Rates of oxygen consumption for Atlantic salmon Salmo salar embryos approaching hatching were determined. Values were recorded using a 'closed system' experimental set-up. A magnetic stirrer was used to ensure that zones of oxygen depletion did not develop in the microenvironment surrounding the respiring eggs. Recorded values of oxygen consumption ranged from 0Á0024 to 0Á0038 mg O 2 egg À1 h À1 , with a mean consumption rate of 0Á0032 mg O 2 egg À1 h À1 . The values of oxygen consumption were similar to those reported in other studies using a closed system experimental set-up, however, they were lower than those reported in a study adopting a flow-through system. The introduction of clay-sized sediment to the incubation chamber created a thin film (<1 mm) of sediment on the egg surface, and resulted in reduced rates of oxygen consumption. The additional 0Á3 g of clay sediment reduced oxygen consumption by an average of 41% and the addition of a further 0Á2 g of clay sediment reduced consumption by an average of 98%. Two explanations for the recorded reduction in consumption were proposed: (i) the creation of a low permeability seal around the eggs restricted the availability of oxygen to the incubating embryos and (ii) the clay-sized fine sediment physically blocked the micro-pore canals in the egg membrane, thereby restricting oxygen uptake. # 2005 The Fisheries Society of the British Isles

In situ studies on waste stabilization ponds (in Portugal) showed that faecal coliform numbers were lowest at positions in the water column where pH, temperature, dissolved oxygen and algae were high. Numbers were not always lowest at the surface where light intensities were highest or in ponds where light penetration had increased through algal grazing by Daphnia. Laboratory studies showed that pH values approaching 9.0 or above increased faecal coliform die-off particularly under nutrient-poor conditions. Elevated temperatures enhanced the pH effect but the level of dissolved oxygen made little difference. Streptococcus, Salmonella and Campylobacter isolates all behaved similarly to the faecal coliforms. Daphnia grazing of the algal population in maturation ponds may reduce the microbial quality of the final effluent. These findings are discussed in relation to pond design.

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Keywords:Sediment-bound organic matter Sources Carbon and nitrogen stable isotopes Near infra-red reflectance spectroscopy Salmonids Farm manures A B S T R A C TThe biodegradation of organic matter ingressing spawning gravels in rivers exerts an oxygen demand which is believed to contribute to detrimental impacts on aquatic ecology including salmonids. Catchment management strategies therefore require reliable information on the key sources of sediment-bound organic matter. Accordingly, a novel source fingerprinting procedure based on analyses of bulk stable 13 C and 15N isotope values and organic molecular structures detected using near infrared reflectance (NIR) spectroscopy was tested for assessing the primary sources of sediment-bound organic matter infiltrating artificial Atlantic salmon spawning redds in five rivers across England and Wales. Statistically-verified source fingerprints were identified using a combination of the Kruskal-Wallis Htest, principal component analysis and GA-driven discriminant function analysis. Interstitial sediment samples were obtained from artificial redds using retrievable basket traps inserted at the start of the salmonid spawning season and extracted subsequently in conjunction with critical juvenile phases (eyeing, hatch, emergence, late spawning) of fish development associated with incubation and emergence. Over the duration of these four basket extractions, the overall relative frequency-weighted average median source contributions to the interstitial sediment-bound organic matter sampled in the study rivers ranged between 26% (full uncertainty range 0-100%) and 44% (full uncertainty range 0-100%) for farm yard manures/slurries, 11% (full uncertainty range 0-75%) and 48% (full uncertainty range 0-99%) for damaged road verges, 16% (full uncertainty range (0-78%) and 52% (full uncertainty range (0-100%) for decaying instream vegetation and 4% (full uncertainty range 0-31%) and 10% (full uncertainty range (0-44%) for human septic waste. The results of mass conservation tests suggest that the procedure combining bulk 13 C and 15 N isotope values and NIR spectroscopy data on organic molecular structures is sensitive to the risks of significant non-conservative tracer behaviour in the fluvial environment and will therefore not necessarily work at all in-channel sites in all catchments.

In situ and laboratory experiments were performed on species of the waste stabilization pond algae Chlorella, Scenedesmus, Euglena and Chlamydomonas to investigate the utilization of various organic acids and sugars, light limitation on species dominance and the toxicity of ammonia and sulphide. Euglena showed the most flexible metabolism and was able to utilise butyrate. Scenedesmus did not grow on any of the substrates in the dark. Pond populations of Euglena and Chlamydomonas were able to incorporate acetate in situ in competition with the heterotrophic bacterial population but Chlamydomonas was the more successful. Light availability affected speciation in facultative ponds where rapid motility by flagellates was a clear advantage. All the algal species were sensitive to sulphide at µM concentrations in a tolerance sequence ChlamydomonasChlorellaScenedesmusEuglena. Ammonia was less toxic than sulphide and the tolerance sequence was ChlorellaScenedesmusChlamydomonasEuglena. It was the undissociated forms of both sulphide and ammonia which were toxic, Toxicity was influenced by pH and this would be a critical factor controlling ammonia inhibition of algal photosynthesis in ponds. The effects of these findings are related to species dominance and pond performance.