Spatial distribution and historical records of mercury sedimentation in urban lakes under urbanization impacts

Coupling sedimentary records of anthropogenic metal(loid)s in urban waterscape parks with the "Coal to Gas" transition

Energy consumption structure has been adjusted worldwide as a measure to reduce CO2 emission and mitigate air pollution. The "Coal to Gas" transition in mainland China has successfully controlled air pollution in recent decades, but its impacts on the environment beyond air quality improvement remain unknown. With 210Pb dating, this study chronicled profiles of eight anthropogenic metal(loid)s in sediment core from 14 waterscape parks across the Ring Road Network of Beijing, China. Six sediment cores were dated showing a timing coupling of metal(loid) loadings with annual coal consumption during the increasing period before 2000. Two downwind sediment cores in downtown Beijing presented such couplings in both increasing and descending periods for coal consumption before and after 2000, respectively, close to the tipping point observed in 2002 for primary energy consumption efficiency. Evidence from stable Pb isotope composition and exceedances of Cu loadings against sediment quality guidelines of China and the USA suggest that vehicular sources have been dominating metal(loid) loadings in sedimentation in these waterscape parks after the "Coal to Gas" transition. These findings would be helpful in identifying environmental impact patterns resulting from shifts in energy consumption structure and dominance of emission sources thereafter.

Source-sink relationships of anthropogenic metal(loid)s from urban catchment to waterway in relation to spatial pattern of urban green infrastructures

Surface sediment in urban waterways originates from fine topsoil particles within catchments via surface erosion, often bonded with non-degradable metal(loid)s. This study posited that urban green infrastructures (UGIs) can influence anthropogenic metal(loid) transport from catchment topsoil to waterway sediment by retaining moveable particles. In multiply channeled downtown Suzhou, China, UGIs' spatial patterns were examined in relations to metal(loid)s source (catchment topsoil) - sink (waterway surface sediment) dynamics. Anthropogenic metal(loid)s - As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn - were spatially quantified in sediment at 144 waterway points and in topsoil at 154 UGIs' points across 7 subwatersheds. Integrated metal(loid) loads revealed significantly higher sediment loads (except for As) than topsoil, varying with element specificity and spatial unmatching across the subwatersheds. Loads of metal(loid)s in topsoil showed no significant differences among UGI types, but sediment loads of As, Cr, and Ni correlated positively with topsoil loads in roadside and public facility UGIs within 100 m- and 200 m-wide riparian buffer zones. However, waterfront UGIs negatively impacted on these correlations for Cr, Hg, and Ni loads within the riparian buffer zones. These findings highlight metal(loid) specificity and UGIs' spatial pattern effects on anthropogenic metal(loid) loads between catchment topsoil (source) and waterway surface sediment (sink), offering valuable guidelines for UGIs' design and implementation.

Process of mercury accumulation in urban strip river artificial wetland ecosystems: a case study of Changchun, a typical industrial city in Northeast China

Mercury (Hg), as a global pollutant, is persistent, migratory, insidious, highly biotoxic and highly enriched, and is widely distributed in the atmosphere, hydrosphere, biosphere and lithosphere. Wetland ecosystems, as active mercury reservoirs, have become the most important sources and sinks of heavy metal mercury. Distinguished from natural wetlands, artificial wetlands located in urban sections of rivers face problems such as diverse urban pollution sources and complex spatial and temporal changes. Therefore, in this study, five intermittently distributed artificial wetlands were selected from the upstream to the downstream of the Changchun section of the Yitong River, a tributary of the Songhua River basin in the old industrial base of Northeast China. The mercury levels in the water bodies, sediments and plants of the artificial wetlands were collected and tested in four quarters from April 2023 to analyse the spatial and temporal distribution characteristics of total mercury. The results showed that the mercury levels in the water bodies, sediments and plants of the five wetlands showed a fluctuating trend with the river flow direction and had certain spatial and temporal distribution characteristics. This phenomenon was attributed to the sinking of external mercury pollution sources. In general, the wetland ecosystems showed a decreasing trend in the total Hg output of the downstream watershed. This may be due to the retention of particulate matter by aquatic plants in artificial wetlands to regular salvage of dead aquatic plants. At the same time urbanization and industrialization affect mercury levels in aquatic environments, so the risk of residential exposure needs to be looked at.

Spatial-temporal variations and pollution risks of mercury in water and sediments of urban lakes in Guangzhou City, South China

This study aims to investigate the spatial and temporal characteristics, pollution degrees, and potential ecological risks of mercury (Hg) in urban lake waters and sediments in Guangzhou, where is a typical area of Hg emission and population-economic-industrial concentration in South China. In different districts of this city, the water from 15 lakes were collected continuously from June 2020 to May 2021, and the sediments from 9 lakes were collected in 2015 and 2021. The seasonal changes of Hg concentration (Hg-C) in the water were found to be high in winter and low in summer. The spatial distribution of Hg-C in sediments showed that it was high in urban central areas and low in suburbs. The Nemero index and geological accumulation index showed that there were uncontaminated of Hg in the collected lake water, and above moderately contaminated in the lake sediments in urban center, respectively. The Hg pollution potential ecological risk index showed that there was low risk in the collected water, high and extremely high risk in the lake sediments in urban center, respectively. The principal component analysis (PCA) and correlation analysis (CA) of Hg and meteorological factors showed that precipitation, temperature, and vapor pressure had negative effects on the seasonal changes of Hg-C in water, and air pressure and wind direction had positive effects. The PCA and CA of Hg and other geochemical elements showed that anthropogenic emissions may be the main sources of Hg in sediments, which was also supported by the data of population density, road density, and motor vehicles per 1000 people. This study provided a reference for urban lake pollution treatment, resident health, and ecological environment protection.

Anthropogenic metal loads in nearshore sediment along the coast of China mainland interacting with provincial socioeconomics in the period 1980-2020

Metal pollutions have been accused of consequences of the anthropogenic activities but few quantitative delineations between environmental metal loads and socioeconomic development presented. A meta-data analysis study was carried out on metal loads in coastal sediment in the provinces of China mainland reported in literature in the period 1980-2020. Eight metals with well-recognized anthropogenic sources were selected including arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn). Screened with three criteria, a total of 1173 records from 405 published studies were finalized as the metal loads dataset in coastal sediment. Evident provincial patterns were observed among the selected metals but element dependent after transformed to sample number weighted contents (C_w). Against the regional marine backgrounds, anthropogenic increment rate (R_anthrop) of metal loads in nearshore sediment presented better provincial differentiation with the extremes at 7.58 for As and 62.13 for Cu in Guangdong, 91.25 for Hg in Zhejiang, 3.19 for Ni in Tianjin, 7.72 for Pb in Fujian, and 13.51 for Zn in Liaoning. Metal loads in coastal sediment could be explained by characteristic industries in the provinces. Nearshore sediment in Guangdong had high risk to metal loads and other provinces at low-to-medium risk to the lowest thresholds of sediment quality guidelines in China and USA. Canonical correlations identified considerably interactive explanations between integrative hazard quotients (ƩHQ) of the selected metals in nearshore sediment and non-agricultural GDP per capita of non-agricultural population/urban population percentile provincially but few significant fittings by the classic environmental Kuznets Curve model quantitatively. Findings of this study explored uncertainty from both sides in explaining the interactions, i.e., data integrity of metal loads in coastal sediment in literature and appropriation of socioeconomic indicators in relation to metal emission industries.

Historical trends in atmospheric metal(loid) contamination in North China over the past half-millennium reconstructed from subalpine lake sediment

Trace metal (loid) contamination in the atmosphere is widely monitored, but there is a gap in understanding its long-term patterns, especially in North China, which is currently a global contamination hotspot mainly caused by heavy industry emissions and coal combustion. Herein, historical trends of atmospheric As, Cd, Cr, Cu, Hg, Ni, Pb and Zn contamination in North China over the past ∼500 years are comparatively studied with sediment cores from two subalpine lakes (Gonghai and Muhai). Arsenic, Pb, Cd and Hg were main pollutants according to Pb isotopes and enrichment factors. Mercury contamination has increased continuously since the late 1800s and increasing As, Pb and Cd contamination started in the 1950s in Gonghai. In contrast, the contamination in Muhai lagged two decades for As, Cd and Pb and a half-century for Hg behind that in Gonghai, although the trends were similar. This contamination lag was attributed to the low sensitivity of Muhai sediment to early weak atmospheric metal contamination under 2.1-fold higher detrital sedimentation. As, Pb and Cd contamination has intensified since the 1980s, and the metals showed similar sedimentary fluxes in the cores. However, sedimentary fluxes of Hg contamination were 3.4-fold higher in Gonghai than in Muhai due to combination with organic matter. No obvious Cr, Cu and Ni contamination in the cores was mainly because of the low atmospheric deposition from anthropogenic sources relative to detrital input, although some of their atmospheric emissions were higher than those of As, Cd and Hg. Atmospheric As, Pb and Cd contamination was mainly from domestic sources of coal combustion and nonferrous smelting. Mercury contamination was mainly from global and Asian sources in the first half of the 20th century, and domestic emissions gradually dominated Hg contamination after the mid-1900s.

Response of mercury accumulation to anthropogenic pollution in the past 1000 years based on Lake Huguangyan sediments, Southern China

A new ²¹⁰Pb-dated record of Hg accumulation derived from a sediment core from a Hg-enriched area in Huguangyan Lake (HGY) in South China is presented. Based on synthetic analyses of multi-proxy records including chemical composition, total organic matter, and grain-size distribution in surface sediments and nearby soil samples, it is inferred that the influx of Hg into the lake is mainly a result of atmospheric deposition, with no or minor hydroclimate-induced lithogenic input from the catchment and limited adsorption effects of organic matter and clay. Significantly enhanced anthropogenic input of Hg started in the early 1900s. Since then, several anomalies of Hg accumulation have been the results of wars or intensified economic activities in China. HGY sediments provide a rare and reliable natural archive for detecting atmospheric Hg deposition, which is closely related to anthropogenic activities.

Metal(loid) accumulation levels in submerged macrophytes and epiphytic biofilms and correlations with metal(loid) levels in the surrounding water and sediments

The pollution of wetlands with metal(loid) s is a major ecological and environmental problem all over the world. However, the accumulation characteristics of metal(loid)s in submerged macrophytes and epiphytic biofilms in wetland systems where sediments are polluted by metal(loid)s are still unclear. In July (the wet season) and November (the dry season) 2018, surface water, sediments, submerged macrophytes (Potamogeton lucens L. and Myriophyllum verticillatum L.) and their epiphytic biofilms were collected to analyze the levels of Pb, Cd, Cu, Cr, Hg and As in Caohai wetland (China). Metal(loid) concentrations in sediments were ranked as follows: Cr > Pb > Cu > As > Cd > Hg. Although Pb, Cd and Hg levels exceeded the sediment background threshold levels of Guizhou Province, the water was not polluted by metal(loid)s. Except for Hg and Cr, most of the metal(loid) concentrations in epiphytic biofilms were higher than those in submerged macrophytes. No significant correlations were found between any of the metal(loid) concentrations in submerged macrophytes or biofilms and the metal(loid) concentrations in the surrounding water and sediments. Although the accumulation of As and Hg in submerged macrophytes had a very significant negative correlation with a few elements, the correlation between other elements was not significant. No co-accumulation phenomenon was found in submerged macrophytes; however, co-accumulation and competition among different metal(loid)s did occur in the epiphytic biofilms, which may be related to the different accumulation mechanisms of metal(loid)s in submerged macrophytes and epiphytic biofilms. This study enriches our understanding of the accumulation of metal(loid)s in submerged macrophytes and epiphytic biofilms in wetlands.

Bioaccumulation and growth characteristics of Vallisneria natans (Lour.) Hara after chronic exposure to metal-contaminated sediments

Metal-contaminated sediments in lakes is a global concern that poses toxicological risk to aquatic organisms. This study performed bioassays using the submerged macrophyte, Vallisneria natans (Lour.) Hara, exposed to contaminated sediments collected from five locations in Dianchi Lake, Yunnan, China. Among the sediments collected, I_geo showed enrichment of As and Cd in Dianchi Lake sediments. In spite of enriched toxic metals at some locations, laboratory bioassays found no significant difference in leaf biomass or leaf photosynthesis rate between the sites. Root biomass and root activity showed significant differences between locations and were negatively correlated with the concentration of As, Cd, Hg, and Pb in sediment but not related to Cr. The above correlations were strongest for Hg and As, respectively. Accumulation of Cd and Pb to leaves of bioassay plants was observed, but this was not evident for As and Cr. Overall, the results indicate that V. natans can be used as a bioassay organism and measures of root toxicity are sensitive to metal concentrations present in Dianchi Lake sediments. Furthermore, the study species holds promise for use as a biomonitor of Cd and Pb sediment metal content.

Historical anthropogenic mercury in two lakes of Central Chile: comparison between an urban and rural lake

Mercury concentrations in the environment tend to decrease in recent years due to environmental restrictions. Lakes store mercury in their sediments, making them potential secondary contamination sources. In South America, the occurrence of mercury in lake systems has been associated mainly with volcanic emissions and only few records anthropogenic contamination in the pre-Hispanic period. The objective of this research was to study historical anthropogenic mercury concentration in two lakes in Central Chile (La Señoraza and Pillo), in order to establish background mercury levels and their variations from preindustrial to modern periods. Different background levels and mercury concentrations were found in each lake, with significantly higher concentrations in Lake La Señoraza during the last 150 years. Mining-related activities during the nineteenth century could have a negligible influence on mercury concentrations. Later on, the use of coal railroads and subsequent employment of mercury in the cellulose industry were associated with three- and fourfold increases in mercury concentration over the nineteenth century background levels, which decrease once these activities ceased. However, in the case of Lake Pillo, an important increase in mercury concentration can be observed between 1990 and the early twenty-first century, which could be related to a higher watershed/lake area ratio, extensive agriculture, and volcanic emission, being the latter that could have contributed with mercury to both systems. Nevertheless, sedimentological characteristics in Lake Pillo can be favorable to retain mercury in this aquatic system up to the present day.

Mercury pollution in the lake sediments and catchment soils of anthropogenically-disturbed sites across England

Sediment cores and soil samples were taken from nine lakes and their catchments across England with varying degrees of direct human disturbance. Mercury (Hg) analysis demonstrated a range of impacts, many from local sources, resulting from differing historical and contemporary site usage and management. Lakes located in industrially important areas showed clear evidence for early Hg pollution with concentrations in sediments reaching 400-1600 ng g^-1 prior to the mid-19th century. Control of inputs resulting from local management practices and a greater than 90% reduction in UK Hg emissions since 1970 were reflected by reduced Hg pollution in some lakes. However, having been a sink for Hg deposition for centuries, polluted catchment soils are now the major Hg source for most lakes and consequently recovery from reduced Hg deposition is being delayed.

An extended study on historical mercury accumulation in lake sediment of Shanghai: The contribution of socioeconomic driver

Rapid industrialization and urbanization has caused large emission and potential contamination of mercury (Hg) in urban environment. However, little is known about the impact of socioeconomic factor on Hg accumulation in sediment. In the present study, historical record of anthropogenic Hg deposition of Shanghai was reconstructed by using three sediment cores from three park lakes (C1: Luxun Park; C2: Fuxing island Park; C3: Xinjiangwan Park). Meanwhile, the influence of socioeconomic factor to Hg emissions and sedimentary record was calculated based on an extended STIRPAT (stochastic impacts by regression on population, affluence and technology) model. The profiles of Hg levels and fluxes in the three sediment cores showed that Shanghai has recently undergone urbanization. The anthropogenic Hg fluxes exhibited fluctuant increases from ∼1900 to present and accelerated after the establishment of the People's Republic of China in 1949 and the implementation of reform and opening up policy in 1978. The mean flux ratios of Hg in post-2000 were 2.2, 12, and 2.7 in the C1, C2 and C3 cores, respectively. The extended STIRPAT model was constructed based on strong positive relationships between socioeconomic factors and Hg fluxes, revealing that the proportion of coal consumption, the urbanization rate, and the proportion of heavy industry were the three most important driving factors for Hg accumulations in urban sediment of Shanghai.

Mercury pollution in fish from South China Sea: levels, species-specific accumulation, and possible sources

Both total mercury (THg) and methylmercury (MeHg) levels in fish collected from South China Sea (SCS) were studied to understand Hg pollution in Chinese tropical marine ecosystems. The average THg concentrations in fish species ranged from 39.6 μg/kg for rabbitfish (Siganus fuscessens) to 417 μg/kg for thornfish (Terapon jarbua), while those of MeHg varied from 13 μg/kg (rabbitfish) to 176 μg/kg (thornfish). The median values of MeHg/THg ratios in different fish species ranged from 36 to 85%. Significant inter-species differences of THg and MeHg in fish were observed due to feeding habits and fish sizes. Overall, carnivorous fish had higher levels of THg, MeHg and MeHg/THg ratios than omnivorous and herbivorous fish. High Hg levels in fish of the SCS were probably related to Hg input from atmospheric deposition and anthropogenic activities.