Life Cycle Assessment (LCA) is an analytical tool used primarily for evaluating environmental conditions. The sources of decomposed organic matters in Cirata Reservoir originate from industrial activities, household waste, agricultural waste, and effluent from floating fish net cages. The wastes consist mainly of fat, protein, and carbohydrate. Bacteria are responsible for aerobic decomposition process of organic matters in the sediment. As bacteria consume oxygen during the decomposition processes, significant depletion of dissolved oxygen level in the waters may occur. This happens in Cirata Reservoir where a low level of oxygen in the water leads to anaerobic decomposition processes at the bottom of the reservoir. The porpuse of this study was to evaluate Cirata Reservoir water conditions, in terms of water quality, organic sediment and organic materials level based on the application of LCA. In this study, water and sediment samples were collected. Water quality conditions were measured in-situ. Water and sediment samples were analyzed in the laboratories. The results of the analyses showed that water quality condition in all sampling stations was relatively homogeneous. Based on the level of decomposition of organic matter, water quality conditions in Cirata reservoir could be classified as Class I, II, and III in IKA_STORET scale and categorized as poor. DO, sulfide, phenol, BOD, COD, total phosphate were outside the ranges of acceptable water quality standards.
In the inner part of Ariake Bay, Japan, hypoxia frequently occurs in summer at the organically enriched bottom with salinity stratification caused by flooding after the rainy season. Sediment organic enrichment can work as a stressor for macrobenthos. To investigate the effects of both hypoxia and sediment organic enrichment on macrobenthos, samples were collected at 20 stations by grab sampling in May and August, representing the situation before and after hypoxia, respectively. Although sediment grain size did not change, sediment TOC increased significantly in August. Multivariate analyses showed that the community structure changed significantly in August. The variation in the community structure among stations also increased, which indicated disturbance by stressors during the study period. Similarly, the species richness and total abundance of macrobenthos decreased significantly after hypoxia even after the TOC effect was removed. In addition, the amount of TOC change and the abundance of the main species did not correlate in any case. These results suggest that the community changes during the study period are not caused by stress from the increased sediment TOC but are mainly from the subsequent hypoxic stress.
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