Search results for "WATER COLUMN"
showing 10 items of 123 documents
Interannual variability of circulation under spring ice in a boreal lake
2014
A small range (, 1uC) of under-ice water temperature is shown to result in remarkably different circulation regimes under spring ice in a deep, oligotrophic boreal lake. With the water column at , 4uC, melting of snow led to deepening vertical convection before ice break and a final depth of convection inversely correlated with earlier deep-water temperature. We attribute that to the nonlinear dependence of water density on temperature, albeit further affected by stochastic weather factors. In four of nine study years, convection led to complete under-ice overturn of the lake, indicating that this may not be uncommon in similar lakes with steep topography. River inflow and more intensive wa…
CH4 oxidation in a boreal lake during the development of hypolimnetic hypoxia
2020
AbstractFreshwater ecosystems represent a significant natural source of methane (CH4). CH4 produced through anaerobic decomposition of organic matter (OM) in lake sediment and water column can be either oxidized to carbon dioxide (CO2) by methanotrophic microbes or emitted to the atmosphere. While the role of CH4 oxidation as a CH4 sink is widely accepted, neither the magnitude nor the drivers behind CH4 oxidation are well constrained. In this study, we aimed to gain more specific insight into CH4 oxidation in the water column of a seasonally stratified, typical boreal lake, particularly under hypoxic conditions. We used 13CH4 incubations to determine the active CH4 oxidation sites and the …
Surface–bottom relationships in the Gulf of Salerno (Tyrrhenian Sea) over the last 34 kyr: Compositional data analysis of palaeontological proxies an…
2009
The palaeontological, geochemical and mineralogical records of core GNS84-C106 were analysed in order to reconstruct palaeohydrological changes and palaeoproductivity patterns in the Gulf of Salerno for the last 34 kyr. This approach, including compositional analysis of planktonic and benthic assemblages, gave an insight into the relationships between continental, sea surface and bottom environmental changes. The main source of variability of planktonic and benthic assemblages is related respectively to sea surface temperature and palaeobathymetry. Interrelated changes in surface salinity, nutrients, density gradient in the water column and organic fluxes at the bottom act as a secondary fa…
The response of calcareous nannoplankton to sea surface variability at Ceara Rise during the early Pleistocene glacial-interglacial cycles
2019
The Ceara Rise lies just beyond the edge of the Amazon River Fan and sediments from this site may record the complex interplay of different climatic systems and processes, including past changes in southern America monsoon activity, Intertropical Convergence Zone setting, different Atlantic Meridional Overturning Circulation (AMOC) strength and phytoplankton blooming triggered by Amazon River plumes. Here we investigate early Pleistocene calcareous nannoplankton at Ceara Rise, between about 1150 and 850 kiloyears ago. Our investigation shows abrupt variations in water column dynamics across glacial/interglacial cycles or, even better, linked with different AMOC modes. Dominant placoliths in…
Night, day, sunrise, sunset: do fish under snow and ice recognize the difference?
2008
1. Although boreal lakes are ice-covered for several months annually, little is known about the behaviour of fish under ice. To consider the reasons for diel vertical migrations (DVM) it is important to compare periods under ice as opposed to under open water. Echosounding provides a tool for non-intrusive continuous monitoring of fish, even in winter. 2. Changes in the vertical distribution of fish through six 48-h periods were monitored using a stationary, mounted echosounder that beamed vertically either from the bottom up or from the surface down from February to April, 2003. The up-beaming and down-beaming transducers were run alternately for 24 h each over the 48-h period. Standard ec…
The toxicity and concentrations of PAHs in creosote-contaminated lake sediment
1999
Sediment samplers, divided into three layers (0 – 10, 10 – 20 and 20 – 30 cm), were collected from 16 sites in Lake Jamsanvesi, Central Finland. The acute toxicity of pore waters and elutriates (sediment + water 1:4 v/v) were studied by bioluminescence inhibition test and by immobilisation of water fleas (Daphnia magna Straus). Concentrations of polycyclic aromatic hydrocarbons (PAHs) in sediments and elutriates were measured by gas chromatography using flame ionization detection (GC/FID). The highest total PAH concentration was 3.3 mg/g dry weight in the sediment and up to 1.7 mg/l in the elutriate of the uppermost (0 – 10 cm) layer, also being the most toxic to photoluminencent bacteria, …
Biomethylation of thallium by bacteria and first determination of biogenic dimethylthallium in the ocean
2000
To investigate a possible biomethylation of thallium, incubation experiments were carried out under aerobic conditions with a sewage sludge and with a mixed bacterial culture isolated from a sewage sludge, as well as under anaerobic conditions with a fresh-water lake sediment, by adding Tl(I) nitrate to these systems. Only in the case of the anaerobic sediment was a significant production of dimethylthallium observed (after three-weeks). Analysing different surface seawater samples and those from a single depth profile down to 4000 m, dimethylthallium was determined above the detection limit of 0.4 ng L−1 in about 20% of all samples, ranging from 0.5 to 3.2 ng l−1. The proportion of dimethy…
La remontée du saumon pour le frai dans le fleuve Tornionjoki, suivie au moyen d'un sonar à double faisceau horizontal.
2000
Fixed location split-beam horizontal echosounding was used to assess the size and timing of the Atlantic salmon (Salmo salar) spawning run in the River Tornionjoki. Four transducers, two on each river bank, were mounted across the river at the study site 4 km upstream from the river mouth. Net weirs were used on both shores to direct the passage of fish through the acoustic beams. Hydroacoustic monitoring covered 40-50% of the river cross-sectional area. Also test fishing and yearly catch statistics of salmon were used as an indication of the size of the spawning run in the river. Altogether, 7 700, 5 300 and 4 300 salmon-sized targets (target strength, TS ≥ -29 dB) moving upstream were det…
Geosphere-biosphere interactions in bio-activity volcanic lakes: Evidences from Hule and Rìo Cuarto (Costa Rica)
2014
Hule and R ́ıo Cuarto are maar lakes located 11 and 18 km N of Poa ́s volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemica…
Are there steady-state phytoplankton assemblages in the field?
2003
The difficulty in advancing in Ecology is due, in part, to the fact that this science uses a mainly qualitative language instead of a more formal or mathematical one. Therefore, many ecologists' efforts are expended in controversies resulting from the vagueness of ecological concepts, for example: stability, equilibrium, ecosystem, community, and so on. When approaching the study of steady-state phytoplankton assemblage, the different interpretations of these concepts can paralyse fruitful discussion. In the following pages, there is an endeavour to both restrict and precise the meaning of some of the concepts related to this topic and to broaden the range of possibilities of steady-state i…