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The influence of bioturbation induced by bottom‐dwelling macrozoobenthos on nitrogen dynamics in lotic stream sediments remains unclear. In this work, we advance the understanding of faunal bioturbation in lotic environments by developing a fully‐coupled flow and multicomponent reactive transport model and investigate the influence of sediment reworking and burrow ventilation processes on nitrogenous transformations. The model results indicate that sediment reworking and burrow ventilation significantly increase nitrate (NO3−) influx, penetration depth, and reaction rates in the streambed. Denitrification rates were observed up to three times higher in beds with U‐shaped burrows compared to flatbeds. The ratio of mound height to stream water depth ratio (h/H0) is a dominant control on determining the relative importance of the sediment reworking and burrow ventilation processes in modulating nitrogenous reactions. A power‐law scaling framework is ultimately proposed to predict NO3− removal efficiency based on the Damköhler number in bioturbated lotic streambeds. Plain Language Summary: The increase in nitrate (NO3−) levels can harm rivers by causing problems like eutrophication, toxic algal blooms, and low oxygen levels. Microbes, like those involved in denitrification, can help reduce NO3− levels in the riverbed, where surface water and groundwater mix. Creatures like macroinvertebrates that live in the riverbed also play a role in how NO3− moves and is used. We wanted to know if these creatures, by disturbing the sediment and irrigating it, change how NO3− behaves in the riverbed. Our computer modeling showed that having U‐shaped burrows in the sediment can enhance the rate at which NO3− is removed, up to three times more than in flatbed sediments. As the ratio of the mound height to the total depth becomes less than 0.1, the influence of sediment reworking on NO3− influx and consumption rates decreases, and burrow ventilation becomes more important. We also came up with a way to predict NO3− removal efficiency in bioturbated riverbeds under flowing water conditions. These findings underscore the significance of bioturbation in rivers with moving water and have important implications for managing and restoring rivers. Key Points: Developing a Navier‐Stokes‐Brinkman‐Darcy‐Reaction fully‐coupled approach to study interplay between nitrogen cycling and faunal bioturbationSediment reworking and burrow ventilation processes could significantly alter the nitrogenous transformations in low flow environmentsA power‐law scaling framework can be used to predict nitrate removal efficiency within the bioturbated sediments from the Damköhler number [ABSTRACT FROM AUTHOR]

The boom in dam construction and continuous river‐lake exchange has had a profound impact on the transmission and transformation of riverine dissolved inorganic carbon (DIC). An in‐depth understanding of the change mechanisms of DIC concentrations and sources driven by dam operation and lake recharge is crucial for regulating greenhouse gas emissions and evaluating the impact of DIC on the global carbon cycle. This study investigated dam‐ and lakes‐driven DIC via the concentration and δ13C of DIC, combined with anions, cations, δD and δ18O in the main stream of the Yangtze River. DIC showed a decreasing trend from upper reach (2,262.31 ± 113.69 μmol kg−1) to lower reach (1,771.61 ± 89.36 μmol kg−1). Carbonate dissolution proportion (from 36.45% to 28.44%) and atmospheric CO2 proportion (from 37.51% to 22.94%) of DIC decreased from upper reach to lower reach, whereas soil CO2 proportion of DIC (from 26.01% to 48.63%) increased. The control of dam operation on DIC biogeochemical process was revealed from different time scales. From the perspective of short‐term seasonal changes (from 2020 to 2021), the mineralization of organic matter in the dry season strengthened CO2 degassing and calcite precipitation, reducing the DIC and increasing the proportion of soil CO2. Meanwhile, longer periods of runoff retention provided sufficient time for water–rock reactions in the wet season and increased the DIC and carbonate dissolution source in the reservoir area. On a long‐term scale (from 2009 to 2021), a decrease in pH driven by sediment mineralization contributed to an annual increase in DIC in the reservoir. The flow of lakes mixed into the mainstream was revealed by the enrichment of δ18O, and river‐communicating recharge decreased the DIC and carbonate dissolution source. We show that dam operation and lake inflow change DIC concentrations and sources and therefore need to be considered in the transmission and transformation processes of DIC in the river‐ocean continuum. [ABSTRACT FROM AUTHOR]

In this study, the sedimentary records, sources, and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in Dianchi Lake were analyzed. The concentrations of ΣPAH16 in the sediments of Dianchi Lake ranged from 368 to 990 ng/g, with an average value of 572 ng/g, peaking in 1988. Economic development, rapid population growth, and rapid growth of coal consumption have a greater impact on the HMW (high molecular weight) PAHs than on the LMW (low molecular weight) PAHs in the sedimentary environment. The results of the diagnostic ratios and PCA (principal component analysis) model show that the main sources of PAHs were coal and biomass combustion, as well as the fossil fuel combustion in individual years. The risk assessment results showed that the PAH concentrations in the sediment were within a safe range. In the past 100 years of sediment pore water, other 2–3 ring LMW PAHs were within a safe range (except for Phe, which reached chronic toxic pollution levels in some years). With an increase in industrialization and urbanization, the burning of fossil fuels such as coal and petroleum has increased, and some of the 4–6 ring HMW PAHs have reached chronic toxicity or even acute toxicity in the sediment pore water. [ABSTRACT FROM AUTHOR]

The long-term accumulation, burial and release of nutrients, such as carbon (C), nitrogen (N), and phosphorus (P) in lacustrine sediments are responsible for the global lake eutrophication. Interpretation of the spatiotemporal sedimentary record of nutrients (C, N, and P) in contrasting trophic level of lakes is helpful for understanding the evolutionary process of water eutrophication. Based on the radiochronology of 210Pbex and 137Cs, a comparative study of spatial and temporal concentrations, burial of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP), the sources of organic matter were conducted using sediment cores from two plateau lakes Dianchi (DC) and Fuxian (FX) of SW China. Results showed that concentrations and burial of C, N, and P in sediments of DC, a shallow hypertrophic lake with the maximum depth of 5.8 m, were both higher than those in FX, an oligotrophic deep lake with the maximum depth of 155.0 m. For both lakes the molar ratio of TOC/TN increased in the sediments moving from north to south. The values of TOC/TN molar ratios increased over time in DC and were higher than in FX. The extremely high values of TOC/TN appeared in the central and southern parts of FX, indicating the impacts of accumulation effect and sediment focusing in the deeper region and indirect supplement from the Lake Xingyun (XY), an adjoining lake connected with FX via the Gehe River. Time-integrated sources identification in DC indicated the contribution of allochthonous sources was dominant over the past few decades, which contributed to the increased trophic level of the lake. The comparison of relationships of carbon accumulation rates (CAR), nitrogen accumulation rates (NAR), and phosphorous accumulation rates (PAR), the ratios of N/P and the utilizations of N and P fertilizer between DC and FX implied that both of N and P inputs should be limited for reducing the trophic level, but N control was predominant in comparison with P for both lakes. The results indicated that caution is required in plateau lakes to limit transition from oligotrophic to eutrophic in these lakes. [ABSTRACT FROM AUTHOR]

An analysis of the correlation between polycyclic aromatic hydrocarbons (PAHs) and economic parameters demonstrates that the total population, gross domestic product, coal consumption, petroleum, temperature, and day consumption significantly affect PAH concentrations in Dianchi Lake, Yunnan province, China. An artificial neural network (ANN) model was developed to predict the trend in PAH concentrations in the sediments of Dianchi Lake over the next 10 years based on current indicators of economic development. The ANN model estimated the concentration of PAHs from 1980 to 2014. The model was evaluated using available observations for the historical trends; concentrations of PAHs in the sediments of Dianchi Lake are calculated to be at 2128.1 ng/g in 2025 and are expected to decline up to 1044.3 ng/g by 2030. These concentrations are considered relatively high because of their impacts on the health of people and aquatic organisms and the development of surrounding industries. We show the importance of the socioeconomic and climate factors in increasing the pollution levels. Our results could support the local government to formulate effective measures to reduce the pollution levels in the lake. [ABSTRACT FROM AUTHOR]

Remote sensing has become an essential technique in water environment monitoring. However, the cloud contamination of remote sensing images breaks its spatial and temporal continuity in practical application. The current cloud removal algorithms always based on the hypothesis that the ground surface has no significant changes temporally, which is not proper for optically complex water body. Therefore, to overcome the weakness of current cloud removal algorithms on temporally fast-changing landscapes, a temporal unmixing-based cloud removal (TUBCR) algorithm is proposed to estimate the under-cloud information of optically complex water images. In this algorithm, the spatial information and temporal information were separated into temporal abundance images and temporal endmembers. By extracting the high temporal resolution endmembers, the fast-changing water information were estimated. The performance of the proposed algorithm was compared with those of two widely used cloud removal algorithms: the modified neighbourhood similar pixel interpolator (mNSPI) algorithm and the weighted linear regression (WLR) algorithm. The results of four simulated datasets (500 images in total) and two real Geostationary Ocean Colour Imager (GOCI) datasets (8 images in total) show that the proposed algorithm performed better in both quantitative indexes and visual effect compared with the mNSPI algorithm and the WLR algorithm. In satellite image time series, the proposed algorithm could accurately estimate under-cloud water information and correct the offsets of the statistical temporal trends that caused by cloud contamination. Hence, theoretically, the proposed TUBCR algorithm altered the similar pixel-based strategy of classic methods and got a satisfied performance in fast-changing water images. In applications, the TUBCR algorithm has great potential to improve the spatiotemporal coverage of optically complex water remote sensing. [ABSTRACT FROM AUTHOR]

The total amount and morphology of nitrogen and phosphorus in sediments have important environmental significance. The study of the ecological risk assessment of nitrogen and phosphorus in sediments is important to understand the environmental quality of water body in the basin. In this study, taking the Futunxi Basin of Fujian Province as an example, the single factor index and bioavailability coefficient method were used to evaluate the ecological risk of nitrogen and phosphorus in the sediments, and reveal the spatial change and environmental significance of the nitrogen and phosphorus forms. The results showed that different morphological components of the bio-available nitrogen were distributed as organic sulfide bound nitrogen (SOEF-N) > iron-manganese oxidized nitrogen (SAEF-N) > weak acid leached nitrogen (WAEF-N) > ion exchange nitrogen (IEF-N). The inorganic phosphorus included the highest proportion of metal oxide bound phosphorus (NaOH-P), followed by calcium bound phosphorus (HCl-P). The proportion of reduced phosphorus (BD-P) was even lower, and the proportion of weakly adsorbed phosphorus (NH4Cl-P) was the lowest. The results of single factor pollution index showed that the sediment nitrogen in the study area mainly caused moderate pollution and phosphorus mainly caused light pollution. By contrast, the results of the bioavailability index method indicated that nitrogen mainly caused light pollution, and phosphorus mainly caused clean pollution in sediments. Combined with the characteristics of social economy and environment in the study area, it can be inferred that the bioavailability index method based on comprehensive evaluation of total amount and morphology can better characterize the spatial change and ecological risk of nitrogen and phosphorus in sediments. [ABSTRACT FROM AUTHOR]

Xu X, Liu H, Jiao F, Ren Y, Gong H, Lin Z, and Huang C. 2020. Influence of climate change and human activity on total nitrogen and total phosphorus: a case study of Lake Taihu, China. Lake Reserv Manage. 36:186–202. Climate change and human activities can influence lake total nitrogen (TN) and total phosphorus (TP), affecting the overall health of the lake. These factors must be considered for planning and management of lakes in order to maintain their ecosystem integrity and sustain societal development. Using the Ensemble Empirical Mode Decomposition Method (EEMD) and the nonparametric Mann–Kendall test, the changes of TN and TP and their relationship to climate change and human activities were quantitatively evaluated on multiple time scales ranging from 1952 to 2010 using Meiliang Bay of Lake Taihu (China) for a case study. Patterns of TN change could be divided into 4 time scales: 2.73, 5.89, 25.33, and 45 yr, with an evident increasing long-term trend. Patterns of TP change were divided into 2.49, 6.4, 11.5, and 43 yr time scales with an increasing long-term trend. On short time scales, TN and TP were positively correlated with gross domestic product (GDP) and urban area, and negatively correlated with crop area and animal production. For the long-term trends, TN and TP were positively correlated with temperature, GDP, urban area, and animal production, and negatively correlated with precipitation and crop area. Both TN and TP abruptly changed in 2000, consistent with the abrupt changes in temperature, precipitation, and urban area. Collectively, results revealed that specific human activities in the watershed affected TN and TP in the sediments both on short-term and long-term scales, while global climate change affected TN and TP in the sediments on long-term scales. These results suggest that climate change and human activities must be considered to manage and protect lakes. [ABSTRACT FROM AUTHOR]

A spectral–temporal-unmixing-based multitemporal image fusion (MTIF) algorithm is proposed to fuse Geostationary Ocean Color Imager (GOCI) and Himawari images. The algorithm was applied to two data sets. The fusions are quantitatively and qualitatively compared with four widely used algorithms. The results show that the MTIF algorithm performs better using both evaluation indexes and visual comparisons. For optical complex water monitoring, the MTIF-derived chlorophyll-a concentration (${C} _{{\text {chla}}}$) map has better spatial detail and temporal trends compared with the other algorithms. For cloudy images, the MTIF algorithm can estimate part of the undercloud water reflectance information: when there are more than 32.6 cloud-free pixels in the current study area, the MTIF algorithm can successfully recover the under cloud information. The MTIF algorithm has great potential to advance the monitoring of optical complex inland water. [ABSTRACT FROM AUTHOR]

Purpose: Variation in C/N/P stoichiometry during sediment burial is related to elemental biogeochemistry cycles from the hydrosphere to the lithosphere. However, C/N/P stoichiometry change in lakes is still unclear although lakes are an important burial site of terrestrial matter. The purpose of this study was to determine the variation in C/N/P stoichiometry and its influencing factors in the burial processes of lake sediments. Materials and methods: Two sediment cores (cores 4 and 5) were collected from a plateau lake (Dianchi Lake, China) in July 2014. The CRS 210Pb dating model of was used to estimate the vertical chronological distribution for each layer. Total, organic, and inorganic carbon (TC, TOC, TIC), nitrogen (TN, TON, TIN), and phosphorus (TP, TOP, TIP) were analyzed to determine variation patterns in the C/N (RCN, ROCN, RICN), C/P (RCP, ROCP, RICP), and N/P ratios (RNP, RONP, RINP) in lake sediments. Results and discussion: The results showed that TOC, TON, and TIP were the main constituents of TC, TN, and TP in both sediment cores, respectively. After 1960, the burial rates of TOC and TON in core 4 exhibited rapidly increasing trends, coincident with TC and TN. In core 5, the increase occurred after 1980. Significant differences in C/N/P stoichiometry were observed in cores 4 and 5, dominated by allochthonous and autochthonous sources, respectively. RCP and RNP in core 4 were higher than in core 5; the difference in RCN was insignificant. RCN exhibited irregular large fluctuations in the middle layer, with mean values of 20.9 ± 4.0 and 17.3 ± 8.1 for cores 4 and 5, respectively. RCP and RNP declined rapidly with time, indicating that the losses of C and N might be higher than that of P. ROCN, ROCP, and RONP followed the same vertical decreasing pattern as RCN, RCP, and RNP, but RICN and RINP did not. Mineralization could be the primary driver and different sources played a regulatory role in the temporal variation of stoichiometry. Conclusions: Sediment stoichiometry (RCN, RCP, RNP) decreased with time might be mainly due to selective outcome of mineralization and be regulated by different organic matter sources. RCP, ROCP, RNP, and RONP showed significantly decreasing trends with age, whereas RCN and ROCN were relatively consistent. Vertical distribution of inorganic ratios differed from that of organic and total proportions. Further research is needed to determine influencing factors on these ratios and to clarify the role of C/N/P stoichiometry in freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Solar ultraviolet (UV) radiation exhibits a significant degradation for dissolved organic matter (DOM) in natural water ecosystems. However, research on photodegradation process of terrestrial components (e.g., humic-like substances) of DOM are limited due to drastic water dilution and rapid degradation. Here, photochemical degradation of terrestrial soil DOM with abundant humic-like substances from different land use were investigated by utilizing spectral technologies. Simulated UV radiation caused obvious losses on concentration, component structures, and fluorescence characteristic of soil DOM samples. The correlations between absorption specific parameters (a280, SUVA254, and SR) and dissolved organic carbon (DOC) were especially pronounced (p < 0.05), which could be used as valid indicators to determine changes in DOM composition and molecular size during photobleaching process. The decreases of DOM fluorescence intensity were corresponded to first-order kinetic and half-life reactions. The greatest reduction on fluorescence intensity (31.56–81.97%) belonged to peak C (i.e., humic-like substances). Overall, DOM from forest and grass soil ecosystems was more easily photochemical degraded than anthropogenic soil DOM. Enhancive contribution of fresh DOM formed by photodegradation increased autochthonous characteristic and bioavailable nutrition by increasing biological index (BIX) values and ammonia nitrogen (NH4+–N) concentration. The slight microbial decomposition effects on DOM happened in unsterilized dark condition. Our findings provided insights for understanding the rapid photodegradation processes of composition and structure of terrestrial DOM. [ABSTRACT FROM AUTHOR]

Purpose: Large additions of organic carbon (OC) have been introduced into the carbon cycle of lakes from algae during the process of lake eutrophication. The impact of eutrophication on OC burial and CO2 fixing has been widely studied; however, there is still a gap regarding the impact of excess OC from algae on sedimentary OC mineralization. In this study, we aim to fill this gap by analyzing in situ measurements. Materials and methods: Three pairs of sediment cores collected from a plateau lake (Dianchi Lake) in 2006 and 2014 were used to estimate the accumulation loss rate (ALR) of OC (and thus the total mineralization rate) in the sediment. n-Alkanes, measured from the same sedimentary cores, were used to identify the source of OC. An OC mineralization experiment in a laboratory was used to confirm the enhanced effect of excess phytoplankton carbon on ALR and reveal the potential influence of microorganisms. Results and discussion: The results indicate that the sedimentary core (core 3), with high excess OC from algae (located in an algal bloom area), possessed a higher ALR (85.66%) and a higher attenuation coefficient (0.078), indicating the low burial efficiency and short mineralization duration of OC. Sedimentary core 1, controlled by terrestrial OC, had a relatively lower ALR (64.60%) and lower attenuation coefficient (0.029), indicating a high burial efficiency and long period of OC mineralization. The mineralization of OC in core 2 was impacted by terrestrial and endogenous OC, with an ALR of 72.00% and attenuation coefficient of 0.064, which is between that of cores 1 and 3. Excess OC from algae corresponded to an increase in ALR by 32.60% when comparing core 1 to core 3. The increased ALR and attenuation coefficient could be caused by excess OC from algae. Conclusions: Sedimentary OC mineralization indicates that the ALR with dominantly allochthonous OC (64.60%) is much lower than that controlled by autochthonous OC (85.66%). Excess OC from phytoplankton increases the mineralization of OC: not only via increased ALR but also increased mineralization speed. The laboratory experiment on the mixture of algae and sediment suggested that excess phytoplankton OC increased the emission of CO2 by 20–70% (mineralization rate). [ABSTRACT FROM AUTHOR]

In remote sensing analyses of water colour, suspended particle size is an important optical parameter that also plays an important role in inland and coastal biogeochemical processes. Knowledge of the suspended particle size and its changes in month and area can be used to assess the contributions by suspended particulate matter to backscatter coefficient, particle sinking, and carbon sequestration under lake water. In this study, in situ samples collected in the summer and winter from Hongze Lake (HZL), 2016, were used to develop an empirical model to estimate the median diameter (DV50) of suspended particle sizes. The spatial distributions of DV50 were derived using 37 WFV (Wide Field Viewer) images of GF-1 (GaoFen-1), China, and the fluctuational diversification and the potential influencing factors were discussed. Several crucial findings can be drawn: (1) the empirical band ratio algorithm Rrs,green: Rrs,red was suitable for DV50 estimation with a coefficient of determination (R2) of approximately 0.7 for the modelling data. In addition, the validation data showed that the MAPE (mean absolute percentage error) is below 34%, the RMSE (root mean square error) is less than 4.2 μm, and the Mean ratio is close to 1; (2) the average median particle size shows an increasing trend from the northeast of the lake (NE) to Chengzi Lake (CZL) and the wetland (WL) in HZL from 2015 to 2016; (3) the DV50 of HZL is higher in summer than in the other seasons during the study period; (4) the fluctuation in hydrological factors, especially the monthly water discharge and flow, might be the driving force behind the seasonal variations in DV50 of HZL; and (5) channel transportation reduced DV50, and the reduced amplitude might be more than 22%. [ABSTRACT FROM AUTHOR]

Sediment resuspension is closely related to the endogenetic release of nutrients in Lake Taihu. Thus, understanding the factors associated with sediment resuspension is important. In this study, a new technology, which integrates a hydrodynamic model and remote sensing techniques, was applied to derive the distribution of the erosion flux and obtain the spatially variable critical shear stress. Then, the spatially variable critical shear stress was used in the sediment simulations at Lake Taihu. Compared to the traditional model, based on uniform values of critical shear stress, the new method, using variable values of critical shear stress calibrated from the Geostationary Ocean Color Imager (GOCI) data, significantly improved the sediment simulations at Lake Taihu. Based on the erosion flux from August 6-8, 2013, the correlations between erosion and wind speed, wind fetch, mud depth, and water depth were analyzed for different subsections and spots in Lake Taihu. The potential sources of error were also addressed. Further improvement of the model is necessary. [ABSTRACT FROM AUTHOR]

Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianchi Lake, organic and inorganic phosphorus and nitrogen forms were analysed. The 210Pb radiometric dating method was employed to study temporal changes in the phosphorus and nitrogen pools in Dianchi Lake. The result show that the total phosphorus (TP) and total nitrogen (TN) were both at high concentrations, ranging from 697.5-3210.0 mg/kg and 1263.7-7155.2 mg/kg, respectively. Inorganic phosphorus (IP) and total organic nitrogen (TON) were the main constituents, at percentages of 59%-78% and 74%-95%, respectively, in the sediments. Spatially, there was a decreasing trend in phosphorus and nitrogen contents from the south and north to the lake centre, which is related to the distribution pattern of local economic production. The burial rates of the various phosphorus and nitrogen forms increased in same spatially and over time. Particularly in the past two decades, the burial rates doubled, with that TN reached to 1.287 mg/(cm2·yr) in 2014. As the most reactive forms, nitrate nitrogen (NO3-N) and ammonia nitrogen (NH4-N) were buried more rapidly in the south region, implying that the potential for releasing sedimentary nitrogen increased from north to south. Based on their concentrations and burial rates, the internal loads of phosphorus and nitrogen were analysed for the last century. A TP pool of 71 597.6 t and a TN pool of 81 191.7 t were estimated for Dianchi Lake. Bioavailable phosphorus and nitrogen pools were also estimated at 44 468.0 t and 5429.7 t, respectively, for the last century. [ABSTRACT FROM AUTHOR]

Two sediment cores were collected from Dianchi Lake, a plateau lake in Southwest China, to study the temporal trends and to investigate the sources of sedimentary deposited polycyclic aromatic hydrocarbon. The ΣPAH16 concentration in the two sediment cores ranged from 172.5 to 2244.8 ng/g and from 211.4 to 1777.8 ng/g, with mean values of 1106.2 and 865.1 ng/g, respectively. Three temporal trends for the ΣPAH16 concentration and the composition of PAHs in Dianchi Lake all showed three typical changing stages: (1) slight changes in deeper segments before the 1950s; (2) a rapid increase in PAH concentrations between the 1960s and 1990s; and (3) a slight reduction from the 1990s onward. These trends differ from those observed in developed countries due to differences in the timing of industrialization and urbanization processes. According to the results of the molecular ratios and principal component analysis, the PAH deposition was dominated by coal combustion, wood combustion, and vehicle emissions before and after the 1960s, respectively. [ABSTRACT FROM AUTHOR]

We examined the relationship between, and variations in, particulate organic carbon (POC) and particulate organic nitrogen (PON) based on previously acquired ocean and inland water data. The latitudinal dependency of POC/PON is significant between 20 and 90° N but weak in low-latitude areas and in the Southern Hemisphere. The mean values of POC/PON in the Southern Hemisphere and Northern Hemisphere were 7:40±3:83 and 7:80±3:92, respectively. High values of PON/POC appeared between 80-90 (12:2±7:5) and 70-80° N (9:4±6:4), while relatively low POC/PON was found from 20 (6:6±2:8) to 40° N (6:7±2:7). The latitudinal variation of POC/PON in the Northern Hemisphere is much stronger than in the Southern Hemisphere due to the influence of more terrestrial organic matter. Higher POC and PON could be expected in coastal waters. POC/PON growth ranged from 6:89±2:38 to 7:59±4:22 in the Northern Hemisphere, with an increasing rate of 0.0024 km from the coastal to open ocean. Variations of POC/PON in lake water also showed a similar latitude-variation tendency of POC/PON with ocean water but were significantly regulated by the lakes' morphology, trophic state and climate. Small lakes and high-latitude lakes prefer relatively high POC/PON, and large lakes and low-latitude lakes tend to prefer low POC/PON. The coupling relationship between POC and PON in oceans is much stronger than in inland waters. Variations in POC, PON and POC/PON in inland waters should receive more attention due to the implications of these values for the global carbon and nitrogen cycles and the indeterminacy of the relationship between POC and PON. [ABSTRACT FROM AUTHOR]

Reforestation and afforestation have been implemented over large regions in China for decades, and this has significantly reduced dust storms, desertification and soil/water erosion in China. However, the quantificational evaluation of the reforestation program in China is still incomplete, especially in the southwest China, due to the limitation of survey data. In order to assess the effects of reforestation on soil erosion in southwest China, a subtropical monsoon region with acid red soil, a representative watershed (Dianchi, Yunnan, in southwest China), was selected to study the effect of reforestation on soil erosion over nearly five decades. The land surface soil samples and sedimentary core in this watershed were examined in 2012 to evaluate the soil erosion and sediment deposition during the period of deforestation and reforestation. The results from the multi-source indexes (nutrients, radionuclides, metallic and isotope elements) measurement from soil samples and analyses (composite fingerprinting, remote sensing and geographic information system) indicate that reforestation significantly reduced the presence of sand from surrounding basin via the sedimentary records. Natural forests had the greatest soil conservation capacity, followed by economic forests and farmland, according to a composite fingerprinting. The distribution of total phosphorus, total nitrogen (TN), total organic carbon (TOC) and isotope carbon (δC) presents a high consistency to the results of the composite fingerprinting. The loss rate of TN and TOC in farmland is much greater than that in forest. Reforestation will thus increase the storage of TN and TOC in the long term, although this storage is lower than that in farmland during a short time due to the application of fertilizers. The logging of economic forests will significantly increase soil erosion in this region because of low grass coverage. Recommendations include limiting the period of logging in economic forests to periods outside the rainy season and intercropping other kinds of indigenous trees or grasses to reduce soil erosion. [ABSTRACT FROM AUTHOR]

Although remote sensing technology has been widely used to monitor inland water bodies, the lack of suitable data with high spatial and spectral resolutions has seriously obstructed the practical development of inland water color remote sensing. An inversion-based fusion (IBF) algorithm is proposed to fuse water color and high-spatial resolution images. The algorithm was applied to two datasets: The Hyperion simulated dataset (dataset #1) and a pair of Environmental Satellite 1 (HJ1, launched by China in 2009) and medium resolution imaging spectrometer images (dataset #2). The fusions are quantitatively and qualitatively compared with three widely used algorithms. The results show that the IBF algorithm performs better using both evaluation indexes and visual comparisons. A discussion of the free parameter window size n and the contribution of the low-resolution image (LRI) to the spatial distribution ($w_{{{\rm LRI}}}$) shows that a larger n will result in both greater model errors and better control of geometric errors, whereas $w_{{{\rm LRI}}}$ helps stabilize the algorithm. Finally, chlorophyll-a concentration maps are developed from the fusions. The significant advantage of the IBF-derived chlorophyll-a concentration map indicates that the IBF algorithm has the potential to advance the monitoring of optical complex inland water. [ABSTRACT FROM PUBLISHER]

An integrated system including eutrophication simulation and algal bloom predication was established and applied in Lake Taihu. The mechanic models, which are based on a three-dimensional numerical model coupling hydrodynamic module, pollutant transport module, suspended sediment resuspension module, wind wave module and algal bloom predication module, can simulate not only the single function such as current pattern, nutrient distribution, sediment concentration and wave height field, but also the interaction among them. Using these models, some complex phenomenon such as endogenous pollution can be simulated. In the study, some key technologies are introduced to make the simulation reasonable and feasible. First, a new method for predicting algal bloom is introduced. Differing from the traditional phytoplankton dynamic model, judging the algal bloom through biomass or chlorophyll concentration, the method quantitatively estimates algal growth state switching among bloom, collapse and steady based on algal stability criterion in water column. Second, the sediment resuspension is estimated using calibrated critical shear stresses derived from remote sensing data and the wave-enhanced bottom stress during the windy days. Third, a user-friendly operation environment based on plug-in development and geographic information system is developed. The tests demonstrated that the system could both simulate the reactive solutes such as BOD and DO and the suspended sediment correctly under interaction of gravity and turbulent diffusion. The simulation results demonstrated that the system could obtain reasonable and reliable simulated results in Lake Taihu. [ABSTRACT FROM AUTHOR]

ABSTRACT In order to explore the degree of contact between hydrophilic blocks and the substrate, the dewetting behavior of Langmuir-Blodgett (LB) films of polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) induced by PMMA-selective acetone vapor were investigated by atomic force microscopy (AFM) for the first time. With the annealing of acetone vapor, the LB films of PS- b-PMMA undergo the swelling and coalescing of aggregates, the formation of bicontinuous patterns, the formation of droplets, and the periodic increase and decrease of droplets. The emergence of the bicontinuous patterns indicates that the dewetting occurs via the spinodal dewetting mechanism. The periodic droplet evolution is a novel phenomenon observed for the first time and quite different from the single droplet evolution of spin-coated films, which is probably due to the degree of contact between PMMA blocks and the substrate in the LB films being larger than that in the latter. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 825-830 [ABSTRACT FROM AUTHOR]

Land target-based atmospheric correction methods over inland waters are an effective alternative method for when the standard or improved atmospheric correction method that is based on water is invalid. The type of aerosol model that is selected and land dark target that is distinguished are two key factors that could determine the atmospheric correction’s accuracy. We present an improved land target-based iterative method [denoted as dense dark vegetation (DDV)-WC] for the atmospheric correction of Moderate Resolution Imaging Spectroradiometer (MODIS) over Lake Taihu. The improvements include the use of aerosol models in Optical Properties of Aerosols and Clouds (OPAC), which fully consider the impact of relative humidity (RH) on aerosol properties, and a rigorous land dark target selection rule (DDV-WC-Selection). The DDV-WC algorithm includes three steps: the selection of DDV pixels from lakeshore areas, the retrieval of the aerosol optical thickness (AOT) at 550 nm (AOT550) for the selected DDV pixels, and the retrieval of the remote sensing reflectance (Rrs) over water. The AOT550 inversion accuracy of different aerosol models in OPAC is tested in Lake Taihu. The “continental clean model” has the best performance compared with five other aerosol models for every month of the year. Therefore, the aerosol model of the DDV-WC algorithm is fixed to the “continental clean model” in Lake Taihu because of its stable and excellent performance. When using the “continental clean model” to perform these retrievals, the DDV pixels selection (DDV-WC-Selection) in the DDV-WC method (\text MRE(\text Mean\;\text Relative\;\text Error) = 14.63\% ) is more reliable than the DDV pixels selection (DDV-Selection) in the MODIS V5.2 method (\text MRE = 17.24\% ). The atmospheric correction of MODIS indicates that this approach produces superior performance in the green and red bands but poor results in the near-infrared (NIR) and blue bands. The MRE is only 13.15% at 645 nm. These findings illustrate that the DDV-WC algorithm is a practical MODIS atmospheric correction method for inland turbid waters. [ABSTRACT FROM PUBLISHER]

To accurately observe the dynamic concentration of total suspended matter (CTSM) by geostationary satellite, Geostationary Ocean Color Imager (GOCI), a new, regionally empirical combination algorithm, was developed based on the in situ measurement of water properties. Also, the ability of GOCI (with a 1 h temporal resolution) to capture dynamic change inCTSMwas evaluated using in situ buoy-measured data. The validation results indicate that the combination algorithm (combination of two- and three-band ratio algorithms) can achieve acceptable retrieval results forCTSM, with 34.52% root mean square error percentage (RMSP) for validation data and 45.01% RMSP for GOCI match-up points. The depth of reflectance valley at 680 nm (Rrs-depth,680) is considered as an index for deciding whether to utilize a two- (Rrs-depth,680 ≤ 0.005) or three-band (Rrs-depth,680 > 0.005) algorithm in the combination algorithm. This combination algorithm overcomes some shortcomings of two- and three-band ratio algorithms ofCTSMin turbid productive water. The results show that sediment resuspension will significantly change the optical properties of water and decrease the universality of theCTSMretrieval algorithm in the presence of a large area of algae. The influence of sediment resuspension on theCTSMretrieval algorithm is significant in the central lake but less so in the other four lakes studied due to lake morphology and algal biomass. [ABSTRACT FROM AUTHOR]

Treatment of eutrophication and algal blooms in large shallow lakes has been constrained by the endogenetic release of nutrients from sediment resuspension despite the well-controlled input of nutrients from surrounding land in Taihu Lake, China. In this study, we propose a method to simplify regionally empirical algorithms for total suspended matter (${{C}_{{\rm{TSM}}}}$), chlorophyll-a (${{C}_{{\rm{Chl\hbox{-}a}}}}$), and phosphorus concentration (${{C}_{\rm{p}}}$) for the Geostationary Ocean Color Imager (GOCI) for Taihu Lake. The results show that the GOCI-derived ${{C}_{{\rm{TSM}}}}$, ${{C}_{{\rm{Chl\hbox{-}a}}}}$, and ${{C}_{\rm{p}}}$ match well with the in situ measured data. Based on the validated synchronous and timely observation data (${{C}_{{\rm{TSM}}}}$, ${{C}_{{\rm{Chl\hbox{-}a}}}}$ and ${{C}_{\rm{p}}}$) from GOCI level-1b data, the interaction of phosphorus with algae and suspended sediment were analyzed from August 6 to August 9, 2013. The results indicate that phosphorus released from sediment resuspension is significant in Taihu Lake, with a high spatial–temporal variation. The effect of the restriction of nutrients (nitrogen and phosphorus) on algal growth varied temporally and spatially with the hydrodynamic characteristics of the lake. In most cases, restricted phosphorus in the lake is the primary reason for the algal growth, especially in open regions such as Center Lake (CL), Northwestern Lake (NWL), and Southwestern Lake (SWL). Both nitrogen and phosphorus are the restrictive factors to algal growth in Meiliang and Gonghu Bays. More attention should thus be focused on the endogenetic release of phosphorus in Taihu Lake when treating eutrophication and algal blooms in addition to controlling the input of nitrogen and phosphorus from surrounding land. [ABSTRACT FROM PUBLISHER]

Humans have had a significant impact on the terrestrial pedosphere through activities such as agriculture and urbanization. The effects of human activities on land use and the related environmental changes were investigated through point and areal studies surrounding Meiliang Bay, which is an open area of extreme eutrophication in Taihu Lake, China. This study used remote sensing and environmental-tracer profiles [total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), grain size, and geochemical parameters] to determine the causes of changes in land use and the associated environmental parameters. The results of LUCCs (Land use/cover changes) indicate that over the past three decades, total farmland decreased by 862.49 km2, with an annual decrement rate of 28.75 km2/year, and total urbanized land increased by 859.71 km2, with an annual growth rate of 28.66 km2/year. The geochemical results indicate that the trophic state of Taihu Lake was persistently intensifying and that the TN, TP, and TOC concentrations increased twofold, threefold, and twofold, respectively, from 1949 to 2010. The sources of TN, TP, and TOC were highly similar after 1975. However, before 1974, TN and TP originated from different sources than TOC. The grassland and woodland around the lake retain nutrients and sand from the land of study area. The increase in urbanized land and tertiary industries significantly increased the sediment concentrations of TN, TP, and TOC after 1980. [ABSTRACT FROM AUTHOR]

Assessments of specific inherent optical properties (SIOPs) and their variability in highly turbid and productive inland waters are essential for the accurate estimation of water quality. A new optical classification method including two classification criteria [i.e., normalized remote sensing reflectance slope (NS), and normalized remote sensing reflectance depth (ND)] was developed to divide remote sensing reflectance into four classes, i.e., class 1 (NS < −0.0017 and ND < 0.21) is low turbid and productive water; class 2 (NS < −0.0017 and ND > 0.21) is low turbid and high productive water; class 3 (NS > −0.0017 and ND < 0.09) is high turbid and low productive water; and class 4 (NS > −0.0017 and ND > 0.009) is high turbid and high productive water. The relationships between phytoplankton absorption at 440 nm [ a(440)] and chlorophyll- a concentration [ C] as well as between particle backscattering coefficient at 440 nm [ b(440)] and total suspended matter concentration ( C) after classification were obtained from a large number of in situ data in Lake Taihu. The measured specific phytoplankton absorption $$[ {a_{\text{ph}}^{*} \left( \lambda \right)} ]$$ and particle backscattering coefficient $$[ {b_{\text{bp}}^{*} \left( \lambda \right)} ]$$ show significant variations even within the same class. The mean values of $$a_{\text{ph}}^{*} \left( \lambda \right)$$ at 440 nm $$[ {a_{\text{ph}}^{*} \left( {440} \right)} ]$$ for each class are 0.048 ± 0.013, 0.060 ± 0.012, 0.083 ± 0.021, and 0.056 ± 0.017 m/mg, respectively. The mean values of $$b_{\text{bp}}^{*} \left( \lambda \right)$$ at 440 nm $$[ {b_{\text{bp}}^{*} \left( {440} \right)} ]$$ for each class are 0.035 ± 0.01, 0.024 ± 0.004, 0.041 ± 0.009, and 0.038 ± 0.009 m/g, respectively. The power functions of SIOPs and water constituents' concentration indicate that $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ vary with C and C. The validation results show that our proposed values for $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ cover a very wide range of water optical properties, which are characterized from clear water to highly turbid productive water. The validation results also suggest that the retrieval accuracy of C and C bio-optical model was improved after classification. The root mean square error (RMSE) of C was improved from 14.18 to 7.43 μg/L (mean value of all classes) and RMSE of C was improved from 32.98 to 26.10 mg/L (mean value of all classes). Thus, the temporal and spatial variation of $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ should be considered in the bio-optical retrieval model of water quality. Graphical Abstract: In complex optical properties of inland water, retrieving the water constituents with high accuracy needs to classify the water optical properties from the remote sensing spectrum by optical classification method. The figure shows the water color examples of each class[Figure not available: see fulltext.]. [ABSTRACT FROM AUTHOR]

The diffuse attenuation coefficient,Kd(λ), is an important water optical property. Detection ofKd(λ) by means of remote sensing can provide significant assistance in understanding water environment conditions and many biogeochemical processes. Even when existing algorithms exhibit good performance in clear open ocean and turbid coastal waters, accurate quantification of highly turbid inland water bodies can still be a challenge due to their bio-optical complexity. In this study, we examined the performance of two typical pre-existingKd(490) models in inland water bodies from Lake Taihu, Lake Chaohu, and the Three Gorges Reservoir in China. On the basis of water optical classification, newKd(490) models were developed for these waters by means of the support vector machine approach. The obtained results showed that the two pre-existingKd(490) models presented relatively large errors by comparison with the new models, with mean absolute percentage error (MAPE) values above ~30%. More importantly, among the new models, type-specific models generally outperformed the aggregated model. For water classified as Type 1 + Type 2, the type-specific model produced validation errors with MAPE = 16.8% and RMSE = 0.98 m−1. For water classified as Type 3, the MAPE and RMSE of the type-specific model were found to be 18.8% and 1.85 m−1, respectively. The findings in this study demonstrate that water classification (prior to algorithm development) is needed for the development of excellentKd(490) retrieval algorithms, and the type-specific models thus developed are an important supplement to existingKd(490) retrieval models for highly turbid inland waters. [ABSTRACT FROM AUTHOR]

Time-series MODIS data were used to extract and characterize algal blooms from the Taihu Lake study area. Water quality data including total nitrogen, total phosphorus, and dissolved oxygen; local meteorology data; and global climate trends were examined to reveal the factors influencing the formation of the algal blooms. Results for the 2000-2011 study period show that the annual algal bloom typically begins between March and May in Taihu Lake. All large-scale blooms originate from northern Taihu Lake (Meiliang Bay and Zhushan Bay). Some small-scale blooms originate from southwestern Taihu Lake, but the duration of these blooms is very brief because of episodes of turbulent mixing due to high wind speed. Nutrient supply is the main factor influencing algal mass propagation during bloom periods, and temperature changes may trigger algal recovery. The algal bloom area significantly decreased when wind speed is greater than 4 m/s, causing turbulence and changes in algal buoyancy. A strong East Asian summer monsoon transporting warm air to the lake is shown to extend the duration of algal blooms in Taihu Lake, as occurred in 2007. [ABSTRACT FROM AUTHOR]

Pigment C-phycocyanin (C-PC) is a useful indicator for the presence of cyanobacteria in inland waters, which has been well known as a phytoplankton group with many negative effects on human, animal, and aquatic ecosystem health. In recent years, the remote detection of the C-PC concentrations for inland waters has received much attention. However, their accurate quantification by means of remote sensing is still a challenge due to the significant bio-optical complexity of turbid inland waters. In this paper, three typical turbid inland lakes in China were investigated through in situ observed data sets containing optical and water quality parameters. By using a recently proposed TD680 optical classification method, all collected samples were first classified into three types. For each type of water, we determined specific spectral sensitive regions for the pigment C-PC. Then, we developed three type-specific support vector regression (SVR) algorithms and an aggregated SVR algorithm. The performances of these algorithms were evaluated through the validation data sets. The results show that the type-specific algorithms generally have significantly improved performance over the aggregated SVR algorithm. Their assessment errors [mean absolute percentage error (MAPE) and root-mean-square error ( rmse)] were as follows: 1) MAPE = 15.6\% and rmse =\break 30.6\ \mg\cdot \m^-3 for Type 1 water; 2) MAPE = 47.1\% and rmse = 61.5\ \mg\cdot\m^-3 for Type 2 water; and 3) MAPE =\break 26.4\% and rmse = 19.1\ \mg\cdot\ m^-3 for Type 3 water. The findings in this paper demonstrate that a prior water classification is needed for the development of accurate C-PC retrieval algorithms. This paper provides a valid strategy for improving C-PC estimation accuracy and enhancing algorithm commonality for optically complex turbid waters. [ABSTRACT FROM AUTHOR]

For optically complex turbid productive waters, the optical behavior of suspended particles is the keynote of characterizing the unordered variations of inherent optical properties (IOPs). Multiple bio-optical measurements and sampling of optically active substances were performed in Lake Taihu, Lake Chaohu, and Lake Dianchi, and Three Gorges reservoir of China, in 2008, 2009, and 2010. On the basis of obtaining adequate observation data, we developed an improved and robust water classification approach, by which complex water conditions were divided into three types, i.e., Type 1 (Normalized Trough Depth at 675 nm, hereafter NTD675, ≥0.092), Type 2 (0 ＜ NTD675 ＜ 0.092), and Type 3 (NTD675 ≤ 0). Furthermore, the specific inherent optical quantities for suspended particles, including the specific absorption coefficient of non-algal particles (a*nap), the specific absorption coefficient of phytoplankton (a*ph), and the specific scattering coefficient of the suspended particles (b*p), were determined for the three classified types of waters. The validation results showed that our proposed values for these specific inherent optical quantities presented relatively high predictive accuracies, with most mean absolute percentage errors (MAPE) near 30%, and more importantly, performed much better than that of non-classified waters. Additionally, relative contributions of phytoplankton and non-algal particles to the total particulate absorption and scattering, as well as the spectra, were also analyzed, and the differences among the three classified types of waters were clarified. Overall, the results obtained in this study provide us with new knowledge for understanding complex varied inherent optical properties of highly turbid productive waters. [ABSTRACT FROM AUTHOR]

This study develops a novel support vector regression (SVR) model for retrieving the specific cyanobacterial pigment C-phycocyanin (C-PC) concentrations in cyanobacteria-dominated large turbid lakes of China. Lake Taihu, Lake Chaohu, and Lake Dianchi in China were our study areas. Five field cruises were carried out to collect data sets of optical and water quality parameters. To retrieve the C-PC, three types of reflectance forms, including single band, band ratio, and three-band-combination, were compared. The band ratio was the best candidate to serve for algorithm development. On this basis, two types of models, including linear models and a SVR model, were originally established. The previous typical algorithms were also examined. The obtained results showed that the best-performing model was the SVR model. By our validation data set, the proposed SVR model also presented accurate prediction results, with the lowest errors among all methods. The novelty of the SVR model compared to the previous ones lies in the inclusion of band ratios that are located outside of the main pigment absorption peaks but hold information on inflection points, curvature, etc., into empirical optimization. The implications of these findings indicates the potential applicability of the SVR models in lakes of the similar type. [ABSTRACT FROM AUTHOR]

Water spectral absorption characteristics of eutrophic lakes are largely different from those of ocean and coastal waters. We therefore studied them with the aim of establishing an analytical model for inland water colour, to be used in remote sensing. Field measurements were carried out on 16 and 17 August 2006 (summer), 5 and 6 November 2006 (winter), and 29 and 30 March 2007 (spring) at 15 stations in northern Lake Taihu (China). Chromophoric dissolved organic matter (CDOM) absorption coefficients (a CDOM) are higher in summer than in spring and winter, with the ratios of a CDOM in spring, summer and winter being approximately 1 : 4.0 : 1.2 at both UV-C and UV-B. The spectral slope S CDOM values change with wavelength and season, and covary with CDOM concentration, as shown by regression analysis. For the CDOM absorption spectrum in the wavelength region 500-700 nm (important for water colour remote sensing), a linear method simulates better than an exponential method. Seasonal variations in non-algal particulate (NAP) absorption (a NAP) at blue, green and red wavelengths show better consistency, in the order winter>spring>summer. The average S NAP is 0.0065±0.0009 nm-1, which is lower than that in other types of waters. Phytoplankton absorption (a ph) peak height changes with the season, with the pattern summer>winter>spring, and phytoplankton absorption spectra can be expressed with high accuracy by a quadratic model. CDOM absorption contributions in the three seasons are low compared to phytoplankton and NAP. [ABSTRACT FROM AUTHOR]

In order to achieve effective eutrophication control and ecosystem restoration, it is of great significance to investigate the distribution characteristics of nutrient elements in sediments, and to perform ecological risk assessments. In the current grading criteria for nutrient elements in sediments, only the overall or organic components of carbon, nitrogen and phosphorus are considered, while the specific species distributions and bioavailability characteristics are rarely taken into account. Hence, using the current grading criteria, the differences in the release, migration and biological activity of nutrient elements in sediments cannot be accurately reflected. Taking the upper reaches of the Minjiang River watershed as an example, we analyzed the overall distributions and the ratio of nutrient elements in sediments, the spatial changes of nitrogen and phosphorus forms, the bioavailability, and the environmental significance. The ecological risk of nitrogen and phosphorus in sediments was assessed using an evaluation method based upon the biological effective parameter. The results were compared with the results of the evaluation methods based on the single pollution index, and then these evaluation methods were confirmed accordingly. From the results, the following conclusions can be obtained: (1) The spatial distributions of nutrient elements in sediments in the upper reaches of the Minjiang River Watershed (including the Jianxi Basin, Futunxi Basin, and Shaxi Basin) were significantly affected by the local ecology and the urban sewage discharge system. (2) The maximum average contents of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in sediments were observed in the Jianxi Basin, the Futunxi Basin and the Shaxi Basin, respectively. (3) According to the contents of nitrogen and phosphorus in sediments, the bioavailable nitrogen (TTN) accounted for 35.49% of the total contents of TN. The components of TTN can be sorted from high to low as follows: Nitrogen in organic sulfide form (SOEF-N) > nitrogen in iron-manganese oxide form (SAEF-N) > nitrogen in ion exchange form (IEF-N) > nitrogen in weak acid leaching form (WAEF-N). Inorganic phosphorus (IP) was the main component of TP. The components of IP can be sorted from high to low as follows: Metal oxide bound phosphorus (NaOH-P) > calcium bound phosphorus (HCl-P) > reduced phosphorus (BD-P) > weakly adsorbed phosphorus (NH4Cl-P). Meanwhile, bioavailable phosphorus (BAP, BAP = NH4Cl-P + BD-P + NaOH-P) accounted for 36.94% of TP. According to the results of the single pollution index method, the risk level of TOC pollution in the sediments was relatively low in the whole area, while the risk level of TN pollution was low or moderate in most zones, and severe in certain ones. The risk level of TP pollution was low to moderate. (4) From the results of the bioavailability index evaluation method, based on the total amounts and forms of N and P, the risk level of N pollution was moderate, while the risk of P pollution was negligible. In addition, the results of the bioavailability index evaluation method were more consistent with the actual situation and reflected the overall environmental effects of nitrogen and phosphorus. [ABSTRACT FROM AUTHOR]