Changes In Amount Research Articles

Demystifying normalized difference vegetation index (NDVI) for greenness exposure assessments and policy interventions in urban greening

Most nature and health research use the normalized difference vegetation index (NDVI) for measuring greenness exposure. However, little is known about what NDVI measures in terms of vegetation types (e.g., canopy, grass coverage) within certain analysis zones (e.g., 500 m buffer). Additionally, exploration is needed to understand how to interpret changes in average NDVI (e.g., per 0.1 increments) exposure in relation to changes in vegetation amount and types. In this study, we aimed to explore what vegetation types and amounts best explain the average NDVI and how changes in average NDVI values indicate changes in different vegetation coverages. We used spatial modeling to sample mean NDVI and percentages of vegetation for sample locations within the Greater Manchester case study area. We fitted linear, nonlinear, and mixed multivariate and univariate generalized additive models (GAMs) for multiple spatial scales to identify the relationships between NDVI and vegetation amount and types. Our results showed that the relationships between NDVI and individual vegetation types mostly follow nonlinear trends. We found that canopy and shrubs coverage exhibited a greater influence on mean NDVI exposure values than grass coverage at 300 and 500 m indicating that NDVI values are sensitive to certain types and amounts of vegetation within various buffer zones. We also identified increment in mean NDVI exposure values at lower, mid, and high ranges might be associated with varying changes in total greenspace percentage and individual vegetation types. For instance, at 300 m buffer, an increment of mean NDVI in the lower range (e.g., from 0.2 to 0.3) is associated with an about 17% increase in greenspace percentage. Overall, interpreting changes in NDVI values for urban greening interventions would require careful evaluation of the relative changes in types and quantities of vegetation for different buffer zones.

CONTROL OF ASYNCHRONOUS AC ELECTRIC MOTOR ACCORDING TO THE PRINCIPLE OF CONSTANT V/F AND CONVENTIONAL PWM CONTROL

The principle of operation of any automatic control system is to detect deviations of regulated values from set values and to form influences on the control process to eliminate these deviations. Often, a variable value whose value must be maintained constantly or changed according to the desired law is called a controlled value (coordinate). It is customary to call the required value of the regulated value (coordinate) set, and the actual value - current. The difference between the setpoint and the actual value is a deviation or error signal. A set of devices that affect the object of control, maintaining the current value of the controlled quantity (coordinate) equal to the given one, is called an automatic regulator or a dynamic system. The influence of the regulator on the object with the aim of bringing the current value of the controlled value closer to the set value (or adding the desired properties to the closed system) is called the control influence, and the set of devices and physical environments through which the control influence acts on the controlled value is called the control channel. The control process carried out by the regulator manifests itself in a change in the set value of the regulated quantity or a deviation of at least one of the unregulated quantities that affect the regulated one through feedback circuits. A change in the set value of an adjustable quantity is called a controlling or internal setting influence, and a change in unregulated quantities is called an external disturbance. The principle of deviation control is to compare the set value of the regulated value (setting) with its current value. In this case, the error signal Δ is used to create such a regulatory influence on the control object that this error, regardless of the reasons that caused it, does not go beyond the permissible values. In order to protect the environment and reduce the effect of greenhouse gas emissions, regulations are being introduced all over the world that require manufacturers of household electrical equipment and industrial enterprises to produce products that use electricity more economically. Most often, this can be achieved by effectively controlling the speed of the electric motor. This is the reason why consumer appliance developers and semiconductor suppliers are now interested in developing low-cost and economical adjustable actuators.

Directors' and officers' liability insurance and digital transformation – the mediating role of explorative innovation

PurposeThe purpose of this paper is to investigate the relations between the directors' and officers' (D&O) insurance and digital transformation of Chinese-listed companies to provide insights into triggers of digital transformation from the perspective of D&Os' incentive plan.Design/methodology/approachBased on a panel dataset of 2,590 listed manufacturing companies in China from 2017 to 2020, and using a textual analysis of annual reports, this paper empirically examines the impact of D&O insurance on digital transformation. The authors investigate the mechanism through a mediating model and apply a series of robustness tests including firm fixed effect model, propensity score matching and changing key measures.FindingsThe research shows that the digital transformation has been negatively influenced by D&O insurance. The long coverage duration of D&O insurance significantly lowers the level of digital transformation. The moral hazard problem caused by D&O insurance has hampered digital transformation through reducing explorative innovation, while there has been no significant change in innovation quantity. Under the coverage of D&O insurance, firms with worse internal governance and state-owned firms are more reluctant to invest in risky transformation than their counterparts.Originality/valueBased on a textual analysis of annual reports, this paper empirically tests the influential mechanism of D&O insurance coverage on digital transformation. The authors provide insights into non-tech triggers of digital transformation and uncover how incentive plans influences D&Os' behaviors. This paper provides a new angle to the debate on governance-strengthening and governance-weakening role of D&O insurance.

Contractile ring composition dictates kinetics of in silico contractility

Constriction kinetics of the cytokinetic ring are expected to depend on dynamic adjustment of contractile ring composition, but the impact of ring component abundance dynamics on ring constriction is understudied. Computational models generally assume that contractile networks maintain constant total amounts of components, which is not always true. To test how compositional dynamics affect constriction kinetics, we first measured F-actin, non-muscle myosin II, septin, and anillin during Caenorhabditis elegans zygotic mitosis. A custom microfluidic device that positioned the cell with the division plane parallel to a light sheet allowed even illumination of the cytokinetic ring. Measured component abundances were implemented in a three-dimensional agent-based model of a membrane-associated contractile ring. With constant network component amounts, constriction completed with biologically unrealistic kinetics. However, imposing the measured changes in component quantities allowed this model to elicit realistic constriction kinetics. Simulated networks were more sensitive to changes in motor and filament amounts than those of crosslinkers and tethers. Our findings highlight the importance of network composition for actomyosin contraction kinetics.

Variation in riverine dissolved organic matter (DOM) optical quality during snowmelt- and rainfall-driven events in a forested wetland watershed

The spring snowmelt period is an important time for organic matter mobilization and export in peatland and wetland dominated systems. The hydrologic flowpaths that transport melting snow and soil water to surface waters can vary over relatively short time periods (several days to weeks) depending on the timing and rate of melt and the occurrence of freeze–thaw cycles and rain-on-snow events. Dynamic flowpaths can alter dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) optical properties in surface waters due to differential melt and mobilization of snow, ice, and soil waters. In 2018 and 2020, we measured the DOC concentration and DOM optical properties in a woody wetland-dominated watershed in northern Minnesota during spring snowmelt (2018 & 2020) and early growing season (2018 only) events. We examined patterns in riverine DOC, DOM, and hydrochemical tracers across event hydrographs to infer changes in hydrologic connectivity across this seasonal transition. Measurements of riverine DOM optical properties, calcium concentration, and water isotopic composition indicated that DOM shifted from a primarily groundwater source and more fresh character during the dormant season to a more shallow wetland soil source and recalcitrant character during the early growing season. Seasonal variations in DOM optical properties and highly complex hysteresis patterns of DOM indices (e.g., Fluorescence Index, Humification Index, β/α, E250:E365, and the fluorescence peak ratio T:C) during individual events may reflect spatial heterogeneity in soil thawing throughout the watershed and temporal variations in water table elevation, affecting flowpath depths and connectivity to DOM pools within the soil profile. This study provides an important seasonal and event-scale baseline against which to evaluate potential changes in riverine DOM quantity and quality associated with predicted changes in climate and snow cover in organic matter-rich ecosystems.

1281: EXTRACELLULAR MITOCHONDRIA EXACERBATE GRAFT-VERSUS-HOST DISEASE MORTALITY IN A MOUSE MODEL

Introduction: Graft-versus-host disease (GVHD) is a major complication of hematopoietic stem cell transplantation (HSCT). Previous studies have shown an association between pre-transplant conditioning mediated tissue damage and incidence of GVHD, albeit the pathobiology is not clearly delineated. Recent studies have shown that tissue damage mediates release of extracellular mitochondria (exMito) and associated byproducts, which have immunomodulatory functions due to their archaebacterial origin. However, the role of exMito in the pathogenesis of GVHD has not been explored. Methods: Intestinal epithelial cells (Caco-2) were subjected to doses of irradiation used as pre-transplant conditioning. Subsequently, changes in intracellular and extracellular mitochondrial quantity and function were evaluated. BALB/c mice were subjected to total body irradiation (TBI) and plasma was analyzed to evaluate the quantity and function of circulating exMito. Finally, BALB/c mice undergoing a MHC-mismatched allogeneic HSCT were co-transplanted with exogenous isolated syngeneic mitochondria to study the impact of exMito on GVHD mortality. Results: Seahorse XF flux assays revealed that irradiation impaired intracellular mitochondrial function with a decrease in basal, ATP-linked and maximal respiratory capacity in Caco-2 cells. Analyses of the cell-culture supernatant showed elevated exMito and increased oxidative mitochondrial protein modification (carbonylation), following irradiation. BALB/c mice which received TBI demonstrated morphological signs of mitochondrial fission and damage in intestinal epithelium along with an increase in the amount of exMito in the plasma. In addition, exMito isolated from the plasma of irradiated animals had a markedly diminished response to pyruvate/malate-dependent-induction of mitochondrial membrane potential suggestive of damage. Finally, recipient mice co-transplanted with damaged cell-free mitochondria in a MHC-mismatched allogeneic HSCT demonstrated dose-dependent increased GVHD-induced mortality. Conclusions: The results indicate that conditioning regimen-mediated extracellular release of damaged mitochondria plays a role in GVHD mortality. Future studies targeting therapies to preserve mitochondrial function and decrease extracellular mitochondrial load for GVHD management is warranted.

Spatial and Temporal Changes of Sand Mining in the Yangtze River Basin since the Establishment of the Three Gorges Dam.

The global demand for sand and gravel is at 50 billion tons per year, far exceeding global resource capacities. It reached 7.6 billion tons in 2021 in the Yangtze River Basin (YRB), China. However, production is severely limited in the YRB. Therefore, the incongruity between the supply and demand of river sand is prominent. Wise management of decreasing sand resources in the YRB has become critical since the Three Gorges Dam became operational in 2003. This study synthesized spatial and temporal changes in sand mining activities and quantities along the Yangtze River and its major tributaries from 2004 to 2020. Results from the study show that the mining amount during the period reached 76.2 million tons annually. At the same time, riverine suspended sediment discharge (SSD) downstream of the Three Gorges Dam decreased largely. SSD reduction leads to riverbed erosion, further limiting the riverine sand and gravel sources for mining. Thus, alternative sand and gravel resources, as well as optimizing supply/demand balance, are necessary for sustainable development. There is an urgent need to assess the relationship between river sand resources and exploitation in the YRB for creating a sand and gravel data management system in order to cope with the increasing incongruity between their supply and demand.

Quantifi cation of Changes in the Functional Status of a Person During the Aircraft Flight

The article is devoted to the approach to the quantitative estimation of changes in the functional state of a person during an airplane flight based on the results of stabilometric and oculographic examinations of airplane passengers carried out before and after the flight. Fourteen volunteers of both sexes participated in the study. They performed 21 pairs of pre-flight and post-flight examinations. For the existing sample of volunteers, parameters were identified that had a consistent trend of change. These parameters include visual tracking quality and stabilometric characteristics. In 70 % probes a decrease in the slow phases of optokinetic nystagmus average speed was noted. In most volunteers, changes in the stabilometric parameters for the optokinetic test and the balance test on an unstable support in the form of foam plate are noticeable. The tracking speeds, the average velocity of the pressure center, and the quality index of the equilibrium function decreased after the flight in more than 70 % of all samples. It was noted that the Hurst index after the flight decreased compared to background sample, during get up on the polyurethane foam plate in the vast majority of volunteers. In test before the flight the change in this parameter was multidirectional. In a stabilometric test with a "stepped deviation", in which a volunteer on command made quick bends at a small angle due to a change in the angle in the ankle joint, 75 % of the subjects after the flights showed a decrease in the average speed.

ALGAL SPECIES DIVERSITY AND PALMER POLLUTION INDEX OF PUTTENAHALLI LAKE IN BENGALURU, INDIA

In this Anthropocene period, due to high human interference for the developments in the fields of agriculture, industryand urban events, especially around lake water systems have affected significant changes in quality and quantity of theresources and enriched water with mineral nutrients, such as nitrogen and phosphorus as a consequence, lakes gotenriched with increased algal productivity which in turn has led to oxygen depletion, recreational impairment,biodiversity loss and resulted in deterioration of habitat quality. The present study attempts to assess the water quality ofPuttenahalli lake through phytoplankton studies. The Puttenahalli lake has been hysterically polluted by sewage dischargefrom two places, one from the underground drain in Nataraja layout and the other from an unknown source in thesouthern side which has led to a massive fish kill and organic load in the lake. The phytoplankton studies revealed thepresence of harmful algal blooms like Spirogyra sp., Mycrocystis sp., Cylindrospermopsis sp., Arcella sp., Anabena sp.,Scenedesmus sp., Ulothrix sp., Ankistrodesmus sp., Cosmarium sp., Trachelomonas sp., Zygnema sp., Navicula sp., Synedra sp.,Cymbella sp., Nitzschia sp., Cyclotella sp., Selenastrum sp., diatoms sp., and many other cyanohabs were abundantly presentin the studied lake. These Cyanobacterial blooms are currently a great threat to the ecological integrity and sustainabilityof lake water resources.

Hybrid Scheme of Kinematic Analysis and Lagrangian Koopman Operator Analysis for Short-Term Precipitation Forecasting

With the accumulation of meteorological big data, data-driven models for short-term precipitation forecasting have shown increasing promise. We focus on Koopman operator analysis, which is a data-driven scheme to discover governing laws in observed data. We propose a method to apply this scheme to phenomena accompanying advection currents such as precipitation. The proposed method decomposes time evolutions of the phenomena between advection currents under a velocity field and changes in physical quantities under Lagrangian coordinates. The advection currents are estimated by kinematic analysis, and the changes in physical quantities are estimated by Koopman operator analysis. The proposed method is applied to actual precipitation distribution data, and the results show that the development and decay of precipitation are properly captured relative to conventional methods and that stable predictions over long periods are possible.

Probable reasons for interruption of the flow of the Iskrets karst spring

The object of research is the Iskrets spring, one of the large and important karst springs in Bulgaria. A characteristic feature of its regime is the temporary interruptions of its outflow. The purpose of the research is to establish the probable causes and mechanism for these interruptions. After analyzing the hydrogeological situation and data from the results of continuous measurements of changes in water quantities, it is assumed that the main cause of this phenomenon is the processes of erosion, transport and deposition of cave alluvial sediments.

Protection scheme against turn-to-turn fault for novel magnetic valve controllable reactor

This paper focuses on the inter-turn protection scheme of a new type of reactive power compensation device-magnetic valve reactor. Aiming at the problem that the existing inter-turn protection scheme has insufficient sensitivity and causes the protection to refuse to act, this paper first introduces the topology of the new type of magnetic valve reactor in detail and analyzes the working state of the positive half cycle of its power supply and establishes mathematical model and physical model of valve reactor. Based on this model, the excitation winding of the magnetic valve reactor is analyzed, and the differential mode current component of the excitation winding is introduced to characterize the fault characteristics. According to the change of electric quantity before and after the fault, a new inter-turn protection scheme of magnetic valve reactor based on the fundamental frequency component of the differential mode current of the excitation winding group is constructed. After a large number of simulation experiments, the feasibility and effectiveness of the scheme are verified.

Nutrient composition (Si:N) as driver of plankton communities during artificial upwelling

Artificial upwelling brings nutrient-rich deep water to the sun-lit surface to boost fisheries or carbon sequestration. Deep water sources under consideration range widely in inorganic silicon (Si) relative to nitrogen (N). Yet, little is known about how such differences in nutrient composition may influence the effectiveness of the fertilization. Si is essential primarily for diatoms that may increase food web and export efficiency via their large size and ballasting mineral shells, respectively. With a month-long mesocosm study in the subtropical North Atlantic, we tested the biological response to artificial upwelling with varying Si:N ratios (0.07-1.33). Community biomass increased 10-fold across all mesocosms, indicating that basic bloom dynamics were upheld despite the wide range in nutrient composition. Key properties of these blooms, however, were influenced by Si. Photosynthetic capacity and nutrient-use efficiency doubled from Si-poor to Si-rich upwelling, leading to C:N ratios as high as 17, well beyond Redfield. Si-rich upwelling also resulted in 6-fold higher diatom abundance and mineralized Si and a corresponding shift from smaller towards larger phytoplankton. The pronounced change in both plankton quantity (biomass) and quality (C:N ratio, size and mineral ballast) for trophic transfer and export underlines the pivotal role of Si in shaping the response of oligotrophic regions to upwelled nutrients. Our findings indicate a benefit of active Si management during artificial upwelling with the potential to optimize fisheries production and CO2 removal.

Sensitivity of Economic Branches to Changes in Production Volumes

The paper aim is to verify industry sensitivity to changes in production volumes (sales). Sensitivity confirmation is not based on the data describing economic downturn but on permanent internal industry factors. Internal factors take into consideration cost dependency on changes in output quantity produced. Ex ante analysis would discover why some industries would be more vulnerable than the others when significant economic disruption occurs. It has a serious impact on industry performance and business competitiveness position. The examined sensitivity will be expressed by the indicator degree of operating leverage (DOL). The verified assumption should classify neutral industries as sectors with low sensitivity and cyclical branches as industries with high sensitivity. The research is based on the data of more than 1,000 enterprises belonging to four industry sectors. Cyclical industries are represented by CZ-NACE 29 Manufacture of motor vehicles, trailers and semi-trailers and CZ-NACE H Transportation and Storage. Neutral sectors are symbolized by CZ-NACE 10 Manufacture of food products, CZ-NACE 20 Manufacture of chemicals and chemical products. Research conclusions are not demonstrable because initial assumptions were not confirmed and significant differences between cyclical and neutral industry branches were not unexpectedly detected using DOL. It demonstrates that examined issue is more complex and the monitored economic environment does not stay stable even during a period of macroeconomic stability.

Major royal jelly proteins influence the neurobiological regulation of the division of labor among honey bee workers

Age-based division of labor among workers is a fundamental life-history trait of many social insects, including the Western honey bee, Apis mellifera L. Extensive studies of the causation of the most pronounced transition from performing tasks in the nest to outside foraging indicate hormonal regulation of complex physiological changes. However, the proximate neurobiological mechanisms that cause the behavioral repertoire to change are still not understood and require novel approaches to be fully characterized. Thus, we established the first comprehensive monoclonal antibody microarray in honey bees with 16,320 antibodies to directly identify proteins in the brain that regulate the transition to foraging. Major royal jelly protein (MRJP) 1 and MRJP3 were identified as potential protein effectors and further investigated. A series of experimental manipulations of the workers' behavioral transition led to changes in MRJP1 and MRJP3 quantities in accordance with their presumed functional role. Injection of MRJPs into the brain resulted in increased task-reversal from foraging to nursing and decreased task-progression from nursing to foraging, while the latter was increased by injection with MRJP antibodies. Finally, down-regulation of MRJP1 and MRJP3 expression via RNAi injection into the brain increased the transition from in-hive nursing to outside foraging, confirming a causal role of these two proteins in the proximate regulation of behavior and life-history of honey bee workers. Interaction partners of MRJP1 and MRJP3 in the honey bee brain included other regulators of honey bee behavior and life history. Thus, our transformative methodological advancement of proteome analysis in honey bees reveals novel regulators of honey bee behavior, extends our understanding of the functional pleiotropy of MRJPs, and supports a general nutrition-based model of the regulation of the age-based division of labor in honey bees.

High stand density promotes soil organic carbon sequestration in Robinia pseudoacacia plantations in the hilly and gully region of the Loess Plateau in China

Planting density has an effect on the accumulation and stabilization of soil organic carbon (SOC) in plantations. However, the mechanism by which SOC dynamics and sequestration respond to stand density is not well understood in Robinia pseudoacacia plantations. Here, we analyzed R. pseudoacacia plantations in the loess hilly-gully region of northern Shaanxi Province, China with three stand densities: 750 trees ha−1 (low-density), 1125 trees ha−1 (medium-density) and 1550 trees ha−1 (high-density). We determined the effects of stand density on SOC, SOC fractions, microbial carbon (C) use efficiency (CUE), and microbial C metabolism function. In particular, soil microbial metabolism function was investigated with the Biolog-ECO microplate. Carbohydrates and amino acids were the main available C sources for soil microbes in R. pseudoacacia plantations. Microbial biomass C (MBC), mineral-associated organic C (MOC), and dissolved organic C (DOC) content were the highest in high-density plantations, whereas easily oxidizable C (EOC) content, the MBC/SOC ratio, the DOC/SOC ratio, and the EOC/SOC ratio were the lowest in high-density plantations. Compared with low- and medium-density plantations, the average SOC content in high-density plantations increased by 61% and 52%, respectively. Across all stands, the MOC/SOC ratio ranged from 32% to 65%, whereas labile C accounted for only a minor portion of SOC (20 ± 8%). A substantially higher CUE and lower microbial metabolic activity were found in high-density plantations. Pearson correlation analysis showed that SOC content was significantly positively correlated with above-ground litter biomass and CUE but was significantly negatively correlated with microbial metabolic activity and liable C/SOC ratios. Mantel tests showed that soil nitrogen (N) level and the microbial biomass C/N ratio were the main factors affecting SOC quantity and stability changes. These results suggested that R. pseudoacacia plantations under high density increased SOC sequestration by increasing C input via aboveground litter and decreased C loss by improving microbial CUE and suppressing microbial metabolic activity. Thus, increasing stand density may be an effective tool for improving SOC sequestration in R. pseudoacacia plantations.

Correlation between performance and quantity/variability of leg exploration in a contingency learning task during infancy

Quantity and quality of motor exploration are proposed to be fundamental for infant motor development. However, it is still not clear what types of motor exploration contribute to learning. To determine whether changes in quantity of leg movement and/or variability of leg acceleration are related to performance in a contingency learning task, twenty 6–8-month-old infants with typical development participated in a contingency learning task. During this task, a robot provided reinforcement when the infant’s right leg peak acceleration was above an individualized threshold. The correlation coefficient between the infant’s performance and the change in quantity of right leg movement, linear variability, and nonlinear variability of right leg movement acceleration from baseline were calculated. Simple linear regression and multiple linear regression were calculated to explain the contribution of each variable to the performance individually and collectively. We found significant correlation between the performance and the change in quantity of right leg movement (r = 0.86, p < 0.001), linear variability (r = 0.71, p < 0.001), and nonlinear variability (r = 0.62, p = 0.004) of right leg movement acceleration, respectively. However, multiple linear regression showed that only quantity and linear variability of leg movements were significant predicting factors for the performance ratio (p < 0.001, adjusted R2 = 0.94). These results indicated that the quantity of exploration and variable exploratory strategies could be critical for the motor learning process during infancy.

Non-Contact Detection of Delamination in Composite Laminates Coated with a Mechanoluminescent Sensor Using Convolutional AutoEncoder

Delamination is a typical defect of carbon fiber-reinforced composite laminates. Detecting delamination is very important in the performance of laminated composite structures. Structural Health Monitoring (SHM) methods using the latest sensors have been proposed to detect delamination that occurs during the operation of laminated composite structures. However, most sensors used in SHM methods measure data in the contact form and do not provide visual information about delamination. Research into mechanoluminescent sensors (ML) that can address the limitations of existing sensors has been actively conducted for decades. The ML sensor responds to mechanical deformation and emits light proportional to mechanical stimuli, thanks it can provide visual information about changes in the physical quantity of the entire structure. Many researchers focus on detecting cracks in structures and impact damage with the ML sensor. This paper presents a method of detecting the delamination of composites using ML sensors. A Convolutional AutoEncoder (CAE) was used to automatically extract the delamination positions from light emission images, which offers better performance compared to edge detection methods.

Linear response theory-based theoretical approach to structural changes in a polymer induced by β-decay of substituted tritium

Polymers exposed to tritiated water undergo hydrogen defects caused by isotope substitution and subsequent β-decay of substituted tritium, causing structural changes and loss of function in the biopolymers. Here, based on linear response theory, we predict the structural change of tritium-damaged polyethylene using the equilibrium trajectory of undamaged polyethylene to reduce the computation time of molecular dynamics simulations. Specifically, the ensemble average of the change in a physical quantity, such that it represents a structural change before and after damage, was calculated numerically using the time derivative of the total potential energy difference derived analytically and the physical quantity obtained from the simulation of undamaged polyethylene on the basis of linear response theory. A comparison between theoretical and simulation results revealed that the characteristic oscillation behaviors of the structural response of polyethylene can be predicted, whereas the quantitative prediction of the steady-state values over a long period is difficult.

Total Phosphorus and Nitrogen Dynamics and Influencing Factors in Dongting Lake Using Landsat Data

Total phosphorus (TP) and total nitrogen (TN) reflect the state of eutrophication. However, traditional point-based water quality monitoring methods are time-consuming and labor-intensive, and insufficient to estimate and assess water quality at a large scale. In this paper, we constructed machine learning models for TP and TN inversion using measured data and satellite imagery band reflectance, and verified it by in situ data. Atmospheric correction was performed on the Landsat Top of Atmosphere (TOP) data by removing the effect of the adjacency effect and correcting differences between Landsat sensors. Then, using the established model, the TP and TN patterns in Dongting Lake with a spatial resolution of 30 m from 1996 to 2021 were derived for the first time. The annual and monthly spatio-temporal variation characteristics of TP and TN in Dongting Lake were investigated in details, and the influences of hydrometeorological elements on water quality variations were analyzed. The results show that the established empirical model can accurately estimate TP with coefficient (R2) ≥ 0.70, root mean square error (RMSE) ≤ 0.057 mg/L, mean relative error (MRE) ≤ 0.23 and TN with R2 ≥ 0.73, RMSE ≤ 0.48 mg/L and MRE ≤ 0.20. From 1996 to 2021, TP in Dongting Lake showed a downward trend and TN showed an upward trend, while the summer value was much higher than the other seasons. Furthermore, the influencing factors on TP and TN variations were investigated and discussed. Between 1996 and 2003, the main contributors to the change of water quality in Dongting Lake were external inputs such as water level and flow. The significant changes in water quantity and sediment characteristics following the operation of the Three Gorges Dam (TGD) in 2003 also had an impact on the water quality in Dongting Lake.