Eutrophication strengthens the response of zooplankton to temperature changes in a high-altitude lake

Intensified sensitivity and adaptability of zooplankton Bosminidae in subtropical shallow freshwater lakes with increasing trophic level

The deterioration in lake water environments, especially increasing lake eutrophication, is prevalent all over the world, which has seriously affected the balance and stability of the internal ecosystem of lakes. In this study, modern water and sediment samples were collected from three subtropical freshwater lakes with significant differences in nutrient levels to analyze the concentration of the zooplankton Cladocera Bosminidae and its relationship with lakes’ ecological changes. The results show that the deterioration in lake water environments caused by increasing eutrophication limits the survival of most zooplankton. However, the Bosminidae shows a positive adaptability to eutrophication and high sensitivity to the changes in the lake environment. In addition, the lake eutrophication process caused by the intensification of human activities enhances the survival advantage of Bosminidae with more food sources, which is more conducive to its rapid reproduction.

Synergistic effects of warming and eutrophication alert zooplankton predator-prey interactions along the benthic-pelagic interface

Contemporary evidence suggests that climate change and other co-occurring large-scale environmental changes, such as eutrophication, will have a considerable impact on aquatic communities. However, the interactions of these environmental changes on trophic interactions among zooplankton remain largely unknown. Here we present results of a mesocosm experiment examining how a couple of zooplankton predator and prey taxa with different life-history strategies respond to the combined effect of an increase in temperature (4.5°C) and in eutrophication (phosphorus addition), during the crucial recruiting and growing season. We show that the addition of phosphorus alone significantly weakened the top-down effects by the cyclopoid copepod predators on their rotifer prey. In contrast, warming strengthened the top-down effects from the predator, leading to a reduction in the abundance of the rotifer prey. These effects of warming were enhanced by phosphorus addition. Together, our results demonstrate that warming made plankton prey organisms more susceptible to top-down effects from predators, but reduced their sensitivity to nutrient enrichment. In terms of the phenological effects, warming advanced the termination of diapause for both rotifers and cyclopoid copepods by about 2 weeks, but these temporal shifts, akin for both groups, resulted in no apparent trophic mismatch. Hence, from a future perspective, cyclopoid copepods are likely to benefit more from the combination of nutrient enrichment and climate warming to the detriment of their rotifer prey.

Distribution characteristics and pollution risk evaluation of the nitrogen and phosphorus species in the sediments of Lake Erhai, Southwest China

Erhai is a famous tectonic rift lake in China. In this study, the distribution of nitrogen and phosphorus species in Erhai sediment cores and their ecology risk were evaluated. The total nitrogen (TN) in the sediment cores ranged from 1583.3 to 8018.5 mg/kg. Nitrogen (N) was still accumulating in the sediment. For depths of 0 to 25 cm, the TN decreased dramatically and for deeper depths the TN got stabilized. The proportions of various N fractions in the sediments of the study areas ranked as follows: the strong oxidation extractable N (SOEF-N) > the weak acid extractable N (WAEF-N) > the strong alkali extractable N (SAEF-N) > the ion-exchangeable N (IEF-N). The total phosphorus (TP) ranged from 814.9 to 1442.3 mg/kg. The vertical distribution of each fraction of phosphorus showed that there were different sources of sediment phosphorus around the Erhai Lake. The results of nitrogen and phosphorus pollution evaluation in sediments by single pollution standard index method showed that the standard index of the TN (S_TN) ranged from 4.29 to 14.01, and the standard index of the TP (S_TP) ranged from 1.69 to 2.18. It illustrated that N and P in the sediments were the serious ecological pollution risks in Erhai Lake.

Diversity of the Bosmina (Cladocera: Bosminidae) in China, revealed by analysis of two genetic markers (mtDNA 16S and a nuclear ITS)

BACKGROUND

China is an important biogeographical zone in which the genetic legacies of the Tertiary and Quaternary periods are abundant, and the contemporary geography environment plays an important role in species distribution. Therefore, many biogeographical studies have focused on the organisms of the region, especially zooplankton, which is essential in the formation of biogeographical principles. Moreover, the generality of endemism also reinforces the need for detailed regional studies of zooplankton. Bosmina, a group of cosmopolitan zooplankton, is difficult to identify by morphology, and no genetic data are available to date to assess this species complex in China. In this study, 48 waterbodies were sampled covering a large geographical and ecological range in China, the goal of this research is to explore the species distribution of Bosmina across China and to reveal the genetic information of this species complex, based on two genetic markers (a mtDNA 16S and a nuclear ITS). The diversity of taxa in the Bosmina across China was investigated using molecular tools for the first time.

RESULTS

Two main species were detected in 35 waterbodies: an endemic east Asia B. fatalis, and the B. longirostris that has a Holarctic distribution. B. fatalis had lower genetic polymorphism and population differentiation than B. longirostris. B. fatalis was preponderant in central and eastern China, whereas B. longirostris was dominated in western China. The third lineage (B. hagmanni) was only detected in a reservoir (CJR) of eastern China (Guangdong province). Bosmina had limited distribution on the Tibetan plateau.

CONCLUSIONS

This study revealed that the biogeography of Bosmina appear to be affected by historical events (Pleistocene glaciations) and contemporary environment (such as altitude, eutrophication and isolated habitat).

Microbiology and Nitrogen Cycle in the Benthic Sediments of a Glacial Oligotrophic Deep Andean Lake as Analog of Ancient Martian Lake-Beds

Potential benthic habitats of early Mars lakes, probably oligotrophic, could range from hydrothermal to cold sediments. Dynamic processes in the water column (such as turbidity or UV penetration) as well as in the benthic bed (temperature gradients, turbation, or sedimentation rate) contribute to supply nutrients to a potential microbial ecosystem. High altitude, oligotrophic, and deep Andean lakes with active deglaciation processes and recent or past volcanic activity are natural models to assess the feasibility of life in other planetary lake/ocean environments and to develop technology for their exploration. We sampled the benthic sediments (down to 269 m depth) of the oligotrophic lake Laguna Negra (Central Andes, Chile) to investigate its ecosystem through geochemical, biomarker profiling, and molecular ecology studies. The chemistry of the benthic water was similar to the rest of the water column, except for variable amounts of ammonium (up to 2.8 ppm) and nitrate (up to 0.13 ppm). A life detector chip with a 300-antibody microarray revealed the presence of biomass in the form of exopolysaccharides and other microbial markers associated to several phylogenetic groups and potential microaerobic and anaerobic metabolisms such as nitrate reduction. DNA analyses showed that 27% of the Archaea sequences corresponded to a group of ammonia-oxidizing archaea (AOA) similar (97%) to Nitrosopumilus spp. and Nitrosoarchaeum spp. (Thaumarchaeota), and 4% of Bacteria sequences to nitrite-oxidizing bacteria from the Nitrospira genus, suggesting a coupling between ammonia and nitrite oxidation. Mesocosm experiments with the specific AOA inhibitor 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) demonstrated an AOA-associated ammonia oxidation activity with the simultaneous accumulation of nitrate and sulfate. The results showed a rich benthic microbial community dominated by microaerobic and anaerobic metabolisms thriving under aphotic, low temperature (4°C), and relatively high pressure, that might be a suitable terrestrial analog of other planetary settings.

Key Drivers for Copepod Assemblages in a Eutrophic Coastal Brackish Lake

The copepod assemblages and abiotic parameters were investigated at 11 stations in a large coastal lake (Lake Manzalah, Nile Delta) from 2009–2010 in order to verify any impacts of eutrophication and salinity on the copepod species composition. The environmental conditions and the copepod assemblages appeared to have changed in comparison with previous studies, possibly because of increasing eutrophication and invasions of non-indigenous species (NIS). The aim of the present study was the identification of species which can be used as ecological indicators of high trophic status. Among the nine copepod species of Lake Manzalah, Acartia tonsa, Mesocyclops ogunnus, and Apocyclops panamensis were reported for the first time. Acartia tonsa, a well-known NIS for the Mediterranean, numerically dominated the copepod assemblages in some portions of the lake. The distribution of Acanthocyclops trajani and Thermocyclops consimilis was insensible to eutrophication because they can stand high levels of nutrients and hypoxia. Compared with previous reports, the copepod assemblage of Lake Manzalah was richer in species. The invasions of NIS, in addition to the heterogeneous progress of eutrophication in the lake, created an environmental mosaic with many species in total, but with single areas suitable for only a small number of them.

Horizontal distribution of pelagic crustacean zooplankton biomass and body size in contrasting habitat types in Lake Poyang, China

To evaluate the possible effects of habitat type on crustacean plankton (hereafter zooplankton) biomass and body size, a 5-year study (2011 to 2015) was conducted during wet seasons in three habitats in Lake Poyang, China. The lacustrine habitat with the most stable hydrologic regime had the highest zooplankton biomass coinciding with the highest phytoplankton biomass. The riverine habitat with the lowest Secchi depth overall had the largest zooplankton body size, but high zooplankton biomass only in high water level years. The seasonally inundated floodplain habitats had the lowest zooplankton biomass and the smallest individual body size, coinciding with the lowest phytoplankton biomass and the highest predation pressure, the latter indicated by a low zooplankton: phytoplankton biomass ratio (ZB:PB). Multiple linear regression analyses indicated that pelagic zooplankton assemblages were primarily influenced by phytoplankton biomass in lacustrine habitat, by advection and turbidity in riverine regions, and by predation pressure in seasonally inundated floodplain region. We conclude that the importance of bottom-up and top-down effects on zooplankton biomass and body size varied with habitat type in Lake Poyang.