Hydrobiologia

Alcocer, Javier; Lugo, Alfonso; Sánchez, María del Rosario; Escobar, Elva

doi: 10.1023/a:1003239910574pmid: N/A

The Isabela Crater-Lake is a bright-green, hypersaline lake (68–112.5 mS cm-1) on Isabela Island off the Pacific coast of Nayarit, Mexico. Some salient features were documented in November 1993. It appears meromictic, with three well-defined strata separated by sharp pycnoclines. Surface water was warm (32 °C) reaching a subsurface (0.5–1 m) maximum temperature (33 °C), declining gradually to 26.7 °C at maximum depth (17.5 m). Dissolved oxygen was near saturation at the surface, attained 145 percent saturation at 0.5 m, but was completely absent by 2.5 m. Eh was maximum at the surface (123 mV), declining to a minimum at 3 m (–261 mV), and was about –240 mV from 3.5 m to the bottom. The pH varied from 9.3 in surface waters to slightly acid (6.4) in deep anoxic layers. Atypically, NO3 was more abundant than NH4 in both aerobic and anaerobic strata. PO4 and SiO2 concentrations were extremely high. The planktonic microbial community was formed by four groups: bacteria (photosynthetic sulfur bacteria and heterotrophic bacteria), phytoflagellates (mainly cryptomonads), heterotrophic nanoflagellates ( Spumella spp., Bodo spp.) and ciliates (Hypotricha and Oligotricha). Bacteria occurred throughout the water column, but other biota were restricted to surface waters.

Lugo, Alfonso; Alcocer, Javier; del Rosario Sanchez, Ma.; Escobar, Elva

doi: 10.1023/a:1003291927412pmid: N/A

Littoral protozoan assemblages from two hyposaline crater-lakes (Lakes Alchichica and Atexcac) located in the Oriental Valley, center of Mexico, were studied using the polyurethane foam units (PFU) colonization method. Fifteen PFU (5 dates, three replicates per date, 64 × 72 × 50 mm) were located in the littoral area of each lake and collected at 8, 14, 20–21, 28–29 and 38–39 d intervals. Both lakes were hyposaline (Salinity between 6 and 7.1 g l-1) and alkaline (pH range: 8.4–9.1). Eighty seven species were observed in both lakes. In Alchichica 44 species and 43 in Atexcac. Ciliates and flagellates species dominated the assemblages' composition. The flagellates Bodo caudatus and Spumella termo and the ciliate Cyclidium glaucoma were the most abundant species in Alchichica, while in Atexcac the flagellates Cryptomonas ovata and B. caudatus and the ciliates C. glaucoma and Stylonychia notophora were most abundant. Except for S. notophora, which consumes algae, the other species are mainly bactivores.

Halse, S. A.; Shiel, R. J.; Williams, W. D.

doi: 10.1023/a:1003263105122pmid: N/A

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.

Timms, B. V.

doi: 10.1023/a:1003267221960pmid: N/A

Continuing studies of 25 shallow lakes in the semi-desert of northwestern New South Wales during drier years revealed greater physicochemical extremes than previously recorded and wider fluctuations in salinity, even in less saline lakes. Earlier data on species composition and species richness were confirmed, with a few new species reported from either further field collections or the hatching of dried lake muds. A summer filling as against almost regular previous autumn-winter fillings made only a minor difference in faunas, though insects and phyllopods, for different reasons, were less prevalent in the drier years. The fauna of these inland saline lakes is not only biogeographically different from those in southern Australia, but is adapted to a more extreme and irregular environment.

Anati, David A.

doi: 10.1023/a:1003219322869pmid: N/A

The Dead Sea water column is composed, to a first approximation, of two water bodies: the deep waters, constituting most of the lake's volume, and a shallow upper layer a few meters thick. The temperature and salinity profiles can both be either stabilizing or destabilizing, depending on the regime and the season; if salinity is destabilizing, and double-diffusive processes are attained, the two water bodies mix at a much faster rate than normal turbulent diffusion can account for. The trajectories of the Dead Sea brines since 1977 belong to one of three different categories: upper layer under a meromictic regime, upper layer under a holomictic regime, and lower layer under a holomictic regime. The lower layer during the meromictic regime of 1979– 82 remained constant in its properties and its trajectory is thus represented by one single point.

Peng, Q. M.; Palmer, M. R.; Lu, J. W.

doi: 10.1023/a:1003260204213pmid: N/A

The borate deposits in Liaoning, Jilin province, China, are hosted in the Paleoproterozoic meta-volcanic-sedimentary sequence which comprises magnetite-microcline rocks, K- and Na-rich leptynites and leptites, magnesium marbles and amphibolites. The borates are exclusively hosted in the magnesium carbonates and Mg-silicate rocks. The association of these rocks, their sedimentary structures and unusual chemical composition suggest that their protolithes were sediments deposited in evaporite basins: red beds, zeolitized tuffs and evaporites. Therefore, the borate deposits are metamorphosed evaporites. The initial precipitates were magnesium carbonates and hydrous magnesium borates, reflecting a MgSO_4 brine stage in a playa lake environment. During the subsequent metamorphism, these borates were dehydrated to form anhydrous borates, e.g. suanite and ludwigite. These deposits are analogous to many modern evaporite sequences in rift systems. Mineralogically, these borates are comparable to the borates in the saline lakes in the Qinghai-Xizang (Tibet) plateau.

Wang, Ruiliang

doi: 10.1023/a:1003223506939pmid: N/A

Acyclic isoprenoid hydrocarbons are found to be the predominant components in the organic matter extracted from sedimentary cores and oils of various hypersaline settings, including Tertiary Janghan salt lake basin, Cretaceous Taian salt lake basin, and Triassic, Permian and Cambrian Yangtze evaporitic marine platform. Inland saline lake basins are characterized by tremendous predominance of phytane (iC20) ranging up to 15% of the total extract. While the evaporitic marine sediments are unique for their complete series of super-long-chain acyclic isoprenoids, up to C40. These isoprenoids possess head-to-head, tail-to-tail or regular linkages and generally are indicators of the significant contribution from various archaea (archaebacteria), i.e. halophiles, methanogens and acidothermophiles. According to the great discrepancy of distribution and composition of isoprenoids, these modern and Cenozoic inland salt lake sediments are likely dominated by halophilic archaea, while the studied Mesozoic and Paleozoic evaporitic marine sediments are predominantly distinguished by methanogens and acidothermophiles. Concentration of chlorine salt is more directly proportional to the abundance of phytane than sulfate. Reduced species of sulfur, sulfide, S0 and organic sulfur compounds (OSC), however, may have played a key role in the preservation and formation of the highly abundant phytane observed in the inland salt lake basins.

González, Maria R.; Hart, Cheryl M.; Verfaillie, Joseph R.; Hurlbert, Stuart H.

doi: 10.1023/a:1003227624686pmid: N/A

A 15 month long experiment was undertaken to document responses of the Salton Sea biota to experimentally manipulated salinity levels (30, 39, 48, 57, and 65 g l-1) in 312-liter fiberglass tanks maintained outdoors. At two salinities (39 and 57 g l-1) microcosms were set up each having one small tilapia ( Oreochromis mossambicus) in order to assess its influence on the system. To 28 tanks filled with Salton Sea water diluted to 30 g l-1, different salts (NaCl, Na2SO_4, MgSO4 · 7H2O, KCl) were added in constant proportions to produce the desired salinity levels. Salton Sea shoreline sediment was added to the bottom of each tank, and inocula of algae and invertebrates were added on several occasions. Invertebrate populations, phytoplankton, periphyton, and water chemistry were monitored at regular intervals. This article present the results concerning water chemistry and nutrient cycling. There was no apparent increase in salinity over time, though ∼ 1190 l of tapwater with a salinity of ∼ 0.65 g l-1 were added to each tank during the experiment. Ionic composition varied both among treatments and over time to some degree. Ca2 concentrations were the same at all salinities, while K1 concentrations were >3 times greater at the highest salinity than at the lowest. pH showed little consistent variation among salinities until the last few months when it was higher by ∼ 0.4 units at the two higher salinities than at the lower ones; it was unaffected by fish. Absolute oxygen concentrations were negatively correlated with salinity, and occasionally depressed by the presence of fish. PO3-4, dissolved organic phosphorus, and particulate phosphorus concentrations were often reduced by 30–80% at 65 g l-1 relative to lower salinities and by the presence of fish. Early in the experiment NO2-3 concentrations were >2 times higher at 57 and 65 g l-1 than at lower salinities, but otherwise effects of salinity on dissolved forms of nitrogen were not marked; particulate nitrogen was much lower at 65 g l-1 than at other salinities and also was reduced by up to 90% by the presence of fish. Silica concentrations increased over time at all salinities, but, relative to those at lower salinities, were reduced by 60–90% at 65 g l-1 by abundant periphytic diatoms. The TN:TP ratio (molar basis) was 24–30 initially and 35–110 at the end of the experiment; it was positively correlated with salinity and the presence of fish. Mechanisms accounting for the above patterns involve principally the biological activities of phytoplankton and periphyton, as modified by grazing by Artemia franciscana and Gammarus mucronatus, and the feeding and metabolic activities of the tilapia. The large reduction in water column TN and TP levels brought about by the fast-growing, phyto- and zooplanktivorous tilapia suggest that amelioration of the Salton Sea's hypereutrophic state might be assisted by a large scale, sustained yield fish harvesting operation.

Hart, Cheryl M.; González, Maria R.; Simpson, E. Paul; Hurlbert, Stuart H.

doi: 10.1023/a:1003490215005pmid: N/A

The Salton Sea is the largest inland lake in California. Currently (1997) the salinity of the lake is about 44 g l-1 and is increasing gradually as a result of continued agricultural wastewater inflows, high evaporation rates, and lack of an outlet. A microcosm experiment was carried out to determine the effects of salinity (30, 39, 48, 57, and 65 g l-1) on Salton Sea algae and invertebrates in outdoor aquatic microcosms. The experiment was also designed to assess the effects of tilapia ( Oreochromis mossambicus) on this community at two of these salinities (39 and 57 g l-1). Fiberglass tanks containing Salton Sea water were adjusted to the appropriate salinity by the addition of salts, identically inoculated with organisms from the Salton Sea and other saline water bodies in the region, and monitored for 15 months. Planktonic and nektonic invertebrates were sampled monthly at night from the upper part of the water column. The dominant invertebrates present were Gammarus mucronatus, Artemia franciscana, Trichocorixa reticulata, and an assemblage of ciliate protozoans. Gammarus decreased and Trichocorixa increased with increasing salinity. Artemia was present only at the two highest salinities. Rotifers, harpacticoid and cyclopoid copepods, barnacle larvae, and protozoans all showed marked and varied responses. During the latter half of the experiment, the invertebrate assemblage was dominated by Gammarus at 30 and 39 g l-1, by protozoans at 48 g l-1, and by protozoans and Trichocorixa at 57 and 65 g l-1. The presence of tilapia caused a 99 percent reduction in Gammarus at 39 g l-1 and a 70–90 percent decrease in Trichocorixa at 57 g l-1. These were accompanied by substantial increases in rotifers, copepods, and certain protozoans, and decreases in other protozoans. As the salinity of the Salton Sea continues to increase, large changes in the invertebrate populations are expected. This study suggests that the principal change would be an increase in Trichocorixa densities, the loss of Gammarus, and the appearance of Artemia at about 60–70 g l-1, when both fish and invertebrate predators are likely to be scarce or absent. Protozooplankton abundance is likely to increase when tilapia declines and later decrease when and if large Artemia populations develop.

Simpson, E. Paul; González, Maria R.; Hart, Cheryl M.; Hurlbert, Stuart H.

doi: 10.1023/a:1003231708756pmid: N/A

The Salton Sea, the largest lake in California, has a surface elevation 69 m below sea level which is maintained predominantly by the balance of agricultural runoff and evaporation. The lack of outflowing streams is resulting in a gradual buildup of salts in the lake, increasing the salinity. A 15 month microcosm experiment was conducted to determine the effects of salinity and tilapia ( Oreochromis mossambicus) on an assemblage of benthic and planktonic Salton Sea algae and invertebrates. This article reports the responses of the benthic invertebrates. Microcosms (312 l fiberglass tanks) were set up without tilapia at 30, 39, 48, 57, and 65 g · l-1. Additional microcosms were set up with tilapia at 39 and 57 g · l-1. In the absence of fish Gammarus mucronatus dominated the benthos at the lower salinities, and Trichocorixa reticulata and the larvae of Ephydra riparia were most abundant above 48 g · l-1. The most abundant meiofaunal species included the harpacticoid copepod. Cletocamptus deitersi, three nematodes, the rotifer Brachionus plicatilis, ciliates, including Condylosoma sp. and Fabrea salina, two foraminiferans including Quinqueloculina sp., and a large flagellate. Most meiofaunal species responding to salinity were most abundant at 65 g · l-1, especialy after 6 months when Gammarus dominated the lower salinities. The tilapia reduced the abundance of macrofaunal species, especially at 39 g · l-1, and generally increased the abundance of meiofaunal species and ciliates. The microcosm benthic macro- and meiofaunal communities were most likely structured by Gammarus, salinity and tilapia. Gammarus reduced the other species by predation and changing the detritus from an algal base to a fecal pellet base. Gammarus was itself reduced by tilapia and by reduced reproductive success above 39 g · l-1. More species were therefore able to compete at higher salinities and in the presence of tilapia. Tilapia also affected the benthos by depositing loosely packaged fecal material which may support more meiofaunal species than either the robust Gammarus fecal pellets that were abundant at 39 g · l-1 or the algae-fecal pellet mix at 57 g · l-1.