AN INDEX OF STORED FINE SEDIMENT IN GRAVEL BEDDED STREAMS1

An index of sediments less than 0.3 mm stored in the top layer of small streams was estimated by disturbing a fixed area for 2 minutes and catching the resultant sediment drift in downstream traps. The method was used in 24 small northern California streams and was tested by releasing known amounts and sizes of sediments in controlled trails. Field use showed general agreement with an exponential model of decrease in sediment trapped vs. distance. Sites in distrubed reaches (watersheds logged with no streamside buffers or with buffers less than 30 m) had higher indices of stored sediment than control sites. Estimates from controlled trials averaged 7.5 percent higher than actual losses for composite size classes ≤ 0.3 mm, 19.7 percent higher than actual losses for just the ≤ 0.125 mm class, and 15.2 percent for all 14 trials. The method is relatively simple and suitable for remote locations, particularly in studies comparing many small streams.     

Watershed management program on Santiago Island,Cape Verde

The Watershed Management Program (WMP) was put into operation in early 1985 on Santiago Island, Cape Verde, with the stated purpose, “to develop and protect the soil and water resources of the Program-designated watersheds … to stabilize the natural environment and increase agricultural production potential in the Program area.” The approach to soil and water conservation in the program has been to build erosion and flood control structures (engineering approach) and plant trees (biological approach) to decrease rill and gully erosion, trap sediment behind control structures, provide flood protection, increase infiltration, increase fuelwood and fodder production, and increase water supplies for irrigation. There have been many successes resulting from specific management activities, but flawed approach or implementation in a few key areas has acted to impede the program's complete success, including lack of a scientific basis for evaluating its impact on soil and water conservation; poor design, placement, and maintenance of some major hydraulic structures; inadequate intervention in stabilizing farmlands or education of farmers and landowners in the need for and benefits of agroforestry; and incomplete integration of engineering and biological approaches.     

ELECTRONIC DATA PROCESSING SYSTEM FOR STREAMFLOW1

Daily, monthly, and yearly summaries of streamflow and sediment transport are computed from continuous gage height records and discrete measurements of sediment concentration and discharge rate. The system includes computer computation of discharge measurement notes and an accuracy check of gage height and time input data. Maximum volumes of runoff for selected time intervals up to eight days and flow duration data can also be compiled. Electronic data processing equipment including a chart reader, card punch, computers, and card sorter are used. The system software includes 12 Fortran programs.     

A review of sediment predictive techniques as viewed from the perspective of nonpoint pollution management

User-oriented criteria for the evaluation of physically based management models are presented. These criteria emphasize the utility rather than the elegance of the model. The standards are then applied to efforts at predicting non-point pollutant loadings. In particular a critical review of sediment pollution is used as the basis for the evaluation of sediment yield models as management tools. A wide range of sediment yield models are rated and recommendations for their use are made.     

The effects of temperature and resource availability on denitrification and relative N2O production in boreal lake sediments

Anthropogenic environmental stressors(like atmospheric deposition,land use change,and climate warming) are predicted to increase inorganic nitrogen and organic carbon loading to northern boreal lakes,with potential consequences for denitrification in lakes.However,our ability to predict effects of these changes is currently limited as northern boreal lakes have been largely neglected in denitrification studies.The aim of this study was therefore to assess how maximum potential denitrification and N_2O production rates,and the relationship between the two(relative N_2O production),is controlled by availability of nitrate(NO_3~-),carbon(C),phosphorus(P),and temperature.Experiments were performed using the acetylene inhibition technique on sediments from a small,nutrient poor boreal lake in northern Sweden in 2014.Maximum potential denitrification and N_2O production rates at 4°C were reached already at NO_3~-additions of 106–120 μg NO_3~-–N/L,and remained unchanged with higher NO_3 amendments.Higher incubation temperatures increased maximum potential denitrification and N_2O production rates,and Q10 was somewhat higher for N_2O production(1.77) than for denitrification(1.69).The relative N_2O production ranged between 13% and 64%,and was not related to NO_3~-concentration,but the ratio increased when incubations were amended with C and P(from a median of 16% to 27%).Combined,our results suggests that unproductive northern boreal lakes currently have low potential for denitrification but are susceptible to small changes in NO_3 loading especially if these are accompanied by enhanced C and P availability,likely promoting higher N_2O production relative to N_2.     

Nitrogen dynamics in the sediments of a wetland coastal ecosystem of southern India

The study area, Kuttanad Waters is a part of the Cochin estuarine system on the west coast of India. Kuttanad is well known for its agricultural activity and so the major contribution to the inorganic ions of nitrogen will be from fertilisers applied in agriculture. Based on observed salinity the stations have been divided into three zones. The fresh water zones had higher quantities of silt and clay whereas the estuarine zone was more sandy. The chemical speciation scheme applied here distinguishes three forms of ammoniacal nitrogen species: exchangeable, fixed, and organic ammoniacal nitrogen. No significant trends were observed in the seasonal distribution of total, exchangeable, fixed and organic nitrogen. A significant concentration of exchangeable ammonia was observed in the sediment due to their predominantly reducing environment, which restricts nitrification. High NH₄-N concentrations in the pore waters, along with the sedimentary composition leads to a significantly high quantity of fixed NH₄-N. The low values for N org is due to high mineralisation or deamination of organic nitrogen     

吹扫捕集-气相色谱法测定水中四氢呋喃

建立了吹扫捕集-气相色谱测定水中四氢呋喃的方法,不用有机溶剂萃取和浓缩,减少了损失和对环境的污染,具有灵敏度高、检出限低、定量准确、操作简便等特点。当进样量为5 mL时,检出限可达到0.18μg/L级,相对标准偏差为0.9%-4.0%,加标回收率在77.2%-100.8%之间。     

Contamination of butyltin compounds in Malaysian marine environments

Concentration of butyltin compounds (BTs), including tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) and total tin (SigmaSn) were determined in green mussel (Perna viridis), 10 species of muscle fish and sediment from coastal waters of Malaysia. BTs were detected in all these samples ranging from 3.6 to 900 ng/g wet wt., 3.6 to 210 ng/g wet wt., and 18 to 1400 ng/g dry wt. for mussels, fish and sediments, respectively. The concentrations of BTs in several locations of this study were comparable with the reported values from some developed countries and highest among Asian developing nations. Considerable concentration of BTs in several locations might have ecotoxicological consequences and may cause concern to human health. The parent compound TBT was found to be highest than those of its degradation compounds, DBT and MBT, suggesting recent input of TBT to the Malaysian marine environment. Significant positive correlation (Spearman rank correlation: r2=0.82, P<0.0001) was found between BTs and SigmaSn, implying considerable anthropogenic input of butyltin compounds to total tin contamination levels. Enormous boating activities may be a major source of BTs in this country, although aquaculture activities may not be ignored.     

Plant uptake and transport models for neutral and ionic chemicals

BACKGROUND: Models for predicting uptake and transport of chemicals in plants are applied in pesticide design, risk assessment, and environmental biotechnology. OBJECTIVE: This review considers the theoretical basics of the most popular models, and discusses what they have in common. The line is drawn between models for neutral compounds, and models for weak and strong electrolytes. MAIN FEATURES: Neutral Compounds. Neutral compounds undergo only very few processes inside plants (lipophilic interactions, metabolism), in contrast to weak electrolytes. The models developed for neutral compounds are widely applied in the risk assessment of environmental contaminants, but are not of much use for weak electrolytes, such as pesticides. Weak electrolytes. A very important process for weak electrolytes is the 'ion trap', which traps chemicals that dissociate inside plant cells. This is considered in the popular models of Kleier, Satchivi and Briggs. Other relevant processes for electrolytes are electrophilic interactions, speciation and complex formation. None of the currently used models considers these processes. CONCLUSIONS: The accuracy of models for neutral compounds is satisfactory, but the prediction of electrolyte behavior inside plants is still quite difficult due to gaps in knowledge.     

苏州河水体黑臭机理及底质再悬浮对水体的影响

探讨了苏州河水体黑臭现象，证实了水体发黑主要与存在吸附了ＴｅＳ的带负电胶体悬浮颗粒有关，且腐殖质是吸附物或络合物的主要组成。水体发臭为含硫，氮等有机物降解时逸出ＮＨ３、Ｈ２Ｓ等所致。