Selenium Removal from Irrigation Drainage Water Flowing Through Constructed Wetland Cells with Special Attention to Accumulation in Sediments

A flow-through experimental wetland system has been under investigation since 1996 to remove selenium (Se) fromagricultural drainage water in the Tulare Lake Drainage Districtat Corcoran, California, U.S.A. The system consists of ten cellswhich have dimensions of 15 × 76 m continuously flooded andvarious substrates planted. The objectives of this article are topresent the overall performance in Se removal after establishingthe wetland for three years, and to examine factors affecting Seremoval with special attention to accumulation in the sediments.In 1999, The wetland cells reduced Se from inflow water by 32 to65% in concentration and 43 to 89% in mass. Vegetationplays an important role in Se removal as non-vegetated cellshowed the least removal of Se. The inflow drainage water wasdominated by selenate (Se(VI), 91%) with smaller percentages ofselenite (Se(IV), 7%) and organic Se (org-Se(II-), 2%). Theoutflow water from the cells contained an average of 47% Se(VI),32% Se(IV) and 21% org-Se indicating reduction processesoccurring in the wetland cells. The surface sediment appears as alarge sink of Se removal. The highest Se concentration was foundin fallen litter, followed by the fine organic detrital layer onthe sediment surface. The sediment Se concentration dramaticallydecreased with increasing sediment depth. The mass distribution of Se, however, was sediment (0-20 cm) > fine detrital matter >fallen litter. Fractionation of surface sediment (0-5 cm) reveals that elemental Se was the largest fraction (ave. 47%) followedby organic matter-associated Se (34%). Soluble, adsorbed, and carbonate-associated Se accounted for 1.2, 3.1 and 2.5% ofthe total sediment Se, respectively. The major Se sink mechanism in the cells is the reduction of selenate to elemental Se andimmobilization into the organic phase of the sediments.     

A combined technique of floodplain storage and reservoir irrigation for paddy rice cultivation

This paper introduces an irrigation system developed in the floodplain of a lake and studies the water management technique of the irrigation system by estimating the total water balance of the whole system. The system is characterized by a reservoir combined with a dike system in the floodplain of the Tonle Sap Great Lake and an irrigation system. Two main models are used for calculating the total water balance. The first model is the water balance of the reservoir. The inputs to the model are water level of the reservoir, precipitation, lake evaporation, infiltration, and area–volume curve of the reservoir. The outputs are inflow and outflow of the reservoir. The supply from the reservoir to paddy fields is computed from the outflow. The second model is the water balance of paddy fields, based on which the water requirement in paddy fields is derived. The reference evapotranspiration needed to calculate the water requirement is simulated for monthly time series using the FAO Penman–Monteith model. Since there is no drainage network in the irrigation system, surface drainage and runoff are not included in the calculation of the water balance, and seepage is considered negligible in the flat floodplain area. The evapotranspiration, rice variety, soil type and irrigated area are used to simulate water consumption in paddy fields. Finally, the two models are connected to produce the total water balance from the reservoir to paddy fields. The total outflow from the reservoir is estimated and the total water consumption for dry season cultivation is also determined. Finally, the efficiency of the whole system is examined.     

Evaporation ponds as a drainwater disposal management option

Constructed evaporation ponds are being utilized for disposalof saline subsurface drainage waters in San Joaquin Valley,California. These terminal evaporation ponds are located inhydrologically closed basins and/or regions with no surfacedrainage out of the valley. The saline drainwaters disposedinto the ponds are sodium-sulfate or sodium-sulfate-chloridetype waters and upon desiccation produces mirabilite andhalite. The drainwaters contain excessive levels of traceelements from geochemical origins. The trace element of mostconcern, is selenium because it bioaccumulates in the aquaticfood chain and causes death and deformity of waterbirdsattracted to the pond environment. At the present, the onlyeconomic drainwater disposal option in the southern. portionof the valley is evaporation ponds. The operation of theseponds is heavily regulated by waste discharge requirements toreduce and mitigate wildlife impacts. A case study onevaporation ponds and bird usage from a drainage districtillustrates the extensive monitoring and mitigation required.The prognosis is evaporation basins will be needed for theforeseeable future unless breakthroughs occur in economic andeffective drainwater treatment and drainwater reuseoptions.     

Operation of the Ba Lai irrigation system in the Mekong Delta, Vietnam

Ba Lai Irrigation Project is located at coastal area in the Mekong Delta. In dry season when the flow rate decreases and the strong east wind blows into the delta, the salinity intrusion increases and seriously affects agricultural and domestic water use. Intakes of Ba Lai system have to be closed for 1–3 months depending on their locations, and no water supply during this period often causes water pollution in the project area. In order to solve such problems, this study aims to seek gate operation procedures for salinity control and water environment improvement. A numerical model is developed to simulate water movement, salinity concentration and duration of remaining water (water age) within the system under three scenarios: (1) without control structures, (2) with available control structures, (3) with the full control structures. Through the numerical simulations, control structures are confirmed to be an effective measure for the salinity control and suitable gate operation schedules are proposed to improve the water environment in the project.     

广东象头山自然保护区鸟类多样性及保护管理对策

广东象头山国家级自然保护区现有记录的鸟类有184种,隶属13目37科.文章结合象头山自然保护区野生鸟类的监测数据,对保护区内的鸟类多样性组成、区系特征、资源现状、受威胁原因等进行了分析,并提出了相应的保护管理建议.     

Fractionation of N2O isotopomers during production by denitrifier

Isotopomer ratios of N₂O, which include intramolecular ¹⁵N-site preference in addition to conventional isotope ratios for N and O in NNO (we designate N^α and N^β for the center and end N atom, respectively, in the asymmetric molecule), reflect production and consumption processes of this greenhouse gas. Therefore, they are useful parameters for deducing global N₂O budget. This paper reports the first precise measurement of ¹⁵N-site preference in N₂O produced by two species of denitrifying bacteria, Pseudomonas fluorescens (ATCC 13525) and Paracoccus denitrificans (ATCC 17741).Cultures were incubated in a batch mode with a liquid medium that contains KNO₃ as unique nitrogen supply under acetylene/helium (10% v/v) atmosphere at 27 °C. Enrichment factors for ¹⁵N in bulk nitrogen in N₂O (average for N^α and N^β) fluctuated in a few tens permil showing a slight difference between the species. In contrast, ¹⁵N-site preference (difference in isotope ratios between N^α and N^β) showed nearly constant and distinct value for the two species (23.3±4.2 and −5.1±1.8‰ for P. fluorescens and P. denitrificans, respectively). The site preference was also measured for N₂O produced by inorganic reactions (nitrite reduction and hydroxylamine oxidation); a unique value (about 30‰ for the both reactions) was obtained. These results and those recently reported for nitrifying bacteria suggest that ¹⁵N-site preference in N₂O can be used to identify the production processes of N₂O on the level of bacterial species or enzymes involved.     

A study to determine an equation of enveloping curve for regional flood peaks by maximum rainfall data

In this paper, Creagers equation and Groups equation are algebraically examined to determine an equation of an enveloping curve for regional flood peaks from the viewpoint of the curve profile. The applicability of a small drainage area with little observed data on flood peak discharge was examined in comparison to specific flood peak discharge calculated by a rational formula using data of maximum rainfall. In the algebraical consideration, the Creagers equation had an extreme value at a drainage area A=1.0 km², and the specific flood peak discharge became a maximum. Flood peak discharge calculated by Groups equation had an extreme value at a drainage area A=6,568 km², and it became a maximum. Except for Hokkaido, in catchment areas not exceeding 1,178 km², Groups curve q _K was closer to the curve q _DAD of specific flood discharge than Creagers curve qc. From the above research results, the Groups equation is applicability better than the Creagers equation, as the drainage area A is 1,178 km² or less.     

Performance diagnosis of Mae Lao irrigation scheme in Thailand (II). Application of the UIWDC model for water distribution system analysis

The Unsteady Irrigation Water Distribution and Consumption (UIWDC) model is applied to analyze causes of uneven water distribution between the upstream and downstream beneficial areas of the Mae Lao Irrigation Scheme (MLIS). The uneven water distribution may be caused by inadequate water distribution facilities or improper operation rule; therefore, its causes are examined systematically and quantitatively from the aspects of “water allocation” and “operation rule”. The water allocation is considered focusing on the dry season irrigation, where equity and efficiency should be especially balanced because of the scare water resources. The “EQTY index” (the equity index) is defined to widen the range of consideration between the equity and the efficiency, instead of alternative judgment of which has a priority. The operation rule for facilities in the MLIS is assumed considering their capacities, and two coordinate values of “ineffective spillage” and “water deficit” in the scheduled areas are incorporated into operation rule to quantitatively diagnose the system performance. As a result, the original causes of uneven water distribution will presumably be identified. The informative and quantitative results are utilized to set a new benchmark performance of the MLIS for the water distribution. It can be described by the “Expected Ratio of Irrigable Area” (ERIA) and “Present Ratio of Irrigable Area” (PRIA). Based on this standard, the general recommendations can be more concretely proposed to raise the water distribution performance of the MLIS such as by improving distribution facilities and/or by installing vertical pumps.     

Ring dike system to harness floodwater from the Mekong River for paddy rice cultivation in the Tonle Sap Lake floodplain in Cambodia

Located in the floodplain of the Mekong River and the Tonle Sap River, Batheay irrigation system and its reservoir directly receive floodwater from the Mekong. The Batheay reservoir formed by a ring dike functions as both a reservoir and a paddy field. In the wet season, the ring dike prevents floodwater from entering the reservoir and rainy season rice is grown inside the dike. After harvesting, the gates on the ring dike are opened to receive floodwater. The water is stored inside the dike for cultivating dry season rice outside the dike. In this paper, the irrigation system is studied as a model site for future development of the floodplain of the Tonle Sap Lake of Cambodia. Specifically, this paper is concerned with the study of water balance and analysis of the hydrologic components of the Batheay irrigation system, and the effectiveness of the ring dike system. The study found that floodwater of the Mekong River contributed about 74% to the total inflow to the Batheay reservoir. Contributions to the total water supply of reservoir water, floodwater remaining in the fields, and precipitation were 73, 12, and 15%, respectively. The efficiency of the system was found to be 92%. The dike system is expected to be a paradigm for the floodplain of the Tonle Sap Lake.