Search results for "Anoxic waters"

Ecology of Cryptomonas at the chemocline of a karstic sulfate-rich lake

2001

In a study from October 1989 to January 1992, a dense population ofCryptomonas cf. erosa (maximum density 38 000 cells mL–1) consistently developed at the chemocline of Lake Arcas, central Spain,where sharp physical and chemical gradients occurred during stratification. This population developed following the establishment of vertical water stratification and declined when the lake was near autumnal mixis. Population growth in situ, attributable to photosynthetic adaptation to low light intensities rather than to phagotrophy, causes these algal maxima. The population densities and net growth rates of C. cf. erosa in situ were influenced by the coexisting phototrophic prokaryotes at the che…

Vertical distribution and rotifer concentrations in the chemocline of meromictic lakes

1983

The vertical distribution of planktonic rotifers has been analysed in relation to season in several meromictic lakes; a coastal lagoon with sea-water intrusion and three dissolution lakes from two karstic systems. Two species, Filinia hofmanni and a form of Anuraeopsis fissa have been found to be more or less restricted to the chemocline or adjacent strata any time they occurred. Many species common in the upper water layers developed large populations near or in the chemocline and more strikingly in summer. Some species had two vertical maxima (one in the surface or the thermocline and another near the chemocline), while others successively shifted their maxima between the upper layers and…

Responses and adaptations of collembolan communities (Hexapoda: Collembola) to flooding and hypoxic conditions

2009

Standard ecological methods (pitfall traps, trunk eclectors and soil cores) were used to evaluate collembolan community responses to different flooding intensities. Three sites of a floodplain habitat near Mainz, Germany, with different flooding regimes were investigated. The structures of collembolan communities are markedly different depending on flooding intensity. Sites more affected by flooding are dominated by hygrophilic and hygrotolerant species, whereas the hardwood floodplain is dominated by mesophilic species. The survival strategies of the hygrophilic and hygrotolerant species include egg diapause and passive drifting. The physiological adaptations to hypoxic conditions of sever…

2001

The main limnological characteristics of the biogenic meromictic Lake La Cruz, a small karstic lake located on a dolomitic substrate, are outlined below. The lake owes its chemical stratification mainly to high concentrations of bicarbonate and calcium in the permanent monimolimnion, located below a depth of 19 m. A massive precipitation of CaCO3 crystals ("whiting"), occurring in the euphotic zone every summer, leads to further sedimentation and redissolution in deep waters with enhanced CO2 concentrations. Other ions, like magnesium, ammonium, reduced iron, silicate, etc. also contribute to the chemically-induced stability of the monimolimnion. The patterns of stratification during two co…

The adaptations to tube-dwelling life of Propsilocerus akamusi (Diptera: Chironomidae) larvae and its eutrophication-tolerant mechanisms

2019

Propsilocerus akamusi (Diptera: Chironomidae) is a dominant macroinvertebrate species in many eutrophic lakes in subtropical and temperate zones. P. akamusi larvae can migrate deep into the sediment (>30 cm) during summer where is no oxygen. However, to our knowledge, the specific adaptive tactics of its tube-dwelling life (>30 cm) and underlying mechanisms why this species is favored by nutrient-rich lakes remain limited. With the understanding above-mentioned issues, we can provide important information for the development of sensitive biomonitoring. We examined monthly morphological dynamics and physiological adaptations of P. akamusi to anoxic conditions, and environmental relationships…

Holocene Spatiotemporal Redox Variations in the Southern Baltic Sea

2021

Low oxygen conditions in the modern Baltic Sea are exacerbated by human activities; however, anoxic conditions also prevailed naturally over the Holocene. Few studies have characterized the specific paleoredox conditions (manganous, ferruginous, euxinic) and their frequency in southern Baltic sub-basins during these ancient events. Here, we apply a suite of isotope systems (Fe, Mo, S) and associated elemental proxies (e.g., Fe speciation, Mn) to specifically define water column redox regimes through the Baltic Holocene in a sill-proximal to sill-distal transect (Lille Belt, Bornholm Basin, Landsort Deep) using samples collected during the Integrated Ocean Drilling Program Expedition 347. At…

Methane-oxidizing and photoautotrophic bacteria are major producers in a humic lake with large anoxic hypolimnion

2011

Heterotrophic processes are considered to prevail in lakes with high terrestrial loading and a high content of dissolved organic carbon. However, previous studies have shown abundant methanotrophic bacteria (MOB) and photoautotrophic green sulphur bacteria (GSB) in some boreal lakes. We used genetic and lipid biomarkers to follow the seasonal succession of the abundance and carbon biomass of the major bacterial groups in Lake Mekkojarvi, a small Finnish polyhumic lake with a large anoxic hypolimnion. Biomarkers were based on length heterogeneity analysis of 16S rRNA gene amplification by polymerase chain reaction (PCR) (LH-PCR) and on phospholipid fatty acid (PLFA) analysis. Representative …