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1.
Baseflow has become an important source of nitrate nonpoint source pollution in many intensive agricultural watersheds. Uncertainties in baseflow nutrient load separation are caused by the effects of hydrometeorological factors on both baseflow recession and baseflow nutrient load recession. These uncertainties have not been addressed well in the existing separating algorithms, which are based on simple baseflow rate–load relationships. In the present study, a recursive tracing source algorithm (RTSA) was developed based on a nonlinear reservoir algorithm and hydrometeorology-corrected baseflow nutrient load recession parameter. This approach was used to reduce the uncertainty of baseflow nitrate load estimation caused by variations in different load recessions under varying climate conditions. RTSA validation in a typical rainy agricultural watershed yielded Nash–Sutcliffe efficiency, root mean square error-observation standard deviation ratio, and R2 values of 0.91, 0.30, and 0.91, respectively. The baseflow nitrate–nitrogen (N─NO3–) loads from 2003 to 2012 in the Changle River watershed of eastern China were estimated with the RTSA. The results indicated that baseflow nitrate export accounted for 62.0% of the mean total annual N─NO3– loads (18.0 kg/ha). The total baseflow N─NO3– export was highest in spring (3.6 kg/ha), followed by summer (3.2 kg/ha), winter (2.3 kg/ha), and autumn (2.1 kg/ha). The contribution of baseflow to total nitrate in the stream decreased in the order of winter (69.88%) >spring (66.59%) >autumn (60.36%) >summer (54.04%). The monthly baseflow N─NO3– loads and flow-weighted concentrations greatly increased during the research period (Mann–Kendall test, Zs > 2.56, p < .01). Without proper countermeasures, baseflow nitrate may represent a serious long-term risk for water surfaces in the future. 相似文献
2.
《Continental Shelf Research》2005,25(9):1081-1095
The mesoscale distribution and seasonal variation of the size structure of phytoplankton biomass, as measured by chlorophyll a (chl a), was studied in the Ebro shelf area (NW Mediterranean) during three different seasons: autumn, winter and summer. In autumn and summer, when the water column was, respectively, slightly or strongly stratified and nutrient concentrations were low at surface, average total chl a values were 0.31 and 0.29 mg m−3, respectively. In winter, the intrusion of nutrients into the photic zone by intense vertical mixing and strong riverine inputs, produced an increase of the total autotrophic biomass (0.76 mg m−3). In the three seasons, the main contributor to total chl a was the picoplanktonic (<2 μm) size fraction (42% in winter and around 60% in autumn and summer). The nanophytoplankton (2–20 μm) contribution to total chl a showed the lowest variability amongst seasons (between 29% and 39%). The microplanktonic (>20 μm) chl a size fraction was higher in winter (27%) than in the other seasons (less than 13%). The maximum total chl a concentrations were found at surface in winter, at depths of 40 m in autumn and between 50 and 80 m in summer. The relative contribution of the <2 μm size fraction at these levels of the water column tended to be higher than at other depths in autumn and winter and lower in summer. In autumn and winter, nutrient inputs from Ebro river discharge and mixing processes resulted in an increase on the >2 μm contribution to total chl a in the coastal zone near the Ebro Delta area. In summer, the contribution of the <2 and >2 μm chl a size fractions was homogeneously distributed through the sampling area. In autumn and summer, when deep chl a maxima were observed, the total amount of the autotrophic biomass in the superficial waters (down to 10 m) of most offshore stations was less than 10% of the whole integrated chl a (down to 100 m or to the bottom). In winter, this percentage increased until 20% or 40%. The >2 μm chl a increased linearly with total chl a values. However, the <2 μm chl a showed a similar linear relationship only at total chl a values lower than 1 mg m−3 (in autumn and summer) or 2 mg m−3 (winter). At higher values of total chl a, the contribution of the <2 μm size fraction remained below an upper limit of roughly 0.5 mg m−3. Our results indicate that the picoplankton fraction of phytoplankton may show higher seasonal and mesoscale variability than is usually acknowledged. 相似文献
3.
An optimized analysis method based on headspace liquid phase microextraction (HS‐LPME) and gas chromatography coupled with mass spectrometry was proposed for the determination of trihalomethanes (THMs) in drinking water. The response surface method (RSM) was used to optimize the extraction of THMs for analysis by HS‐LPME. The temperature, extraction time and NaCl concentration were found to be important extraction parameters. The coefficient of determination (R2) for the model was 94.97%. A high probability value (P < 0.0001) for the regression indicated that the model had a high level of significance. The optimum conditions were seen to be: temperature 42.0°C, NaCl concentration 0.30 g/mL, and extraction time 28 min. The response variable was the summation of the THMs chromatography peak areas and the reproducibility of this was investigated in five replicate experiments under the optimized conditions. The relative standard deviations (RSD%) of the THMs ranged from 8.0–11.6%. The limits of detection (LODs), based on a signal‐to‐noise ratio (S/N) of three ranged from 0.42–0.78 μg/L, and were lower than the maximum limits for THMs in drinking water established by the WHO. 相似文献
4.
110 samples from two swimming-pools were gas-chromatographically investigated for halogenated hydrocarbons. In spite of varying chlorine concentrations between 0.1 and 2.5 mg/l Cl2 the bacteriological results were unobjectionable. The total of the haloforms was between 1.2 and 182 μg/l, with the average value of 90 μg/l. Besides CHCl3, CHBrCl2, CHBr2Cl and CCl3NO2 there were observed other, still unidentified compounds in the chlorinated bathing water which clearly are successive products of disinfection, too. The water treatment by flocculation and filtration does not bring about any elimination of trihalomethanes. Of special importance is the occurrence of trichloronitromethane in concentrations of 0.13 … 1.2 μg/l, whose LC50 in the Daphnia test is 189 μg/l, at a threshold concentration of 160 μg/l. To limit the pollution of water and air to a minimum, specific conditions must be adhered to in the operation of indoor swimming-pools. 相似文献
5.
The sandy littoral zone of Lake Tegel (Berlin, Germany) was investigated during 2004–2006 down to sediment depths ≥26 cm to derive a scheme of seasonal carbon turnover under induced bank filtration conditions. Carbon turnover processes were quantified regarding external and internal sources of dissolved and particulate organic matter (DOM and POM), primary production, community respiration, redox potential as well as specific loads of soluble chemical compounds such as nitrogen, iron, manganese and DOC.Over the course of the year, infiltrating DOC decreased by about 13–20% within the upper 26 cm sediment of the infiltration stretch. Gradients of all observed soluble compounds that are highly cross-linked to biological activities were highest in the topmost centimetre. In this depth mass balances (output–input) were negative concerning NO3-N (−1 mg dm−2 d−1, summer mean) and DOC (−2 mg dm−2 d−1, winter mean), respectively, while specific loads of cations such as manganese reached up to 0.2 mg dm−2 d−1 during summer. Carbon mineralization ranged between 3 and 7 mg C dm−2 d−1 and was nearly twice as high in summer as in winter. The turnover of the infiltrating DOC contributed maximally 25% in summer to 50% in winter to the entire organic carbon mineralization. Gross and net primary production differed up to a factor of >10, indicating very fast turnover reactions and the predominance of community respiration and mineralization, respectively. The POC in the upper sediment layer (10 cm) temporally varied around 1% sediment d.w.; benthic algae, organic seston input and autumnal leaf fall contributed similar percentages to the POC pool. 相似文献
6.
《Journal of Atmospheric and Solar》2002,64(12-14):1409-1412
Recent studies using model calculation and ionospheric observations have revealed the existence of an additional layer in the topside equatorial ionosphere, the F3 layer. The observations using bottomside ionograms from locations close to the magnetic equator in Brazilian region have shown that the occurrence of the layer is very high from December to February (local summer) and from June to August (local winter). In fact, for the year 1995 the occurrence of the F3 layer is >75% during the months of January, February and December, and it is >65% for the period of June, July and August (Geofisica Int. 39 (2000) 57). In this work, we use 25 years of data for the months of January and August to investigate how the layer occurrence varies with the magnetic dip angle and solar activity. 相似文献
7.
《Marine pollution bulletin》2009,58(6-12):313-324
This study investigated the seasonal and spatial dynamics of nutrients and phytoplankton biomass at 12 stations in Hong Kong (HK) waters during a three year period from 2004 to 2006 after upgraded sewage treatment and compared these results to observations before sewage treatment. Pearl River estuary (PRE) discharge significantly increased NO3 and SiO4 concentrations, particularly in western and southern waters when rainfall and river discharge was maximal in summer. Continuous year round discharge of sewage effluent resulted in high NH4 and PO4 in Victoria Harbour (VH) and its vicinity. In winter, spring and fall, the water column at all stations was moderately mixed by winds and tidal currents, and phytoplankton biomass was relatively low compared to summer. In summer, the mean surface phytoplankton chl biomass was generally >9 μg L−1 in most areas as a result of thermohaline stratification, and high nutrients, light, and water temperature. In summer, the potential limiting nutrient is PO4 in the most productive southern waters and it seldom decreased to limiting levels (∼0.1 μM), suggesting that phytoplankton growth may be only episodically limiting. The mean bottom dissolved oxygen (DO) remained >3.5 mg L−1 at most stations, indicating that the eutrophication impact in HK waters was not as severe as expected for such a eutrophic area. After the implementation of chemically enhanced primary sewage treatment in 2001, water quality in VH improved as indicated by a significant decrease in NH4 and PO4 and an increase in bottom DO. In contrast, there were an increase in chl a and NO3, and a significant decrease in bottom DO in southern waters in summer, suggesting that hypoxic events are most likely to occur in this region if phytoplankton biomass and oxygen consumption keep increasing and exceed the buffering capacity of HK waters maintained by monsoon winds, tidal mixing and zooplankton grazing. Therefore, future studies on the long-term changes in nutrient loading from PRE and HK sewage discharge will be crucial for developing future strategies of sewage management in HK waters. 相似文献
8.
On a former waste water disposal field with water repellent sandy soil under grass vegetation we analyzed the persistency of flow patterns on a 150 m × 25 m plot by (i) continuous TDR-measurements on a 2 m × 1 m transect combined with seasonal soil moisture sampling campaigns, and (ii) a time-delayed double tracer experiment on a second 3 m × 1 m transect. Here, we applied bromide under wettable soil conditions in spring and chloride under water repellent soil conditions in autumn. At the end of the tracer experiment, after a travel time of 328 days for Br and 87 days for Cl, respectively, the transect was excavated and sampled in high spatial resolution. Tracer concentration, water content, water drop penetration times (WDPT), and soil organic matter content (SOM) of each sample were analyzed in order to characterize flow patterns. The TDR readings were used to predict the effective cross section (ECS) of subsurface flow and flow shifts over the season.During summer, when ECS is low and consecutive precipitation events occur, flow paths – once created – persist over time. However, over longer times (from autumn to autumn), the spatial arrangements of the flow paths can change completely. The Cl distribution showed typical fingering structures with high concentrations in the less water repellent flow paths. In contrast, Br was found mostly in the dry, hydrophobic areas indicating that it was transported before the soil became water repellent. Consequently, the flow patterns generated in spring and early summer differ completely from those in autumn and winter because of water repellent structures established during the vegetative period. These structures could be identified using a critical water content (θcrit) concept, considering both soil water content and SOM.As not all soil parts being active during to season, four flow categories could be identified: about 10% permanent (=stable flow paths), 45% periodic (i.e. water repellent in summer), 40% occasional (water repellent in summer and autumn), and 5% permanent water repellent. 相似文献
9.
Spectra of the O2(a1g) airglow emission band at 1.27 µm have been recorded during twilight at Maynooth (53.2°N, 6.4°W) using a Fourier transform spectrometer. Synthetic spectra have been generated for comparison with the recorded data by assuming a particular temperature at the emitting altitude, and modelling the absorption of each line in the band as it propagates downward through the atmosphere. The temperature used in generating the synthetic spectra was varied until an optimum fit was obtained between the recorded and synthetic data; this temperature was then attributed to the altitude of the emitting layer. Temperatures derived using this technique for 91 twilight periods over an 18-month period exhibit a strong seasonal behaviour with a maximum in winter and minimum in summer. Results from this study are compared with temperatures calculated from the OH(3, 1) Meinel band recorded simultaneously. In winter OH temperatures exceed O2 values by about 10 K, whereas the opposite situation pertains in summer; this result is interpreted in terms of a possible change in the altitude of the mesopause as a function of season. Estimates of the twilight O2(0, 0) total band intensity indicate that its intensity is lower and that its decay is more rapid in summer than in winter, in agreement with earlier observations. 相似文献
10.
《Limnologica》2019
The CO2 degassing from lakes on Pico Island (Azores archipelago) were characterized in order to estimate the total diffuse CO2 output and identify the possible sources of CO2. Two surveys have been made in each lake (Capitão, Caiado, Rosada, Peixinho, Paúl and Seca), in the winter and summer periods. These water bodies show small surface areas and are rather shallow, with depths ranging from 1.8 to 8.6 m. Water samples are cold, both in winter and summer periods, not presenting variations along the water column, with acid to neutral pH (5.26–7.06). The electrical conductivity values point out to very diluted waters (mean range between 27 and 33.4 μS cm−1), of the Na-Cl type, corresponding to meteoric waters influenced by marine salts.To measure the CO2 flux at the lakes surface the modified accumulation chamber method was used, and a total of 1632 measurements were accomplished (711 in winter surveys and 921 in summer). Two statistical analysis (GSA and sGs) were applied to the results of diffuse CO2 flux measurements, showing that the CO2 flux values measured in theses lakes are relatively low (0.60–20.47 g m−2 d−1), what seems to indicate a single source for CO2 (biogenic source), also suggested by the water δ13C isotopic signature.CO2 emissions range between 0.04 t d−1 (Rosada_1) and 0.25 t d−1 (Caiado_1) during the winter surveys, being in general similar to the values recorded during the summer surveys that vary between 0.03 t d−1 (Peixinho_2 and Seca_1) and 0.30 t d−1 (Caiado_2). Taken into account the surface area of the lakes, the highest values were estimated for both surveys made in Seca Lake (˜13 t km−2 d−1). The occurrence of a dense macrophyte mass in a few of the studied lakes, such as Caiado and Seca, seems to enhance the CO2 flux from these water bodies. 相似文献
11.
为探究长江中下游富营养化浅水湖泊的浮游植物初级生产力季节性演替特征及其驱动因子,本研究于2020年4月(春)、8月(夏)、10月(秋)及2021年1月(冬)对湖北长湖浮游植物进行采样调查,同时运用黑白瓶测氧法及VGPM模型估算法分别估算了其浮游植物生产力水平,并探究驱动初级生产力季节性变化的主要环境因子。结果显示,4个季节共鉴定出浮游植物194种,其中绿藻门(95种,49%)和硅藻门(40种,21%)居绝对优势地位;黑白瓶法测得浮游植物水柱总生产力(Pt)季节变化为:夏季((1841.24±345.93) mg C/(m2·d))>秋季((1324.14±208.34) mg C/(m2·d))>春季((847.50±247.72) mg C/(m2·d))>冬季((711.43±133.52) mg C/(m2·d)),其中M2站位在夏季采样时(2424.66 mg C/(m2·d))水柱总生产力最高;在垂直空间上,浮游植物总生产力(G... 相似文献
12.
In this study, a field experiment was conducted to investigate the soil water dynamics and water percolation through the deep vadose zone. A calibrated HYDRUS‐1D model was used to simulate the process of soil water movement and the water budget. Based on the measured volumetric soil water contents, the model was well calibrated and validated. Then, we conducted scenario analyses to determine the combined effects of irrigation amount (IA), antecedent soil moisture (AM), crop evapotranspiration, and deep percolation (DP) in an irrigation event. Four IAs (5, 10, 15, and 20 cm) and three AM conditions (AM‐1, AM‐2, and AM‐3) were controlled in the scenario analyses. The results indicate that according to the Se's (effective saturation) values status and the observed or simulated depth, there could be different conclusions on the influence of DP. Under different IAs in dry (AM‐1) and medium (AM‐2) AM status, DP changed slightly; it was 0.39 and 2.47 cm in AM‐1 and 0.40 and 2.48 cm in AM‐2 for the summer maize and winter wheat crop, respectively; the AM had a crucial contribution to DP. While under the condition of wet AM (AM‐3) or small observation depth, the water inputs could have a significant effect on DP. According to increasing irrigation intensity, the higher values of Se (>0.6) in the whole profile were only displayed between 70 and 300 cm at AM‐1, 70–500 cm at AM‐2, and 70‐below 600 cm at AM‐3, which were gradually extended and moved down with increasing AM. Hence, the IA significantly affected the water percolation at a depth of 200 cm, whereas there was a weak influence at 600 cm except in AM‐3. Furthermore, in the higher values of the Se (>0.65) domain, the correlation between IA and DP was an exponential function and significantly under P < 0.05. In addition, DP began to occur when the soil water content was equal to or greater than 0.75 times that of the field water capacity or the Se > 0.65. When the coarse silt layer became embedded in the silt clay soil profile, it lagged the process of water transport but did not affect permeability in the end. 相似文献
13.
V. V. Blinov N. G. Granin I. B. Mizandrontsev R. Yu. Gnatovskii A. A. Zhdanov 《Water Resources》2017,44(3):417-427
For the first time, T,S-analysis was used to determine the specifics of seasonal variations in the vertical structure of Lake Baikal active layer. In the under-ice period, the active layer includes the under-ice, top winter, and upper intermediate water masses. The under-ice water mass, unlike other masses, shows an increase in mineralization to 100.74 mg/kg, which corresponds to a release of 71.1 g salt under 1 m2 of water surface in a layer 0–40 m in the process of salt freezing out during ice cover formation and accretion. In the phases of mixing (homothermy), the water masses of the active layer transform into a surface homogeneous mass. In summer and autumn, surface and upper intermediate water masses, separated by a water mass of summer thermocline can be identified. A specific feature of the summer thermocline water mass is the increased sum of ions because of an increase in HCO 3 - concentration at the decay of organic matter accumulating in the bottom part of the thermocline. The existence of the under-ice water mass and the water mass of summer thermocline was established in Lake Baikal for the first time. In the deep-water zone (>250 m), except for the bottom parts, the lower water masses (the lower intermediate and the deep) are permanent, their characteristics remaining stable during the year. The changes in the bottom water mass are due to the character of the processes of bottom water renewal. 相似文献
14.
Recent studies in many developing countries have shown that Small Scale Independent Providers (SSIPs) in low-income areas (LIAs) are practical alternatives to water utilities. This study explored supply dynamics and quality of alternative water sources in four LIAs of Lilongwe City in Malawi using qualitative and quantitative methods. Household-level surveys (n = 120) and transect walks were employed to determine the socio-economic activities in the areas. One-on-one discussions were made with water source owners (SSIPs) (n = 24). Data on policy and institutional frameworks was collected through desktop study and Key Informant Interviews (n = 25). Quality of the water sources (shallow wells and boreholes) was determined by collecting grab samples (n = 24) in triplicate using 500 mL bottles. Selected physico-chemical and microbiological parameters were measured: pH, EC, TDS, turbidity, water temperature, salinity, K, Na, Ca, Mg, Cl−, F−, NO3−, alkalinity, water hardness, Fecal coliform (FC) and Faecal Streptococci (FS) bacteria. Water quality data was compared with Malawi Bureau of Standards (MBS) and World Health Organization (WHO) guidelines for drinking water. Shallow wells were reported (65%, n = 120) to be the main source of water for household use in all areas. Some policies like prohibition of boreholes and shallow wells in City locations were in conflict with other provisions of water supply, sanitation and housing. High levels of FC (0–2100 cfu/100 mL) and FS (0–1490 cfu/100 mL) at several sites (>90%, n = 24) suggest water contamination likely to impact on human health. This calls for upgrading and recognition of the water sources for improved water service delivery. 相似文献
15.
The influence of winter on methane (CH4) stored in pore water and emitted through snow was investigated in a temperate poor fen in New Hampshire over two winters. Methane accumulated beneath ice layers (1 cm) deposited by freezing rain, resulting in snow-pore air mixing ratios as high as 140 ppmv during the first winter and 600 ppmv during the second. An early winter snow crust of 300 kg m?3 caused no discontinuity in a linear mixing ratio profile and therefore was not observed to retard snowpack emissions. Methane concentration-depth profiles in pore water steepened and concentrations increased by as much as 400 μM at the 10 and 20 cm depths as the ice cover formed. This suggests that the peat-ice cover plays an important part in CH4 build-up in pore water by limiting the transport of gases between the peat and the atmosphere. Pore water concentrations gradually declined through late winter. The seasonality of dissolved CH4 in pore water over two winters and one summer showed an average annual amplitude of 1.3 gCH4m?2 (25–75cm depth range), with a winter maximum of 4.7gCH4m?2. Emissions during the winter with average snowfall accounted for a larger percentage (9.2% in 1993–1994) of total annual emission than the winter with below-average snowfall and warmer air temperature (2% in 1994–1995). Emissions averaged 56 and 26mg m?2 day?1 during the first and second winter (December, January and February), respectively. 相似文献
16.
Controls on Methane Occurrences in Aquifers Overlying the Eagle Ford Shale Play,South Texas 
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下载免费PDF全文 Jean‐Philippe Nicot Toti Larson Roxana Darvari Patrick Mickler Kristine Uhlman Ruth Costley 《Ground water》2017,55(4):455-468
Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo‐Wilcox Aquifer (250‐1200 m depth range) and Queen City‐Sparta Aquifer (150‐900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ13Cmethane (>?55‰) and δDmethane (>?180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ13Cmethane and δDmethane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs. 相似文献
17.
太湖草/藻型湖区沉积物-水界面环境特征差异 总被引：3，自引：0，他引：3
在太湖草、藻型湖区进行冬、夏两季多点采样,分别对采样点的水环境特征、泥面以上5 cm上覆水中营养盐以及沉积物的含水量、中值粒径、有机碳、氮、磷、金属元素和溶解氧进行测定.结果表明:夏季藻型湖区表层水体pH高于中、底层,冬季草型湖区各层水体pH高于藻型;草型湖区水体浊度夏季低于藻型,冬季反之;藻型湖区上覆水中的硝态氮和磷酸根浓度显著高于草型;草型湖区沉积物中含水量冬季显著高于夏季;草型湖区沉积物中总有机碳显著高于藻型;Fe、Zn、Ca、Pb、Na和K等元素在草、藻型湖区间差异显著;沉积物中溶解氧表现为冬季深于夏季,藻型深于草型的规律. 相似文献
18.
Assessing crop yield and crop water productivity and optimizing irrigation scheduling of winter wheat and summer maize in the Haihe plain using SWAT model 下载免费PDF全文
下载免费PDF全文 Haihe plain is an important food production area in China, facing an increasing water shortage. The water used for agriculture accounts for about 70% of total water resources. Thus, it is critical to optimize the irrigation scheduling for saving water and increasing crop water productivity (CWP). This study first simulated crop yield and CWP for winter wheat and summer maize in historical scenario during 1961–2005 for Haihe plain using previously well‐established Soil and Water Assessment Tool model. Then, scenarios under historical irrigation (scenario 1) and sufficient irrigation (scenario 2) were, respectively, simulated both with sufficient fertilizer. The crop yield in scenario 2 was considered as the potential crop yield. The optimal irrigation scheduling with sufficient fertilizer (scenario 3) was explored by iteratively adjusting irrigation scheduling based on the scenario 1 and previous studies related to water stress on crop growth. Results showed that net irrigation amount was, respectively, reduced 23.1% and 18.8% in scenario 3 for winter wheat and summer maize when compared with scenario 1. The CWP was 12.1% and 8.2% higher with very slight change of crop yield. Using optimal irrigation scheduling could save 8.8 × 108 m3 irrigation water and reduce about 16.3% groundwater over‐exploitation in winter wheat growth period. The corresponding yield was 18.5% and 12.9% less than potential yield for winter wheat and summer maize but using less irrigation water. Therefore, it could be considered that the optimal irrigation was reasonable, which provided beneficial suggestions for increasing efficiency of agricultural water use with sustainable crop yield in Haihe plain. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
Communicating human health risks associated with disinfection by-products in drinking water supplies: a fuzzy-based approach 总被引：1，自引：2，他引：1
Rehan Sadiq Manuel J. Rodriguez Syed A. Imran Homayoun Najjaran 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):341-353
Chlorine used for the disinfection of water supplies can react with naturally occurring organic compounds and form potentially
harmful disinfection by-products (DBPs). A risk index for two regulated groups of chlorinated DBPs—trihalomethanes (THMs)
and haloacetic acids (HAAs), using fuzzy C-means (FCM) clustering algorithm and fuzzy rule-based modeling is proposed for risk communication. The proposed index evaluates
the cancer and non-cancer risks individually for THMs and HAAs using the FCM algorithm. Subsequently, two different fuzzy
rule-bases were used to evaluate the overall risk-index based on cancer and non-cancer risks. The overall risk-index will
provide drinking water utilities with an effective communication tool for communicating aggregated water quality compliance.
Simulated DBP occurrence data obtained from the City of Quebec, Canada, is used to demonstrate the application of this methodology. 相似文献
20.
云南程海浮游植物初级生产力的时空变化及其影响因子 总被引：1，自引：0，他引：1
2016年4月-2017年2月，采用黑白瓶法研究了云南程海单点（码头点位）浮游植物初级生产力的垂直分布及其季节变化，同时基于全湖9个点位的现场调查和生产力垂向归纳模型（VGPM）估算并探讨了程海浮游植物初级生产力的时空变化及其主要影响因子.结果显示，码头点位的年均（均值±标准误）水柱（0~3 m）总初级生产力（GPPC）、净初级生产力（NPPC）和呼吸消耗量（RC）分别为5.40×103±0.64×103、2.36×103±0.63×103和3.06×103±0.82×103 mg O2/（m2·d）；不论春夏季（4-8月）、秋冬季（9月-次年2月）还是全年，码头点位的单位生物量GPP（GPP/Chl.a）和单位生物量NPP（NPP/Chl.a）的最大值和最小值均分别出现在水下0.5 m和3.0 m处.经VPGM估算，程海全湖的初级生产力（PPeu）年均值为6.54×103±0.30×103 mg C/（m2·d）（2.74×103~18.62×103 mg C/（m2·d））.PPeu的时空变化方面，春夏季是PPeu快速上升的时节，秋冬季PPeu的月变化则呈波动状态，春夏季与秋冬季PPeu无显著性差异；PPeu整体空间异质性较弱，仅在降水最为充沛的7、8月表现出南北向的异质性，这与降水条件和流域营养盐输入的空间异质性有关.回归分析发现，虽然程海PPeu的主要影响因子具有季节异质性，但不论春夏季、秋冬季还是全年，浮游植物生物量均是重要的影响因子，水温亦是春夏季的重要影响因子. 相似文献