Irrigated Rice Fields Research Articles

Analisis Karakteristik Fisik Lahan Kawasan Perumahan di Dusun Jering VI, Desa Sidorejo, Kecamatan Godean, Kabupaten Sleman

Land characteristics include land factors that can be measured or estimated in size such as slope, rainfall, soil texture, available water and so on. The study was conducted at a housing location in Jering VI Hamlet, Sidorejo Village, Godean District, Sleman Regency which is located on Mount Wungkal. The condition of Mount Wungkal before being used as housing had dense vegetation, but with the large-scale opening of housing land, there were changes that occurred on Mount Wungkal. The opening of the land caused several impacts on the environment so it is important to know the physical characteristics of the land in the area. Thus, the purpose of this study was to determine the physical characteristics of the land in the research area. The method used is the survey and mapping method in data collection and descriptive analysis. The results of the study obtained are the physical characteristics of the land of the Godean Jogja Hills housing area, there are several criteria that are appropriate and inappropriate. The criteria that are not appropriate are slope gradient, area of green open space, drainage infrastructure capacity, not located in a disaster-prone area (landslides, floods, erosion, and abrasion), not located in an agricultural/buffer cultivation area, distance to educational facilities, health facilities and trade and commerce facilities and the appropriate criteria are the area for building houses, water availability, not located in the border area of rivers/coasts/reservoirs/lakes/springs/irrigation channels/railways and safe flight areas, not located in protected areas, avoiding technical irrigation rice fields, wastewater disposal systems and garbage disposal systems

An Analysis Management by Mike 21 Modelling at Rolak 70 Retention Pool in Jombang Regency, East Java Province, Indonesia

Some areas in Indonesia have high level of sedimentation problems that able to cause flooding, and one apparent solution is to build a retention pool. Sedimentation is deposition of material into the reservoir or dam due to environmental damage or erosion occurs in the river basin area. Sedimentation becomes the main factor in constructing the Rolak 70 Retention Pool, as an important component in controlling floods on the Konto River when the water discharge exceeds the maximum limit. From geography perspective, the modelling location is in waters located between 112° 11′ 22.85″ South Latitude and 7° 38′ 42.23″ East Longitude. The model area has northern boundary at the tip of Rolak 70 pool, while western boundary at the outlet of Rolak 70 pool. The lowest water depth value is located in upstream area of Konto River at coordinates of 112°11’27.81″ South Latitude and 7°38’49.27″ East longitude. Weight of soil sample taken from the research site was ± 1000 grams at each point, and the result of sediment sample test performed at the Soil Mechanics Laboratory of Civil Engineering Department, Sultan Agung University, Semarang showed that the research area is dominated by sand, followed by mud and gravel. There were several tests conducted include grain size analysis, hydrometer analysis, and specific gravity analysis to determine the D50 of the sediment. In the study area, several sampling points were taken, started from upstream area of the river in front of Rolak 70 building to the Rolak 70 Retention Pool. For this purpose, a MIKE 21 software modelling was used to determine distribution and lines of sedimentation in the study area. As visible from changes found in bed level morphology that occurred in Rolak 70 Retention Pool by cross section extraction, it can be seen that the largest change occurred in analysis for line 1 and the smallest bed level changes occurred in the analysis for line 6. Then, the result revealed that sedimentation tends to occur at large locations in upstream area of Rolak 70 Retention Pool, while the smallest sedimentation potential will happen at the downstream area of Rolak 70 Retention Pool. These results can be caused by changes of speed from the river flow which tends to decrease towards the end of Rolak 70 Retention Pool. So, the river flow has no more energy to carry heavy amount of sediments originating from the upstream area of the Konto River. By the existence of this retention pool, the need for rice field irrigation will not be disturbed by sediment deposits. In addition, the Rolak 70 Retention Pool can be used as temporary storage for material from Mount Kelud eruption where these materials can be utilized as building material or other useful purposes.

Geographical Distribution and Abundance of Species of the Pycreus Genus in Rice Production Regions in Rio Grande do Sul

Theoretical Reference: Identifying, tracking, and analyzing weed infestation levels in rice crops are essential for developing more effective control strategies, ultimately enhancing efficiency, reducing costs, and minimizing environmental impact. This study focuses on the geographic distribution and abundance of species within the Pycreus genus (family Cyperaceae) in rice fields in Rio Grande do Sul (RS), Brazil. Method: During the 2005/06 growing season, collections and abundance assessments of Pycreus species were conducted across three irrigated rice fields located in three municipalities within five major rice production regions of RS. Plants were collected during vegetative or reproductive stages, dried, and identified using specialized literature. Specimens were then deposited as vouchers in the PEL Herbarium at the Department of Botany, Federal University of Pelotas. Results and Conclusion: The study revealed the presence of Pycreus species in rice fields across RS, with P. polystachyos (Rottb.) P. Beauv. being the most abundant and frequently observed species. P. macrostachyos (Lam.) J. Raynal and P. lanceolatus (Poir.) C.B. Clarke were also identified, though less commonly. The highest abundance of Pycreus species was recorded in the coastal physiographic region, particularly within the Internal Coastal Plain of Lagoa dos Patos and southern rice production areas. Implications of Research: These findings emphasize the need for targeted weed management strategies in rice cultivation, particularly in regions where Pycreus species are most prevalent, to enhance crop productivity and sustainability. Originality/Value: This study provides valuable insights into the distribution and abundance of Pycreus species in RS rice fields, contributing to the understanding of weed dynamics in rice production and offering a basis for the development of more effective control measures.

The impact of Bacillus thuringiensis var. israelensis (Vectobac® WDG) larvicide sprayed with drones on the bio-control of malaria vectors in rice fields of sub-urban Kigali, Rwanda

BackgroundThe core vector control tools used to reduce malaria prevalence are currently long-lasting insecticidal nets (LLINs), and indoor residual spraying (IRS). These interventions are hindered by insecticide resistance and behavioural adaptation by malaria vectors. Thus, for effective interruption of malaria transmission, there is a need to develop novel vector control interventions and technologies to address the above challenges. Larviciding using drones was experimented as an innovative tool that could complement existing indoor interventions to control malaria.MethodsA non-randomized larviciding trial was carried out in irrigated rice fields in sub-urban Kigali, Rwanda. Potential mosquito larval habitats in study sites were mapped and subsequently sprayed using multirotor drones. Application of Bacillus thuringiensis var. israelensis (Bti) (Vectobac® WDG) was followed by entomological surveys that were performed every two weeks over a ten-month period. Sampling of mosquito larvae was done with dippers while adult mosquitoes were collected using CDC miniature light traps (CDC-LT) and pyrethrum spraying collection (PSC) methods. Malaria cases were routinely monitored through community health workers in villages surrounding the study sites.ResultsThe abundance of all-species mosquito larvae, Anopheles larvae and all-species pupae declined by 68.1%, 74.6% and 99.6%, respectively. Larval density was reduced by 93.3% for total larvae, 95.3% for the Anopheles larvae and 61.9% for pupae. The total adult mosquitoes and Anopheles gambiae sensu lato collected using CDC-Light trap declined by 60.6% and 80% respectively. Malaria incidence also declined significantly between intervention and control sites (U = 20, z = − 2.268, p = 0.023).ConclusionsThe larviciding using drone technology implemented in Rwanda demonstrated a substantial reduction in abundance and density of mosquito larvae and, concomitant decline in adult mosquito populations and malaria incidences in villages contingent to the treatment sites. The scaling up of larval source management (LSM) has to be integrated in malaria programmes in targeted areas of malaria transmission in order to enhance the gains in malaria control.

Pembangunan Rumah Pompa Air Sebagai Upaya Untuk Meningkatkan Efektivitas Pengairan Sawah Di Desa Sukomulyo

Sukomulyo is a village located in Kaliwungu Selatan District, Kendal Regency, most of whose residents work as farmers. The rice fields in Sukomulyo village are irrigated using river water which is taken directly from the Waridin River with a diesel water pump. The process of irrigating the rice fields takes a long time, so the water pumps are simply left alone by the farmers because they are doing other activities. Often farmers forget to turn off the water pumps they turn on, resulting in wasteful use of river water and fuel. When the dry season arrives, there could be a decrease in the river water discharge to the ground which has the potential to result in farmers not being able to irrigate their rice fields with water. To overcome this problem, the Sukomulyo farmer group in collaboration with the PPL (Agricultural Extension Worker) of Kaliwungu Selatan District built a water pump house which is used for their rice field irrigation needs. With the construction of the water pump house, it is hoped that it can irrigate farmers' rice fields during the dry season and can increase agricultural production in Sukomulyo Village and can reduce farmers' worries when the river water does not flow

Internet of things-based rice field irrigation evaporation monitoring system

The urgency for efficient irrigation in Indonesia’s agriculture sector, particularly in paddy fields, is evident. However, existing methods for monitoring water levels are antiquated, often requiring manual measurements with a ruler. This research introduces a comprehensive “monitoring system for light intensity and water temperature as an analysis of evaporation for rice irrigation based on the internet of things”. The system integrates various sensors an anemometer for wind speed, an ultrasonic sensor for water level, a DS18B20 waterproof sensor for water temperature, and a GY-8511 sensor for sunlight intensity. All data are collected by an Arduino Mega controller, connected to an ESP32 for transmitting the readings to the Blynk app and an I2C 20×4 liquid crystal display (LCD) screen. The control mechanism employs a closed-loop system with a direct current (DC) motor actuator to operate the water gate, which can also be manually controlled via a cellphone. The system effectively meets daily evapotranspiration requirements of 1.44 mm, with optimal conditions yielding water levels of 3 cm, water temperatures of 38.53 °C, sunlight intensity of 4.59 mW/cm², and wind speed of 0.21 m/s.

Information system for collecting data on the area of ​​irrigated rice fields at the Jombang district agricultural service

Irrigation is one of the important elements in agriculture, especially in rice fields. Irrigation makes water more available to plants and can increase yields. Therefore, irrigation efficiency and monitoring are important to support agricultural productivity. Looking at the rapid development of technology utilization, it is also needed to help irrigation managers at the Department of Agriculture to collect data systematically. One of them is creating a data collection system in a more modern way. regarding the case of irrigation managers at the Department of Agriculture who have so far been using manual methods. The purpose of this study is to design an Information System for recording the area of ​​rice field irrigation. The SDLC (System development life cycle) method is used with a Waterfall process model: analysis, design, code generation, testing, and support. This system is created using PHP and MySQL programs, Google Chrome software, XAMPP, and MySQL database. The results of the study show that the designed system can help facilitate data collection on the area of ​​rice field irrigation at the Department of Agriculture, Jombang Regency. Keywords: Information System; Data Collection; Irrigation; waterfall

Hydrus-1D Model for Simulating Potassium Transport in Rice Crop Irrigated with Alternate Wetting and Drying Practice

ABSTRACT Potassium (K) is one of the essential nutrients that play a crucial role in rice fields; however, its availability, transport, and balance components can be influenced by alternating wetting and drying (AWD) irrigation practice. This study used the Hydrus-1D solute transport model to simulate K transport and balance components in AWD irrigated rice fields. Thirty lysimeter field experiment plots with three different irrigation treatments (No: no soil water stress, MS: mild soil water stress (400 cm), and SS: severe soil water stress (750 cm)) were used for rice cultivation. Daily measurements of soil matric potential head (SMPH) and ponding water depth (PWD) were recorded. Throughout the rice-growing season, leachate water samples from the surface (ponding water) and soil profiles were collected to measure K content. Using the lysimeter field experiment data, the Hydrus-1D model simulated K transport in the AWD rice field. The simulation results indicate that the K distribution predominantly occurred within the top puddled soil layer (0–20 cm) in AWD practice. This suggests that the recommended K fertilizer dose with a 4–5 cm PWD and SMPH of 400 cm optimizes K availability for rice while limiting K leaching loss. The Hydrus-1D model proves to be a valuable management tool, aiding in determining optimal K application rates and ponding water depths for AWD irrigation, ensuring sufficient K nutrients for rice, and controlling K loss for sustainable rice production.

Smart irrigation system using node microcontroller unit ESP8266 and Ubidots cloud platform

The agricultural irrigation system is extremely important. For optimal harvest yields, farmers must manage rice plant quality by monitoring water, soil, and temperature on agricultural fields. If market demand rises, traditional rice field irrigation in Indonesia will make things harder for farmers. This modern era requires a system that lets farmers monitor and regulate agricultural fields anywhere, anytime. We need a solution that can control the irrigation system remotely using an internet of things (IoT) device and a smartphone. This study employed the Ubidots IoT cloud platform. In addition, the study uses soil moisture and temperature sensors to monitor conditions in agricultural regions, while pumps function as irrigation systems. The test results indicate the proper design of the system. Each trial collected data. The pump will turn on and off automatically based on soil moisture criteria, with the pump active while the soil moisture is less than 20% and deactivated when the soil moisture exceeds 20%. In simulation mode, the pump operates for an average of 0–5 seconds of watering. The monitoring system shows the current soil temperature and moisture levels. Temperature sensors respond in 1-3 seconds, whereas soil moisture sensors respond in 0–4 seconds.

Smart irrigation system using node microcontroller unit ESP8266 and Ubidots cloud platform

The agricultural irrigation system is extremely important. For optimal harvest yields, farmers must manage rice plant quality by monitoring water, soil, and temperature on agricultural fields. If market demand rises, traditional rice field irrigation in Indonesia will make things harder for farmers. This modern era requires a system that lets farmers monitor and regulate agricultural fields anywhere, anytime. We need a solution that can control the irrigation system remotely using an internet of things (IoT) device and a smartphone. This study employed the Ubidots IoT cloud platform. In addition, the study uses soil moisture and temperature sensors to monitor conditions in agricultural regions, while pumps function as irrigation systems. The test results indicate the proper design of the system. Each trial collected data. The pump will turn on and off automatically based on soil moisture criteria, with the pump active while the soil moisture is less than 20% and deactivated when the soil moisture exceeds 20%. In simulation mode, the pump operates for an average of 0–5 seconds of watering. The monitoring system shows the current soil temperature and moisture levels. Temperature sensors respond in 1-3 seconds, whereas soil moisture sensors respond in 0–4 seconds.

Analysis of Factors Causing Difficulties in Use of Rice Land in the Irrigation Area of the Tojo Region and West Tojo

In one of the areas in Tojo Una-Una Regency, the rice fields are irrigated rice fields with a surface irrigation system, where the water source comes from a river which flows into the rice fields. However, in the dry season, the water demand for rice fields in these two regions cannot evenly meet the water needs of rice fields in both regions, thus affecting farmers' production results. The aim of this research is to find out what factors make it difficult for farmers to utilize rice fields in the irrigation areas of the Tojo and West Tojo regions and to find out the strategies used by farmers to overcome difficulties in utilizing rice fields in the irrigation areas of the Tojo and West Tojo regions . Respondents in this study were 281 respondents including rice field farmers in the Tojo region and farmers in the West Tojo region. Data analysis uses Factor Analysis. The magnitude of the influence resulting from all these factors reached 62,445%, while the remaining 37,555% was influenced by other factors whose influence was not significant. The strategies implemented by farmers to overcome difficulties in utilizing rice fields in the irrigation areas of Tojo and West Tojo regions include repairing irrigation networks, building groundwater irrigation pumps, improving the quality of farmers' human resources through regular extension activities, arranging planting pattern schedules, changing systems. distributing water during the dry season, and reactivating the P3A (Water User Farmers Association).

One policy but different interpretations: A case of agricultural policy implementation in Indonesia

AbstractThe Indonesian governments developed the Upsus Pajale policy to achieve a goal and solve the problem of food self‐sufficiency. Rice, corn, and soybean were the main commodities in the plan of Upsus Pajale Policy implementation. UPSUS Pajale improve rice, corn, and soybean production for food self‐sufficiency. This study examined UPSUS Pajale policy implementation at the province, district, subdistrict, and farmer levels. This study examined rice growing in Banyuasin's tidal lowlands, Ogan Komering Ilir's swamplands, and East Ogan Komering Ulu's irrigated rice fields. The research method used a combination model of quantitative and qualitative (mixed method). Sampling data used purposive sampling. NVivo 12 software examined provincial, district, subdistrict, farmer interviews, and group discussions. Results affected typology management constraints differently. Production input costs were the most common issue. This study found that policy was differently implemented at various levels. It would be impacted to the success of the policy.

Evaluating Cadmium (Cd) Pollution in Sleman Regency’s Rice Fields

The research aims to investigate the Cadmium (Cd) contamination in rice fields within Sleman Regency due to its potential environmental and human health impact. The study was conducted from January to June 2023 and involved collecting soil samples from 23 irrigated rice fields within Sleman Regency with a grid sampling approach. Composite soil samples were created by blending five individual sub-samples from the cultivated layer (0-20 cm). The Cd levels in these samples were investigated using the Atomic Absorption Spectro-photometer (AAS) method. The findings revealed that all the sampled rice fields in Sleman Regency exceeded the critical limit of Cd concentration. The analysis of contamination factors (CF) and potential ecological risks (Er) indicated that the Cd contamination in Sleman Regency had reached a highly polluted level, carrying potential ecological risks. The extent of Cd contamination, primarily resulting from human activities (EF > 1), fell within the severe to extreme range (I-geo = 4-5). As a result, remediation measures are required to address the Cd contamination in Sleman Regency’s rice fields. These findings call for reducing the usage of chemical fertilizers, pesticides, and fungicides. Future studies should determine the possibility of cadmium accumulation in rice and its transfer from soil to rice.

Implementasi Pemanfaatan Pembangkit Listrik Tenaga Surya (PLTS) untuk Peningkatan Produktivitas Budidaya Ikan dan Pertanian di Kalurahan Sumbersari

Kalurahan Sumbersari, a border village in Sleman Regency, possesses significant potential in natural resources, particularly in agriculture and fisheries. However, the village faces substantial challenges, including inadequate aeration systems for fishponds and irrigation difficulties for rice fields. This community service initiative aims to address these issues by implementing solar energy-based solutions. The activities involved the design of an optimized aeration system for fishponds, the strategic installation of water pumps to facilitate rice field irrigation, and the construction of a Solar Power Plant (PLTS). The adoption of solar energy not only aims to meet the electricity needs but also contributes to Indonesia's achievement of the Sustainable Development Goals (SDGs), particularly Goal 7, which focuses on Affordable and Clean Energy. The success of this project hinged on the active participation of the local community. Socialization and training sessions were conducted to ensure understanding of the aeration systems, water pump operations, and PLTS maintenance. It is anticipated that the implementation of these activities will resolve the fish health issues and irrigation difficulties, thereby enhancing fish and agricultural production in Kalurahan Sumbersari. In addition to these direct benefits, the use of renewable energy is also expected to mitigate the negative environmental impacts associated with fossil fuel energy consumption.

Species diversity of Odonata as a bioindicator of water pollution in the Batang Harau watershed, Tanah Datar District, West Sumatra

The Batang Harau River was located in Nagari Paninjauan, X Koto District, Tanah Datar Regency, West Sumatra. The local community uses this river as a water source to carry out various daily activities, such as the irrigation of rice fields; household activities, and household waste disposal. The research aimed to analyze the comparison of dragonfly species diversity as a bioindicator for pollution in several habitat types (natural, rice fields, and settlements). The observations were made by exploring and walking along the river in the morning (9 am – 12 am) and evening (3 pm - 5 pm). The Visual Encounter Survey (VES) method was modified using a 20 m x 10 m plot, and all dragonflies found in this area were collected using an insect net. The data obtained were analyzed using the ShannonWienner diversity index, the Margalef species richness index, and Simpson’s dominance index. A total of 280 individuals, 12 species from 7 families, were collected in this study site. Most Odonata species were found in natural areas, followed by rice fields and settlements. The environmental conditions have affected the diversity of Odonata. The odonates can be used as bioindicators of the aquatic environment, especially in the suborder Zygoptera, which is dominantly found in natural habitats.

Application of Planting System and Organic Fertilizer on the Yield of Inpari IR Nutri Zinc in Lampung

The low rice productivity in Lampung needs to be increased. The objectives of this study were to introduce new superior Inpari IR Nutri Zinc rice and determine the effect of planting systems and biofertilizer on the growth and yield of Inpari IR Nutri Zinc rice in technically irrigated rice fields in Lampung. The experiment was carried out in technically irrigated rice fields in Kalirejo Village, Negeri Katon District, Pesawaran Regency, Lampung Province, using a split-plot design in a randomized block design with three replications. The treatments tested were three rice planting systems as the main plot and the dose of biofertilizer as a sub-plot. The parameters observed components of growth and yield components. Data were analyzed with the SAS software 5.4 version. The results showed that the application of biofertilizers gave effects on rice yield. From the results of this study, it can be concluded that the use of biofertilizers can increase rice yields by 10-12% compared to those without biofertilizers, in the three cropping systems. The application of biofertilizers resulted in the highest harvested dry grain production, namely 6.61 tons per hectare and significantly different than that without biofertilizers, namely 5.96 tons per hectare. The production of dry grain harvested by the three cropping systems was not significantly different at an average of 6.28 tons per hectare.

Education Of Water Needs And Management For Agriculture In Garagahan Irrigation Area

Irrigation Areas (DI) were built to meet various needs of life, especially to achieve the level of community welfare. D I Sangkir Garagahan was built by the Department of Water Resources and Construction Development in 1986 and is located in the Lubuk Basung sub-district, Agam regency. The current irrigation management is 671 hectares covering 3 working areas, namely Nagari Garagahan which has an area of ​​415 hectares of irrigated rice fields, Nagari Kampuang Tangah 136 hectares and Nagari Manggopoh 120 hectares. On April 15, 2022 an educational training was conducted to determine the needs and management of water for agricultural land. The methods used are lectures, discussions and training on the use of formulas to regulate plant water and soil management. The training was attended by the Nagari Garagahan community who are members of the Water User Farmers Association (P3A) and Water User Farmers Association (GP3A). Availability of water by adjusting plant water in the field and at the entrance gate for an area of ​​415 hectares of irrigated rice fields, the water requirement is 0.7204 m3/second. Soil management for agriculture is carried out by biological, non-biological and mechanical methods. By adjusting the capacity of the nagari for its implementation

Substituting Partial Chemical Fertilizers with Bio-Organic Fertilizers to Reduce Greenhouse Gas Emissions in Water-Saving Irrigated Rice Fields

Conventional water and fertilizer management practices have led to elevated greenhouse gas emissions from rice fields and decreased the efficiency of water and fertilizer utilization in agricultural land. The implementation of water-saving irrigation and the substitution of chemical fertilizers with organic alternatives can influence CH4 and N2O emissions in rice fields. However, it remains unclear how the simultaneous application of both methods will affect the CH4 and N2O emissions in rice fields. Therefore, two irrigation methods (F: flooded irrigation; C: controlled irrigation) and three fertilization modes (A: full chemical fertilizer; B: bio-organic fertilizer replacing 15% chemical nitrogen fertilizer; C: bio-organic fertilizer replacing 30% chemical nitrogen fertilizer) were set up through field experiments to explore the effect of greenhouse gas emission reduction in rice fields by combining controlled irrigation and bio-organic fertilizers. Substituting some chemical fertilizers with bio-organic fertilizers can lower the peak CH4 and N2O fluxes in rice fields, leading to a decrease in the cumulative CH4 and N2O emissions by 11.9~29.7% and 10.8~57.3%, respectively. The reductions led to a considerable decrease in the global warming potential (GWP) and the greenhouse gas emission intensity (GHGI) by 16.1~48.1% and 16.3~48.1%, respectively. Controlled irrigation significantly reduced CH4 emissions by 55.2~69.4% compared with flooded irrigation in rice fields. However, it also increased N2O emissions by 47.5~207.9%, considerably reducing their GWPs by 11.8~45.5%. Neither bio-organic fertilizer substitution nor controlled irrigation significantly affected rice yield. Replacing 15% of chemical nitrogen fertilizers with bio-organic fertilizers in controlled irrigation rice fields can minimize rice GWP and GHGI. The study’s results are of significant importance for enhancing the regulation of greenhouse gases in farmland and achieving sustainable agriculture through cleaner production.

Storm water management model to evaluate urban inundation in Lowokwaru and Blimbing sub-catchments in the city of Malang

In the city of Malang, which is a highland area, there are still floods, including Blimbing and Lowokwaru sub-districts. One of the causal factors is the change of undeveloped areas becoming relatively large built-up areas in the Upper Brantas sub-watershed, from initially 20.5% in 2000 to 69.6% 20 years later. This change also impacts the transformation of irrigation canals that once irrigated rice fields, causing them to shift their function into drainage channels that carry runoff water toward natural channels (natural drainage). Consequently, the existing canal conditions cannot accommodate the runoff water. The research employed an approach that involved analyzing floodwater management models using the Storm Water Management Model (SWMM 5.1) and surveying existing canal data. The analysis results revealed that, within the studied areas of Blimbing Village and the Blimbing Catchment Area, 10 out of the existing 170 drainage channels were incapable of handling the discharge associated with rainfall intensities designed for return periods of 5 years (112.48 mm/day) and ten years (117.09 mm/day). In the Lowokwaru Catchment Area, it was evident that 18 out of the 216 existing canals experienced overflow events with designed flood discharge for 5-year and 10-year periods.

Food web structures of irrigated rice fields estimated from carbon and nitrogen stable isotopes: Special reference to the role of filamentous green algae as a food resource of aquatic consumers

AbstractRice fields are characterized by high algal production and dense mats of filamentous green algae, and they function as habitats for various aquatic organisms. However, how algal production supports the secondary production of aquatic consumers in rice fields has not been assessed. Herein, aquatic food web structures in two adjacent rice fields in northeastern Japan were examined using carbon and nitrogen stable isotope analyses. Filamentous algae often showed higher δ13C values (mean, −23.1‰ to −21.4‰) than other organic matter sources, including particulate organic matter, benthic microalgae, and soil organic matter (−30.1‰ to −25.4‰). A δ13C‐based isotopic mixing model estimated that among 19 taxa of herbivores and omnivores, most taxa depended on filamentous algae‐derived carbon (ca. >30%). Particularly, Peltodytes intermedius larvae, a specialist feeder for filamentous algae, showed the highest reliance (mean, 66.7%–80.0%). The microcrustacean, Ostracoda sp. also utilized a diet consisting of a substantial proportion of filamentous algae‐derived carbon (57.6%). Seven out of 10 carnivorous taxa showed reliance on filamentous algae‐derived carbon by >30%. Particularly, larvae of beetles (Berosus sp., Enochrus sp., and Hydrochara affinis) showed the highest reliance (40.2%–44.3%). They could assimilate filamentous algae‐based carbon by consuming herbivores, such as P. intermedius. Because fresh filamentous green algae were eaten less by aquatic consumers, the herbivores could consume decomposed filamentous algae rather than fresh ones. Our results suggest that filamentous algae are one of the major organic matter sources supporting secondary production in rice field food webs.