Quantum yield spectra for the photochemical formation of biologically labile photoproducts from dissolved organic matter (DOM) have not been available previously, although they would greatly ...facilitate attempts to model photoproduct formation rates across latitudinal, seasonal, and depth-related changes in spectral irradiance. Apparent quantum yield spectra were calculated for two coastal environments from the southeastern United States using postirradiation bacterial respiration as a measure of total labile photoproduct formation and a cutoff filter method to model spectral dependence. As has been the case for previously studied classes of DOM photoproducts (i.e., dissolved inorganic carbon, CO, and H2O
2), ultraviolet (UV)-B irradiance was significantly more efficient at forming labile photoproducts (i.e., compounds readily assimilated by marine bacterioplankton) than UV-A and visible irradiance. Calculations of DOM photoproduct formation in southeastern U.S. coastal surface waters indicate a formation ratio for biologically labile photoproducts : CO of 13 : 1. The slope of a natural log plot of the apparent quantum yield spectrum obtained for biologically labile photoproducts was similar to that for CO (0.028 nm-1vs. 0.034 nm-1). Modeled kinetic rates therefore indicate that the production ratio of these photoproduct classes is approximately maintained despite variations in the solar spectrum that occur with depth in a water column or distance from shore. Application of the apparent quantum yield to coastal regions worldwide predicts an annual formation rate of biologically labile photoproducts in coastal waters of 206 x 1012g C.
Exposure of riverine waters to natural sunlight initiated alterations in stable carbon isotope ratios (δ13C) of the associated dissolved organic carbon (DOC). Water samples were collected from two ...compositionally distinct coastal river systems in the southeastern United States‐the Satilla River which has high DOC concentrations (10–35 mg/l), and the Altamaha River which has relatively low DOC concentrations (3–9 mg/1). Approximately 21–26% of the DOC was remineralized to DIC. The δ13C of remineralized DIC was isotopically “light” (δ13C = −28.8 to −33.2‰), relative to the initial DOC (δ13C = −27.4‰), leaving a residual fraction of isotopically “heavy” (δ13C = −25.8 to −26.6‰) DOC. Photochemically‐induced fractionation of 13C results from selective degradation of certain biochemical constituents including lignin phenols. These results are consistent with shifts in δ13C of DOC observed during mixing of river and marine waters, suggesting that photochemically‐induced alterations are a factor in determining these changes.
The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with two focal issues. The first focus is ...the effects of increased UV radiation on human health, animals, plants, biogeochemistry, air quality, and materials. The second focus is on interactions between UV radiation and global climate change and how these may affect humans and the environment. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than believed previously. As a result of this, human health and environmental problems will be longer-lasting and more regionally variable. Like the other panels, the EEAP produces a detailed report every four years; the most recent was published in 2010 (Photochem. Photobiol. Sci., 2011, 10, 173-300). In the years in between, the EEAP produces less detailed and shorter progress reports, which highlight and assess the significance of developments in key areas of importance to the parties. The next full quadrennial report will be published in 2014-2015.
Achieving sustainable agricultural productivity and global food security are two of the biggest challenges of the new millennium. Addressing these challenges requires innovative technologies that can ...uplift global food production, while minimizing collateral environmental damage and preserving the resilience of agroecosystems against a rapidly changing climate. Nanomaterials with the ability to encapsulate and deliver pesticidal active ingredients (AIs) in a responsive (for example, controlled, targeted and synchronized) manner offer new opportunities to increase pesticidal efficacy and efficiency when compared with conventional pesticides. Here, we provide a comprehensive analysis of the key properties of nanopesticides in controlling agricultural pests for crop enhancement compared with their non-nanoscale analogues. Our analysis shows that when compared with non-nanoscale pesticides, the overall efficacy of nanopesticides against target organisms is 31.5% higher, including an 18.9% increased efficacy in field trials. Notably, the toxicity of nanopesticides toward non-target organisms is 43.1% lower, highlighting a decrease in collateral damage to the environment. The premature loss of AIs prior to reaching target organisms is reduced by 41.4%, paired with a 22.1% lower leaching potential of AIs in soils. Nanopesticides also render other benefits, including enhanced foliar adhesion, improved crop yield and quality, and a responsive nanoscale delivery platform of AIs to mitigate various pressing biotic and abiotic stresses (for example, heat, drought and salinity). Nonetheless, the uncertainties associated with the adverse effects of some nanopesticides are not well-understood, requiring further investigations. Overall, our findings show that nanopesticides are potentially more efficient, sustainable and resilient with lower adverse environmental impacts than their conventional analogues. These benefits, if harnessed appropriately, can promote higher crop yields and thus contribute towards sustainable agriculture and global food security.
Seagrasses play a variety of important ecological roles in coastal ecosystems. Here we present evidence that seagrass detritus from the widespread species Thalassia testudinum is an important source ...of ocean color and a DV-protective substance in a low latitude coastal shelf region of the United States. The production and light-induced degradation of chromophoric (sunlightabsorbing) dissolved organic matter (CDOM) from T. testudinum was examined under field and controlled laboratory conditions to obtain data that could be used to estimate the contribution of seagrass-derived CDOM to the coastal pool. The laboratory studies measured the temperature dependence and photodegradation of the spectral (UV-visible, fluorescence) and molecular mass properties of CDOM produced during the degradation of T. testudinum detritus. The rate of CDOM production is temperature-dependent with rates doubling when temperature increases from 21.4 to 32.6 degree C. The magnitude of this increase is close to the widely observed Q sub(10) factor for microbial decomposition, indicating that the CDOM production was likely microbially mediated. The absorption coefficients and fluorescence of CDOM from T. testudinum decreased on exposure to solar UV radiation (UVR) and the wavelength dependence was determined for this photobleaching process.
The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with UV radiation and its effects on human ...health, animals, plants, biogeochemistry, air quality and materials. Since 2000, the analyses and interpretation of these effects have included interactions between UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than believed previously. As a result of this, human health and environmental problems will likely be longer-lasting and more regionally variable. Like the other panels, the EEAP produces a detailed report every four years; the most recent was that for 2006 (Photochem. Photobiol. Sci., 2007, 6, 201-332). In the years in between, the EEAP produces a less detailed and shorter progress report, as is the case for this present one for 2009. A full quadrennial report will follow for 2010.
Chromophoric dissolved organic matter (CDOM) in the Mississippi plume region may have several distinct sources: riverine (terrestrial soils), wetland (terrestrial plants), biological production ...(phytoplankton, zooplankton, microbial), and sediments. Complex mixing, photodegradation, and biological processes make differentiation of the specific sources of CDOM difficult. Using a combination of high resolution in situ observations on an undulating vehicle, the ECOShuttle, a pumping system mounted on the vehicle, and detailed chemical and biological analyses of discrete samples allowed us to characterize two specific sources of CDOM in the Louisiana Bight: the river water constrained in the upper 12 m of the Mississippi River plume and several subsurface layers of CDOM below the plume. The subsurface CDOM maxima were coincident with steep pycnoclines and sometimes with maxima in chlorophyll
a fluorescence. Both sources were actively supplying CDOM to the same location by entirely different processes. The subsurface CDOM was more biologically labile and photochemically refractory than the surface CDOM. Optical properties were also different with a relatively higher protein fluorescence and a lower spectral slope coefficient in the subsurface CDOM. The geographical extent of the two sources was determined by three-dimensional mapping of the area, and due to the relatively calm conditions in the summer of 2000, thin layers of CDOM produced in the subsurface were observed throughout the region. While riverine inputs dominated the distribution of CDOM in surface waters <12 m in depth, biological production of CDOM, probably due to the bacterial degradation of phytoplankton produced DOM dominated the subsurface waters.
Using closed chamber techniques, soil fluxes of NO, N2O, and CO2 were measured from September 1999 to November 2000 in savanna areas of central Brazil (cerrado) subjected to prescribed fires. Our ...studies focused on two vegetation types, cerrado stricto sensu (20–50% canopy cover) and campo sujo (open, grass dominated), which were either burned every 2 years or protected from fire. Soil moisture and vegetation type were more important in controlling NO and CO2 fluxes than fire regime (early dry season, middle dry season or late dry season burning). N2O fluxes, however, were very low and below detection limit in any of the vegetation‐fire treatments. NO emissions increased after burning (1.0 ng NO–N cm−2 h−1), but flux returned quickly to prefire levels and even lower. In comparison, NO emissions increased 100‐fold (to 10.5 ng NO–N cm−2 h−1) during a water‐addition experiment in unburned campo sujo, and to 1.0 ng NO–N cm−2 h−1 in unburned cerrado and 1.9 ng NO–N cm−2 h−1 in burned cerrado with the first rains. Low NO and N2O emissions, low nitrification rates, and the majority of inorganic N in the form of NH4+ all indicate a conservative N cycle in the cerrado. CO2 fluxes increased with the onset of the rainy season and after artificial water addition. The highest CO2 measured in the wet season was 6.3 μmol CO2 m−2 s−1 in burned campo sujo. During the dry season, soil respiration in burned and unburned treatments were similar (average flux = 1.6–2.3 μmol CO2 m−2 s−1). Differences between fire treatments of cerrado and campo sujo CO2 fluxes are attributed to differences in relative litter production and root activity.
The objective of this work was to evaluate the effects of fire regimes and vegetation cover on the structure and dynamics of soil microbial communities, through phospholipid fatty acid (PLFA) ...analysis. Comparisons were made between native areas with different woody covers ("cerrado stricto sensu" and "campo sujo"), under different fire regimes, and a 20-year-old active palisadegrass pasture in the Central Plateau of Brazil. Microbial biomass was higher in the native plots than in the pasture, and the highest monthly values were observed during the rainy season in the native plots. No significant differences were observed between fire regimes or between communities from the two native vegetation types. However, the principal component (PC) analysis separated the microbial communities by vegetation cover (native x pasture) and season (wet x dry), accounting for 45.8% (PC1 and PC3) and 25.6% (PC2 and PC3), respectively, of the total PLFA variability. Changes in land cover and seasonal rainfall in Cerrado ecosystems have significant effects on the total density of soil microorganisms and on the abundance of microbial groups, especially Gram-negative and Gram-positive bacteria.
O objetivo deste trabalho foi avaliar os efeitos de regimes de queima e cobertura vegetal sobre a dinâmica e a estrutura de comunidades microbianas do solo, por meio da análise de perfis de ácidos graxos de fosfolipídeos (PLFA). Compararam-se áreas nativas com diferentes coberturas vegetais (cerrado stricto sensu e campo sujo), sob diferentes regimes de queima e uma pastagem de capim-braquiária de 20 anos, no Planalto Central do Brasil. A biomassa microbiana foi maior nas parcelas com vegetação nativa que na pastagem, e os maiores valores mensais foram observados durante a estação chuvosa nas parcelas nativas. Apesar de não terem sido observadas diferenças significativas como consequência das queimadas ou entre as vegetações nativas, a análise de componentes principais separou as comunidades microbianas pela cobertura vegetal (nativa x pastagem) e pela sazonalidade (chuvosa x seca), tendo explicado 45,8 e 25,6%, respectivamente, da variabilidade de PLFA total. Mudanças na cobertura do solo e a sazonalidade na precipitação têm efeito significativo sobre a densidade total e a abundância de grupos de microrganismos do solo no Cerrado, especialmente bactérias Gram-negativas e Gram-positivas
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