[Effects of Fertilization and Straw Mulching on Nitrogen and Phosphorus Loss in Chengdu Plain].

In recent years, the excessive application of nitrogen and phosphorus fertilizers has caused serious pollution and eutrophication, especially in paddy fields. Accordingly, a two-year (2018-2019) study was conducted at a rice paddy field under different fertilizer application rates and straw mulching in Chengdu Plain. N and P losses through the rainfall and surface runoff in the paddy field were measured under natural rainfall conditions. The results showed that nitrogen mainly existed in the form of ammonium nitrogen, and phosphorus mainly existed in the form of soluble phosphorus in the wet deposition. The wet deposition of nitrogen and phosphorus mainly occurred in June, July, and August. Surface runoff was positively correlated with rainfall, whereas surface runoff nitrogen concentration was inversely correlated with rainfall. The highest runoff losses of TN (4.75 kg·hm-2 in 2018 and 2.68 kg·hm-2 in 2019) were produced by TR3 practice and were 26.73% and 43.32% higher than that of the conventional practice. TN runoff loss was significantly decreased by reducing the rate of N fertilizer (P<0.05). Compared with that in the conventional practice TR1, TR4 reduced the N loss by 36.33% in 2018 and 26.74% in 2019, respectively. Optimized fertilizer TR2 and nitrogen reduction practice TR4 decreased P loss from surface runoff, and high intensity rainfall could reduce the content of granular phosphorus in surface runoff. The surface runoff occurring in July, August, and September contributed mostly to the total N loss, whereas the loss of total P mainly occurred before July. Consequently, the use of balanced fertilizer and decreased nitrogen fertilization amount might be effective strategies to attenuate non-point source pollution in the Chengdu Plain in the paddy fields.

[Emission Characteristics of Nitrogen and Phosphorus in a Typical Agricultural Small Watershed in Tuojiang River Basin].

The emission of nitrogen and phosphorus via non-point source pollution from a small watershed has become the main pollution source of river waters, while climatic conditions and human activities directly affect the changes in rainfall-runoff and types of land use that are closely related to nitrogen and phosphorus pollution. In this study, we explore the runoff loss, nitrogen and phosphors concentration, and nitrogen and phosphorus emission in Huajiaogou small watershed on the upper reaches of Yangtze River. The rainfall, runoff, and temporal changes of nitrogen and phosphorus were analyzed using the continuous position monitoring data. The results showed that:① the runoff volumes were 10.05×105 m3 and 3.34×105 m3 from July 1st to September 30th, accounting for 76.58% and 56.51% in 2012 and 2013, respectively, and they were positively correlated to rainfall. The peak concentrations of ammonia nitrogen (NH4+-N) from April 1st to June 30th were 11.51 mg ·L-1 and 4.44 mg ·L-1in 2012 and 2013, respectively. ② The NH4+-N emission risk period was from July 1st to September 30th, accounting for 78.45% and 62.24% in 2012 and 2013, respectively. The peak concentration and emission risk period of total nitrogen (TN) and nitrate nitrogen (NO3--N) were from July 1st to September 30th, and NO3--N was the main form of the total nitrogen emission. The peak concentration of NO3--N was 6.06 mg ·L-1 and 11.43 mg ·L-1in 2012 and 2013, respectively, and the loss in NO3--N from July 1st to September 30th accounted for 88.74% and 65.55% in 2012 and 2013, respectively. ③The emission risk period of total phosphorus (TP), dissolved total phosphorus (DTP), and particulate phosphorus (PP) was also from July 1st to September 30th, and the particulate phosphorus was the main form of the total phosphorus emission. The particulate phosphorus emission from July 1st to September 30th accounted for 36% and 68% in 2012 and 2013, respectively, and the ration of particle phosphorus to total phosphorus was easily affected by rainfall.

[Effect of Rainfall Intensity on the Content of Nitrogen and Phosphorus Components in Plateau Areas: A Case Study of the Fengyu River Watershed].

The runoff formed by rainfall carrying various land surface materials into rivers and lakes is an important factor leading to a change in water quality, and the characteristics of nitrogen and phosphorus output of rivers under different rainfall intensities are different. This study explores the impact of rainfall intensity on the water quality of the Fengyu River Watershed in the plateau agricultural region, based on the water quality monitoring data of the export section of the Fengyu River Watershed from 2011 to 2013, combined with local rainfall monitoring. The effects of four rainfall intensities (light rain, moderate rain, heavy rain, and torrential rain) on the content of different nitrogen and phosphorus components in water were analyzed. The results show that the rainfall intensity has a significant effect on the nitrogen and phosphorus emissions of the Fengyu River Watershed. The average nitrogen and phosphorus concentrations of all components are lower in light rain (<10 mm) and moderate rain (10-25 mm), and higher in heavy rain (25-50 mm) and torrential rain (50-100 mm). The percentage of NH4+-N (57.14%-76.85%) to TN is larger than that of PN (23.15%-42.86%), and the percentage of TDP (22.73%-28.00%) to TP is smaller than that of PP (72.00%-77.27%). The nitrogen concentration of different forms is:TN > NH4+-N > PN; the phosphorus concentration of different forms is:TP > PP > TDP.

[Impact of Human Activities on Net Anthropogenic Nitrogen Inputs (NANI) at Township Scale in Erhai Lake Basin].

Excessive nitrogen inputs from human activities have become the main cause of water eutrophication and related ecological hazards. In order to study the impact of human activities on nitrogen in the basin, and based on statistical data of administrative units in 16 towns and villages, this study used the NANI model to calculate net anthropogenic nitrogen inputs (NANI) at township scale in Erhai Lake basin. Results show that the total amount of NANI in Erhai Lake basin was 29.81×103 t in 2014, and nitrogen input intensity per unit area was 10986 kg·(km2·a)-1, significantly higher than the national average. The input of nitrogen from food by the local tourist population was 0.26×103 t, accounting for 8% of local food nitrogen input. Nitrogen input from chemical fertilizer is the largest NANI input source, accounting for 47% of net nitrogen input in the basin, followed by net nitrogen input of food and feed. The spatial distribution of NANI at township scale shows evident regionalization, with higher values in the north and lower values in the south of the basin. The intensity of NANI in towns with cropland or population is high. The corresponding risk of nitrogen pollution in Erhai Lake basin is therefore a primary concern, and will remain so in the near future.

[Characteristics of Nitrogen and Phosphorus Concentration Dynamics in Natural Ditches Under an Irrigation-Drainage Unit in the Jianghan Plain].

The paddy field in Jianghan Plain usually exists in the form of an irrigation-drainage unit, and the natural ditch is the main part of the unit. A continuous in situ monitoring of the natural ditch water level and water quality through the entire rice growing season in 2015 was conducted to investigate the dynamics of ditch water level and nitrogen and phosphorus concentration in the ditch. Another objective was to determine the effect of these factors. Results showed that during the entire rice growing season, the ditch water depth was maintained between 30 to 70 cm, and the water depth was higher during irrigation events than during rainfall events. Fertilization was the main factor affecting the nitrogen concentration in the ditch water. Two peaks of total nitrogen (TN) concentration appeared on June 18 and July 30 because of topdressing. In the early stage of rice growing, ammonia nitrogen (NH4+-N) concentration was higher than that of nitrate nitrogen (NO3--N). External disturbances (such as rainfall and irrigation events) were the main factors affecting the total phosphorus (TP) concentration in the ditch water. The dynamic of TP concentration in the ditch water was large, and it was consistent with that of the particulate phosphorus (PP) concentration. Drainage of the irrigation-drainage was mainly controlled artificially. The period from rice transplanting to 3 days after the first top dressing was critical in preventing the outflow of ditch water. During the rice harvest stage, the TN and TP concentration were 0.22 and 0.06 mg·L-1, and the water quality reached theⅡclass standard for surface water quality. This reduced the risk from drainage from the irrigation-drainage unit to the surrounding water environment.

[Seasonal Changes of the Pathways of Nitrogen Export from an Agricultural Watershed in China].

Nonpoint source pollution has become a major factor influencing the water quality. Identifying the pathway of nitrogen (N) transport from the source to the watershed mouth is a critical step in taking measures to control this pollution. However, it is difficult to identify the pathway of N transport because the transport pathway varies among different watersheds depending on the difference in the terrain, hydrology, and land cover etc and changes over time. Additionally, there is little knowledge about the major pathway of N transport through agricultural watersheds in the Yunnan Plateau lake area. The pathways of N export and their temporal variations over time were investigated in this study based on a typical agriculture-dominated watershed in a plateau lake area, Yunnan Province, and two-year monitoring data (June 2011-May 2013) in combination with a base flow separation program. The results show that the base flow accounts for most of the streamflow discharge (80.0%) and N export (71.1%). The proportion of the stream flow discharge via storm flow increases significantly with increasing rainfall. Therefore, the percentage of total N (TN) export via storm flow increases with increasing storm flow, which is closely related to rainfall. The major pathway of N export shifts toward storm flow when the storm flow proportion of the stream flow discharge increases up to 40%. During the monitoring period, the proportion of the TN export via storm flow increases up to 65.6% in the rainy season. This study provides important information for the improvement of the management of nonpoint source pollution at the watershed scale.

[Characteristics of Nitrogen and Phosphorus Emissions in the Gufu River Small Watershed of the Three Georges Reservoir Area].

To study the seasonal change characteristics and form composition of nitrogen and phosphorus output concentration and pollutant discharge load with rainfall characteristics at the outlet of Gufu river small watershed,the quality and quantity of water combined with natural rainfall events were monitored from January to December 2014.The results showed that the annual runoff volume of the Gufu river small watershed was 0.6×108 m3.The runoff was concentrated in raining season (from July to September),accounting for 63.9%.There was significant (P<0.01) positive correlation between the runoff flow and the annual rainfall.The annual emission of total nitrogen (TN) was 1432 t·a-1,and the emission was 853 t·a-1 during the raining season,accounting for 59.6% of annual TN emission content.The dissolved nitrogen was the main form of nitrogen emission,and the emission load of each month accounted for 55.4%-91.3% of TN.The positive correlation between the nitrate nitrogen concentration and rainfall was significant (P<0.05).The annual emission of total phosphorus (TP) was 563.1 t·a-1,and the content during the raining season accounted for 78.6% of TP annual emission content.The particle phosphorus (PP) was the main form of phosphorus emission,and the emission load of each month accounted for 41.9%-79.5% of TP.There was significant (P<0.01) positive correlation between the annual rainfall,sediment and TP,PP.The correlation between the total dissolved phosphorus concentration and rainfall was significant (P<0.05).

[Effects of different forms of P fertilizers on phytoremediation for As-contaminated soils using As-hyperaccumulator Pteris vittata L].

Fertilization has become one of the essential measures for enhancing efficiency of phytoremediating contaminated soils with heavy metal. In order to screen optimal P fertilizer for As-phytoremediation, a greenhouse study was conducted on the growth, As-accumulation and uptake of N, P and K by Pteris vittata L. in As-contaminated soils with different forms of P fertilizers. The results indicated that the biomass of plant with As addition decreased compared to no As-addition treatments except fused calcium magnesium phosphate (CaMg-P) treatment. The plants in As addition soils with CaMg-P, calcium dihydrogen phosphate (CDP) and di-ammonium phosphate (DAP) had higher biomass than those with other P fertilizer and control (0.83 g/pot). The As accumulations of plant aboveground in As addition soils are in order of CDP > CaMg-P> DAP> Potassium Phosphate Monobasic > Monosodium phosphate > control > Calcium superphosphate. The efficiency of As removal from As addition soils with CDP was the highest, 7.28%. Thus it can be seen the ability of phytoremediation using P. vittata could be improved by P fertilization, which CDP should be recommended preferentially and CaMg-P and DAP is considered as replaceable fertilizer for sake of pH, N, P and available As in phytoremediated soils.

Adsorption and redox reactions of heavy metals on synthesized Mn oxide minerals.

Several Mn oxide minerals commonly occurring in soils were synthesized by modified or optimized methods. The morphologies, structures, compositions and surface properties of the synthesized Mn oxide minerals were characterized. Adsorption and redox reactions of heavy metals on these minerals in relation to the mineral structures and surface properties were also investigated. The synthesized birnessite, todorokite, cryptomelane, and hausmannite were single-phased minerals and had the typical morphologies from analyses of XRD and TEM/ED. The PZCs of the synthesized birnessite, todorokite and cryptomelane were 1.75, 3.50 and 2.10, respectively. The magnitude order of their surface variable negative charge was: birnessite> or =cryptomelane>todorokite. The hausmannite had a much higher PZC than others with the least surface variable negative charge. Birnessite exhibited the largest adsorption capacity on heavy metals Pb(2+), Cu(2+), Co(2+), Cd(2+) and Zn(2+), while hausmannite the smallest one. Birnessite, cryptomelane and todorokite showed the greatest adsorption capacity on Pb(2+) among the tested heavy metals. Hydration tendency (pK(1)) of the heavy metals and the surface variable charge of the Mn minerals had significant impacts on the adsorption. The ability in Cr(III) oxidation and concomitant release of Mn(2+) varied greatly depending on the structure, composition, surface properties and crystallinity of the minerals. The maximum amounts of Cr(III) oxidized by the Mn oxide minerals in order were (mmol/kg): birnessite (1330.0)>cryptomelane (422.6)>todorokite (59.7)>hausmannite (36.6).

Selecting appropriate forms of nitrogen fertilizer to enhance soil arsenic removal by Pteris vittata: a new approach in phytoremediation.

Certain plant species have been shown to vigorously accumulate some metals from soil, and thus represent promising and effective remediation alternatives. In order to select the optimum forms of nitrogen (N) fertilizers for the arsenic (As) hyperaccumulator, Pteris vittata L., to maximize As extraction, five forms of N were added individually to different treatments to study the effect of N forms on As uptake of the plants under soil culture in a greenhouse. Although shoot As concentration tended to decrease and As translocation from root to shoot was inhibited, overall As accumulation was greater due to higher biomass when N fertilizer was added. Arsenic accumulation in plants with N fertilization was 100-300% more than in the plants without N fertilization. There were obvious differences in plant biomass and As accumulation among the N forms, i.e., NH4HCO3, (NH4)2S04, Ca(NO3)2, KNO3, urea. The total As accumulation in the plants grown in As-supplied soil, under different forms of N fertilizer, decreased as NH4HCO3>(NH4)2S04 > urea > Ca(NO3)2 >KNO3>CK. The plants treated with N and As accumulated up to 5.3-7.97 mg As/pot and removed 3.7-5.5% As from the soils, compared to approximately 2.3% of As removal in the control. NH4+ -N was apparently more effective than other N fertilizers in stimulating As removal when soil was supplied with As at initiation. No significant differences in available As were found among different forms of N fertilizer after phytoremediation. It is concluded that NH4+ -N was the preferable fertilizer for P. vittata to maximize As removal.

The controlling effect of pH on oxidation of Cr(III) by manganese oxide minerals.

Oxidation of Cr(III) by three types of manganese oxide minerals (birnessite I, birnessite II, and todorokite) and effects of pH were investigated by chemical analysis, equilibrium redox, X-ray diffraction (XRD), and transmission electron microscopy. The effects of pH in the reaction systems on the oxidation of Cr(III) were similar among the three manganese oxide minerals. As pH increased from pH 2.0, the amount of Cr(III) oxidized by the tested manganese oxide minerals first increased, and then peaked at pH 3.0-3.5. While pH continually increased from 3.0 to 3.5, the amount of Cr(III) oxidized by the manganese oxide minerals sharply decreased. Until pH was higher than 5.0-5.5, the Cr(III) oxidation amounts changed to a small extent or kept stable. pH influenced the oxidation of Cr(III) mainly by altering the redox potential in the system, i.e., the concentration of H+, the species of Cr(III), and their distributions in the system. However, the surface charge of the manganese oxide minerals, subjected to the pH in the system, was not found to greatly influence the extent of the oxidation. When pH was below 5.0, oxidation of Cr(III) by the manganese oxide minerals was (or tended to be) an equilibrium reaction and was controlled thermodynamically. When pH was above 5.0-5.5, Cr(OH)3 precipitate was produced in the system and pH had little effect on the oxidation content of Cr(III).