[Influence of Spatial Pattern of Paddy Field on the Losses of Nitrogen and Phosphorus in Three Gorges Reservoir Area].

This paper used three plots of paddy field in Wangjiagou small catchment in Fuling District, Chongqing Municipality as a case study. Wangjiagou, located in Three Gorges Reservoir Area, provided a good case in terms of its closeness of surface runoff. The samples of individual rainfall of twelve times and process of two typical individual rainfalls on three plots of sloping paddy field were collected from 2014 to 2015. These samples were used to analyze the influence of spatial pattern of sloping paddy field on the concentration of nitrogen and phosphorus in the surface runoff. The samples of daily runoff in subcatchments in 2010 and 2015 were used to analyze the influence of spatial pattern change of subcatchments' paddy field on the concentration of nitrogen and phosphorus in the surface runoff. The results indicated that the removal rates of TN, NO3--N and TP of paddy field at the valley bottom were higher than those in the mid-slopes. The removal rate of TP would be higher if plot size of paddy field at the bottom got bigger. During individual rainfall event, the losses concentration of TN, NO3--N and TP in the paddy fields was significantly different among three different spatial patterns during the previous period of heavy rain event, but it became different during the next period of moderate rain event. The two subcatchments' spatial pattern change of paddy field had weakened the intercepting purification ability of nitrogen and phosphorus losses of paddy field in 2015, compared with that in 2010. TN's losses concentration increased significantly during the periods of light and moderate rain event and base flow. TP's losses concentration fluctuated during the event from moderate rain to heavy rain. Hence, increasing the area of paddy field of catchment and optimizing its spatial pattern reasonably were found as effective measures to control agricultural non-point source pollution in the Three Gorges Reservoir Region.

[Comparison of Relationship Between Conduction and Algal Bloom in Pengxi River and Modao River in Three Gorges Reservoir].

Pengxi River is the largest tributary in the northern bank of Yangtze River in the Three Gorges Reservoir (TGR) region, and serious algal bloom has been reported since 2003 when the TGR dam started impounding water. On the other hand, Modao River, a tributary in TGR locating in the same county with Pengxi River, was rarely reported with algal bloom in the same time period. In this study, water samples were collected on the same day in both rivers in spring and summer, the most likely blooming seasons in TGR, to compare the water quality parameters and Chlorophyll-a(Chl-a) concentration dynamics in order to understand the mechanism of algal bloom in TGR. The results showed that the maximum value of Chl-a in Pengxi river reached 60.5 µg·L-1 in spring, and was only 7.8 µg·L-1 in summer, while in Modao river the Chl-a content was 2.92 µg·L-1 in spring and 7.48 µg·L-1in summer. Both rivers stratified during samplings, but having layers of thermocline and hypolimnion with the lack of epilimnion, and most of Chl-a content was located in thermocline. Also in both rivers, TN and TP exceeded the international threshold for eutrophication, with the average TN and TP values of 2.305 mg·L-1 and 0.053 mg·L-1in Pengxi River in spring, and 1.673 mg·L-1 and 0.097 mg·L-1 in summer, respectively, while in Modao River the values were 1.875 mg·L-1 and 0.075 mg·L-1 in spring, and 1.79 mg·L-1 and 0.054 mg·L-1 in summer respectively. Nutrients concentrations showed no significant correlation with Chl-a. On the other hand, conductivity value and trend were totally different between the two rivers:in Modao River in spring, the conductivity in upstream was only 75% of that in the main stream of the Yangtze River, and the backwater from the main stream reached to the middle in Modao river, where the highest Chl-a among all the river sampling sites was detected; summer conductivity distribution was similar with that in spring. Different from Modao River, the conductivity in upstream of Pengxi River in spring was 150% of that in the main stream of Yangtze, the backwater from the main stream reached area between sampling sites of PX04 and PX05 (upper than the middle reach); its upstream had significantly high content of Chl-a and conductivity, and these two factors were significantly positively correlated. The study showed that other than N and P, other ions in the Pengxi River played an important role in bursting "bloom", and need to be considered regarding bloom control.

[Nitrogen Losses Under the Action of Different Land Use Types of Small Catchment in Three Gorges Region].

As an independent water-collecting area, small catchment is the source of non-point source pollution in Three Gorges Region. Choosing 3 kinds of the most representative land-use types and using them to lay monitoring points of overland runoff within the small catchment of Wangjiagou in Fuling of Three Gorges Region, the author used the samples of surface runoff collected through the twelve natural rainfalls from May to December to analyze the feature of spatial-temporal change of Nitrogen's losses concentrations under the influence of different land use types and the hillslopes and small catchments composed by those land use types, revealing the relation between different land-use types and Nitrogen's losses of small catchments in Three Gorges Region. The result showed: the average losses concentration of TN showed the biggest difference for different land use types during the period of spring crops, and the average value of dry land was 1. 61 times and 6.73 times of the values of interplanting field of mulberry and paddy field, respectively; the change of the losses concentration of TN was most conspicuous in the 3 periods of paddy field. The main element was NO3⁻-N, and the relation between TN and NO3⁻-N showed a significant linear correlation. TN's and NO3⁻-N's losses concentrations were significantly and positively correlated with the area ratio of corn and mustard, but got a significant negative correlation with the area ratio of paddy and mulberry; NH4⁺-N's losses concentrations got a significant positive correlation with the area ratio of mustard. Among all the hillslopes composed by different land use types, TN's average losses concentration of surface runoff of the hillslope composed by interplantating field of mulberry and paddy land during the three periods was the lowest, and the values were 2.55, 11.52, 8.58 mg · L⁻¹, respectively; the hillslope of rotation plough land of corn and mustard had the maximum value, and the values were 27.51, 25.11, 27.11 mg · L⁻¹, respectively; different land use types and spatial combination ways of subcatchment had a greater influence on TN's losses concentrations, so using a reasonable way to adjust land use structure and spatial arrangement of whole catchment was an effective measure to control the source of non-point source pollution of Three Gorges Region.

[Reduction Effect of Reduced Phosphorus Fertilizer and Combining Organic Fertilizers on Phosphorus Loss of Purple Soil Sloping Field].

In order to better understand the effect of reduced phosphorus fertilizer and combining organic fertilizers on phosphorus loss of purple soil sloping field, three rainfall-runoff events were monitored using field runoff observation method in the purple soil sloping field in 2014. There were six treatments in this research, including optimized fertilization (P), optimized fertilization+pig manure application (MP), optimized fertilization+straw return (SP), optimized fertilization which was reduced by 20%+pig manure application (MDP), optimized fertilization which was reduced by 20%+straw return (SDP), without phosphate (P0). The results indicated that the interflow was the main pathway of runoff for purple soil sloping field. The average contents of total phosphorus (TP) and the phosphorus loss load of overland flow were all much higher than those of the interflow. The overland flow was the main pathway of the phosphorus loss load for purple soil sloping field. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of purple soil sloping field. Compared with the treatment P, the average content of total phosphorus on SDP was reduced by 57% and that on MDP was reduced by 48% in the storm rainfall. Combining straw was better than pig manure. The average contents of the phosphorus loss load of typical rainfall changed between 0.01 and 0.26 kg·hm-2. In different fertilization treatments, the average contents of the phosphorus loss load followed the order of P > MP > SP > MDP > SDP > P0. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of overland flow, but increased soil phosphorus leaching for purple soil sloping field.

[Variation Characteristics of Inorganic Phosphorus in Purple Soil Profile Under Different Conservation Tillage Treatments].

In this study the effects of tillage methods (rice-winter paddy field conventional farming, CF; rice-winter paddy field combing ridge with no-tillage, RNT1; rice-wheat or rape combing ridge with no-tillage, RNT2; rice-wheat or rape conventional paddy-upland rotation tillage, CR) on purple soil profile of different forms of inorganic phosphorus distribution characteristics were investigated in a long-term experimental site established in 1990, Chongqing City, China. The results showed that compared to the status before the experiment, the total phosphorus, available phosphorus and various morphologies of inorganic phosphorus all increased to a certain degree in the soils with different long-term tillage treatments,and the contents of different forms of inorganic phosphorus in soil size ranked as RNT2> CF> CR> RNT1. Except that the contents of Fe-P in the lower layer were higher than those in the upper layer, contents of Ca2-P, Ca8-P, Al-P, Ca10-P and O-P in the arable layers were all higher than those in the lower layers. The effects of farming practices on the availability of various phosphorus forms were significant. They were in the order of CR> RNT> CF. Long-term conventional paddy-upland rotation tillage was more advantageous to crops in the absorption of phosphorus. It was shown by relevant analysis that the contribution of various groups of inorganic phosphorus to purple soil was in the order of Ca2-P(0.9369)> Al-P(0.9158)> Ca8-P(0.9012)> Fe-P(0.8287)> Ca10-P(0.8059)> O-P(0.7472).

[Characterization of phosphorus forms in different organic materials].

The existing forms of phosphorus in seven organic waste materials including biogas residues of swine manure (ZZ), biogas residues of cattle manure (NZ), compost of cattle manure and corn straw (NJD), compost of sewage sludge (WD) and compost of rural daily garbage (NSLD) were characterized according to phosphorus fractionation procedures developed by DOU et al. The result showed that there was a great difference in the total phosphorus (TP) and the total phosphorus of various forms (P(t)) among different organic materials. ZZ had the highest content of TP with the value of 23.59 g x kg(-1); while NZ had the lowest TP content with the value of 3.61 g x kg(-1). The contents and proportions of phosphorus fractions in ZZ, NZ, NJD and WD followed the order of HCl-P > Residues-P > NaHCO3-P > NaOH-P > H2O-P, while followed the order of HC1-P > Residues-P > H2O-P > NaHCO3-P > NaOH-P in the three NSLDs. The proportion of HCl-P in the total fractionated phosphorus (P(tt)) in seven organic materials ranged from 47.75% to 84.96%, which indicated that most of P in organic materials existed in the forms that were easier to be extracted by strong extracting agents like HCl, which was difficult to be absorbed by plants. The inorganic phosphorus accounted for 79.72% -94.76% of the total phosphorus in the organic materials. Of all the phosphorus forms, the NaHCO3-P had the highest inorganic phosphorus fractions, but the inorganic phosphorus was mainly distributed in HCl-P. The organic phosphorus was mainly distributed in HCl-P and Residues-P. In addition, the higher proportions of inorganic phosphorus in NJD than those of NZ demonstrated that the composting process was benefit for the mineralization of organic phosphorus in organic materials and thus improving its availability.

[Effect of exogenous selenium on accumulation and chemical forms of cadmium in cucumber (Cucumis satiuus L.)].

Pot experiments were carried out to investigate the influence of different selenium (Se) levels (0, 0.5 and 1.0 mg x L(-1)) on the plant growth, concentration of malonaldehyde (MDA), activities of antioxidant enzymes, accumulation and chemical forms of cadmium (Cd) in cucumber when exposed to Cd (20 mg x kg(-1)). The results showed that dry weights of leaf, stem, root, fruit and plant, and concentrations and accumulation of Cd significantly differed between two varieties of cucumber Yanbai and Jinyou 1. With increasing levels of Se, the contents of MDA in the leaves of Yanbai increased, but the contents of MDA in the leaves of Jinyou 1 decreased. The contents of MDA in the roots of Yanbai first increased and then decreased, while the contents of MDA in Jinyou 1 first decreased and then increased. The variation trends of CAT, SOD and POD in the leaves and roots of both varieties were different with increasing levels of Se. The concentrations of different chemical forms of Cd in the fruit decreased after spraying of Se, compared with the control. Cadmium concentrations in the leaves, stem, roots and fruit of both varieties decreased by 3.2%-17.9%, 14.6%-28.2%, 5.1%-18.5% and 60.6%-75.8% in the presence of Se when exposed to Cd. Accumulation of Cd in the plant of both varieties was in order of Jinyou 1 > Yanbai in the presence or absence of Na2SeO3.

[Seasonal variation characteristics of phosphorus speciation in the sediment of Changshou Lake].

To further know the seasonal variation characteristics of phosphorus species in lake sediment, the contents of different phosphorus species in the surface sediment sampling from Changshou Lake were determined by using the SMT sequential extraction method in July and November, 2009, and March, 2010. The contents of total phosphorus (TP) basically show an order of the low-water period, high-water period, and normal-water period from high to low, and the maximum appeared in Shoudao (2960.29 mg/kg) while the minimum in Guanjiakou (586.05 mg/kg). The mass fractions of phosphorus associated with hydrous ferric/aluminum oxides (Fe/Al-P) and organic phosphorus (OP) in TP at all sampling sits are in an order of the normal-water period, high-water period, and low-water period from high to low, and the maximum of Fe/Al-P appeared in Lewen (40.01%) while that of OP in the dam mouth (72.44%). The mass fraction of phosphorus bound to calcium salt (Ca-P) in TP is in an order of the low-water period, normal-water period, and high-water period, and the maximum appeared in Baibudang (15.52%). These results suggested that the phosphorus speciation in the sediment of Changshou Lake shows obviously temporal and spatial distribution characteristics, and Fe/Al-P is mainly influenced by pH of the overlying water, while OP is not apparently influenced by dissolved oxygen (DO).