The annual frequency of red tides from 1977 to 2012 and the monthly frequency of red tides from 2001 to 2012 in China seas were used to establish the time series of red tide annual frequency and monthly frequency, res...The annual frequency of red tides from 1977 to 2012 and the monthly frequency of red tides from 2001 to 2012 in China seas were used to establish the time series of red tide annual frequency and monthly frequency, respectively. The annual frequency fit well with time segments revealed by piecewise linear regression analysis. The seasonal maximum of monthly frequency was in May （-18.22）, and the stochastic volatility tended to increase gradually with time series, with peak values occurring from May to July. Holt exponential smoothing and Holt-winter exponential smoothing were used to predict red tide annual and monthly frequencies, which revealed that the annual frequency of red tides would rise slowly by one time from 2013 to 2020, and that red tides would mainly occur from May to July in 2013-2016 with a peak value of about 25 times in May.展开更多
Debris flows in Jiangjia Ravine in Yunnan province, China are not only triggered by intense storms but also by short-duration and low-intensity rainfalls. This reflects the significance of antecedent rainfall. This pa...Debris flows in Jiangjia Ravine in Yunnan province, China are not only triggered by intense storms but also by short-duration and low-intensity rainfalls. This reflects the significance of antecedent rainfall. This paper tries to find the debris flow- triggering threshold by considering antecedent rainfall through a case study in Jiangjia Ravine. From 23 debris flow events, the I-D （Intensity-Duration） threshold was found, which is very dose to the line of 95th percentile regression line of rainfall events, representing that 95% of rainfalls can potentially induce debris flows and reflects the limitation of I-D threshold application in this area. Taking into account the effect of antecedent rainfall, the debris flowtriggering threshold for rainfall quantity and intensity is statistically and empirically derived. The relationships can be used in debris flow warning system as key thresholds. Coupling with the rainfall characteristics in this area, new thresholds are proposed as triggering and warning thresholds.展开更多
Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianc...Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianchi Lake, organic and inorganic phosphorus and nitrogen forms were analysed. The 210 Pb radiometric dating method was employed to study temporal changes in the phosphorus and nitrogen pools in Dianchi Lake. The result show that the total phosphorus(TP) and total nitrogen(TN) were both at high concentrations, ranging from 697.5–3210.0 mg/kg and 1263.7–7155.2 mg/kg, respectively. Inorganic phosphorus(IP) and total organic nitrogen(TON) were the main constituents, at percentages of 59%–78% and 74%–95%, respectively, in the sediments. Spatially, there was a decreasing trend in phosphorus and nitrogen contents from the south and north to the lake centre, which is related to the distribution pattern of local economic production. The burial rates of the various phosphorus and nitrogen forms increased in same spatially and over time. Particularly in the past two decades, the burial rates doubled, with that TN reached to 1.287 mg/(cm^2·yr) in 2014. As the most reactive forms, nitrate nitrogen(NO_3-N) and ammonia nitrogen(NH_4-N) were buried more rapidly in the south region, implying that the potential for releasing sedimentary nitrogen increased from north to south. Based on their concentrations and burial rates, the internal loads of phosphorus and nitrogen were analysed for the last century. A TP pool of 71597.6 t and a TN pool of 81191.7 t were estimated for Dianchi Lake. Bioavailable phosphorus and nitrogen pools were also estimated at 44468.0 t and 5429.7 t, respectively, for the last century.展开更多
基金financially supported by the Tianjin Marine Science and Technology Project (KJXH2011-05)local colleges and universities in Shanghai liberal arts academic programme (B5201120003)
文摘The annual frequency of red tides from 1977 to 2012 and the monthly frequency of red tides from 2001 to 2012 in China seas were used to establish the time series of red tide annual frequency and monthly frequency, respectively. The annual frequency fit well with time segments revealed by piecewise linear regression analysis. The seasonal maximum of monthly frequency was in May （-18.22）, and the stochastic volatility tended to increase gradually with time series, with peak values occurring from May to July. Holt exponential smoothing and Holt-winter exponential smoothing were used to predict red tide annual and monthly frequencies, which revealed that the annual frequency of red tides would rise slowly by one time from 2013 to 2020, and that red tides would mainly occur from May to July in 2013-2016 with a peak value of about 25 times in May.
基金support from the Key Deployment Project of Chinese Academy of Sciences(Grant No.KZZD-EW-05-01)National Key Technologies R&D Program of China(Grant No.2012BAK10B04)data support from the Dongchuan Debris Flow Observation Station
文摘Debris flows in Jiangjia Ravine in Yunnan province, China are not only triggered by intense storms but also by short-duration and low-intensity rainfalls. This reflects the significance of antecedent rainfall. This paper tries to find the debris flow- triggering threshold by considering antecedent rainfall through a case study in Jiangjia Ravine. From 23 debris flow events, the I-D （Intensity-Duration） threshold was found, which is very dose to the line of 95th percentile regression line of rainfall events, representing that 95% of rainfalls can potentially induce debris flows and reflects the limitation of I-D threshold application in this area. Taking into account the effect of antecedent rainfall, the debris flowtriggering threshold for rainfall quantity and intensity is statistically and empirically derived. The relationships can be used in debris flow warning system as key thresholds. Coupling with the rainfall characteristics in this area, new thresholds are proposed as triggering and warning thresholds.
基金National Natural Science Foundation of China(No.41503075,41673108,and 41571324)Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions,the State Key Laboratory of Lake Science and Environment(No.2016SKL005)China Postdoctoral Science Foundation Funded Project(No.2015M581826)
文摘Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianchi Lake, organic and inorganic phosphorus and nitrogen forms were analysed. The 210 Pb radiometric dating method was employed to study temporal changes in the phosphorus and nitrogen pools in Dianchi Lake. The result show that the total phosphorus(TP) and total nitrogen(TN) were both at high concentrations, ranging from 697.5–3210.0 mg/kg and 1263.7–7155.2 mg/kg, respectively. Inorganic phosphorus(IP) and total organic nitrogen(TON) were the main constituents, at percentages of 59%–78% and 74%–95%, respectively, in the sediments. Spatially, there was a decreasing trend in phosphorus and nitrogen contents from the south and north to the lake centre, which is related to the distribution pattern of local economic production. The burial rates of the various phosphorus and nitrogen forms increased in same spatially and over time. Particularly in the past two decades, the burial rates doubled, with that TN reached to 1.287 mg/(cm^2·yr) in 2014. As the most reactive forms, nitrate nitrogen(NO_3-N) and ammonia nitrogen(NH_4-N) were buried more rapidly in the south region, implying that the potential for releasing sedimentary nitrogen increased from north to south. Based on their concentrations and burial rates, the internal loads of phosphorus and nitrogen were analysed for the last century. A TP pool of 71597.6 t and a TN pool of 81191.7 t were estimated for Dianchi Lake. Bioavailable phosphorus and nitrogen pools were also estimated at 44468.0 t and 5429.7 t, respectively, for the last century.
