Metals In Sediments Research Articles

Assessment of Some Heavy Metals and Ecological Risk in Surface Sediments and Water along the El Tur Coast of Suez Gulf, Red Sea, Egypt

Assessment of Some Heavy Metals and Ecological Risk in Surface Sediments and Water along the El Tur Coast of Suez Gulf, Red Sea, Egypt

Influence of mineralized organic carbon in marine sediments on ecological heavy metal risk: Bohai Bay case study

The organic matter in sediments can mineralize over time, which impacts the morphology of the heavy metals therein, which in turn affects the assessment of the risks posed by heavy metals. We used the sediments of Bohai Bay as the study object and analyzed the effects of different organic carbon mineralization levels on the concentrations of heavy metals (Cr, Pb, Cu, Zn, and Cd) using water extraction and potassium permanganate oxidation. The mean concentrations of Cd, Pb, Cu, and Zn in Bohai Bay were within the limits recommended by the World Health Organization. The proportions of the active and inert organic carbon fractions were 61.72% and 32.94%, respectively. Organic carbon mineralization most strongly impacted Cd and Pb levels, with releases accounting for 47.92% and 25.75%, respectively, of the oxidizable fractions. The release of all heavy metals, except for Cr, increased with increases in organic carbon mineralization, and heavy metals were released at a maximum rate of 12.94% when the organic carbon was highly mineralized, whereas Cr was released at a maximum of 0.023% during the first stage of organic carbon mineralization. In terms of spatial distribution, the concentration of mineralizable organic carbon in the sediments of the estuaries was substantially higher than that in other marine areas. Estuary sediments were more easily affected by organic carbon mineralization; therefore, the heavy metals in the oxidizable fraction of the estuarine region were more easily transformed into unstable heavy metal forms, posing high risk levels. Therefore, this study highlights the effects of organic carbon mineralization on heavy metal morphology and stability, when evaluating the ecological risk of heavy metals in marine sediments.

Ecological risk assessment of heavy metals in the coastal sediment in the South-western Bay of Bengal

Dynamic coastal waters are often polluted by chemical pollutants, affecting coastal ecosystems. A total of four scientific coastal cruises up to 10 km offshore from the coastline along the Chennai-Puducherry coast during 2019-20 were conducted. This study examined the spatiotemporal distribution of heavy metals (Cr, Cu, Pb, Cd, Ni, Zn, As, Co, Mn) in the coastal sediments using various geochemical indices, including the Geo-accumulation Index (Igeo), Enrichment Factor (EF), Contamination Factor (CF), and Ecological Risk Index (ERI), to understand the impacts, environmental risks, and pollution status in coastal and marine systems. The heavy metal concentrations of Cr, Cu, Pb, Cd, Ni, Zn, As, Co, and Mn in sediments are 16.48-74.70 μg/g, 2.01-3.78 μg/g, 1.37-17.54 μg/g, 0.20-21.76 μg/g, and 5.73-40.53 μg/g, 4.73-53.54 μg/g, 2.09-28.18 μg/g, 1.80-9.02 μg/g, 70.27-346.22 μg/g, respectively. The Igeo results revealed that none of the metals reached up to the contamination level except for Cd and As which showed a slightly contaminated level of the sediment. ERI indicated that coastal sediments are at moderate to high ecological risk from heavy metals. This study will help policymakers make informed decisions for combating or remediating metal pollution to safeguard the coastal environment.

Source and pollution assessment of heavy metals in surface sediments of Laoshan Bay, South Yellow Sea, China

A total of 25 surface sediment samples collected from Laoshan Bay, China, during 2018, were analyzed for heavy metal concentrations, sources, and pollution status. The Cu, Zn, and Cr distributions were similar, whereas the distributions of other metals and the total organic carbon (TOC) content were irregular, and high concentrations appeared in one or two areas. Pearson's correlation coefficient, the geoaccumulation index, and principal component analysis were used to distinguish the sources and assess the pollution risk of heavy metals. The results showed that the surface sediments in Laoshan Bay were not polluted by Cu, Zn, Cr, or As, but were unpolluted to strongly polluted with Pb, Cd, and Hg. Cu, Zn, Cr, and As were mainly derived from natural sources; Pb and Cd were mainly derived from anthropogenic sources; and Hg may have had compound sources.

The use of marine sponge species as a bioindicator to monitor metal pollution in Red Sea, Saudi Arabia

The existing data on trace elements of benthic sea organisms is scarce. Yet, the pressing issue of environmental contamination has spurred a surge in the use of organisms as biomonitors. In this study, sediment cores were sampled with the sponges, and metal concentrations were determined in both samples using ICP-MS. The mean concentrations of metals in benthic sediments and sponge species analyzed in this study differed significantly (Sediment >Phorbas species > Negombata magnifica > Callyspongia species > Amphimedon chloros). This could be due to the varying capacity of each sponge species to accumulate a particular metal by different means. Negombata magnifica and Phorbas species appear to be indicators, accumulators, or hyper-accumulators of Cu and Mn, while Callyspongia species is an indicator, accumulator, or hyper-accumulator of Cu only due to bioconcentration factor > 1 for the aforementioned metals. Concentrations of Cu and As in sediment were below the Effects Range Median but above the Effects Range Low threshold, hence the need to give more attention to these metals. This research provides a baseline dataset for designing monitoring strategies on this ecosystem and using sponge species for biomonitoring.

Spatial Distribution and Contamination Level Assessment of Marine Sediment of the Safi Bay (Moroccan Atlantic Coast)

This study assesses the spatial distribution and contamination level of heavy metals in Safi Bay surface sediments. In this order, 28 surface sediment samples were retrieved from the study area and analyzed using the x-fluorescence method. To assess the contamination of the examined sediment, we used geo-ecological indices such as contamination factor (CF), degree of contamination (DC), geo accumulation index, and pollution load index (PLI). The results show that only Pb and Cd present moderate and considerable contamination in some sampling sites, while other elements (Cr, Cu, Zn, and Ni) indicate no contamination and low contamination by these elements. The inhomogeneous distribution of metal concentrations along the bay suggests different heavy metal sources. Given the ecological and socioeconomic importance of the study area, there is a need for a further analysis of both sediments and biological samples for a better understanding of the contamination levels and origin of metals, in addition to the sustainability of Safi Bay.

Potential of Rhizophora apiculata Blume. in Phytoremediation of Heavy Metals Pb and Cu in the Mangrove Forest Nature Reserve East Coast, Alang-Alang Village, Tanjung Jabung Timur, Jambi

The Mangrove Forest Nature Reserve East Coast (CAHBPT) in Jambi Province has functions, one of which is to improve water quality by absorbing dangerous heavy metals such as Pb and Cu which come from various human activities around the waters. This absorption can be done by using hyperaccumulator plants such as Rhizophora apiculata Blume. This study aims to determine the potential and mechanism of R. apiculata in the phytoremediation of heavy metals Pb and Cu in the CAHBPT area, Alang-Alang Village, Tanjung Jabung Timur Regency, Jambi Province. Sampling was carried out using the purposive sampling method at three stations. The calculation of the Bioconcentration Factor (BCF) aims to determine the potential of R. apiculata in phytoremediation Pb and Cu metals, as well as the calculation of the Translocation Factor (TF) to determine the phytoremediation mechanism of R. apiculata. The results of this research found that the accumulation of Pb and Cu metals in sediments ranged from 11.04-12.36 mg/kg and 7.93-9.08 mg/kg. The accumulation of Pb and Cu metals in the roots of R. apiculata ranges from 2.34-2.65 mg/kg and 1.56-2.93 mg/kg. The accumulation of Pb and Cu metals in the shoots of R. apiculata ranged from 2.77-3.16 mg/kg and 0.61-1.05 mg/kg. The phytoremediation potential of R. apiculata at the research site is included in the excluder category or plants still limit the accumulation of heavy metals entering the body (BCF<1). R. apiculata at the research site translocated Pb metal using a phytoextraction mechanism (TF>1) and Cu metal using a phytostabilization mechanism (TF<1).

Distribution and Contamination Level of Cuprum (Cu) and Plumbum (Pb) in Bulk Sediments of the Bangka Island

The distribution and enrichment of heavy metals in sediments will affect the life of the organisms that lives in it. The purpose of this study is to explain the enrichment and contamination levels of heavy metals Cu and Pb in bulk sediments in the northern and southern parts of Bangka Island. This research was conducted in August - September 2019, using a purposive sampling method. Heavy metal analysis using the Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) instrument. The results showed that the concentration of the heavy metal Pb in the sediment bulk of northern Bangka Island (Kelabat Bay) was higher than that of South Bangka Island. The concentration of heavy metal Cu at 8 (eight) sites is still below the quality standard (18.7 mg.kg-1) even if the heavy metal Pb at stations 3, 4, and 5 in the waters of the northern half of Bangka Island (Kelabat Bay) is reported to have exceeded the quality standard limit (30.2 mg.kg-1). The highest level of enrichment of heavy metal Pb occurs at station 4 with a value of EF_62.88, and is categorized as very high enrichment and a contamination factor (CF) value of 2.24 (medium category). This condition is due to station 4 being located in Kelabat Bay (semi-enclosed area) with unstable water conditions due to the influence of many activities. The results of this study can be used as input for local governments for the management of water areas on Bangka Island.

Metal and non–metal dynamics and distribution in soil profiles across selected pans in the Ramsar declared subtropical within a national protected area

ABSTRACT The study investigated the spatial distributions of selected metals, semi–metals and non–metals within a floodplain pan ecosystem in the Ramsar declared Makuleke Wetlands within the Makuleke Contractual National Park, in the northern Kruger National Park (South Africa), along varying soil depths (0–120 cm) at 20 cm intervals. The study identified significant differences in metal concentrations (i.e. Ca, Mn, Fe) and non–metals (i.e. C, S) across sediment depths. Metal and non–metal concentrations in surface sediments (0–40 cm) were generally high. Compared with the sediment quality guidelines, all measured metals were within the ‘no effect’ level across different sites and depths, except for one site (i.e. Mambvumbvanyi pan). In contrast, enrichment factors showed that K, Ca and Mg were enriched in sediments across all the floodplain pans and depths. Principal component and cluster analyses indicated that various metals originated from different sources. Although a high concentration of metals was found in the topsoil, no potential detrimental effects on the aquatic systems could be observed. Based on the findings, this study provides a baseline overview of sediment metal pollution that can inform effective management of these floodplain wetlands systems.

Ecological risk assessment for metals in sediment and waters from the Brazilian Amazon region

Pollution by metals is a matter of concern around the world. In recent decades, the high population growth in urban centers has significantly magnified the entry of these pollutants into aquatic ecosystems. The Amazon region, intense migratory flow, gold mining, and industrialization have been considered the main driving forces for increasing metal pollution. Thus, the main aim of this study is to conduct, for the first time, an Ecological Risk Assessment (ERA) based on metal concentrations measured in the sediment and water of several aquatic environments from the Amazon basin, based on the risk quotient values (RQ = measured environmental concentration - MEC/predicted no effect concentration - PNEC). In addition, the metal contamination factor (CF) was estimated. Although metal concentrations in water were generally low, these values were far above the limits established by current national legislation in many areas, showing higher concentrations for the metals Co, Pb, Cr, Cu, and Ni. Concentrations of Mn, Cu, Ba, Pb, Co, Ni, Cr, Zn, Cd, and As were especially high in the sediment for several evaluated environments. The ERA for the water compartment revealed that 56% of the studied areas presented high risk (RQ > 1) for aquatic biota. In the sediment, 66% of the sites presented a high risk and 40% medium risk (RQ = 0.1–1). The CF indicated that 49% of the sampling points had high contamination and only 24%, had low contamination. These results reveal that monitoring studies in the Amazon region, provides important information so that public policies for the preservation of water resources can be strengthened in the Amazon.

Distribution, sources, and risk analysis of heavy metals in sediments of Xiaoqing River basin, Shandong province, China.

The accumulation of heavy metals in river sediment poses a major threat to ecological safety. The Xiaoqing River originates in western Jinan, with higher population density and per capita gross domestic product (GDP) in its basin compared to the Shandong province average. This study analyzed the spatial characteristics, ecological risk, human health risk, and contamination sources of heavy metals by collecting sediment samples from Xiaoqing River. We use the methods such as geo-accumulation index (Igeo), ecological risk assessment based on the interval number sorting method, and health risk assessment to evaluate the risk of heavy metals in sediments. The research finding suggests heavy metals including Pb, As, Ni, and Cr are low ecological risks, while Hg and Cd have reached high and extreme ecological risks. Correlation analysis and principal component analysis were used to analyze the correlation and sources of different heavy metals. The six heavy metals were categorized into three groups. Factor 1, comprising Hg, Cr, and Pb, was identified as a mixed source with a contribution rate of 37.76%. Factor 2 is an agricultural source and comprises Ni, Cd, and As with a contribution rate of 27.05%. Factor 3 includes Pb and Ni contributing to 15.30% as a natural source. This study offers valuable insights for the prevention of heavy metal pollution, as well as promoting sustainable urban development.

The decomposition of algae has a greater impact on heavy metal transformation in freshwater lake sediments than that of macrophytes

Heavy metal (HM) pollution is a major concern in freshwater ecosystem management. The different types of endogenous organic matter and the way their decomposition affects HM transformation in freshwater lakes is not well understood. An ex situ mesocosm study was conducted to compare HM transformation in sediments during anaerobic decomposition of cyanobacterial bloom biomass (CBB) and submerged cyanobacterial vegetation in Lake Taihu, known as Potamogeton malaianus (PM). Microbial community structures were examined through Illumina sequencing of 16S rDNA. Results indicate that Zn had a remarkably higher amount of potential mobile fraction than other heavy metals (Cr, Pb, Cu, Ni, and Cd) detected in sediments, especially in sediments collected from CBB-dominated areas (approximately 150 mg kg−1). CBB decomposition has caused a significant increase in exchangeable Zn content in sediments and a decrease in reducible Zn that was three times greater than PM decomposition. Additionally, oxidizable Zn content declined during CBB decomposition but increased during PM decomposition. Furthermore, the relative abundance of the main fermentative bacteria and some sulfate-reducing bacteria genera (e.g., Desulfomicrobium) were significantly associated with the HM content of exchangeable and reducible fractions during CBB decomposition. Overall, the findings indicate that Zn is more susceptible to endogenous organic matter decomposition than other metals in freshwater lakes, and the impacts of CBB decomposition on the transformation of heavy metals in sediment are greater than that of submerged macrophyte decomposition.

Spatial distribution of heavy metals in surface sediments of the Kalametiya Lagoon in southern Sri Lanka: Insights into the pollution status and socio-economic interactions 

Heavy metal pollution has become a serious threat to coastal aquatic ecosystems. Therefore, this study, aimed to assess the spatial distribution of five selected heavy metals/metalloids, arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg), in surface sediment samples collected from the Kalametiya Lagoon in southern Sri Lanka. Sixteen (16) areas of the lagoon were sampled. The sediment samples were analysed for heavy metal content by using ICP-MS while the water samples were measured for salinity and pH. A questionnaire survey was conducted to investigate the possible sources of heavy metal pollution in the Lagoon. Water pH and salinity showed significant variations across the lagoon. The overall mean value of pH and salinity were 6.68 ± 0.17 and 2.9 ± 2.2 PSU, respectively. The spatial distribution of the heavy metals was not monotonous and showed a high spatial variation. The kernel density maps of the measured heavy metals demarcated several spatially different patches in the lagoon. The mean levels of As, Cd, Cr, Hg, and Pb were lower than the threshold effect level (TEL) although it was higher for Hg in the North inlet. Nevertheless, it was still lower than the potential effect level (PEL). Industrial sewage, river suspended sediments, and agrochemicals such as fertilizers and pesticides were identified as the possible sources for heavy metal loads. Accumulation of toxic heavy metals can be minimized by by-passing the freshwater inflow to the lagoon.

Distribution and assessment of heavy metals in sediments from the Red Sea, Egypt during 2019

Distribution and assessment of heavy metals in sediments from the Red Sea, Egypt during 2019

Ecological and Human Health Risk Assessment of Heavy Metals in Sediment of Selected Creeks in Rivers State, Nigeria

There has been much concern about the rate at which industrial and household wastes are released into Creeks in Rivers State. The study examined the status of heavy metal pollutants (Cd, Cu, Zn, Cr, Pb, and Ni) in sediment and to determine the extent of damage caused by these human factors using the most recent pollution index and Sediment quality guidelines (SQGs). The research was carried out in four important creeks along the Delta River network in Rivers State, Nigeria (Okrika, Borokiri, Eagle Island, and Kaa). Triplicate sediment samples were collected at a depth of 0-20 cm and extracted with 20cm3 of aqua ragia (a 3:1 mixture of HCl and HNO3) and 10cm3 of 30% H2O2. The metal concentrations were measured using an Atomic Absorption Spectrophotometer (AAS). The concentrations of the heavy metals ranged from 11.147–18.919mg/kg, 11.918–14.379mg/kg, 8.321–11.691 mg/kg, 6.405–11.72mg/kg, and 5.718–12.125mg/kg, and 2.429-7.725mg/kg respectively and followed the sequence Zn > Pb > Cr > Ni >Cu > Cd. Geo-accumulation Index (Igeo) calculated was less than 0 i.e. uncontaminated for all metals except Pb in Borokiri Creek and Cd in all sampled creeks, showing moderate contamination. Eco-toxicological risk assessment (RI) indicated that the creeks were uncontaminated. Despite the low level of contamination, it is recommended that relevant authorities to regulate the indiscriminate dumping of domestic waste and untreated industrial effluents into the river to prevent the deterioration of the creeks

Pollution indices and ecological risk assessment of major elements and trace metals in the marine sediment of the western Nigeria continental shelf, Gulf of Guinea

The Gulf of Guinea is known to be highly productive owing to its ecological and economical significance. Given its importance, detailed evaluation of the major elements (Fe, Mn, Ca, Mg, Na, Al, K and Si) and trace metals (Cu, Zn, Pb, Cr, Ni, As, Sc, V, Th and U) were analyzed from the sediment core within this basin for the first time. This study aims to determine their baseline composition, pollution level, and ecological risk. Analyses of these metals using inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) with Agilent SPS3 Autosampler showed the descending order of Na > Fe > Ca > Si > Mg > Al > K > Mn and Zn > U > V > Ni > Cr > Th > Pb > As > Cu > Sc for major and trace element respectively. The pollution indices and sediment qualities were assessed using the contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), potential ecological risk factor (Er), modified hazard quotient (mHQ), pollution load index (PLI), ecological risk index (RI), single metal toxic risk index (TRIi) and integrated Toxic risk index (TRI) at three stations (stations A, B, and C). Except for As and U, the mean concentrations of the metals were lower than their respective background values. Based on the pollution indices, the studied trace metals were found to have severe EF (>25) with respect to Zn and V, considerable CF (3 ≤ CF ≤ 6) for As, and high CF (> 6) for U. The Igeo values of all the trace metals indicated unpolluted to moderately polluted status (0 ≤ lgeo ≤ 1). The Er ranges (0.05–41.80) indicate low to moderate ecological risk, while mHQ (< 1) values indicate very low severity of contamination. There was no significant risk from the combined metals recovered from the sediment core of the study area to the marine ecosystems according to RI (<150), PLI (< 1), and TRI (< 5) values. The findings from this study will serve as a preliminary baseline chemical composition for rational ecological protection measures off the Nigerian coast.

Spatial-temporal Variations and Pollution Assessment of Heavy Metals in Sediments of Qionghai Lake in Xichang City

Based on the analysis of the total concentrations of 10 metals in the sediment core and total concentrations and chemical fractions of seven metals in the surface sediments of Qionghai Lake in Xichang City, Sichuan Province, the spatial-temporal characteristics of metal accumulation and pollution over the past century and the potential ecological risk of metals in surface sediments were studied. Before the 1970s, metal concentrations in the sediment core were stable. The total concentrations of Al, Fe, K, and Cr in the sediment core exhibited visible peaks in the 1970s, which were related to the enhanced input of fine-grained topsoil caused by increasing precipitation, lake reclamation, and deforestation. Since the 1990s, the total concentrations of Al, Fe, K, and Cr decreased with the reduced topsoil erosion, whereas the total concentrations of As, Cd, Cu, Pb, and Zn gradually increased or remained stable. The enrichment factor results showed that Cd, Pb, and Zn were the main contaminants, with Cd as the typical contaminant in the sediment core. The Cd contamination started in the 1960s and has remained at a moderate level since the 1990s. In the surface sediments, the total concentrations of Cd were higher in the northwest lake area, and no visible spatial concentration trends of the other metals were displayed. The bioavailable fractions of Cd, Pb, and Zn accounted for 95%, 63%, and 48% of the total metal concentrations on average. Among the bioavailable fractions, Cd was mainly in the acid-soluble fraction, and Pb and Zn were mainly in the reducible and oxidized fractions. The bioavailable fractions of the other metals were less than 27%. The results of total concentrations and bioavailable fractions of metals revealed that Pb and Zn in the surface sediments were slightly or moderately contaminated, and Cd was moderately contaminated on average. Cd contamination was at a severe level in the northwest lake area. The concentrations of anthropogenic Cd, Pb, and Zn in the surface sediments estimated from the total and bioavailable concentrations were comparable (P>0.05), indicating that anthropogenic metals primarily existed in bioavailable fractions in the sediment. Integrating the assessment results from sediment quality guidelines, potential ecological risk index, and chemical forms of metals, Cd in surface sediments may pose a high ecological risk, whereas the other metals has a low ecological risk.

Comprehensive geochemical assessment, probable ecological and human health risks of heavy metals in water and sediments from dredged and non-dredged Rivers in Lagos, Nigeria

The study was conducted to demystify the geochemical distributions of heavy metals in water and sediments from dredged and non-dredged riverine systems, with a view to ascertain the source, and the deleterious ecological and human health risks of these metals. Ojo and Badagry Rivers were considered as the dredge-mined sites, while Gbaji River was chosen as the non-mined site. The level of heavy metals in water samples are as follows; [Cd (0.040 – 0.360), Cu (0.010 – 0.130), Cr (0.001 – 0.080), Fe (0.170 – 1.040), Pb (0.001 – 0.050), Mn (0.050 – 0.230–), Zn (0.050 – 0.160), As (0.001 – 0.030), Co (0.003 – 0.040) and Ni (0.001 – 0.050) mg/L]. The Cd and Mn contents in the water from the mined sites were higher than their permissible limits. The heavy metal contents [Cd (0.190 – 1.490), Cu (1.390 – 5.950), Cr (1.180 – 2.630), Fe (144.820 – 261.490), Pb (1.960 – 24.250), Mn (5.170 to 24.110), Zn (5.180 – 35.420), As (0.170 – 0.690), Co (0.190 – 0.840) and Ni (0.740 – 2.140) mg/kg] in sediments are within the background levels, except for Cd from the mined sites. The hazard index was lower than 1 (HI ≤ 1), inferring no likelihood of non-carcinogenic incidents. Contrarily, the outcome of the cancer risk index revealed that exposure to sediments from the mined sites could lead to cancer risk. The contamination and enrichment factors of the sediments from mined sites showed “high contamination” and “extremely enriched,” respectively. Notably, the potential ecological risk index of Cd (high) in sediments from the mined areas contribute significantly to the ultra-high risk of these ecosystems, which might result in ecological collapse of the riverine systems. The calculated Nemerow multifactor index (YN) values of the mined sites implies extreme pollution. The coefficient of variation (CV), Pearson's correlation matrix, and principal component analysis (PCA) clearly indicate that heavy metals in water and sediments are from multiple rather than a single source. Although this study could not ascertain whether the mining activities are solely responsible for the elevated heavy metals in water and sediments from the dredge-mined sites since the study sites frequently experience other anthropogenic activities, the study showed that significant pollution and ecological adversities are associated with water and sediment from the dredged-mined sites.

Distribution, Sources, and Ecological Risk Evaluation of Heavy Metals in Surface Sediments of Taihu Lake

For the surface sediment samples of Taihu Lake in 2010, the eight physicochemical indices of pH, temperature, Eh, water content, porosity, grain size, total phosphorus, and Loss-on-ignition were measured and analyzed, along with the contents of nine heavy metals:Cu, Zn, Ni, Cr, Pb, Ba, Mn, Co, and V. The order of magnitudes of heavy metal content of surface sediments in Taihu Lake was:Mn>Ba>Zn>Cr>V>Ni>Pb>Cu>Co. This suggested that the contents of the nine heavy metals were beyond the background value, which had a close connection to the geology of the Taihu Lake Basin and were influenced by human activity to varying degrees. The clustering analysis and the spatial distribution of the heavy metals revealed that the concentrations of heavy metals in the North and South Taihu Lake sections decreased from the lake shore to the lake center, the concentrations of heavy metals in the West Taihu Lake section increased from the lake shore to the lake center, and the distribution of heavy metals in the center of the lake remained relatively uniform. According to the correlation study, the metal elements were positively correlated with one another to varying degrees, indicating that they originate from the same source of pollution. According to the PCA and PMF analyses, there were some different sources of heavy metals in Taihu Lake, in which the transportation and industrial complex source were the most important sources, the diagenesis was the second major source, and agriculture was the third major source. Furthermore, the heavy metal pollution was evaluated using the geoaccumulation and the potential ecological risk indices. This offers a solid theoretical backing for the future management of heavy metal pollution in Taihu Lake.

Geochemical dynamics of phosphorus and metals in sediments of a shallow coastal lake (Xuño Lake, Galicia-NW Iberian Peninsula)

The shallow lakes are important freshwater ecosystems, since they support much of biodiversity and ecosystem services of life on land. Shallow lakes are highly dynamic ecological entities that can exist in several alternative stable states through regime shift caused by a natural or human disturbance that exceeds ecological thresholds for biological communities composition and structure equilibria. The sediment as a reservoir has a key role in the limnological regulation of wetlands linked to the fluxes of nutrients and elements in the biogeochemical interplay with the water and macrophytes. For this reason, the role of sediment in the limnology of the shallow coastal lake of Xuño (NW Iberian Peninsula) was explored by seasonally monitoring the chemical composition of water and sediments, also according to macrophyte species. The shallow depth determines the high availability of light in the bottom and a well-mixed water column maintain the surface of the water–sediment interface oxygenated. The oxic conditions of the bottom implies a top-down regulation of the water column in the Xuño shallow lake that limits the diffusion of phosphorus and trace metals (Fe, Mn, Cu, and Co) to the water, buffering eutrophication or contamination levels by immobilization in the sediments. In fact, the concentration of Hg in the lake water in spring, and also its bioavailability, are high due to its release from the sediment in suboxic conditions. The cover of helophyte species Phragmites Australis and Schoenoplectus Lacustris showed differences in the assimilation of organic monoester and diester phosphorus forms in the sediment. However, the water of the Xuño Lake shows an eutrophic status by the nutrient input associated with the birds populations as indicated by microbiological data.