The Ayeyarwady Delta in the Bay of Bengal, the rice bowl of Myanmar, depends on natural conditions, especially rainfall. During the dry season, the delta’s coastal zone experiences saline water intrusion due to its low-lying topography. On May 2, 2008, Cyclone Nargis made landfall and crossed Ayeyarwady Region and Yangon City, affecting more than 50 townships and causing massive destruction of personal property and natural ecosystems. There is no doubt that Nargis caused an unprecedented large-scale disaster, but there is no objective method to quantify crop yield and salinity damage in the delta post-Nargis. The purpose of this study, therefore, is to clarify the changes in vegetation in paddy fields in the Ayeyarwady Delta using Moderate Resolution Imaging Spectroradiometer data pre- and post-Nargis and determine whether this method can be applied to measure crop and salinity damage. The study used daily composite data at a 250-m resolution (MOD09GQ, collection 6) from 2004 to 2013 and calculated NDVI and salinity indices smoothed by locally weighted regression (Lowess). Based on the results of our studies, NDVI peak value in 2008 was lower by 19% compared to 2007 data, and that the NDVI peak values declined for three straight years since May 2008 when Nargis struck. However, salinity damage evaluation pre- and post-Nargis (using the salinity index equation) showed that soil electrical conductivity did not tend to move up in the post-Nargis dry season (2009), indicating that the decrease in NDVI values was not due to salinity damage.
In the last 40 years, the rice-cropping system has considerably changed in the Ayeyarwady Delta. The large archive of satellite imagery provides a history of how land and water resource managements have changed in the face of growing populations, resource demand, and climate change. This study aimed to assess the decadal changes in the rice-cropping system in the Ayeyarwady Delta by using the large archive of satellite imagery for the last 40 years (1981 − 2020). The long-term NDVI dataset provided various information on rice cultivation. Signal processing techniques were used to detect on the historical changes in the rice-cropping system, and the impact of climate change was assessed by using trend analysis. Until the 1980s, single-cropping of summer rice was dominant in the Delta. To enhance the grain yield of rice, the irrigation facilities were introduced in 1992 under an initiative of the Myanmar government. As a result, the annual cropping intensities increased from 1.087 ± 0.390 in the 1980s to 1.422 ± 0.499 in the 2010s. The information on historical change in the rice-cropping system would be useful to consider the practical and cost-effective utilization of remaining land and water resources. Moreover, the trend analysis of NDVI time-series showed negative trends in coastal areas. This indicates that the rice production in coastal areas has been constrained by the saline intrusion. The salt-affected areas are expected to expand under future climate change scenarios. Government support is highly required for sustainable rice production in the Delta.
Soil salinity is a major soil degradation problem that limits agricultural production. The cut‐soiler constructed preferential shallow subsurface drainage (PSSD) method is a promising salinity management technology for small‐scale application and adoption in drylands. This study assessed the effectiveness of rice residue‐filled PSSD in managing soil salinity and its effect on the physiology and yield of pearl millet. The cut‐soiler simulated drains were constructed manually in semi‐controlled lysimeter. A double replicated, split–spilt plot experiment, comprising with and without cut‐soiler drainage (main‐plot), two soil types (sub‐plot) and three irrigation water salinity (4, 8, 12 dS m−1) (sub‐sub plot) were conducted during 2019–2020. The cut‐soiler PSSD reduced ~60% soil salinity after 2 years. The PSSD reduced soil salinity by 23.28 and 41.46% in April 2019 and April 2020 (before pearl millet sowing). This reduction was 32.24 and 46.23% in October 2019 and 2020 (at harvest). Cut‐soiler drainage (PSSD) areas recorded lower soil moisture (%) indicated greater outflow of water and salinity. The salinity Inhibition efficiency increased upto 2 years of construction and then decline. The pearl millet grain and biological yields were improved by 23.54 and 12.64%, respectively and a positive effect on plant water relations and physiology was observed. The cut‐soiler PSSD was found to enhance salt removal and reduce salt accumulation under saline water irrigation. These drains can be constructed in a single farm operation at individual farm levels. Therefore, it could be a potential alternative for soil salinity management in semi arid regions irrigated with saline groundwater.
We examined the effect of poly-γ-glutamic acid flocculant (PGAF) on the removal of ultrafine cement (UFC) particles stabilized by a poly-carboxylate co-polymer, which is a superplasticizer (SP). The flocculation–sedimentation treatment with PGAF successfully removed the SP-stabilized cement particles through the gravitational settling of the formed flocs. The removal efficiency reduced with the increase in the ionic strength, probably because of the shrunk form of poly-γ-glutamic acid (γ-PGA) at high ionic strengths. Increasing the mixing intensity during rapid mixing improved the removal efficiency. A series of flocculation–sedimentation experiments provided a diagram showing the relationship between ionic strengths and the addition amount of PGAF. Our results suggest that PGAF is a good candidate for the purification of cement suspension by flocculation–sedimentation, and a better removal performance can be obtained at lower ionic strengths with intense rapid mixing. From the diagram of the control charts presented in this study, we can determine the optimal addition amount of PGAF for achieving the target removal rate for cement suspension under any ionic strength.
Summer rice cannot be grown near the coast of the Ayeyarwady Delta, Myanmar, because of the high salinity in river water during the dry season. This means that saline intrusion should be monitored to manage the irrigated rice-growing area. The aim of this study therefore is to develop a model to estimate the salinity of river water using satellite imagery. The imagery of Sentinel-2 was suitable for monitoring saline intrusion because of their high spatial (10-m) and temporal (10-day) resolutions. We found that the reflectance of the visible bands was correlated with electrical conductivity, which was influenced by the concentration and composition of dissolved salts. When the river water mixed with the salt water from the sea, suspended particles tended to flocculate and settle, as a result, less turbid water was more saline. The best-fitting model was obtained with the green band (coefficient of determination R2 of 0.776, root mean square error of 4.896 dSm−1, and mean absolute error of 3.340 dS m−1). The saline intrusion showed considerable spatial and temporal variability during the dry season. The salinity intrusion extended approximately 80 km inland at the end of the dry season in March in the Pathein River. The 1 ppt salt concentration line in March marked the boundary between cultivated and non-cultivated areas of paddy field, which indicates that cultivable areas were strongly affected by saline intrusion. The results show that more frequent and higher resolution monitoring than before of the Sentinel-2 can support effective water resource management.
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