The recovery of crustacean zooplankton from acidification depends on lake type

Acidification has harmed freshwater ecosystems in Northern Europe since the early 1900s. Stricter regulations aimed at decreasing acidic emissions have improved surface-water chemistry since the late 1980s but the recovery of biotic communities has not been consistent. Generally, the recovery of flora and fauna has been documented only for a few lakes or regions and large-scale assessments of long-term dynamics of biotic communities due to improved water quality are still lacking. This study investigates a large biomonitoring dataset of pelagic and littoral crustacean zooplankton (Cladocera and Copepoda) from 142 acid-sensitive lakes in Norway spanning 24 years (1997–2020). The aims were to assess the changes in zooplankton communities through time, compare patterns of changes across lake types (defined based on calcium and humic content), and identify correlations between abiotic and biological variables. Our results indicate chemical and biological recovery after acidification, as shown by a general increase in pH, acid neutralizing capacity, changes in community composition and increases in the total number of species, number of acid-sensitive species and functional richness through time. However, the zooplankton responses differ across lake types. This indicates that the concentration of calcium (or alkalinity) and total organic carbon (or humic substances) are important factors for the recovery. Therefore, assessment methods and management tools should be adapted to the diverse lake types. Long-term monitoring of freshwater ecosystems is needed to fully comprehend the recovery dynamics of biotic communities from acidification.     

Acidification history and crustacean remains: some ecological obstacles

Crustacean remains are not yet useful as parameters for assessing the recent acidification phenomenon, due to too few studies on their ecology. The changes observed in the sediments are related not just to changes in lake chemistry, but also to predatory and competitive interactions. Moreover, the habitat pH of the organism may differ from the measured lake pH, and may as such not be representative. Therefore, species in some acidic lakes may decrease their abundance, whereas the same species in nearby acidic lakes increase. The caution mainly concerns species with no clear pH distribution. Species predominant in acidic or alkaline lakes generally follow patterns more closely related to their physiology. Study of pelagic species, including both body size and shape measurements, should be included in the analysis. If all the ecological factors are included, animal as well as algal remains would form powerful tools to reveal lake histories.     

Fluctuations in water level and the dynamics of zooplankton: a data‐driven modelling approach

1. The zooplankton in Lake Kinneret (Israel) have undergone large fluctuations in recent decades, which have been linked to both biotic and abiotic processes. 2. By applying a data‐driven modelling approach to a long‐term database, and focusing on key abiotic (lake‐level change) and biotic (prey abundance) variables, we attempted to identify the possible factors impacting the lake’s zooplankton community. 3. We hypothesised that changes in the predatory zooplankton (adult cyclopoids) assemblage are driven by changes in lake level during years of large changes. We further postulated that lake‐level changes would have a similar impact on the herbivorous zooplankton (cladocerans and cyclopoid copepodites) but an opposite effect on the microzooplankton. In the years of moderate changes to lake level, however, the abundance of predatory zooplankton would determine the size of the herbivore and microzooplankton populations rather than their food sources, that is, top‐down control. 4. The resulting decision trees supported the hypotheses stressing the importance of the annual rate of lake‐level change in shaping the zooplankton community in the lake. In addition, and in contrast to expectations, bottom‐up processes seem to play a role in determining zooplankton abundance.     

Complex controls on ostracod palaeoecology in a shallow coastal brackish‐water lake: implications for palaeosalinity reconstruction

1. The low‐Mg calcite shells of Ostracoda (Crustacea) are often well preserved in the sediments of alkaline lakes. In coastal waters that have undergone large temporal changes in salinity, ostracod assemblages preserved in the sediment record have been used to reconstruct palaeosalinity, often assuming that salinity is the only significant control on the faunas. 2. We evaluate the performance of ostracods as palaeosalinity indicators in Hickling Broad, a shallow brackish coastal lake in Norfolk, U.K., by comparing fossil ostracod assemblages covering two centuries with geochemical inferences and instrumental records of past salinity and water composition along with other palaeolimnological indicators. 3. Despite large changes in the salinity of the lake and the supposed salinity sensitivity of ostracods, the fossil ostracod assemblages do not clearly reflect the salinity trends inferred from the other independent data. Rather, a complex series of changes has occurred in the lake over the past 200 years and factors other than salinity, including eutrophication, toxicity and associated complex alterations in habitat availability have probably influenced ostracod assemblages. In contrast, there is a good broad agreement between inferred or measured salinity and the trace‐element chemistry of ostracod shells. 4. We conclude that ostracod faunas may not always provide unambiguous palaeosalinity records and should therefore not be used to reconstruct salinity changes except as part of a multi‐proxy investigation that includes other palaeoecological and/or geochemical indicators.     

Evaluating putative ecological drivers of microcystin spatiotemporal dynamics using metabarcoding and environmental data

Microcystin is a cyanobacterial hepatotoxin of global concern. Understanding the environmental factors that cause high concentrations of microcystin is crucial to the development of lake management strategies that minimize harmful exposures. While the literature is replete with studies linking cyanobacterial production of microcystin to changes in various nutrients, abiotic stressors, grazers, and competitors, no single biotic or abiotic factor has been shown to be reliably predictive of microcystin concentrations in complex ecosystems. We performed random forest regression analyses with 16S and 18S rRNA gene sequencing data and environmental data to determine which putative ecological drivers best explained spatiotemporal variation in total microcystin and several individual congeners in a eutrophic freshwater reservoir. Model performance was best for predicting concentrations of the congener MC-LR, with ca. 88% of spatiotemporal variance explained. Most of the variance was associated with changes in the relative abundance of the cyanobacterial genus Microcystis. Follow-up RF regression analyses revealed that factors that were the most important in predicting MC-LR were also the most important in predicting Microcystis population dynamics. We discuss how these results relate to prevailing ecological hypotheses regarding the function of microcystin.     

Sediment chemistry of lakes formed by surface-mining for coal in the midwestern U.S.A.

Sediment from lakes on abandoned coal mines in the Midwestern U.S.A. was examined to determine the factors controlling chemical composition and the role the sediment plays in lake neutralization. Sediment concentrations of many cations, (especially heavy metals) are strongly correlated with sediment sulfide concentration, but poorly correlated with the pH of the overlying water. Leaching the sediment of one lake with 1 N ammonium acetate, 0.1 N HCl, and 6 N HCl revealed that cations were mostly bound in weak acid-leachable and strong acid-leachable forms. The weak acid-leachable form is likely to be metal sulfides and calcium carbonate. The sulfide-poor sediments of extremely acid lakes contained few weak acid-leachable cations. Raw mine-spoil contained large amounts of easily leached cations. There is little relationship between changes in sediment chemistry over time determined from cores of lake sediment and past lake pH. Rates of sulfide deposition were examined in sediment cores because sulfate reduction and deposition has been suggested as a major source of alkalinity in lakes influenced by acid precipitation. Although the rate of sulfate deposition in surface mine lakes is high, it alone seems to be insufficient to cause neutralization.     

Trichinella spiralis: Alterations of blood chemistry in the mouse

Alterations in host blood chemistry during mouse trichinosis were studied. Mice infected with Trichinella spiralis showed depressions in serum glucose, serum pyruvate, serum total cholesterol, serum bilirubin, serum alkaline phosphatase, serum total proteins, serum total globulin, uric acid, albumin, and A/G ratio below levels found in uninfected animals. The concentrations of serum lactic dehydrogenase, serum glutamic-oxaloacetic transaminase, and serum creatine phosphokinase in infected mice were above that of uninfected mice. Hemoglobin, packed-cell volume (Hematocrit), creatinine, and calcium were at similar levels in infected and uninfected mice. These changes are discussed in terms of primary pathophysiologic lesions occurring in the gut and muscles of the trichinous host.     

Shifts in phenology of Bythotrephes longimanus and its modern success in Lake Maggiore as a result of changes in climate and trophy

In Lake Maggiore, the density of the invertebrate predator Bythotrepheslongimanus increased following lake re-oligotrophication inthe late 1980s. This "invasion" was followed by dramatic changesin the pelagic food web, consistent with those that followedthe establishment of B. longimanus in North American lakes whereit is not native. In this contribution, we explore the modernsuccess of B. longimanus in Lake Maggiore by investigating itsphenology and population density, and their correlations withabiotic and biotic factors during the period from 1981 to 2003.A 10-fold increase in the abundance of B. longimanus followedan earlier start and longer duration of annual population growth.Increased prey resources and decreased predation pressure werenot observed during the B. longimanus density increase. Instead,a rise in lake temperature may have altered the reproductivecycle of this species. Furthermore, the depth and duration ofa refuge from visually orienting fish predators increased duringthese 20 years, as a result of changes in the thermal stratificationregime of the lake. This case study provides a timely exampleof how climatic changes may interact with biotic drivers (e.g.fish predation) to influence the density and phenology of aninvertebrate predator.     

Contrasting roles of water chemistry, lake morphology, land-use, climate and spatial processes in driving phytoplankton richness in the Danish landscape

Understanding of the forces driving the structure of biotic communities has long been an important focus for ecology, with implications for applied and conservation science. To elucidate the factors driving phytoplankton genus richness in the Danish landscape, we analyzed data derived from late-summer samplings in 195 Danish lakes and ponds in a spatially-explicit framework. To account for the uneven sampling of lakes in the monitoring data, we performed 1,000 permutations. A random set of 131 lakes was assembled and a single sample was selected randomly for each lake at each draw and all the analyses were performed on permuted data 1,000 times. The local environment was described by lake water chemistry, lake morphology, land-use in lake catchments, and climate. Analysis of the effects of four groups of environmental factors on the richness of the main groups of phytoplankton revealed contrasting patterns. Lake water chemistry was the strongest predictor of phytoplankton richness for all groups, while lake morphology also had a strong influence on Bacillariophyceae, Cyanobacteria, Dinophyceae, and Euglenophyceae richness. Climate and land-use in catchments contributed only little to the explained variation in phytoplankton richness, although both factors had a significant effect on Bacillariophyceae richness. Notably, total nitrogen played a more important role for phytoplankton richness than total phosphorus. Overall, models accounted for ca. 30% of the variation in genus richness for all phytoplankton combined as well as the main groups separately. Local spatial structure (<30 km) in phytoplankton richness suggested that connectivity among lakes and catchment-scale processes might also influence phytoplankton richness in Danish lakes.     

The influence of earthquakes on large lacustrine ecosystems, with particular emphasis on Lake Sevan, Armenia

This paper discusses the influence of earthquakes on large water ecosystems, with particular emphasis on Lake Sevan, Armenia. Earthquakes impact on large lacustrine ecosystems in seismically active areas in a number of ways, including chemistry and lake dynamics. Conclusions are drawn from a large database that includes biological, hydrological, geochemical and seismic information. Strong earthquakes change the water chemistry and pH of the lake and consequently the chemical and biological processes that take place in the lake bed sediments. Analysis of historical earthquakes shows their influence on the organic carbon in the sediments, the changes of the lake dynamics and variations in bacteria, phytoplankton and zooplankton at the base of the food chain.     

Ecological periodic tables: in principle and practice

“Science is organized knowledge.” Immanuel Kant (1724–1804) Ecological periodic tables are an information organizing system with categorical habitat types as elements and predictably recurring (periodic) properties of a target biotic community, such as its relative species richness, abundance and biomass, as attributes. Ecological periodic tables are founded on the ecological tenet that habitats structure biotic communities and its corollary that habitats are templets for ecological strategies. They are a durable, open and flexible system that accommodates all operationally defined habitat types and biotic communities for which the periodicity of habitat usage patterns by a biotic community have been empirically substantiated. Discovering quantitative, periodic habitat usage patterns requires quantitative, representative, unbiased sampling of a biotic community across habitat types at ecologically relevant temporal and spatial scales. Like chemical periodic tables, the Linnaean system of classification and the Hertzsprung–Russell diagram in chemistry, biology and astronomy, respectively, ecological periodic tables are simple, easy to understand, exceptionally useful and they foster the expansion of scientific understanding, inquiry and theory.     

On the limnology of two alkaline lakes (Nakuru and Naivasha) in the East Rift Valley System in Kenya

The present study aims to contribute to the general knowledge of Lakes Naivasha and Nakuru, the latter lake strongly saline and alkaline. Results are presented concerning water chemistry, chlorophyll a concentrations, phytoplankton, Zooplankton, bottom fauna and fish material obtained from these lakes. Algal photosynthetic rates were calculated by the oxygen method.     

Benthic diatoms and phytoplankton to assess nutrients in a large lake: Complementarity of their use in Lake Geneva (France–Switzerland)

Lakes can be monitored using different bioindicators, among which phytoplankton and benthic diatoms. We compared these two indicators in Lake Geneva for nutrient assessment. Bimonthly samplings were carried out during one year in the euphotic layer of a pelagic site. In the same time four littoral sites were sampled at 40–50 cm depth. Species compositions and abundances of both bioindicators were analyzed following European standards. Water physico-chemical composition was analyzed at the same time. Seasonal succession of benthic diatom guilds was observed. The dynamics of benthic diatom communities were better correlated to the pelagic chemistry than to the local littoral chemistry. We also observed that in the sampling sites frequently exposed to winds and waves, benthic diatoms showed lower correlations to physico-chemical dynamics, because of an increase of pioneer diatoms abundance adapted to turbulent environment, such sites must be avoided for lake monitoring. Finally, biotic indices calculated with benthic diatoms in wind protected sites showed higher correlations with pelagic nutrient concentration (PO₄³⁻) than indices calculated with phytoplankton. This unexpected situation can be explained by differences of temporal variability of chemical and biological compartments. Littoral chemistry changed faster than pelagic chemistry because of rains, diffuse flow from watershed and rivers flowing in the littoral zone whereas pelagic chemistry has a much smoother evolution because it is situated 10 km from the coast. But phytoplankton showed a high temporal variability because of wind influence, which explained the low correlation with the smooth evolution of pelagic chemistry. On the other hand, benthic diatoms from sites protected from the dominant wind, showed a lower temporal variability and were more in synchrony with the smooth evolution of pelagic chemistry.Even if we show that diatom seem to be promising indicator of nutrient level of the lake, we also underline the complementarity of using both indicators: benthic diatom and phytoplankton. Each of them brings different information about temporal variability of the lake and about the functioning of different habitats. Comparing these two bioindicators only on the basis of nutrient correlation ability would be an over-simplification whom managers must be warned.     

洪湖沉积物中真菌群落结构的垂直分布

湖泊沉积物中真菌的类群及其作用所知甚少。以长江中上游代表性湖泊洪湖为研究对象,从湖心截取了一个72cm长的沉积柱,通过rDNA内转录间隔区（ITS）的变性梯度凝胶电泳（DGGE）,对洪湖沉积物中真菌群落结构的垂直变化进行了分析。结果显示,DGGE条带以14－18cm层次为过渡,在2－14cm和14－72cm之间存在一定差异。Shannon-Weaver index（H′）在上下层之间有波动。聚类分析上层2－18cm和中下层18－72cm分别以不同的小类聚在一起。表明14－18cm以上和以下的类群存在差异,     

Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa)

The role of biotic processes in a warm, monomictic, hypertrophic African impoundment (Hartbeespoort Dam) is examined using ³²P radiobioassays. Phosphorus demand is assessed by phosphorus turnover times, alkaline phosphatase activity, cellular phosphorus status and the phosphorus deficiency index. Long turnover times indicative of an enriched system were recorded, ranging from 9 h to 1992 h, with no evidence of phosphorus stress being present. These turnover times support the hypothesis that the phosphorus cycle in Hartbeespoort Dam is dominated by the algal community which is shown to play an important role in phosphorus cycling within the water column. However, hydrological processes remain the driving force in phosphorus seasonality in the lake.     

以浮游植物评价达赉湖水质污染及营养水平

1987—1988年在30个样点,四季采样,对达赉湖的浮游植物进行了种类组成,生物量、种群数量、优势种、污染指示种、硅藻指数、综合指数等群落生态学的初步研究,应用后五项参数对达赉湖水质污染及营养水平进行了评价。达赉湖浮游植物年均值达54.7×106个/L(细胞数,或个体数为2.3×106个/L),硅藻指数为149.3,综合指数为5.6。群落组成中污染指示种占65%,春季以绿藻的十字藻、卵囊藻为优势种,其它3个季节均以蓝藻中的微囊藻、鱼腥藻、腔球藻占优势,表明达赉湖已受到中等程度污染,属于蓝、绿藻型富营养湖。       

Exploring lake ecosystems: hierarchy responses to long‐term change?

Shifts in climate regime have provoked substantial trophic‐ and species‐dependent changes within ecosystems. With growing concerns of present global warming, we examined potential lake ecosystem responses, natural hierarchy responses (i.e. immediate responses at lower system levels as opposed to delayed responses at higher system levels), and possible shifts among abiotic (physics, nutrients) and biotic (phytoplankton, zooplankton) system components. Specifically, we analyzed decadal data collected from Müggelsee, a lake in Berlin, Germany, for climate‐induced abiotic and biotic changes, their timing and type, and classified them as abrupt permanent, gradual permanent, abrupt temporary, or monotonic. We further categorized variable changes as a function of system hierarchy, including lake physics (ice, temperature, stratification), nutrients (phosphorus, nitrogen, silicate), plankton, and levels of integration (i.e. species, taxonomic groups, and total plankton). Contrary to current theory, data suggest abrupt responses did not occur in a hierarchy‐dependent manner, nor was a clear pattern observed among functional system‐based categories. Abrupt permanent changes were the most prominent response pattern observed, suggesting they may be driven by large‐scale climatic oscillations and by surpassed thresholds, as noted in previous case studies. Gradual changes coincided with affected abiotic parameters spanning an expansive time range; for example, climatic effects in spring preceded changes in nutrient limitation. Variables displaying no long‐term changes pointed to compensation processes caused by, e.g., simultaneously acting forces of warming trends and climate‐independent changes in trophic state. Nevertheless, the complexity of response patterns at the single system level manifested clear chronological regime shifts in abiotic and biotic parameters in spring and, to a lesser extent, in summer. With regard to projected global warming, the majority of currently unaffected system levels may face impending thermal thresholds, achievement of which would result in an accelerated shift in ecosystem state.     

Bacterial Community Composition in the Water Column of a Lake Formed by a Former Uranium Open Pit Mine

Mining of pyrite minerals is a major environmental issue involving both biological and geochemical processes. Here we present a study of an artificial lake of a former uranium open pit mine with the aim to connect the chemistry and bacterial community composition (454-pyrosequencing of 16S rRNA genes) in the stratified water column. A shift in the water chemistry from oxic conditions in the epilimnion to anoxic, alkaline, and metal and sulfide-rich conditions in the hypolimnion was corresponded by a strong shift in the bacterial community, with few shared operational taxonomic units (OTU) between the water layers. The epilimnetic bacterial community of the lake (～20?years old) showed similarities to other temperate freshwater lakes, while the hypolimnetic bacterial community showed similarity to extreme chemical environments. The epilimnetic bacterial community had dominance of Actinobacteria and Betaproteobacteria. The hypolimnion displayed a higher bacterial diversity and was dominated by the phototrophic green sulphur bacterium of the genus Chlorobium (ca. 40?% of the total community). Deltaproteobacteria were only represented in the hypolimnion and the most abundant OTUs were affiliated with ferric iron and sulfate reducers of the genus Geobacter and Desulfobulbus, respectively. The chemistry is clearly controlling, especially the hypolimnetic, bacterial community but the community composition also indicates that the bacteria are involved in metal cycling in the lake.