Urea accounted for 30, 36, and 56%, respectively, of the water-soluble organic nitrogen (DON) compounds deposited from the atmosphere at two sites in New Zealand and one site in japan. The other DON compounds were not identified but they were all of low molecular size, apparently anionic, and did not include detectable quantities of amino acids or uric acid. In axenic culture, Chlorella spp. grew successfully using DON from New Zealand precipitation as its only source of N; Pediastrum biwae, a phytoplankton endemic to Lake Biwa in Japan, also achieved successful growth using DON separated from Japanese precipitation. Ammonium-N and DON were deposited from the atmosphere in the absence of rain or snow, and we suggest that particulate matter, possibly soil, is a major source of these N compounds in atmospheric precipitation.

No abstract

Dissolved salts in lake waters of the Taupo Volcanic Zone consist predominantly of HCO 3 " salts from 'normal' weathering of rocks and soils by carbonic acid, Cl~ salts from precipitation and geothermal water, and SO 4 2~ salts from injection into the lakes or catchments of sulphuric acid from geothermal steam. Precipitation and cold spring waters are considered to be the input and final product, respectively, of normal weathering. The concentrations of major ions (Na + , K + , Ca 2+ , Mg 2+ , HCO 3 -, C1 -, SO 4 2-) in these waters and in geothermal water and steam were used to calculate the origins of the dissolved salts in each lake. Rhyolitic strata dominate most lake catchments, but in some the presence of andesite, basalt, or hydrothermal ejecta influences the major ion ratios in the fraction of the dissolved salts derived from weathering. Each of the 32 lakes studied was classified according to the origins of its lakewater dissolved salts and the effect on these salts of its catchment geology.

Lake Wilson, a perennially ice-capped, deep (>lo0 m) lake at 80"s in southern Victoria Land was investigated in January 1993. Water chemistry and physical structure showed three distinct layers; an upper c. 35 m mixed layer of low salinity, moderately turbid water; a less turbid mid layer, 20 m thick of slightly higher salinity and supersaturated with oxygen; and a deep 20 m brackish layer (conductivity c. 4000 pS cm") with anoxic conditions in the lower 5 m. Extreme supersaturation of N,O (up to 400 times air saturation) together with high nitrate concentration (4000 mg m") was recorded in the deep layer. Phytoplankton biomass and photosynthetic activity was confined to the upper mixed layer and the band of supersaturated dissolved oxygen located at 40-55 m appears to represent a relict layer from when the lake level was lower. The evidence from a comparison of profiles between 1975 and 1993 suggests that Lake Wilson has risen 25 m since 1975, synchronous with a period of lake level rise in the McMurdo Dry Valleys lakes to the north at 77"s. Geochemical diffusion models indicate that Lake Wilson had evaporated to a smaller brine lake about 1000 yrs BP, which also fits the pattern shown by the McMurdo Dry Valleys lakes. Climate changes influencing lake levels have thus covered a wide area of southern Victoria Land.

The toxicity to embryo and adult zebrafish (Danio rerio) of Cu complexes with two substituted malonic acids, benzyl‐ and n‐hexadecyl‐, chosen as models for low‐molecular‐weight natural dissolved organic matter, were investigated. Toxicity test solutions at pH 6.5 ± 0.1 with the required Cu speciation were designed using the chemical speciation model MINTEQA2, and the speciation was confirmed by Cu ion‐specific electrode. In the absence of malonic acids, concentrations of Cu2+ up to 1.13 μmol/ L increased the embryo hatching time from approx. 2 d in control solutions (no Cu or malonic acid) and solutions containing malonic acids without Cu to approx. 8 d. The Cu‐benzylmalonic acid complex (n‐octanol/water distribution coefficient [ρow] = 0.00) in the presence of inorganic Cu species did not delay hatching beyond that attributable to Cu2+, In contrast, 0.60 μmol/L Cu‐n‐hexadecylmalonic complexes (ρow = 6.89) delayed hatching by 5.5 d in excess of that attributable to 1.13 μmol/L Cu2+, assuming that the hatching delays caused by the different Cu species were additive, possibly because of Cu entry into the embryo as the lipophilic Cu‐ n‐hexadecylmalonic complex. None of the Cu‐malonic acid complexes was acutely toxic to adult zebrafish at concentrations up to 1.4 μmol/L, possibly because Cu was removed from the Cu‐malonic acid complexes by stronger chelating groups at the gill surface. Substituted malonic acids with similar proton and Cu association constants can be readily prepared with a variety of simple substituents, radiolabeled if required. Our results show that these acids could be useful ligands for investigating intracellular transport and metabolism of metal‐organic complexes.