Spatiotemporal distribution, risk assessment and source appointment of metal(loid)s in water and sediments of Danjiangkou Reservoir, China.

Danjiangkou Reservoir is the biggest artificial reservoir in China. But spatiotemporal distribution and risks of metal(loid)s in it were still unclear after the operation of Middle Route of South-to-North Water Diversion Project. In this study, distribution pattern of fifteen metal(loid)s in the Danjiangkou Reservoir was investigated. It was shown that metal(loid)s concentrations in the water were much lower than the drinking water quality standards in China, while Sb, Co, Cd and Cr were identified as the major pollutants in the sediments. Environment-metal(loid)s correlation analysis revealed total organic carbon, sulfate, temperature, dissolved oxygen and total phosphorus markedly controlled metal(loid)s distribution in the water, while organic carbon, total phosphorus and ammonia nitrogen shaped their distribution in the sediments. Results of risk assessment further revealed that the sediments of Danjiangkou Reservoir were minor to moderate polluted, and Sb, Cd exhibited the highest potential ecological risk. Additionally, source identification showed agricultural activities (25.3%), industrial and mining activities (17.5%) and natural processes (57.2%) were the dominant sources of metal(loid)s burden in the sediments. Overall, the results are of significance to understanding the ecological risk and pollution sources in the Danjiangkou Reservoir, which is essential for the effective management of metal(loid)s pollution.

Quantifying effects of conservation practices on non-point source pollution in the Miyun Reservoir Watershed, China.

Non-point source (NPS) pollution, including fertilizer and manure application, sediment erosion, and haphazard discharge of wastewater, has led to a wide range of water pollution problems in the Miyun Reservoir, the most important drinking water source in Beijing. In this study, the Soil and Water Assessment Tool (SWAT) model was used to evaluate NPS pollution loads and the effectiveness of best management practices (BMPs) in the two subwatersheds within the Miyun Reservoir Watershed (MRW). Spatial distributions of soil types and land uses, and changes in precipitation and fertilizer application, were analysed to elucidate the distribution of pollution in this watershed from 1990 to 2010. The results demonstrated that the nutrient losses were significantly affected by soil properties and higher in both agricultural land and barren land. The temporal distribution of pollutant loads was consistent with that of precipitation. Soil erosion and nutrient losses would increase risks of water eutrophication and ecosystem degradation in the Miyun Reservoir. The well-calibrated SWAT model was used to assess the effects of several Best Management Practices (BMPs), including filter strips, grassed waterways, constructed wetlands, detention basins, converting farmland to forest, soil nutrient management, conservation tillage, contour farming, and strip cropping. The removal rates of those BMPs ranged from 1.03 to 38.40% and from 1.36 to 39.34% for total nitrogen (TN) and total phosphorus (TP) loads, respectively. The efficiency of BMPs was dependent on design parameters and local factors and varied in different sub-basins. This study revealed that no single BMP could achieve the water quality improvement targets and highlighted the importance of optimal configuration of BMP combinations at sub-basin scale. The findings presented here provide valuable information for developing the sustainable watershed management strategies.

Performance of Saturated Riparian Buffers in Iowa, USA.

Nitrate from artificial drainage pipes (tiles) underlying agricultural fields is a major source of reactive N, especially NO, in surface waters. A novel approach for reducing NO loss is to intercept a field tile where it crosses a riparian buffer and divert a fraction of the flow as shallow groundwater within the buffer. This practice is called a saturated riparian buffer (SRB), and although it is promising, little data on the performance of the practice is available. This research investigated the effectiveness of SRBs in removing NO at six sites installed across Iowa, resulting in a total of 17 site-years. Water flow and NO in the tile outlets, diverted into the buffers, and NO concentration changes within the buffers were monitored throughout the year at each site. Results showed that all the SRBs were effective in removing NO from the tile outlet, with the average annual NO load removal ranging from 13 to 179 kg N for drainage areas ranging from 3.4 to 40.5 ha. This is NO that would have otherwise discharged directly into the adjoining streams. The annual removal effectiveness, which is the total NO removed in the SRB divided by the total NO draining from the field, ranged from 8 to 84%. This corresponds to an average removal rate of 0.040 g N m d with a range of 0.004 to 0.164 g N m d. Assuming a 40-yr life expectancy for the structure and a 4% discount rate, we computed a mean equal annual cost for SRBs of US$213.83. Given the average annual removal of 73 kg for all site-years, this cost equates to $2.94 kg N removed, which is very competitive with other field-edge practices such as denitrification bioreactors and constructed wetlands. Thus, SRBs continue to be a promising practice for NO removal in tile-drained landscapes.

Development of PLEAD: A Database Containing Event-based Runoff Phosphorus Loadings from Agricultural Fields.

Computer models are commonly used for predicting risks of runoff P loss from agricultural fields by enabling simulation of various management practices and climatic scenarios. For P loss models to be useful tools, however, they must accurately predict P loss for a wide range of climatic, physiographic, and land management conditions. A complicating factor in developing and evaluating P loss models is the relative scarcity of available measured field data that adequately capture P losses before and after implementing management practices in a variety of physiographic settings. Here, we describe the development of the P Loss in runoff Events from Agricultural fields Database (PLEAD)-a compilation of event-based, field-scale dissolved and/or total P loss runoff loadings from agricultural fields collected at various research sites located in the US Heartland and southern United States. The database also includes runoff and erosion rates; soil-test P; tillage practices; planting and harvesting rates and practices; fertilizer application rate, method, and timing; manure application rate, method, and timing; and livestock grazing density and timing. In total, >1800 individual runoff events-ranging in duration from 0.4 to 97 h-have been included in the database. Event runoff P losses ranged from <0.05 to 1.3 and 3.0 kg P ha for dissolved and total P, respectively. The data contained in this database have been used in multiple research studies to address important modeling questions relevant to P management planning. We provide these data to encourage additional studies by other researchers. The PLEAD database is available at .

In Situ Denitrification in Saturated Riparian Buffers.

Excess NO leaching from the agricultural Midwest via tile drainage water has contributed to both local drinking water and national Gulf of Mexico benthic hypoxia concerns. Both in-field and edge-of-field practices have been designed to help mitigate NO flux to surface waters. Edge-of-field practices focus on maximizing microbial denitrification, the conversion of NO to N gas. This study assessed denitrification rates from two saturated riparian buffers (SRBs) for 2 yr and a third SRB for 1 yr, for a total of five sample years. These SRBs were created by diverting NO-rich tile drainage water into riparian buffers soils. The SRBs in this study removed between 27 and 96% of the total diverted NO load. Measured cumulative average denitrification rate for each SRB sample year accounted for between 3.7 and 77.3% of the total NO removed. Both the cumulative maximum and 90% confidence interval denitrification rates accounted for all of the NO removed by the SRBs in three of the five sample years, indicating that denitrification can be a dominant NO removal mechanism in this edge-of-field practice. When adding the top 20 cm of each core to the cumulative denitrification rates for each SRB, denitrification accounted for between 33 and over 100% of the total NO removed. Buffer age (time since establishment) was speculated to enhance denitrification rates, and there was a trend of the soil closer to the surface making up the majority of the total denitrification rate. Finally, both NO and C could limit denitrification in these SRBs.

Modeling the non-point source pollution risks by combing pollutant sources, precipitation, and landscape structure.

Traditional models of nutrient simulation usually focus on the pollutant sources and precipitation, lacking the quantification of landscape structure. We developed a new prediction model of pollution risks by combing pollutant sources, precipitation, and landscape structure, which was defined as the source-precipitation-landscape model (SPLM). The SPLM was applied to simulate the non-point source (NPS) total nitrogen (TN) exports in one of the largest river basins in China (the Haihe River Basin, HRB). TN concentrations of 35 sampling catchments in 2013 were used to test the accuracy of the SPLM. Simulated results showed that (1) the SPLM had a relative high accuracy in the simulation of NPS TN export and intensity, especially for TN intensity. (2) The mean TN export and intensity of all the 1578 catchments in the HRB were 441.97 t and 2.08 t/km2, respectively. (3) The TN export intensities differed greatly among the sub-basins in the HRB, ranging from 0.64 to 6.81 t/km2. On the whole, the TN export intensities of the plain sub-basins (e.g., the Tuhaimajia River, the Heilonggang River, and the Beisihe River) were much higher than those of mountainous sub-basins (e.g., the Yongding River, the Beisanhe River, and the Luanhe River). (4) The contributions to TN exports, from high to low, were land use (38.82%), livestock husbandry (33.57%), and rural population (27.61%). Among all the ten pollution sources, arable land (30.87%), rural population (27.61%), and large livestock (17.73%) had the top three contributions to TN exports. This study provides a feasible tool for policymakers and administrators to develop workable management measures for the mitigation of NPS pollution. This SPLM can be extended to other regions in a rapid urbanization context.

Decreasing farm number benefits the mitigation of agricultural non-point source pollution in China.

Agricultural non-point source pollution causes global warming and the deterioration of air and water quality. It is difficult to identify and monitor the emission sources of agricultural pollution due to the large number of farms in China. Many studies focus on the technological aspect of achieving agricultural sustainability, but its socioeconomic aspect is poorly understood. Here, we report how group size (number of farms in a certain region) affects agricultural pollution governance through conducting a social science experiment. We found that when communication was allowed among group members, a small group size facilitated cooperation. Although deviations from the cooperation equilibrium occurred with time in all groups, the smaller the group size, the slower the cooperation equilibrium became frangible. These findings suggest that reducing number of farms and extending the length of farm property rights can benefit the mitigation of agricultural non-point pollution in China. Social science experiments can be a useful tool to understand the socioeconomic aspect of agricultural sustainability.

Reduction of non-point source contaminants associated with road-deposited sediments by sweeping.

Road-deposited sediments (RDS) on an expressway, residual RDS collected after sweeping, and RDS removed by means of sweeping were analyzed to evaluate the degree to which sweeping removed various non-point source contaminants. The total RDS load was 393.1 ± 80.3 kg/km and the RDS, residual RDS, and swept RDS were all highly polluted with organics, nutrients, and metals. Among the metals studied, Cu, Zn, Pb, Ni, Ca, and Fe were significantly enriched, and most of the contaminants were associated with particles within the size range from 63 µm to 2 mm. Sweeping reduced RDS and its associated contaminants by 33.3-49.1% on average. We also measured the biological oxygen demand (BOD) of RDS in the present work, representing to our knowledge the first time that this has been done; we found that RDS contains a significant amount of biodegradable organics and that the reduction of BOD by sweeping was higher than that of other contaminants. Significant correlations were found between the contaminants measured, indicating that the organics and the metals originated from both exhaust and non-exhaust particles. Meanwhile, the concentrations of Cu and Ni were higher in 63 µm-2 mm particles than in smaller particles, suggesting that some metals in RDS likely exist intrinsically in particles, rather than only as adsorbates on particle surfaces. Overall, the results in this study showed that sweeping to collect RDS can be a good alternative for reduction of contaminants in runoff.

Statistical assessment of nonpoint source pollution in agricultural watersheds in the Lower Grand River watershed, MO, USA.

The water quality in many Midwestern streams and lakes is negatively impacted by agricultural activities. Although the agricultural inputs that degrade water quality are well known, the impact of these inputs varies as a function of geologic and topographic parameters. To better understand how a range of land use, geologic, and topographic factors affect water quality in Midwestern watersheds, we sampled surface water quality parameters, including nitrate, phosphate, dissolved oxygen, turbidity, bacteria, pH, specific conductance, temperature, and biotic index (BI) in 35 independent sub-watersheds within the Lower Grand River Watershed in northern Missouri. For each sub-watershed, the land use/land cover, soil texture, depth to bedrock, depth to the water table, recent precipitation area, total stream length, watershed shape/relief ratio, topographic complexity, mean elevation, and slope were determined. Water quality sampling was conducted twice: in the spring and in the late summer/early fall. A pairwise comparison of water quality parameters acquired in the fall and spring showed that each of these factors varies considerably with season, suggesting that the timing is critical when comparing water quality indicators. Correlation analysis between water quality indicators and watershed characteristics revealed that both geologic and land use characteristics correlated significantly with water quality parameters. The water quality index had the highest correlation with the biotic index during the spring, implying that the lower water quality conditions observed in the spring might be more representative of the longer-term water quality conditions in these watersheds than the higher quality conditions observed in the fall. An assessment of macroinvertebrates indicated that the biotic index was primarily influenced by nutrient loading due to excessive amounts of phosphorus (P) and nitrogen (N) discharge from agricultural land uses. The PCA analysis found a correlation between turbidity, E. coli, and BI, suggesting that livestock grazing may adversely affect the water quality in this watershed. Moreover, this analysis found that N, P, and SC contribute greatly to the observed water quality variability. The results of this study can be used to improve decision-making strategies to improve water quality for the entire river basin.

Nonpoint Source Pollution.

A review of the literature published during year 2017 on topics relating to nonpoint source pollution (NPS) is presented. This article is written with a view to cater the need of nonpoint source pollution research and to summarize the new advancements in NPS control. Research developments on assessing, monitoring, and controlling the nonpoint source pollution are the main focus of this review. Future research topics related to NPS are also recommended.

A national assessment of the effect of intensive agro-land use practices on nonpoint source pollution using emission scenarios and geo-spatial data.

China's intensive agriculture has led to a broad range of adverse impacts upon ecosystems and thereby caused environmental quality degradation. One of the fundamental problems that face land managers when dealing with agricultural nonpoint source (NPS) pollution is to quantitatively assess the NPS pollution loads from different sources at a national scale. In this study, export scenarios and geo-spatial data were used to calculate the agricultural NPS pollution loads of nutrient, pesticide, plastic film residue, and crop straw burning in China. The results provided the comprehensive and baseline knowledge of agricultural NPS pollution from China's arable farming system in 2014. First, the nitrogen (N) and phosphorus (P) emission loads to water environment were estimated to be 1.44 Tg N and 0.06 Tg P, respectively. East and south China showed the highest load intensities of nutrient release to aquatic system. Second, the amount of pesticide loss to water of seven pesticides that are widely used in China was estimated to be 30.04 tons (active ingredient (ai)). Acetochlor was the major source of pesticide loss to water, contributing 77.65% to the total loss. The environmental impacts of pesticide usage in east and south China were higher than other parts. Third, 19.75% of the plastic film application resided in arable soils. It contributed a lot to soil phthalate ester (PAE) contamination. Fourth, 14.11% of straw produce were burnt in situ, most occurring in May to July (post-winter wheat harvest) in North China Plain and October to November (post-rice harvest days) in southeast China. All the above agricultural NPS pollution loadings were unevenly distributed across China. The spatial correlations between pollution loads at land unit scale were also estimated. Rising labor cost in rural China might be a possible explanation for the general positive correlations of the NPS pollution loads. It also indicated a co-occurred higher NPS pollution loads and a higher human exposure risk in eastern regions. Results from this research might provide full-scale information on the status and spatial variation of various agricultural NPS pollution loads for policy makers to control the NPS pollution in China.

Nonpoint Source Pollution.

Research advances on non-point source pollution in the year 2015 have been depicted in this review paper. Nonpoint source pollution is mainly caused by agricultural runoff, urban stormwater, and atmospheric deposition. Modeling techniques of NPS with different tools are reviewed in this article.