The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.

Large benthic accumulations of cyanobacteria occur in sheltered embayments within Myall Lake, New South Wales, Australia. The lake is shallow, with the entire bottom within the euphotic zone, and it is generally considered pristine, having low nutrient concentrations. The accumulations are highly organic and contain a mix of species mainly from the order Chroococcales, with two forms of Aphanothece being dominant. However polymerase chain reaction (PCR) analysis indicates a close similarity to Microcystis flos-aquae. The cells appear to lack aerotopes and form sticky mucilaginous amalgamations, which may enhance their benthic habit. Although Chroococcales also dominate the planktonic cyanobacterial community, the benthic species are seldom, if ever, found entrained within the water column. Some hepatotoxicity was indicated by mouse bioassay, protein phosphatase inhibition assay, enzyme-linked immuno-sorbent assay (ELISA) for microcystins, PCR and by chromatographic evidence for a microcystin. Ecological aspects of the distribution, gross morphology of the organisms and management implications for recreational water-users are discussed.

No abstract

A study of oxygen transfer efficiency (OTE) in aeration basins, using measurements of oxygen depletion in offgas collected from them, was carried out over a period of several years by collaborations between the University of California, Los Angeles and the Bureau of Sanitation Research Group of the City of Los Angeles. Measurements were taken of dissolved oxygen (DO), water temperature, oxygen depletion, and air flux at each sampling location as part of the process to obtain standardized OTE. Field instruments, permanently located near the tanks and galleries, are connected to the control room that automatically records return activated-sludge flow, influent flow, tank DO sensor readings, and air flow. Data from the control room and field instruments were collected for the times of the samples to provide context and some degree of quality control for the samples obtained by the measurement team.The combined air flux and OTE measurements not only agree with the familiar inverse relationship between OTE and air flux but have allowed detection of strong evidence that serious leakage has developed in a few weeks in the air distribution systems of tanks 4 and 5, which was indirectly confirmed by observation of water ejection from the air release valves on the tanks. However, the detail provided by OTE measurements allows more specific understanding of the magnitude of the problem and its significance for the operation of these tanks. Analysis of the OTE measurements made at the site since 1991 also indicates that the diffusers in some of the tanks may now be in need of cleaning or replacement. Water Environ. Res., 72, 363 (2000).

Myall