In the first quarter of 1992, 118 dolphin carcases, of which 54 were positively identified as common dolphins (Delphinus delphis), were found stranded on the coast of Cornwall and Devon. To determine the cause, detailed post mortem examinations were carried out on 38 of the carcases, and the results were compared with those from 20 common dolphins that stranded on the coast of Cornwall and Devon in the previous 15 months. There was no evidence that the deaths were due to an infectious or parasitic disease, or acute intoxication by any of the algal toxins, trace metals or chlorinated hydrocarbons measured. However, 30 of the 38 dolphins showed signs associated with incidental capture in fishing gear. Skin lesions characteristic of capture in a small-meshed net and the predominance of recently ingested Atlantic mackerel (Scomber scombrus) and pilchard (Sardina pilchardus) in the stomachs of the dolphins suggested that they had been caught in the trawl or purse seine nets used for these fish. There is insufficient information to explain why this high mortality occurred in 1992 and not in other years.
Recent efforts to quantify the terrestrial inputs and cycling of P in agricultural systems are allowing management strategies to be developed to minimize the loss of P. While this approach has had clear advantages for standing waters, potential benefits for flowing freshwater systems are more difficult to predict. As a consequence of the unidirectional and dynamic nature of flow in rivers, temporal and spatial separations between the source of P and the point of potential impact arc introduced when considering a whole watershed. The ability to quantify the residence time of P within any particular part of a river system is therefore essential so that the specific contribution of individual P sources to biological demand can be determined. The smaller algal biomass productivity measured in flowing, compared with standing, waters at a similar supply rate of P indicates the need to consider the roles of other watershed factors in modifying the relationship between growth and P supply. The site‐specific nature of responses to P suggests a need to develop a hierarchical classification system where individual river sections can be ranked according to their likely responsiveness to P. The ecoregion concept, combined with stream order, would integrate spatial and temporal aspects of gradient, land use, flow velocity, and water quality. For this to be successful, we must demonstrate a link between perturbations to the terrestrial P cycle, the delivery of P to flowing waters, and a biological impact.
Early accounts by European explorers and settlers of South Australia contain numerous references to
scums or discoloured water that are consistent with cyanobacterial blooms. Documented reports refer
back to at least 1853. The first detailed scientific account of toxic cyanobacteria appeared in 1878. In
a perceptive and prescient paper in Nature, the Adelaide assayer and chemist George Francis reported
on stock deaths at Milang on the shores of Lake Alexandrina in South Australia. Francis attributed
the deaths to the ingestion and toxicity of scums of the cyanobacterium Nodularia spumigena. Reports
of cyanobacterial blooms, scums and associated problems in Lake Alexandrina and in the River Murray
between about 1851 and 1888 are discussed and comparisons are made with the reactions to blooms a
century later.
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