[Correlation Analysis of Water Quality Between Lake Inflow and Outflow: A Case Study of Poyang Lake].

The relationships between inflow and outflow water quality data for Poyang Lake from 1996 to 2016 are discussed and the main influencing factors are identified. TN and TP were the main factors causing a decline in water quality in Poyang Lake during the study period. The water quality of both the inflow and outflow rivers was generally good between 1996 and 2003; however, water quality declined over the study period, which is attributed to an increase in nutrients loads in the watershed. From 2004 to 2011, the water quality of the "Five Rivers" decreased significantly, which caused the water quality of Poyang Lake to decline. Due to the high purification capacity of Poyang Lake, the water quality of the outflow during this period was relatively good. A decline in water quality after this point was affected by pollution loads and hydrological conditions. Specifically, from 2012 to 2016, water quality in Poyang Lake and of the inflow water declined further. This was combined with a decrease in the water-purification capacity of the lake due to changes in the hydrological conditions, resulting in lower water quality at the outflow. Overall, the water quality of the inflow river has been closely related to the water quality in Poyang Lake. The concentrations of TN were significantly higher in the southern and eastern areas of Poyang Lake compared to the western areas. Higher nutrient loading from the Ganjiang River and the Xinjiang River has been an important driver. The concentrations of TP in the southern area of the lake have been significantly higher than in the eastern and western areas. This is attributed to comparatively high TP loads in the Ganjiang River and the Fuhe River. Compared to the changes in hydrological conditions, variations in nutrient loading have had a greater effect on water quality in the lake.

[Characteristics of nitrogen cycling in farm systems in a small watershed of Three Gorges Reservoir Area, China].

In China, the agricultural activities are often carried out by single family, and the balance of nitrogen in every farm may have great effect on agricultural production and environment. A farm survey was carried out on the amounts of chemical fertilizers consumed, the amounts of food and feed purchased, and the livestock manures used in Zhangjiachong watershed of Three Gorges Reservoir Area for each farmer. According to the characteristics of nitrogen flow, farms in this watershed could be divided into 5 types: breeding specialized farms, orange-growing farms, tea-growing farms, vegetable-growing farms and traditional farms. Differences in environmental nitrogen load were observed among the five farm types in the following order: breeding specialized farms > vegetable-growing farms > orange-growing farms > tea-growing farms approximately = traditional farms, being (363 +/- 129), (355 +/- 127), (345 +/- 107), (152 +/- 60) and (151 +/- 73) kg x (hm2 x a)(-1) respectively by nitrogen. Nitrogen cycle for different farm fields showed that field surplus nitrogen ranged from (102 +/- 68) to (303 +/- 134) kg x (hm2 x a)(-1) among different farms. Among the five farm types, the field surplus nitrogen followed the order of vegetable-growing farms > citrus-growing farms > tea-growing farms > breeding specialized farms approximately = traditional farms, being (303 +/- 134), (262 +/- 100), (111 +/- 46), (102 +/- 68) and (103 +/- 67) kg x (hm2 x a)(-1). The nitrogen from farm life activities accounted for 28% of the total N load, while the field surplus nitrogen was 72%. It was estimated that field nitrogen consumption was the predominated nitrogen pollution source in the watershed. However, the farmer's daily life pollution should not to be neglected. Breeding specialized farms, vegetable-growing farms and orange-growing farms were the high potential pollution sources for the water environment in the watershed, and the major attention should be paid to these types of farms. Field survey on farm nitrogen cycle is of significance in evaluating the nitrogen flows in the agro-ecosystems and revealing the characteristics of nitrogen cycling in the region.

[Effects of long-term fertilization on paddy soil organic carbon mineralization].

An incubation test was conducted with the paddy soil samples collected from three national long-term experiment stations in Hunan Province to study the characteristics of organic carbon mineralization under different fertilization treatments and its relationships with organic carbon fractions, i.e., total organic carbon (TOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC). The results showed that in all fertilization treatments, the cumulative amounts of CO2 and CH4 ranged from 448.64 to 1516.77 microg x g(-1) and from 15.60 to 33.34 microg x g(-1), respectively. In the 58 days of incubation, the mineralized carbon accounted for 3.59%-5.57% of TOC. The CO2 production rate was higher in the early phase of incubation, decreased rapidly then, and tended to stable afterwards; while the CH4 production rate had a slow increase first and declined rapidly then. A combined application of chemical fertilizers and manure or straw increased the cumulative amounts of CO2 and CH4 significantly. In all fertilization treatments, the cumulative mineralized C had significant correlations with TOC, MBC and WSOC, but less correlation with its percentage in TOC.

[Soil N2O flux and its affecting factors under different land use patterns in Three Gorges Reservoir Area of China].

By using static chamber techniques, the N2O emission from soils under different land use patterns was measured. The results showed that the N2O flux ranged from -21 to 435 microg x m(-2) h(-1), and the annual N2O flux was decreased in the order of vegetable field > orchard > upland > upland transferred from paddy field > woodland, being 447.14, 313.57, 167.00, 124.875 and 7.24 mg x m(-2), respectively. The N2O flux presented significant seasonal fluctuation, with the maximum in spring and summer, followed by in autumn, and the minimum in winter, which was approximately consistent with the changes of air- and soil temperature. N2O flux had significant positive correlation with the soil temperature at 5 cm depth and soil NO3(-)-N content, but no significant correlation with soil moisture and NH4(+)-N contents.

[Variations and influencing factors of nitrate nitrogen concentration in water in a small watershed of Three Gorges area].

In order to study the water quality and response to influencing factors in typical watersheds of Three Gorges area between 2004 and 2005, the variation characteristics of nitrate nitrogen concentration were analyzed under heterogeneous landscape condition through continuous observation with method of dividing into sub-watersheds in Quxi watershed (the first-grade branch, located in Three Gorges). The results suggested that nitrate nitrogen concentration fluctuated between 0.4 and 14.6 mg x L(-1) with the highest in winter,higher in autumn and summer and lower in spring. Discrepancy also exists in different years. In addition, nitrate nitrogen concentration shows increasing trends with the aggravating impacts of agricultural activities on environment. Moreover, nitrate nitrogen concentration had some relationships with different land use types and space layout to some extent, and was also affected by geological and hydrological characters in the sub-watersheds, which indicated that response of nitrate nitrogen concentration in water was evident to influencing factors.

[Dissolved silicon, inorganic nitrogen and phosphorus in the stream water of two small watersheds in Three Gorges area].

By using the method of fixed-pointed monitoring in streams of two small watersheds in Three Gorges Reservoir Area, the contents of dissolved silicon (DSi), dissolved inorganic nitrogen (DIN) and dissolved phosphorus (DP) are analyzed. The seasonal variation, the content ratio of DSi, DIN and DP, and the potential environmental problems are also discussed. The results indicate that: (10 In the two rivers, DSi content ranges from 0.18 to 19.89 mg x L(-1), DIN from 0.39 to 6.85 mg x L(-1) , and both are higher in the dry period than in the wet period; (2) DP content is from 0.01 to 0.08 mg x L(-1), which shows no significant difference between the dry and wet period; (3) The contents of DSi and DIN in Quxi River are higher than in Baota River, which may relate with the local agricultural activities, land use/land cover, fertilizer and so on; (4) The contents of DSi, DIN and DP in two small watersheds are all higher than in Three Gorge Reservoir, and the content ratio of DSi, DIN, DP is about 138 : 81 : 1 in Baota River, and 500 : 350 : 1 in Quxi River, which suggests that more attention should be paid to a potential threat to water environment such as Water-bloom.