Open Waters Of Lake Research Articles

Enhancing sustainable development through Spatiotemporal analysis of Ramsar wetland sites in South Asia

The ecological significance of wetlands makes it imperative to study changes in their inundation extent and propose necessary conservation measures. Monitoring wetland dynamics and implementing strategies to protect these essential ecosystems is crucial for maintaining the balance of natural systems. This study used pre-processed Landsat imagery (1991–2020) to generate yearly composites and produce inundation maps based on an automated Short-Wave Infrared thresholding technique within the Google Earth Engine platform. The analysis was executed on individual wetlands to describe their typical condition owing to regional climatic and geographical circumstances. The Mann-Kendall test was used to understand the trends in the change of inundation extent. The thresholding method achieved an overall accuracy of 89.0 %, with average dry and wet Producer's accuracies of 90.6 % and 86.6 %, respectively. The accuracy was higher for open water lakes compared to wetlands with complex vegetation dynamics. The trend analysis revealed that 46 sites follow an increasing trend, while the remaining 43 sites were found to be decreasing. Among these 43, 12 sites were found to be significantly decreasing, with the Upper Ganga River showing a maximum decrease of about 59 % in the inundation extent. Factors such as elevation, precipitation, temperature, and climate type were found to influence the trends in wetland inundation. Wetlands at high altitudes (>4000 m) and those receiving less than 500 mm of annual precipitation were more likely to exhibit decreasing trends. Coastal wetlands showed varying trends, with five increasing and three significantly increasing. The findings of this study provide valuable insights into the relationship between sustainable development and wetland conservation, supporting the Ramsar Convention's goals and the UN's Sustainable Development Goals. The individualized analysis of Ramsar sites enables the development of localized management strategies, climate change adaptation, and informed policy-making, ultimately contributing to the sustainable use of these critical ecosystems in South Asia.

Self-attention transformer model for pan evaporation prediction: a case study in Australia

ABSTRACT In drought-prone regions like Australia, accurately assessing evaporation rates is essential for effectively managing and maximising the use of precious water resources and reservoirs. Current estimates show that evaporation reduces Australia's open water lake capacity by about 40% annually. With climate change, this water loss is expected to become an even greater concern. This study investigates a transformer-based neural network (TNN) to estimate monthly evaporation in three Australian locations. The models were trained and tested using monthly weather data spanning from 2009 to 2022. Input parameters were chosen based on Pearson's correlation coefficient values to identify the most impactful combinations. The developed TNN model was compared with two widely used empirical methods, namely Thornthwaite and Stephens and Stewart. The TNN model's impressive accuracy in evaporation prediction, attributed to its unique self-attention mechanism, suggests its promising potential for future use in evaporation forecasting. Additionally, the study revealed an intriguing result: Despite using the same input datasets, the TNN model surpassed traditional methods, achieving an average improvement of 18% in prediction accuracy. The TNN prediction model accurately predicts water loss (average R² = 0.970), supports irrigation management and agricultural planning and offers financial benefits to farming and related industries.

Role of trace metal co-limitation in cyanobacterial blooms of Maumee Bay (Lake Erie) and Green Bay (Lake Michigan)

The open waters of large lakes can sometimes become so depleted in important metals that phytoplankton communities become either growth limited or limited in some metabolic function. Metals such as Fe, Ni, Mo, and Zn are used as co-factors for enzymes by phytoplankton in core metabolic functions, as well as metabolic pathways that allow phytoplankton to use less preferred forms of N and P (e.g. nitrates, urea, and organic phosphorus). In the Laurentian Great Lakes, metal limitation has been observed primarily in waters that are isolated from tributary inputs and sediment exchange. These are situations where the supply of metals is very low relative to demand. We hypothesized that another situation where metal limitation could occur is within algal blooms, where the demand for metals is high because preferred forms of N and P are often low or absent and the phytoplankton biomass is extremely high. As a preliminary test of this hypothesis, we performed seven laboratory incubation experiments on naturally occurring phytoplankton communities from two nearshore habitats that frequently experience blooms (Green Bay in Lake Michigan and Maumee Bay in Lake Erie). Metals and labile nutrients (inorganic N and P) were often present at low concentrations or below the method detection limit. Amendments of inorganic N (5 experiments) and P (1 one experiment) resulted in increased chlorophyll in laboratory incubations, but metal amendments alone never appeared to stimulate growth. Although we attempted to sample during conditions when we hypothesized metal limitation would be most likely, we cannot rule out the possibility that metal limitation is occurring at other times in these eutrophic nearshore areas. Further, metal availability could affect other aspects of the phytoplankton community, such as the production of cyanotoxins or the interactions between different phytoplankton taxa.

The potential of synthetic aperture radar interferometry for assessing meltwater lake dynamics on Antarctic ice shelves

Abstract. Surface meltwater drains on several Antarctic ice shelves, resulting in surface and sub-surface lakes that are potentially critical for the ice shelf collapse. Despite these phenomena, our understanding and assessment of the drainage and refreezing of these lakes is limited, mainly due to lack of field observations and to the limitations of optical satellite imagery during polar night and in cloudy conditions. This paper explores the potential of backscatter intensity and of interferometric coherence and phase from synthetic aperture radar (SAR) imagery as an alternative to assess the dynamics of meltwater lakes. In four case study regions over Amery and Roi Baudouin ice shelves, East Antarctica, we examine spatial and temporal variations in SAR backscatter intensity and interferometric (InSAR) coherence and phase over several lakes derived from Sentinel-1A/B C-band SAR imagery. Throughout the year, the lakes are observed in a completely frozen state, in a partially frozen state with a floating ice lid and as open-water lakes. Our analysis reveals that the meltwater lake delineation is challenging during the melting period when the contrast between melting snow and lakes is indistinguishable. Despite this finding, we show using a combination of backscatter and InSAR observations that lake dynamics can be effectively captured during other non-summertime months. Moreover, our findings highlight the utility of InSAR-based observations for discriminating between refrozen ice and sub-surface meltwater and indicate the potential for phase-based detection and monitoring of rapid meltwater drainage events. The potential of this technique to monitor these meltwater change events is, however, strongly determined by the satellite revisit interval and potential changes in scattering properties due to snowfall or melt events.

Perfluoroalkyl substances (PFASs) in the Ugandan waters of Lake Victoria: Spatial distribution, catchment release and public exposure risk via municipal water consumption

Perfluoroalkyl substances (PFASs) have scarcely been studied in the Lake Victoria Basin and Africa in general. We investigated spatial profiles of PFASs in the Ugandan part of Lake Victoria, their influxes and human exposure via drinking water. We analyzed open lake water, riverine water (Rivers Kagera and Sio), urban drainage water (Nakivubo Channel), over-lake bulk atmospheric deposition and municipal tap water (Kampala, Jinja and Entebbe). The average concentrations (ng/L) for individual target PFASs were in the ranges of 0.08–23.8 (Nakivubo Channel), 0.01–10.8 (Murchison Bay), <MDL-5.38 (Kampala tap water), 0.01–3.64 (R. Kagera), <MDL-3.56 (Jinja tap water), <MDL-3.35 (R. Sio), <MDL-1.96 (Entebbe tap water), <MDL-1.46 (open lake) and <MDL-1.00 (atmospheric deposition). Estimated contribution of input pathways to ∑PFAS fluxes into Lake Victoria was in the order atmospheric deposition > R. Kagera, >R. Sio > Nakivubo Channel. Perfluorohexanoic acid (PFHxA) and perfluorooctane sulfonic acid (PFOS) had the highest influx and retention estimates, respectively. Perfluoroalkane sulfonates (PFSAs) were mostly associated with urban drainage samples. PFASs were likely recycled from the Nakivubo Channel, through the Murchison Bay, into municipal drinking water. The estimated human exposure to ∑11PFASs via drinking water indicated low risk of adverse health effects.

Diversity of Avian Fauna of Al-Dalmaj Wetlands and the surrounding terrestrial areas, Iraq

Dalmaj area, or Hor Ad-Dalmaj wetlands, is considered as one of the Key Biodiversity Areas (KBAs) and Important Bird Areas (IBAs) in Iraq and the Middle East region due to various ecological values and richness in species and habitat diversity. Dalmaj area includes wide spectrum of habitats that ranges of wetlands: open-water lake, reed-beds marsh, marsh margins, mudflats, and the open lake; in addition to the terrestrial habitats that include the arid lands, shrub-lands, and the desert and semi-desert areas. This wide range of habitats in Dalmaj and the surrounding areas have enriched the avifauna and bird diversity. Based on the results of intensive field surveys that extended over more than a decade (in addition to some observations back to 30 years made by MS) important observations were made on the numbers of the species and their counts in addition to their distribution within the study area where considerable numbers of resident and migrant bird species were observed. This includes 261 of the resident and migrant bird species (breeding and non-breeding) have been recorded in Dalmaj wetlands and the surrounding areas. Such a level of richness in bird diversity, that exceeds 60% of the Iraqi bird checklist, illustrates the necessity of taking the required measures to protect the biodiversity in general and the birds and their habitats in particular in this important hotspot on the national, regional, and global levels. The process of watching the birds and their habitats in Dalmaj along more than a decade have included long-term capacity-building activities that ended in creating solid, capable national team. The team of the Iraqi Organization for Conservation of nature (IOCN) has contributed in quite extensive surveys in Dalmaj area during the field work. The results of the 30-years surveys presented by this paper represent the most comprehensive work on the avifauna of Dalmaj area and in Iraq as well. The team is confident that this work would contribute positively to the conservation effort in Dalmaj area.

Evaporation rates in a vital lake: a 34-year assessment for the Karaoun Lake

ABSTRACT The evaporation of water is an indispensable process in the earth water cycle. While high rates of evaporation made access to water resources harsher and costlier, monitoring the spatial and temporal variability of the evaporation rates, particularly in an open lake, is critical. Such information would enable to establish adequate management plans focusing on the sustainable use of available water resources. In this research, a vital lake in Lebanon, namely Karaoun or Qaraoun, was investigated. The importance of such reservoir lies in providing, solely, the required water for more than 500 000 households and 19 000 ha of agricultural lands. The evaporation rates were evaluated, both spatially and temporally, between 1985 and 2018 using the widely acknowledged Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) system. This latter is based on 30 m. Landsat 4, 5, 7 and 8 satellite images. Main results emphasize the evaporation rates increase over the lake, particularly noticed since 2005. Between 1985 and 2018, the annual mean evaporation rate was 2.24 mm day−1. More precisely, the annual mean evaporation rate has nearly doubled between 1985–1989 and 2014–2018 periods (i.e. 1.87 vs. 3.12 mm day−1). Mann-Kendall test and Sen’s Slope estimates were produced to check the significance of the observed trends as well as to investigate the main driving factors behind this increase. Main causes were divided into natural (i.e. significant increase at α = 0.001 for temperatures and at α = 0.05 for solar radiations) and anthropogenic (i.e. deteriorating water quality) related factors. The most probable future scenario would highlight a fearful increase of 1°C in the next decade and an evaporation rate multiplied one and half times by 2038. These findings should help local management authority to mitigate water quality and turbidity effects, as well as to accurately estimate the water budget in an open-water lake. The concerned government should also benefit from these results to draw clear policies on how to conserve water resources with an increasing global warming trend. Such study could be portable to other regions where evaporation-related datasets are missing.

Results of studies of the coastal zone of Lake Ladoga in the area of Valaam Archipelago (1998–2019) at RSHU

Ecological monitoring data of pelagic communities and environmental factors for the coastal zone of the Valaam archipelago and also littoral and sublittoral samples analyses of contrasting hydrological conditions zones are generalized. Values ranges of the focused parameters have been identified for the unique coastal zone of Lake Ladoga with a significant biotopes diversity over than 20 years of research. Phyto- and zooplankton abundance relatively high indices are characteristic of water area closed from wind and wave mixing. This area is characterized by an active vegetation period of macrophytes and highly productive macrozoobenthos formation. According to the open water area temperature (conducted since 2013) continuous data (logger) observations, a significant average monthly temperature values interannual variability is shown, warm period duration with a surface water horizon temperature value more than 10 °C is equal to 100 days. In shallow closed areas, zooplankton biomass values differ strongly from another parts of the water area. However, in some cases, extremely high values of phytoplankton biomass (up to 29.5 mg / l) were observed in Lake Ladoga open areas, associated mostly with surges. In general, the phyto- and zooplankton biomass in the Valaam archipelago open areas coastal zone is comparable with the data for the northern Lake Ladoga deep-water area, for the closed areas biomass has been lower than the published earlier data for the coastal zone of the lake. Plankton quantitative development interannual differences are caused by the hydrological conditions of specific years. Despite the relatively small coastal zone area and macrophytesmosaic distribution, this community was characterized by a high species richness (more than half of the species recorded for Ladoga). In terms of quantitative characteristics, the invertebrates littoral communities are not less then to well-studied communities of the coastal area at depths up to a meter and significantly much bigger those observed in the open lake water area. The littoral fauna (including groups of larva insects, some crustaceans and molluscs) is observed in various conditions (10-12 m depth), thus, with macrophytes distribution data, it makes possible to expand the littoral boundary zone equals to 10 m depth, instead of the previously depth equals 8.5 m. The water area, for all studied biological communities, is classified as oligo-mesotrophic.

Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

Sedimentary deposits characterized by the Mars Science Laboratory Curiosity rover provide evidence that Gale crater, Mars intermittently hosted a fluvio-lacustrine environment during the Hesperian. However, estimates of the CO2 content of the atmosphere at the time the sediments in Gale crater were deposited are far less than needed by any climate model to maintain temperatures warm enough for sustained open water lake conditions due to the low solar energy input available at that time. To reconcile some of the in-situ sedimentological evidence for liquid water with climate modeling studies, we perform the water budget of evaporation against precipitation to estimate the minimum lifetimes and the rainfall requirements for open water and ice-covered lakes in Gale crater, for a wide range of pressures and temperatures. We found that both open water and ice-covered lakes are possible, and that ice-covered lakes provide better consistency in regards of the low erosion rates estimates for the Hesperian. We incrementally test the existence of open water conditions using energy balance calculations for the global, regional, and seasonal temperatures, and we assess if the preservation of liquid water was possible under perennial ice covers. We found scenarios where lacustrine conditions are preserved in a cold climate, where the resupply of water by the inflow of rivers and high precipitation rates are substituted by an abutting glacier. For equatorial temperatures as low as 240 K–255 K, the ice thickness ranges from 3 to 10 m, a value comparable to the range of those for the perennially ice-covered lakes in Antarctica (3–6 m). The ice-covered lake hypothesis is a compelling way to decouple the mineralogy and the climate by limiting the gas exchanges between the sediment and the CO2 atmosphere, and it eliminates the requirement for global mean temperatures above the freezing point. Not only do ice-covered lakes provide a baseline for exploring the range of possible lake scenarios for Gale crater during the Hesperian that is fully consistent with climate studies, but also they might have been ideal environments to sustain life on Mars.

A Historical Perspective on Water Levels and Storage Capacity of Lake Okeechobee, Florida: Pre- and Early Drainage Periods

Evaluating the water storage function of Lake Okeechobee can provide important insight into understanding the lake’s historical role in attenuating the magnitude and timing of flows (particularly during the wet season) in the Greater Everglades region. This article investigates the predrainage and early postdrainage spatial extent, lake stages, and changes to plant communities. Two periods of time were assessed: predrainage (prior to 1880) and early postdrainage (1880–1945). Analyses were conducted by integrating written historical accounts, lake stages, and hydrographs with a geospatial analysis derived from nautical charts and other historical maps from additional points in time (1913 and 1926). Results indicate that predrainage lake stages were much higher than the current water management regime, but the spatial extent of the lake open water is relatively unchanged. We estimated a reduction in storage volume of Lake Okeechobee from 6,922 million m3 to 4,347 million m3 during the early postdrainage period (1880–1945) at high lake stages. This represents a loss in volume of 2,575 million m3 at a high lake level and of 3,016 million m3 at a low lake level. The loss in storage volume has changed the historical flow patterns from the Lake Okeechobee region with consequences to downstream watersheds. Key Words: bathymetry, environmental history, Everglades, geographic information systems, shoreline.

Effect of land use-land cover change on the regimes of surface runoff-the case of Lake Basaka catchment (Ethiopia).

In this study, the effect of land use-land cover change (LULCC) on surface (direct) runoff was estimated for Lake Basaka catchment using the soil conservation services-curve number model in the geospatial information system (ArcInfo), assisted by remote sensing. The result indicated that Lake Basaka catchment experienced a significant LULCC. About 86% of forest coverage and 46% of grasslands were lost over the study period (1973-2015), which were shifted to open bushy woodlands, farms, lake water and wetlands. The runoff responses were observed to be increasing since 1970s, especially after the inception of large-scale irrigation schemes to the region. The highest increase of surface runoff was observed to occur after mid-1980s, which is in line with the significant LULCC and the corresponding increment of lake level in that period. The reduction in vegetation cover has resulted in an increase of runoff coefficient (rc) from 0.07 in the 1960s to about 0.23 in 2000s. The sensitivity analysis result indicated that about 70% of the increase runoff rate in the lake catchment is attributed to LULCC, and the remaining proportion is due to rainfall. However, the effect of extreme rainfall on runoff process could not be underemphasized since it has significant impact especially during extreme events (observed rc of 0.33 in 2008). Overall, when predicting the runoff response of the lake catchment, it is importance to take into account possible future LULCC and evolution.

Seasonal and spatial variation in hydrochemical parameters of Lake Onego (Russia): insights from 2016 field monitoring

ABSTRACTThis study describes seasonal water quality parameters measured in Petrozavodsk Bay, Lake Onego, Russia. Petrozavodsk Bay (PB) lies in the north of Lake Onego and adjacent to the city of Petrozavodsk. PB water quality is controlled by anthropogenic input, inflow of the Shuya River, and water exchange with open areas of the greater Lake Onego. We measured ion composition, organic matter, nutrients, gas composition, trace elements, and mercury throughout 2016, to evaluate PB water quality. Elevated humic content and organic matter, including total organic carbon (TOC = 17.0 mg L−1), total phosphorus (TP = 36 µg L−1), and water color (134 mg Pt L−1), demonstrated the eutrophic character of Shuya River input. Low humic and organic matter content (TOC = 6.5 mg L−1, TP = 7 µg L−1, water color = 26 mg Pt L−1) indicated the oligotrophic character of open lake waters. During winter, the PB hydrochemical regime was primarily controlled by Shuya River inflow because water exchange between the bay and open lake was restricted during its ice-covered period. As a result, PB chemical indices varied considerably. TOC varied from 7.6 to 17.8 mg L−1, TP from 7 to 55 µg L−1, and О2 from 69% to 87% saturation during this period. Total filterable mercury concentrations (THg = inorganic mercury plus methylmercury) at all measurement sites remained low. Overall, these results help constrain understanding of lake dynamics, anthropogenic influence, and river input to the lake during ice-covered periods.

Convergent evolution misled taxonomy in schizothoracine fishes (Cypriniformes: Cyprinidae)

Highly specialized grade (HSG; genera Gymnocypris, Oxygymnocypris, Schizopygopsis, Platypharodon and Chuanchia) of the Schizothoracinae (Cypriniformes: Cyprinidae) are endemic to the Qinghai-Tibet Plateau (QTP). Previously, two distinct ecomorphs were recognized according to trophic traits. One was a limnetic omnivore with normal lower jaw morphology, terminal mouth, and moderate or dense gill rakers, mostly inhabiting in open water of lakes, including Gymnocypris and Oxygymnocypris. Another was a benthic feeder with inferior mouth, sparse gill rakers and sharp horny sheath on the lower jaw for scraping of attached prey off hard substrates, including Schizopygopsis, Platypharodon and Chuanchia. However, traditional taxonomy of HSG based on these trophic traits presented extensive conflicts with the molecular studies in recent years. The possible cause could be convergent evolution in morphology, retention of ancestral polymorphisms or mitochondrial introgression, but these hypotheses could not be assessed due to incomplete taxon sampling and only mitochondrial data employed in previous works. Here, we conducted the most comprehensive molecular analysis on HSG fishes to date, using four mitochondrial loci and 152,464 genome-wide SNPs, and including 21 of 24 putative species and one undescribed Schizopygopsis species. Both SNP and mtDNA trees confirmed extensive paraphyly of genera Gymnocypris and Schizopygopsis, where species often were clustered together by watershed instead of by genus. Basal split into the north clade B and the south clade C (ca. 3.03 Ma) approximately by the Tanggula-Tanitawen Mountains in SLAF tree coincided with a violent uplift of the QTP during the phase A of ‘Qingzang movement’ (ca. 3.6 Ma). Ancestral state reconstruction of the trophic ecomorph showed that the limnetic omnivore ecomorph had evolved repeatedly in clade B and C. Furthermore, we presented a striking case of convergent evolution between two ‘subspecies’ Gymnocypris chui chui and G. chui longimandibularis, which had diverged as early as two million years ago (ca. 2.42 Ma). Ecological analyses revealed that similar food utilization, particularly in zooplankton, was the main underlying driving force. This work showed an example of taxonomy with the most extensive errors at the genus/species levels due to convergent evolution and suggested that trophic traits could be misleading in fish taxonomy. Therefore, we propose a major generic revision for HSG species.

Factors controlling evaporation and the CO2 flux over an open water lake in southwest of China on multiple temporal scales

Interactions between lakes and the atmosphere are poorly understood, especially for lakes in highland areas. A better understanding of the physical processes controlling turbulent exchange dynamics over lakes is crucial to improve the numerical modelling of the lake–climate interaction. Four years of continuous measurements of energy and CO2 fluxes are conducted over a shallow highland lake (Lake Erhai) in China using eddy covariance (EC) technique from 2012 to 2015. It is found that the latent heat flux (LE) and sensible heat flux (H) has distinct diurnal and seasonal variations. The diurnal H and LE ranges from −31 to 21 W/m2 and from 31 to 171 W/m2, respectively. The heat is stored in the lake from January to June and released from July to the end of the year. The annual total evaporation of Lake Erhai varies from 1120.8 to 1228.5 mm/a, which is always higher than the annual total precipitation. On diurnal scale, the CO2 uptake is observed during most of the midday period. On an annual scale, the Lake Erhai behaves as a net CO2 source, with an annual CO2 budget ranging from 117.5 to 161.7 g C m−2 a−1. The temperature difference (ΔT) between the water surface (T s) and the air temperature (T a), and the product of ΔT and wind speed (U) are the major drivers of H from half‐hourly to monthly scale. The main factors controlling LE are U and the product of U and the vapour pressure difference (VPD) on half‐hourly and daily scales, the total cloud cover, and net radiation (R n) on the monthly scale. Photosynthetic active radiation (PAR) and U has a close relationship with half‐hourly and daily CO2 fluxes, respectively, while annual precipitation and T s has a larger effect on annual CO2 fluxes.

Updated Polychlorinated Biphenyl Mass Budget for Lake Michigan.

This study revisits and updates the Lake Michigan Mass Balance Project (LMMBP) for polychlorinated biphenyls (PCBs) that was conducted in 1994-1995. This work uses recent concentrations of PCBs in tributary and open lake water, air, and sediment to calculate an updated mass budget. Five of the 11 LMMBP tributaries were revisited in 2015. In these five tributaries, the geometric mean concentrations of ∑PCBs (sum of 85 congeners) ranged from 1.52 to 22.4 ng L-1. The highest concentrations of PCBs were generally found in the Lower Fox River and in the Indiana Harbor and Ship Canal. The input flows of ∑PCBs from wet deposition, dry deposition, tributary loading, and air to water exchange, and the output flows due to sediment burial, volatilization from water to air, and transport to Lake Huron and through the Chicago Diversion were calculated, as well as flows related to the internal processes of settling, resuspension, and sediment-water diffusion. The net transfer of ∑PCBs is 1240 ± 531 kg yr-1 out of the lake. This net transfer is 46% lower than that estimated in 1994-1995. PCB concentrations in most matrices in the lake are decreasing, which drove the decline of all the individual input and output flows. Atmospheric deposition has become negligible, while volatilization from the water surface is still a major route of loss, releasing PCBs from the lake into the air. Large masses of PCBs remain in the water column and surface sediments and are likely to contribute to the future efflux of PCBs from the lake to the air.

Evidence for climatic changes around the Matuyama-Brunhes Boundary (MBB) inferred from a multi-proxy palaeoenvironmental study of the GBY#2 core, Jordan River Valley, Israel

The Acheulian site of Gesher Benot Ya‘aqov (GBY) in the Upper Jordan Valley revealed important data on environment and material culture, as well as evidence for hominin behavioural and cognitive patterns documented at the margins of the Hula Palaeo-lake. A 50m long core (GBY#2) drilled at the archaeological site has provided a long Pleistocene geological, environmental and climatological record, which expands the existing knowledge of hominin-habitat relationships. Bracketed by two basalt flows dated by 40Ar/39Ar and based on the identification of the Matuyama-Brunhes Boundary (MBB) and correlation with the GBY excavation site, the sedimentary sequence provides the climatic history around the MBB. Multi-proxy data including pollen and non-pollen palynomorphs, macro-botanical remains, molluscs and ostracods provide evidence for lake and lake-margin environments during Marine Isotope Stages (MIS) 20 and 19. Semi-moist conditions were followed by a pronounced dry phase during MIS 20, and warm and moist conditions with Quercus-Pistacia woodlands prevailed during MIS 19. In contrast to the reconstructed climate change from relatively dry to moister conditions, the depositional environment developed from an open-water lake during MIS 20 to a lake margin environment in MIS 19. Generally shallower conditions at the core site in MIS 19 resulted from the progradation of the lake shore due to the filling of the basin. Micro-charcoal analysis suggests a likelihood of human-induced fire in some parts of the core, which can be correlated with artefact-containing layers of the GBY excavation site. The Hula Palaeo-lake region provided an ideal niche for hominins and other vertebrates during global glacial-interglacial climate fluctuations at the end of the Early Pleistocene.

On the methane paradox: Transport from shallow water zones rather than in situ methanogenesis is the major source of CH4 in the open surface water of lakes

AbstractEstimates of global methane (CH4) emissions from lakes and the contributions of different pathways are currently under debate. In situ methanogenesis linked to algae growth was recently suggested to be the major source of CH4 fluxes from aquatic systems. However, based on our very large data set on CH4 distributions within lakes, we demonstrate here that methane‐enriched water from shallow water zones is the most likely source of the basin‐wide mean CH4 concentrations in the surface water of lakes. Consistently, the mean surface CH4 concentrations are significantly correlated with the ratio between the surface area of the shallow water zone and the entire lake, fA,s/t, but not with the total surface area. The categorization of CH4 fluxes according to fA,s/t may therefore improve global estimates of CH4 emissions from lakes. Furthermore, CH4 concentrations increase substantially with water temperature, indicating that seasonally resolved data are required to accurately estimate annual CH4 emissions.

Reconstruction of Holocene paleohydrological and sedimentological characteristics of Umm Ar-Rimam basin (northern Kuwait)

The paleohydrological and sedimentological characteristics of a playa lake in northern Kuwait (Arabian Gulf) are reconstructed using sedimentological, geochemical, and isotopic techniques. The sequence consists of up to 8 cycles of S-poor, alluvial sediments capped by a thin organic soil interbedded with gravity-fall calcrete sediments. The succession is locally derived from mainly Quaternary sediments and is regressive with upsection filling of the subsiding basin by cycles of sheetwash flow in response to climatic change. There is no natural, open-water lake water as indicated by low total organic carbon (TOC) data, but the presence of incised calcrete yardangs suggests that more extensive open-water conditions were operative in the past. Stable isotope (δ18O‰ and δ13C‰) values of the authigenic carbonates indicate the following three distinct processes: evaporation, meteoric fluid infiltration, and rapid per-descensum flow (rapid downward movement of water and playa sediment through pipes) through a porous, clastic sequence. Because evaporites are scarce, other factors besides evaporation action control chemical and isotopic compositions of the per-decensum lake fluids. Consequently, the isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO2 during groundwater discharge may explain the enriched carbon isotope values for the authigenic carbonates precipitated in the sediments. Hydrologically closed lake water bodies tend to show low negative carbonate oxygen and carbon isotopic signatures. Isotopically negative δ13C values imply a strong input of soil-zone carbon to the groundwater of the top 60 cm of the sediment. Lakes that are hydrologically closed and evaporate or equilibrate with atmospheric CO2 will tend to have low negative δ18O and δ13C values in the carbonates as reported by Talbot (Chem Geol: Isotope Geosci Sect 80(4):261–279, 1990). Biologically active lakes will tend toward lower δ13C of dissolved carbon due to the photosynthetic effects of 12C withdrawal as reported by Dunagan and Driese (J Sed Res 69:772–783, 1999). Increased biological activity during sedimentation may account for low carbon isotope values where plants were abundant, but in shrinkage-dominated systems (those of clay-rich soil subjecting to wet-dry conditions), carbon isotopes will be largely inherited from the calcretic limestones in the land extending landward of the coast and not influenced by coastal processes (known as hinterland), such as Umm Ar-Rimam depression. This basin does not fit the classic shallow playa-type basins of the Arabian Peninsula but rather the recharge playas of the southwestern USA.

Potential risk assessment in stream sediments, soils and waters after remediation in an abandoned W>Sn mine (NE Portugal)

The mining complex of Murçós belongs to the Terras de Cavaleiros Geopark, located in Trás-os-Montes region, northeast Portugal. A stockwork of NW-SE-trending W>Sn quartz veins intruded Silurian metamorphic rocks and a Variscan biotite granite. The mineralized veins contain mainly quartz, cassiterite, wolframite, scheelite, arsenopyrite, pyrite, sphalerite, chalcopyrite, galena, rare pyrrhotite, stannite, native bismuth and also later bismuthinite, matildite, joseite, roosveltite, anglesite, scorodite, zavaritskite and covellite. The exploitation produced 335t of a concentrate with 70% of W and 150t of another concentrate with 70% of Sn between 1948 and 1976. The exploitation took place mainly in four open pit mines as well as underground. Three lakes were left in the area. Remediation processes of confination and control of tailings and rejected materials and phytoremediation with macrophytes from three lakes were carried out between 2005 and 2007. Stream sediments, soils and water samples were collected in 2008 and 2009, after the remediation process. Most stream sediments showed deficiency or minimum enrichment for metals. The sequential enrichment factor in stream sediments W>Bi>As>U>Cd>Sn=Ag>Cu>Sb>Pb>Be>Zn is mainly associated with the W>Sn mineralizations. Stream sediments receiving drainage of a mine dump were found to be significantly to extremely enriched with W, while stream sediments and soils were found to be contaminated with As. Two soil samples collected around mine dumps and an open pit lake were also found to be contaminated with U. The waters from the Murçós W>Sn mine area were acidic to neutral. After the remediation, the surface waters were contaminated with F−, Al, As, Mn and Ni and must not be used for human consumption, while open pit lake waters must also not be used for agriculture because of contamination with F−, Al, Mn and Ni. In most waters, the As occurred as As (III), which is toxic and is easily mobilized in the drainage system. The remediation promoted a decrease in metals and As concentrations of soils and waters, however the applied processes were not enough to rehabilitate the area.

Characterization of bulk and chromophoric dissolved organic matter in the Laurentian Great Lakes during summer 2013

The Laurentian Great Lakes contain ~ 21% of the Earth's surface freshwater and are experiencing dramatic decadal-scale changes to their water quality, biogeochemistry and ecosystem functions.We report here the first data set of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (DOM), including UV–visible absorbance and derived optical properties and fluorescence excitation–emission matrices (EEMs), for open-lakesurface waters from each of the Great Lakes. Concentrations of DOC ranged from 86 to 240 μmol/L and the absorption coefficient at 254 nm (a254) varied from 2.67 to 10.47 m− 1 in Great Lakes waters.UV–visible and fluorescence characterization indicated that the DOM in open-lake waters in all the Great Lakes was primarily autochthonous. Both DOC and a254 increased from Lake Superior to Lakes Erie and Ontario where aromaticity, molecular weight and humification degree of DOM were also higher.These variations are consistent with both the water transport pathway and the trend of increasing human population and relative watershed drainage area along the Great Lakes. Parallel factor analysis on fluorescence-EEM data revealed three terrestrial humic-likeDOM components (C1, C2 and C4) and one protein-likeDOM component (C3). Open Lake Huron had the highest protein-like/humic-like DOM ratio (C3/C1), while sites in Lakes Erie and Ontario had lower C3/C1 ratios, indicating a greater proportional influence of terrestrial DOM. Changes in DOM composition along the water transport pathway in the Great Lakes indicate varying impacts from terrestrial inputs and human activities in the different lake systems.