The accumulation of heavy metals (HMs) in lakes can pose a serious risk to aquatic ecosystems. Caohai Lake is the largest plateau freshwater lake in Guizhou Province, China. However, the spatial and ...temporal dynamics and ecological risks of HM contamination in Caohai sediments in recent years remain unclear. Here, we analyzed the HM content of sediments in Caohai Lake in 2022 and collected historical (2011–2021) data from published articles to explore the spatiotemporal distribution characteristics, toxicity risks and potential sources of HMs. The mean concentrations (2011–2022) of Ni, As, Cd, Zn, Hg and Pb in the Caohai Lake sediments were all higher than the background values, and the values of As (32.0 mg/kg), Cd (14.19 mg/kg), Pb (87.6 mg/kg) and Zn (406.2 mg/kg) were 1.9, 4.0, 2.4 and 1.3 times their probable effect level (PEL) values, respectively. Sediment As and Cd concentrations in Caohai Lake showed significant decreasing and increasing trends from 2011 to 2022, with mutation points occurring in 2018 and 2020, respectively. The Caohai Lake sediment aquatic life risk index (TRI) for HMs showed a gradual increase until 2019, when it reached a sudden change point, leading to a very high toxicity risk in 2020, with Cd contributing the most to the TRI (43.66). Cd, Pb and Zn, the main pollutants in the sediments of Caohai Lake, originate from traffic, mining and agricultural sources. Our integrated results demonstrated the severity of HM pollution in Caohai Lake and can be helpful for formulating reasonable pollution prevention and control measures.
Long-term fishing bans have spurred extensive debate regarding their impacts on ecosystem structures, functions, and water qualities. However, data on the effects of specific changes induced by ...fishing bans on ecosystem structures, functions, and water qualities in lakes are still lacking. Therefore, the present study addresses this knowledge gap by employing an Ecopath model to assess alterations in an ecosystem’s structure and function before (2011) and after (2021) the implementation of the fishing ban in Caohai Lake and its association with changes in water quality. (1) We observed a substantial reduction in the area covered by submerged aquatic vegetation after the ban, amounting to a 65% decrease in coverage compared with that before the ban, and a 60% reduction in the total ecosystem’s biomass. (2) Following the ban, the number of fish species increased from 7 to 14, and this was accompanied by a rise in the fish biomass from 14.16 t·km−2 to 25.81 t·km−2; a 4.5-fold increase in the total system consumption was observed, signifying accelerated energy and material flows within the ecosystem. (3) The fishing ban exhibited no significant impact on the total nitrogen concentration; however, it significantly reduced the water’s transparency and increased the total phosphorus, ammonia nitrogen, chemical oxygen demand, and chlorophyll contents (p < 0.05). This shift in nutrient dynamics fostered a transformation from a macrophyte-dominant lake to an alga-dominant lake. The fish abundance and diversity increase in closed-type macrophytic lakes, thereby accelerating energy and material flows within food webs. These findings present novel insights into the effective policy management of fishing bans within the Yangtze River Basin, thus enhancing our understanding of sustainable lake ecosystem management.
Classification trees (CT) have been used successfully in the past to classify aquatic vegetation from spectral indices (SI) obtained from remotely-sensed images. However, applying CT models developed ...for certain image dates to other time periods within the same year or among different years can reduce the classification accuracy. In this study, we developed CT models with modified thresholds using extreme SI values (CT
m
) to improve the stability of the models when applying them to different time periods. A total of 903 ground-truth samples were obtained in September of 2009 and 2010 and classified as emergent, floating-leaf, or submerged vegetation or other cover types. Classification trees were developed for 2009 (Model-09) and 2010 (Model-10) using field samples and a combination of two images from winter and summer. Overall accuracies of these models were 92.8% and 94.9%, respectively, which confirmed the ability of CT analysis to map aquatic vegetation in Taihu Lake. However, Model-10 had only 58.9–71.6% classification accuracy and 31.1–58.3% agreement (i.e., pixels classified the same in the two maps) for aquatic vegetation when it was applied to image pairs from both a different time period in 2010 and a similar time period in 2009. We developed a method to estimate the effects of extrinsic (EF) and intrinsic (IF) factors on model uncertainty using Modis images. Results indicated that 71.1% of the instability in classification between time periods was due to EF, which might include changes in atmospheric conditions, sun-view angle and water quality. The remainder was due to IF, such as phenological and growth status differences between time periods. The modified version of Model-10 (i.e. CT
m
) performed better than traditional CT with different image dates. When applied to 2009 images, the CT
m
version of Model-10 had very similar thresholds and performance as Model-09, with overall accuracies of 92.8% and 90.5% for Model-09 and the CT
m
version of Model-10, respectively. CT
m
decreased the variability related to EF and IF and thereby improved the applicability of the models to different time periods. In both practice and theory, our results suggested that CT
m
was more stable than traditional CT models and could be used to map aquatic vegetation in time periods other than the one for which the model was developed.
► Traditional CT couldn’t be applied without modification between time periods. ► 71.1% of the instability of traditional CT between time periods was due to EF. ► Our CT
m
could be used to map aquatic vegetation in time periods.
Numerous studies have demonstrated the feasibility of remotely sensing water clarity of lakes, reservoirs, and larger rivers using medium‐resolution spatial images. However, addressing relatively ...small rivers or river sections is very challenging due to the adjacency effect from the riverbanks. The objectives of this study are to quantify the minimum river width for water quality remote sensing and to validate the feasibility of using medium‐resolution spatial images for estimating the Secchi disk depth (SDD). A methodology was developed to quantify the minimum river width for water quality remote sensing using high‐resolution spatial images from WorldView‐2 and Pléiades. Our results suggest that the influential distance of the adjacency effect from the riverbank is 17.3 m, i.e., water pixels with a distance of more than 17.3 m from the shoreline experienced a minimal disturbance from the riverbank. For the 30 m spatial resolution HJ‐1A image (one of Chinese civilian satellites launched in 2008), the minimum river width is 64.6–98.5 m (the variation was determined according to the river flow direction and the pixel position relative to the shoreline). Using the sections that satisfied the minimum river width requirement, a significant estimation model was established between the spectral reflectance and the SDD (R2 = 0.94), demonstrating that the minimum river width recommended in this study is practical. This work is the first study to quantify the minimum river width for water quality remote sensing and thus provides a valuable reference for remote sensing of relatively small rivers.
Key Points
We developed a procedure for water pixel selection for river remote sensing
A minimum river width (MRW) of 64.6–98.5 m was identified for a 30 m image
A successful estimation of river water clarity proved the MRW effectiveness
Understanding PAH and OCP distributions and sources in lakes is necessary for developing pollutant control policies. Here, we assessed the occurrence, risk, and sources of PAHs and OCPs in the ...sediment of Caohai Lake. The PAHs were predominantly high-molecular-weight compounds (mean 57.5 %), and the diagnostic ratios revealed that coal, biomass burning, and traffic were the sources of PAHs. HCHs (6.53 ± 7.22 ng g−1) and DDTs (10.86 ± 12.16 ng g−1) were the dominant OCPs and were primarily sourced from fresh exogenous inputs. RDA showed that sediment properties explained 74.12 % and 65.44 % of the variation in PAH and OCP concentrations, respectively. Incremental lifetime cancer risk (ILCR) assessment indicated that hazardous PAHs in Caohai Lake sediment posed moderate risks to children and adults (ILCR>1.0 × 10−4), while the risk from OCPs was low; however, the recent influx of HCHs and DDTs requires additional attention.
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•PAHs were predominantly high molecular-weight PAHs and derived from coal, biomass burning and traffic sources.•DDTs dominated OCPs and fresh exogenous input of HCHs and DDTs should be given more attention.•PAHs in sediments pose a moderate risk to children and adults, while OCPs pose a low risk to humans.•Sediment properties affect PAHs and OCPs levels, and COPs content is mainly influenced by sediment MBC.
An integrated assessment of heavy metal (HM) contamination in dissolved matter, suspended particular matter (SPM) and sediments in lakes is essential. This study assessed the risks of HMs in the ...water, SPM and sediment of Caohai, China, and analyzed the changes in sediment HM contamination in conjunction with historical data. The HM transport was dominated by the SPM load, and the concentrations of Zn (179.07–1821.24 mg kg−1), Pb (53.63–181.46 mg kg−1), and Cd (3.68–21.31 mg kg−1) in SPM and sediment were 5.34–149.11 times higher than the upper continental crust (UCC) values. SPM and sediments were lightly to extremely polluted and had moderate to very high toxicity risks with Cd, Pb and Zn, and these three HMs originated from industrial and agricultural sources. The concentrations of Zn, Pb, and Cd in Caohai sediments increased by 36.7–187.9 % in 2022 compared to pre-2020. This research provides valuable reference data for the remediation of polluted karst lakes.
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•The Caohai sediment contents of Fe, Zn, Cr, Pb and Cd increased by 17.2–187.9 % compared to pre-2020.•The transport of HMs in SPM in Caohai ranged from 55.7 % to 81.5 %, and HM transport was dominated by the SPM load (lgKd >3.9).•SPM and sediments were lightly to extremely polluted with Cd, Pb and Zn and originated from agriculture and industry.•Cd, Zn, and Pb were mainly toxic, while Cd and Cr indicated potential health risks.
A large-scale photovoltaic (PV) power plant is composed of hundreds or thousands of solar panels, which makes fault diagnosis a challenging problem due to its complexity. It is known that the PV ...power output characteristics dramatically change with environmental conditions. Thus, it is difficult to distinguish a short-circuit line fault from mismatching conditions induced by partial shading or unbalanced generation. The article proposes a novel fault diagnosis scheme that is based on real-time system identification to determine normal or abnormal operations. It does not require any additional hardware or measurement support. The identification and analysis include both short- and long-term characteristics of the generation system to mitigate disturbances and improve the robustness. The effectiveness of the proposed scheme is validated by simulations and experiments under a wide range of test conditions.
Numerous studies have shown that ecological factor changes along the spatial gradient of urban and rural sites have a strong similarity to the temporal gradient of global change. Therefore, based on ...environmental gradients between urban and rural areas, a space-for-time substitution experiment called the "urban nature experimental field" method is developed to research the response of the terrestrial ecosystem to global climatic change. In recent related studies, the characteristics of ecological factors in urban and rural areas were observed in many cities around the world, most of which were focused on temperature and carbon dioxide. However, some reports showed that the disturbance from near-ground ozone was one of the most influential factors in determining the effectiveness and applicability of the method. We conclude that the disturbance of plant growth from variation of near-ground ozone concentrations between the urban and rural sites was negligible in the urban space-for-time substitution experiments.
Constructed wetlands (CWs) had been widely used to treat the tailwater from sewage treatment plants. However, the enduring effectiveness of CWs was still unclear. Therefore, this study aimed to ...investigate the chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) removal efficiencies (RE) of the Hongze CW (HZ-CW) after multi-years’ operation. The average COD RE were 7.6% and 15.14% in the 4th and 5th year, respectively. The NH4+-N RE was 78.33% and 46.04% in the 4th and 5th year, respectively, while the TP RE remained high at 66.86% and 64.68%. The high-throughput sequencing analysis revealed that the bacterial community of HZ-CW at the end of the 5th year exhibited a substantial abundance and diversity, and Proteobacteria and Bacteroidota were the dominant phyla with a relative abundance of 33.75–71.8% and 11.28–24.53% in different zones of HZ-CW. Ammonia oxidizing organisms (AOMs) presented much higher relative abundance (0.43–0.79%) in aerated pond (AP) and four free water surface flow CWs (FWS1–FWS4) than those of anammox bacteria, indicating the dominant role of nitrification in NH4+-N removal.
•We tested digital hemispherical photography (DHP) on submerged vegetation.•An exposure setting of 4–8 times the sky reference exposure was identified.•A photographic distance of 60–90cm is ...recommended for PAI estimation by DHP.•We proved the feasibility of DHP for PAI estimation for submerged vegetation.
Digital hemispherical photography (DHP) has been widely used to estimate the plant area index (PAI, a surrogate for leaf area index, LAI) for terrestrial vegetation. However, DHP has not been applied in aquatic environment fields for submerged vegetation, where only a few methods are available for LAI measurement. The objective of this study was to identify whether DHP could be used to estimate the PAI of submerged vegetation (the total projected area of leaf and stem per unit of ground surface area) using the submerged plant species Potamogeton malainus. The results suggested that the exposure setting and photographic distance from the water surface significantly influenced the gap fraction derivation of upward photographs taken from beneath the water surface. To derive the gap fraction accurately from upward photographs, we recommend an exposure setting of 4–8 times the sky reference exposure and photographic distances of 60–90cm from the water surface to take upward photographs. A simple model was developed to calculate the percentage of projected stem (or leaf) area deeper than the camera lens to the entire projected area of aquatic vegetation; the model was proven effective by field-truth data and could thus be used to compensate for the projected area that is undetected by the camera. Using our recommended exposure settings, photographic distance and adjusted model, a significant linear relationship was observed between the measured PAI and PAI estimated using DHP (p<0.001), and only a 5.1% deviation was found between the measured and estimated PAI. Therefore, DHP can be used to estimate the PAI for certain submerged vegetation species, such as Potamogeton malainus, using our recommended optimum procedure.
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