Development of natural and ecological wastewater treatment system for decentralized community in Korea

A pilot study of the natural and ecological wastewater treatment system (NEWS) was performed to treat sewage in decentralized small rural communities in Korea. The absorbent-biofilter system (ABS) provided secondary level pretreatment and demonstrated high removal efficiency especially for SS and BOD₅ showing 88.5 and 82.9%, respectively. The influent and effluent concentrations of TN were 42.1 and 26.2 mg L⁻¹, respectively, with the removal efficiency of 37.8%. In case of TP, the removal efficiency was 45.1% with the influent and effluent concentrations of 3.1 and 1.7 mg L⁻¹. The ABS effluent could not meet the effluent standards, and the further treatment was required. The subsequent up- and down-flow constructed wetland (UDCW) provided further polishing of the ABS effluent and demonstrated effective removal of nutrients as well as SS and BOD₅ with over 70% removal rates. Overall performance of the NEWS, which was composed of ABS and UDCW, demonstrated remarkably high removal rates for BOD₅ (>95.7%), SS (>97.5%), TN (>91.8%) and TP (>90.1%) and met all the effluent standards stably independent of temperature and influent loading in the experimental range. The UDCW used light and porous granular substrate (∅ 5–10 mm, specific gravity of 1.2) with large surface area, and clogging problem was not observed during the study period. The system was cost effective and required minimal maintenance and negligible amount of electricity, and problems associated with noise, odor, files, and sludge were not observed. Considering characteristics of decentralized wastewater treatment systems, the NEWS system was found to be a practical alternative and its application is recommended up to 300 m³ day⁻¹. The NEWS system has an economic problem above 300 m³ day⁻¹, because of complicated equipment, higher operation costs, and maintenance specialists. The NEWS system was coast effective and required minimal maintenance and negligible amount of electricity, and problems associated with noise, odor, files, and sludge were not observed.     

Nitrogen and phosphorus runoff modeling in a flat low-lying paddy cultivated area

Chiyoda basin is located in Saga Prefecture in Kyushu Island, Japan, and lies next to the tidal compartment of the Chikugo River to which the excess water in the basin is drained away. Chiyoda basin has a total area of about 1,100 ha and is a typical flat and low-lying paddy-cultivated area. The main environmental issue in this basin is total nitrogen (TN) and total phosphorus (TP) load management because TN and TP, which loaded from farmlands, degrade surface water as a result of anthropogenic eutrophication. This paper presents a mathematical model of TN and TP runoff during an irrigation period in Chiyoda basin in order to elucidate the pollutant fluxes that accompany water transportation in paddy fields and drainage canals, and to evaluate pollutant removal from the study area to the Chikugo River. First, the water flow and the algorithm of gate operation were simulated by a continuous tank model and the accuracy of the model was then evaluated by comparing the simulated water levels with observed ones during an irrigation period. The observed and simulated water levels were in good agreement, indicating that the proposed model is applicable for drainage and water supply analyses in flat, low-lying paddy-cultivated areas. Second, the TN and TP runoff during an irrigation period was simulated based on the TN and TP loads that were determined by observed data in paddy fields. For TN runoff, the simulated results and observed data were in good agreement whereas for TP runoff, the simulated results were higher than the observed data. However, if the settled TP within the paddy tank was calculated as 6%, then the simulated results and the observed data were in good agreement. We concluded that TN runoff from paddy field to the drainage canal system was not affected much by the sediment related process. The present study could provide farmers and managers with a useful tool for controlling the water distribution in an irrigation period, and the TN and TP loads in the downstream area as well as the Chikugo River.     

Long-term changes in nitrogen loads of a stream in the vicinity of an earthen waste storage pond

It is not sufficiently known for how long earthen waste storage ponds that are no more in use continue to affect surface water quality. In 2006, we carried out an investigation on the water quality and hydrology at the outlet of a small agricultural catchment area (area A) by estimating the in-stream nitrogen loads and nitrogen inputs. In this area, swine waste had been retained in an earthen waste storage pond, which was not in use since 1990. Similar investigations were conducted at the same location in 1992 and 2002, and the results of all these three studies were compared. The average nitrate nitrogen (NO₃-N) concentrations were 26, 4.9, and 4.0 mg L⁻¹ in 1992, 2002, and 2006, respectively. Despite 76% of the land use of area A being forest, the average NO₃-N concentration was relatively high, indicating that effluents from the earthen waste storage pond continued to affect surface water quality in 2006. The ranges of in-stream nitrogen loads derived from the earthen waste storage pond were estimated to be 154 to 207, −14 to 39, and 14 to 74 kg ha⁻¹ for 1992, 2002, and 2006, respectively. The results suggested that although the effects of effluents from the earthen waste storage pond on water quality decreased over 14 years, they still continued in 2006.     

Characteristics of effluent load from a watershed including irrigation ponds

This paper describes an attempt to estimate the mass budget of irrigation ponds within a watershed and the possibilities to control the effluent load of nutrients from the watershed located in the Kyotanabe area. The paddy field lots were irrigated by the ponds and several mountain streams. In the study watershed, there were two ponds located on the upper and lower sides of a paddy area. Water could be pumped up from the lower pond to the upper pond as necessary. At the ponds, the total amount of nitrogen and phosphorus in the inflow loads including the sediment release was larger than those in the outflow loads. In SS, the effect of load reduction in the ponds was high. It is assumed that organic load reduction was not expected in the ponds. The study result indicates that it is possible to remove the nutrients in the ponds when a larger amount of water is pumped up than when the ponds are only in irrigation use. Moreover, the removal capacities of the nutrients could probably be increased in both ponds by controlling the amount of sediment releases. Electronic Publication     

Fertilization management of paddy fields in Piedmont (NW Italy) and its effects on the soil and water quality

The fertilization management of the rice crop in Piedmont was analyzed at a regional scale, and the agronomic and environmental sustainability of the actual fertilization strategy of rice was evaluated through the analysis of its effect on the soils and waters quality. On average, a total amount of 127 kg ha⁻¹ of N, 67 kg ha⁻¹ of P₂O₅ and 161 kg ha⁻¹ of K₂O were supplied to the rice crop. In most cases N and P fertilization was rather well balanced with crop removal. The N balance was in the range ±50 kg for 77% of the surface. The low concentration of N in the groundwater reflected the small N surplus. P fertilization resulted to be smaller than removal for 53% of the surface. Nevertheless, the soil extractable P was very high, probably because of former higher P inputs. This resulted in a high concentration in water courses and aquifers. The K fertilization was excessive (surplus >100 kg ha⁻¹) for 53% of the surface, but most soils showed a low K content. K is probably contributing to nutrient leaching to a great extent. The average soil organic matter (SOM) content of paddy fields was higher than that of normally-cultivated soils in Piedmont, and the C/N was higher, owing to the low mineralization rate in waterlogged conditions. The SOM content was in relation with the management of the crop residues, as the tradition of burning straw after harvest was still widespread on 65% of the paddy surface.     

Evaluation of the management practice for controlling herbicide runoff from paddy fields using intermittent and spillover-irrigation schemes

Two water management practices, an intermittent irrigation scheme using automatic irrigation system (AI) and a spillover-irrigation scheme (SI), were compared for the fate and transport of commonly used herbicides, mefenacet (MF) and bensulfuron-methyl (BSM) in experimental paddy plots. Maximum mefenacet concentrations in paddy water were 660 and 540 μg L⁻¹ for AI and SI plot, respectively. The corresponding values for bensulfuron-methyl were 46.0 and 42.0 μg L⁻¹. Dissipation of the herbicides in paddy water appeared to follow the first-order kinetics with half-lives (DT₅₀) of 1.9–4.5 days and DT₉₀ (90% mass dissipation) of 7.8–11.3 days. The AI plot had no surface drainage, hence no herbicide was lost through paddy-water discharge. However, SI plot lost about 38 and 49% of applied mefenacet and bensulfuron-methyl, respectively. The intermittent irrigation scheme using automatic irrigation system with a high drainage gate was recommended to be a best management practice for controlling the herbicide losses from paddy fields. The paddy field managed by spillover-irrigation scheme may cause significant water and herbicide losses depending on the volume of irrigation and precipitation. The water holding period after herbicide application was suggested to be at least 10 days according to the DT₉₀ index.     

Feasibility of SRI methods for reduction of irrigation and NPS pollution in Korea

An experimental study on the System of Rice Intensification (SRI) methods was conducted to investigate the feasibility of using them to conserve irrigation water and reduce non-point source (NPS) pollution in Korea. Eight experimental runoff plots were prepared at an existing paddy field. Runoff and water quality were measured during the 2010 growing season in which a Japonica rice variety was cultivated. The irrigation water requirements of SRI methods and conventional (CT) plots were 243.2 and 547.3 mm, respectively, meaning that SRI methods could save 55.6% of irrigation water. Runoff from SRI methods plots decreased 5–15% compared with that from CT plots. Average NPS pollutant concentrations in runoff from SRI methods plots during rainfall-runoff events were SS 89.4 mg/L, COD_Cr 26.1 mg/L, COD_Mn 7.5 mg/L, BOD 2.0 mg/L, TN 4.2 mg/L, and TP 0.4 mg/L. Except for COD_Cr and TN, these concentrations were significantly lower than those from CT plots. Measured pollution loads from SRI methods plots were SS 874 kg/ha, COD_Cr 199.5 kg/ha, COD_Mn 47 kg/ha, BOD 13 kg/ha, TN 36.9 kg/ha, and TP 2.92 kg/ha. These were 15.8–44.1% lower than those from CT plots. Rice plants grew better and healthier in SRI methods plots than in CT plots. However, rice production from SRI methods plots ranged between 76 and 92% of that of CT plots because the planting density in SRI methods plots was too low. It was concluded that SRI methods could be successfully adopted in Korea and could help save a significant amount of irrigation requirement in paddies and reduce NPS pollution discharge.     

Microorganism repair after UV-disinfection of secondary-level effluent for agricultural irrigation

A pilot study of microorganism repair after UV disinfection was performed for agricultural reuse of secondary-level effluent in paddy rice fields in Korea. Effluent from the bio-filter of a 16-unit apartment was used in a flow-through type UV-disinfection system. The average concentration of suspended solids (SS) and biochemical oxygen demand (BOD) were 3.4 and 5.9 mg L⁻¹, respectively. The mean total coliform level was in the range of 1.5 × 10⁴ MPN 100 mL⁻¹. Photoreactivation and dark repair were apparent at a low UV dose (6 mW s cm⁻²). In low-dose UV disinfection, microorganisms increased within 12 h by approximately 5 and 1% due to photoreactivation and dark repair, respectively. This increase was not significant at a high UV dose (16 mW s cm⁻²). The repaired microorganisms were further inactivated, rather than reactivated, by solar irradiation, and numbers decreased to non-detectible levels after 4 h of exposure to solar irradiation. Based on UV disinfection and repair studies, a UV dose of 30 mW s cm⁻² is recommended as sufficient to produce reclaimed water virtually free of pathogens and may be adequate for disinfection of secondary effluent for agricultural irrigation in paddy rice culture.     

Surface and subsurface losses of N and P from salt-affected rice paddy fields of Saemangeum reclaimed land in South Korea

The present study was carried out to evaluate nutrient losses that occur during the course of agricultural activity from rice paddy fields of reclaimed tidal flat. For this study, we chose a salt-affected rice paddy field located in the Saemangeum reclaimed tidal area, which is located on the western South Korean coasts. The plot size was 1,000 m² (40 m × 25 m) with three replicates. The soil belonged to the Gwanghwal series, i.e., it was of the coarse silty, mixed, mesic type of Typic Haplaquents (saline alluvial soil). The input quantities of nitrogen and phosphorus (as chemical fertilizer) into the experimental rice paddy field were 200 kg N ha⁻¹ and 51 kg P₂O₅ ha⁻¹ per annum, and the respective input quantities of each due to precipitation were 9.3–12.9 kg N ha⁻¹ and 0.4–0.7 kg P ha⁻¹ per annum. In terms of irrigation water, these input quantities were 4.5–8.2 kg N ha⁻¹ and 0.3–0.9 kg P ha⁻¹ per annum, respectively. Losses of these nutrients due to surface runoff were 22.5–38.1 kg N ha⁻¹ and 0.7–2.2 kg P ha⁻¹ for the year 2003, and 26.8–29.6 kg N ha⁻¹ and 1.6–1.9 kg P ha⁻¹ for the year 2004, respectively. Losses of these nutrients due to subsurface infiltration during the irrigation period were 0.44–0.67 kg N ha⁻¹ and 0.03–0.04 kg P ha⁻¹ for the year 2003, and 0.15–0.16 kg N ha⁻¹ and 0.05–0.06 kg P ha⁻¹ for 2004. When losses of nitrogen and phosphorus were compared to the amount of nutrients supplied by chemical fertilizers, it was found that 11.3–19.1% of nitrogen and 0.5–1.7% of phosphorus were lost via surface runoff, whereas subsurface losses accounted to 0.2–0.8% for nitrogen and only 0.02–0.04% for phosphorus during the 2-year study period.     

Critical water content and water stress coefficient of soybean (Glycine max [L.] Merr.) under deficit irrigation

The objective of this research was to investigate the critical water content (θ _c) and water stress coefficient (K _s) of soybean plant under deficit irrigation. This research was conducted in a plastic house at the University of Lampung, Sumatra in Indonesia from June to September 2000. The water deficit levels were 0–20%, 20–40%, 40–60%, 60–80%, and 80–100% of available water (AW) deficit, arranged in Randomized Completely Block (RCB) design with four replications. The results showed that the soybean plant started to experience stress from week IV within 40–60% of AW deficit. The fraction of total available water (TAW) that the crop can extract from the root zone without suffering water stress (p) was 0.5 and θ_c was 0.305 m³ m⁻³. The values of K _s at p=0.5 were 0.78, 0.86, 0.78, and 0.71 from week IV to week VII, respectively. The optimum yield of soybean plant with the highest yield efficiency was reached at 40–60% of AW deficit with an average K _s value of 0.78; this level of deficit irrigation could conserve about 10% of the irrigation. The optimum yield of soybean plant was 7.9 g/pot and crop water requirement was 372 mm.     

Impact of earthen waste storage on nitrate concentration of surface water

In 1992 and 2002, investigations on the water quality and hydrology were carried out in a small agricultural catchment where swine waste was stored in earthen waste storage. The in-stream nitrogen loads and the nitrogen inputs on a sub-catchment scale were estimated and compared between 1992 and 2002. For the entire catchment, the estimated nitrogen inputs increased from 22.5 to 32.9 ton year⁻¹ (from 406 to 594 kg ha⁻¹ year⁻¹), whereas the nitrate nitrogen concentration at the outlet was constant—27 mg l⁻¹. In a sub-catchment (area C) with earthen waste storages, the nitrate nitrogen concentrations at the outlet were high, 42–51 mg l⁻¹. In a sub-catchment (area A) with an earthen waste storage, which was not in service since 1990, although the nitrogen inputs were maintained at 390 kg year⁻¹ (53 kg ha⁻¹ year⁻¹), the nitrate nitrogen concentrations at the outlet decreased from 26 to 4.9 mg l⁻¹. With assuming that the nitrogen transport rates for sources except swine waste are equal to the rates estimated for a sub-catchment without earthen waste storage, the in-stream nitrogen loads for area A were estimated to decrease from 1,334 to 94 kg year⁻¹ and the transport rates for area A were estimated to decrease from 3.95 to 0.73. These results suggest that the effluent from earthen waste storage has affected surface water quality two years after the storage was out of service and its effect largely decreased after a decade.     

鱼塘种稻对养殖水体营养物质的去除作用研究

以黄颡鱼精养塘为例,探索鱼塘种植高秆型水稻对精养池塘水体氮磷养分等水质指标的修复作用。结果表明,在水稻生长期,种稻黄颡鱼精养塘水体氮、磷养分含量显著低于单养鱼池塘。在水稻收获期,单养鱼塘水体总氮(TN)和总磷(TP)含量高达11.98mg/L和0.52mg/L,超过了《淡水池塘养殖水排放要求》标准;而种稻鱼塘水体中TN、TP含量则仅为0.49mg/L和0.08mg/L,达到《淡水池塘养殖水排放要求》一级排放标准。种稻鱼塘水体中TN、NH4+-N、NO3--N、TP和PO43--P含量比不种稻单养鱼塘分别降低95.95%、98.09%、98.07%、84.47%和64.57%。种稻鱼塘COD含量和pH值低于单养鱼塘。可见,种稻能有效降低水体养分含量,改善养殖水体水质。     

Application of system of rice intensification practices in the arid environment of the Timbuktu region in Mali

Cereal production is chronically deficit in the Timbuktu region of Mali, sufficient for only 4.5 months of annual household consumption. Small-scale, village-based irrigation schemes, usually 30–35 ha in size, irrigated by a diesel motor pump, have become important to improve food security in this arid region. The NGO Africare has worked during the past 12 years with farmers in Goundam and Dire circles to establish irrigation schemes and provide them with technical assistance. In 2007, Africare undertook a first test of the System of Rice Intensification (SRI) in Goundam circle. After farmers observed a yield of 9 t ha⁻¹ of paddy compared to 6.7 t ha⁻¹ in the control plot there was interest in larger scale testing of the SRI system. In 2008, Africare, in collaboration with the local Government Agriculture Service and with support from the Better U Foundation, implemented a community-based evaluation of SRI with 60 farmers in 12 villages. Farmers in each village selected five volunteers, who each installed both SRI and control plots, side by side, starting the nurseries on the same day and using the same seed. For SRI plots, seedlings were transplanted one plant hill⁻¹ at the two-leaf stage (on average, 11.6 days old), with spacing of 25 cm × 25 cm between hills and aligned in both directions. This allowed farmers to cross-weed with a cono-weeder, on average 2.4 times during the season. In the control plots, farmers planted 3 plants hill⁻¹ with seedlings 29.4 days old and spaced on average 23.7 cm, not planted in lines. Weeding was done by hand. 13 t ha⁻¹ of organic matter was applied under SRI management, and 3 t ha⁻¹ in the control plots. Fertilizer use was reduced by 30% with SRI compared to the control. Although alternate wetting and drying irrigation is recommended for SRI, this was not optimally implemented due to constraints on irrigation management within the scheme; thus water savings were only 10% compared to the control. Average SRI yield for all farmers reached 9.1 t ha⁻¹, with the lowest being 5.4 t ha⁻¹ and highest being 12.4 t ha⁻¹. SRI yields were on average 66% higher than the control plots at 5.5 t ha⁻¹, and 87% higher than the yields in surrounding rice fields at 4.9 t ha⁻¹. Number of tillers and panicles hill⁻¹, number of tillers and panicles m⁻², and panicle length and number of grains panicle⁻¹ were clearly superior with SRI compared to control plants. Farmers tested five varieties, all of which produced better under SRI. The SRI system allowed for a seed reduction of 85–90%: from 40–60 kg ha⁻¹ for the control plots to 6.1 kg ha⁻¹ under SRI. Although production costs per hectare were 15% higher for SRI, revenue was 2.1 times higher than under the control. Farmers were very satisfied with these results. In 2009/2010, Africare and the Government’s agriculture service worked with over 270 farmers in 28 villages to scale up SRI practices and to test innovations, including composting techniques, optimization of irrigation, and techniques to reduce labor requirements and production costs. The good crop performance along with other advantages was confirmed in this third year with SRI yields of 7.7 t ha⁻¹ (n = 130 farmers) compared to 4.5 t ha⁻¹ in farmers’ fields.     

Application of system dynamics approach for time varying water balance in aerobic paddy fields

Increasing water scarcity has necessitated the development of irrigated rice systems that require less water than the traditional flooded rice. The cultivation of aerobic rice is an effort to save water in response to growing worldwide water scarcity with the pressure to reduce water use and increase water productivity. An accurate estimation of different water balance components at the aerobic rice fields is essential to achieve effective use of limited water supplies. Some field water balance components, such as percolation, capillary rise and evapotranspiration, can not be easily measured; therefore a soil water balance model is required to develop and to test water management strategies. This paper presents results of a study to quantify time varying water balance under a critical soil water tension based irrigation criteria for the cultivation of non-ponded “aerobic rice” fields along the lower parts of the Yellow River. Based on the analysis and integration of existing field information on the hydrologic processes in an aerobic rice field, this paper outlines the general components of the water balance using a conceptual model approach. The time varying water balance is then analyzed using the feedback relations among the hydrologic processes in a commercial dynamic modeling environment, Vensim. The model simulates various water balance components such as actual evapotranspiration, deep percolation, surface runoff, and capillary rise in the aerobic rice field on a daily basis. The model parameters are validated with the observed experimental field data from the Huibei Irrigation Experiment Station, Kaifeng, China. The validated model is used to analyze irrigation application soil water tension trigger under wet, dry and average climate conditions using daily time steps. The scenario analysis show that to conserve scarce water resources during the average climate years the irrigation scheduling criteria can be set as −30 kPa average root zone soil water tension; whereas it can be set at −70 kPa during the dry years, however, the associated yields may reduce. Compared with the flooded lowland rice and other upland crops, with these two alternatives irrigation event triggers, aerobic rice cultivation can lead to significant water savings.     

Irrigation water reduction using System of Rice Intensification compared with conventional cultivation methods in Iraq

A field study was conducted at Al-Mishkhab Rice Research Station (MRRS) during the summer season 2009 to evaluate irrigation water use efficiency (IWUE) using Anbar 33 variety with the System of Rice Intensification compared to traditional methods. During the growth phase, the number of leaves, stems, and roots, and the average plant height were measured every 15 days for the two sets of methods. At maturity, the depth and length of plant roots was assessed, along with leaf area index (LAI) of the flag leaf and plant height. The amount of irrigation water applied was measured by water meter for both methods. SRI principles for plant age, spacing, etc., were implemented in the SRI plots. The results indicated more vigorous growth of roots under SRI methods, reaching 13,004 cm plant⁻¹ compared with non-SRI results of 4,722 cm plant⁻¹. There was 42% increase in grain yield when SRI methods were used. These had water use efficiency (WUE) of 0.291 kg m⁻² compared with WUE of 0.108 kg m⁻² for non-SRI cultivation, almost a threefold difference. SRI practices reduced the need for irrigation water by 38.5%.     

2005～2014年苏州市农业面源污染源强变化特征

利用清单分析的方法,对2005～2014年苏州市农业面源污染排放量进行了计算,分析该地区农业面源污染源强的时间变化特征.研究结果表明,2014年苏州市农业面源污染化学需氧量(COD)、氨氮(NH4+-N)、总氮(TN)和总磷(TP)的排放总量分别为131 843.8 t、6 150.2 t、20 848.5 t和2 922.8 t,属于畜禽养殖型和农村生活双重污染区.而近十年苏州市农业面源污染总体呈现逐年下降趋势,较2005年分别降低38.40％、21.80％、17.13％和25.26％.同时,选用等标污染负荷法分析了苏州市的农业面源污染风险,按照污染物等标排放量TN＞TP＞COD,而按照行业等标排放量畜禽养殖＞农村生活＞种植业＞水产养殖.近十年苏州市农业面源污染等标污染排放量从554.1亿m3降至420.6亿m3,降低24.09％,污染风险降低.随着工业经济的逐年提升,苏州市农业面源污染排放量逐渐下降,但农业面源污染风险依旧存在,TN污染风险最高,且污染来源复杂,应加强各行业的协同减控.     

Nitrogen and phosphorus leaching losses from paddy fields with different water and nitrogen managements

While many water-saving rice production techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study aims to assess nitrogen (N) and phosphorus (P) leaching losses under real conditions in different water and N managements. Two water and three N treatments are conducted in the Taihu Lake region of China. Results show that the total N leaching losses during the rice season under flooding irrigation (FI) are 12.4, 9.31, and 7.17 kg ha⁻¹ for farmers’ fertilization practices (FFP), site-specific N management (SSNM), and controlled-release nitrogen fertilizer management (CRN), respectively. Under controlled irrigation (CI), the respective losses were 7.40, 5.86, and 3.79 kg ha⁻¹ for the same management methods. The total P leaching losses during the rice season under FI were 0.939, 0.927, and 0.353 kg ha⁻¹ for FFP, SSNM, and CRN, respectively. Under CI, the losses were 0.424, 0.433, and 0.279 kg ha⁻¹, respectively, for the same management methods. Ammonium and nitrate N accounted for 42.2–65.5% and 11.8–14.7% of the total nitrogen leaching losses under different water and N management methods, respectively. Due to significant decrease of volumes of percolation water and nitrogen and phosphorus concentrations in percolation water, N and P leaching losses were reduced in the CI treatment compared to the FI treatment under the same N management. The reduction of N input and application of controlled-release nitrogen fertilizer can reduce N and P leaching losses from paddy fields.     

Estimation of pollutant loads in an estuarine reservoir considering pollution source characteristics and seasonal variation

The Total Maximum Daily Load (TMDL) program is an integrated process of watershed assessment and management to address surface water quality impairment. The management of organic contaminants and nutrients is a primary concern in conserving surface water bodies. Watershed-scale pollutant loads simulation can assist stakeholders and watershed planners in making decisions on immediate and long-term land use schemes to improve water quality. However, the behavior of contaminants in a watershed needs to be characterized prior to such model applications. The objectives of this study were to characterize point and nonpoint pollutants runoff at a watershed scale and to develop a Pollutant Load Calculation Model (PLCM), which facilitates the estimation of pollutant delivery to a watershed outlet. The developed model was applied for the six sub-watersheds of the Saemangeum estuarine watershed in Korea, where a large tidal reclamation project has been underway. Two years stream flow and water quality data were used for the model calibration, while 1 year data were utilized for the model validation. The model calibration resulted in the R ² values of 0.58, 0.53, and 0.35 for BOD, TN, and TP, respectively. Overall performance for the validation period was similar with that for the calibration period although the R ² values were slightly decreased. The PLCM tends to substantially under or overestimate delivery pollutants loads during the summer rainy seasons when most rainfall events occur. This is probably because once-a-month-measured water quality data, which might not represent appropriately monthly water quality, particularly, for rainy seasons, were used for the loads calculation. Thus, more frequently monitored water quality data should be used for the delivery loads estimation at least for a rainy season in order to improve the PLCM performance. Nevertheless, the developed model took the pollutant reduction process into account, which is not allowed with the conventional unit loading method, and furthermore temporal variations of pollutant loads based on stream flows were also incorporated into the pollutant loads estimation. The developed PLCM can be a useful tool to assess pollutants delivery loads at a watershed scale and thus assist decision makers in developing watershed pollution management schemes.     

The effect of irrigation and nitrogen on powdery scab and yield of potatoes

Summary Powdery scab, caused by the fungusSpongospora subterranea, has developed in the Cappodocia region of Turkey because of changes in agronomic practices, such as excessive irrigation and nitrogen fertilizer use and growth of highly susceptible cultivars. The most suitable irrigation and nitrogen application levels were established to maintain powdery scab at minimum levels without affecting potato yield. Three irrigation levels were used in 1998 (673, 897, 1121 mm) and five in 1999 (329, 494, 658, 823, 987 mm). Nitrogen levels were applied 150, 300, 450, 600 kg N ha⁻¹. In 1998, least powdery scab occurred with 673 mm irrigation, which yielded 41 t ha⁻¹ potatoes. The lowest disease severity occurred in 1999 with 494 mm irrigation and 150 kg N ha⁻¹. At these levels, tuber yield was 34 t ha⁻¹ which was not significantly different from the highest yield measured. In 1999 and at two of the three irrigation levels inl998, nitrogen increased disease severity.     

Economic valuation of cultivated lands as nitrogen removal/effusion sites by newly proposed replacement cost method

To valuate the multifunctionality economically is effective to make it possible to realize the value for the nation and to compare functionalities among countries of the world. In this paper, the external economies of paddy fields and fallow paddy fields including wetlands as N removal function sites, and of upland fields and orchards as pollution sites are valuated by the newly proposed replacement cost method, by replacing them with construction costs of water quality improvement facilities. In addition, we discuss an agricultural land-use scenario in which cultivated land has no net negative economic effect on the water environment. The results showed that (1) paddy fields and fallow paddy fields including wetlands were respectively valued at 1.2×10³ and 2.81×10³ JPY m⁻² on average as the N removal sites, (2) upland fields had 0.32×10³ JPY m⁻² on average of economic value, and suggested that paddy fields have an external economic value that compensates for the negative external economic value of upland fields 3.65 times their size.