Spatiotemporal characteristics of cultivated land use eco-efficiency and its influencing factors in China from 2000 to 2020

Improving cultivated land use eco-efficiency(CLUE)can effectively promote agricultural sustainability,particularly in developing countries where CLUE is generally low.This study used provincial-level data from China to evaluate the spatiotemporal evolution of CLUE from 2000 to 2020 and identified the influencing factors of CLUE by using a panel Tobit model.In addition,given the undesirable outputs of agricultural production,we incorporated carbon emissions and nonpoint source pollution into the global benchmark-undesirable output-super efficiency-slacks-based measure(GB-US-SBM)model,which combines global benchmark technology,undesirable output,super efficiency,and slacks-based measure.The results indicated that there was an upward trend in CLUE in China from 2000 to 2020,with an increase rate of 2.62%.The temporal evolution of CLUE in China could be classified into three distinct stages:a period of fluctuating decrease(2000-2007),a phase of gradual increase(2008-2014),and a period of rapid growth(2015-2020).The major grain-producing areas(MPAs)had a lower CLUE than their counterparts,namely,non-major grain-production areas(non-MPAs).The spatial agglomeration effect followed a northeast-southwest strip distribution;and the movement path of barycentre revealed a"P"shape,with Luoyang City,Henan Province,as the centre.In terms of influencing factors of CLUE,investment in science and technology played the most vital role in improving CLUE,while irrigation index had the most negative effect.It should be noted that these two influencing factors had different impacts on MPAs and non-MPAs.Therefore,relevant departments should formulate policies to enhance the level of science and technology,improve irrigation condition,and promote sustainable utilization of cultivated land.

Progress in the research on aquatic environmental nonpoint source pollution in China

In this paper, the authors reviewed the development process of China's research on aquatic environmental nonpoint pollution, and the situation of nonpoint source pollution in east China was also analyzed.

Spatial and temporal variations of water quality in Cao-E River of eastern China

Evaluation and analysis of water quality variations were performed with integrated consideration of water quality parameters, hydrological-meteorologic and anthropogenic factors in Cao-E River, Zhejiang Province of China. Cao-E River system has been polluted and the water quality of some reaches are inferior to Grade V according to National Surface Water Quality Standard of China （GB2002）. However, mainly polluted indices of each tributary and mainstream are different. Total nitrogen （TN） and total phosphorus （TP） in the water are the main polluted indices for mainstream that varies from 1.52 to 45.85 mg/L and 0.02 to 4.02 mg/L, respectively. TN is the main polluted indices for Sub-watershed Ⅰ, Ⅱ, Ⅳ and Ⅴ（0.76 to 18.27 mg/L）. BOD5 （0.36 to 289.5 mg/L）, CODMn （0.47 to 78.86 mg/L）, TN （0.74 to 31.09 mg/L） and TP （0 to 3.75 mg/L） are the main polluted indices for Sub-watershed Ⅲ. There are tow pollution types along the river including nonpoint source pollution and point source pollution types. Remarkably temporal variations with a few spatial variations occur in nonpoint pollution type reaches （including mainstream, Sub-watershed Ⅰ and Ⅱ） that mainly drained by arable field and/or dispersive rural dwelling district, and the maximum pollutant concentration appears in flooding seasons. It implied that the runoff increases the pollutant concentration of the water in the nonpoint pollution type reaches. On the other hand, remarkably spatial variations occur in the point pollution type reaches （include Sub-watershed Ⅲ, Ⅳ and Ⅴ） and the maximum pollutant concentration appears in urban reaches. The runoff always decreases the pollutant concentration of the river water in the seriously polluted reaches that drained by industrial point sewage. But for the point pollution reaches resulted from centralized town domestic sewage pipeline and from frequent shipping and digging sands, rainfall always increased the concentration of pollutant （TN） in the river water too. Pollution controls were respectively suggested for these tow types according to different pollution causes.

Estimation of ammonia nitrogen load from nonpoint sources in the Xitiao River catchment, China

Ammonia nitrogen (NH4+-N) is one of the three main forms of total nitrogen (TN). Most studies have estimated the load of TN from nonpoint sources instead of one specific form. The relationship between land use and concentrations of NH4+-N in runoff was analyzed using the hydraulic analysis functions of a Geographic Information Systems (GIS), and the annual loads of NH4+-N in the Xitiao River catchment were estimated according to model results. The results suggested that the calculated annual loads of NH4+-N...

Phosphorus removal by the multipond system sediments receiving agricultural drainage in a headstream watershed

Wetland systems in headstream watersheds are important to control the nonpoint source pollutant phosphorus. Experiments were conducted using intact sediment-water columns obtained from the multipond system in Liuchahe watershed of Chaohu Lake to determine its capacity to retain P. It was found that pond sediments had strong P retention ability. For the Hill pond, Village pond and Rice pond, their retention coefficient(A) were 288.3, 279.2 and 260.8 L/m2, respectively. The equilibrium P concentration(EPC_w) were 0.016, 0.028 and 0.018 mg/L, respectively. The Hill pond indicated the highest P retention ability. P retained in the pond sediments indicated high stable degree. P removal from the overlying water column into the pond sediments followed a first-order kinetic model. Under the experimental hydrological conditions, the retention time had a positive correlation with the P loading. The multipond system could provide enough retention time to retain P in drainage runoffs. At the P levels evaluated, the sediments of the multipond system are effective sinks to retain P from nonpoint source runoffs.

Phosphorus sorption capacities in a headstream landscape—The pond chain structure

Understanding phosphorus sorption phenomena in different wetland sediments is important in controlling the P output in headstream watersheds. The pond chain structure （PCS） is widespread in the headstream agricultural watersheds in the southeast of China. Phosphorus sorption characteristics were determined for pond surface sediments （0-12 cm） along a pond chain structure in Liuchahe watershed of Chaohu Lake. Results showed that P sorption capacities （expressed by P sorption index （PSI）） varied both with the landscape position of the ponds and sediment depth. From foothill ponds to riverside ponds the P sorption capacities indicated a significant gradient variability. The higher elevation ponds showed greater sorption capacities, and with the pond elevation decline, P sorption capacities gradually decreased. Some physico-chemical properties, such as pH, oxalate-extractable Fe （Feox）, organic matter （TOC） and Mehlich l-extractable Ca, Mg of pond sediments also indicated significant gradient variability from high elevation ponds to low elevation ponds. Feox was the sediment parameters most highly positively correlated with PSI and was the key factor in controlling P sorption capacity in the pond chain structure （r=0.92, p〈0.001）. Long-term hydrologic and sediment inputs can affect the distribution of sediment constituents and further affect the P sorption capacity. Making the best of the spatial difference of sorption capacities of ponds in watersheds to control nonpoint source P pollutant is necessary.

Regional partitioning of agricultural non-point source pollution in China using a projection pursuit cluster model

A projection pursuit cluster（PPC） model was used to analyze the regional partitioning of agricultural non-point source pollution in China.The environmental factors impacting the agricultural non-point source pollution were compiled into a projection index to set up the projection index function.A novel optimization algorithm called Free search（FS） was introduced to optimize the projection direction of the PPC model.By making the appropriate improvements as we explored the use of the algorithm,it became simpler,and developed better exploration abilities.Thus,the multi-factor problem was converted into a single-factor cluster,according to the projection,which successfully avoided subjective disturbance and produced objective results.The cluster results of the PPC model mirror the actual regional partitioning of the agricultural non-point source pollution in China,indicating that the PPC model is a powerful tool in multi-factor cluster analysis,and could be a new method for the regional partitioning of agricultural non-point source pollution.

Modelling spatial variation in the treatment costs of nonpoint source pollution in mountainous regions of southwest China

Non-point source(NPS) pollution is considered to be one of the main threats of the aquatic environment. Mountainous regions are particularly important water sources for urban areas. The various driving factors of NPS pollution such as terrain, precipitation, and vegetation type in mountainous regions show clear spatial heterogeneity. Consequently, the management systems required for NPS pollution in mountainous regions are complex. In this study, we developed a framework to estimate and map the treatment costs for NPS pollution in mountainous regions and applied this method in Baoxing County, a typical mountainous county in Sichuan Province of southwest China. The export levels of total nitrogen(TN) and total phosphorus(TP) in Baoxing County were estimated using the water purification model in InVEST(Itegrated Valuation of Ecosystem Services and Tradeoffs) tool. NPS pollutant treatment costs were calculated based on the level of pollutants exports, water yield, water quality targets, and treatment costs of NPS pollutants per unit mass. The results show that at the watershed level the amounts of TN and TP exported in Baoxing County were below threshold limits. However, at the sub-watershed level, TN and TP excesses of 291.64 and 2.96 tons per year were found, respectively, with mean TN and TP treatment costs of 6.58 US$/hm^2 and 0.35 US$/hm^2. Appraising pollution treatment cost intuitively reflects the overall expenditure in NPS pollution reduction from an economic perspective. This study provides a foundation for the implementation of Payment for Ecosystem Service(PES) and the prevention and control of NPS pollution.

Identifying Nonpoint Sources of Phosphorus and Nitrogen: A Case Study of Pollution That Enters a Freshwater Wetland (Laguna Cartagena, Puerto Rico)

Point and nonpoint sources of phosphorus (P) and nitrogen (N) can cause reductions in water quality, including eutrophication. Nonpoint pollution represents a special challenge because of dispersed not easily identifiable sources such as the runoff from soil, nutrients, and other chemicals from agricultural fields and residential areas. Laguna Cartagena is a tropical freshwater wetland, situated in southwestern Puerto Rico. It is a eutrophic ecosystem, and its eutrophication is caused by both external nutrient loading and internal, mainly by phosphorus. This wetland has been affected by phosphorus loading from inorganic agricultural fertilizer in this historically oligotrophic wetland system until the end of subsidized fertilizer use and sugar cane cultivation in the late 1990s. This study identifies: 1) nonpoint sources of phosphorus (SRP, Soluble Reactive Phosphorus and TP, Total Phosphorus) and nitrogen (nitrate, nitrite, and ammonia) that enter Laguna Cartagena;and 2) the role of precipitation events on the contributions of phosphorus and nitrogen loading to ecosystems. Herein we assess water samples from five channelized external sources of P and N that enter Laguna Cartagena at two-week intervals from October 2013 through November 2014. Rainfall data were obtained weekly from a rain gauge. Standard methods were used for all chemical analyses. Results showed that the channelized waterways that carry water to the lagoon can be classified as hypereutrophic (>100 μg/L) for TP concentrations and oligotrophic (<200 μg/L) for nitrogen concentrations. Currently agriculture (rice and cattle) is the predominant land use at the nearby University of Puerto Rico (UPR) Lajas Agricultural Experiment Substation, the predominant nonpoint source of nutrient pollution (SRP, TP and ammonia) in the principal channelized water sources to the lagoon. Current nutrient loads are likely derived from fertilizers applied to the Substation’s rice fields, and a high density livestock. The second important cause of external surface water degradation (SRP, TP and ammonia) is the discharge from rural households in the drainage basin that discharge greywater directly to the environment, as indicated by the results from Cerro Alto hills immediately to the north of the lagoon. Precipitation also was associated with SRP, TP and ammonia loads.

Factors affecting flocculation performance of synthetic polymer for turbidity control

A multilateral effort into managing nonpoint source pollution from agriculture has gotten much attention for many years. Particularly during the heavy rain season, run-off of turbid water from sloped farmlands, fallow ground and/or unmanaged uplands is deteriorated. Flocculant polymer, commonly used in wastewater treatment facilities, but now exploited to improve control of sediment turbidity by promoting flocculation of particles in construction site. This study used the flocculant polymer to control the discharge of agricultural nonpoint source pollution and focused on the understanding of how soil-water and polymer properties affect flocculation performance. Therefore, a series of flocculation experiments under different conditions was evaluated for better polymer clarification efficiency. Various factors such as flocculant dose, end-over-end inversion of a cylinder, and soil-water properties (pH, NaCl, organic matter) were studied. The effective flocculant dose that fulfilled fast settling rate was 10mg·L-1. Additional findings included that 1) increasing pH decreased the settling rate of soil particle;2) a positive relationship between the percentage of turbidity reduction and a level of salinity in Kaolin suspension was observed, and 3) organic matter in soil solution inhibited PAM adsorption onto soil particles, which caused the reduction of flocculation performance. The findings of this study revealed that flocculant polymer possess good results as a turbidity reducetion measure and couldfurther provide valuable information to make better decision on establishment of Best Management Practice for handling agricultural nonpoint source pollution.

Study on Control Scheme for Nonpoint Source Pollution in Dahe Reservoir Water Source Protection Area of Dianchi Lake Basin

[ Objective] The research aimed to study control scheme for nonpoint source pollution in Dahe Reservoir water source protection area of Dianchi Lake basin.[ Method] On the basis of the SPOT5 satellite remote sensing imagery in 2010 and field investigation of GPS record, ecological design for nonpoint source pollution control in Dahe Reservoir water source protection area of Dianchi Lake basin was conducted. Then, the effects of optimization measures were evaluated by the reductions of N and P outputs on different land-use types. E Resultl Control functions of the water source protection area on soil erosion and the emissions of N, P and other pollutants would be promoted after optimization. The optimization meas- ures had a significant effect for prevention and control of the non-point source pollution in the water source protection area. [ Conclusion] The re- search provided scientific basis for promoting ecological construction of the small green basin in Dahe Reservoir water source protection area of Di- anchi Lake basin.

Do Water Matrix and Particulate Buffering Capacity Affect the Rate and Extent of P Release?

The aim of this study was to investigate the release of inorganic and organic phosphorus species from particles in rivers and estuaries during resuspension events such as storm, wind and tidal induced turbulence. To achieve this aim, laboratory beaker experiments were designed with autoanalyzer 3 (AA3). The study first investigates phosphorus equilibration in ultra-pure water (UHP) water, biotic river water and abiotic river water under short term and long term conditions. Then, three typical organic and inorganic phosphorus compounds were selected (orthophosphate, phytic acid (PTA) and β-D-glucose-6-phosphate monosodium salt (G-6-P)) to simulate the effect of addition input to river and estuaries in the time period of 150 h. The results show that in a turbulent river, dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) will reach equilibrium between the particulate matter and the water column within 24 h. Additional input of DIP or DOP to the river, has different effects to the river nutrients balance. The buffering capacity of the suspended particulate matter (SPM) plays an important role and behavior difference to the inorganic and various organic phosphorus compounds.

Phosphorus Mass Balance of the Illinois River Watershed in Arkansas and Oklahoma

Water quality degradation in the Illinois River Watershed (IRW) has been linked to excess nutrients, primarily phosphorus (P). A mass balance study was performed on the IRW in Oklahoma and Arkansas to quantify the magnitude of P entering the watershed between the closure of Lake Tenkiller’s dam in 1954 to 2006. Results showed that a substantial mass of P was, and is, being imported into the watershed relative to the mass of P leaving the watershed. The study demonstrated that poultry production has been the major contributor of P imported to the watershed since 1964, and is currently responsible for more than 76% of the net annual P additions to the IRW. Between 1949 and 2002, more than 200,000 tonnes of P was added to the IRW. A P delivery ratio for the IRW was computed from the mass balance results and observed loads indicating that 4% of annual P applied to the IRW landscape reached Lake Tenkiller between 1999 and 2006. Allocation of P loads from 1949 to 2002 to Lake Tenkiller computed with the delivery ratio showed that wastewater treatment plant (WWTP) discharges were responsible for more than 50% of P reaching Lake Tenkiller in 1949, followed by dairy cattle (32% of loads). Poultry contribution to P reaching Lake Tenkiller was 5% in 1949 but increased rapidly to become the largest source in 1969 at approximately 49%, and in 2002 at 54%. Both dairy and WWTP portions of the loads declined from 1949 levels with less than 4% attributable to dairy and less than 34% assigned to WWTP in 2002.

Development of a Hybrid Best Management Practice System for Control of Agricultural Nonpoint Water Pollution

Agricultural drainage ditches play an important role in removing surplus water;however, these can also potentially act as major conduits of agricultural nonpoint source pollutants, including sediment, nitrogen, and phosphorus. A supplementary hybrid system to limit such pollution was developed in this study;this consists of biodegradable fiber check dams, used in combination with a synthetic polymer (Polyacrylamide, PAM). An open channel experiment was conducted to optimize the design of the hybrid system, taking into account a variety of physical and hydraulic conditions. Subsequent field application of the hybrid system improved runoff water quality, such as 10.0% to 98.3% reduction for suspended solids, 25.2% to 98.4% reduction for turbidity, 21.1% to 91.1% increase for BOD, 19.2% to 75.4% increase for COD, 21.0% to 73.3% reduction for T-N, 5.9% to 91.2% reduction for T-P and 35.7% to 97.6% reduction for fecal coliforms. This clearly showed that this hybrid system could play a significant role in supplementing conventional best management practices.

A WEPp-Water Quality model for simulating nonpoint source pollutants in nonuniform agricultural hillslopes:Model development and sensitivity

The Water Erosion Prediction Project(WEPP)model code was modified extensively to support the simulation of nonpoint source(NPS)pollutant sourcing and transport in nonuniform hillslopes based on NPS science from the Soil and Water Assessment Tool(SWAT).This was accomplished utilizing WEPP's overland flow element(OFE)in place of SWAT's hydrologic response unit(HRU)construct which enabled more physically plausible routing within a hillslope.In addition,several improvements to the NPS code base were implemented.These include:free-source format,modern-Fortran conventions,minor enhancements to NPS model science,and code refactoring.This manuscript documents all model development activities,presents a comparison of relevant WEPP and WEPP-WQ code bases,and performs a local sensitivity analysis of the final model code for the most important input parameters and processes.Sensitivity results indicated that the model performed as expected according to its design and provided important insights for potential subsequent validation studies.

Field test of best management practice pollutant removal efficiencies in Shenzhen,China

This paper presents a study on the use of best management practices(BMPs)for controlling nonpoint pollution in the Xikeng Reservoir watershed located in Shenzhen,China.A BMP treatment train design,including a pond,a wetland,and a buffer strip placed in series was implemented at the reservoir location.A separate grass swale was also constructed at the site.Low impact development(LID)BMPs,namely a planter box and bioboxes,were used at the parking lot of the reservoir’s Administration Building.Samples were collected during storm events and were analyzed for total suspended solids(TSS),biochemical oxygen demand(BOD5),ammonia nitrogen(NH3-N),and total phosphorus(TP).The removal efficiencies of both BMP systems were evaluated using the Efficiency Ratio(ER)method based on the event mean concentration(EMC)data.In summary,the pond/wetland treatment train removed 70%–90%of TSS,20%–50%of BOD5,and 30%–70%of TP and NH3-N.The swale removed 50%–90%of TSS,30%–55%of BOD5,–10%–35%of NH3-N,and 25%–70%of TP.For the planter box and biobox,the ranges of removal rates were 70%–90%,20%–50%,and 30%–70%for TSS,BOD5,and ammonia and phosphorus,respectively.

Modeling the effects of constructed wetland on nonpoint source pollution control and reservoir water quality improvement

This article describes the integrated modeling approach for planning the size and the operation of constructed wetlands for maximizing retention of nonpoint source pollutant loads and reservoir water-quality improvement at a catchment scale. The experimental field-scale wetland systems （four sets, 0.88 ha each） have been in operation since 2002, where water depth was maintained at 30-50 cm and hydraulic loading rate was at 6.3-18.8 cm/day. The wetland system was found to be adequate for treating polluted stream water with stable removal efficiency even during the winter. The integrated modeling system （modified-BASINS） was applied to the Seokmoon estuarine reservoir watershed and calibrated with monitoring data from constructed wetland, stream, and reservoir. The calibrated integrated modeling system estimated that constructing wetlands on 0.5% （about 114 ha） of the watershed area at the mouth of reservoir could reduce 11.61% and 13.49% of total external nitrogen and phosphorus loads, respectively. It also might improve the nitrogen and phosphorus concentration of the reservoir by 9.69% and 16.48%, respectively. The study suggested that about 0.1%-1.0% of the watershed area should be allocated for constructed wetland to meet specified water-quality standards for the estuarine reservoir at the polder area where land use planning is relatively less complicated.

Development of integrated catchment and water quality model for urban rivers

This paper presents the development of an urban river water quality model which considers the physical-biochemical processes within rivers and the incorporated urban catchment rainfall-runoff process developed with the time-area method. Unlike other models that simulate the hydrological and receiving water quality processes in the rural areas of the watershed scale, the model developed here is typically efficient for simulating the water quality response to nonpoint loadings from urban drainage systems, where the hydrological process is disturbed by artificially pumped discharge in wet-weather periods. This model is employed to assess the river water quality restoration in Nanfei River in Hefei City, China, where the model is calibrated against the measured data（i.e., the COD, the BOD5, the NH3-N, and the DO） in 2010, and the model parameters are suggested. It is shown that the nonpoint pollutants from the urban catchments contribute 34%-47% of the total pollutant inputs（i.e., the COD, the BOD5, and the NH3-N）, despite their low flow component of 13.4%. Apart from the improvement of the wastewater treatment plant effluent（i.e., Grade IV of the Surface Water Quality Standard）, a nonpoint loading reduction of 27.2%, 25.1%, and 35.3% of the COD, the BOD5, and the NH3-N are anticipated to meet the designated surface water quality standards of Grade V.

Predicting the impacts of climate change on nonpoint source pollutant loads from agricultural small watershed using artificial neural network

This study described the development and validation of an artificial neural network （ANN） for the purpose of analyzing the effects of climate change on nonpoint source （NPS） pollutant loads from agricultural small watershed. The runoff discharge was estimated using ANN algorithm. The performance of ANN model was examined using observed data from study watershed. The simulation results agreed well with observed values during calibration and validation periods. NPS pollutant loads were calculated from load-discharge relationship driven by long-term monitoring data. LARS-WG （Long Ashton Research Station-Weather Generator） model was used to generate rainfall data. The calibrated ANN model and load-discharge relationship with the generated data from LARS-WG were applied to analyze the effects of climate change on NPS pollutant loads from the agricultural small watershed. The results showed that the ANN model provided valuable approach in estimating future runoff discharge, and the NPS pollutant loads.

Nanomaterials for environmental burden reduction,waste treatment,and nonpoint source pollution control:a review

Nanomaterials are applicable in the areas of reduction of environmental burden,reduction/treatment of industrial and agricultural wastes,and nonpoint source(NPS)pollution control.First,environmental burden reduction involves green process and engineering,emissions control,desulfurization/denitrification of nonrenewable energy sources,and improvement of agriculture and food systems.Second,reduction/treatment of industrial and agricultural wastes involves converting wastes into products,groundwater remediation,adsorption,delaying photocatalysis,and nanomembranes.Third,NPS pollution control involves controlling water pollution.Nanomaterials alter physical properties on a nanoscale due to their high specific surface area to volume ratio.They are used as catalysts,adsorbents,membranes,and additives to increase activity and capability due to their high specific surface areas and nano-sized effects.Thus,nanomaterials are more effective at treating environmental wastes because they reduce the amount of material needed.