Aquatic resources [fish, amphibians, some reptiles, various invertebrates (prawns, crabs, snails, insects), and varieties of wild aquatic plants] are an important but neglected wild food resource to address food security and poverty reduction in the Lao People’s Democratic Republic. Food security is strongly affected by the relationship between aquatic resources and rice. Intensification of rice production could negatively impact wild aquatic resources through conversion of wetland areas, among other factors. This summary is not an official abstract. Users should refer to the original published version of the material for the full abstract
This study identified characteristics of aquatic environments associated with high levels of Hg in fish. Multiple regression revealed significantly higher mean Hg levels in key species during descending waters in lotic environments and low waters in lentic environments. Watersheds with high aquatic vegetation cover and low forest cover corresponded to high Hg concentrations in fish and the converse suggesting watershed land uses play a key role in Hg contamination levels of local fish. This summary is not an official abstract. Users should refer to the original published version of the material for the full abstract
This study demonstrates how soil erosion increases surficial sediment mercury concentrations in aquatic systems of the Tapajós and Arapiuns rivers, exploited by human riverine populations. It reveals how environmental changes associated with recent colonization of drainage basins and growing exploitation of new land disturb mineral, organic matter and mercury cycles. This summary is not an official abstract. Users should refer to the original published version of the material for the full abstract
Focusing principally on pastoral grazing and integrated crop- livestock systems, this paper examines the less widely documented case of positive environmental externalities associated with livestock production (e.g. enhancing soil fertility and nutrient cycling, supporting sustainable rangeland management, preserving wildlife and other forms of biodiversity). This summary is not an official abstract. Users should refer to the original published version of the material for the full abstract
Toxic substances, particularly pesticides, bio-accumulate in the food chain and can accumulate enough to place top levels at risk. Less known are the many complex pathways by which human alterations of ecosystems pose public health risks. Among these are changes in the distribution of human pathogens as a result of human-created ecological imbalance. Connections between human health outcomes and the health of ecosystems are complex and not easy to quantify owing to the complexity of the relationship. We need to take into account the capacity of human societies to buffer adverse health effects (through public health and medical services), inherent lags between environmental changes and organism response and the fact that health outcomes are the summation of many influences. This summary is not an official abstract. Users should refer to the original published version of the material for the full abstract
Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined; more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet.
Parasitic and infectious diseases (PIDs) are a significant threat to human, livestock, and wildlife health and are changing dramatically in the face of human-induced environmental changes such as those in climate and land use. In this article we explore the little-studied but potentially important response of PIDs to another major environmental change, that in the global nutrient cycles. Humans have now altered the nitrogen (N) cycle to an astonishing degree, and those changes are causing a remarkable diversity of environmental and ecological responses. Since most PIDs are strongly regulated by ecological interactions, changes in nutrients are likely to affect their dynamics in a diversity of environments. We show that while direct tests of the links between nutrients and disease are rare, there is mounting evidence that higher nutrient levels frequently lead to an increased risk of disease. This trend occurs across multiple pathogen types, including helminths, insectvectored diseases, myxozoa, and bacterial and fungal diseases. The mechanistic responses to increased nutrients are often complex and frequently involve indirect responses that are regulated by intermediate or vector hosts involved in disease transmission. We also show that rapid changes in the N cycle of tropical regions combined with the high diversity of human PIDs in these regions will markedly increase the potential for N to alter the dynamics of disease. Finally, we stress that progress on understanding the effects of nutrients on disease ecology requires a sustained effort to conduct manipulative experiments that can reveal underlying mechanisms on a species-specific basis.
The fundamental biophysical cause of stagnant per capita food production in Africa is soil fertility depletion. Because mineral fertilizers cost two to six times as much as those sold worldwide, a soil fertility replenishment approach has been developed based on naturally available resources: nitrogen-fixing leguminous tree fallows that accumulate 100 to 200 kg N ha, indigenous rock phosphate applications, and biomass transfers of the nutrient-accumulating shrubTithonia diversifolia. Tens of thousands of farmers in East and Southern Africa are becoming food secure with these technologies. Soil fertility depletion must be addressed before other technologies and policies can become effective in overcoming hunger in Africa.
Black carbon in soot is the dominant absorber of visible solar radiation in the atmosphere. Anthropogenic sources of black carbon, although distributed globally, are most concentrated in the tropics where solar irradiance is highest. Black carbon is often transported over long distances, mixing with other aerosols along the way. The aerosol mix can form transcontinental plumes of atmospheric brown clouds, with vertical extents of 3 to 5 km. Because of the combination of high absorption, a regional distribution roughly aligned with solar irradiance, and the capacity to form widespread atmospheric brown clouds in a mixture with other aerosols, emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions. In the Himalayan region, solar heating from black carbon at high elevations may be just as important as carbon dioxide in the melting of snowpacks and glaciers. The interception of solar radiation by atmospheric brown clouds leads to dimming at the Earth's surface with important implications for the hydrological cycle, and the deposition of black carbon darkens snow and ice surfaces, which can contribute to melting, in particular of Arctic sea ice.
Biological productivity in most of the world's oceans is controlled by the supply of nutrients to surface waters. The relative balance between supply and removal of nutrients—including nitrogen, iron and phosphorus—determines which nutrient limits phytoplankton growth. Although nitrogen limits productivity in much of the ocean1, 2, large portions of the tropics and subtropics are defined by extreme nitrogen depletion. In these regions, microbial denitrification removes biologically available forms of nitrogen from the water column, producing substantial deficits relative to other nutrients3, 4, 5. Here we demonstrate that nitrogen-deficient areas of the tropical and subtropical oceans are acutely vulnerable to nitrogen pollution. Despite naturally high nutrient concentrations and productivity6, 7, 8, nitrogen-rich agricultural runoff fuels large (54–577 km2) phytoplankton blooms in the Gulf of California. Runoff exerts a strong and consistent influence on biological processes, in 80% of cases stimulating blooms within days of fertilization and irrigation of agricultural fields. We project that by the year 2050, 27–59% of all nitrogen fertilizer will be applied in developing regions located upstream of nitrogen-deficient marine ecosystems. Our findings highlight the present and future vulnerability of these ecosystems to agricultural runoff.
The concentration of carbon dioxide in Earth’s atmosphere may double by the end of the 21st century. The response of higher plants to a carbon dioxide doubling often includes a decline in their nitrogen status, but the reasons for this decline have been uncertain. We used five independent methods with wheat and Arabidopsis to show that atmospheric carbon dioxide enrichment inhibited the assimilation of nitrate into organic nitrogen compounds. This inhibition may be largely responsible for carbon dioxide acclimation, the decrease in photosynthesis and growth of plants conducting C3 carbon fixation after long exposures (days to years) to carbon dioxide enrichment. These results suggest that the relative availability of soil ammonium and nitrate to most plants will become increasingly important in determining their productivity as well as their quality as food.
Simultaneous measurements of CO and O fluxes from wheat () shoots indicated that short-term exposures to elevated CO concentrations diverted photosynthetic reductant from NO or NO reduction to CO fixation. With longer exposures to elevated CO, wheat leaves showed a diminished capacity for NO photoassimilation at any CO concentration. Moreover, high bicarbonate levels impeded NO translocation into chloroplasts isolated from wheat or pea leaves. These results support the hypothesis that elevated CO inhibits NO photoassimilation. Accordingly, when wheat plants received NO rather than NH as a nitrogen source, CO enhancement of shoot growth halved and CO inhibition of shoot protein doubled. This result will likely have major implications for the ability of wheat to use NO as a nitrogen source under elevated CO.
Nitrogen (N) is the most limiting nutrient for plant growth and primary productivity. Inorganic N is available to plants from the soil as ammonium (NH4+) and nitrate (NO3–). We studied how wheat grown hydroponically to senescence in controlled environmental chambers is affected by N form (NH4+ vs. NO3–) and CO2 concentration (‘subambient’, ‘ambient’, and ‘elevated’) in terms of biomass, yield, and nutrient accumulation and partitioning. NH4+-grown wheat had the strongest response to CO2 concentration. Plants exposed to subambient and ambient CO2 concentrations typically had the greatest biomass and nutrient accumulation under both N forms. In general NH4+ plants had higher concentrations of total N, P, K, S, Ca, Zn, Fe, and Cu, while NO3– plants had higher concentrations of Mg, B, Mn, and NO3–-N. NH4+ plants contained amounts of phytate similar to NO3– plants but had higher bioavailable Zn, which could have ramifications for human health. NH4+ plants allocated more nutrients and biomass to aboveground tissues whereas NO3– plants allocated more nutrients to the roots. The two inorganic nitrogen forms influenced plant growth and nutrient status so distinctly that they should be treated separately. Moreover, plant growth and nutrient status varied in a non-linear manner with atmospheric CO2 concentration.
Food production requires application of fertilizers containing phosphorus, nitrogen and potassium on agricultural fields in order to sustain crop yields. However modern agriculture is dependent on phosphorus derived from phosphate rock, which is a non-renewable resource and current global reserves may be depleted in 50–100 years. While phosphorus demand is projected to increase, the expected global peak in phosphorus production is predicted to occur around 2030. The exact timing of peak phosphorus production might be disputed, however it is widely acknowledged within the fertilizer industry that the quality of remaining phosphate rock is decreasing and production costs are increasing. Yet future access to phosphorus receives little or no international attention. This paper puts forward the case for including long-term phosphorus scarcity on the priority agenda for global food security. Opportunities for recovering phosphorus and reducing demand are also addressed together with institutional challenges.
We summarize the impacts of elevated CO2 on the N concentration of plant tissues and present data to support the hypothesis that reductions in the quality of plant tissue commonly occur when plants are grown under elevated CO2. Synthesis of existing data showed an average 14% reduction of N concentrations in plant tissue generated under elevated CO2 regimes. However, elevated CO2 appeared to have different effects on the N concentrations of different plant types, as the reported reductions in N have been larger in C3 plants than in C4 plants and N2-fixers. Under elevated CO2 plants changed their allocation of N between above- and below-ground components: root N concentrations were reduced by an average of 9% compared to a 14% average reduction for above-ground tissues. Although the concentration of CO2 treatments represented a significant source of variance for plant N concentration, no consistent trends were observed between them. [ABSTRACT FROM AUTHOR]Copyright of Global Change Biology is the property of Blackwell Publishing Limited and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts)
With respect to European growth conditions very little information is available on how future atmospheric CO2 concentrations [CO2] might affect quality characteristics of important crops. Winter wheat cv. ‘Batis’ and winter barley cv. ‘Theresa’ were grown for two growing seasons each under ambient [CO2] (ca. 375 μmol mol−1) and elevated [CO2] (550 μmol mol−1) with two different nitrogen (N) fertilization levels (adequate N supply / ca. 50% of adequate N) in the course of a six year crop rotation. Effects on grain quality and grain elemental composition were investigated. Grain crude protein concentrations were lowered under elevated [CO2] by −4% to −13% in wheat and by −11% to −13% in barley. Reduced N supply decreased crude protein concentrations in wheat and barley by −14% to −22% and by −12% to −19%, respectively. In both species, starch concentration was increased by +4% on average due to reduced N fertilization. In wheat, both CO2 enrichment and low N supply reduced the activity of total and soluble β-amylase (−11% and −7%), Hagberg falling number (−7%), and single kernel hardness (−18%). In barley, both of the treatments induced reductions in the viscosity of the water extract (−25% on average). Concerning minerals, sulphur concentrations were depleted under both elevated [CO2] and low N supply by averages of −5% in wheat and −14% in barley. Reduced N supply caused −8% lower means of wheat grain calcium concentrations and reduced zinc concentrations on average by −23%. According to these results, flour from cereal grains grown under elevated [CO2] and/or low N fertilization will have a diminished nutritional and processing quality and an altered elemental composition.
Potato crops were grown at seven sites across Europe to test the effects of elevated atmospheric carbon dioxide and/or tropospheric ozone concentrations on growth, yield and various aspects of potato tuber quality within the framework of the EC funded programme Changing Climate and Potential Impacts on Potato Yield and Quality (CHIP). Field exposure systems were used to enrich the atmosphere in CO2 and/or ozone. At five of the sites, nutrient element conconcentrations (macronutrients: nitrogen, phosphorus, potassium, calcium, magnesium, and micronutrients: mangenese, zinc, iron) in different parts of plants from the various treatments were analysed. Under elevated CO2, nearly all nutrient elements tended to decrease in concentration. At maximum leaf area, a significant reduction was observed for the concentrations of nitrogen and potassium both in aboveground biomass and in tubers, and for calcium in tubers. Since CO2 enrichment promoted early tuber growth, these effects could in part be attributed to tuber developmental stage. At maturity, potato grown under CO2 enrichment exhibited significantly lower concentrations of nitrogen, manganese and iron in aboveground organs, and of nitrogen, potassium and magnesium in tubers which means a reduction of tuber quality. In contrast to CO2, elevated ozone tended to increase tuber nutrient element concentrations. This was significant for nitrogen and manganese. CO2 effects on tuber biomass increase were more pronounced than CO2 effects on nutrient element decrease. Thus, the total amount of nutrient elements taken up by potato crops increased under elevated CO2. Fertilizer practice in a future, CO2-rich world will have to be adjusted accordingly.