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O2 L (o2 + l)
Kinds of O2 L Selected AbstractsFish habitat requirements as the basis for rehabilitation of eutrophic lakes by oxygenationFISHERIES MANAGEMENT & ECOLOGY, Issue 3-4 2004R. Müller Abstract Eutrophic lakes often suffer from hypolimnetic oxygen depletion during summer and autumn, and the accumulation of reduced substances in the hypolimnion. The space fish can occupy is therefore reduced, and the potential for fish kills caused by toxic algae and the upwelling of anoxic water increases. Fish, such as coregonids, require at least 4 mg O2 L,1 to survive in the long-term. This critical level has been postulated as one of the major goals for the rehabilitation of several eutrophic Swiss lakes. It was predicted that this oxygen criterion would reduce phosphorus release from the sediment and increase phosphorus retention, and re-establish natural reproduction of coregonids. Rehabilitation measures applied to three eutrophic Swiss lakes were hypolimnetic oxygenation during summer stratification, and artificial mixing using compressed air to enhance circulation in winter. These lake-internal measures carried out for more than 15 years showed the 4 mg O2 L,1 criterion can be achieved most of the time. The measures have led to an expansion of habitat for oxygen-dependent organisms to greater depths. However, other goals were not attained, such as increasing phosphorus retention by the sediment. In addition, natural reproduction of coregonids could not be re-established. Excessive oxygen consumption by the sediment, arising from the decomposition of deposited organic matter produced during summer, caused death by suffocation of coregonid eggs developing on the sediment. Thus rehabilitation of eutrophic lakes by oxygenating the hypolimnion and artificial mixing will not be successful, unless it is accompanied by lowering the nutrient loading and thus primary production and oxygen consumption by the sediment. Nevertheless, positive effects of lake aeration were the expansion of living space for fish and benthic invertebrates, and the prevention of fish kills by upwelling anoxic hypolimnetic water. [source] Behavioural responses of a south-east Australian floodplain fish community to gradual hypoxiaFRESHWATER BIOLOGY, Issue 3 2007DALE G. MCNEIL Summary 1. Hypoxic conditions occur frequently during hot, dry summers in the small lentic waterbodies (billabongs) that occur on the floodplains of the Murray-Darling River system of Australia. Behavioural responses to progressive hypoxia were examined for the native and introduced floodplain fish of the Ovens River, an unregulated tributary of the Murray River in south-east Australia. 2. Given the high frequency of hypoxic episodes in billabongs on the Ovens River floodplain, it was hypothesised that all species would exhibit behaviours that would confer a degree of hypoxia-tolerance. Specifically, it was hypothesised that as hypoxia progressed, gill ventilation rates (GVRs) would increase and aquatic surface respiration (ASR) would become increasingly frequent. Fish were subjected to rapid, progressive hypoxia from normoxia to anoxia in open tanks. 3. All tested species exhibited behaviours consistent with their use of potentially hypoxic habitats. As hypoxia progressed, GVRs increased and all species, with the exception of oriental weatherloach, began to switch increasingly to ASR with 90% of individuals using ASR at various oxygen concentrations below 1.0 mg O2 L,1. Australian smelt, redfin perch and flat-headed galaxias were the first three species to rise to ASR, with 10% of individuals using ASR by 2.55, 2.29 and 2.21 mg O2 L,1 respectively. Goldfish and common carp were the last two species to rise to ASR, with 10% of individuals using ASR by 0.84 and 0.75 mg O2 L,1 respectively. In contrast to other species, oriental weatherloach largely ceased gill ventilation and used air-gulping as their primary means of respiration during severe hypoxia and anoxia. 4. Australian smelt, redfin perch and flat-headed galaxias were unable to maintain ASR under severe hypoxia, and began exhibiting erratic movements, termed terminal avoidance behaviour, and loss of equilibrium. All other species continued to use ASR through severe hypoxia and into anoxia. Following a rise to ASR, GVRs either remained steady or decreased slightly indicating partial or significant relief from hypoxic stress for these hypoxia-tolerant species. 5. Behavioural responses to progressive hypoxia amongst the fish species of the Ovens River floodplain indicate a generally high level of tolerance to periodic hypoxia. However, species-specific variation in hypoxia-tolerance may have implications for community structure of billabong fish communities following hypoxic events. [source] Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya BayAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2006Yoshikuni Hodoki Abstract 1.Ariake Bay, which is located in western Japan, has a large tidal range (>6 m) and a vast tidal flat (200 km2). In the early 1990s, the government-managed Isahaya Reclamation Project began in the western part of Ariake Bay. A 16-km2 area of tidal flat in the inner part of Isahaya Bay was destroyed through reclamation and separated from the sea by a dyke, which created land and a freshwater reservoir. 2.Since the initiation of the project, fishery yields around Isahaya Bay have dramatically decreased. The objective of this study was to clarify the relationship between the work associated with the Isahaya Reclamation Project and the recent environmental deterioration in Ariake Bay, with references to present sediment thickness and organic matter content, and hypoxic water distributions in Isahaya Bay. 3.The organic matter load from the reservoir has increased since the initiation of the reclamation project and has been associated with a thick layer of fine sediment at the bottom of Isahaya Bay. The thickness of fine sediment and the total organic carbon content were higher in Isahaya Bay than in the freshwater reservoir. 4.Based on measurements in August 2001, hypoxic water spread widely in and around Isahaya Bay; the lowest dissolved oxygen (DO) concentration (0.53 mg L,1) was observed just outside the dyke. An analysis based on a two-layered box model using data obtained in August 2001 showed that the DO consumption rate in the bottom layer was high (0.61 mg O2 L,1 day,1), and that 22,41% of the total organic carbon load needed to induce the hypoxic water was derived from the reclamation area. 5.Our findings strongly suggest that enclosed seas may suffer from eutrophic and hypoxic conditions because of their low seawater-exchange rate. A comprehensive conservation programme and environmental assessment including physical and material transport processes in the system is needed to manage the environment of the enclosed sea. Copyright © 2005 John Wiley & Sons, Ltd. [source] Hypoxia tolerance of the mummichog: the role of access to the water surfaceJOURNAL OF FISH BIOLOGY, Issue 3 2003K. L. Stierhoff Low dissolved oxygen (DO) had a significant effect on specific growth rate (GS), length increment (IL) and haematocrit (Hct) of the mummichog Fundulus heteroclitus. Regardless of access to the water surface, F. heteroclitus maintained high growth rates (GS and IL) at DO concentrations as low as 3 mg O2 l,1. With access to the water surface, both GS and IL of F. heteroclitus decreased by c. 60% at 1·0 mg O2 l,1 compared to all higher DO treatments. When denied access to the water surface, a further decrease in GS (c. 90%) and IL (c. 75%) was observed at 1 mg O2 l,1. There was no effect of diel-cycling DO (1,11 mg O2 l,1) with or without surface access on GS, IL or Hct of F. heteroclitus. Similar trends between GS and faecal production across DO treatments suggest that decreased feeding contributed significantly to the observed decrease in growth rate. Haematocrit was significantly elevated at 1 mg O2 l,1 for fish with and without access to the water surface. Increased Hct, however, was not sufficient to maintain high GS or IL at severely low DO. When permitted to respire in the surface layer, however, F. heteroclitus was capable of maintaining moderate growth rates at DO concentrations of 1 mg O2 l,1 (c. 15% saturation). Although aquatic surface respiration (ASR) was not quantified in this study, F. heteroclitus routinely swam in contact with the water surface and performed ASR at DO concentrations ,3 mg O2 l,1. No hypoxia-related mortality was observed in any DO or surface access treatment for as long as 9 days. This study demonstrates that surface access, and thus potential for ASR, plays an important role in providing F. heteroclitus substantial independence of growth rate over a wide range of low DO conditions commonly encountered in shallow estuarine environments. [source] | |||||||||||||