Takao Nakagiri

A Field Monitoring Station Network for Supporting the Development of Integrated Water Resources Management

Field monitoring systems were installed in six locations of interest for field weather and environment monitoring in support of the development of an integrated water resources management system in two watersheds, Saba in Bali province and Jeneberang in South Sulawesi province, Indonesia. The stations were situated in lower, middle, and upper sections of the watersheds, with an intention of obtaining information regarding variation in weather and soil that represents variation in the parameters of the respective watersheds. The systems include an automatic weather station, a soil monitoring system, and a Field Router remote monitoring system that delivers data daily via Internet. Data handling procedures were developed to process the data and calculate the water balance of each field. The result yielded a description of the current condition of each field that can serve as a basis for local field water management assessment. This real-time monitoring network can support water management in watersheds that are facing water-related risks resulting from land-use change and climate change. Keywords: water resources, remote monitoring, climate change, agricultural water management.

Variation in Speciation and Availability of Phosphorus in Paddy Soil

There is a global concern about the depletion in phosphorus (P) resources in the near future. Some attempts for effective reuse of P, including recovery from municipal wastes, have been conducted. However, a strong sorption of P onto some minerals may result in low P availability for crops. Therefore, it is necessary to understand the speciation of the chemical forms of P and to elucidate the relationships between P availability and chemical forms of P in soil. This study focuses on the variation in P speciation and the chemical forms of available P in a paddy soil. Incubation experiments with/without drainage, simulating the situation in a paddy field, were performed at a laboratory scale to evaluate the variation in speciation and P availability in soil. The speciation of P was analyzed according to Wilson’s sequential extraction method and measured using Bray No. 2 and Truog methods. Two kinds of chemical forms, i.e. , Fe and Mn (oxy)hydroxides (Fe-Mn-P) and organic and biogenic P (Org-P) were predominant in the soil, and they were easily interconverted by changing soil redox conditions. Available P using the Bray No. 2 method was increased in 21 days owing to the anaerobic condition; thereafter, it reached a constant value by the end of both the incubation experiments. However, a drastic decrease was detected in available P, using Truog-P. It occurred owing to the drying of soil, which suggested that some chemical form(s) of P other than Truog-P might be generated. A comparison between the concentrations of available P and that of each chemical form showed that available P included some Org-P, which might be less absorbed by plants compared to the exchangeable and pore water fraction (Ex-P) and Fe-Mn-P. We conclude that anaerobic soil conditions play an important role in the efficient consumption of P.

Hydrogeochemical Assessment of the Contribution of Caldera Lakes and Paddy Irrigation to River Water Stability

On-site water sampling surveys were carried out from 2012 to 2014 to sample rainwater, river water, and paddy water in the Saba River Basin in Bali Island and three caldera lakes adjacent to this basin, in order to characterize the different isotopic ratios in this range of water samples. The results showed that the water isotopic ratios of river water could be expressed by the linear combination of the isotopic ratios of the constituent waters such as rainwater and paddy water. Furthermore, the results suggested that there was likely a stable inflow from the caldera lakes, which were located outside of the basin area, to the Saba River via its tributaries (the Panas River and the Ling River). Based on the water isotopic relationship, the return flow from the paddy fields was inferred to contribute considerably to the river flow to the extent beyond its area ratio to the total basin area, especially in dry seasons. We concluded that the caldera lakes and the paddy irrigation practices in the Saba River Basin contributed to the stabilization of the river water flow and that this contribution was especially strong in the dry seasons. The water isotopic properties should be regarded as “scientific information for society,” which can provide strong support for the diagnosis of river basins and decision-making for water resources management in the future.