Main Water Body Research Articles

Aquatic invertebrates of Lake Gregory, northwestern Australia, in relation to salinity and ionic composition

Lake Gregory is a large semi-permanent lake system in arid north-western Australia. Its catchment extends into humid areas and as a result the lake has dried only twice in the last 25 years. Although the system is mostly fresh, parts of it become saline as they dry. We identified aquatic invertebrates and undertook chemical analysis of water samples from several sites at Lake Gregory in 1989, when the main water-body was saline, and in 1991 and 1993, after the system had flooded and was fresh. During the period 1989–1993, salinities varied from 0.1‰ to 82‰, and ionic composition ranged from strong sodium chloride dominance, in saline water and fresh water of the eastern part of the system, to bicarbonate dominance in fresh water of the western area. At least 174 invertebrate species were recorded, including two mollusc species that were never collected live. This species richness is much higher than that recorded from other Australian arid zone lakes, probably owing to long periods of inundation with fresh water. The fauna was dominated by insects (42 per cent of total species richness), crustaceans (27 per cent) and rotifers (22 per cent). Most species (160) were restricted to fresh water; only 12 species were found in saline water. Only one ostracod occurred in saline conditions, although ostracods are a dominant group in Australian saline lakes. Among species restricted to fresh water, the proportion of rotifer and protozoan fauna that occurred in bicarbonate-dominated water was greater than the proportion of insect, crustacean and hydracarine fauna that did so.

Habitat selection and clutch fate of Piping Plovers (Charadrius melodus) breeding at Lake Diefenbaker, Saskatchewan

We studied habitat selection by Piping Plovers (Charadrius melodus) at Lake Diefenbaker, Saskatchewan, during the 1992 and 1993 breeding seasons. Habitat selection was investigated at three levels: beach, territory, and nest site. Nest beaches had significantly more gravel substrate than non-nest beaches (F[1,11] = 21.52, p < 0.01). There was no significant difference in width between nest and non-nest beaches. All Piping Plover nests were located on gravel, though this substrate only accounted for approximately 43% of nest beach area. Nest sites were significantly farther from the nearest water (F[1,181] = 12.24, p < 0.01), the main water body (F[1,181] = 6.55, p < 0.05), and had significantly more stones (F[1,161] = 10.98, p < 0.01) and rocks (Z = 2.93, p < 0.01) than random sites. Distance to the nearest water source, number of stones per square metre, and distance to the vegetation line were the three variables used by the stepwise discriminant function analysis to correctly classify 41.8% of nest sites and 87.1% of random sites. This was still significantly better than chance (Z = 3.66, p < 0.01). The low percentage of correctly classified nest sites may indicate that some plovers at this lake used nest sites on lower quality substrate. Flooded nests were significantly closer to water than successful nests and depredated nests were closer to the vegetation line than successful nests.

Distribution of Carbon in a Tropical Hypersaline Estuary, The Casamance (Senegal, West Africa)

The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO3 in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I−1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.

Temporal and spatial variations of phytoplankton from Boeckella Lake (Hope Bay, Antarctic Peninsula)

The main water body at Hope Bay, Boeckella Lake, was sampled at four sites for phytoplankton during summer 1991 to assess the influence of nutrients from nearby penguin rookeries on both phytoplankton density and composition. The site located at the base of the rookeries had total phosphorus values comparable to those reported from the most eutrophic Antarctic lakes. During the ice-free period most of the Chlorophyceae and Cyanophyceae recorded were concentrated at this site. Phytoplankton density increased strongly in the area opposite to the rookeries where ice began to form; an under-ice bloom of Ochromonas aff. ovalis (Chrysophyceae) was observed in this area.

The spray sheets produced during vertical wedge impact and steady planing

“Added mass” theory is usually employed in a momentum analysis. In connection with the vertical impact of a wedge, Pierson noted an anomaly when it is employed in an energy analysis, because the two approaches yielded different results. This led the writer to conjecture that the “difference” might be due to the energy dissipated in the spray sheets. The analysis which follows appears to support that conjecture, in that the size of the spray sheets so calculated is the same as those of Pierson's [(1950), The penetration of a fluid surface by a wedge. Stevens Institute of Technology Report No. 381 (July) (IAS paper FF-3)] numerical calculations. The theory predicts, for both vertical wedge impact at constant vertical velocity and for the steady high speed planing of a slender prismatic hull, that half the pressure drag energy ( Du o ) appears as kinetic energy in the spray sheets, the other half being absorbed by the downward deflection of the main body of water. This does not agree with the conclusions drawn from the experimental work of Latorre and Tamiya [(1975), An experimental technique for studying the planing boat spray. Proceedings of the Fourteenth International Towing Tank Conference, Ottawa, Canada, Vol. 4, pp. 562–571] and Latorre [(1983), Study of prismatic planing model spray and resistance components. J. Ship Res. 27, 187–196]. Nor does it agree with two-dimensional planing theory [summarized in ch. 3 of Payne [(1988), Design of High-speed Boats, Volume I: Planing. Fishergate, Inc., Annapolis, Maryland]] where all the energy appears in the spray sheet at very high Froude numbers. But the equal division of energy into spray and water deflection for slender surfaces was predicted for a high speed slender planing surface by both Wagner [(1932), Uber Stoss-und Gleitvorgänge an der Oberfläche von Flüssig-keiten.

Radon concentration levels in ground water from Toluca, Mexico

Concentration levels of 222Rn have been analysed in water samples from deep wells of the aquifers around the City of Toluca, Mexico. The 222Rn source is the decay of 226Ra within the solid matrix of the aquifer. With a half life of 1600 years the 226Ra continuously releases 222Rn to the pores, from which it diffuses into the main body of water. This paper describes the methods used for sampling and measuring solubilized and 226Ra-supported 222Rn in the water samples, in order to evaluate possible health hazards due to the presence of radon in the drinking water supplies. The relationship of 222Rn with the hydrogeologic characteristics of the zone is also described. The analytical method involves laboratory extraction of 222Rn into toluene. Alpha disintegrations of 222Rn and contributions from short-lived daughters are counted by the liquid scintillation technique. The system was calibrated using a 226Ra standard solution. Results up to 11.3 Bq/l of 222Rn were obtained in the water samples.

Fluctuations in fyke-net catches during the spawning period of the Eurasian perch ( Perca fluviatilis) in the Rimov Reservoir, Czechoslovakia

The perch spawning stock catch (1985–1988) of the Rimov Reservoir was studied using Rimov fyke-nets and Klicava traps. Spawning and an increased catch were found in the tributary area 1 week earlier than in the main waterbody. The peak catches moved from depths of 3–4 m to the surface during the spring homothermy. After the development of thermal stratification, the peak catch moved to depths with a temperature range of 8–12°C. Catch per unit effort decreased during the second half of the spawning period but shifting the fyke-nets to depths where spawning activity was maximum increased the total seasonal catch by at least 100%. At the end of spawning, the peak activity was found at 6–9 m. Normal spawning stock is characterised by a strong predominance of males in the catch of the fyke-nets; postspawning females predominate in the later catches in shallow areas. Catches in the fyke-nets in the formerly wooded areas were more than four times higher than the catches from areas without tree stumps.

Visualization of Entrainment of a Thin Layer at Water Surface due to Collision of a Vortex Ring

A vortex ring colliding against water surface is visualized. The vortex ring is generated by ejecting a volume of water from a nozzle. As the vortex ring collides against water surface, it generates some secondary vortex rings of opposite rotation to that of the original one. It is observed that collapse of a vortex ring entrains water in a thin layer at water surface into the main water body.

A theoretical study on drop impact sound and rain noise

This paper examines the sound waves generated when a spherical water drop impacts upon an initially quiescent water surface. The pressure fluctuations and the acoustic energy radiated by the initial impact are calculated analytically. It is shown that the rapid momentum exchange between the fluid in the falling drop and that in the main water body causes the radiation of compressive waves. These waves are radiated in the form of a wave packet with a densely packed edge which is heard in the far field as a noisy shock-like pulse followed by a quickly decreasing tail. The wave packet carries with it sound energy proportional to the kinetic energy of the falling drop and to the cube of the impact Mach number. Applications of these analytic results to the study of noise from natural rain are discussed, and an illustrative example is given where the noise level due to rain showers is linearly related to the rainfall rate, which is shown to be consistent with observations.

The ecology of the Corixidae (Hemiptera: Heteroptera) in the Corrib catchment, Ireland

Two surveys were carried out in the Corrib catchment (Ireland) to determine the physical and chemical factors that govern the distribution of Corixidae. Of the twenty one species recorded, five species, Sigara scotti (Fieber), S. distincta (Fieber), S. fossarum (Leach), S. fallenoidea (Hungerford) and Cymatia bonsdorffii (Sahlberg) comprised 82% of the numerical total. Although individual species occurred in chemically diverse sites species assemblages and changes in the relative abundance of the majority of species and in species richness and diversity were evident in the progression from hard to soft water. High altitude soft water sites had a much lower number of species compared with chemically similar low altitude sites. In Lough Corrib, the main body of water in the catchment, most species were abundant only in sheltered areas with mud substrates and high percentage vegetation cover. Species diversity was high in these areas and either C. bonsdorffii, S. fossarum, S. fallenoidea or Callicorixa praeusta (Fieber) dominated numerically. However, S. scotti, S. dorsalis (Leach) and Arctocorisa germari (Fieber) were more abundant in exposed areas with sand, gravel or mearl substrates. In temporary ponds and in lotic water species diversity was also high but species composition (mainly C. praeusta, Sigara nigrolineata (Fieber), Corixa punctata (Illiger), C. panzeri (Fieber), C. bonsdorffii) was different to that of temporally stable lentic habitats.

Suivi de populations nouvelles. Compte-rendu ornithologique camarguais pour les années 1988-1989

This ornithological report for the Camargue and neighbouring areas covers the years 1988-1989. It is not just a list of rare species but summarises the results of long-term monitoring of many of the aquatic bird communities which make up the extreme richness of the area throughout the year. A short climatological report and graphs showing annual precipitation and the fluctuations of the level and salinity of the main water body of the Rhone delta, the Vaccarès, help to explain some of the changes which the populations of some species have undergone. The two winters in question were unusually mild and 1989 was characterised by the lowest rainfall on record for the area. Amongst the most striking changes in the numbers of birds using the delta in recent years have been the increase of the wintering Greylag goose population and the increase of both Slender-billed and Mediterranean Gulls whilst the Penduline tit, abundant on migration and in winter, still has not returned to breed in the Camargue where it was so conspicuous twenty years ago.

Convection lines on a heated bottom plate at large Rayleigh number

The microstructure of thermal convection at large Rayleigh number was studied experimentally. Sheetlike plumes generated at the heated bottom plate are composed of several thermals generated successively. The projection of the sheetlike plumes on the bottom plate is called convection lines. On the other hand, in the area surrounded by sheetlike plumes where descending compensational flow prevails, the conduction layer always remains in the vicinity of the bottom, within which excess temperature is still high. The heat supplied from the bottom is transported horizontally by weak flow in the conduction layer toward the convection lines where rising sheetlike plumes carry the converged heat into the main body of water. Fluctuation of the convection lines was investigated. It is found that phenomenologically, the merging of thermals causes much stronger sheetlike plumes and accelerates the formation of large‐scale convection.

Levels of heavy metals in the tidal Elbe and its estuary and the heavy metal input into the sea

Surface water samples were collected during missions in 1977, 1978, 1980 and 1983 at different sampling stations along the tidal Elbe, from river km 632 downstream from Hamburg to the outer end of the estuary. Special care was taken to minimize contamination during sampling, handling and analysis. Within the tidal Elbe five distinct zones of substantial anthropogenic heavy metal pollution inputs can be detected. An attempt is made to define anthropogenic background levels, which are extremely low for the dissolved trace metals Cd and Pb; 35 and 65 ng/kg, respectively. The level of dissolved Cu is 2200 ng/kg. Total baseline levels of Cd, Pb and Cu are, respectively, 120, 2500 and 4200 ng/kg. In the five river zones affected by anthropogenic trace metal inputs, distinctly larger maximum levels can occur. They decrease to the backgroud values after mixing with the main water body. More elevated levels caused by re-suspension in the mixing zone with maximum turbidity can be assumed. Nickel and Co data are from one mission only. The order of magnitude of the trace metal input from the Elbe into the sea is evaluated.

Effects of Impoundment and Diversion on the Crustacean Plankton of Southern Indian Lake

Planktonic crustaceans in Southern Indian Lake were surveyed in 1972 before impoundment, during 1975 when water levels rose above the recorded high level, and then annually from 1977 to 1980 after full impoundment and diversion. Synoptic data were collected in each of these years in midsummer during July or August from a set of 53 stations covering all regions of the lake. Vertical hauls were made at each station using twin nets of 77-μm mesh and 25-cm mouth diameter. In 1972, the crustacean plankton fauna of Southern Indian Lake was composed mainly of 15 copepod and 15 cladoceran species. At least 25 of these species were truly pelagic, while 5 were littoral. Cyclopoids comprised 46% of total crustacean abundance, calanoids 33%, and cladocerans 21%. Dominant species within these three groups were Cyclops bicuspidatus thomasi (37.6% of total abundance), Diaptomus ashlandi (20.1%), and Chydorus sphaericus (8.9%). Total abundance averaged 76 individuals (ind)∙L−1, comparable to more southerly waters such as Lake Ontario (80 ind∙L−1) and Lake Winnipeg (53–108 ind∙L−1) (K. Patalas. 1975. Int. Ver. Limnol. Verh. 19: 504–511). Throughout the lake, total crustacean abundances varied from 10 ind∙L−1 near the Churchill River inflow to between 100 and 200 ind∙L−1 in a few well protected areas. From 50 to 100 ind∙L−1 occurred within the main body of Southern Indian Lake. In 1975, an unusually high water year, lake mean plankton abundance was 61 ind∙L−1. Following diversion in 1976, no dramatic changes in species composition were observed. However, the mean abundance of crustaceans decreased to 40–46 ind∙L−1 during the period 1977–80. Regional zooplankton responses were varied. No significant changes occurred in areas adjacent to the Churchill River inflow, with pre- and post-diversion densities being 35 and 36 ind∙L−1, respectively. In the main water bodies north of the diversion route, abundances declined by 60% and biomass by 50%. A 2–3 °C drop in northern basin water temperatures, related to diversion, reduced growth rates by approximately 20% and resulted in a 60% decline in crustacean production. Not all groups of crustaceans responded similarily to impoundment and diversion. Lakewide average numbers of cladocerans declined from 16 to 4 ind∙L−1 and the area of their distribution was reduced particularly in northern regions of the lake following impoundment. Cyclopoids declined from 35 to 16 ind∙L−1 but showed no change in their distribution. These reductions were related to decreased water temperatures, lower midsummer chlorophyll a concentrations, and decreased water transparencies. The mean abundance of calanoids as a group did not change, but the abundance and distribution of individual species were variably altered. Smaller calanoid species showed either no change or a decrease in their numbers and distribution. Larger species, e.g. Limnocalanus macrurus, Senecella calanoides, and Diaptomus sicilis, were significantly more abundant and widespread following diversion. Similar increases in Mysis relicta were also observed. These large species, preferred food items for both whitefish and cisco, are cold stenotherms, inhabiting deeper water layers. Their increased abundance is likely associated with decreased water transparency offering better protection against predatory fish, decreased water temperature creating more favorable conditions, and increased water depth enlarging the volume of deeper waters suitable for these species.

Bathymetry, heat output and convection in Ruapehu Crater Lake, New Zealand

Bathymetric observations of Ruapehu Crater Lake show that it became shallower and its volume decreased by 3 × 10 6 m 3 between 1965 and 1970. It is likely that this was due to lava moving upwards in the region under the lake. From the regular measurements of Crater Lake temperature, outflow, and chloride and magnesium ion concentrations, the inflows of steam, cold water and chloride and magnesium ions were calculated, using the 1970 volume. Only about half the precipitation falling on and around the lake mixes with the lake water, since the cold fresh water floats on top of the denser lake water, and travels to the outlet without mixing with the main body of water in the lake. The chloride content of the input steam appears to vary with time, in a similar fashion to that of White Island fumaroles. Temperature and density profiles of the lake in 1965 and 1966 indicated that convection was occurring. The temperature profile of the top 175 m of the lake agreed with a model of turbulent convection in small cells, giving a temperature gradient at any level in the lake proportional to the heat flux at that level. The convection model predicted that the temperature at depth would exceed the local boiling point if the thermal power input reached a value which would sustain a surface temperature approaching 60°C. This prediction of instability was not inconsistent with observations. Convection in the present Crater Lake probably occurs in the form of thermal plumes from small sources.

Overwintering at Low Oxygen Concentrations in the Mayfly Leptophlebia Vespertina

The survival of L. vespertina (L.) nymphs in three humic forest ponds in southern Norway was investigated. The main water bodies of the ponds were apparently anoxic for part of the winter due to ice cover and organic decomposition. However, laboratory experiments showed that the nymphs are unable to survive long-term anoxia even at low temperatures. Their oxygen level for 95% sustained survival at 0.3C is 0.4-0.5 mg 0, I-'. Although most of the water body is anoxic for several months, oxygen is present in the shore areas and also, during thaws, in the water layer immediately under ice. Laboratory experiments. demonstrated that the nymphs are both positively phototactic and negatively thermotactic in low oxygen concentrations. Coupled with an ability to withstand short-term anoxia, this results in a movement of nymphs into the shore areas, where temperatures approach O0C, percolation of meltwater containing oxygen occurs and food is available. Under such conditions the nymphs can survive and even grow slowly.

Strategies of adaptation to extreme conditions in aquatic microorganisms

Aquatic ecosystems include the two extremes: constant environmental conditions in the main bodies of water, and unstable fluctuating conditions in the shallow margins of the aquatic ecosystems. Aquatic microorganisms living in the main oceans can thus be characterized by a single prototype being moderately halophilic, psychrophilic, to some extreme barophilic and all must be oligotrophs managing to survive and multiply in extremely low nutrient concentrations. On the other hand those populating the shallow margins must be adapted to rapidly fluctuating environments and thus have multipotential metabolic patterns. Oscillatoria limnetica can serve as a model for this being capable of shifts from oxygenic to non-oxygenic photosynthesis, having multiple dark energy generating systems, fixing nitrogen anaerobically and capable of induction of resistance mechanisms to overcome oxygen toxicity.

Distribution of Culicoides molestus (Skuse) (Diptera : Ceratopogonidae) in Man-made Canals in South-eastern Queensland

In soil samples flooded for 18 h C. molestus larvae were scarce in the top 0.5 cm, most dense in 0.5-1.5 cm and most numerous in 1.5-8.5 cm depth. They were recovered from mean high water springs to mean tide level but were concentrated (87.6%) in a narrow zone above mean tide level and including mean high water neaps. There was no evidence that their distribution was influenced by remoteness from the main body of tidal water. Higher density fluids than normal, e.g. syrup, specific gravity > 1.3, were required to extract larvae of C. molestus.

Rates of remineralization and assimilation of urea by fractionated plankton populations in coastal waters

Planktonic populations from three contrasting sites collected in March, May, and August, 1976, were fractionated by differential filtration into a larger fraction (LF) and smaller fraction (SF) and the kinetics of remineralization and assimilation of 14C urea in the dark by these fractions and the total populations examined. The data were plotted according to the treatment of Wright & Hobbie. Linear kinetics was generally found for total 14C turnover by the LF and SF collectively. Turnover times of the in situ urea were greatest in March when minimal phytoplankton was present and least in May at the time of the spring bloom of phytoplankton. Lowest turnover times were always found at the station in open water outside the Lough. There was no relation between turnover time and in situ urea concentrations. Maximum velocity of uptake of urea ( V) was greatest in May and least in August: the lowest values of V were always encountered in the main water body of the Lough. Comparable data for the LF followed a similar pattern. Linear kinetics of 14C urea turnover was not shown by the SF, a fraction which accounted for up to 40 % of 14C turnover. The proportion of 14C utilized by the SF increased with increasing concentration of added urea. 14C was only assimilated by the LF, the amount being 10 % or less of the total 14C turnover.

Petrology and alteration of selected units of Mid-Atlantic Ridge basalts sampled from sites 332 and 335, DSDP

Closely spaced samples spanning 'flow units' at sub-bottom depths of 500 and 590 m in the drill hole at site 332B and a pillow at depth of 460 m, site 335, as well as a few individual samples at various depths in these holes and in the hole at site 332A, were studied with a view to determining compositional changes effected by submarine alteration. The rocks are predominantly plagioclase-olivine phyric tholeiitic basalts, with the exception of the lower unit of 332B, which is a picrite formed by the concentration of olivine megaphenocrysts in olivine tholeiitic basalt, is markedly flow-differentiated, and is assumed to be a sill. Three generations of plagioclase and olivine evident in some of the samples as corroded megaphenocrysts (An86−78, Fo89), euhedral microphenocrysts (An76−72, Fo85−84), and groundmass crystals (An72−61, Fo85−84), record a crystallization history that begins at depth, continues en route to the surface, and ends with quenching on the sea floor. Filling interstices of the groundmass are intergrowths, commonly submicroscopic, of pyroxene–plagioclase and dark, poorly resolved titanomagnetite-charged magmatic residue. The pyroxenes arc augites, ranging to subcalcic and ferroaugite. In places, particularly near pillow and flow unit margins, magma residue partially or completely in-fills vesicle cavities (segregation vesicles). Volatile-bearing phases (notably chlorophaeites, saponite, palagonite, amorphous silica-bearing hydrous iron oxides, and carbonates) tend to be characteristic of the three principal sites in which they are found: palagonite in the glassy margins of pillows and (or) flow units, complex hydrous mineraloids adjoining veins, and chlorophaeites and saponites in the interstices of the crystalline matrix of rocks remote from veins. The latter have the aspect of primary minerals. Palagonitization results in gains in K, Fe, Ti, and Cl, and losses in Ca, Mg, and Na, but net gains and losses in the other sites are less certain. Hydration and oxidation of iron invariably accompany development of volatile-bearing phases, but there is no correlation between these parameters and variation in content of the other analysed elements. Principal component analysis shows that the major part of the compositional variation can be explained by primary factors. In these samples chemical exchange with seawater appears to be limited, possibly because of their rapid isolation by burial from the main body of ocean water.