The ambient radical concentrations were measured continuously by laser-induced fluorescence during the STORM (STudy of the Ozone foRmation Mechanism) campaign at the Shenzhen site, located in the ...Pearl River Delta in China, in the autumn of 2018. The diurnal maxima were 4.5x10.sup.6 cm.sup.-3 for OH radicals and 4.2x10.sup.8 cm.sup.-3 for HO.sub.2 radicals (including an estimated interference of 23 %-28 % from RO.sub.2 radicals during the daytime), respectively. The state-of-the-art chemical mechanism underestimated the observed OH concentration, similar to the other warm-season campaigns in China. The OH underestimation was attributable to the missing OH sources, which can be explained by the X mechanism. Good agreement between the observed and modeled OH concentrations was achieved when an additional numerical X equivalent to 0.1 ppb NO concentrations was added into the base model. The isomerization mechanism of RO.sub.2 derived from isoprene contributed approximately 7 % to the missing OH production rate, and the oxidation of isoprene oxidation products (MACR and MVK) had no significant impact on the missing OH sources, demonstrating further exploration of unknown OH sources is necessary. A significant HO.sub.2 heterogeneous uptake was found in this study, with an effective uptake coefficient of 0.3. The model with the HO.sub.2 heterogeneous uptake can simultaneously reproduce the OH and HO.sub.2 concentrations when the amount of X changed from 0.1 to 0.25 ppb. The RO.sub.x primary production rate was dominated by photolysis reactions, in which the HONO, O.sub.3, HCHO, and carbonyls photolysis accounted for 29 %, 16 %, 16 %, and 11 % during the daytime, respectively. The RO.sub.x termination rate was dominated by the reaction of OH+NO.sub.2 in the morning, and thereafter the radical self-combination gradually became the major sink of RO.sub.x in the afternoon. As the sum of the respective oxidation rates of the pollutants via reactions with oxidants, the atmospheric oxidation capacity was evaluated, with a peak of 11.8 ppb h.sup.-1 around noontime. The ratio of P(O.sub.3).sub.net to AOC.sub.VOCs, which indicates the yield of net ozone production from VOC oxidation, trended to increase and then decrease as the NO concentration increased. The median ratios ranged within 1.0-4.5, with the maximum existing when the NO concentration was approximately 1 ppb. The nonlinear relationship between the yield of net ozone production from VOC oxidation and NO concentrations demonstrated that optimizing the NO.sub.x and VOC control strategies is critical to controlling ozone pollution effectively in the future.
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•Sediment yield of Italian rivers compared to world datasets.•No significant correlation between catchment area and sediment yield.•Higher variability of annual sediment yield in ...rivers with lower annual rainfall.•Smaller rivers sediment yield is predicted by the flow exceeded 10 days a year.•Recent sediment yield decrease for rainfall reduction and forestland increase.
The knowledge about river sediment yield in Italy is rather scarce and mainly based on small reservoir sedimentation data. This study used the suspended sediment yield field data measured by the national and regional hydrological services. The data of nine rivers and 11 selected flow gauges were used to investigate the control of basic parameters such as catchment area, annual precipitation and a characteristic discharge on sediment yield. The average sediment yield of Italy is close to the world mean but the relationship between catchment area and sediment yield is not significant, though a general decreasing trend with increasing catchment area can be distinguished. The variation of sediment yield with annual precipitation is poorly significant, although a general increasing trend with increasing catchment area can be observed. Sediment yield varies widely. The largest range of variability occurs for annual precipitation between 700 and 800 mm. The data indicate an average suspended sediment yield of 220 t km−2yr−1 and an upper limit of 3000 t km−2yr−1 which is observed in all the study rivers, no matter the catchment size which ranges from 580 to 70091 km2. Such a high value seems to be the maximum sediment yield possible in Italy given the local climatic, tectonic and land use characteristics. The discharge exceeded 10 days a year (2.7% of time) was found to exert a substantial control on sediment yield. Groups of rivers with similar catchment area show significant correlations and almost parallel trendlines. The occurrence of data gaps and multiple years interruptions allowed the investigation on the decadal variation of sediment yield of only very few rivers. The reduction of sediment yield is remarkable. The decrease in annual precipitation and the unprecedented expansion of forests are considered as the main factors causing such marked decrease of sediment yield in Italy.
Although the proxies based on elemental geochemistry of siliciclastic sediments have been well developed to indicate the intensity of chemical weathering in various catchments, their geological ...indications and limitations, and especially how the differentiation of minerals and sediment grain size influences the applications of these proxies needs more clarification. This paper investigates the interactive effects of weathering, hydraulic sorting and sedimentary recycling on river sediment chemistry, and further validates the application of various weathering indices by measuring mineralogical and geochemical compositions of bank sediments and suspended particulate matters (SPMs) from five rivers in East China bearing various sizes, geologic settings and climatic regimes. For a specific river, the silicate weathering intensity registered in the fine SPMs is systematically stronger than that in the coarse-grained bank sediments. Most of the weathering indices not only reflect the integrated weathering history of various catchments but also depend on hydraulic sorting effect during sediment transport and depositional processes. The correlation between CIA (chemical index of alteration) and WIP (weathering index of Parker) offers an approach to predict the weathering trends of the fine SPMs, coarse bank sediments and recycled sediments under the influence of quartz dilution. To minimize the effects of hydrodynamic sorting and sedimentary recycling, we suggest that the fine sediments (e.g. SPMs and <2 μm fraction of bank sediments) in rivers can better reflect the average of present-day weathering crust in catchments and the weathered terrigenous materials into marginal seas and oceans.
The hybrid between diploid Isoetes echinospora and tetraploid I. laurentiana is reported from six sites along the St. Lawrence River near Quebec City. Morphological characteristics and distinguishing ...features are identified, and the binomial I. *blondeaui, hyb. nov. is proposed. All occurrences are in biogeographically significant freshwater tidal marsh habitat. The hybrid is expected to occur in small numbers within most large I. laurentiana populations.
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