Lacustrine Areas Research Articles

Spatiotemporal distribution of pCO2 and CO2 flux and the regulatory factors: From the perspective of a subtropical canyon-shaped reservoir, southwest China

Reservoir carbon cycling is a critical component of the global carbon cycle, particularly in subtropical canyon-shaped reservoirs where unique geomorphological features and hydrological regulation under monsoon climate provide a distinct perspective for carbon cycle research. This study takes the Zipingpu Reservoir (ZPPR) in southwestern China as an example and reveals significant seasonal variations in partial pressure of carbon dioxide (pCO2) and carbon dioxide flux at the water-air interface (FCO2) through annual monitoring. The average pCO2 in ZPPR is 486 μatm, and the average FCO2 is 0.093 g C m-2d-1, with approximately 42.4 % of FCO2 measurements being negative, indicating the reservoir's role can act as a carbon sink. The study also estimated the gas transfer coefficient (K), with an average value of 1.888 md-1. Peak FCO2 during spring and summer is three times higher than in other seasons, consistent with the main influencing factors of inflow dynamics, metabolic processes, and reservoir operation strategies. Inflow and operational activities, particularly during spring and summer, drive CO2 emissions in the downstream reach and upstream tributary, while biological activity facilitates CO2 uptake in the lacustrine area and forebay tributary, with enhanced absorption occurring in the autumn. Concurrently, high-intensity FCO2 emissions from the upstream river section during summer underscore the importance of carbon emission monitoring and management during critical periods. The findings not only enhance the understanding of FCO2 assessment accuracy but also provide a framework for evaluating and optimizing carbon dynamics management strategies in canyon-shaped reservoirs, contributing valuable insights to global carbon cycle research.

Discovery and environmental implications of Santorini tephras (Cape Riva and Minoan) in sediments of Lake Yayla (West Anatolia)

Throughout the long eruption history of the Santorini volcano, the Cape Riva/Y-2 and Minoan/Z-2 eruptions had a profound impact on the environment. The Minoan eruptions also had a significant impact on society. These two tephras, as well as the Y-2 tephra individually, have been recorded for the first time in a lacustrine area in western Anatolia. This study examines the geochemical properties of Y-2 (23 cm) and Z-2 tephra layers (19 cm; 14 cm pure and 5 cm mixed) from 18 m sediment cores in Lake Yayla (Denizli-Buldan). Additionally, high-resolution µXRF, fossil pollen, charcoal, and dating analyses were conducted on the cores to determine the chronologies and environmental effects of the tephra layers. Fossil pollen findings show consistent forest and steppe/grassland vegetation before and after the Z-2 tephra, with the forest impact lasting for 240 years after the eruption. Increased aquatic vegetation and changes in specific taxa (e.g. Pinus sp. and Amaranthaceae increased, while Quercus deciduous, Olea europaea, and cereals decreased) were observed following the Minoan eruption. Charcoal analysis indicates heightened fire activity post-Minoan eruption, while XRF data reveal no associated climatic change. At the same time, no correlation has been identified between the Cape Riva eruption and ecological changes (climate, vegetation, and fire activity). Contribution to dating the tephra was provided by radiocarbon dating from the lowest part of the tephra layer (17,684 ± 63 years BP). This study sheds light on the extensive impacts of the Y-2 and Z-2 tephra eruptions, focusing on their dating, geochemistry, environmental effects, tephra transport directions, and thicknesses. It demonstrates the presence of a significant geological event for the settlements in the Büyük Menderes Valley.

Hydrochemical processes and inorganic nitrogen sources of shallow groundwater in the Sanjiang Plain, northeast China.

This study investigates the chemical characteristics, formation, and sources of inorganic nitrogen (IN) of shallow groundwater across the Sanjiang Plain, aiming to enhance drinking water safety management and pollution control. A total of 167 groundwater and 27 surface water samples were collected for constituents and isotopes (H2 and O18). The hydrogeochemical characteristics showed that the major type is HCO3- Ca·Mg, with low total dissolved solids and a neutral to weak alkaline nature. Rock weathering processes govern the hydrochemical composition of groundwater. Hydrogen and oxygen stable isotopes analyses revealed that precipitation serves as the main water source. In alluvial areas, oxidative conditions lead to the enrichment of NO3-N concentrations, with sewage, manure, and fertilizers being the primary IN sources. In lacustrine areas, intensive rice cultivation results in reductive conditions and strong denitrification processes, causing the loss of NO3-N and leaving NH4-N as the dominant IN form. Organic matter mineralization is likely a more significant contributor to NH4-N concentrations than ammonium fertilizers. These findings provide valuable information for further research on natural sources and groundwater pollution in areas with similar hydrogeological conditions. PRACTITIONER POINTS: Rock weathering processes govern the hydrochemical composition of groundwater, and precipitation serves as the main water source. In alluvial areas, oxidative conditions lead to the enrichment of NO3-N. In lacustrine areas, intensive rice cultivation results in reductive conditions and strong denitrification processes. Organic matter mineralization is likely a more significant contributor to NH4-N concentrations than ammonium fertilizers. These findings provide references for water management and information for further research on natural sources and groundwater pollution in areas with similar hydrogeological conditions.

Mapping the occurrence of Eustrongylides spp. in fish species caught from six lakes in Central Italy (Tuscany and Latium regions): Implications for local fishery supply chains

In the present study, in order to expand the knowledge on the distribution of parasites of the genus Eustrongylides in never investigated Italian lacustrine areas of Tuscany and Latium, fish specimens from four Tuscan lakes (Bilancino, Chiusi, Montedoglio and San Cipriano) and two Latium lakes (Bolsena and Bracciano) were collected and analyzed. The parasitological analysis, consisting of a visual inspection followed by a chloro-peptic digestion, was performed on 1650 specimens belonging to 17 species: European perch (Perca fluviatilis), Pumpkinseed (Lepomis gibbosus), Pike-perch (Sander lucioperca), Largemouth black bass (Micropterus salmoides), Pike (Esox lucius), Big-scale sand smelt (Atherina boyeri), Tench (Tinca), European Whitefish (Coregonus lavaretus), Channel catfish (Ictalurus punctatus), Chub (Squalius cephalus), Rudd (Scardinius erythrophthalmus), Common bleak (Alburnus alborella), South European roach (Sarmarutilus rubilio), South European nase (Protochondrostoma genei), Italian riffle dace (Telestes muticellus), Goldfish (Carassius auratus), and Freshwater bream (Abramis brama). Eustrongylides spp. larvae were only found in one specimen of European perch caught in Bracciano Lake and purchased from a local fishmonger (P = 3.3%; MI = 1; MA = 0.03). The only isolated Eustrongylides spp. larva was submitted to molecular analysis of the ITS gene region and identified as E. excisus. This finding adds Bracciano Lake to the list of the several Italian lakes in which nematodes belonging to this genus have been reported. Even if the observed prevalence is currently low, the presence of the parasite in this local freshwater fish supply chain requires FBOs to adopt risk management measures to prevent contaminated products from reaching final consumer. Moreover, future investigations will show if the parasite expands in these areas.

PALYNOSTRATIGRAPHIC AND PALAEOENVIRONMENTAL INVESTIGATIONS OF THE MAASTRICHTIAN FROM OARDA DE JOS (SOUTHWESTERN TRANSYLVANIAN BASIN)

A palynological, palynofacies and organic geochemical investigation of the Upper Cretaceous continental vertebrate site of Oarda de Jos allowed us to constrain its age and to make more detailed inferences about its depositional environment. The recovered palynomorph assemblage is represented mainly by angiosperm pollen and fern spores, alongside rare taxa of gymnosperms. Biostratigraphically significant taxa identified in the assemblage restrict the age of the studies deposits to the later early Maastrichtian. The palynofloral evidence indicates plant communities that mainly preferred higher-altitude areas and cooler-wetter conditions. However, a spore and pollen assemblage which derives from vegetation typical of lacustrine areas or riverbanks also occurs in the studied deposits. The studied palynoflora shows quite significant differences compared to previously published palynological assemblages from the same geological unit (the Sebeș Formation), although from deposits located slightly to the north, at Pâclișa. Organic geochemical data show that certain organic biomarkers such as n-alkanes n-C16 to n-C18 reach the highest values, and indicate that they may derive from freshwater colonial green algae such as Scenedesmus. The palynofacies constituents used to reconstruct the depositional environment suggest an exclusive terrestrial organic matter deposited in a stagnant-water fluvial/lacustrine environment.

Garnys: An underwater riverine site with delayed Neolithisation in the southeastern Baltic

This paper presents the first results of both dryland and underwater investigations at the multi-period Garnys riverine site situated on the Žeimena River in eastern Lithuania. There, during 2017–2020 a professional diver and amateur archaeologist collected hundreds of Mesolithic-Neolithic archaeological finds made of wood, bone, antler, stone, and ceramic from the riverbed and on its bank. Moreover, in eroded places of the riverbed, the wooden remains of several fish weirs were observed. In 2021 professional archaeologists continued the research, including field investigations followed by various laboratory analyses. These included AMS 14C dating of 16 various ecofacts, artefacts and wooden constructions, wood and animal taxa determinations, and the results of traceological analysis of the flint and osseous artefacts. Our research demonstrates that the site was intensively used for hunting, gathering and fishing during the Mesolithic and subsequent Subneolithic and Neolithic. Intriguingly, there was no evidence for agriculture, while the numerous Neolithic ceramics largely follow the Subneolithic traditions. The Garnys site is therefore unique and a clear example for delayed Neolithisation in a forested and lacustrine area in the eastern Baltic region. During the Metal Ages, the site had been used exclusively for stationary fishing.

Consolidation behaviors of gas-bearing sediments with modulus varying along depth under horizontal loads

Gas-bearing sediments are widely distributed in marine and lacustrine areas. The engineering properties of gas-bearing sediments, containing enclosed bubbles, are significantly different with that of saturated and unsaturated sediments. This paper investigates the consolidation behaviors of gas-bearing sediments with modulus varying along depth subjected to horizontal load using an extended precise integration method (XPIM). The compressibility of enclosed bubble is introduced to a new derived seepage equation and a varying modulus along depth is considered in governing equations. With the aid of integral transformation and Taylor expansion, such problems are solved by XPIM, which is proved to be markedly efficient and precise for boundary value problems of porous media than traditional numerical methods. Detailed comparisons against analytical solutions are performed to confirm the accurateness of XPIM. Extensive parametric investigations are conducted to examine the influence of saturation degree, varying modulus along depth and type of external load on the consolidation behaviors of gas-bearing sediments. The present work is conveniently utilized to evaluate the behavior of gas-bearing sediments, and subsequently the response of foundations built in gas-bearing soil areas.

A comparing vision of the lakes of the basin of Mexico: from the first physicochemical evaluation of Alexander von Humboldt to the current condition

The Basin of Mexico is an endorheic lacustrine basin with an outstanding ecological and social history. There is evidence that it hosted human settlers since the late Pleistocene. This basin was home to great antique civilizations and many endemic species of flora and fauna. The main lake in the Basin was the Great Lake of Mexico, which was divided into five lakes and provided goods and services to the native communities. After the Spanish conquest, a rule was established to drain the lakes to prevent flooding in the city. The naturalist Alexander von Humboldt visited Mexico City in the early 1800s, and carried out the first formal scientific water quality analysis of the lakes of the basin. The Basin of Mexico gone through serious modifications due to urbanization and changes of land use reducing the lacustrine area to the virtual extinction of the lakes. The lakes are currently reduced to wetlands accounting for only 2.83% of the former lake and receiving mainly treated wastewater discharges. We carried out a comparative study between Humboldt’s results and the current characteristics of water from these lake remnants analyzed with the same methods that he used. In addition, we assessed several morphometric parameters and performed water quality assessments using modern methods. Changes in water quality characteristics and ionic composition were detected, with Xochimilco being the lake with the highest water quality score and Texcoco and Chalco showing major alterations. The drastic reduction in the area of the remaining water bodies and the modifications in their water quality are discussed.

Youngest Iberian Holocene volcanic eruptions and paleoenvironmental evolution of a barrier-paleolake in the Garrotxa Volcanic Field (NE Spain)

Volcanic eruptions are key drivers of climate variability, with complex environmental consequences at regional and local scales that are rarely documented in high-resolution sedimentary records. In this work we present the results of a 15 m long paleolake core (Pla de les Preses core, Vall d’en Bas, Girona, NE Spain) covering the Late Pleistocene-Holocene transition. Multiproxy analyses including chronostratigraphy, sedimentology, micropalaeontology and geochemistry are used to reconstruct the paleoenvironmental framework of the Late Pleistocene-Holocene transition and to detect the youngest Holocene volcanic eruptions in the Garrotxa Volcanic Field (GVF) and the Iberian Peninsula. The studied sedimentary record covers the last ca. 13.5 ka cal BP and was punctuated by several rapid climatic changes including the 9.3, 8.2 and 7.1 ka events, affecting the hydrological evolution of a barrier-lake formed due to the volcanic damming of the Fluvià river. Sedimentological and geochemical analyses unveil the environmental history of Vall d’en Bas valley; the formation of a lacustrine area within a fluvial environment around 13.5 ka cal BP and later a wetland phase between 9.3 and 8.2 ka cal BP. Abrupt sedimentary changes marking the onset and demise of the wetland phase were linked to hemispheric cooling and drying events (e.g. 9.3 and 8.2 ka cal BP), provoking a decline in the water table during these phases. In addition, 30 tephra layers are detected thorough the core, showing previously unknown intense volcanic activity from 13.5 to 8.3 ka cal BP in the GVF. In that sense, the Pla de les Preses sequence provides, for the first time, evidence for early Holocene volcanic activity in NE Iberia that should be taken into account in future tephra studies in the western Mediterranean realm.

Significant spatiotemporal variability of nitrous oxide emissions from a temperate reservoir experiencing intensive aquaculture disturbance

Freshwater reservoirs are known as important sources of atmospheric N2O; however, the patterns and controls of N2O emissions from these reservoirs remain poorly understood, particularly for reservoirs severely disturbed by aquaculture activities. This study aimed to bridge this knowledge gap by determining the spatiotemporal and magnitude variations of N2O concentrations, dynamics of the drivers of N2O concentration and diffusive flux, and N2O emission patterns from reservoirs severely affected by human activities. We measured N2O concentrations and estimated diffusive fluxes in a temperate reservoir—including the upstream river inflow zone—in northern China, which was experiencing acute aquaculture disturbance. A thin boundary layer equation was employed, and we analyzed the thermal and dissolved oxygen stratification conditions and other environmental auxiliary factors to identify crucial factors and underlying mechanisms that regulate N2O emissions. Our results showed that aquaculture activities led to the accumulation of high levels of organic matter and nutrients in sediments. The annual average water-dissolved N2O concentration and diffusive flux across the water–air interface in the reservoir were 24.97 ± 11.16 nmol L-1 and 0.43 ± 0.36 μmol m-2·h-1, respectively. The water-dissolved N2O concentrations exhibited supersaturation, indicating the reservoir as a net source of atmospheric N2O. Both N2O concentrations and diffusive fluxes exhibited strong spatiotemporal variability during the study period. The lacustrine area of the reservoir was the hotspot for N2O emissions. The statistical results indicated that nitrogen loading, temperature, and dissolved oxygen (DO) were the key drivers of N2O emissions. Moreover, dam construction and intensive aquaculture disturbances have altered aquatic conditions and significantly affected N2O emissions. Our results indicated that N2O emission estimates for the entire reservoir should cover different reservoir zones and sampling seasons. We suggest measures such as sediment dredging to reduce sediment organic matter and nutrient loading for mitigating N2O emissions from the reservoir.

PAHs, PCBs, PBDEs, and OCPs trapped and remobilized in the Lake of Cavazzo (NE Italy) sediments: Temporal trends, quality, and sources in an area prone to anthropogenic and natural stressors

Under the present climatic emergency, the environmental quality of freshwater reservoirs is an increasingly urgent topic as its deterioration threatens humans and ecosystems. It is evident that pollution by natural and anthropogenic contaminants must be avoided or reduced. The Lake of Cavazzo (NE Italy) is a natural perialpine basin which, from the mid-20th century, has sustained several anthropogenic impacts that added to the effects of the intense regional seismicity. Starting from 2015, in response to concerns raised by local authorities, a multidisciplinary investigation of the lake floor and sub-floor was conducted, including a geophysical survey and the collection of sediment cores. Two of them were studied to detect contamination by Polycyclic Aromatic Hydrocarbons (PAHs) and specific Persistent Organic Pollutants (POPs; i.e. PolyChlorinated Biphenyls - PCBs, PolyBrominated Diphenyl Ethers - PBDEs, and OrganoChlorine Pesticides - OCPs), and to verify the link with known anthropogenic stressors. Results were interpreted in light of previous studies suggesting modified conditions after the ‘50s, and recognized the effects of the 1976–1977 MW 6.5 seismic sequence in resuspending sediments within the basin. Analyzed pollutants defined a potential critical situation only for few OCPs, above all 2,4’- and 4,4′-DDT isomers. In addition, PBDEs were found at concentrations exceeding those of other heavily polluted alpine lakes. Mass movements (either seismic or human induced) have likely resuspended and transferred pollutants from shallower locations to the lake depocenter, showing the potential of re-exposing contaminated layers to biomagnification processes along the lacustrine food chain. Local inputs of pollutants prevail over distributed sources, suggesting a link with local agricultural or industrial activities. Indeed, works connected to the construction of the hydroelectric power plant in the ‘50s might have reworked local sediments perturbing their natural accretion. Results of this work might inspire similar studies in other problematic lacustrine areas that sustain both natural and anthropogenic stressors.

Anthropocene Trails on Geomorphology of Meghalayan Chilika Basin Odisha

The Chilika gulf in the pre-Meghalayan era has transformed into Greater Chilika, later a leaky lagoon and now downsizing. During early Anthropocene epoch (1950) became a restricted lagoon with the stable southern half of the barrier spit and fragile the northerly half. The sediment balance governed by the inland riverine flood flows from south Mahanadi delta (SMD), and through diurnal tides during other periods. The present anthropogenic development are the emerging Bhubaneswar capital (1948), rising population, and peripheral growth of urbans. Chilika, have deteriorated its eco-bio-hydro system and its associated delta. The anthropogenic interventions to flow by dams, barrages, new mouth dredging, Gobakund cut and natural sea-level changes, frequent storms, high waves, and longshore drift, have altered the geomorphology of the area. The present search envisages the physical changes that occurred in about 6000km2 of study area. The Remote Sensing and GIS technology and the ERDAS software tool were in use to concoct for the years 1984, 1994 and 2022, and compared the basic geophysical features geospatially (1975 to 2022). The erratic changes have developed over the lacustrine area, tidal inlets variability, increase in stable barrier spit and ecosystem with the land slamming of storms. Excess tourism activities, exploitation of fishery, motorized communications, poaching and increase of stakeholders have lost its forests, hills, solitude, and tranquility within.

Depositional conditions at the Aptian pre-salt margins: evidence from quantitative petrography and textural analysis of the Mucuri Member, Espírito Santo Basin, Brazil

Aptian siliciclastic onshore deposits of the Mucuri Member are important reservoirs in the Espírito Santo Basin (eastern Brazil). A detailed quantitative petrographical and textural analysis of well core samples was performed in order to unravel their depositional processes and conditions, in relation to previously proposed depositional models. The results allowed differentiation between two groups of sandstone samples, characterized by different textural characteristics associated to different depositional processes and environments within the Mucuri depositional system. Fluvial sandstones are represented by medium- to coarse-grained, poorly sorted arkoses, rich in plutonic rock fragments and feldspar grains, mainly transported by traction. Coastal-lacustrine sandstones correspond to very fine- to fine-grained, moderately sorted micaceous arkoses, mainly transported in suspension. The application of a discriminant function based on grain-size parameters validated previously proposed depositional settings for the studied sample groups. The combination of grain-size and shape data revealed differences in hydraulic equivalence and shape between grains from different depositional settings. In terms of hydraulic equivalence, micas in the fluvial sediments present lower settling velocity values, in contrast to the relatively large mica grains in the coastal sediments, which are hydraulically equivalent with the associated quartz and feldspar grains. The results of this study provide key information regarding depositional conditions (transportation mechanisms, grain-settling velocity and mineral hydraulic fractionation) at the margins of the Aptian pre-salt system, which can constrain the hydrological conditions and the sediment type available for distal lacustrine areas.

Long-Term Interannual and Seasonal Links between the Nutrient Regime, Sestonic Chlorophyll and Dominant Bluegreen Algae under the Varying Intensity of Monsoon Precipitation in a Drinking Water Reservoir.

Long-term variations in reservoir water chemistry could provide essential data in making sustainable water quality management decisions. Here, we analyzed the spatiotemporal variabilities of nutrients, sestonic chlorophyll-a (CHL-a), nutrient enrichment, dominant algal species, and overall chemical water health of the third-largest drinking water reservoir in South Korea during 2000–2020. Our results distinctly explained the strong influence of monsoon rainfall on spatial and annual water chemistry variations. We observed a consistent increase in the chemical oxygen demand alluding to organic matter pollutants, while a steady declining trend in the sestonic CHL-a. The long-term total phosphorus (TP) level showed a steady reduction from the riverine zone to the lacustrine area. However, a higher total coliform bacteria (TCB) was observed at the water intake tower sites. TP displayed a strong link to algal CHL-a and ambient nitrogen phosphorus ratios, suggesting a robust phosphorus-limitation state. The severe phosphorus-limitation was also corroborated by the findings of trophic state index deviation. The high and low flow dynamics exhibited the strong influence of intensive rainfall carrying many nutrients and sediments and flushing out the sestonic CHL-a. Successive eutrophic conditions prevailed along with dominating blue-green algae species (Microcystis and Anabaena). We observed a strong positive correlation (r = 0.62) between water temperature and CHL-a and between total suspended solids and TP (r = 0.65). The multi-metric water pollution index characterized the overall water quality as ‘good’ at all the study sites. In conclusion, the long-term spatiotemporal variabilities of the ecological functions based on the nutrient-CHL-a empirical models are regulated mainly by the intensive monsoon precipitation. The drinking water could become hazardous under the recurrent eutrophication events and chemical degradations due to uncontrolled and untreated inflow of sewage and wastewater treatment plant effluents. Therefore, we strongly advocate stringent criteria to mitigate phosphorus and organic pollutant influx for sustainable management of Daecheong Reservoir.

Geomorphological control of habitat distribution in an intermittent shallow saline lake, Gallocanta Lake, NE Spain

The aim of the present study consists on the establishment of any relationship or interaction between geomorphological processes and vegetation/habitat distribution in an area with strong environmental gradients: an active saline lake in NE Spain. The resulting maps of the major geoforms and CORINE habitats within the lacustrine area were overlain to determine any significant relationships, taking into account the elevation derived from Lidar data. Whereas the geoforms resulted to have a roughly concentric distribution, the habitats appeared to be spread across different areas, and flooding frequency seemed not to be a determining factor in their altitudinal distribution. The correspondence matrix for geoforms and habitats underlined the coincidence between presently active morphodynamic units, flooding/salinity, and habitats typical of saline environments. Geomorphological units associated with the presently active shoreline dynamics host the habitats more typically related to frequent flooding and high salinity levels. The delay between geomorphological dynamics and vegetation changes, together with the opportunistic character of vegetation, promote the coexistence of different geomorphological processes and a great variety of plant communities and habitats. As a major conclusion, the present study provides a method through which a standard procedure may be set up to further determine the interaction between geomorphological processes and vegetation distribution, very useful for understanding vegetation patterns and conservation biodiversity, and the planning and managing of Natura 2000 sites.

Study on Performance of Cement Mixing Pile in Marine and Continental Deposition Soft Soil Area

Soft soil was widely distributed in the coastal area, and the key characters were high water content and low capacity. Cement Mixing Pile (CMP) is an effective method to treat soft soil foundation. While CMP construction quality was difficult to control and it was of different reinforce effect for different geology origin. In this paper, five geology origins have been divided for the littoral area, lagoon area, alluvial area (Yangtse River), alluvial area (Ancient Yellow River) and lacustrine area. CMP, used in 26 expressways which were constructed during the period of 2008 - 2016, has been divided two-part (Upper & Lower part) to test the construction quality of CMP through Standard Penetration Test (SPT), Unconfined Compaction Strength (UCS) and Cement Mixing Pile Quality Designation (CMPQD). Results show that geology origins have great influence on the construction quality of CMP at the same construction maintenance condition. Depth has a significant effect on UCS of the lower part of CMP while the little effect on UCS of the upper part. Construction quality of long CMP was more difficult to control than short CMP. The high quality of the upper part may cause the unqualified lower part evaluated as qualified or good, which may lead to some engineering accidents.

Sediment pollution in an urban water supply lake in southern Brazil.

Urbanization and anthropogenic activities create many environmental issues in urban water supply reservoirs, especially in metropolitan regions. Thus, this study was carried out aiming to evaluate the variance in the physical-chemical characteristics of bottom sediment along the Lake Guaíba, Brazil. Lake Guaíba is a freshwater lake situated in a metropolitan region in southern Brazil, being the main water supply to the region. Surface sediment was evaluated to pH, electrical conductivity, particle-size, total organic carbon and nitrogen, metals and inorganic elements (Fe, Al, Ca, Ba, Sr, Co, Tl, Zn, Cu, Cr, Ni, Pb, Cd, and Hg), and organic compounds. The sediments in the Lake Guaíba show a wide range in the physical-chemical characteristics. Metals Zn, Cu, Cr, and Ni appear in higher concentrations near to the margin of southern Porto Alegre, where there was also more clay plus silt. Sediments of Lake Guaíba have physical-chemical variability by the settle tendency and water flow from the riverine to lacustrine areas. The sediment in Lake Guaíba had a median of: Zn, 132; Cu, 78; Cr, 42; Ni, 28; Pb, 33; Cd, 0.3; and Hg, 0.07μg/g. Bed sediments of Lake Guaíba are polluted with Zn, Cu, Cr, and Ni, major in the east margin (near to Porto Alegre). The potential toxic metals and organic compounds found in Lake Guaíba are commonly reported in urban regions around the world. Those elements and compounds derive from many anthropic activities, as industries, sewage, and vehicles. With diffuse sources in the region, the pollution control in Lake Guaíba is very complex.

Spatial distribution characteristics and environmental significance of phytoliths in surface sediments of Qingshitan Lake in Southwest China

Fossil phytolith assemblages in lake sediments are widely used to reconstruct past vegetation patterns and dynamics, especially in subtropical environments. However, our understanding of how hydrodynamic conditions (river input and lake basin sedimentological processes) influence the transportation and taphonomy of phytoliths in lacustrine sediments is limited. The aim of this study is to use phytolith assemblage and grain size analyses of Qingshitan Lake surface sediments to identify the distribution characteristics and main transportation modes of phytoliths in lakes. Our results show that the grain size of surface sediments changes across different lacustrine areas of Qingshitan Lake. The median diameter (Md) and volume moment mean diameter (D(4,3)) of surface sediments gradually decreases with distance from the inlet river mouth. The phytolith assemblages of surface sediments vary between sampling locations in the lake. The percentage of woody dicotyledon phytoliths decreases from the estuary delta to the central lake basin, and correlates with the Md and D(4,3) of lake sediments. We find that phytolith assemblages in the riverine delta are mainly influenced by hydrodynamic (river input) processes and record the vegetation cover of the Gongping River catchment. Assemblages in the central lake basin are affected not only by riverine influences but also by eolian transport and similarly reflect the local vegetation. Investigating the relationships between the phytolith assemblages and sediment grain sizes in lakes may make it possible to identify the phytolith source area, which is crucial information to interpret assemblages and indices.

Late glacial and early Holocene hydroclimate variability in northwest Iran (Talesh Mountains) inferred from chironomid and pollen analysis

We reconstructed the paleohydrologic and climatic history of the Lake Neor region, NW Iran, from the end of the late glacial to the middle Holocene (15,500–7500 cal yr BP). Subfossil chironomid and pollen assemblages in a sediment core from a peatland located south of Lake Neor enabled identification of four main hydrologic phases. The period 15,500–12,700 cal yr BP was characterized by a relatively dry climate with an open landscape, suggested by the abundance of Irano-Turanian steppe plants (e.g. Amaranthaceae, Artemisia and Cousinia). Dominance of several shallow-water and semi-terrestrial chironomid taxa (e.g. Pseudosmittia, Smittia/Parasmittia and Paraphaenocladius/Parametriocnemus) during this period is indicative of lower water tables in the wetland. Between 12,700 and 11,300 cal yr BP, chironomid taxa indicate higher wetland water tables, as suggested by the presence of Zavrelia, Chironomus anthracinus/plumosus-type and Micropsectra, which are inhabitants of open-water, lacustrine areas. The open-steppe vegetation remained dominant in the watershed during this time. Increasing wetland moisture could be explained by: (1) cool summers that reduced the evaporation rate; and/or (2) a decrease in duration of the summer dry season. The period 11,300–8700 cal yr BP was characterized by lower wetland moisture, contemporaneous with a delay in the expansion of deciduous forest, suggesting persistent dry climate conditions throughout the beginning of the Holocene, which may have been related to the intensified seasonality of precipitation. Around 8700 cal yr BP, higher wetland water levels, inferred from chironomids, occurred simultaneously with the onset of regional deciduous forest expansion, probably caused by a shortening of the summer dry period. We concluded that chironomids are appropriate paleoecological proxies to investigate global and local hydrologic variability in the Middle East.

Vegetation and climate reconstruction based on a ∼4 ka pollen record from north Chhattisgarh, central India

ABSTRACTWe present pollen proxy records of the variability in the Indian Summer Monsoon (ISM) precipitation during the last ∼4ka (ka= thousand years ago; Late Holocene) from a lacustrine area of Koriya District in Chhattisgarh (C'garh), (central Indian core monsoon zone [CMZ]), India. The results show that open, mixed tropical, deciduous forest occupied the region under a warm and moderately humid climate probably indicative of moderate monsoon precipitation between ∼3796 and ∼2428 cal yr BP. Subsequently, between ∼2428 and ∼1431 cal yr BP, the forest became dense and succeeded the open, mixed tropical, deciduous forest owing to the prevalence of a warm and relatively more humid climate with increased monsoon precipitation. The forest became less diversified from ∼1431cal yr BP to Present under the regime of a warm and relatively less humid climate with decreased monsoon precipitation.