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[1] This study reports the first high and low molecular weight measurements of dissolved organic nitrogen (DON) in size-fractionated atmospheric particles. The variations in concentration of nitrogen species corresponded to varying sources and weather conditions. The results indicate that continental, local, and marine origins are the key factors controlling the particle size distribution of inorganic and organic nitrogen species. For dissolved inorganic nitrogen and DON, relatively high concentrations and fine-mode particle (particle diameter <1 mm) enrichment were significantly affected by continental and locally derived sources, which were mainly attributable to anthropogenic activities. However, the coarse/fine ratios indicate that DON was derived from a coarse particle (particle diameter >1 mm) source that may be sea salt particles. To investigate the possible sources of DON, an ultrafiltration method was used to separate DON into high (HMW) and low (LMW) molecular weight categories. The results indicate that HMW-DON and LMW-DON contributed 57 ± 9% and 43 ± 9%, respectively, to the total DON concentration. Correlations and positive matrix factorization analysis of HMW-DON and LMW-DON levels with major and non-sea-salt ions indicated that HMW-DON and LMW-DON in coarse particles may be generated from continental soil dust and sea spray, respectively, whereas, in fine particles, DON may originate from aerosols derived from combustion processes. The annual fluxes of HMW-DON and LMW-DON were estimated to be 11.0 and 11.3 mmol m −2 yr −1 , respectively. Consequently, the inputs of HMW-DON and LMW-DON appear to make equal contributions to DON in aerosols over the studied coastal area.

BackgroundProkaryotic microbes, the most abundant organisms in the ocean, are remarkably diverse. Despite numerous studies of marine prokaryotes, the zonation of their communities in pelagic zones has been poorly delineated. By exploiting the persistent stratification of the South China Sea (SCS), we performed a 2-year, large spatial scale (10, 100, 1000, and 3000 m) survey, which included a pilot study in 2006 and comprehensive sampling in 2007, to investigate the biological zonation of bacteria and archaea using 16S rRNA tag and shotgun metagenome sequencing.ResultsAlphaproteobacteria dominated the bacterial community in the surface SCS, where the abundance of Betaproteobacteria was seemingly associated with climatic activity. Gammaproteobacteria thrived in the deep SCS, where a noticeable amount of Cyanobacteria were also detected. Marine Groups II and III Euryarchaeota were predominant in the archaeal communities in the surface and deep SCS, respectively. Bacterial diversity was higher than archaeal diversity at all sampling depths in the SCS, and peaked at mid-depths, agreeing with the diversity pattern found in global water columns. Metagenomic analysis not only showed differential %GC values and genome sizes between the surface and deep SCS, but also demonstrated depth-dependent metabolic potentials, such as cobalamin biosynthesis at 10 m, osmoregulation at 100 m, signal transduction at 1000 m, and plasmid and phage replication at 3000 m. When compared with other oceans, urease at 10 m and both exonuclease and permease at 3000 m were more abundant in the SCS. Finally, enriched genes associated with nutrient assimilation in the sea surface and transposase in the deep-sea metagenomes exemplified the functional zonation in global oceans.ConclusionsProkaryotic communities in the SCS stratified with depth, with maximal bacterial diversity at mid-depth, in accordance with global water columns. The SCS had functional zonation among depths and endemically enriched metabolic potentials at the study site, in contrast to other oceans.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1434-3) contains supplementary material, which is available to authorized users.

Depth distributions of pH, dissolved oxygen, dissolved inorganic carbon (DIC), total alkalinity (TA), and δ13CDIC in the water column across the Luzon Strait from the South China Sea to the west Philippine Sea were investigated thoroughly to attest whether the South China Sea subsurface water outflow could act like a “shelf pump” to export the carbon from the interior of the South China Sea into the open Pacific. Results show that the outflow is capable of transporting 17.6 ± 9.0 Tg C a−1 in DIC form out from the South China Sea to the western Pacific, a quantity equivalent to ∼35 ± 18% of the annual export production of the entire South China Sea. Furthermore, owing to the input of this South China Sea outflow, the subsurface waters of the Kuroshio Current become enriched in DIC/TA ratio but depleted in δ13CDIC. Such a change in seawater carbon chemistry might further attenuate the capacity of CO2 sequestration and hamper the use of δ13CDIC data as a tracer to estimate anthropogenic CO2 uptake rate in seawaters around the Kuroshio main path. More importantly, since these modifications can make all their ways northward along with the Kuroshio Current, the effect may reach even as far as to the higher‐latitude region in the northwestern Pacific.

River water samples were collected at five sites in the state of Colorado, USA, to assess the impact of municipal and industrial discharges on Ag concentrations and speciation in surface waters. Samples were collected and analyzed for total (unfiltered collections), filtered (0.1 and 0.4 microm), particulate (> or = 0.45 microm), and colloidal Ag (3 kDa-0.1 m) using ultraclean protocols. A series of laboratory experiments were conducted to assess bias from sample storage, digestion, and preconcentration protocols. In general, upstream unfiltered and particulate Ag concentrations fell within a fairly narrow range, 3.1 to 21 ng/L and 0.2 to 1.7 microg/g, respectively. Downstream unfiltered and particulate Ag concentrations showed a more broad range, 2.8 to 1,110 ng/L and 0.5 to 104 microg/g, respectively, and reflected attenuated impacts of Ag-laden discharge effluents. However, Ag concentrations in the 0.1-microm filter-passing fraction 0.8 to 1.2 km downstream from major treatment plant effluents were all below the chronic silver criteria. On average, more than 60% of the 0.1-microm filter-passing Ag was associated with colloidal macromolecular organic matter. Silver concentrations in colloids (microg/g) were, on average, the same as those in suspended particulate matter. The percentage abundance of colloidal Ag was similar to that of dissolved organic carbon, suggesting that strong Ag binding ligands exist in both the colloidal and the particle size fractions, as these macromolecular ligands likely play a major role in Ag speciation.