Heavy metal contamination in the paddy soils of China is a serious concern because of its health risk through transfer in food chains. A field experiment was conducted in 2014–2015 to investigate the long-term effects of different biochar amendments on cadmium (Cd) and arsenic (As) immobilisation in a contaminated paddy field in southern China. Two types of biochar, a rice-straw-derived biochar (RB) and a coconut-by-product-derived biochar (CB), were amended separately to determine their impacts on rice yield and their efficacy in reducing Cd and As in rice. The two-year field experiment showed that biochar amendments significantly improved the rice yields and that CB is superior to RB, especially in the first growth season. Using a large amount of biochar amendment (22.5tha–1) significantly increased soil pH and total organic carbon, and concomitantly decreased the Cd content in rice grains over the four growth seasons, regardless of biochar type and application rate. Arsenic levels in rice were similar to the control, and results from this study suggest that there was a sustainable effect of biochar on Cd sequestration in soil and reduction of Cd accumulation in rice for at least two years. Biochar amendment in soil could be considered as a sustainable, reliable and cost-effective option to remediate heavy metal contamination in paddy fields for long periods.

Interannual and seasonal variability of the biogeochemical characteristics of fast ice were analysed in relation to ambient conditions, water column properties and ice biota. According to Zubov's Law, the annual atmospheric cooling should generate 2.5 m thick fast ice sheets in this coastal zone, but katabatic wind peaks in July–August often cause ice breakouts, resulting in highly variable growth periods (2–9 months) and thickness (1.0–2.5 m). In spring, atmospheric forcings significantly modulate brine content (5–20%) and drainage in fast ice, as well as salinity oscillations in bottom and platelet layers (15 psu). In the water column, the formation of nutrient-impoverished Summer Surface Waters is triggered by seawater warming (-1.9 to 0.7°C), ice melting (0.03 m d-1) and pelagic production. Negative NO3 and SiO2 balances and positive NH4 balances (-41, -153 and +173 kg km-2, respectively) were estimated in fast ice in spring, whereas nutrient budgets in the platelet layer are regulated by its variable level of isolation from seawater. The large accumulation of dissolved organic carbon (3890 kg km-2) in the ice system and its release in seawater in late spring are important features of the carbon cycle in these Antarctic coastal zones, with possible implications for the modulation of climate.

Measurements of the release of dissolved organic nitrogen (DON) and carbon (DOC) were carried out on an axenic batch culture of the coccolithophorid Emiliania huxleyi. This unicellular marine alga was cultured using a media with nitrate as the sole N source and the changes of DOM concentrations measured over 14 days. Results showed that there was a significant release of DON, i.e.7.6 µM N day−1 during mid-exponential growth phase (days 5–7). The highest release of DOC was also recorded in the same growth phase and accounted for 24.0 μM C day−1.

Temporal and spatial variations of the hydrogen peroxide accumulation were measured in off-shore waters and in intertidal rockpools near Jubany Station, King George Island, South Shetland Islands. As H2O2 photoformation is mainly driven by the short wavelength radiation in the UV-B and the UV-A range of the solar spectrum, the study was conducted between the beginning of October and the end of December 1995, the period of Antarctic spring ozone depletion. Wet deposition of H2O2 containing snow was identified as a major source of hydrogen peroxide in the surface waters of Potter Cove. As the concentrations of dissolved organic carbon (DOC) in Potter Cove surface waters were low (121 ± 59 μmol Cl−1), when compared to the highly eutrophicated waters on the German Wadden coast (6000–7000 μmol Cl−1), direct UV-induced DOC photo-oxidation was of only limited significance in the Antarctic sampling site. Nonetheless, under experimental conditions, H2O2 photoformation in Potter Cove surface waters amounted to 90 ± 40 nmol H2O2 h−1 l−1 under a UV-transparent quartz plate. When high energy UV-B photons were cut-off by a WG320 filter formation continued at a rate of 66 ± 29 nmol H2O2 h−1 l−1 due to UV-A and visible light photons. Samples from freshly deposited snow contained between 10 000 and 13 600 nmol H2O2 l−1, and a snowfall event in mid November resulted in a maximum concentration of 1450 nmol H2O2 l−1 in the upper 10 cm layer of Potter Cove surface waters. Maximal H2O2 concentrations in intertidal rockpools were even higher and reached up to 2000 nmol H2O2 l−1 after the snowfall event. During a grid survey on December 17 1995, H2O2 concentrations and salinity displayed a north to south gradient, with higher concentrations and PSU at the south coast of the cove. The reasons for this spatial inhomogenety are as yet unknown, but may relate to a minor local input of photo-reactive organic matter from creeks entering the cove in the south-east, as well as to waste water discharge from the station, located on the south beach.

Several studies have found that, since 1975 at least, the atoll lagoon of Takapoto exhibits high salinities and high planktonic chlorophyll concentrations. We used observations gathered in Takapoto and 23 other atoll lagoons between 1995 and 2000 to study the water renewal rate (determined by different approaches) of Takapoto relative to that of the other lagoons. This rate is controlled by reef rim aperture, which is abnormally low in Takapoto. Across this set of lagoons, average water residence time was correlated with salinity, and with two descriptors of water column biological properties, chlorophyll and dissolved organic matter contents. In parallel to these bulk quantitative variations, qualitative variations were found inside this trophy gradient, concerning the size of primary producers (proportion of cells > 2.7 μm) and the composition of seston (relative phosphorus content). Takapoto Lagoon fits into a gradient of water residence time that controls the overall trophic web organization.