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Organic materials containing humic acids (HAs) play important roles in regulating the bioavailability of cadmium (Cd) in soils and thus its accumulation in crops. The effects of the two active components of HAs, humic acid (HA) and fulvic acid (FA), in organic materials and their different ratios (HA/FA) on Cd uptake and accumulation in rice were investigated using a field plot experiment, and their relationships with the Cd fractions and availability in paddy soil as influenced by the use of these organic materials were analyzed in combination with the fractionation method of chemical continuous extraction. The results showed that the effects of HAs on Cd availability in soil and Cd accumulation in rice grains were controlled by the ratios of the active components in the organic materials. The treatments with an HA/FA ratio ≥ 4/6 had a passivating effect on soil Cd, resulting in a significant reduction in Cd availability. Compared with that in the control without the application of HAs (CK), rice grain Cd concentration was reduced by 15.2%-33.3%, whereas those with an HA/FA ratio ≤ 2/8 activated Cd in soil, and the available Cd content was significantly increased. Compared with that in CK, rice grain Cd concentration was increased by 24.2%-42.4%. The ratios of HA/FA in HAs affected the morphological transformation of soil Cd. Compared with the CK treatment, the treatments with ratios of HA/FA ≥ 4/6 promoted the transformation of soil Cd from the exchangeable form (EX-Cd) with high activity to the carbonate bound form (CA-Cd) and Fe and Mn oxide-bound forms (FM-Cd) with low activity, whereas those with ratios of HA/FA ≤ 2/8 showed the opposite effects. The effects of HA and FA on soil pH and available sulfur concentration differed. Soil pH had a significant positive correlation with HA addition but a negative correlation with FA addition, and soil available sulfur content had a significant positive correlation with FA addition at the rice tillering stage. Therefore, to ensure the quality and safety of rice, organic materials with an HA/FA ratio ≥ 4/6 should be selected. The results provided a scientific basis for the directed utilization of organic materials containing HAs.

The article researched the effect of Iris pseudacorus L., Paspalum distichum L., Leersia hexandra Swartz, Ludwigia peploides and Hydrocotyle vulgaris on the nitrogen and phosphorus repression in sandy soil from lower reaches of Yangtze River and clay from stored littoral zone. The result indicated that plants had a significant inhibitory effect on total phosphorus release from sediment, with concentration in overlaying water below 0.02 mg·L -1 in Paspalum distichum L., Hydrocotyle vulgaris, Iris pseudacorus group, below 0.03 mg·L -1 in Leersia hexandra Swartz, Ludwigia peploides group; with release rate below 0.1 d -1 in Leersia hexandra Swartz and Ludwigia peploides group, below 0.05 d -1 in Paspalum distichum L., Hydrocotyle vulgaris , Iris pseudacorus group. While the plants were proved to aggravate total nitrogen release by accumulating in sediment, with concentration in overlaying water below 0.4 mg·L -1 in Paspalum distichum and Iris pseudacorus L. group; with release rate below 0.02 mg·L -1 . Root weight density, root length density, root surface area density were major factors, which increased the proportion of particles in sediment with diameter of below 50 μm, therefore decreased sediment resuspension against hydraulic disturbance; the root system also enriched total nitrogen in sediment and absorbed phosphorus from sediment. These five kinds of plants in terrestrial-aquatic transverse actually repressed nitrogen and phosphorus release from sediment in two ways mentioned above, Paspalum distichum L. and Iris pseudacorus L. possessed the best effect due to their developed root system, followed by Leersia hexandra Swartz and Hydrocotyle vulgaris , and Ludwigia peploides had the least effect.

The inherent relationship between land use pattern and inflow water quality is essential for nonpoint source pollution study. Response of inflow river quality to land use pattern in Northern part of Lake Erhai Watershed was analyzed in aspects of land use composition and configuration using spatial analysis and statistical analysis methods. The results indicated that as land use composition indexes, average slope and vegetation area percentage had significant relationship with TN and TP of inflow rivers. As land use configuration indexes, patch density, patch density of agriculture land and landscape shape index of water had significant relationship with TP and NH 4 + -N of inflow rivers. Response of inflow river quality to land use pattern was better at class level than at landscape level. Water quality response indicators were TP in rainy season and NH 4 + -N in dry season, of which regression adjustment coefficient R 2 was 0.761 and 0.978, respectively. Response of inflow river quality to land use pattern was better in dry season than in rainy season, and the water quality response indicators were TN, TP and NH 4 + -N. Improving vegetation coverage and agriculture land intensive degree and avoiding human disturb to natural water area especially in dry season were suggested in nonpoint source pollution control of northern watershed of Lake Erhai Watershed. Later research on relationship between land use configuration and inflow river quality should better be at class level.

In order to illuminate pollutants distribution characteristics in sediment of Shanmei Reservoir, sediment samples at 47 sampling stations were collected (include 8 column samples), and concentrations of total nitrogen, total phosphorus and organic matter in the sediment of each station were measured. C/N and the correlation of TN, TP and OM were also analyzed. Finally, pollution assessment for contaminated layer sediments was conducted. The results showed that the average contents of TN, TP and OM (mass fraction) were 1,180 mg · kg⁻¹, 642 mg · kg⁻¹ and 3.30% in the contaminated layer of sediments. Concentrations of total nitrogen and total phosphorus were low and stable at the depth of the normal layer. C/N of the contaminated layer of sediments was much higher than those in normal lakes, which showed that large part of OM came from natural land-based sources. Besides, a small part of OM came from phytoplankton, zooplankton and algae. Any two of TN,TP and OM were significantly correlated. This result showed that most of the nitrogen and phosphorus were in the organic form, and they came from similar sources. Evaluation results showed that both organic index and organic nitrogen belonged to the clean category. TP was at a moderate pollution level but not far from the category of heavy pollution.

The influence of temperature on P release from sediment of Lake Dianchi was discussed. Two kinds of inactivation agent schemes (Al2SO4.18H2O and PAC-Polymeric Aluminum Chloride) were used. The results show that the P release amount from sediment increased as the environmental temperature increased. As temperature raised 10 degrees C, the TP release amount increased 1.22%-38.69%, the DTP release amount increased 4.79%-76.82%. From 25 degrees C to 35 degrees C, the sediment had the largest P release increment. When temperature rose, the oxygen demand in the overlying water increased. Then the transformation speed of Fe3+ to Fe2+ increased, and then the release of Fe-P in sediment accelerated. On the other hand, microbe activity made the release possible through the transformation from organic-phosphorus to inorganic-phosphorus. The inactivation agents used here have significant effect on restraining the phosphorus release from sediment and the capture of particles containing phosphorus in overlying water. PAC had better P inactivation effect than Al2SO4 at 25 degrees C. Inhibition rate of P release from sediment by PAC was about 0.49%, 1.32%, 1.03% higher than Al2SO4 at 5, 15 and 25 degrees C, respectively. As the temperature rose to 35 degrees C, the capacity that PAC restricted P was weakened, so the effect of P release inhibition was weakened. Inactivation rate of Al2SO4 was higher about 2.25% than PAC to P from sediment at 35 degrees C. Temperature of sediments in PAC sets is 2-3 degrees C lower than that of Al2SO4 sets.