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© 2019, Springer Nature B.V. Abstract: The contamination and risk by nutrients (NH4+, NO2−, NO3− and PO43−), COD, BOD5, coliform and potentially toxic elements (PTEs) of As, Cd, Ni, Hg, Cu, Pb, Zn and Cr were investigated in urban river (Nhue River), Vietnam during 2010–2017. The extensive results demonstrated that concentrations of these contaminants showed significant spatial and temporal variations. The Nhue River was seriously polluted by NH4+ (0.025–11.28 mg/L), PO43− (0.17–1.72 mg/L), BOD5 (5.8–179.6 mg/L), COD (1.4–239.8 mg/L) and coliform (1540–326,470 CFU/100 mL); moderately polluted by As (0.2–131.15 μg/L) and Hg (0.11–4.1 μg/L); and slightly polluted by NO2− (0.003–0.33 mg/L) and Cd (2.1–18.2 μg/L). The concentrations of NH4+, PO43−, COD, BOD5 and coliform frequently exceeded both drinking water guidelines and irrigation water standards. Regarding PTEs, As, Cd and Hg concentrations were frequently higher than the regulatory limits. Human health risks of PTEs were evaluated by estimating hazard index (HI) and cancer risk through ingestion and dermal contacts for adults and children. The findings indicated that As was the most important pollutant causing both non-carcinogenic and carcinogenic concerns. The non-carcinogenic risks of As were higher than 1.0 at all sites for both adults (HI = 1.83–7.4) and children (HI = 2.6–10.5), while As posed significant carcinogenic risks for adults (1 × 10−4−4.96 × 10−4). A management strategy for controlling wastewater discharge and protecting human health is urgently needed. Graphical abstract: [Figure not available: see fulltext.]

© Inter-Research 2014 The contribution of planktonic diazotrophs to the overall N budget is a key unknown in the eastern Indian Ocean. Here we investigated the relationships between dissolved inorganic nutrients, phytoplankton pigment composition, microbial community structure, nitrogen fixation rates and the δ15N of fractionated zooplankton samples along the shelf break of Western Australia (32° to 12° S) in September 2012. Bulk nitrogen fixation rates declined from 4.8 nmol l-1 h-1 in the colder and more saline sub-tropical waters at higher latitudes to 1.5 nmol l-1 h-1 in the warmer and fresher Timor Sea at lower latitudes. A regional bloom of Trichodesmium was identified between 13° and 9° S in the Timor Sea. Trichodesmium-specific N2 fixation rates were 0.05 ± 0.01 nmol colony-1 h-1. Highest dissolved inorganic nitrogen (DIN) concentrations occurred at the highest NH4+:NO3- ratios, thereby deviating from the paradigm that greater DIN concentrations come primarily from increased NO3- through advection, mixing or upwelling. Both the microplankton and nanoflagellate fraction declined significantly in warmer waters, with higher DIN concentrations but decreasing % NO3-. A clear increase in the prokaryotic diagnostic pigment zeaxanthin was seen with increasing temperatures from higher to lower latitudes. The microbial community, measured using automated ribosomal intergenic spacer analysis (ARISA), clustered strongly according to the water mass biogeochemistry including temperature, salinity, DIN and phosphate concentrations (p < 0.001). Isotope analysis suggested that injections of low δ15N from N2 fixation lowered the zooplankton δ15N signature of animals up to ∼500 μm in size and that nearly 47% of the fixed nitrogen was used by zooplankton (≤500 μm fraction) in the Timor Sea.