post‐precipitation, denitrification and filtration treatments. The recovery of the lake is due to be completed by the year 2005. Altogether, during the last 20 years recovery measures have reduced the external P load from about 250 to 70–80 tonnes year^–1; the goal to be reached is 40 tonnes year^–1. In‐lake phosphorous concentrations have decreased from 140 to 50–60 mg m^–3, with the target at 30 mg m^–3. Dissolved oxygen concentration is satisfactory only between the depths of 0 and 50 m, falling rapidly to zero in the deepest layers. Below a depth of 90 m, high CH₄, HS^–, NH₄⁺, Fe²⁺ and Mn²⁺ concentrations exist. Primary production has decreased from 420 to 310 g C_ass m^–2 year^–1, notwithstanding an increase in the thickness of the trophogenic layer. Structure and dynamic biomass show marked changes: phytoplankton dry weight has decreased from 16 to 7 g m^–2, while zooplankton dry weight has increased from 3 to 4.5 g m^–2. Chlorophyll concentration has fallen from 14 to 9 mg m^–3 and Secchi disk transparency has increased from 3.5 to 5.5 m. The current sources of the external load are uncollected small urban conglomerations, storm‐water overflows from outfall sewers, and the residual load from sewage treatment plants, particularly those without P post‐precipitation.     

Impacts of small dams on the phytoplankton and invertebrates in an Amazonian river

The construction of small hydroelectric plants (SHPs) has increased greatly worldwide, and the impacts of these impoundments can cause changes in the aquatic biota. Here, we investigated the ecological attributes (abundance, richness, and species diversity) of three communities (phytoplankton, invertebrates in the water column, and benthos) and the functional groups of phytoplankton, before and after the construction of five SHPs in an Amazonian river. The communities were sampled at two sites, one upstream and another downstream of each dam or construction site, before the dam closure. The dam did not change the limnological factors, and the acid waters and low electrical conductivity, typical of “cerrado” rivers, were characteristic of both the pre- and post-dam phases. For aquatic communities, the phytoplankton abundance increased and the diversity of groups decreased in the post-dam phase. Regarding the morphology-based functional groups (MBFG), there was an increase in groups I (small algae with a high surface/volume ratio) and V (phytoflagellates), with a reduction in groups VI (diatoms) and VII (large mucilaginous colonies) in the post-dam phase. The relative abundance of zooplankton species increased in the post-dam phase, and the opposite was observed for the benthic community, with reductions in abundance, richness, and group diversity in the post-dam phase. The structure of the three communities differed between the pre- and post-dam phases, but no difference in communities' similarity was observed between the upstream and downstream sites in both phases. The results show that the change in hydrodynamics, from lotic to semi-lentic, in the reservoirs of the SHPs, was the main driving force for the alterations in the three communities. For phytoplankton, SHPs are favorable in the sense of decreasing the incidence of algal blooms, particularly of cyanobacteria.     

白洋淀浮游生物群落动态变化与生物量模拟研究

为探究白洋淀浮游生物群落结构动态特征及其关键影响因子,基于2017年秋,2018年春、夏3个季节的水环境因子与浮游生物野外采样调查结果,采用冗余分析(ＲDA)、广义可加模型(GAMs)等方法探究了白洋淀不同季节的浮游生物群落动态变化,建立了浮游植物生物量与环境因子的非线性关系并进行了率定验证。结果表明:与1992年白洋淀干淀后重新蓄水时相比,浮游植物与浮游动物物种数分别下降了59%与37%,优势群落从绿藻门转化为蓝藻门。根据ＲDA排序结果可知,温度、透明度是影响浮游生物丰度的关键环境因子。运用GAMs构建了环境因子与浮游植物生物量的定量模型,最优模型结构为Biomass-phy～s(T)+s(TN)+s(Cond)+s(Biomass-zoo)+s(Biomass-pro)+te(Biomass-pro_TN)+te(Biomass-pro_Cond)+te(Biomass-pro_Biomass-zoo)。将2019年6月采样数据进行模型验证,计算模拟效果良好,实现了对浮游植物生物量的定量模拟,能够为白洋淀生态恢复与保护提供决策支持。     

Effect of Spatial Heterogeneity on Zooplankton Diversity: A Multi‐Scale Habitat Approximation in a Floodplain Lake

Environmental heterogeneity is an essential quality of ecosystems as it has important implications in community structure. Macrophytes are a main component of environmental heterogeneity in floodplain lakes, and their dynamics are highly influenced by water level changes. In this context, we analysed at different spatial scales the relationship among hydrological variations, environmental heterogeneity associated to macrophytes and zooplankton regional diversity (γ diversity) in a South American floodplain lake adjacent to the Paraná River, and we also compared the local zooplankton diversity (α diversity) among the different environments that comprised the lake heterogeneity. At very low waters, the environmental heterogeneity was reduced as the lake was mainly limited to open water areas with low zooplankton diversity. At high waters, the profuse vegetation development (emergent and free‐floating), in mixed or homogeneous patches, determined a higher lake environmental heterogeneity with enhanced regional zooplankton diversity; littoral species increased over limnetic ones. Zooplankton α diversity was higher in environments with free‐floating macrophytes than in those without these plants. The structural complexity in the water column provided by plant roots would be closely related to the enhanced diversity found under free‐floating mats. This study contributes to the knowledge on the effects of strong water level variations on environmental heterogeneity, which is strongly associated to macrophytes and on zooplankton diversity, and highlights the role of free‐floating plants as diversity hosts and ‘key structures’ in floodplain lakes. Copyright © 2013 John Wiley & Sons, Ltd.     

Oxidative effects of the harmful algal blooms on primary organisms of the food web

Degraded water quality from nutrient pollution, physical, biological, and other chemical factors contributesto the development and persistence of many harmful algal blooms (HABs). The complex dynamics of the HABs isa challenge to marine ecosystems for the toxic effects reported. The consequences include fish, bird, and mammalmortality, respiratory or digestive tract problems, memory loss, seizures, lesions and skin irritation in many organisms.This review is intended to briefly summarize the recent reported information on harmful marine toxin deleteriouseffects over the primary organisms of the food web, namely algae, zooplankton and invertebrates. Special focus is madeon oxidative stress status of cells and tissues. Even though in situ field research is less controlled than laboratory studies,in which the organisms are directly exposed to the toxins under consideration, both types of approaches are required tofully understand such a complex scenario. On top of that, the contribution of the increasing water temperatures in thesea, as a consequence of the global climate change, will be addressed as a topic for further studies, to evaluate the effecton regulating algal growth, species composition, trophic structure, metabolic stress and function of aquatic ecosystems.