Lake Geochemistry Research Articles

Preface to the Special Issue on "The Hydrochemistry and Isotope Geochemistry of Alkaline Lakes and Brine Systems": A Tribute to Paolo Censi

Preface to the Special Issue on "The Hydrochemistry and Isotope Geochemistry of Alkaline Lakes and Brine Systems": A Tribute to Paolo Censi

Hydrochemical and isotopic baselines for understanding hydrological processes across Macquarie Island.

Isotopic and hydrochemical data from lakes provide direct information on catchment response to changing rainfall, evaporation, nutrient cycling, and the health of ecosystems. These techniques have not been widely applied to lakes in the Southern Hemisphere high latitudes, including Southern Ocean Islands (SOIs) experiencing rapid, significant shifts in climate. Historical work has highlighted the localised nature of geochemical drivers in controlling the hydrochemical evolution of lakes, such as geology, sea spray contribution, vegetation, geographical location, and ice cover extent. The role of groundwater in lake hydrology and hydrochemistry has not been identified until now, and its omission will have major implications for interpreting soil-water-air processes affecting lakes. Here we present the first comprehensive, island-wide hydrochemical and isotopic survey of lakes on a SOI. Forty lakes were examined across Macquarie Island, using comparable methods to identify key environmental processes and their geochemical drivers. Methods include stable carbon (δ13CDOC: dissolved organic carbon and δ13CDIC: dissolved inorganic carbon), oxygen (δ18O), hydrogen (δ2H) and strontium isotopic ratios (87Sr/86Sr) in water. These provide essential baseline data for hydrological, biological, and geochemical lake processes. Lakes on the western side of the island are influenced by sea spray aerosols. In general, it was found that lakes at higher elevations are dilute and those located in lower elevation catchments have experienced more water-rock interactions. The hydrochemical and isotopic tracers suggest that lakes in lower elevations contain more terrestrial sourced ions that may be contributed from groundwater. Increasing temperatures and changing rainfall patterns predicted for the region will lead to shifts in nutrient cycles, and impact the island's unique ecosystems. Future research will focus on long-term monitoring to understand seasonal, annual, and long-term variability to test fundamental hypotheses concerning ecosystem function and the consequences of environmental change on SOIs.

Boron isotope geochemistry of Bangor Co Salt Lake (central Tibet): implications for boron origin and uneven mixing of lake water

Boron isotope geochemistry of Bangor Co Salt Lake (central Tibet): implications for boron origin and uneven mixing of lake water

Boron Isotope Geochemistry of the Lakkor Co Salt Lake (Tibet) and Its Geological Significance

The origin of boron in modern salt lakes has long been a controversial subject. This study focuses on the boron geochemistry of Lakkor Co salt lake, located on the Shiquanhe-Lakkor Co-Yongzhu-Jiali Ophiolite Mélange Zone (SYMZ). Lakkor Co is one of the main boron-rich salt lakes in the Tibetan plateau where the boron concentration ranges from 401 to 849 mg L-1. The boron isotope value ( δ 11 B ) of the carbonate deposit within the Lakkor Co region is -28.08‰. The boron isotope value of the Somme river decreases from -9.97‰ to -11.15‰ after it flows through the carbonate deposit region, indicating that the carbonate deposit in this region releases boron, which has a more negative isotope value. However, the boron isotope value of Bai Kok river increases from -15.63‰ to -13.76‰, when it flows through the Quaternary clay region in Ganga Co, indicating that the carbonate deposit undergoes a process of boron adsorption. It can be concluded that the Quaternary carbonate deposits may be a source of boron and also serve as a temporary boron reservoir, thus playing an important role in the formation of modern salt lake boron deposits in Tibet.

Rapa Nui (Easter Island) Rano Raraku crater lake basin: Geochemical characterization and implications for the Ahu-Moai Period.

Rano Raraku, the crater lake constrained by basaltic tuff that served as the primary quarry used to construct the moai statues on Rapa Nui (Easter Island), has experienced fluctuations in lake level over the past centuries. As one of the only freshwater sources on the island, understanding the present and past geochemical characteristics of the lake water is critical to understand if the lake could have been a viable freshwater source for Rapa Nui. At the time of sampling in September 2017, the maximum lake depth was ~1 m. The lake level has substantially declined in the subsequent years, with the lake drying almost completely in January 2018. The lake is currently characterized by highly anoxic conditions, with a predominance of ammonium ions on nitrates, a high concentration of organic carbon in the water-sediment interface and reducing conditions of the lake, as evidenced by Mn/Fe and Cr/V ratios. Our estimates of past salinity inferred from the chloride mass balance indicates that it was unlikely that Rano Raraku provided a viable freshwater source for early Rapa Nui people. The installation of an outlet pipe around 1950 that was active until the late 1970s, as well as grazing of horses on the lake margins appear to have significantly impacted the geochemical conditions of Rano Raraku sediments and lake water in recent decades. Such impacts are distinct from natural environmental changes and highlight the need to consider the sensitivity of the lake geochemistry to human activities.

The impact of cyclical, multi-decadal to centennial climate variability on arsenic sequestration in lacustrine sediments

Examining paleoclimate-driven changes of elemental contaminants, such as Arsenic (As), increases the understanding of the mobility and fate of elements under a warming climate scenario. To characterize the variability in As sequestration in the sediments of a freshwater system in response to decadal- to centennial-scale climate oscillations, a freeze-core (CON01) was recovered from Control Lake, Northwest Territories. Radiocarbon dating of 13 bulk-organic samples provided temporal reference to core depth. Sediment geochemistry was determined using Itrax X-ray fluorescence core-scanning (Itrax-XRF). Elemental concentrations were measured on a sub-set of samples using ICP-MS after multi-acid (MA) digestion to assess the accuracy of Itrax-XRF results through a multivariate log-ratio (MLC) calibration. Comparison of Itrax-XRF to ICP-MS using the MLC in ItraXelerate software show Pearson's R2 values >0.75, with the exception of As (R2 = 0.44). MLC-calibrated Itrax-XRF elemental data were centered log-ratio (CLR) transformed to eliminate issues related to data closure. During the ca. 3300-yr sedimentary record, moderate-strength negative correlations between AsCLR and KCLR (Spearman's ρ = −0.38, p-value < 0.001, n = 785), and AsCLR and TiCLR, (Spearman's ρ = −0.52, p-value < 0.001, n = 785) suggest that As is primarily sequestered in sediments during intervals of warmer temperatures and higher productivity. Proxies for sediment particle size (TiCLR, KCLR) and As concentration (AsCLR) were examined for response to quasi-periodic climate oscillations using spectral analysis. Significant periodicities were observed with approximately 4–13, 30–60, 90–120, and 160–280 yr periods in TiCLR, KCLR, and AsCLR records. These frequencies are interpreted as corresponding to the North Atlantic Oscillation and/or 8–14-yr Schwabe sunspot cycles, 30–60-yr Pacific Decadal Oscillation, and centennial-scale solar cycles (e.g., 90-yr Gleissberg cycle; 205-yr Suess cycle). Coeval occurrence of these periodicities revealed through wavelet analysis of Control Lake geochemistry data suggests that these climate cycles only impact Control Lake when they occur concurrently.

Geochemistry of Lakes in a Zone Impacted by an Arctic Iron-Producing Enterprise

The paper presents data on the chemical composition of waters and bottom sediments in lakes variably affected by liquid wastes from facilities of the Olkon Joint-Stock Company in Olenegorst, Murmansk oblast, which mines and processes iron ores. Since Olkon started operating, the composition of water in nearby water bodies has underwent significant changes. The mineralization (TDS) and pH of the lacustrine waters have increased (to 100 mg/L and 7.6 respectively). The qualitative composition of the water has also changed (the water type has changed from hydrocarbonate to sulfate), as also have the proportions of the dominant cations. The waters of the lakes have enriched in nitrogen-group compounds. The $${\text{NO}}_{3}^{ - }$$ concentrations in some of the lakes are higher than the concentrations of the dominant ions (Na+, K+, and Cl–) recalculated into equivalent concentrations. The inflow of contaminants with the waste waters has suppressed biological productivity and reduced concentrations of organic compounds in the lacustrine waters. The waters of the lakes that received waste waters form the iron-producing facilities contain the highest Ni, Cu, Co, Al, and Sr concentrations, whereas the Fe concentrations are the lowest, which is reportedly explained by a decrease in the concentrations of organic compounds and an increase in pH of the lacustrine waters (and a corresponding decrease in the Fe solubility). The paper reports data on the speciation of metals in the lacustrine waters: Fe and Cu occur in them mostly in compounds with organic ligands Fe(III)–L and Cu(II)–L; Mn is contained as Mn(II)– $${\text{SO}}_{4}^{{2 - }}$$ /Cl–/OH– compounds; and Ni, Co, and Zn form compounds with hydroxyl groups Ni(II)–OH, Co(II)–OH, and Zn(II)–OH. Concentrations of heavy metals in the lacustrine bottom sediments depend on the dominant form of their occurrence in the waters. The surface layers of the bottom sediments are significantly enriched in heavy metals (Ni, Cu, Co, Cd, Pb, As, Hg, Fe, and Mn), which are tens of times higher than the background concentrations. The highest values of the contamination factor (Cf) and degree of contamination (Cd) were found in the lakes contaminated with waste waters from the facilities.

Holocene temperature and landscape history of southwest Greenland inferred from isotope and geochemical lake sediment proxies

Terrestrial temperature reconstructions from the ice-free margins of Greenland are critical for constraining the sensitivity of the Greenland ice sheet to past climate change. Numerous investigations have clarified the glacial history of southwest Greenland in recent decades; however, very few local quantitative temperature reconstructions exist as context for changes in the cryosphere. We examine sedimentary records from two lakes south of Nuuk, Greenland (informally named lakes T1 and T2), and investigate millennial scale Holocene climate change using a multi-proxy approach. Changes in X-Ray fluorescence spectroscopy (XRF), δ15N, δ13C and biogenic silica concentrations of bulk lake sediments mark the transition from a marine environment to isolated lakes as relative sea level fell in the early Holocene. δ18O values of subfossil insects (chironomids) from lakes T1 and T2 decreased by 2–3‰ from c. 8.8 ka BP (minimum limiting age for the onset of lacustrine sediment deposition in lake T2; ka BP = thousands of years before 1950) to 1 ka BP. Existing isotope-independent temperature reconstructions from the west coast of Greenland suggest that these changes in δ18O values accompanied gradual cooling of 2–4 °C, concomitant with decreasing summer insolation. There is widespread regional evidence that this cooling resulted in progressive regrowth of local glaciers and of the ice sheet. The regional consensus on the magnitude of this temperature change indicates that the local, modern modeled temperature - precipitation δ18O relationship cannot be used to quantify millennial-scale temperature changes at these sites through the Holocene. This reinforces that studies utilizing δ18O-based proxies to infer temperature change should carefully assess local isotope-temperature relationships over space and time.

Metallic elements and oxides and their relevance to Laurentian Great Lakes geochemistry.

The Laurentian Great Lakes are the most studied system in lake geochemistry and have well-preserved chronological profiles. Metals play numerous critical roles in natural and anthropogenic characteristics of lake ecosystems, so patterns in the historical records of metals from sedimentary cores provide important information about environmental baselines and human impacts. Relevant studies of Great Lakes geochemistry are listed, and we follow with encyclopedic descriptions of metals and their oxides in the lakes. These descriptions include likely natural and anthropogenic sources of elements, their known history from previous paleoecological studies, and their status as potential contaminants of concern. Despite the well-studied geology of the Great Lakes catchment, sourcing elements was sometimes difficult due to materials often being moved long distances by glaciation and the global prevalence of atmospheric pollutants. We summarized available information on metals and their roles as geochemical indicators in the Great Lakes.

The Hydrochemistry and Recent Sediment Geochemistry of Small Lakes of Murmansk, Arctic Zone of Russia

This paper presents the first study of five small lakes located in the city of Murmansk. Field work was carried out during 2018–2019. Water samples were collected using a bathometer, while the sediments were sampled using an Ekman grab and Limnos gravity corer. It was found that the water of the studied lakes in Murmansk belong to the sodium group of the chloride class and to the calcium group of the hydrocarbonate class. Compared to the background level, elevated pH, concentrations of the main cations of alkali and alkaline-earth metals, N compounds, total dissolved solids, and heavy metals were found in the lakes, which indicate exposure to anthropogenic impacts. The sediments of the lakes, composed of organomineral and mineral silts, also have an elevated content of heavy metals compared to the background. The most significant excessive concentrations were found for V, Ni, Sb, Pb, Co, Cr, and W. Based on the calculated pollution load index and geoaccumulation index of the sediments, the studied water bodies in Murmansk can be classified as lakes with heavy and extremely heavy pollution levels. The primary pollution sources are emissions from the Murmansk thermal power plant, coal port, road and, rail transport.

Mercury geochemistry and microbial diversity in meromictic Glacier Lake, Jamesville, NY.

Meromictic lakes are stratified lakes that typically stimulate phototrophic anoxic microbial metabolism, including the transformation of sulphur. Less studied are the transformations of mercury in these environments, and the microorganisms, which mediate these reactions. In order to further an understanding of redox species, mercury and microbial populations in meromictic lakes, we examined the geochemistry and microbiology of Glacier Lake in Jamesville, NY. We found an anoxic transition at a depth of 6 m, followed by active nitrate and sulphate utilization. A chlorophyll a maximum was located at 11 m, coinciding with peaks of several photoautotrophic microbial lineages and total mercury and methyl mercury. Via amplicon sequencing, the microbial population showed pronounced peaks of cyanobacteria at 10 m, Chlorobi at 12 m and Chloroflexi at 14 m. Sulphate-reducing bacteria were also most abundant between 10 and 14 m depth. A functional gene indicating the potential for the production of methyl mercury, hgcA, was detected at several depths in the lake. Our work suggests that in addition to the sulphur cycle, the cycling of mercury may be indirectly coupled with phototrophic processes in Glacier Lake.

Aquatic environment and anthropogenic factor effects on distribution of trace elements in surface waters of European Russia and Western Siberia

The distribution of trace elements of anthropogenic origin, especially toxic metals, is an environmental problem. We present the first results of research into the geochemistry of lake waters and metallic pollution in European Russia (ER) and Western Siberia (WS), based on a survey of 367 lakes from the tundra to the steppe zones. The content of more than 80 elements in the lake water was studied; the influence of airborne contamination and the geochemistry of water were estimated. We found that the concentrations of alkaline and alkaline-earth elements, as well as As, V, Co, U, Nb, Sb, increase with a change in the climatic gradient. This fact is explained not only by airborne contamination, but also by the geochemistry of lakes and the climatic factor (increased evaporation concentration). Anthropogenic eutrophication leads to an increase in the content of Fe, Sr, Mo, and acidification—Zn, Cd, Ni, Cu, and especially Pb. There are industry-specific influences: the waters of the northern regions of ER are enriched by Ni, Cd, As, Sb and especially Se because of the emissions from copper-nickel smelters. The oil and gas industry (WS) leads to increased concentrations of V, Pb and Mo in water. We assess the metallic pollution status of surface water in the Eurasian region of Russia using an enrichment factor (EF). In surface waters of ER and WS, metal concentrations do not exceed the maximum permissible concentration, but we have established higher concentrations of many elements in the background, including toxic ones. Prolonged low doses of toxic elements can be a potential hazard to ecosystems and humans. The results showed that from the northern to the southern regions the EF increases for most of the analyzed elements. It can be assumed that with climate warming the concentration of metals in these bodies of water will increase and this is dangerous for the environment.

Tracking Open Versus Closed‐Canopy Boreal Forest Using the Geochemistry of Lake Sediment Deposits

AbstractIdentifying geochemical paleo‐proxies of vegetation type in watersheds could become a powerful tool for paleoecological studies of ecosystem dynamics, particularly when commonly used proxies, such as pollen grains, are not suitable. In order to identify new paleological proxies to distinguish ecosystem types in lake records, we investigated the differences in the sediment geochemistry of lakes surrounded by two boreal forest ecosystems dominated by the same tree species: closed‐canopy black spruce‐moss forests (MF) and open‐canopy black spruce‐lichen woodlands (LW). This study was designed as a first calibration step between terrestrial modern soils and lacustrine sediments (0–1000 cal yr BP) on six lake watersheds. In a previous study, differences in the physical and geochemical properties of forest soils had been observed between these two modern ecosystems. Here we show that the geochemical properties of the sediments varied between the six lakes studied. While we did not identify geochemical indicators that could solely distinguish both ecosystem types in modern sediments, we observed intriguing differences in concentrations of C:N ratio, carbon isotopic ratio, and aluminum oxide species, and in the stabilization of their geochemical properties with depth. The C accumulation rates at millennial scale were significantly higher in MF watersheds than in LW watersheds. We suggest that these variations could result from organic matter inflows that fluctuate depending on forest density and ground vegetation cover. Further investigations on these highlighted geochemistry markers need to be performed to confirm whether they can be used to detect shifts in vegetation conditions that have occurred in the past.

Multidecadal climate‐induced changes in Arctic tundra lake geochemistry and geomorphology

AbstractHigh‐latitude lakes are sensitive indicators of climate and important ecological components of Northern landscapes. The response of Arctic lakes to accelerated 20th century warming has largely been inferred from paleolimnological and shorter‐term observational studies (&lt; 20 yr). Here, we present a long‐term observational dataset outlining a suite of chemical, biological, and physical changes in three Russian tundra lakes over a 43‐yr period (1953–1996). In all three lakes, epilimnetic water temperature, alkalinity, and calculated pCO2, measured during the ice‐free period in late summer, increased over time. Over the same period, the rates of primary and bacterial production increased significantly. Permafrost thaw at the base and margins of the lakes likely resulted in the observed increase in size, as measured by average depth, surface area, and total volume. The observed changes show strong correlation with temperature, suggesting an overall pronounced response to warming. Importantly, CO2 sourced from either in situ or allochthonous respiration of thawed permafrost would indicate the destabilization of a large C reservoir.

Carbon isotope and environmental changes in lakes in arid Northwest China

The stable carbon isotope composition ( δ 13C) of lacustrine sediments, which can record changes in past environmental conditions such as the C4/C3 terrestrial vegetation composition, has been widely used for the reconstruction of terrestrial ecosystems and global climate changes. It has also been widely used in paleolimnological studies in arid northwestern China. In recent years, however, an increasing number of studies have enriched the environmental significance reflected by the stable carbon isotope geochemistry of lakes; therefore, the interpretation of lake δ 13C variations in paleoenvironmental reconstructions should be carefully evaluated from various aspects. In this paper, previous studies from the past several decades on the lacustrine δ 13C variations in arid northwestern China were reviewed, and the possible mechanisms of the δ 13C variations were discussed. Our study will provide a reference for the application of carbon isotope geochemistry in paleoenvironmental reconstructions.

Effects of road salt deicers on an urban groundwater-fed kettle lake

Road salt deicers significantly influence the chemistry and physical mixing of urban lakes, even causing transition from dimixis to monomixis or meromixis. In this study, the water column geochemistry of Asylum Lake, a primarily groundwater-fed, eutrophic kettle lake in urban Kalamazoo, MI, was monitored for over a year to determine the extent of road salt deicer influence on the lake chemistry and the physical mixing of the lake. Water column samples from the surface to the deepest part of Asylum Lake were analyzed monthly for nineteen months for a suite of parameters including dissolved oxygen, pH, conductivity, temperature, alkalinity, Fe2+, Mn2+, orthophosphate, total NH4+, alkalinity, total sulfide, Cl−, SO42−, Ca2+, Mg2+, K+, and Na+. During the study period, spring mixing was never observed and a nearly complete fall turnover was observed only in November 2013. The hypolimnion of Asylum Lake was always hypoxic or anoxic and redox-stratified, with seasonal development of suboxic and sulfidic zones, which were disrupted in fall and winter following partial fall turnover and subsequent ice cover. This study suggests that road salt deicers have caused Asylum Lake to transition from dimixis to meromixis or periodic monomixis with significant consequences for biogeochemical cycles in the lake waters.

Impacts of changes in groundwater recharge on the isotopic composition and geochemistry of seasonally ice-covered lakes: insights for sustainable management

Abstract. Lakes are under increasing pressure due to widespread anthropogenic impacts related to rapid development and population growth. Accordingly, many lakes are currently undergoing a systematic decline in water quality. Recent studies have highlighted that global warming and the subsequent changes in water use may further exacerbate eutrophication in lakes. Lake evolution depends strongly on hydrologic balance, and therefore on groundwater connectivity. Groundwater also influences the sensitivity of lacustrine ecosystems to climate and environmental changes, and governs their resilience. Improved characterization of groundwater exchange with lakes is needed today for lake preservation, lake restoration, and sustainable management of lake water quality into the future. In this context, the aim of the present paper is to determine if the future evolution of the climate, the population, and the recharge could modify the geochemistry of lakes (mainly isotopic signature and quality via phosphorous load) and if the isotopic monitoring of lakes could be an efficient tool to highlight the variability of the water budget and quality. Small groundwater-connected lakes were chosen to simulate changes in water balance and water quality expected under future climate change scenarios, namely representative concentration pathways (RCPs) 4.5 and 8.5. Contemporary baseline conditions, including isotope mass balance and geochemical characteristics, were determined through an intensive field-based research program prior to the simulations. Results highlight that future lake geochemistry and isotopic composition trends will depend on four main parameters: location (and therefore climate conditions), lake catchment size (which impacts the intensity of the flux change), lake volume (which impacts the range of variation), and lake G index (i.e., the percentage of groundwater that makes up total lake inflows), the latter being the dominant control on water balance conditions, as revealed by the sensitivity of lake isotopic composition. Based on these model simulations, stable isotopes appear to be especially useful for detecting changes in recharge to lakes with a G index of between 50 and 80 %, but response is non-linear. Simulated monthly trends reveal that evolution of annual lake isotopic composition can be dampened by opposing monthly recharge fluctuations. It is also shown that changes in water quality in groundwater-connected lakes depend significantly on lake location and on the intensity of recharge change.

Water geochemistry of shallow lakes from the southeastern Pampa plain, Argentina and their implications on mollusk shells preservation

A seasonal sampling of sediments, column and interstitial water for physico-chemical analysis were performed in littoral and open water areas in three freshwater shallow lakes (Nahuel Rucá, Las Mostazas and Los Carpinchos) from Southeastern Pampa plain, Argentina. The main objective of the present study is to evaluate how the characteristics of the depositional environments could be affecting mollusk shell preservation. These lakes are very shallow (2m) and are characterized by an extensive littoral area, dominated by the emergent macrophyte Schoenoplectus californicus, which forms a complete ring around the lake, and an open water area, in general free of vegetation. Five samples of sediments in each compartment were extracted for analysis of pH, moisture, organic matter and carbonates content using a gravity corer, while five samples from column and interstitial water were extracted for chemical analysis (pH, conductivity, major ions, minor ions and hardness). Besides, calcite and aragonite saturation indices and the redox potential were calculated for each lake. The results show the significant impact of water chemistry and redox conditions on the preservation potential of freshwater mollusk and consequently in the quality of paleonvironmental reconstruction based on the biological record from the study region. The higher concentration of organic matter and lower pH registered in the littoral area, mainly during warm months (autumn and summer), suggest worst environments for mollusk preservation, compared to open waters. Moreover, water geochemistry analysis showed aragonite and calcite indices near equilibrium or slightly subsaturated in interstitial water associated with more acid pHs, while column water is strongly oversaturated related to alkaline pHs. These results suggest that carbonate remains within sediments will be subject to dissolution affecting negatively their preservation potential. However, mollusk shells in contact with the column water are not expected to be dissolved.

Lake geochemistry reveals marked environmental change in Southwest China during the Mid Miocene Climatic Optimum

The Mid-Miocene Climatic Optimum (MMCO; ~ 15–17Ma) was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, most of our understanding comes from marine cores. In this report, we first present new palaeomagnetic data that revises the dating of our 400m-thick lacustrine section in Wenshan (Yunnan), previously thought to be Late Miocene. These new data suggest an older age, ca. 15.2–16.5Ma, coinciding with the MMCO. We measured δ13C on bulk organic matter (δ13Corg), total organic carbon (TOC), total nitrogen (TN) and C/N ratios at a high sample resolution to: (1) reconstruct the palaeoenvironmental changes in the lake catchment area, and (2) infer mechanisms responsible for these changes. Our results show that all four geochemical parameters demonstrate that a strong environmental change occurred around the middle of the section, shortly after the C5Cn/C5Br geomagnetic reversal and the Early/Middle Miocene boundary at 15.97Ma. We propose that the environmental shift may be due to a combination of a change in climate, which became cooler, together with a change in organic matter cycling within the lake. This study provides a new insight into the MMCO and demonstrates that although the MMCO was generally a warm event, it was also a time of climatic instability and abrupt environmental changes.

Concentrations of toxic metals and ecological risk assessment for sediments of major freshwater lakes in China

A systematic geochemical lake sediment survey has been carried out in major freshwater lakes in China. Surface lake sediment (0–20cm) at a density of 1sample/4km2 and deep lake sediment (150–180cm) at a density of 1sample/16km2 were collected and analyzed with standard procedures. This overview provides a current ecological risk assessment for toxic metal contamination (As, Cd, Cr, Cu. Hg, Ni, Pb, and Zn) in the surface sediments of major freshwater lakes in China. Lake sediment in China poses a moderate ecological risk on a nationwide basis using a potential ecological risk index (PERI). Mercury ranked as presenting the greatest ecological risk, followed by Cd, As, Pb, Cu, Ni, Cr, and Zn. Liangzi Lake was classified as having high ecological risk; Dalonghu Lake, Dianchi Lake, Dongting Lake, Fuxian Lake, and Qilu Lake as having moderate ecological risk; while the other surveyed lakes were classified as having low ecological risk. Uncertainties of risk assessment are also discussed by considering geochemical background, the eco-toxicity of metals and the sensitivities of local benthic communities. These comprehensive findings have provided valuable information for improvement of lake management and pollution prevention and control in China.