The diversity and distribution of freshwater rotifers have been under-explored in China, especially from high altitude regions. We used molecular data to explore these points in the monogonont ...rotifer
Brachionus calyciflorus
species complex across China, covering both the low- and high-altitude regions. Populations of this species complex were detected in 44 of the 251 waterbodies sampled across China. Analysis of partial sequences of the nuclear ribosomal internal transcribed spacer (ITS-1) placed these populations in four distinct species (
B. dorcas
,
B. elevatus
,
B. calyciflorus
sensu stricto (
s.s.
) and
B. fernandoi
), and phylogenies based on sequences from a portion of the mitochondrial cytochrome
c
oxidase subunit I gene recognized seven groups within the
B. calyciflorus
species complex in China. The four species were congruent with the four morphogroups that we identified. All four species were present in the Eastern Plain and
B. dorcas
occurred nowhere else.
Brachionus elevatus
and
B. calyciflorus s.s.
were the only species present in the Northeast Plain and in the Yunnan-Guizhou Plateau, respectively. Cases of mito-nuclear discordance were detected in our specimens, suggesting occasional hybridization between different species of the
B. calyciflorus
species complex. Our results revealed the phylogeography and gene introgression in this species complex across China.
Environmental factors such as nutrient and light availability may play important roles in determining the magnitude and direction of microbial priming and detrital decomposition and, therefore, the ...relative importance of microbial priming in carbon (C) dynamics in freshwater ecosystems.
We integrated light availability with an existing conceptual model predicting the magnitude of the priming effect (PE) along a dissolved nutrient gradient (i.e. nutrient PE model). Our modified light‐nutrient PE model hypothesises how light may mediate priming at any given nutrient concentration and provides a calculation method for quantitative PE values (i.e. light effect size at a given nutrient concentration).
We used recirculating stream mesocosms with Quercus stellata (post oak) leaf litter as an organic matter (OM) substrate in a 150‐day experiment to test our model predictions. We manipulated light levels ambient (full light), shaded (c. 19% of ambient) and phosphorus (P) concentration (10, 100, 500 µg PO4‐P/L) in a fully factorial design. We also supplied all mesocosms with 500 µg/L dissolved inorganic nitrogen. Microbial biomass, water column dissolved organic C, and leaf litter dry mass and recalcitrant OM i.e. the fibre (cellulose + lignin) component of post oak substrate were measured. Recalcitrant OM (ROM) k‐rates (day−1) were used to calculate the light effect size within P treatments as a log response ratio (lnambient k‐rate/shade k‐rate) to ascertain PE magnitude and direction (positive or negative).
Light was an important driver of dissolved organic C, a potential source of additional labile organic matter essential for priming heterotrophic microbes. There were weak PEs in total leaf litter dry mass remaining, but PEs were more pronounced in leaf litter ROM remaining. The strongest positive PEs (specific to litter ROM pools) occur in the highest P treatment, presumably due to a change in which nutrient, nitrogen versus P, was a limiting factor for microbes based on nutrient ratios rather than P concentration alone. These results illustrate the importance of considering light levels, nutrient ratios (rather than individual nutrients), and detrital ROM components in further PE model development.
Russell, I. C., Aprahamian, M. W., Barry, J., Davidson, I. C., Fiske, P., Ibbotson, A. T., Kennedy, R. J., Maclean, J. C., Moore, A., Otero, J., Potter, E. C. E., and Todd, C. D. 2012. The influence ...of the freshwater environment and the biological characteristics of Atlantic salmon smolts on their subsequent marine survival. - ICES Journal of Marine Science, 69: 1563-1573.Atlantic salmon have declined markedly in the past 20-30 years throughout their range. Much of the focus for this decline has been on increased mortality during the marine phase of the life cycle. However, marine mortality does not operate independently of factors acting in freshwater and the biological characteristics of smolts migrating to sea. Over recent decades, juvenile salmon in many rivers have grown faster and migrated to sea at a younger age, so have been typically smaller than earlier. This has shortened the generation time for many individuals and may dampen the impact of increased marine mortality, assuming that expected higher in-river survival prior to smolting is not outweighed by increased mortality of smaller smolts at sea. Over the same period, smolt run-timing across the geographic range has been earlier, at an average rate of almost 3 d per decade. This has given rise to growing concerns about smolts potentially missing the optimum environmental migration "window", the timing of which may also be changing. Contaminants and other factors operating in freshwater also impact smolt quality with adverse consequences for their physiological readiness for life at sea. Given that managers have very limited ability to influence the broad scale factors limiting salmon survival at sea, it is vital that freshwater habitats are managed to both maximize the smolt output and to minimize the impact of factors acting in freshwater that may compromise salmon once they migrate to sea.
Freshening and warming of Antarctic Bottom Water (AABW) between the 1980s and 2000s are quantified, assessing the relative contributions of water-mass changes and isotherm heave. The analysis uses ...highly accurate, full-depth, ship-based, conductivity–temperature–depth measurements taken along repeated oceanographic sections around the Southern Ocean. Fresher varieties of AABW are present within the South Pacific and south Indian Oceans in the 2000s compared to the 1990s, with the strongest freshening in the newest waters adjacent to the Antarctic continental slope and rise indicating a recent shift in the salinity of AABW produced in this region. Bottom waters in the Weddell Sea exhibit significantly less water-mass freshening than those in the other two southern basins. However, a decrease in the volume of the coldest, deepest waters is observed throughout the entire Southern Ocean. This isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential temperature maximum. The water-mass freshening of AABW in the Indian and Pacific Ocean sectors is equivalent to a freshwater flux of 73 ± 26 Gt yr−1, roughly half of the estimated recent mass loss of the West Antarctic Ice Sheet. Isotherm heave integrated below 2000m and south of 30°S equates to a net heat uptake of 34 ± 14 TW of excess energy entering the deep ocean from deep volume loss of AABW and 0.37 ± 0.15 mm yr−1of sea level rise from associated thermal expansion.
Purpose
In recent years, several methods have been developed which propose different freshwater use inventory schemes and impact assessment characterization models considering various cause–effect ...chain relationships. This work reviewed a multitude of methods and indicators for freshwater use potentially applicable in life cycle assessment (LCA). This review is used as a basis to identify the key elements to build a scientific consensus for operational characterization methods for LCA.
Methods
This evaluation builds on the criteria and procedure developed within the International Reference Life Cycle Data System Handbook and has been adapted for the purpose of this project. It therefore includes (1) description of relevant cause–effect chains, (2) definition of criteria to evaluate the existing methods, (3) development of sub-criteria specific to freshwater use, and (4) description and review of existing methods addressing freshwater in LCA.
Results and discussion
No single method is available which comprehensively describes all potential impacts derived from freshwater use. However, this review highlights several key findings to design a characterization method encompassing all the impact pathways of the assessment of freshwater use and consumption in life cycle assessment framework as the following: (1) in most of databases and methods, consistent freshwater balances are not reported either because output is not considered or because polluted freshwater is recalculated based on a critical dilution approach; (2) at the midpoint level, most methods are related to water scarcity index and correspond to the methodological choice of an indicator simplified in terms of the number of parameters (scarcity) and freshwater uses (freshwater consumption or freshwater withdrawal) considered. More comprehensive scarcity indices distinguish different freshwater types and functionalities. (3) At the endpoint level, several methods already exist which report results in units compatible with traditional human health and ecosystem quality damage and cover various cause–effect chains, e.g., the decrease of terrestrial biodiversity due to freshwater consumption. (4) Midpoint and endpoint indicators have various levels of spatial differentiation, i.e., generic factors with no differentiation at all, or country, watershed, and grid cell differentiation.
Conclusions
Existing databases should be (1) completed with input and output freshwater flow differentiated according to water types based on its origin (surface water, groundwater, and precipitation water stored as soil moisture), (2) regionalized, and (3) if possible, characterized with a set of quality parameters. The assessment of impacts related to freshwater use is possible by assembling methods in a comprehensive methodology to characterize each use adequately.
•Ecological preferences of freshwater species were collated into an online database.•654 fishes, 8586 invertebrates, 1083 macrophytes, 8868 diatoms, and 1976 phytoplankton.•106 bio-/ecological ...parameters.•Various options and tools for finding and tracing back information.•Applicable for research, monitoring, assessment, restoration, and modelling.
Species’ ecological preferences are progressively important for understanding distribution patterns, for conserving biodiversity or for assessing and evaluating the status of freshwater ecosystems. Comprehensive databases compiling species traits are already established in the terrestrial realm, but widely missing in freshwater science. We established a database for European taxa of five aquatic organism groups by compiling information on taxonomy, ecology and distribution based on extensive literature surveys, which were performed by experts for the targeted organism groups. The database includes fishes (654 taxa/21 ecological preferences), macro-invertebrates (8586/40), macrophytes (1083/5), diatoms (8868/36) and phytoplankton (1976/4). It is available online with various options and tools for finding information and has currently over 800 users. The reviewed literature as well as examples given in this paper, highlight the importance of the general availability of knowledge on ecological preferences for various aspects in ecological assessment. Freshwaterecology.info is considered a service for basic research, applied scientists, water managers or other stakeholders. It serves as base for bioassessment and monitoring.
Summary
A novel conceptual model linking anoxia, phosphorus (P), nitrogen (N), iron (Fe) and sulphate to the formation of noxious filamentous and colonial cyanobacteria blooms is presented that ...reconciles seemingly contradictory ideas about the roles of P, N and Fe in bloom formation.
The model has several critical concepts: (i) P regulates biomass and productivity in fresh waters until excessive loading renders a system N‐limited or light‐limited, but it is the availability of ferrous ions (Fe2+) that regulates the ability of cyanobacteria to compete with its eukaryotic competitors; (ii) Fe2+ diffusing from anoxic sediments is a major Fe source for cyanobacteria, which acquire it by migrating downwards into Fe2+‐rich anoxic waters from oxygenated waters; and (iii) subsequent cyanobacterial siderophore production provides a supply of Fe3+ for reduction at cyanobacteria cell membranes that leads to very low Fe3+ concentrations in the mixing zone.
When light and temperature are physiologically suitable for cyanobacteria growth, bloom onset is regulated by the onset of internal Fe2+ loading which in turn is controlled by anoxia, reducible Fe content of surface sediments and sulphate reduction rate.
This conceptual model provides the basis for improving the success of approaches to eutrophication management because of its far‐reaching explanatory power over the wide range of conditions where noxious cyanobacteria blooms have been observed.
Recently, the Beaufort Gyre has accumulated over 20,000 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades. Here we ...explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy‐resolving model of the Beaufort Gyre. We demonstrate that a realistic halocline can be achieved when its deepening tendency due to Ekman pumping is counteracted by the cumulative action of mesoscale eddies. Based on this balance, we derive analytical scalings for the depth of the halocline and its spin‐up time scale and emphasize their explicit dependence on eddy dynamics. Our study further suggests that the Beaufort Gyre is currently in a state of high sensitivity to atmospheric winds. However, an intensification of surface stress would inevitably lead to a saturation of the freshwater content—a constraint inherently set by the intricacies of the mesoscale eddy dynamics.
Key Points
Wind‐driven Beaufort Gyre dynamics is simulated within an eddy‐resolving model
Mesoscale eddies play a key role in constraining variations in freshwater content
The Beaufort Gyre is currently at its highest sensitivity to wind stress forcing
•Opioid drug Tramadol and antidepressant Citalopram alter crayfish behaviour at environmentally relevant concentrations.•Our results highlight the ecological importance of PhACs in aquatic ...ecosystems.•Simple method for assessing PhACs effects on aquatic organisms is presented.•Further research is necessary to assess the effects in detail.
Environmental pollution by pharmaceutically active compounds, used in quantities similar to those of pesticides and other organic micropollutants, is increasingly recognized as a major threat to the aquatic environment. These compounds are only partly removed from wastewaters and, despite their low concentrations, directly and indirectly affect behaviour of freshwater organisms in natural habitats. The aim of this study was to behaviourally assess the effects of an opioid painkiller (tramadol) and antidepressant drug (citalopram) on behaviour patterns of a clonal model species, marbled crayfish. Animals exposed to environmentally relevant concentrations of both tested compounds (∼1 μg l−1) exhibited significantly lower velocity and shorter distance moved than controls. Crayfish exposed to tramadol spent more time in shelters. Results were obtained by a simple and rapid method recommended as suitable for assessment of behaviour in aquatic organisms exposed to single pollutants and combinations.
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