Pervasive soil phosphorus losses in terrestrial ecosystems in China.

Future phosphorus (P) shortages could seriously affect terrestrial productivity and food security. We investigated the changes in topsoil available P (AP) and total P (TP) in China's forests, grasslands, paddy fields, and upland croplands during the 1980s-2010s based on substantial repeated soil P measurements (63,220 samples in the 1980s, 2000s, and 2010s) and machine learning techniques. Between the 1980s and 2010s, total soil AP stock increased with a small but significant rate of 0.13 kg P ha-1 year-1 , but total soil TP stock declined substantially (4.5 kg P ha-1 year-1 ) in the four ecosystems. We quantified the P budgets of soil-plant systems by harmonizing P fluxes from various sources for this period. Matching trends of soil contents over the decades with P budgets and fluxes, we found that the P-surplus in cultivated soils (especially in upland croplands) might be overestimated due to the great soil TP pool compared to fertilization and the substantial soil P losses through plant uptake and water erosion that offset the P additions. Our findings of P-deficit in China raise the alarm on the sustainability of future biomass production (especially in forests), highlight the urgency of P recycling in croplands, and emphasize the critical role of country-level basic data in guiding sound policies to tackle the global P crises.

TP or Not TP? Successful Comparison of Two Independent Methods Validates Total Phosphorus Inference for Long-Term Eutrophication Studies.

Validating paleo total phosphorus (TP) inference methods over long time scales is essential for understanding historic changes in lake P supply and the processes leading up to the present-day global lake eutrophication crisis. Monitored lake water TP time series have enabled us to identify the drivers of eutrophication over recent decades. However, over longer time scales, the lack of reliable TP inference means our understanding of drivers is speculative. Validation of lake water TP reconstruction, therefore, remains the "ultimate aim" of eutrophication studies. Here, we present the first critical comparison of two fully independent paleo TP inference approaches: the well-established diatom method (DI-TP) and a recently developed sediment geochemical method (SI-TP). Using lake sediment records from a small eutrophic U.K. lake (Crose Mere), we find a statistically significant agreement between the two inferred TP records with greater than 60% shared variance. Both records show identical timings, with a 19th century acceleration in TP concentration and subsequent declines following a peak in 1930. This significant agreement establishes the validity of long-term paleo TP inference for the first time. With this, we can now test assumptions and paradigms that underpin understanding of catchment P sources and pathways over longer time scales.

Implications of the operation of continuous granular activated carbon filters on the effluent quality.

Granular activated carbon (GAC) filtration is a commonly used method for advanced wastewater treatment. Filters can be operated continuously or discontinuously, with continuous operation not requiring feed flow interruption for backwashing and circulation (B/C). This study investigated the influence of B/C on the effluent quality of continuous filters. Two continuous GAC filters were operated for 1.5 years, with analysis of dissolved substances and particulate matter in the influent and effluent. The results indicated that various B/C modes had no impact on the removal of dissolved organic carbon and organic micropollutants (OMP), achieving an OMP removal of over 70% after 5,600 treated bed volumes (m3 treated wastewater per m3 GAC). However, it was evident that continuous B/C over 2-4 h resulted in increased turbidity, total suspended solids over 30 mg/L and total phosphorus concentrations of 1.3 mg/L in the filter effluent. Additionally, the study demonstrated that longer and more intensive B/C processes resulted in GAC size degradation with AC concentrations of up to 6.9 mg/L in the filter effluent, along with a change in GAC particle size. Furthermore, the importance of pre-filtration in reducing particulate matter in the filter influent and decreasing hydraulic head loss could be demonstrated.

Examining contaminant transport hotspots and their predictability across contrasted watersheds.

Hydrobiogeochemical processes governing water quantity and quality are highly variable in space and time. Focusing on thirty river locations in Québec, Canada, three water quality hotness indices were used to classify watersheds as contaminant transport hotspots. Concentration and load data for suspended solids (SS), total nitrogen (TN), and total phosphorous (TP) were used to identify transport hotspots, and results were compared across hotness indices with different data requirements. The role of hydroclimatic and physiographic characteristics on the occurrence and temporal persistence of transport hotspots was examined. Results show that the identification of transport hotspots was dependent on both the type of data and the hotness index used. Relationships between temporal and spatial predictors, however, were generally consistent. Annual transport hotspot occurrence was found to be related to temporal characteristics such as the number of dry days, potential evapotranspiration, and snow water equivalent, while hotspot temporal persistence was correlated to landcover characteristics. Stark differences in the identification of SS, TN, and TP transport hotspots were attributed to differences in mobilization processes and provided insights into dominant water and nutrient flowpaths in the studied watersheds. This study highlighted the importance of comparing contaminant dynamics across watersheds even when high-frequency water quality data or discharge data are not available. Characterizing hotspot occurrence and persistence, among hotness indices and water quality parameters, could be useful for watershed managers when identifying problematic watersheds, exploring legacy effects, and establishing a prioritization framework for areas that would benefit from enhanced routine monitoring or targeted mitigation strategies.

Airport Deicers: An Unrecognized Source of Phosphorus Loading in Receiving Waters.

Airport ice control products contributed to total phosphorus (TP) loadings in a study of surface water runoff at a medium-sized airport from 2015 to 2021. Eleven airport ice control products had TP concentrations from 1-807 mg L-1 in liquid formulas, while solid pavement deicer had a TP concentration of 805 mg kg-1. Product application data, formula TP concentrations, and surface water sampling results were used to estimate TP concentration and loading contributions from these ice control products to receiving streams. Airport ice control products were found to contribute to TP in 84% of the water samples collected at downstream sites during deicing events, and TP concentrations at those sites exceeded aquatic life benchmarks in 70% of samples collected during deicing. A receiving stream 6 km downstream had TP attributed to airport ice control sources in 78% of the samples. TP loadings at an upstream site and the receiving stream site were greatest during the largest runoff events as is typical in urban runoff, but this pattern was not always followed at airport outfall sites due to the influence of TP in deicer products. Products analyzed in this study are used at airports across the United States and abroad, and findings suggest that airport deicers could represent a previously unrecognized source of phosphorus to adjacent waterways.

Exploration of the factors that influence total phosphorus in surface water and an evaluation of surface water vulnerability based on an advanced algorithm and traditional index method.

Due to the continuous influence of human activities, phosphorus pollution in surface water has become a persistent problem that needs to be addressed since phosphorous entails certain risks and degrees of damage to ecosystems and humans. The presence and accumulation of total phosphorus (TP) concentrations in surface waters is the result of a combined effect of many natural and anthropogenic factors, and it is often difficult to intuitively identify the individual importance of each factor in regard to the pollution of the aquatic environment. Considering these issues, this study provides a new methodology to better understand the vulnerability of surface water to TP pollution and the factors that influence TP pollution through the application of two modeling approaches. This includes the boosted regression tree (BRT), an advanced machine learning method, and the traditional comprehensive index method (CIM). Different factors, such as natural variables (including slope, soil texture, normalized difference vegetation index (NDVI), precipitation, and drainage density) and point and nonpoint source anthropogenic factors were included to model the vulnerability of surface water to TP pollution. Two methods were used to produce a vulnerability map of surface water to TP pollution. Pearson correlation analysis was used to validate the two vulnerability assessment methods. The results showed that BRT was more strongly correlated than CIM. In addition, the importance ranking results showed that slope, precipitation, NDVI, decentralized livestock farming and soil texture had a greater influence on TP pollution. Industrial activities, scale livestock farming and population density, which are all contributing sources of pollution, were all relatively less important. The introduced methodology can be used to quickly identify the area most vulnerable to TP pollution and to develop problem specific adaptive policies and measures to reduce the damage from TP pollution.

Experimental checking and modeling of the influence of operation conditions on the first order kinetic constants in free water surface wetlands.

The most commonly used model in constructed wetlands is the first-order removal model, and first order kinetic constants (k) are the key parameters. The presumption is often made that k are constants. However, it is possible that k are functions of operating conditions, but the influence of operation conditions on k is unclear. In this study, response surface methodology was used to explore the variation patterns of ka (area rate constants) and kV (volume rate constants) for the removal of total nitrogen (TN) and total phosphorus (TP) in free water surface (FWS) wetlands. The experimental variables included hydraulic loading rate (HLR), water depth, and inlet concentration (Cin). The results showed that kV was more variable than ka, and the area-based first-order model is more suitable for simulating TN and TP in FWS wetlands. Inlet concentration (Cin) was significant for ka; Cin and water depth were significant for kV; HLR and the interaction between factors were insignificant. The effects of Cin on ka and kV can be described by an upward convex quadratic curve, while the effect of water depth on kV demonstrates a downward convex quadratic curve. The first-order area rate constant for TN removal was given by k = -47.66 + 22.01 Cin - 1.154 Cin2; the first-order area rate constant for TP removal was given by k = -27.75 + 95.88 Cin - 30.73 Cin2. Based on the variation patterns, the traditional k-C model was modified to the kψ-C model. The kψ-C model produced the best results at simulating the outlet concentration and removal efficiency (RE).

Decomposition of Phosphorus Pollution and Microorganism Analysis Using Novel CW-MFCs under Different Influence Factors.

A constructed wetland (CW)-coupled microbial fuel cell (MFC) system was constructed to treat wastewater and generate electricity. The total phosphorus in the simulated domestic sewage was used as the treatment target, and the optimal phosphorus removal effect and electricity generation were determined by comparing the changes in substrates, hydraulic retention times, and microorganisms. The mechanism underlying phosphorus removal was also analyzed. By using magnesia and garnet as substrates, the best removal efficiencies of two CW-MFC systems reached 80.3% and 92.4%. Phosphorus removal by the garnet matrix mainly depends on a complex adsorption process, whereas the magnesia system relies on ion exchange reactions. The maximum output voltage and stabilization voltage of the garnet system were higher than those of the magnesia system. Microorganisms in the wetland sediments and electrode also changed considerably. It indicates that the mechanism of phosphorus removal by the substrate in the CW-MFC system is adsorption and chemical reaction between ions to generate precipitation. The population structure of proteobacteria and other microorganisms has an impact on both power generation and phosphorus removal. Combining the advantages of constructed wetlands and microbial fuel cells also improved phosphorus removal in coupled system. Therefore, when studying a CW-MFC system, the selection of electrode materials, matrix, and system structure should be taken into account to find a method that will improve the power generation capacity of the system and remove phosphorus.

Analysis of the characteristics of major pollutants discharged from wastewater in China's provinces.

In recent years, the discharge of major pollutants in China's wastewater has been decreasing but remains at a high level. Controlling the discharge of pollutants in sewage is of great importance for protecting water quality and maintaining ecological balance. Based on data collected from 31 provinces in China from 2011 to 2020 (except 2018), this study analyzes the spatiotemporal variation emissions of the wastewater pollutants: chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP). The entropy method was used to evaluate the effectiveness of water pollution control in different provinces. Our results revealed that the total emission per gross domestic product (GDP) for COD, NH3-N, TN and TP in China decreased by 50.7%, 81.9%, 65.4% and 70.8%, respectively. In terms of regional annual emission differences, the Northwest region was the lowest compared with other regions, accounting for 4.87%-6.59% of the national pollutant emissions, and the Central China region was the highest, accounting for 22.4%-26.05% of the national pollutant emissions. The average value of pollutant emissions per unit of GDP decreased year-to-year overall, but Guangxi and Tibet showed a trend of first decreasing and then increasing. The correlation results indicated a significant correlation (0.977) between TN and TP emissions in wastewater in China during 2011-2020. Through clustering and Multidimensional Scaling model (MDS) analysis, Beijing and Shanghai have been performing well in controlling water pollution discharge, while the provinces of Tibet and Guangxi must still increase their efforts in water pollution control. Furthermore, these results demonstrate the experience and achievements of the Chinese government in the treatment of wastewater pollution and provide a useful reference for treatment of wastewater pollution in the world.

Removal of nutrients from pulp and paper biorefinery effluent: Operation, kinetic modelling and optimization by response surface methodology.

This study investigated the effectiveness of extended aeration system (EAS) and rice straw activated carbon-extended aeration system (RAC-EAS) in the treatment of pulp and paper biorefinery effluent (PPBE). RAC-EAS focused on the efficient utilization of lignocellulosic biomass waste (rice straw) as a biosorbent in the treatment process. The experiment was designed by response surface methodology (RSM) and conducted using a bioreactor that operated at 1-3 days hydraulic retention times (HRT) with PPBE concentrations at 20, 60 and 100%. The bioreactor was fed with real PPBE having initial ammonia-N and total phosphorus (TP) concentrations that varied between 11.74 and 59.02 mg/L and 31-161 mg/L, respectively. Findings from the optimized approach by RSM indicated 84.51% and 91.71% ammonia-N and 77.62% and 84.64% total phosphorus reduction in concentration for EAS and RAC-EAS, respectively, with high nitrification rate observed in both bioreactors. Kinetic model optimization indicated that modified stover models was the best suited and were statistically significant (R2 ≥ 0.98) in the analysis of substrate removal rates for ammonia-N and total phosphorus. Maximum nutrients elimination was attained at 60% PPBE and 48 h HRT. Therefore, the model can be utilized in the design and optimization of EAS and RAC-EAS systems and consequently in the prediction of bioreactor behavior.

Causal impact analysis of enhanced phosphorus effluent standard on river water quality.

The effect of environmental policies on water quality is an important factor in evaluating a project's impact and economic feasibility. The aim of this study was to evaluate the causal relationship between strengthening the total phosphorus (TP) concentration standard in wastewater treatment plant (WWTP) effluents and river water quality in the Geum River watershed (Rep. of Korea). Data, including precipitation, streamflow, and water quality, were collected for 2005-2020 and temporally divided into "before" and "after" the event of strengthening standards (in 2012). Further, the data were spatially divided into influence sites (impact) affected by the event and control sites (control) unaffected by the event. A median difference test for a before/after and control/impact (BACI) analysis and a causal impact analysis (CIA) based on a Bayesian structural time-series model were performed to evaluate the changes in water quality after the event. The BACI test showed that the TP concentration was reduced significantly (p-value<0.05) at all impact sites after the event, whereas the difference was not significant at the control sites. In contrast, other water quality variables, except TP, showed different statistical significance depending on the site. The CIA was performed by controlling the rainfall, flow rate, suspended solids, water temperature, biochemical oxygen demand, and chemical oxygen demand as covariates, which were selected based on a directed acyclic graph and bi-variable correlation analysis. The CIA results showed that the TP concentration was reduced significantly (p-value<0.05) at all impact sites, except for the control sites after the event, which is consistent with the BACI results. The causal impact of environmental management policies was previously difficult to evaluate by objectively targeting the natural systems because of the confounding bias. Our study demonstrated that strengthening the TP concentration standard from WWTPs majorly contributed to reducing TP in the receiving river, even when confounding factors, such as fluctuations in non-point source pollution loads caused by rainfall and runoff, were excluded. The statistical approaches used in this study can be valuable and practical methods for such evaluations if sufficient prior and posterior data and appropriate covariates are obtained.

Effects of vegetation and terrain changes on spatial heterogeneity of soil C-N-P in the coastal zone protected forests at northern China.

Soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) are important indicators reflecting soil quality, and they can be used to effectively evaluate the effect of soil remediation. Many studies have evaluated the content of SOC, TN and TP in different ecosystems. However, after constructing protected forests for ecological restoration in the ecologically fragile coastal zone, the spatial distribution and influencing mechanism of SOC, TN and TP content is still uncertain. In this study, the spatial heterogeneity and influencing factors of SOC, TN and TP in surface (0-20 cm) soil were analyzed by traditional analysis and geostatistics. A total of 39 soil samples were collected under the coastal zone protected forest types including Quercus acutissima Carruth (QAC), Pinus thunbergii Parl (PTP), mixed PTP and QAC (QP) and Castanea mollissima BL (CMB) in the coastal zone protected forests in northern China. The results show that SOC, TN and TP content were defined as moderate variation, and they also show significant changes under different protected forest types (P < 0.05). The semivariance results indicate that SOC, TN and TP all exhibited strong spatial dependence class, with Range of 224 m, 229 m and 282 m respectively, which were more than the sampling scale of 200 m. The spatial prediction results showed that SOC, TN and TP content all appear in large areas of extremely low value in CMB, and its cross validation results showed that using vegetation and terrain factors as covariates in the spatial prediction of SOC, TN and TP can improve the prediction accuracy. The results of correlation analysis showed that the influencing factor for SOC and TN, and TP were NDVI and topographical changes, respectively. In general, vegetation and terrain factors as auxiliary factors can improved the accuracy of soil C-N-P spatial distribution prediction after afforestation in coastal zone.

Influence of the catchment area use on the water quality in the Utrata River.

The present paper discusses the impact of land use and seasons on the concentration of nutrients in the waters of the Utrata River (Pruszków Poviat, Mazowieckie Voivodeship) from April 2018 to March 2019. The pollution of rivers by nutrients is a major problem for society. Surface water is a source of drinking water, water used for industrial and agricultural purposes. With the increasing pollution of rivers, the purification process for these purposes becomes more expensive and more challenging. To assist in carrying out activities aimed at reducing the inflow of biogenic substances into large river systems and then down to the Baltic Sea, we analyzed the spatial and temporal dynamics of loads from the entire Utrata River catchment area. We divided the entire catchment area into three impact zones: grasslands and wastelands, urbanized areas, and agricultural land and examined changes in nutrient concentrations (total phosphorus, nitrate nitrogen, ammonium nitrogen) in each of the zones. The results were statistically processed using the 1-factor ANOVA method with the p-value of significance below 0.05. Research indicates an increase in the concentration of total phosphorus and nitrogen forms down the course of the river in urban and agricultural areas with persistently low concentrations of these biogenic substances in grasslands.

Filtration for improving surface water quality of a eutrophic lake.

Algal blooms and the presence of cyanotoxins in surface water restrict the public from accessing lakes and beaches for drinking and recreational activities. An effort was taken in this on-site study to improve the surface water quality of a eutrophic lake, which has been under a swimming advisory for many years. A floating filtration unit with non-woven geotextiles as a sole filter media was tested for removing algae, nutrients, and suspended solids from overlying water under different lake conditions. Three non-woven geotextiles of different pore sizes were examined in different combinations and lake water quality was monitored for different physico-chemical, biological parameters. A YSI-EXO2 multiparameter probe was used for continuous online water quality monitoring during filtration. Depending on the initial water quality, excellent removal efficiency was observed as follows: 85-98% turbidity, 98-100% total suspended solids (TSS), 57-88% total phosphorus (TP), 33-66% chemical oxygen demand (COD) and 80-96% chlorophyll a (Chl. a.). The filtered lake water quality satisfied the norm set for oligotrophic lakes for TP and Chl. a. Results from this on-site study are very promising, showing the potential applicability of geotextile filtration as an ecologically attractive technique to improve the surface water quality of small aquatic bodies.

Shifts in precipitation and agricultural intensity increase phosphorus concentrations and loads in an agricultural watershed.

Fertilizers and manure applied to cropland to increase yields are often lost via surface erosion, soil leaching, and runoff, increasing nutrient loads in surface and sub-surface waters, degrading water quality, and worsening the 'dead zone' in the Gulf of Mexico. We leverage spatial and temporal variation in agricultural practices and precipitation events to examine how these factors affect stream total phosphorus (TP) concentrations and loads in the Sugar River (Wisconsin), recently listed as impaired. To perform our analysis, we first collected water quality data from 1995 to 2017 from 40 sites along the Sugar River and its tributaries. Starting in 2004, three dairy farms expanded to become concentrated animal feeding operations (CAFOs) in this watershed. We then estimated how time of year, stream position, discharge volume, and proximity to the newly expanded CAFOs affected TP concentrations and loads. Total P concentrations, which ranged from 0.02 to 1.4 mg/L and often exceeded the EPA surface water standard of 0.1 mg/L, increased with increases in stream discharge and proximity to dairy operations, peaking in early spring to mid-summer coincident with extreme precipitation events. Our empirical analysis also shows that TP concentrations downstream from the newly permitted CAFOs increased by 19% relative to upstream concentrations. When examining total daily phosphorus loads (concentration × discharge) from this 780 km2 watershed, we found that loads ranged from 5.88 to 4801 kg. Compared to upstream TP loads, those downstream from the CAFOs increased by 91% after the expansions - over four times that of concentration increases - implying that the rate of downstream phosphorus transfer has increased due to CAFO expansion. Our results argue for standards that focus on loads rather than concentrations and monitoring that includes peak events. As agriculture intensifies and extreme rainfall events become more frequent, it becomes increasingly important to limit soil and TP runoff from manure and fertilizer. Siting CAFOs carefully, limiting their size, and improving farming practices in proximity to CAFOs in spring and early summer could considerably reduce nutrient loads.

A flow-weighted approach to generate daily total phosphorus loads in streams based on seasonal loads.

Phosphorus (P) is an essential nutrient for all forms of life but its over-enrichment can result in eutrophication of surface waters. For many watersheds around the world, some seasonal total P (TP) load datasets may exist but the continuous and multi-year daily TP concentrations and/or load datasets are not available due to the lacks of in situ P sensor measurement, time-consuming, and budget constraint. Traditionally, the seasonal TP loads are normally obtained with measuring daily TP concentrations for a couple of times within a season in a watershed, and then these daily TP concentrations along with their respective daily discharges are used to calculate the seasonal TP loads for the watershed. However, without the continuous and multi-year daily TP load dataset, development of total maximum daily load (TMDL) and calibration of watershed models for TP cannot be achieved. A flow-weighted method was developed (with detailed procedures) here to generate the daily TP loads based on the seasonal loads. The method was rigorously validated using the measured daily TP datasets from three different US Geological Survey gage stations. With very good statistical comparisons between the method predicted and field measured TP loads, we demonstrated that the flow-weighted method herein is a useful tool to disaggregate the seasonal TP loads into the daily TP loads when the measured daily TP data are not available while the TMDL development and model calibrations/validations are inevitable.

Spatiotemporal variation of nitrogen and phosphorus and its main influencing factors in Huangshui River basin.

The foundation of managing excess nutrients in river is the identification of key physical processes and the control of decisive influencing factors. The existing studies seldom consider the influence of rainfall-runoff relationship and only focus on a few anthropogenic activities and natural attributes factors. To address this issue, a comprehensive set of influencing factors including rainfall-runoff relationship (represented by runoff coefficient), basic physical and chemical parameters of water quality, land use types, landscape patterns, topography, and socioeconomic development was constructed in this study. M-K test and cluster analysis were conducted to identify the temporal mutation and spatial clustering characteristics of NH3-N and TP in Huangshui River basin, respectively. Partial least squares regression was used to elucidate the linkages between water contaminants and the factors. As shown in the results, the temporal mutations of NH3-N and TP were obvious in the middle reaches, with 4 out of 7 catchments in the middle reaches have a larger number of mutations of NH3-N than other catchments. The cluster analysis results of NH3-N and TP among catchments were similar. This study also indicated that although the Huangshui River basin was located in the upper reaches of the Yellow River, the influences of rainfall-runoff relationship on spatiotemporal changes of NH3-N and TP in its sub-basins were limited. Only the temporal change of NH3-N in Jintan catchment in the upstream area was significantly affected by runoff coefficient. The indexes of proportion of water area (PWA), proportion of impervious area (PIA), and proportion of primary industry (PPI) were the top three influencing factors of temporal variation of NH3-N and TP for most catchments in the middle reaches. The temporal change of NH3-N in Jintan catchment in the upstream area was obviously affected by runoff coefficient. The spatial variation of NH3-N and TP were all affected by PWA and proportion of secondary industry significantly. The results of this study can provide theoretical basis and technical support for the control and management of nitrogen and phosphorus pollution in upper reaches of rivers.

Phytoremediation capabilities of Salvinia molesta, water hyacinth, water lettuce, and duckweed to reduce phosphorus in rice mill wastewater.

The objective of this study was to investigate the reduction of phosphorus from rice mill wastewater by using free floating aquatic plants. Four free floating aquatic plants were used for this study, namely water hyacinth, water lettuce, salvinia, and duckweed. The aquatic plants reduced the total phosphorus (TP) content up to 80% and chemical oxygen demand (COD) up to 75% within 15 days. The maximum efficiency of TP and COD reduction was observed with water lettuce followed by water hyacinth, duckweed, and salvinia. The study also aims to predict phosphorus removal by three modeling techniques, for example, linear regression (LR), artificial neural network (ANN), and M5P. Prediction has been done considering hydraulic retention time (HRT), hydraulic loading rate (HLR), and initial concentration of phosphorus (Cin) as input variables whereas the reduction rate of TP (R) has been considered as a predicted variable. ANN shows promising results as compared to M5P tree and LR modeling. The model accuracy is analyzed using three statistical evaluation parameters which are coefficient of determination (R2), root mean square error (RMSE), and means absolute error (MAE).

Assessment and analysis of agricultural non-point source pollution loads in China: 1978-2017.

China's successful agriculture development has resulted in public concerned environmental problems. However, continuous and detailed data about Chinese agricultural non-point source pollution (ANPSP) loads are lacking. To assess and analyze Chinese ANPSP loads from 1978 to 2017, an inventory analysis was performed, and a socioeconomic and spatiotemporal analysis in the scale of provinces was conducted. The results showed that the pollution loads of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) increased by 91.0%, 196.2% and 244.1%, respectively, and their variation underwent a free development stage, reform promotion stage, market regulation stage and policy incentive stage. The results of the pollution source analysis showed that over the past 40 years, the total percent contribution to COD by livestock and poultry breeding (LPB) and rural household waste (RHW) accounted for 83.1%-96.6%, the total percent contribution to TN by mineral fertilizers (MF) and LPB accounted for 72.3%-80.8%, and the total percent contribution to TP by LPB, RHW and MF accounted for 69.1%-88.6%. In addition, Shandong, Guangdong, Sichuan, and Henan were the top producers of ANPSP loads, and their COD, TN, and TP loads accounted for approximately 32%, 30%, and 35% of the national totals, respectively. The discharge intensity of COD, TN and TP decreased by 79.2%, 67.8%, and 62.6%, respectively. The discharge intensity exhibited a phasic feature that aligned with the national economic plan in the temporal scale and was closely related to the agricultural conditions in the spatial scale.

Characterization of Total-Phosphorus (TP) Pretreatment Microfluidic Chip Based on a Thermally Enhanced Photocatalyst for Portable Analysis of Eutrophication.

To minimize conventional total-phosphorus (TP) analysis systems, TP pretreatment microfluidic chip is proposed and characterized in this paper. Phosphorus (P) is one of the most important elements in ecosystem but it causes the eutrophication due to its overdose. TP analysis systems are increasingly receiving attention as a means to prevent eutrophication. Even though conventional TP analysis systems have high accuracy and sensitivity, they are not frequently utilized outside the laboratory because of their bulky size, complicated pretreatment processes, long response times, and high cost. Thus, there is a growing need to develop portable TP analysis systems. The microfluidic chip in this study is proposed with the aim of simplifying and minimizing TP analysis by replacing the conventional pretreatment process with a new method employing a thermally enhanced photocatalytic reaction that can be applied directly to a microfluidic chip of small size. The fabricated TP pretreatment microfluidic chip with thermally enhanced photocatalyst (TiO2) was optimized compared to the conventional pretreatment equipment (autoclave). The optimum pretreatment conditions using the proposed chip were pretreatment time of 10 min and temperature of 75 °C. The optimized pretreatment process using the proposed microfluidic chip showed similar performance to the conventional pretreatment method, even with shorter pretreatment time. The shorter pretreatment time and small size are advantages that enable the TP analysis system to be minimized. Therefore, the proposed TP pretreatment microfluidic chip based on thermally enhanced photocatalytic reaction in this study will be utilized to develop a portable TP analysis system.