Bottom Sediment Type Research Articles

Freshwater mollusks of the Priplotinny Ples Reach, the Kuibyshev Reservoir (middle Volga River, Russia)

In September 2020, the fauna of mollusks was studied at the Priplotinny Ples Reach of the Kuibyshev Reservoir, the Volga River, Russia. In total, 23 taxa were registered, including four invasive species. Extrapolating of the species richness, taking into account the sampling effort, allowed to assess the estimated species pool according to the Chao 2 algorithm. Bivalve mollusks predominated in the studied area. The mollusks Dreissena (Pontodreissena) bugensis and Dreissena (Dreissena) polymorpha have been found most frequently at the study sites. Both abundance and biomass varied in wide range, as 391 ± 325 ind. m−2 and 256.693 ± 228.355 g m−2, respectively. The complex of dominant species was mainly represented by alien mollusks. The type of bottom sediment was a significant ecological factor (p ≤ 0.05) that determined the distribution of mollusks at the Priplotinny Ples Reach. The water quality of the study area was assessed by bioindication method according to the composition and structure of the mollusk fauna, formed mainly by species of European and European-West Siberian ranges.

Local Neighbourhood Edge Responsive Image Descriptor for Texture Classification Using Gaussian Mutated JAYA Optimization Algorithm

Local feature descriptor plays a significant role in texture classification. However, in the traditional local binary pattern method, image pixels are converted into a binary pattern based on the relationship between center and neighborhood pixels. This paper introduces a novel feature extraction method named local neighbourhood edge responsive binary pattern to extract and categorize reliable texture features from images for achieving an automated classification of different types of ocean bottom sediments. Initially, the basic magnitude variance pixel values are derived depending on an odd and even pixel value of a 3 × 3 image patch. Further, the edge information is extracted using the local directional pattern method from all images. The edge response of the image is obtained using a kirsch mask in all eight directions. The encoding condition is then applied to both the local intensity and the edge information to create a unique descriptor value. Finally, a new learning algorithm called GMJAYA-ELM combines the Gaussian mutated JAYA (GMJAYA) with an extreme learning machine (ELM) for texture classification. The GMJAYA is used to optimize the input weights and hidden biases of single-hidden-layer feed-forward neural networks. Experimental findings indicate that the suggested method yields better accuracy and sensitivity efficiency among various groups. The proposed algorithm is tested by contrasting outcomes with standard learning schemes such as PSO-ELM, GA-ELM, ABC-ELM, Birdswarm-ELM, and JAYA-ELM, suggesting the dominance of GMJAYA-ELM.

Suspended particulate matter is a key factor shaping the spatial arrangement of Micropogonias furnieri (sciaenidae) population in a Southwestern Atlantic temperate estuary

The relative influence of suspended particulate matter (SPM), sea surface temperature, depth, and type of bottom sediment in the spatial distribution of the Micropogonias furnieri (Sciaenidae) population structure was studied in the Río de la Plata estuary. Eight size-assemblages were defined (Cluster Analysis) showing a significant association with environmental variables. The application of the Boosted Regression Trees model for presence/absence and relative abundance showed that the SPM (46.24% and 34.24%, respectively), followed by the depth (31.47% and 33.50%, respectively) were the most important environmental variable in predicting the spatial distribution. Results showed a population segregation pattern. Juvenile and small adolescent fish increased their probability of occurrence and their relative abundance with increments of SPM and decrease of depth. The large adolescent and adult fish substantially increased their occurrence and relative abundance with the decreasing of SPM concentrations at low values. This study quantified and showed the high importance of the SPM in the spatial distribution pattern of the population structure of an estuarine species. In this context, it proposed that the SPM in the Río de la Plata could be used as an indicator of habitat availability of juveniles/adults within an ecosystem approach for fisheries management.

The role of oceanographic processes and sedimentological settings on the deposition of microplastics in marine sediment: Icelandic waters

The global distribution of microplastic debris on the sea floor poses an increasing risk to marine organisms and ecosystems. Here, we present a distribution analysis of microplastics collected from eight marine multicores recovered from the Iceland continental shelf and surrounding areas at water depth between 241 and 1628 m. We report a total of 306 microplastics from the size range > 250 μm −5 mm, of which all were fibers. Microplastic numbers range between 0.119 and 0.768 per gram of dry sediments. In the analysis we assess the potential role of oceanic surface and bottom water currents, organic content, and sediment type on the distribution, deposition, and burial of microplastics in marine sediments. Our results provide the first record of microplastic pollution of marine sediments from the Iceland continental shelf and identify Atlantic Cod feeding and breeding grounds as potential hot spot for the accumulation of marine debris.

Potentially toxic elements distribution in the contaminated bottom sediments by the industrial genesis within Lower Don river system

The work presents the results of studying the content of potentially toxic elements (Mn, Cu, Zn, Cr, Pb, Ni and Cd) in bottom sediments sampled at monitoring stations in the natural-anthropogenic systems of the Lower Don adjacent to the impact zone of the Novocherkassk Power Plant. The relationship between the content of metals in bottom sediments and their sorption properties is largely determined by the conditions of formation and the type of bottom sediments. Evaluation of the potentially toxic element content in sediments indicated that in particle size fractions (≤ 0.001 mm) could accumulate more than 15 times the levels of Cr and Zn and more than 6 times the levels of Cu, Cd and Ni in comparison to the particle size fractions that are 1.0 mm. Local zones of polyelemental pollution of bottom sediments with respect to Cu, Zn, Pb Cd and Cr were determined. These zones are confined to the geochemical sorption barriers of small watercourses of the power plant.

Study on the development of the desert pasture agrophytocenoses using a wide range of forage plants

The drained bottom of the Aral Sea covers an area of about 6 million hectares, of which 3.2 million hectares are located on the territory of the Republic of Uzbekistan. In addition to the fact that salt is spread from the drained bottom, dust and sand causing enormous damage to the environment, on the drained bottom there is a forest suitable area of 1.5 million hectares where it is possible to create desert shrub agrophytocenoses. The purpose of the work was to develop the most effective methods for creating desert agrophytocenoses on forest suitable types of bottom sediments of the dried bottom of the Aral Sea and the selection of desert forage plants to increase the productivity of the created pastures. Studies shown that when using focal, pasture protection and reclamation-fodder methods, as well as such fodder plants as teresken, boialich, keyreuk, it is possible to create pastures with a fodder capacity of up to 500 fodder units per hectare. This will increase the number of grazed animals by 20-30%. The field of application of the results arising from this work are forest suitable types of bottom sediments of the drained bottom of the Aral Sea. The drained bottom of the Aral Sea is a reserve of a forage base for animals in the near future, which will give a new impetus to the development of animal husbandry in the Aral Sea region, and at the same time, fodder plants, fixing the soil of the drained bottom of the Aral Sea, will significantly improve the ecological situation in the Region.

РАСЧЕТ ЗНАЧЕНИЙ ПАРАМЕТРОВ ДЛЯ ХАРАКТЕРИСТИКИ ПОСЛЕДСТВИЙ РАБОТ ПО ДНОУГЛУБЛЕНИЮ И ДАМПИНГУ ДОННЫХ ОСАДКОВ: ОЦЕНКА С ПОМОЩЬЮ ВВ-МОДЕЛИ

The developed SM-model, describing the suspended matter concentrations in water environment, was used to assess the consequences of the works on dredging and dumping ground during the reconstruction and modernization of the water body area in the Pionersky Port (Kaliningrad region). The complex of recreated works includes 11 stages of the dredging works during which the various types of bottom sediments are extracted, some part of these sediments are transported outside the port water area and discharged into the marine underwater dump, while other their part are used for hydraulic engineering works in the port area. At the dredging and dumping the sediments, additional zones of water turbidity are formed (with a suspended matter concentration > 50 mg/L), its deposition causes the formation of a layer of sediments on the bottom. For each work stages, the technological data on the currents in the port water area are used for mathematical modeling and calculations of the amounts of various types of sediments extracted from the bottom, their redistribution over the sea area, the concentration of suspended matter in sea water, and the indicators (areas and volumes) of the emerging turbidity zones water due as a result of the construction works. Calculated data may be used to compile a report “Assessment of influence on the water environment state” (or AIWES) in the frame of these works.

Ecotoxicological and chemical properties of the rożnów reservoir bottom sediment amended with various waste materials

In the study, an attempt was made to create innovative mixtures based on bottom sediment and various types of waste to be tested for use as a substrate in the cultivation of consumer and non-consumer plants. The aim of the study was to assess the chemical and ecotoxicological properties of the growing medium prepared on the basis of bottom sediment (BS) and different carbon rich waste (cellulose waste (CW), biomass ash (BA), coffee hulls (CH), and sludge from water treatment (SW)) with a combination of 75% bottom sediment and 25% waste material. The mixtures had deacidifying properties, significant content of total organic carbon (TOC), the total quantities of macro- and micronutrients, and good sorption properties. The study showed a low total content of heavy metals in the mixtures. Moreover, a low share of the mobile fraction (F1) of metals indicated a low risk related to the metals mobility and potential bioavailability. The highest toxic effect was found in the mixture of bottom sediment and cellulose waste. Heterocypris incongruens was the most sensitive organism to substances present in the tested mixtures. Due to its low toxicity, the mixture of bottom sediment and water treatment sludge (BS+SW) constituted a potentially suitable substrate for its environmental application in agriculture, horticulture (for consumer crops) or land reclamation. Other mixtures exhibited valuable chemical properties (BS + BA, BS + CH BS + CW), but ended up being eco-toxic to the organisms, excluding them from agricultural or horticultural use for consumer crops. The proposed technology, which includes the production of growing medium based on the use of bottom sediment, is a promising way of transforming the sediment from a waste material to a valuable resource, thus enhancing the environmental benefits.

Optimization of environmental variables in habitat suitability modeling for mantis shrimp Oratosquilla oratoria in the Haizhou Bay and adjacent waters

Habitat suitability index (HSI) models have been widely used to analyze the relationship between species abundance and environmental factors, and ultimately inform management of marine species. The response of species abundance to each environmental variable is different and habitat requirements may change over life history stages and seasons. Therefore, it is necessary to determine the optimal combination of environmental variables in HSI modelling. In this study, generalized additive models (GAMs) were used to determine which environmental variables to be included in the HSI models. Significant variables were retained and weighted in the HSI model according to their relative contribution (%) to the total deviation explained by the boosted regression tree (BRT). The HSI models were applied to evaluate the habitat suitability of mantis shrimp Oratosquilla oratoria in the Haizhou Bay and adjacent areas in 2011 and 2013–2017. Ontogenetic and seasonal variations in HSI models of mantis shrimp were also examined. Among the four models (non-optimized model, BRT informed HSI model, GAM informed HSI model, and both BRT and GAM informed HSI model), both BRT and GAM informed HSI model showed the best performance. Four environmental variables (bottom temperature, depth, distance offshore and sediment type) were selected in the HSI models for four groups (spring-juvenile, spring-adult, fall-juvenile and fall-adult) of mantis shrimp. The distribution of habitat suitability showed similar patterns between juveniles and adults, but obvious seasonal variations were observed. This study suggests that the process of optimizing environmental variables in HSI models improves the performance of HSI models, and this optimization strategy could be extended to other marine organisms to enhance the understanding of the habitat suitability of target species.

NON-ERODING WATER VELOCITIES FOR INCOHERENT BOTTOM SEDIMENTS

There are the values of non-eroding water velocities for various types of bottom sediments (incoherent and cohesive) given in the normative documentation in the form of tables and graphs. Also there are a number of regulatory documents containing methods for calculation such velocities. These methods are based on empirical dependencies adapted to specific conditions. The calculated mean non-eroding water velocities are proportional to the depth of flow and bottom particle size in the case of incoherent bottom sediments erosion. The authors made an attempt to estimate non-eroding water velocity by a physical approach to the problem depending on the internal friction angle, the calculated clutch of incoherent bottom sediments and the depth of the water over the bottom. This approach should be universal. An analysis of the results indicated that the proposed formula for calculating bottom non-eroding water velocities in all considered cases gives results significantly higher than the values given in the regulatory documents for the corresponding size of incoherent bottom sediments. As a result authors obtained non-eroding water velocities, which were overestimated at times on the basis of expert evaluation. When the depth changes from 0.5 to 10 m, the spread of estimated bottom velocities varies from 14 to 22%, depending on the size of the incoherent soil. It was concluded that for smaller particles of incoherent soil, the less deviation of the calculated values of bottom non-eroding water velocities from the normative ones (for massive gravel sands at a 10 m flow depth, the deviation from the normative values reaches 375-510%). In addition, the dependence of the value bottom non-eroding water velocity on the depth is traced, which is not provided in regulatory documents. The authors offer the scientific community to join to discussion of the reasons for these discrepancies.

К вопросу о расчетах расхода взвешенных наносов

The article deals with the questions of the contribution of suspended sediment in the processes of formation of the channel, and includes several formulas of suspended sediment discharge calculation and the results of calculations by these formulas. An analytical formula of sediments, in which the absolute exponent of the degree of arguments is equal to one shown the lower error probability. The calculated probability of calculation error is explicitly related to the average relative deviation between the calculated and observed values of sediment flow: the formulas with a lower error probability show better correspondence to the observed values. At the same time, the parameters of the analytical formula of sediment flow integral with respect to the type of bottom sediments represent a more stable dependence of the hydraulic variables of the flow state and sediments in contrast to the formulas of a similar purpose with data on sediment size included in them. This is explained by the fact that even quantum estimates of particle size are often unreliable and have high variability within one phase of water content, whereas the parameters focused on the qualitative state of the system (category of sediment size) characterize the properties of the bottom soil on average (integrally) over the cross-section of the flow.

Sedimentation rates (data on 210pb and 137cs radionuclides) in different facial-genetic types of the Kara sea bottom sediments

In the article original data on isotope composition of natural excess Pb-210 and artificial Cs-137 radionuclides in upper 2550-cm layer of sea-bottom sediments at the Kara Sea (from Ob and Yenisei estuaries, Eastern-Novaya-Zemlya trough, Voronin trough, as well as Sedov bay (Novaya Zemlya)) are presented. The research results showed close tie between sedimentation rates and facial-genetic types of the sea-bottom sediments. Highest sedimentation rates are typical for the terrigenic-estuarine type. The type is divided on tractional load with sedimentation rate 0.40.7 cm per year and mud bank sediments with sedimentation rate 0.71.0 cm per year. The terrigenic-shallow-marine type is characterized by lowest sedimentation rate 0.10.3 cm per year. The background terrigenic-marine type has a broadest spectrum of the sedimentation rates: on trough slope the rates are minimal (likely to terrigenic-shallow-marine type), within central parts of the trough (as a result of gravity creep) the rates may increase up to 0.9 cm per year. Single facial-genetic type is glacial sediments of Navaya Zemlya bays. Measured recent sedimentation rate within inner depression of the Sedov bay is 0.10.2 cm per year.

On mechanical fragmentation of single-use plastics in the sea swash zone with different types of bottom sediments: Insights from laboratory experiments

Mechanical fragmentation of four commonly used plastics, from 2-cm squares or cubes to microplastics (MPs, <5 mm), is experimentally investigated using a rotating laboratory mixer mimicking the sea swash zone with natural beach sediments (large and small pebbles, granules, sand). Macro-samples were prepared from brittle not-buoyant PS (disposable plates), flexible thin film of LDPE (garbage bags), highly buoyant foamed PS (building insulation sheets), and hard buoyant PP (single-use beverage cups). With a great variety of behaviors of plastics while mixing, coarser sediments (pebbles) have higher fragmentation efficiency than sands (measured as the mass of generated MPs), disregarding sinking/floating or mechanical properties of the samples. It is confirmed that, under swash-like mixing with coarse sediments, the MPs tend to burry below the sediment surface. The obtained relationship between the mass of MPs and the number of items is similar to that for MPs floating at the ocean surface.

Geochronology of the southern Baltic Sea sediments derived from 210Pb dating

Based on the vertical distribution of 210Pb activity concentrations in bottom sediment, linear accumulation rates (LAR) and mass accumulation rates (MAR) were determined for 31 locations in the southern Baltic Sea region by applying models: Constant Flux Constant Sedimentation Rate (CF:CS) and Constant Rate of Supply (CRS). The dating of sediment layers in selected locations was also carried out. The reliability of the results was verified using radiotracers: 137Cs and, for the first time, 90Sr. The results obtained were the basis for the development of maps of continuous distributions of LAR and MAR values in the areas where a particular type of bottom sediments were found: silt-clay, sandy silt, silty sand and mixtites covering the region of the southern Baltic. The maps constitute a tool supporting basic and applied research. Data for marine open areas were supplemented with sediment accumulation rate data for the areas of the Szczecin Lagoon and the Vistula Lagoon. The linear accumulation rates of bottom sediments of the southern Baltic varied from 0.61 to 3.54 mm y−1 while mass accumulation rates ranged from 390 g m−2 y−1 to 910 g m−2 y−1, largely reflecting the LAR values.

Sedimentation Rates in Different Facies–Genetic Types of Bottom Sediments in the Kara Sea: Evidence from the 210Pb and 137Cs Radionuclides

The paper presents authors' original data on the isotope composition of the natural “excess” Pb‑210 and artificial Cs-137 radionuclides in the upper 25- to 50-cm layer of sea-bottom sediments in the Kara Sea (from the Ob and Yenisei estuaries, Eastern Novaya Zemlya trough, Voronin trough, and Sedov bay at the Novaya Zemlya). Sediment cores were collected during Cruises AMK-63 and AMK-66 of the R/V Akademik Mstislav Keldysh in 2015 and 2016. Results of this research show strong correlations between the sedimentation rates and facies-genetic types of the sea-bottom sediments. The highest sedimentation rates are typical of the terrigenous–estuarine sediments, which are subdivided into tractional load, whose sedimentation rate is 0.4–0.7 cm per year, and “mud bank” sediments, whose sedimentation rate is 0.7–1.0 cm per year. The terrigenous shallow marine sediments are characterized by the lowest sedimentation rate of 0.1–0.3 cm per year. The background terrigenous marine sediments show broad variations in the sedimentation rates: these rates are at a minimum (and comparable to the sedimentation rates of the terrigenous shallow marine sediments) on trough slopes and can increase to 0.9 cm per year in the central parts of the trough (as a result of gravity creep). The glacial sediments of Novaya Zemlya bays belong to a separate individual type. The measured “current” sedimentation rate within the inner depression of the Sedov bay is 0.1–0.2 cm per year.

Application of a fish finder system to spatial distribution mapping for the razor clam Solen gordonis: Case study from coastal waters, northwestern Kyushu, Japan

Effective spatial management planning for sedentary fishery resources requires accurate spatial distribution mapping of a focal stock including both fished and associated unfished populations. This study focuses on (sub-)adult razor clams (Solen gordonis), with shell lengths ≥25 mm, in Sasebo Bay and Omura Bay, northwestern Kyushu, Japan. They are commercially harvested, but little is known about their spatial distribution pattern. The objective was to estimate the spatial distribution and configuration of clam beds existing within an area of ca. 12 km2. For this, clam and sediment sampling by scuba-equipped divers, acoustic bathymetric surveys using a recreational-grade fish finder (single-beam acoustic) system, and presence–absence modelling using generalized linear models were performed. For the collected clams, catch per unit effort (CPUE; number of clams collected/h) was calculated and used as a proxy for clam individual density. The results showed that the presence–absence variation in the spatial distribution of (sub-)adult clams was associated with the bottom sediment type. (Sub-)adult clams occurred frequently in the sediments with higher gravel (particles with diameters ≥2 mm, mainly shell fragments) and lower mud (diameters <0.063 mm) contents than the sediments of the absence sites. Acoustic signals of the fish finder system were backscattered more intensely from gravel-sand beds (i.e., typical of the presence sites) than from muddy sand beds (i.e., absence sites). Using the relationships among the presence–absence variation of (sub-)adult clams, sediment type, and backscatter strength, spatial distribution of clams was predicted with high accuracy. The presence probability of (sub-)adults (= x; continuous values from 0 to 1) predicted from the results was significantly regressed on CPUE (= y) [i.e., y = exp(−0.7984 + 4.9350x) − 0.05]. Using this relationship, a map for the relative abundance of (sub-)adult clams was obtained. This map depicted several clam beds including both exploited and unexploited ones. The latter beds virtually conform to no-take zones in the razor clam fishery.

Emergence of Midges (Chironomidae, Diptera) from a Saline Lake as a Source of Organic Matter and Essential Biochemical Compounds for Arid Ecosystems in South Siberia

Midges (Chironomidae, Diptera) are dominant amphibiotic insects in zoobenthos of the large saline Lake Shira located in the arid landscape of South Siberia. During two vegetation seasons we measured the dynamics of chironomid emergence from littoral parts of four stations in the lake. During one of the vegetation seasons we also measured chironomid emergence from profundal parts (depth of 6 m) of the same stations using original floating traps. Both seasonal dynamics and daily means of emergence values significantly varied among the studied stations and depths and were related to the bottom sediment type. The annual export of wet biomass (calculated as the sum of daily values for a vegetation season) was equal to 0.61 g per square meter of water surface and included proportional contributions of the areas with various bottom sediment types. Based on the values of benthic secondary production, we estimated additional annual export of chironomid biomass from the profundal part of the lake of approximately 1 g of wet weight · m−2. Besides, the total export of polyunsaturated fatty acids (PUFA) calculated using the previous data on PUFA content in the studied chironomid taxa (~ 2 mg · m−2 year−1) appeared to be one of the lowest when compared to estimations for chironomids and some other amphibiotic taxa from similar steppe landscapes

MACROBENTHOS OF THE CRENAL AND RITHRAL ZONES OF A TYPICAL «SALMON» RIVER IN NORTHEASTERN SAKHALIN ISLAND (ON EXAMPLE OF THE DAGI RIVER)

Structure and quantitative indices of macrobenthos, features of its distribution along the river bed, and basic communities of macrobenthos are described for the crenal and rithral zones of the Dagi River (northeastern Sakhalin) on the data collected in the expedition of Sakhalin State University in September 2017. Five river landscapes are described: 1) plain riverbed with significant alluvial forms; 2) mountain riverbed with significant alluvial forms; 3) plain riverbed with weak alluvial forms; 4) wellhead zone of a plain riverbed with significant alluvial forms; 5) estuary. The main elements of the river bed are partially mixed in the middle stream: the mountainous landscapes with significant alluvial forms are overlapped with the plain landscapes with weak alluvial forms. Distribution of macrobenthos along the river bed and the types of bottom communities are clearly corresponded with the river landscapes. So, the macrobenthos distribution in the Dagi River is physically controlled: the species diversity and abundance of macrozoobenthos increases downstream from the crenal to the rithral zone and further to the combined rithral-potamal zone. A significant increasing of the biomass is noted in the middle and lower rithral zone due to aggregations of freshwater pearl mollusc Margaritifera dahurica which confine with the spawning grounds of pacific salmons. The most common are the bottom communities of Hexatoma and Gammarus lacustris, which are noted almost in all surveyed areas. Other bottom communities are landscape-specific. In the rithral zone, composition and structure of macrobenthos are determined by distance to the riverbank, type of bottom sediments, flow velocity, and lithodynamic regime, so the communities form a consequence determined mainly by lithodynamic regime — the Hexatoma community in the lithodynamic zone of transportation could be followed either by the communities of Trichoptera, Plecoptera, and Diptera in the lithodynamic zone of erosion or by the communities of amphipods G. lacustris and larvae of day-flies Ephemera sachalinenesis in the lithodynamic zone of accumulation.

Biogeochemistry and sedimentology of Lago di Lesina (Italy)

The Lago di Lesina (Lesina Lake, southeastern Italy) is a coastal pond located on an alluvial plain to the north of Gargano Promontory. The aim of this work was to study the depositional and hydrological processes, the benthic environment and the heavy metal sediments pollution of Lesina Lake. The study was carried out by Redox potential, water content, grain-size, mineralogical and biogeochemical analyses in surface sediments collected from 100 sampling stations in the coastal pond bottom. The results showed a predominance of three types of bottom pelitic sediments of different origins and compositions: siliciclastic, carbonatic, and organic. Siliciclastic sediments, which were found especially in the western basin and in the northwestern sector of the central basin, are due to inputs from Acquarotta Canal, some intermittent western streams, and deflation by northerly winds of the sandy barrier that separates the lake from the sea. Carbonate sediments are carried by streams and canals draining the carbonate rocks of the Gargano Mountains and entering the lake from its eastern and southeastern border, these sediments are predominant in the eastern basin and in the southeastern sector of the central basin. Organic matter is abundant throughout the whole lake; it is due to the high productivity of the Lago di Lesina waters that are rich of nutrients for inputs of waters draining the surrounding intensively cultivated agricultural areas. The finer bottom sediments of the lake tend to be removed from the shallower bottoms between the central and eastern sub-basins and near the borders to be deposited in the central portion of the central and western sub-basins. Heavy metal sediment pollution due to anthropic inputs is limited and consists of As, Pb, Cu, and Ni in the western basin, Cu, Zn, and Ni in the eastern basin, and Pb along the northern border.

Distribution Patterns and Habitat Requirements of Freshwater Snails in Man-Made Ponds

The study was carried out to understand the factors that affect community structure and generate heterogeneity in gastropod species diversity in various types of man-made ponds (e.g., subsidence ponds, sand pits and fish ponds at forested and non-forested locations). The studied waterbodies differed in water chemistry, bottom sediment type, source and drainage of water and in terms of snail occurrence patterns. Differences in gastropod species composition were related to differences in bottom sediments and water chemistry. Two-way indicator species analysis split the clusters into four groups with respect to substratum type and location. Forest ponds were important for the gastropod diversity and specifically for Planorbidae species.