Search results for "LEVEL"
showing 10 items of 3465 documents
Trophic Status of the South-Eastern Baltic Sea: A Comparison of Coastal and Open Areas
2001
Primary production, nutrient concentrations, phytoplankton biomass (incl. chlorophyll a) and water transparency (Secchi depth), are important indicators of eutrophication. Earlier basin-wide primary production estimates for the Baltic Sea, a shallow shelf sea, were based mainly on open-sea data, neglecting the fundamentally different conditions in the large river plumes, which might have substantially higher production. Mean values of the period 1993–1997 of nutrient concentrations (phosphate, nitrate, ammonium and silicate), phytoplankton biomass, chlorophyll a (chl a) concentration, turbidity and primary production were calculated in the plumes of the rivers Oder, Vistula and Daugava and …
Contributions of autochthonous and allochthonous sources to dissolved organic matter in a large, shallow, eutrophic lake with a highly calcareous cat…
2013
We traced the origin of dissolved organic matter (DOM) in the large, shallow, eutrophic Lake Vortsjarv in Estonia. Allochthonous DOM (Al-DOM) had higher δ13C values than autochthonous DOM (Au-DOM). The δ13C of inflow DOM varied from −28.2‰ to −25.4‰ (mean −26.7‰) and in-lake DOM varied from −28.4‰ to −26.1‰ (mean −27.2‰). Low stable isotope (SI) signatures of Au-DOM were caused by relatively 13C-depleted values of its precursors (mainly phytoplankton) with mean δ13C of −28.9‰. SI signatures of dissolved inorganic carbon (DIC) in the inflows and in the lake were also relatively low (from −15.1‰ to −3.28‰). SI values of DOM were lower during the active growing season from May to September and…
Experimental Modeling of Submerged Pivot Weir
2020
An inclined rectangular overflow structure, also called a pivot weir, consists of a rectangular plate, angled downstream from the vertical, that can be used as an upstream water level control device. A pivot weir is submerged when the upstream water level is influenced by the downstream flow depth. In this paper, to investigate factors influencing submerged flow conditions, an extensive experimental program including 251 experimental trials was carried out using weir inclination angles of 39.6°, 53°, 85°, and 90° and weir heights ranging from 0.263 to 0.312 m. A formula to distinguish between free and submerged flow conditions was developed using the Π theorem of dimensional analysis and th…
Discharge estimation in open channels by means of water level hydrograph analysis
2010
A new methodology, based on the synchronous measurement of stage hydrographs in two river sections located some kilometers from each other, was developed to estimate the discharge hydrograph in the upstream section. The methodology is based on the one-parameter calibration of a numerical flow routing algorithm, solving the Saint-Venant equations in diffusive or complete form. The methodology was validated using results of laboratory experiments carried out at the Polytechnic of Bari University. A known discharge hydrograph was generated in the upstream tank of a rectangular flume, where two water level sensors were located. Two different bed materials have been used, to account for differen…
Water Level Measurement Locations for Coastal Aquifer Management
2003
The coefficient of variation of the optimal cost (CVOC) method is applied to the Acqua dei Corsari coastal aquifer in Sicily's north coast to find the best point for a new water-level measurement location. The purpose of collecting data from the new measurement location is to reduce uncertainty associated with a stochastic management model for salt-water intrusion control. Assuming that uncertainty mainly stems from spatial variability of permeability, the structural parameters of the stochastic spatial permeability field are estimated using data from a nearby aquifer with similar geological properties. It is first shown through sensitivity analysis that the lack of previous information inh…
The effect of mariculture facilities on biochemical features of suspended organic matter (southern Tyrrhenian, Mediterranean)
2006
Abstract A comparison of a Mediterranean aquaculture impacted area and control areas was made to assess the effect of fish farm waste discharge on the biochemical features of the water column. Trophic variables commonly used in marine ecology such as total suspended matter, suspended chlorophyll- a , biochemical features of particulate organic matter (proteins, lipids and carbohydrates) and biopolymeric carbon were chosen as the best descriptors of trophic conditions. An initial analysis of data from the impact area was carried out in order to test the effect of farm waste using a gradient of distances downstream from the fish farm cages (50 m, 300 m, 1000 m). The results were then compared…
Oxygen isotope composition of natural waters in the Mt. Etna area
2004
Oxygen isotopes of both rainwater and groundwater samples from Mt Etna were used to obtain information on recharge areas, flow paths, and the origin of wet air masses. Oxygen isotope composition was determined in rainwater samples collected for a period of 3 years (October 1997– October 2000), in 11 rain-gauges distributed along the flanks of Mt Etna from sea level to 2900 m of altitude. Values ranged from 213.8 to þ 1.9‰, the lowest values being measured at higher altitudes and/or during cooler periods. For rain-gauges located from sea level up to 1000 m altitude, volume weighted values defined an isotopic gradient of 22.7‰/km, which is in the range observed in the Mediterranean area. High…
Long-term changes in hydrological regime of the lakes in Latvia
2013
Changes in the hydrological regime of the lakes of Latvia depend on natural and anthropogenic causes. This publication summarises the results of the research on the long-term changes in the water level, thermal and ice regimes in the seven largest lakes of Latvia: Liepājas, Usma, Ķīšezers, Burtnieks, Rāzna, Sventes and Lielais Ludzas, and their regional specifics from 1926 to 2002. For most of the studied lakes, the water level has been regulated, except for the lakes Liepājas, Burtnieks and Ķīšezers. Global climate warming has caused considerable changes in the hydrological regime of the lakes during the last decades and the surface water temperature has increased. At the same time, the nu…
Role of hydrological and hydromorphological factors in ecological quality of medium-sized lowland streams
2010
The development of biological communities is an important research issue regarding biological quality elements. However, it is still uncertain how different organism groups and their metrics are affected by different environmental factors. A study of high-quality sites of medium-sized lowland streams typical for Latvia (ecoregion Baltic province) was carried out with an emphasis on hydrological and hydromorphological characteristics. The investigations were carried out within the STAR project using the project designated standard methods. We found that the level of saprobity according to benthic macroinvertebrates was mainly linked with substrate type and stream depth. The trophic diatom in…
Water-level fluctuations in Mediterranean reservoirs: Setting a dewatering threshold as a management tool to improve water quality
2005
Water-level fluctuations, often linked to seasonal climatic trends, are a natural phenomenon which occur in almost all aquatic ecosystems. In some climatic regions, as the Mediterranean one, they are particularly wide due to the occurrence of two well separated periods: the rainy winter and the almost completely dry summer. Precipitation is concentrated in the first period, whereas in the second strong evaporation losses take place. According to these climatic features, and to ensure a continuous supply of water throughout the year, man-made lakes store water during winter and are subjected to dewatering during summer to compensate the lack of precipitation. These ecosystems are thus charac…