1951-2010年珠江流域洪水极值序列平稳性特征研究

水文序列的平稳性假设是传统水文统计学方法在水文序列分析研究中的基本假设,随着气候变化与人类活动对地表水文过程的影响,这种假设往往存在问题,使水文分析得出误导性结论。以珠江流域28个测站1951—2010年年最大洪峰流量序列为例,用Pettitt方法结合Loess参考函数检验序列中均值和方差变异,用Mann-Kendall(MK)和Spearman法检测时间趋势性,用广义可加模型(GAMLSS)和长期持续效应等具体分析序列的平稳性。研究结果表明:1均值/方差变异主要集中在西江和东江流域,变异时间分别集中在1990年左右和1968—1987年间;2变异点的存在与否对序列趋势检验结果有重要影响,在考虑变异点前提下,珠江流域年最大洪峰流量序列基本无显著趋势性;3在GAMLSS模型中,对于不具有和具有突变点序列,Gamma分布均为选择次数最多的最优极值分布,不具有突变点序列分布参数θ1或θ2非平稳模型与平稳模型差距较小,具有突变点序列则相反;4统计上检测出具有突变点或者显著时间趋势性的测站,同样检测出高Hurst系数,反之亦然。Hurst系数估计因样本容量较小具有较大不确定性。东江流域受流域内水利工程的剧烈影响,尽管检测出高Hurst系数,但仍认定为非平稳序列;西江干流主要受支流汇流和气候变化影响,高Hurst系数表明其水文过程可能是长期稳定过程中局部波动的结果。     

The persistence and disappearance by washoff and dryfall of methoxychlor from soybean foliage—a preliminary study

Abstract

The persistence and disappearance (washoff or dryfall) of methoxychlor [2,2‐bis(p‐methoxypheny1)‐1,1,1‐trichloroethane] from mature soybean [Glycine max (L.) Merrill] foliage was investigated in a small field plot study under natural rainfall conditions in 1977 and 1978. Residue analyses were conducted using whole plant samples‐ Methoxychlor washoff rate was 8±4% of the amount on plants (prior to rain) per centimeter of rainfall, regardless of time after application. Total seasonal washoff for 1978 accounted for 33.5% of the applied pesticide; however, 30.5% of the total loss was removed by washoff on the second day after application. Dryfall or dislodgeable residue accounted for less than 1% of the amount applied. The amount of dryfall was significantly greater in plots entered by workers than in those where entry was avoided. More than 19% of the applied methoxychlor was lost as a result of through‐fall to the ground during application to the plots. Statistical analyses indicated that within‐sample variation for mechanical chopping of plant samples was significantly smaller at the 5% level than for a hand chopping method. Results from this study will be useful in defining research objectives for the development of algorithms to describe the behavior of foliar‐applied compounds. Such algorithms are necessary for estimating runoff losses of insecticides to water bodies.     

Bioavailability of diuron,imazapic and isoxaflutole in soils of contrasting textures

This research was aimed at understanding the dynamics of the herbicides diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], imazapic [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-methylnicotinic acid] and isoxaflutole [5-cyclopropyl-4-(2-methanesulfonyl-4-trifluoromethyl benzoyl)isoxazole] in two soils of different physico-chemical properties. To accomplish such intent, several greenhouse experiments were run. The bioavailability of diuron (0; 1.6 and 3.2 kg ha^{? 1}), imazapic (0; 98 and 122.5 g ha^{? 1}) and isoxaflutole (0; 35 and 70 g ha^{? 1}) was measured in samples from a sandy loam soil and a clay soil, by sowing a bioindicator (Brachiaria decumbens), at 0, 25, 50, 75 and 100 days after herbicides application (DAA). Diuron was very stable in clay soil, providing control equal to or higher than 92% of bioindicator, up to 100 DAA, as assumed by biomass accumulation. No differential effect was observed in sandy loam soil, even when 2x labeled rate were applied. Imazapic provided a short bioavailability in relation to B. decumbens, independent of rates applied. The persistence of isoxaflutole was longer in clay soil (28 to 30 days).     

Persistence of granular and EC formulations of chlorpyrifos in a mineral and an organic soil incubated in open and closed containers

Abstract

Samples of a mineral soil (Plainfield sand) and an organic soil (muck) were treated with granular and EC formulations of chlorpyrifos and incubated at 27±1°C and 65±5% RH in open and closed containers. Duplicate samples of each soil‐formulation‐container combination were analyzed for residual chlorpyrifos during a 23 wk period. The disappearance rates observed demonstrate that the relative importance of formulation and containment on overall persistence depends on soil type. For the mineral soil, disappearance was slower from closed containers and formulation had only a slight effect while, in the organic soil the granular formulation disappeared slower than the EC and there was little difference between open and closed containers. The relative importance of degradation and volatilization in the disappearance of chlorpyrifos from soil is discussed.     

Leaching and persistence of ametryn and atrazine in red–yellow latosol

This study evaluated the mobility and persistence of atrazine and ametryn in red–yellow latosols using polyvinyl chloride columns with a diameter of 100 mm and a height of 15 cm. The assays simulated 60-mm rainfall events at 10-day intervals for 70 days. The persistence and leaching were evaluated for these two herbicides. The analytes obtained from the samples were quantified by gas chromatography using flame ionization detection. Compared with ametryn, atrazine showed a greater potential to reach depths below 15 cm over 30 days of simulated rain. Ametryn, however, showed greater persistence in soil at 70 days after application. The persistence of atrazine and ametryn in soil under sunlight was 10 and 144 days respectively. Atrazine was more susceptible to sunlight than ametryn because sunlight favored atrazine degradation in hydroxyatrazine. The results indicate that in red–yellow latosol, atrazine has a high leaching potential in short term, but that ametryn is more persistent and has a high leaching potential in long term.     

Dissipation of pendimethalin in the soil of field pea (Pisum sativum L.) and detection of terminal residues in plants

Dissipation of pendimethalin in the soil of field peas (Pisum sativum L.) at 0 to 110 days, and terminal residues in green and mature pea were studied under field conditions. Pendimethalin was applied as pre-emergence herbicide at 750, to 185 g a.i. ha^?1 in winter, in field peas. Dissipation of pendimethalin in the soil at 0 to 110 days followed first-order kinetics showing a half-life of 19.83 days averaged over all doses. Low pendimethalin residues were found in mature pea grain (0.004, 0.003, <0.001 μg g^?1), and straw (0.007, 0.002, <0.001 μg g^?1) at 750, 350 and 185 g a.i. ha^?1 treatments, respectively. The study indicated that residues of pendimethalin in green and mature pea were within the prescribed MRL limits.     

Comparative hersistence of chlorpyrifos in a mineral soil after granular and drench applications

Abstract

Lorsban 15G (15% chlorpyrifos) at 1.6 and 2.2 g a.i./10 m row, and Lorsban 4E (40.7% chlorpyrifos) at 2.0 g a.i./10 m row were applied respectively to a silt loam soil as a band treatment at seeding and as a drench after seeding. The rate of disappearance of chlorpyrifos [Q,Q‐diethyl Q‐(3,5,6‐trichloro‐2‐pyridinyl) phosphorothioate] was relatively fast in the first 15 days but slowed down considerably thereafter regardless of the methods of application and application rates; and there was a statistically significant (p=0.05) linear relationship between the natural logarithm of chlopyrifos concentration and time. Based on the linear regression equations, the calculated pseudo‐first‐order rate constants were 0.041 day^‐1 and 0.044 day^‐1 respectively for the band treatments at 1.6 and 2.2 g a.i./10 m row; and 0.040 day^‐1 for the drench. The calculated half‐lives for all three treatments were similar and they ranged frcm 15.8 days to 17.3 days. The degradation product 3,5,6‐trichloro‐2‐pyridinol (TP) was detected in soil but not 3,5_/6‐trichloro‐2‐methoxypyridine (TMP). The concentration of TP increased steadily to a peak and declined thereafter. The highest mean concentration of TP was 2.21 ppm (dry wt) detected 29 days after band treatment at the high rate. After 90 days the concentration of TP decreased to 0.43 ppm (dry wt).     

Persistence of seven pesticides as influenced by soil moisture1

Abstract

Pesticides are often applied in combination, but less‐often is soil persistence measured this way. The present field and laboratory study determined relative persistence of five herbicides and two insecticides, co‐applied, as a function of three soil water contents. Losses were modeled adequately by first‐order dissipation, with no significant improvement by using a two‐compartment model. The order of persistence in a silt loam, at 25% moisture, was carbofuran < cyanazine < metribuzin = alachlor < atrazine < ethoprop < metolachlor (t_½ ranged from 7–91 days). Carbofuran degradation increased greatly from 12–25% soil moisture; atrazine was unaffected by 12–35%, whereas the remaining compounds showed limited increasing loss in wetter soil. Field‐based persistence was more variable, but generally similar to lab rankings.     

Screening of a potential leafhopper attractants and their applications in tea plantations

Abstract

Pheromones can be used as leafhopper attractants. However, commercial pheromone products, such as the Ingle lure, have certain limitations, including poor persistence in the field. In this study, (E)-2-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, (E)-ocimene, linalool, and geraniol were selected and behaviorally tested as potential leafhopper attractants. Y-tube olfactometer tests showed that the C2 formulation was more effective than other formulations. In tea field trials, the number of leafhoppers caught by sticky board traps baited with C2 lures was greater than that caught by treatment. The number of leafhoppers attracted by the C2 lures was greater than that attracted by the commercial Ingle lures. Additionally, the total amount of active C2 components on lures was greater than that of the active components on the lure after 14 days. Thus, the results indicated that the C2 formulation may attract leafhoppers and have a greater persistence than other formulations in tea field.