Nepal Journal of Environmental Science

Ecotoxic response of Rhizobium sp. to the commonly used pesticides (paraquat and dichlorvos)

Anwuli U. Osadebe, Chukwudi Amadi — Thu, 21 Dec 2023 00:00:00 +0000

This study investigated the 96-hour ecotoxicity response of Rhizobium sp. to paraquat and dichlorvos at application concentrations ranging from 0.01 mg/L to 100 mg/L. The test organism was isolated and enumerated using yeast extract mannitol agar. Paraquat proved to be more toxic than dichlorvos based on the toxicity parameters established using probit regression analysis. Rhizobium sp. showed no growth (100% mortality) at the higher concentrations of 10 mg/L and 100 mg/L for paraquat; for dichlorvos, this absence of growth was only seen at the highest application concentration of 100 mg/L. Overall, Rhizobium sp. tolerated the insecticide, dichlorvos, better than the herbicide, paraquat. At the lowest concentration of 0.01 mg/L, it displayed moderate tolerance indices of between 0.534 and 0.589 for both pesticides. At 0.1 mg/L and 1.0 mg/L pesticide concentrations, the 96-hour tolerance indices obtained were less than 0.39, indicative of very low tolerance. Neither pesticide was tolerated at 10 mg/L and 100 mg/L. Statistical comparisons of the tolerance indices between the two pesticides and from one pesticide concentration to the other showed significant differences both within and the between groups (p≤0.05). The median lethal concentrations (LC₅₀) were 0.0158 mg/L and 0.0350 mg/L for paraquat and dichlorvos, respectively. The lowest observed effect concentration (LOEC) and no observed effect concentration (NOEC) were 0.0011 and 0.0027, respectively for paraquat and 0.0017 and 0.0047, respectively for dichlorvos. The results indicated that pesticides have adverse acute effects on key microbial ecosystem service providers like Rhizobium sp. and should, thus, be used with restraint.

River channel dynamics and flooding: A case of motorable bridge collapse due to abrupt flood in Chhabdi Khola, Tanahun, Nepal

Madhav Adhikari, Bharat Bhandari — Thu, 21 Dec 2023 00:00:00 +0000

The monsoon season in Nepal brings calamitous events like riverbank erosion, toe cutting, and the structural failure of bridges due to floods. In July 2021, a motorable bridge in Bhadgaun, Tanahun district, Nepal, collapsed during a massive flood in Chhabdi Khola. The study aims to comprehensively document the aftermath, specifically focusing on the causal factors that led to the damage of the Chhabdi Khola Dovan Bridge. The study delves into an in-depth analysis of the stream's channel morphology, with the 5.85 kilometers Chhabdi Khola partitioned into 28 distinct segments, each spanning approximately 200 meters. These segments, sequentially labeled from Site 1 to Site 28, encompass the area extending from the upstream at Chhabdi Barah temple to the downstream at bridge’s location. Rigorous measurements of length, breadth, and depth at each site form the basis for volumetric assessments of the stream. The study revolves around contrasting paleo channel attributes with contemporary alterations within the Chhabdi Khola catchment. The analysis leverages precipitation data sourced from the Department of Hydrology and Meteorology (DHM) to discern precipitation trends within the Chhabdi Khola catchment area. The hydrographic data underwent trend analysis utilizing Mann-Kendall and Sen's slope method through R software (version 4.3.2). The collapse of the Chhabdi Khola Dovan Bridge resulted from intense water flow and debris due to heavy rainfall and a narrow outlet near the bridge, impacting the local population and land users facing the enduring aftermath of a catastrophic monsoon event. The study highlights the significance of understanding river dynamics in small streams and advocates for proactive disaster preparedness measures, even in seemingly small river channels.

Habitat status of the Smooth-coated Otter (Lutrogale perspicillata) in Geruwa-Khaurahi River, Bardia National Park, Nepal

Sarjan Gwachha, Madan Koirala, Purna Man Shrestha — Sat, 30 Dec 2023 00:00:00 +0000

Smooth-coated Otter (SCO), a top predator and health indicator of the aquatic ecosystem is included as vulnerable on the IUCN red list and listed in Appendix I. Geruwa-Khaurahi River (GKR) was observed to determine the habitat status of SCO between Bardiya National Park (BNP) and Khata Corridor (KC), and to evaluate factors affecting the SCO habitat, data on habitat parameters and SCO signs were collected in each transect of 500 m. Principal component analysis was used for the most probable habitat parameter selection. An SCO group of eight was observed at Lalmati on the broad, shallow, and fast-flowing GKR with a sandy island and a flat stone bank with a vast escape distance. All signs were found on the sandy shoreline of the riverine forest with nearby tall Saccharum coverage over a narrow escape cover with a gentle bank slope. Diversions of water from the Geruwa River to the narrow and shallow Khaurahi River resulted in fast-flowing water where SCO pugmarks were found abundant. But at KC, human disturbances, over-fishing, river mining, and infrastructures have made the river unsuitable for SCO. SCO preferred dense riverine forests where the gentle riverbank has sand and/or tall Saccharum in between a narrow escape distance. Also, the narrow river with shallow depth and slow flow of good water quality was preferred by SCO. Lastly, with minimal human disturbance, further study on feeding ecology and population dynamics is requisite to conserve the suitable habitat of the SCO.

Landslide susceptibility mapping of the Main Boundary Thrust region in Mandre - Khursanibari section of Arghakhanchi and Palpa Districts, Lumbini Province, Nepal

Kabi Raj Paudyal, Rupendra Maharjan — Sun, 31 Dec 2023 00:00:00 +0000

The Mandre-Khursanibari section of Arghakhanchi and Palpa districts consists of numerous landslides, small to large. Prospecting weak geological sections like the location of the Main Boundary Thrust (MBT) and inherently weak lithological settings in addition to other factors are the main objectives of the present research. In this study, the results of the landslide susceptibility analysis using frequency ratios (FR) are assessed. The Mandre-Khursanibari segment was subjected to landslide detection using imagery (Google Earth) with a spatial resolution of 50 cm. The landslide inventory was used to construct training and testing data. Based on topographic, geological, and land-use maps, nine contributing variables were identified. The FR ratings were established using the contributing elements and training data. The map illustrating landslide risk was produced by integrating the influencing components that determined FR ratings. The ROC-AUC curve shows a validation rate of 82.2 % in the present model of LSI. The three most important elements in the occurrence of the landslide, out of the nine potential causes, are distance from the thrust (MBT), land use, and distance from the road. However, the role of adverse lithological setting is found to be a minor in many sections of this region. The MBT is one of the main causes of landslides in this area.

Immobilized enzymes for nutraceuticals production

Aprna Baban Gunjal — Sun, 31 Dec 2023 00:00:00 +0000

Due to the various advancements in enzyme development, enzymes have different applications in industries, agriculture, and medical field as well as to make various compounds or molecules. Immobilization refers to the combining the physico-chemical properties of enzyme with the carrier which will enhance the stability of any biocatalyst. The market of nutraceutical products is gaining wide importance. With this view, the present chapter here will focus on various immobilized enzymes with recent advances, and application of immobilized enzymes in production of various nutraceutical compounds. The nutraceutical compounds improve the flavour, structure and digestion of different food products. The immobilized enzymes can be capsulated which can be used effectively for nutraceuticals production. The use of immobilized enzymes for nutraceutical compounds is very eco-friendly, easy with sustainable approach.