Phosphorus (P) is a non-renewable resource, a major plant nutrient that is essential for modern agriculture. Currently, global food and feed production depends on P extracted from finite phosphate ...rock reserves mainly confined to a small number of countries. P limitation and its potential socio-economic impact may well exceed the potential effects of fossil fuel scarcity. The efficiency of P usage today barely reaches 20%, with the remaining 80% ending up in wastewater or in surface waters as runoff from fields. When recovered from wastewater, either chemically or biologically, P is often present in a form that does not meet specifications for agricultural use. As an alternative, the potential of microalgae to accumulate large quantities of P can be a way to direct this resource back to crop plants. Algae can acquire and store P through luxury uptake, and the P enriched algal biomass can be used as bio-fertilizer. Technology of large-scale algae cultivation has made tremendous progress in the last decades, stimulated by perspectives of obtaining third generation biofuels without requiring arable land or fresh water. These new cultivation technologies can be used for solar-driven recycling of P and other nutrients from wastewater into algae-based bio-fertilizers. In this paper, we review the specifics of P uptake from nutrient-rich waste streams, paying special attention to luxury uptake by microalgal cells and the potential application of P-enriched algal biomass to fertilize crop soils.
We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland ...waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of carbon transformation in inland waters. This synthesis demonstrates that the global annual emissions of carbon dioxide from inland waters to the atmosphere are similar in magnitude to the carbon dioxide uptake by the oceans and that the global burial of organic carbon in inland water sediments exceeds organic carbon sequestration on the ocean floor. The role of inland waters in global carbon cycling and climate forcing may be changed by human activities, including construction of impoundments, which accumulate large amounts of carbon in sediments and emit large amounts of methane to the atmosphere. Methane emissions are also expected from lakes on melting permafrost. The synthesis presented here indicates that (1) inland waters constitute a significant component of the global carbon cycle, (2) their contribution to this cycle has significantly changed as a result of human activities, and (3) they will continue to change in response to future climate change causing decreased as well as increased abundance of lakes as well as increases in the number of aquatic impoundments.
Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, ...we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium
Synechocystis
sp. PCC 6803, the green alga
Chlorella sorokiniana
and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga
C. sorokiniana
were similar in blue and red light, but lower in orange light. Oxygen production rates of
Synechocystis
sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as
Prochlorococcus
, green algae and terrestrial plants.
Advances in ecological stoichiometry, a rapidly expanding research field investigating the elemental composition of organisms and their environment, have shed new light on the impacts of climate ...change on freshwater and marine ecosystems. Current changes in the Earth's climate alter the availability of carbon and nutrients in lakes and oceans. In particular, atmospheric CO₂ concentrations will rise to unprecedented levels by the end of this century, while global warming will enhance stratification of aquatic ecosystems and may thereby diminish the supply of nutrients into the surface layer. These processes enrich phytoplankton with carbon, but suppress nutrient availability. Phytoplankton with a high carbon-to-nutrient content provide poor-quality food for most zooplankton species, which may shift the species composition of zooplankton and higher trophic levels to less nutrient-demanding species. As a consequence, climate-driven changes in plankton stoichiometry may alter the structure and functioning of entire aquatic food webs.
Summary
1. Rising atmospheric CO2 concentrations might affect the primary production and community composition of freshwater ecosystems.
2. We investigated these potential effects in laboratory ...mesocosms (Limnotrons), using monoculture experiments and competition experiments with the green alga Scenedesmus obliquus and the cyanobacterium Synechocystis sp. PCC6803. The Limnotrons were sparged with ambient air (controls, 380 parts per million volume (ppmv) CO2), moderately elevated CO2 levels (3000 ppmv CO2) or highly elevated CO2 levels (18 800 ppmv CO2).
3. Growth at ambient air led to the depletion of dissolved CO2 during algal bloom development and hence a high pH. In contrast, growth at elevated CO2 levels resulted in high concentrations of dissolved CO2 and dissolved inorganic carbon (DIC), lower pH and low concentrations of nitrate and soluble reactive phosphorus. Elevated CO2 levels did not have a significant effect on the biomass of the algal species, but shifted their elemental composition towards higher carbon‐to‐nutrient ratios.
4. Competition experiments at ambient air were driven mainly by competition for inorganic carbon. In this case, the cyanobacterium Synechocystis was displaced by the green alga Scenedesmus. Elevated CO2 alleviated the community from carbon limitation, which shifted the species interactions towards competition for nitrogen and phosphorus, and resulted in coexistence of the two species. Hence, our findings do not support the hypothesis that cyanobacteria are generally better competitors for inorganic carbon than green algae.
5. In conclusion, our results show that elevated CO2 levels may cause major changes in freshwater ecosystems, including a reduction in pH, shifts in resource limitation patterns, and changes in the ecological stoichiometry and species composition of phytoplankton communities.
A community-wide outbreak of Legionnaires' disease (LD) occurred in Genesee County, Michigan, in 2014 and 2015. Previous reports about the outbreak are conflicting and have associated the outbreak ...with a change of water source in the city of Flint and, alternatively, to a Flint hospital.
The objective of this investigation was to independently identify relevant sources of
that likely resulted in the outbreak.
An independent, retrospective investigation of the outbreak was conducted, making use of public health, health care, and environmental data and whole-genome multilocus sequence typing (wgMLST) of clinical and environmental isolates.
Strong evidence was found for a hospital-associated outbreak in both 2014 and 2015:
) 49% of cases had prior exposure to Flint hospital A, significantly higher than expected from Medicare admissions;
) hospital plumbing contained high levels of
;
)
control measures in hospital plumbing aligned with subsidence of hospital A-associated cases; and
) wgMLST showed
isolates from cases exposed to hospital A and from hospital plumbing to be highly similar. Multivariate analysis showed an increased risk of LD in 2014 for people residing in a home that received Flint water or was located in proximity to several Flint cooling towers.
This is the first LD outbreak in the United States with evidence for three sources (in 2014):
) exposure to hospital A,
) receiving Flint water at home, and
) residential proximity to cooling towers; however, for 2015, evidence points to hospital A only. Each source could be associated with only a proportion of cases. A focus on a single source may have delayed recognition and remediation of other significant sources of
. https://doi.org/10.1289/EHP5663.
Effects of food quality and quantity on consumers are neither independent nor interchangeable. Although consumer growth and reproduction show strong variation in relation to both food quality and ...quantity, the effects of food quality or food quantity have usually been studied in isolation. In two experiments, we studied the growth and reproduction in three filter-feeding freshwater zooplankton species, i.e. Daphnia galeata x hyalina, D. pulicaria and D. magna, on their algal food (Scenedesmus obliquus), varying in carbon to phosphorus (C∶P) ratios and quantities (concentrations). In the first experiment, we found a strong positive effect of the phosphorus content of food on growth of Daphnia, both in their early and late juvenile development. Variation in the relationship between the P-content of animals and their growth rate reflected interspecific differences in nutrient requirements. Although growth rates typically decreased as development neared maturation, this did not affect these species-specific couplings between growth rate and Daphnia P-content. In the second experiment, we examined the effects of food quality on Daphnia growth at different levels of food quantity. With the same decrease in P-content of food, species with higher estimated P-content at zero growth showed a larger increase in threshold food concentrations (i.e. food concentration sufficient to meet metabolic requirements but not growth). These results suggest that physiological processes such as maintenance and growth may in combination explain effects of food quality and quantity on consumers. Our study shows that differences in response to variation in food quality and quantity exist between species. As a consequence, species-specific effects of food quality on consumer growth will also determine how species deal with varying food levels, which has implications for resource-consumer interactions.
1. In order to test the effect of Ochromonas sp., a mixotrophic chrysophyte, on cyanobacteria, grazing experiments were performed under controlled conditions. We studied grazing on three Microcystis ...aeruginosa strains, varying in toxicity and morphology, as well as on one filamentous cyanobacterium, Pseudanabaena sp. Furthermore, we analysed the co-occurrence of Ochromonas and Microcystis in natural systems in relation to various environmental parameters (TP, TN, DOC, temperature, pH), using data from 460 Norwegian lakes. 2. Ochromonas was able to feed on all four cyanobacterial strains tested, and grew quickly on all of them. The chrysophyte caused net growth reductions in all three Microcystis strains (the very toxic single-celled strain PCC 7806; the less toxic colony-forming Bear AC and the less toxic single-celled Spring CJ). The effect of Ochromonas was strongest on the Spring CJ strain. Although the effect of Ochromonas grazing on the growth of Pseudanabaena was relatively smaller, it also reduced the net growth of this cyanobacterium significantly. 3. After 4 days of incubation with Ochromonas the total amount of cyanotoxins in the three Microcystis strains was reduced by 91.1-98.7% compared with the controls. 4. Ochromonas occurred in similar densities across all 460 Norwegian lakes. Microcystis occurred only at higher TN, TP, temperature and pH values, although its density was often several orders of magnitude higher than that of Ochromonas. Ochromonas co-occurred in 94% of the samples in which Microcystis was present. 5. From our study it is not clear whether Ochromonas could control Microcystis blooms in natural lakes. However, our study does demonstrate that Ochromonas usually occurs in lakes with Microcystis, and our small scale experiments show that Ochromonas can strongly reduce the biomass of Microcystis and its toxin content.
Resource edibility is a crucial factor in ecological theory on the relative importance of bottom-up and top-down control. Current theory explains trophic structure in terms of the relative abundance ...and succession of edible and inedible species across gradients of primary productivity. We argue that this explanation is incomplete owing to its focus on inedibility and the assumption that plants and herbivores have fixed defense levels. Consumer-induced defenses are an important source of variation in the vulnerability of prey and are prevalent in natural communities. Such induced defenses decrease per capita consumption rates of consumers but hardly ever result in complete inedibility. When defenses are inducible a prey population may consist of both undefended and defended individuals. Here we use food chain models with realistic parameter values to show that variation in consumption rates on different prey types causes a gradual instead of stepwise increase in the biomass of all trophic levels in response to enrichment. Such all-level responses have been observed in both aquatic and terrestrial ecosystems and in microbial food chains in the laboratory. We stress that, in addition to the known food web effects of interspecific variation in edibility, intraspecific variation in edibility is another form of within-trophic-level heterogeneity that also has such effects. We conclude that inducible defenses increase the relative importance of bottom-up control.
Inducible defenses are dynamic traits that modulate the strength of both plant-herbivore and herbivore-carnivore interactions. Surprisingly few studies have considered the relative contributions of ...induced plant and herbivore defenses to the overall balance of bottom-up and top-down control. Here we compare trophic cascade strengths using replicated two-level and three-level plankton communities in which we systematically varied the presence or absence of induced defenses at the plant and/or herbivore levels. Our results show that a trophic cascade, i.e., significantly higher plant biomass in three-level than in two-level food chains, occurred whenever herbivores were undefended against carnivores. Trophic cascades did not occur when herbivores exhibited an induced defense. This pattern was obtained irrespective of the presence or absence of induced defenses at the plant level. We thus found that herbivore defenses, not plant defenses, had an overriding effect on cascade strength. We discuss these results in relation to variation in cascade strengths in natural communities.
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