Atmospheric Iron and Aluminium Deposition and Sea-Surface Dissolved Iron and Aluminium Concentrations in the South China Sea off Malaysia Borneo (Sarawak Waters)

South China Sea (SCS) is an oligotrophic sea which usually receives low nutrients supply. However, massive atmospheric dust input was occurred during the haze event in Southeast Asia for almost every year. The input of dissolved iron (DFe) and dissolved aluminium (DAl) from dust and nearby land into SCS off Sarawak Borneo region during the worst haze event in 2015 of the Southeast Asia were investigated. The estimation dust deposition during this study was 0.162 mg/m2/yr. The atmospheric fluxes of total Fe and total Al at the offshore Sarawak waters were 0.611 µmol/m2/yr and 2.03 µmol/m2/yr, respectively, where the readily available dissolved Fe and Al from the dust were 0.11 µmol/m2/yr (DFe) and 0.31 µmol/m2/yr (DAl). Fe has higher solubility (17.78%) than Al (15.21%). The lateral fluxes (e.g. from the nearby land) were 37.08 nmol/m2/yr (DFe) and 125 nmol/m2/yr (DAl), with strong Fe organic ligand class L1 (log K:22.43 – 24.33). High concentrations of DFe and DAl at the surface water of the offshore region, coincided with high concentration of macronutrients due to the prevailing south-westerly winds originated from the west Kalimantan. Low residence times, ~0.92 (DFe) and ~1.31 (DAl) years, corresponded well with DAlexcess in surface seawater due to biological utilization of DFe. Future works emphasize on natural organic Fe(III) ligands and phytoplankton study are needed for better understanding on biogeochemistry of Fe and Al at SCS off Malaysia Borneo.

Antarctic meltwater-induced dynamical changes in phytoplankton in the Southern Ocean

IIt has been suggested that the freshwater flux due to the recent melting of the Antarctic ice-sheet/shelf will suppress ventilation in the Southern Ocean. In this study, we performed idealized earth system simulations to examine the impacts of Antarctic meltwater on surface phytoplankton biomass in the Antarctic Ocean. The enhanced stratification due to the meltwater leads to a decrease in the surface nitrate concentration but an increase in the surface dissolved iron concentration. These changes are associated with the reduced upwelling of nitrate-rich deep water and the trapped iron exported from the terrestrial sediment. Because of the limited iron availability in the Southern Ocean, the trapped iron in surface water enhances the chlorophyll concentration in the open ocean. However, in the marginal sea along the Antarctic coastline where the iron is relatively sufficient, a nitrate reduction induces a chlorophyll decrease, indicating a regime shift from iron-limited to nitrate-limited conditions.

Variations in and environmental controls of primary productivity in the Amundsen Sea

The Amundsen Sea is one of the regions with the highest primary productivity in the Antarctic. To better understand the role of the Southern Ocean in the global carbon cycle and in climate regulation, a better understanding of the variations in and environmental controls of primary productivity is needed. Using cluster analysis, the Amundsen Sea was divided into nine bioregions. The biophysical differences among bioregions enhanced confidence to identify priorities and regions to study the temporal and spatial variations in primary productivity. Four nearshore bioregions with high net primary productivity or rapidly increasing rates were selected to analyze temporal and spatial variations in primary productivity in the Amundsen Sea. Due to changes in net solar radiation and sea ice, primary production had significant seasonal variation in these four bioregions. The phenology had changed at two bioregions (3 and 5), which has the third and fourth highest primary production, due to changes in the dissolved iron, nitrate, phosphate, and silicate concentrations. Annual primary production showed increasing trends in these four bioregions. The variation in primary production in the bioregion (9), which has the highest primary production, was mainly affected by variations in sea surface temperatures. In the bioregion, which has the second-highest primary production (8), the primary production was significantly positively correlated with sea surface temperature and significantly negatively correlated with sea ice thickness. The long-term changes of primary productivity in bioregions 3 and 5 were thought to be related to changes in the dissolved iron, nitrate, phosphate, and silicate concentrations, and dissolved iron was the limiting factor in these two bioregions. Bioregionalization not only disentangle multiple factors that control the spatial differences, but also disentangle limiting factors that affect the phenology, decadal and long-term changes in primary productivity.

Combining Coagulation and Electrocoagulation with UVA-LED Photo-Fenton to Improve the Efficiency and Reduce the Cost of Mature Landfill Leachate Treatment

This study focused on the reduction of the treatment cost of mature landfill leachate (LL) by enhancing the coagulation pre-treatment before a UVA-LED photo-Fenton process. A more efficient advanced coagulation pretreatment was designed by combining conventional coagulation (CC) and electro-coagulation (EC). Regardless of the order in which the two coagulations were applied, the combination achieved more than 73% color removal, 80% COD removal, and 27% SUVA removal. However, the coagulation order had a great influence on both final pH and total dissolved iron, which were key parameters for the UVA-LED photo-Fenton post-treatment. CC (pH = 5; 2 g L−1 of FeCl36H2O) followed by EC (pH = 5; 10 mA cm−2) resulted in a pH of 6.4 and 100 mg L−1 of dissolved iron, whereas EC (pH = 4; 10 mA cm−2) followed by CC (pH = 6; 1 g L−1 FeCl36H2O) led to a final pH of 3.4 and 210 mg L−1 dissolved iron. This last combination was therefore considered better for the posterior photo-Fenton treatment. Results at the best cost-efficient [H2O2]:COD ratio of 1.063 showed a high treatment efficiency, namely the removal of 99% of the color, 89% of the COD, and 60% of the SUVA. Conductivity was reduced by 17%, and biodegradability increased to BOD5:COD = 0.40. With this proposed treatment, a final COD of only 453 mg O2 L−1 was obtained at a treatment cost of EUR 3.42 kg COD−1.

Cyanide Removal and Recovery by Electrochemical Crystallization Process

Alkaline chlorination, an efficient but high chemical cost process, is commonly employed for cyanide (CN−) removal from CN-rich wastewater streams. CN− removal and recovery through the precipitation of Prussian Blue (Fe4III[FeII(CN)6]3, PB) or Turnbull’s Blue (Fe3II[FeIII(CN)6]2, TB) were realized using iron salts, leading to a cost-effective and sustainable process producing a valuable recovery product. However, the precipitation of PB and TB is highly affected by pH and dissolved oxygen (DO). CN− removal and recovery from CN-containing water by crystallization of PB and/or TB were investigated using dissolved iron that was electrochemically generated from a sacrificial iron anode under various pH values, initial CN− levels (10 to100 mg/L) and DO levels (aeration, mechanical mixing, and N2 purging). It was shown that the complexation of CN− with Fe ions prevented the vaporization of HCN under acidic pH. At pH of 7 and initial CN− concentration of 10 mg/L, CN− removal efficiency increases linearly with increasing Fe:CN− molar ratios, reaching 80% at the Fe:CN− molar ratio of 5. A clear blue precipitate was observed between the pH range of 5–7. CN− removal increases with increasing initial CN− concentration, resulting in residual CN− concentrations of 8, 7.5 and 12 mg/L in the effluent with the Fe:CN− molar ratio of 0.8 for initial concentrations of 10, 50 and 100 mg CN−/L, respectively. A polishing treatment with H2O2 oxidation was employed to lower the residual CN− concentration to meet the discharge limit of <1 mg CN−/L.

Trace Element (Fe, Co, Ni and Cu) Dynamics Across the Salinity Gradient in Arctic and Antarctic Glacier Fjords

Around the Greenlandic and Antarctic coastlines, sediment plumes associated with glaciers are significant sources of lithogenic material to the ocean. These plumes contain elevated concentrations of a range of trace metals, especially in particle bound phases, but it is not clear how these particles affect dissolved (&lt;0.2 µm) metal distributions in the ocean. Here we show, using transects in 8 glacier fjords, trends in the distribution of dissolved iron, cobalt, nickel and copper (dFe, dCo, dNi, dCu). Following rapid dFe loss close to glacier outflows, dFe concentrations in particular showed strong similarities between different fjords. Similar dFe concentrations were also observed between seasons/years when Nuup Kangerlua (SW Greenland) was revisited in spring, mid- and late-summer. Dissolved Cu, dCo and dNi concentrations were more variable and showed different gradients with salinity depending on the fjord, season and year. The lack of consistent trends for dCu and dNi largely reflects less pronounced differences contrasting the concentration of inflowing shelf waters with fresher glacially-modified waters. Particles also made only small contributions to total dissolvable Cu (dCu constituted 83 ± 28% of total dissolvable Cu) and Ni (dNi constituted 86 ± 28% of total dissolvable Ni) within glacier plumes. For comparison, dFe was a lower fraction of total dissolvable Fe; 3.5 ± 4.8%. High concentrations of total dissolvable Fe in some inner-fjord environments, up to 77 µM in Ameralik (SW Greenland), may drive enhanced removal of scavenged type elements, such as Co. Further variability may have been driven by local bedrock mineralogy, which could explain high concentrations of dNi (25–29 nM) and dCo (6–7 nM) in one coastal region of west Greenland (Kangaatsiaq). Our results suggest that dissolved trace element distributions in glacier fjords are influenced by a range of factors including: freshwater concentrations, local geology, drawdown by scavenging and primary production, saline inflow, and sediment dynamics. Considering the lack of apparent seasonality in dFe concentrations, we suggest that fluxes of some trace elements may scale proportionately to fjord overturning rather than directly to freshwater discharge flux.