Hydrophysical Data Research Articles

Soil data from the Barbastro-Balaguer gypsum belt, NE Spain.

The dataset [1] hosts pedological info and images of the lands -locally known as chesas- of the outcropping gypsiferous core of the Barbastro-Balaguer anticline (Fig. 1). It stands out in the landscape for the linear reliefs due to outcrops of dipping strata with differential resistance to erosion, and also because of its whitish color (Fig. 2) and gypsophilous vegetation. This gypsum outcrop was named in the 19th Century [2] as a gypseous belt, and has been further studied by other geologists like [3,4] and by civil engineers e.g. Hué and Llamas [5]. Traditionally chesas were rangeland, with sparse almond and olive trees and rainfed winter cereals confined at the flat -and often terraced- valley bottoms, or vales as known in NE Spain. The chesas have attracted the attention of botanists [[6], [7], [8]], foresters [9,10], and soil hydrophysical properties researchers [11]. Moreover, public interest is increasing as the administrations are establishing rules for nature protection in the gypseous lands, e.g., a demarcation of 137 km2 set within the chesas was declared a Special Conservation Area "ES2410074 Yesos de Barbastro", and then protected by the Habitats Directive of European Union. Also, plant physiologists are focusing on the adaptations of plants to gypsum as reviewed by Escudero et al. [12]. No soil map is available, but according to [13,14] the Gypsic Haploxerepts [15] are dominant. In the absence of a soil map, our dataset can help in the decisions to be made by the authorities, as is the case for water allocation to irrigated estates both in operation and planned, or for authorizations for the spreading of pig slurry. The herein presented soil data were collected with the classical techniques of pedological prospection. The dataset [1] contains the scans in .TIFF format of 150 whole thin sections of the soils, under both plane polarized light (PPL) and cross polarized light (XPL). Moreover, this dataset directs to a freely downloadable book [16] with the corresponding pedological descriptions, chemical and physical analyses, hydrophysical data, and scanning electron microscope images of the soils, plus micrographs of relevant pedofeatures of thin sections seen under petrographic microscope. The dataset [1] also presents a .xlsx file with an English translation of all figure captions of [16], including those of micrographs, and two more .xlsx files with analytical data. All data can be reused directly by naturalists, engineers, technicians and public servants in charge of environmental law development and enforcement, as well as by people involved in citizen science activities. Thin sections remain stored at EEAD and can be examined at our premises upon request.

DISTRIBUTION ANALYSIS OF CLEAN WATER QUALITY USING HYDROPHYSICAL DATA IN MARSELA VILLAGE, MASELA ISLAND DISTRICT, SOUTHWEST MALUKU REGENCY, MALUKU PROVINCE

In situ measurements of hydrophysical parameters have been carried out in groundwater in dug wells, drilled wells, and reservoirs related to temperature, electrical conductivity, degree of acidity, salinity, and total dissolved solids (TDS). This study aims to analyze the characteristics of hydrophysical parameters in water samples and create a water quality distribution model based on hydrophysical data in the study area. The results showed that water zoning based on air temperature and water temperature is included in the mesothermal zone category, and this zone water may originate from free/leaking aquifers. The results of hydrophysical parameter measurements were TDS with a concentration value of < 1000 mg/L, conductivity parameter (s) with a concentration value of s < 2500 mS/cm, a pH parameter ranging from 7, and a salinity parameter with a concentration value < 1000 ppm which is allowed according to water quality standards which are found in dug wells (old wells, SGM-3), drilled wells (SBM) and pond (Em). While the hydrophysical parameters for measuring other groundwater samples are not in accordance with water quality standards. Modeling the distribution of water quality based on three hydrophysical parameters (TDS, s, and S) in the study area shows a shallow groundwater pattern and seawater intrusion has occurred in several wells (SGM-1, SGM-2, and SGM-4). The distribution of TDS, s, and S concentration values at study sites varies with distance from the coastline and topography.

Information technologies for automation of hyddrophisical situation molelling and forecasting in the Black Sea region

The article offers a solution to the scientific and applied problem of automating the acquisition and analysis of a certain set of hydrophysical indicators with the subsequent formation of a forecast of the hydrophysical situation in the Black Sea water area. This topic is of great relevance both in peacetime and in the conditions of the current armed aggression of the Russian Federation against Ukraine. The solved task is an important element of solving the more complex problem of operational obtaining of oceanographic data for highlighting the hydrographic situation in the Black Sea water area, collection, accumulation and visualization of oceanographic data in the interests of navigation and hydrographic support of users of such information. To solve this problem, a software environment was created for automatic search and selection of hydrophysical data, as well as their automatic input into specialized software for modeling and forecasting the hydrophysical situation with subsequent calculation of forecasts of hydrophysical fields. A set of the most important data was formed, which includes indicators of salinity, temperature, circulation. Automatic search and selection of meteorological and hydrophysical data takes place from international GFS and COPERNICUS profile databases. Also, to increase the effect of the simulations and forecasts, a specialized interface was developed for searching, visualization, and the possibility of downloading by the user the results of the forecast module of the mathematical modeling of the spatio-temporal variability of the hydrophysical fields of the northwestern part of the Black Sea. The developed scientific and practical approaches and toolkit are designed to function within the framework of the distributed and centralized Bank of Oceanographic Data of the National Academy of Sciences of Ukraine, part of which is an intellectual information system for highlighting the hydrographic situation in the Black Sea water area. The obtained results are also aimed at increasing the level of environmental safety in the Black Sea water area and can be used to monitor nature management in this region.

In situ Field Capacity in Brazilian Soils and a Derived Irrigation Management Practice Based on Water Suction

Field capacity (FC) is a fundamental parameter in soil and water engineering and hydrologic modeling. Despite its relevance, the in situ determination of this parameter is not standardized and its determination by indirect methods is dubious. This study presents a method of calculation of in situ FC and its corresponding water suction (hFC), using the van Genuchten equation for water retention and the pedotransfer function by Ottoni Filho et al. (2016) for standardized in situ determination of FC. The methodology was applied to HYBRAS, a database of hydrophysical data for Brazilian soils with 1,075 soil samples from 15 Brazilian states. FC and hFC were confirmed to depend on textural class and pedogenetic origin (weathered and unweathered soils). Our analysis justified why FC must not be determined based only on a single predetermined water suction value. A simplified method is proposed for the management of irrigated soils through the determination of water suction in the root zone and the mode and confidence interval values of hFC corresponding to soil groups formed from textural classes and pedological nature. Various statistical calculations of FC and hFC are presented for these groups.

Термопрофилирующая система онлайн-мониторинга деятельного слоя на базе глубоководного нейтринного телескопа Baikal-GVD

For continuous monitoring of the vertical distribution of temperature in Lake Baikal, as an indirect measure of dynamic processes, a system of distributed temperature sensors was developed in the Laboratory of Hydrology and Hydrophysics of the Limnological Institute of the SB RAS. The system allows to obtain instant vertical temperature profiles with up to 1 Hz frequency and 1 mK resolution. Additionally, each sensor is equipped with a microheater activated by adressed command to implement the thermanemometric mode of operation, to estimate the velocity of water flows. The pilot sample of the thermistor chain contains 11 temperature sensors located along the depth from 20 to 120 meters with a 10 meters step, and covers the active layer of Lake Baikal with the major changes during the year. The developed thermistor chain was integrated into one of the strings of the BaikalGVD neutrino telescope and connected to the specially developed data logger which placed in the telecommunication spherical module. In this article, we give a brief description of the temperature profiling system and preliminary results of tests in the open Baikal during 2022. The obtained measurement results allowed us to consider the temporal variability of the active layer temperature by analyzing its power spectral density. The developed monitoring system allows obtaining qualitatively new hydrophysical data on the state of the active layer of the pelagic part of Lake Baikal in real time.

The Study of the State of the World Ocean Areas Based on Modern Technologies for Processing and Analysing Data

This paper is devoted to the processing of hydrophysical data on the state of marine areas utilizing modern data processing technologies. Author uses Python programming language to process marine data. The results on the processing of the remote sensing data on the Baltic and the Black Seas surface temperature are presented in the study. Daily satellite data for the years 1982–2018 were processed using Python scripts for both water areas. The analysis of the obtained information was conducted with R programming language. This language supports a wide range of statistical and numerical methods and is convenient to use to determine the statistical characteristics of the studied quantities. Data analysis reveals statistically significant positive trend in the sea surface temperature (SST) values in the both studied water areas over the past decades. The paper has also analyzed the spatial variability of the surface temperature within considered areas. The analysis illustrates the temperature variability in certain areas of the sea and identifies areas with the highest rate of temperature increase. Conclusions are made on the usability of the programming languages for various data processing tasks.

The role of vegetation, soils, and precipitation on water storage and hydrological services in Andean Páramo catchments

Understanding how tropical montane catchments store and release water, and the resulting water ecosystem services they provide is crucial for improving water resource management. But while research in high–elevation tropical environments has made progress in defining streamflow generation processes, we still lack fundamental knowledge regarding water storage characteristics of catchments. Here we explore catchment storage and the factors controlling its spatial variability in seven Páramo catchments (0.20–7.53 km2) in southern Ecuador. We applied a field-based approach using hydrometeorological, water stable isotopic, and soils hydrophysical data from a 3 year collection period to estimate the passive (PasS) and dynamic (DynS) storage of the catchments. We also investigated relations between these storages and landscape and hydrometric variables using linear regression analysis. PasS estimates from hydrophysical soil properties and soil water mean transit times were consistent with estimates using streamflow mean transit times. Computed catchment PasS and DynS for the seven watersheds were 313–617 mm and 29–35 mm, respectively. PasS increased directly with the areal proportion of Histosol soils and cushion plant vegetation (wetlands). DynS increased linearly with precipitation intensity. Importantly, only 6–10% of the mixing storage of the catchments (DynS/PasS) was hydrologically active in their water balance. Wetlands internal to the catchments were important for PasS, where constant input of low intensity precipitation sustained wetlands recharge, and thus, the water regulation capacity (i.e., year–round water supply) of Páramo catchments. Our findings provide new insights into the factors controlling the water regulation capacity of Páramo catchments and other peaty soils dominated environments.

The structure of the mesoplankton community in the area of the continental slope of the St. Anna Trough (Kara Sea)

Zooplankton samples and concomitant hydrophysical data have been obtained in the outer Kara shelf over the continental slope and adjacent deepwater region of the western spur of the St. Anna Trough in the last ten days of September in 2007 and 2011. Mesoplankton biomass in the examined regions in 2007, the warmest year of the last three decades, was 1.5–2 times higher than the relatively cold year of 2011. A frontal zone, distinct in temperature, salinity, and chlorophyll fluorescence in the surface sea layer was located over the continental slope. The temperature gradient in the frontal zone reached 0.25–0.67°C/km, and its salinity gradient reached 1.6–4.7 psu/km. An increase in mesoplankton biomass was associated with the frontal zone, which was especially pronounced in the upper layers of the water column. The average biomass content in the upper 50 m in the frontal maximum amounted to 1210 mg/m3 in 2007 and 972 mg/m3 in 2011, being two orders of magnitude higher than the outer shelf and the deepwater domain of the basin. The pteropod Limacina helicina was dominant at the slope maximum, accounting for up to 80% of mesoplankton biomass. The frontal zone over the slope also represented a distinct boundary separating the shelf mesoplankton community from the deepwater community, which drastically differed in composition and biomass.

Hydrophysical features of deep water troughs in the western Kara Sea

In the 59th cruise of the RV Akademik Mstislav Keldysh (September–October, 2011) a large amount of hydrophysical data was obtained with the help of various measuring systems. The data allowed us to study the dynamics and hydrological structure of deep-sea troughs of the western part of the Kara Sea at a high spatial resolution. In particular, the analysis of this material showed that a cyclonic jet exists in the central spur of the St. Anna Trough at depths of 150–300 m and penetrates down to the bottom. The jet is able to play a role of a dynamic barrier that prevents the penetration of water from the southwestern part of the Kara Sea to higher latitudes. In the eastern spur of the St. Anna Trough, the jet weakens, becomes less barotropic, and can no longer inhibit the northward spreading of the shelf waters of the Kara Sea. The weakest and least coherent currents were recorded in the Novaya Zemlya trough, in the southern part of which we traced waters of a Barents Sea origin.

Russian

Soil water retention curve (WRC) - the most important hydrological characteristics of soils, which determines the movement of moisture and soluble substances in soils. This relationship between soil moisture and capillary pressure of moisture, is included in all forecasting mathematical models of moisture movement in the soils. To assess the adequacy of model calculations with using the WRC, obtained by different methods, WRC was defined by experimental laboratory methods, or was calculated by using pedotransfer functions (PTF). Then the calculated data and field nature experiments on the movement of moisture were compared with. The precision of moisture movement modeling in the soil was significantly determined by the method of obtaining WRC. The results of the experimental modeling of soils water regime, significantly the results of the simulation were located in the following descending order of precision: regional PTF > WRC (water retention curve), obtained by the method of sand-kaolin boxes > WRC, obtained using capillarimeters > PTF used in the program Agrotool (on the basis of the experimentally obtained hydrological constants) > PTF using as predictor of granulometric structure (from the data base ROSETTA) > WRC obtained using the centrifuge method > PTF based on Voronin‘s «secants». It is recommended to create regional hydrophysical data base to calculate pedotransfer functions for forecasting modeling of soil water movement.

Mathematical models of soil moisture transfer: Importance of experimental assurance and upper boundary conditions

Soil moisture movement strongly depends on the upper boundary conditions (presence or absence of hydraulic pressure). The field experiments on the agrogrey medium loamy soil have shown that in the presence of pressure the movement follows preferential ways of migration. The accuracy of simulating this process depends on the initial experimental reliability of the mathematical model. This paper proposes an approach for the comparative evaluation of different methods of obtaining hydrophysical data for precise predictable modeling at the pedon scale. It should be noted that all the results are given for only one soil type, so one cannot confidently assert the relevance of similar data for other soil types.

Soil hydrophysical characteristics in the Nitra river basin (Slovakia): Their monitoring, analysis, online publishing

The paper is focused on the purpose made, or local monitoring of areal unit of the Nitra river basin (Slovakia, Central EU with total area 4501 km 2 ) in order to obtain the inputs on soil, moisture and hydrophysical characteristics of the given area. In this study, there was evaluated the share of individual soil texture classes in the Nitra river basin on the basis of map records and its comparison with the soil samples taken from the 111 selected sites. Soil samples were taken from two depths of soil profile (15-20 cm, 40-45 cm). The sites were chosen according to the percentage representation of individual soil texture classes. Based on the identification of sampling points localization and following analysis of granularity ratio, it can be concluded that the grain composition from the soil samplings does not correspond fully with the map records. Subsequently, drainage branches of moisture retention curves were measured for all sites Obtained hydrophysical data were enabled on the web-portal. With the use of OpenGeo Suite software, version 4.0.2 and its components Geoserver and Geoexplorer, the data on soil characteristics were published online at: http://fzki.uniag.sk/02FacultyStructure/02Departments/KBH/02Research/Hydrophysics.Thus, information about the soil characteristics in the basin is available to specialists.

Soil Erosion Prediction Using Morgan-Morgan-Finney Model in a GIS Environment in Northern Ethiopia Catchment

Even though scientific information on spatial distribution of hydrophysical parameters is critical for understanding erosion processes and designing suitable technologies, little is known in Geographical Information System (GIS) application in developing spatial hydrophysical data inputs and their application in Morgan-Morgan-Finney (MMF) erosion model. This study was aimed to derive spatial distribution of hydrophysical parameters and apply them in the Morgan-Morgan-Finney (MMF) model for estimating soil erosion in the Mai-Negus catchment, northern Ethiopia. Major data input for the model include climate, topography, land use, and soil data. This study demonstrated using MMF model that the rate of soil detachment varied from <20 t ha−1y−1to >170 t ha−1y−1, whereas the soil transport capacity of overland flow (TC) ranged from 5 t ha−1y−1to >42 t ha−1y−1. The average soil loss estimated by TC using MMF model at catchment level was 26 t ha−1y−1. In most parts of the catchment (>80%), the model predicted soil loss rates higher than the maximum tolerable rate (18 t ha−1y−1) estimated for Ethiopia. Hence, introducing appropriate interventions based on the erosion severity predicted by MMF model in the catchment is crucial for sustainable natural resources management.

Circulation in the southwestern part of the Kara Sea in September 2007

During cruise 54 of the R/V Akademik Mstislav Keldysh to the southwestern Kara Sea (September 6 to October 7, 2007), a large amount of hydrophysical data with unique spatial resolution was obtained on the basis of measurements using different instruments. The analysis of the data gave us the possibility to study the dynamics and hydrological structure of the southwestern Kara Sea basin. The main elements of the general circulation are the following: the Yamal Current, the Eastern Novaya Zemlya Current, and the St. Anna Trough Current. All these currents are topographically controlled; they flow over the bottom slopes along the isobaths. The Yamal Current begins at the Kara Gates Strait and turns to the east as part of the cyclonic circulation. Then, it turns to the north and propagates along the Yamal coast over the 100-m isobath. The Eastern Novaya Zemlya Current (its core is located over the eastern slope of the Novaya Zemlya Trough) flows to the northeast. Near the northern edge of Novaya Zemlya, it encounters the St. Anna Trough Current, separates from the coast, and flows practically to the east merging with the continuation of the Yamal Current. A strong frontal zone is formed in the region where the two currents merge above the threshold that separates the St. Anna Trough from the Novaya Zemlya Trough and divides the warm and saline Arctic waters from the cooler and fresher waters of the southwestern part of the Kara Sea. This threshold, whose depth does not exceed 100–150 m, is a barrier that prevents the spreading of the Barents Sea and Arctic waters to the southwestern part of the Kara Sea basin through the St. Anna Trough.

Climate sensitivity of soil water regime of different Hungarian Chernozem soil subtypes

In this study the possible effects of two predicted climate change scenarios on soil water regime of Hungarian Calcic Chernozem soils has been investigated. Soil profiles classified as Calcic Chernozem — in total 49 — were selected from the MARTHA soil physical database that incorporates soil data at national scale. These profiles were subdivided into three groups (sandy loam, loam and clayey loam) in accordance with their mechanical composition. Soil water retention curves were scaled separately for each of the three textural groups, using similar media scaling in order to represent the variability of soil hydrophysical data with one parameter, the scaling factor (SF). Reference soil profiles were chosen according to the cumulative distribution function of the scaling factor, six for each textural group. Daily downscaled meteorological data from A2 and B2 climate scenarios of the Hadley Centre (2070–2100) and data from a reference period (RF, 1961–1990) were used in this study to characterize different climatic situations. Nine representative years were selected in case of all the three scenarios, using the cumulative probability function of the annual precipitation sum. Scenario analyses were performed, validating the SWAP soil water balance simulation model for the 18 reference soil profiles and 27 representative years in order to evaluate the expected changes in soil water regime under different from the present (RF) climatic conditions (A2 and B2 scenarios). Our results show that the scaling factor could be used as a climate sensitivity indicator of soil water regime. The large climate sensitivity of the majority of Chernozem soil subtypes water regime has been proven.

Modelling of Soil Respiration in Hungary

The climatology of soil respiration in Hungary is presented. Soil respiration is estimated by a Thornthwaite-based biogeochemical model using soil hydrophysical data and climatological fields of precipitation and air temperature. Soil respiration fields are analyzed for different soil textures (sand, sandy loam, loam, clay loam and clay) and time periods (year, growing season and months). Strong linear relationships were found between soil respiration and the actual evapotranspiration for annual and growing season time periods. In winter months soil respiration is well correlated with air temperature, while in summer months there is a quite variable relationship with water balance components. The strength of linear relationship between soil respiration and climatic variables is much better for coarser than for finer soil texture.

On Transpiration and Soil Moisture Content Sensitivity to Soil Hydrophysical Data

Sensitivity of evapotranspiration E and root zone soil moisture content θ to the parameterization of soil water retention Ψ(θ) and soil water conductivity K(Ψ), as well as to the definition of field capacity soil moisture content, is investigated by comparing Psi1-PMSURF and Theta-PMSURF models. The core of PMSURF (Penman–Monteith Surface Fluxes) consists of a 3-layer soil moisture prediction module based on Richard’s equation in combination with the Penman–Monteith concept for estimating turbulent heat fluxes. Psi1- PMSURF and Theta-PMSURF differ only in the parameterization of the moisture availability function Fma. In Psi1,Fma is parameterized by using Ψ(θ) and K(Ψ) hydrophysical functions; in Theta, Fma is parameterized by using hydrophysical parameters: the field capacity θf and wilting point θw soil moisture contents. Both Psi1 and Theta are based on using soil hydrophysical data, that is, there is no conceptual difference between them in the parameterization of E even if in Psi1Fma depends on 12 parameters, while in Theta only on two soil/vegetation parameters. Sensitivity tests are performed using the Cabauw dataset. Three soil datasets are used: the vG (van Genuchten), CH/vG (Clapp and Hornberger/van Genuchten) and CH/PILPS (Clapp and Hornberger/Project for Intercomparison of Land-surface Parameterization Schemes) datasets. The vG dataset is used in van Genuchten’s parameterization, while in Clapp and Hornberger’s the CH/vG and CH/PILPS datasets are used. It is found that the consistency of soil hydrophysical data in the simulation of transpiration is quite important. The annual sum of E obtained by Psi1EPsi1, differs from the annual sum of E obtained by Theta, E Theta , because of the inconsistency between the fitting parameters of Ψ(θ) and K(Ψ) and the θf, and not because of the differencies in the parameterization of Fma. Further, θf can be estimated not only on the basis of using soil hydrophysical functions (the θf so obtained is θSoilf) but also on the basis of analysing the transpiration process (the θfso obtained is θtrf). θtrf values estimated from the condition E Theta ≈ EPsi1 are in acceptable accordance with the θSoilf values proposed by Wosten and co-workers. The results are useful in optimizing the parameterization of transpiration in land-surface schemes.

Estimating soil water retention characteristics from the soil taxonomic classification and mapping informations: Consideration of humus categories

The main limiting factors of soil fertility in Hungary are related to soil water management. For this purpose the water management category systems was elaborated in the scale of 1:100 000 and 1:10 000 (Varallyay et al., 1980, Varallyay, 1989). Soil water-retention characteristics (SWRC) are important factors of that category system, but they can only be measured at limited number of sites in a routine soil survey. From this reason most of the soil survey organizations have established soil information systems for further investigations. Data collected in fields and laboratories, for example soil horizons, texture, structure, organic matter, and carbonate content, etc. are prepared for mapping and for further evaluation, and utilization. Even systematic sampling to obtain spatially distributed hydrophysical input data for simulation models is also practically impossible because direct measurement of soils' hydraulic properties is expensive, time consuming, and labor intensive. Alternatively these properties are predictable from available soil data as bulk density (BD), organic matter (OM) content and particle-size distribution (e.g. Gupta and Larson, 1979; Rawls et al., 1982; Ahuja et al., 1985; Fodor and Rajkai, 2004; Rajkai et al., 2004). Estimating functions of the required parameters from easily obtainable input data are called pedotransfer functions (PTFs) according to Bouma and Van Lanen (1987). Soil maps are visualizing the data collected by the standard soil survey methods. Soil surveys are usually built on soil taxonomic classification and additional data, depending on the special requirement of the survey. Soil maps display not only the soil type, but also other soil attributes with certain categorization. Land evaluation is one of the most widespread applications of soil data for land use planning purposes. For land evaluation purposes maps of a scale of 1:10.000 are required. About 60 % of the agricultural area of Hungary is mapped in this scale (Toth et al., 2004). Many of the maps are digitized, georeferenced and integrated to GIS systems. The 1:10.000 maps in Hungary contain information on soil types (subtypes), parent material and texture. Five additional cartograms complement the basic soil map: (1) humus cartogram (with information on depth of humic layer and humus content of the plough layer); (2) pH and calcium carbonate content cartogram; (3) ground water cartogram (depth of soil water level); (4) cartogram of soil salinity (with information on salt content and distribution in the soil profile) (5) cartogram of soil characteristics those are important in soil fertility and management (rooting depth, erosion, stone content, etc.). The 1:10.000 scale map database is the most extensive and it represents the most soil types in Hungary. Therefore it would be very advantageous to find estimation methods for converting the raw data of soil maps and cartograms as readily available information for determining the soil water management categories. This paper aims to formulate the SWRC dependency of the Hungarian soil taxonomic classification in the case of brown forest soils.

Hydrochemical properties of the Aral Sea water in summer 2002

In August 2002, new hydrochemical and hydrophysical data were collected in the Aral Sea. The survey includes cross-sections in three locations: within the Small Aral close to Tastubek Bay, in the Large Aral at the northern tip that is Tschebas Bay and within the western basin at Chernishov Bay. All three locations represent different stages in the hydrochemical evolution of the Aral Sea. Depth profiles of pressure, temperature, conductivity, pH and dissolved oxygen were measured with a YSI 6600 profiler. Water samples were taken with a Niskin bottle and analyzed for dissolved oxygen and nutrients by standard photometric methods. Major anions and cations were analyzed by ion chromatography and ICP-OES, respectively. Benthic flux experiments were carried out with sediment cores in a batch mode assay on-site. In the Small Aral, the changes in the hydrochemical properties are not as dramatic as in the Large Aral. The Small Aral represents a brackish inland water body with salinities of 17–18 g kg−1. The wind-mixed layer reached 8 m during the survey. The salinity is vertically and horizontally almost uniform. Below 8 m, a temporally hypoxic layer forms during summer. Salt redissolution was found to be an important source of salt in the water. About 33.5 g SO42− m−2 day−1 and about 30.7 g Cl− m−2 day−1 are released from the sediment in summer. In the Large Aral, the salinity distribution is uniform in shallow waters (less than 5 m) but varies strongly in deeper water. Tschebas Bay at the northern tip of the large Aral represents a shallow lagoon with a maximum depth of about 6 m. The water column was well mixed down to the bottom (∼6 m) having salt concentrations of 82 g kg−1 on average. Almost no gradients in dissolved substances were observed. It is suspected that salinity is balanced by fresher water inflow originating from the Syr Darya flowing south and by groundwater exfiltration. Chernishov Bay in the north of the western basin is meromictic. Below a wind-mixed layer, a very strong pycnocline of 20 g kg−1 per m at 5 m depth isolates the water below from exchanges with the water above and led to the formation of huge anoxic water body down to the bottom at about 25 m depth. Below 10 m, the water contains hydrogen sulphide. The salt concentration increases from 82 g kg−1 in the surface water to 110 g kg−1 at depth. The salt release from the sediment is as high as 1143 g SO42− m−2 day−1 and 1626 g Cl− m−2 day−1. Benthic release of salt is considered as an important source for salt in the bottom water of the western basin and in sustaining the stable density stratification.

Hydrochemical properties of the Aral Sea water in summer 2002

In August 2002, new hydrochemical and hydrophysical data were collected in the Aral Sea. The survey includes cross-sections in three locations: within the Small Aral close to Tastubek Bay, in the Large Aral at the northern tip that is Tschebas Bay and within the western basin at Chernishov Bay. All three locations represent different stages in the hydrochemical evolution of the Aral Sea. Depth profiles of pressure, temperature, conductivity, pH and dissolved oxygen were measured with a YSI 6600 profiler. Water samples were taken with a Niskin bottle and analyzed for dissolved oxygen and nutrients by standard photometric methods. Major anions and cations were analyzed by ion chromatography and ICP-OES, respectively. Benthic flux experiments were carried out with sediment cores in a batch mode assay on-site. In the Small Aral, the changes in the hydrochemical properties are not as dramatic as in the Large Aral. The Small Aral represents a brackish inland water body with salinities of 17–18 g kg −1. The wind-mixed layer reached 8 m during the survey. The salinity is vertically and horizontally almost uniform. Below 8 m, a temporally hypoxic layer forms during summer. Salt redissolution was found to be an important source of salt in the water. About 33.5 g SO 4 2− m −2 day −1 and about 30.7 g Cl − m −2 day −1 are released from the sediment in summer. In the Large Aral, the salinity distribution is uniform in shallow waters (less than 5 m) but varies strongly in deeper water. Tschebas Bay at the northern tip of the large Aral represents a shallow lagoon with a maximum depth of about 6 m. The water column was well mixed down to the bottom (∼6 m) having salt concentrations of 82 g kg −1 on average. Almost no gradients in dissolved substances were observed. It is suspected that salinity is balanced by fresher water inflow originating from the Syr Darya flowing south and by groundwater exfiltration. Chernishov Bay in the north of the western basin is meromictic. Below a wind-mixed layer, a very strong pycnocline of 20 g kg −1 per m at 5 m depth isolates the water below from exchanges with the water above and led to the formation of huge anoxic water body down to the bottom at about 25 m depth. Below 10 m, the water contains hydrogen sulphide. The salt concentration increases from 82 g kg −1 in the surface water to 110 g kg −1 at depth. The salt release from the sediment is as high as 1143 g SO 4 2− m −2 day −1 and 1626 g Cl − m −2 day −1. Benthic release of salt is considered as an important source for salt in the bottom water of the western basin and in sustaining the stable density stratification.