Managing nitrogen to restore water quality in China.

The nitrogen cycle has been radically changed by human activities1. China consumes nearly one third of the world's nitrogen fertilizers. The excessive application of fertilizers2,3 and increased nitrogen discharge from livestock, domestic and industrial sources have resulted in pervasive water pollution. Quantifying a nitrogen 'boundary'4 in heterogeneous environments is important for the effective management of local water quality. Here we use a combination of water-quality observations and simulated nitrogen discharge from agricultural and other sources to estimate spatial patterns of nitrogen discharge into water bodies across China from 1955 to 2014. We find that the critical surface-water quality standard (1.0 milligrams of nitrogen per litre) was being exceeded in most provinces by the mid-1980s, and that current rates of anthropogenic nitrogen discharge (14.5 ± 3.1 megatonnes of nitrogen per year) to fresh water are about 2.7 times the estimated 'safe' nitrogen discharge threshold (5.2 ± 0.7 megatonnes of nitrogen per year). Current efforts to reduce pollution through wastewater treatment and by improving cropland nitrogen management can partially remedy this situation. Domestic wastewater treatment has helped to reduce net discharge by 0.7 ± 0.1 megatonnes in 2014, but at high monetary and energy costs. Improved cropland nitrogen management could remove another 2.3 ± 0.3 megatonnes of nitrogen per year-about 25 per cent of the excess discharge to fresh water. Successfully restoring a clean water environment in China will further require transformational changes to boost the national nutrient recycling rate from its current average of 36 per cent to about 87 per cent, which is a level typical of traditional Chinese agriculture. Although ambitious, such a high level of nitrogen recycling is technologically achievable at an estimated capital cost of approximately 100 billion US dollars and operating costs of 18-29 billion US dollars per year, and could provide co-benefits such as recycled wastewater for crop irrigation and improved environmental quality and ecosystem services.

Land use change and coastal water darkening drive synchronous dynamics in phytoplankton and fish phenology on centennial timescales.

At high latitudes, the suitable window for timing reproductive events is particularly narrow, promoting tight synchrony between trophic levels. Climate change may disrupt this synchrony due to diverging responses to temperature between, for example, the early life stages of higher trophic levels and their food resources. Evidence for this is equivocal, and the role of compensatory mechanisms is poorly understood. Here, we show how a combination of ocean warming and coastal water darkening drive long-term changes in phytoplankton spring bloom timing in Lofoten Norway, and how spawning time of Northeast Arctic cod responds in synchrony. Spring bloom timing was derived from hydrographical observations dating back to 1936, while cod spawning time was estimated from weekly fisheries catch and roe landing data since 1877. Our results suggest that land use change and freshwater run-off causing coastal water darkening has gradually delayed the spring bloom up to the late 1980s after which ocean warming has caused it to advance. The cod appear to track phytoplankton dynamics by timing gonadal development and spawning to maximize overlap between offspring hatch date and predicted resource availability. This finding emphasises the importance of land-ocean coupling for coastal ecosystem functioning, and the potential for fish to adapt through phenotypic plasticity.

Climate change vulnerability of Arctic char across Scandinavia.

Climate change is anticipated to cause species to shift their ranges upward and poleward, yet space for tracking suitable habitat conditions may be limited for range-restricted species at the highest elevations and latitudes of the globe. Consequently, range-restricted species inhabiting Arctic freshwater ecosystems, where global warming is most pronounced, face the challenge of coping with changing abiotic and biotic conditions or risk extinction. Here, we use an extensive fish community and environmental dataset for 1762 lakes sampled across Scandinavia (mid-1990s) to evaluate the climate vulnerability of Arctic char (Salvelinus alpinus), the world's most cold-adapted and northernly distributed freshwater fish. Machine learning models show that abiotic and biotic factors strongly predict the occurrence of Arctic char across the region with an overall accuracy of 89 percent. Arctic char is less likely to occur in lakes with warm summer temperatures, high dissolved organic carbon levels (i.e., browning), and presence of northern pike (Esox lucius). Importantly, climate warming impacts are moderated by habitat (i.e., lake area) and amplified by the presence of competitors and/or predators (i.e., northern pike). Climate warming projections under the RCP8.5 emission scenario indicate that 81% of extant populations are at high risk of extirpation by 2080. Highly vulnerable populations occur across their range, particularly near the southern range limit and at lower elevations, with potential refugia found in some mountainous and coastal regions. Our findings highlight that range shifts may give way to range contractions for this cold-water specialist, indicating the need for pro-active conservation and mitigation efforts to avoid the loss of Arctic freshwater biodiversity.

Drivers of change in China's energy-related CO2 emissions.

CO2 emissions are of global concern because of climate change. China has become the largest CO2 emitter in the world and presently accounts for 30% of global emissions. Here, we analyze the major drivers of energy-related CO2 emissions in China from 1978 when the reform and opening-up policy was launched. We find that 1) there has been a 6-fold increase in energy-related CO2 emissions, which was driven primarily (176%) by economic growth followed by population growth (16%), while the effects of energy intensity (-79%) and carbon intensity (-13%) slowed the growth of carbon emissions over most of this period; 2) energy-related CO2 emissions are positively related to per capita gross domestic product (GDP), population growth rate, carbon intensity, and energy intensity; and 3) a portfolio of command-and-control policies affecting the drivers has altered the total emission trend. However, given the major role of China in global climate change mitigation, significant future reductions in China's CO2 emissions will require transformation toward low-carbon energy systems.

Greenhouse gas emissions from extractive industries in a globalized era.

The extractive industry consumes vast amounts of energy and is a major contributor to greenhouse gas (GHG) emissions. However, its climatic impacts have not yet been fully accounted for. In this study, we estimated the GHG emissions from extractive activities globally with a focus on China, and assessed the main emission drivers. In addition, we predicted the Chinese extractive industry emissions in the context of global mineral demand and cycling. As of 2020, GHG emissions from the global extractive industry had reached 7.7 billion tons of CO2 equivalents (CO2e), accounting for approximately 15.0% of the global anthropogenic GHG emissions (excluding GHG emissions from land use, land-use change, and forestry activities (LULUCF), with China being the largest emitter, accounting for 3.5% of global emissions. Extractive industry GHG emissions are projected to peak by 2030 or even earlier to achieve low-carbon peak targets. The most critical pathway for reducing GHG emissions in the extractive industry is to control emissions from coal mining. Therefore, reducing methane emissions from mining and washing coal (MWC) should be prioritized.

Landscape determinants of pelagic and benthic primary production in northern lakes.

Global change affects gross primary production (GPP) in benthic and pelagic habitats of northern lakes by influencing catchment characteristics and lake water biogeochemistry. However, how changes in key environmental drivers manifest and impact total (i.e., benthic + pelagic) GPP and the partitioning of total GPP between habitats represented by the benthic share (autotrophic structuring) is unclear. Using a dataset from 26 shallow lakes located across Arctic, subarctic, and boreal northern Sweden, we investigate how catchment properties (air temperature, land cover, hydrology) affect lake physico-chemistry and patterns of total GPP and autotrophic structuring. We find that total GPP was mostly light limited, due to high dissolved organic carbon (DOC) concentrations originating from catchment soils with coniferous vegetation and wetlands, which is further promoted by high catchment runoff. In contrast, autotrophic structuring related mostly to the relative size of the benthic habitat, and was potentially modified by CO2 fertilization in the subarctic, resulting in significantly higher total GPP relative to the other biomes. Across Arctic and subarctic sites, DIC and CO2 were unrelated to DOC, indicating that external inputs of inorganic carbon can influence lake productivity patterns independent of terrestrial DOC supply. By comparison, DOC and CO2 were correlated across boreal lakes, suggesting that DOC mineralization acts as an important CO2 source for these sites. Our results underline that GPP as a resource is regulated by landscape properties, and is sensitive to large-scale global changes (warming, hydrological intensification, recovery of acidification) that promote changes in catchment characteristics and aquatic physico-chemistry. Our findings aid in predicting global change impacts on autotrophic structuring, and thus community structure and resource use of aquatic consumers in general. Given the similarities of global changes across the Northern hemisphere, our findings are likely relevant for northern lakes globally.

Water Browning Controls Adaptation and Associated Trade-Offs in Phytoplankton Stressed by Chemical Pollution.

The acquisition of tolerance to an environmental stressor can result in organisms displaying slower growth after stress release. While well-grounded in the theory, empirical evidence of the trade-off between stress tolerance and organism fitness is scarce and blurred by the interaction with different environmental factors. Here, we report the effects of water browning on the responses, tolerance acquisition, and associated trade-offs in a population of microalgae exposed to sublethal concentrations of organic micropollutants over multiple generations. Our results show that dissolved organic matter (DOM) reduces toxic responses and modulates tolerance acquisition by the algae, possibly by complexing micropollutants. Microalgae that acquire tolerance allocate resources to fitness at the cost of reduced cell size. They yield higher productivity than nonadapted ones when grown in the presence of micropollutants but lower in their absence. The net trade-off was positive, indicating that adaptation can result in a higher productivity and fitness in tolerant species in recurrently stressed environments.

Relative and absolute cancer risks among Nordic kidney transplant recipients-a population-based study.

Kidney transplant recipients (KTRs) have an increased cancer risk compared to the general population, but absolute risks that better reflect the clinical impact of cancer are seldom estimated. All KTRs in Sweden, Norway, Denmark, and Finland, with a first transplantation between 1995 and 2011, were identified through national registries. Post-transplantation cancer occurrence was assessed through linkage with cancer registries. We estimated standardized incidence ratios (SIR), absolute excess risks (AER), and cumulative incidence of cancer in the presence of competing risks. Overall, 12 984 KTRs developed 2215 cancers. The incidence rate of cancer overall was threefold increased (SIR 3.3, 95% confidence interval [CI]: 3.2-3.4). The AER of any cancer was 1560 cases (95% CI: 1468-1656) per 100 000 person-years. The highest AERs were observed for nonmelanoma skin cancer (838, 95% CI: 778-901), non-Hodgkin lymphoma (145, 95% CI: 119-174), lung cancer (126, 95% CI: 98.2-149), and kidney cancer (122, 95% CI: 98.0-149). The five- and ten-year cumulative incidence of any cancer was 8.1% (95% CI: 7.6-8.6%) and 16.8% (95% CI: 16.0-17.6%), respectively. Excess cancer risks were observed among Nordic KTRs for a wide range of cancers. Overall, 1 in 6 patients developed cancer within ten years, supporting extensive post-transplantation cancer vigilance.

Possible adverse impact of contaminants on Atlantic cod population dynamics in coastal ecosystems.

While many in-laboratory ecotoxicological studies have shown the adverse impact of pollutants to the fitness of an individual, direct evidence from the field on the population dynamics of wildlife animals has been lacking. Here, we provide empirical support for a negative effect of pollution on Atlantic cod (Gadus morhua) population dynamics in coastal waters of Norway by combining unique time series of juvenile cod abundance, body size, environmental concentration of toxic contaminants and a spatially structured population dynamics model. The study shows that mercury concentration might have decreased the reproductive potential of cod in the region despite the general decline in the environmental concentration of mercury, cadmium and hexachlorobenzene since the implementation of national environmental laws. However, some cod populations appeared to be more resistant to mercury pollution than others, and the strength and shape of mercury effect on cod reproductive potential was fjord-specific. Additionally, cod growth rate changed at scales smaller than fjords with a gradient related to the exposure to the open ocean and offshore cod. These spatial differences in life-history traits emphasize the importance of local adaptation in shaping the dynamics of local wildlife populations. Finally, this study highlights the possibility to mitigate pollution effects on natural populations by reducing the overall pollution level, but also reveals that pollution reduction alone is not enough to rebuild local cod populations. Cod population recovery probably requires complementary efforts on fishing regulation and habitat restoration.

Global change-driven effects on dissolved organic matter composition: Implications for food webs of northern lakes.

Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.

Will Invertebrates Require Increasingly Carbon-Rich Food in a Warming World?

Elevated temperature causes metabolism and respiration to increase in poikilothermic organisms. We hypothesized that invertebrate consumers will therefore require increasingly carbon-rich diets in a warming environment because the increased energetic demands are primarily met using compounds rich in carbon, that is, carbohydrates and lipids. Here, we test this hypothesis using a new stoichiometric model that has carbon (C) and nitrogen (N) as currencies. Model predictions did not support the hypothesis, indicating instead that the nutritional requirements of invertebrates, at least in terms of food quality expressed as C∶N ratio, may change little, if at all, at elevated temperature. Two factors contribute to this conclusion. First, invertebrates facing limitation by nutrient elements such as N have, by default, excess C in their food that can be used to meet the increased demand for energy in a warming environment, without recourse to extra dietary C. Second, increased feeding at elevated temperature compensates for the extra demands of metabolism to the extent that, when metabolism and intake scale equally with temperature (have the same Q10), the relative requirement for dietary C and N remains unaltered. Our analysis demonstrates that future climate-driven increases in the C∶N ratios of autotroph biomass will likely exacerbate the stoichiometric mismatch between nutrient-limited invertebrate grazers and their food, with important consequences for C sequestration and nutrient cycling in ecosystems.

Cascading effects of mass mortality events in Arctic marine communities.

Mass mortality events caused by pulse anthropogenic or environmental perturbations (e.g., extreme weather, toxic spills or epizootics) severely reduce the abundance of a population in a short time. The frequency and impact of these events are likely to increase across the globe. Studies on how such events may affect ecological communities of interacting species are scarce. By combining a multispecies Gompertz model with a Bayesian state-space framework, we quantify community-level effects of a mass mortality event in a single species. We present a case study on a community of fish and zooplankton in the Barents Sea to illustrate how a mass mortality event of different intensities affecting the lower trophic level (krill) may propagate to higher trophic levels (capelin and cod). This approach is especially valuable for assessing community-level effects of potential anthropogenic-driven mass mortality events, owing to the ability to account for uncertainty in the assessed impact due to uncertainty about the ecological dynamics. We hence quantify how the assessed impact of a mass mortality event depends on the degree of precaution considered. We suggest that this approach can be useful for assessing the possible detrimental outcomes of toxic spills, for example oil spills, in relatively simple communities such as often found in the Arctic, a region under increasing influence of human activities due to increased land and sea use.

A rapid and sustained improvement of calcification propensity score (serum T50 ) after successful kidney transplantation: Reanalysis of a randomized controlled trial of ibandronate.

A serum test called T50 assesses the overall propensity for calcification of the blood and is associated with cardiovascular outcomes. We aimed to examine T50 over time in kidney transplant recipients and also address any effects of ibandronate. Serum samples taken from kidney transplant patients included in a prospective, randomized placebo controlled study of ibandronate were analyzed in retrospect. Adequate analyses were performed at baseline (approximately 3 weeks after transplantation) in 129 patients, at 10 weeks in 127 patients and at 1 year in 123 patients. There were no statistical differences between ibandronate and placebo treatment in terms of T50 at 10 weeks (P = .094) or at 1 year (P = .116). Baseline T50 was a significant covariate (P < .0001) for T50 scores at 10 weeks and 1 year. In the total cohort, there was a highly significant (P < .0001) increase in T50 of 26.6% after 10 weeks and T50 remained stable after 1 year. T50 change was inversely correlated to phosphate of -0.515 (P < .0001) and to change in serum albumin (P < .03). We found that T50 increased from baseline to 10 weeks after transplantation with no further change after 1 year. Ibandronate had no effect on T50 .

The impact of irradiance on optimal and cellular nitrogen to phosphorus ratios in phytoplankton.

Phytoplankton acclimates to irradiance by regulating the cellular content of light-harvesting complexes, which are nitrogen (N) rich and phosphorus (P) poor. Irradiance is thus hypothesised to influence the cellular N : P ratio and the N : P defining the threshold between N and P limitation (the 'optimal' N : P). We tested this hypothesis by first addressing the response of the optimal N : P to irradiance in a controlled experiment with Chlamydomonas reinhardtii. Then, we did a meta-analysis of experimental data on optimal and cellular N : P ratios across light gradients to test the generality of an N : P to light response within species. In both the experiment and the meta-analysis, N : P ratios decreased with irradiance, indicating that factors affecting underwater irradiance, like depth and the composition of the water, may influence the relative N : P requirement. The effect of irradiance did not differ between optimal and cellular N : P ratios, but observations of optimal N : P were on average 2.8 times higher than observations of cellular N : P.

Can IVF influence human evolution?

IVF, a procedure in which pharmacological and technological manipulation is used to promote pregnancy, offers help to infertile couples by circumventing selection at the most fundamental level. Fertility is clearly one of the key fitness-promoting drivers in all forms of sexually reproducing life, and fertilization and pregnancy are fundamental evolutionary processes that involve a range of pre- and post-zygotic screening mechanisms. Here, we discuss the various selection and screening factors involved in fertilization and pregnancy and assess IVF practices in light of these factors. We then focus on the possible consequences of these differences in selection pressures, mainly at the individual but also at the population level, to evaluate whether changes in the reproducing genotype can affect human evolution. The aim of the article is not to argue for or against IVF, but to address aspects of assisted reproduction in an evolutionary context.

Plasma levels of marine n-3 polyunsaturated fatty acids and renal allograft survival.

BACKGROUND: Marine n-3 polyunsaturated fatty acids (PUFAs) may exert beneficial effects on inflammation, fibrosis, endothelial function, lipid profile and blood pressure that may prevent graft loss. METHODS: In this observational cohort study in Norwegian renal transplant recipients (n = 1990), transplanted between 1999 and 2011, associations between plasma marine n-3 PUFA levels and graft loss were assessed by multivariable Cox proportional hazard regression analysis. Plasma phospholipid fatty acid composition was determined by gas chromatography and individual fatty acids recorded as weight percentage (wt%) of total fatty acids in a stable phase 10 weeks after transplantation. RESULTS: During a median follow-up time of 6.8 years, 569 (28.6%) renal allografts were lost, either due to patient death (n = 340, 59.8% of graft loss) or graft loss in surviving patients (n = 229, 40.2%). Plasma marine n-3 PUFA levels ranged from 1.35 to 23.87 wt%, with a median level of 7.95 wt% (interquartile range 6.20-10.03 wt%). When adjusting for established graft loss risk factors, there was a 11% reduced risk of graft loss for every 1.0 wt% increase in marine n-3 PUFA level [adjusted hazard ratio (HR) 0.89; 95% confidence interval (CI) 0.84-0.93], and a 10% reduced risk of graft loss in surviving patients (adjusted HR 0.90; 95% CI 0.84-0.97). CONCLUSION: High levels of plasma marine n-3 PUFAs were associated with better renal allograft survival.

Temperature and developmental responses of body and cell size in Drosophila; effects of polyploidy and genome configuration.

Increased adult body size in Drosophila raised at lower temperatures could be attributed both to an increase in the cell volume and cell number. It is not clear, however, whether increased cell size is related to (or even caused by) increased nuclear volume and genome size (or configuration). Experiments with Drosophila melanogaster stocks (Oregon-R and w1118) raised at 16, 22, 24, and 28°C resulted in larger adult body and wing size with lower temperature, while eye size was less affected. The increase in wing size reflected an increase in cell size in both males and females of both stocks. The nucleus size, genome size, and DNA condensation of adult flies, embryos, and Schneider 2 cells (S2 cells, of larval origin) were estimated by flow cytometry. In both adult flies and S2 cells, both nucleus size and DNA condensation varied with temperature, while DNA content appears to be constant. From 12% to 18% of the somatic cells were tetraploid (4C) and 2-5% were octoploid (8C), and for the Oregon strain we observed an increase in the fraction of polyploid cells with decreasing temperature. The observed increase in body size (and wing size) at low temperatures could partly be linked with the cell size and DNA condensation, while corresponding changes in the haploid genome size were not observed.

Unimodal response of fish yield to dissolved organic carbon.

Here, we demonstrate a contrasting effect of terrestrial coloured dissolved organic material on the secondary production of boreal nutrient poor lakes. Using fish yield from standardised brown trout gill-net catches as a proxy, we show a unimodal response of lake secondary productivity to dissolved organic carbon (DOC). This suggests a trade-off between positive and negative effects, where the initial increase may hinge upon several factors such as energy subsidising, screening of UV-radiation or P and N load being associated with organic carbon. The subsequent decline in production with further increase in DOC is likely associated with light limitations of primary production. We also show that shallow lakes switch from positive to negative effects at higher carbon loads than deeper lakes. These results underpin the major role of organic carbon for structuring productivity of boreal lake ecosystems.

Multigenerational genomic responses to dietary phosphorus and temperature in Daphnia.

Temperature and nutrient availability are both hypothesized to affect organisms at the cellular and genomic levels. In this multigenerational study, Daphnia magna (D. magna) and Daphnia pulex (D. pulex) were maintained at high (20 °C) and low (10 °C) temperatures and nourished with phosphorus (P)-sufficient (50 µmol/L) and P-deficient (2 µmol/L) algae for up to 35 generations to assess the multigenerational impacts on genome size and nucleus size. Analysis by flow cytometry revealed significant increases in nucleus size for both species as well as genome size for D. magna in response to a low temperature. The degree of endoreplication, measured as cycle value, was species specific and responded to temperature and dietary composition. Under dietary P deficiency, D. magna, but not D. pulex, showed an apparent reduction in haploid genome size (C-value). These genomic responses are unlikely to reflect differences in nucleotide numbers, but rather structural changes affecting fluorochrome binding. While the ultimate and proximate causes of these responses are unknown, they suggest an intriguing potential for genomic responses that merits further research.