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Published By "Publishing House For Science And Technology Vietnam, Vietnam Academy Of Science And Technology"

1859-3097, 1859-3097

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
Trong Dai Vu ◽  
Thi Khanh Pham ◽  
Nhu Thuy Mai ◽  
Son Lam Ho

Mangrove snail (Nerita balteata) belongs to gastropoda species distributed in the coastal intertidal and offshore islands of Quang Ninh province. Although the artificial seeds production of this species have been successful but still having a bottle neck as a low survival rate in the process by veliger larvae are transformed into spat larvae stage. Experiments were conducted to determine effects of salinity and food on growth rate and survival rate of mangrove snail in the stage of spat larvae in Quang Ninh province. The results showed that the optimal salinity for growth and developtment of spat larvae was 25‰ that resulted in a absoluted growth rate of 16.5 ± 2.19 µm/day and survival rate of 26.5 ± 0.57% and significantly higher compared to other treatments. The diet of benthic microalgae (Navicula sp.) combined with formulated feed (AP0 and Frippak) were most suitable for the growth and development of mangrove snail at the spat larvae stage with absoluted growth rate of 25,7 ± 1,28 µm/day; Whereas the survival rate of larvae of 32,3 ± 2,52% was significantly higher than those in the other treatments.


2021 ◽  
Vol 21 (3) ◽  
pp. 233-245
Author(s):  
Van Tac Vu

Based on the monthly averaged sea surface chlorophyll-a concentration data continuously for more than 17 years (Jul. 2002–Dec. 2019), the analyzed results show that the averaged chlorophyll-a concentration in Khanh Hoa waters was 0.58 mg/m3, and the monthly average variation was ± 0.14 mg/m3 (that is equivalent to about ± 24%). Under the impact of ENSO phenomena, in the years when the double La Niña events occurred (two consecutive years in the La Nina event occurs), the chlorophyll-a anomaly index fluctuated from -0.99 mg/m3 to 1.62 mg/m3. These are very strong fluctuation levels, corresponding to the decrease or increase in chlorophyll-a concentration from 86% to 279%. In the El Niño years, the fluctuations of chlorophyll-a concentration were little affected unless the two previous years in which the double La Niña event occurred. These fluctuations have significantly impact nutritional resources and water quality because chlorophyll-a concentration is one of the key indices in studying the health status of any natural marine ecosystem. In addition, chlorophyll-a concentration in Khanh Hoa waters often varies between seasons. The averaged chlorophyll-a concentration reaches its maximum value in the winter, then decreases gradually in the spring and usually reaches the minimum value in the summer, then rises gradually again in the autumn.


2021 ◽  
Vol 21 (3) ◽  
pp. 311-318
Author(s):  
Thu Hue Pham ◽  
Van Tuyen Anh Nguyen Nguyen ◽  
Yen Kieu Thi Hoang ◽  
Nguyen Nguyen ◽  
Hai Nam Hoang ◽  
...  

This study studied the content and composition of the total lipid, lipid classes and fatty acids in 13 brown seaweed Sargassum species collected from Con Dao and Van Phong, Vietnam. The total lipid has a low content and varies among species from 0.10–1.70% of the fresh weight. From 13 species, seven lipid classes including polar lipid (Pol), free fatty acids (FFA), sterol (ST), hydrocarbon and wax (HW), triacylglycerol (TG), diacylglycerol (DG), and monoalkydiacylglycerol (MADG). Using the GC-FID technique, we have identified 29 fatty acids classified into 3 groups of saturated fatty acid, monounsaturated fatty acids, polyunsaturated fatty acids with an average content of 44.93%, 24.57% and 27.44%, respectively. Among those, many value fatty acids have been detected with high content such as C18:3n-3, C20:4n-6, 20:5n-3, and 22:6n-3. The lipid of 13 brown seaweed Sargassum species also fully contains omega-3,6,9 fatty acids with the content of 9.28%, 16.28% and 16.63%, respectively.


2021 ◽  
Vol 21 (3) ◽  
pp. 341-352
Author(s):  
Doan Thai Vu ◽  
Van Nam Thai

Mangrove plants play a viral role in protecting the coast, retraining erosion. Especially in areas considered the variable wave conditions, complex dynamic conditions such as the coastal region of Hai Phong city. However, due to various reasons, the development/additional planting of mangrove forests in the coastal area of Hai Phong in some locations has not achieved the desired result. This study was conducted survey measurements of mangroves, terrain, and practical experience to assess the ecological impact of certain dynamic and sedimentary conditions on mangroves. Thereby proposing several solutions to build sea dykes/embankments suitable to Hai Phong conditions, strengthen sediment traps, and create favorable conditions for developing mangrove trees in this area.


2021 ◽  
Vol 21 (3) ◽  
pp. 361-374
Author(s):  
Tra Mai Ngo ◽  
Thi Thanh Hang Phan

This research simulates and forecasts the area as well as the level of pollution dispersion of Muc Son Paper Factory’s wastewater to the downstream of Chu River under two scenarios: Scenario 1 - wastewater treatment system is broken; treatment efficiency is equal to 0; Scenario 2 - wastewater treatment system is working with its designed capacity. The applied results of the MIKE 11 model show that: the impacted area from the plant’s discharge is 0.2 km upstream and 2 km downstream of the confluence point. The simulation results under Scenario 1 show TSS, BOD5 and COD contents being 18.3–35.7 mg/L, 8.3–17.2 mg/L and 12.2–23.7 mg/L, respectively, negatively affect the water environment downstream of Chu river. The results are then compared with measured data to confirm the reliability of the model. This research is a scientific and practical basis for the Muc Son Paper factory to operate the wastewater treatment system and manage the water quality output to ensure environmental regulations.


2021 ◽  
Vol 21 (3) ◽  
pp. 319-327
Author(s):  
Nhu Da Le ◽  
Thi Thu Ha Hoang ◽  
Thi Mai Huong Pham ◽  
Thi Thuy Duong ◽  
Truong Dong Nguyen ◽  
...  

Aquaculture in the coastal zone has contributed significantly to economic development in Giao Thuy district, Nam Dinh province. Therefore, water quality for aquaculture plays a vital role in sustainable aquaculture production. In this paper, iron (Fe) and manganese (Mn) concentrations in aquaculture coastal water of Giao Thuy district were analyzed during the rainy season (September 2017, August 2018) and dry season at low tide. The results showed that Fe concentration varied from 0.09 mg/L (at VT5) to 2.42 mg/L (at VT4), averaging 1.12 ± 0.71 mg/L, which exceeded the critical value of the national technical regulation on marine water quality in Vietnam for coastal aquaculture water (QCVN 10:2015/BTNMT) from 1.5 times (at VT4) to 3.0 times (at VT1). Mn concentrations ranged from 0.02 mg/L (at VT9) to 0.10 mg/L (at VT1), averaging 0.05 ± 0.02 mg/L, which was lower than the critical value in the QCVN 10:2015/BTNMT. The results showed that no apparent seasonal variation was observed for both Fe and Mn concentrations. In the dry season, the Fe and Mn concentrations averaged 1.10 mg/L and 0.05 mg/L respectively, whereas they were 1.15 mg/L and 0.05 mg/L in the rainy season. The monitoring results showed that Fe was polluted in the study area and may affect aquaculture productivity. Therefore, helpful measures should be taken to minimize Fe pollution to protect water quality and develop sustainable aquaculture in Giao Thuy district, Nam Dinh province.


2021 ◽  
Vol 21 (3) ◽  
pp. 353-360
Author(s):  
Duong Nguyen Thi Bach ◽  
Dan Nguyen Anh

Now, the field experiments according to the non-destructive test method are developing widely in diagnostics and verification of structural engineering. To research and apply the impact vibration test, one of these non-destructive methods, the construction of the design dynamic analysis model is significant. The paper goes into research on the formulas to determine the dynamic spring coefficients according to Japanese and Vietnamese standards. Then, apply calculations for dynamic analysis models of pile foundations built in the Binh Thuan sea area. The impact vibration test in the field shows the appropriate formula for calculating the coefficient of dynamic springs in Binh Thuan, Vietnam.


2021 ◽  
Vol 21 (3) ◽  
pp. 271-282
Author(s):  
Minh Hai Nguyen ◽  
Sylvain Ouillon ◽  
Duy Vinh Vu

We analyzed the seasonal variation of suspended sediment and its relationship with Turbidity in Cam - Nam Trieu estuary based on data measured during three different seasons: Early wet season (May 2015), wet season (September 2015) and dry season (January 2016). The results highlighted the seasonal variation of suspended particle matter (SPM) concentrations with river flow. The average SPM concentration was highest during the dry season, with 62.95 mg/L. They were not significantly different between the early wet and wet seasons, with 59.65 mg/L and 50.94 mg/L, respectively. This study also demonstrated a strong dependence between SPM and Turbidity in the study area. The coefficients of determination varied from 0.867 to 0.971 (linear relationship), and from 0.95 to 0.991 (proportional relationship). Therefore, turbidity can be used to estimate SPM concentration. However, this relationship changed markedly with the seasons, and hence when determining SPM concentration, seasonal factors must be considered.


2021 ◽  
Vol 21 (3) ◽  
pp. 247-257
Author(s):  
Ngoc The Nguyen ◽  
Thanh Tung Tran ◽  
Trung Viet Nguyen

Over the past years, there have been several studies on the hydrodynamic regime, beach erosion, and accretion at the Cua Dai beach in Hoi An city. However, there is still a lack of in-depth research on the effects of hydrodynamic factors on beach evolution in extreme weather conditions such as a storm event or during the Northeast monsoons, characterized by large waves mainly, especially. The wave set-up directly impacts on the evolution of upper beaches and coastal dunes, consequently causing beach erosion. This paper presents the results of nearshore wave propagation and transformation and the distribution of wave set-up during storms in the coastal area of Cua Dai, Hoi An, using the SWAN model and the XBEACH model. The models have been calibrated and validated using measured wave and water level data observed in the study area in October 2016. The simulation results have shown the overall picture of the influence of wave set-up on the morphology evolution of beach profiles in the study area.


2021 ◽  
Vol 21 (3) ◽  
pp. 259-270
Author(s):  
Vu Duy Vinh ◽  
Sylvain Ouillon ◽  
Minh Hai Nguyen

Median diameters (D50) of suspended particles were inferred in the wet season in the Cam - Nam Trieu estuary (Hai Phong, Vietnam) based on the particle size distribution measured by LISST-100X on five transects along the river from 23 to 26 September 2015. The results showed that floc diameters varied between 3.6 μm to 146.5 μm and averaged 49.14 μm. At high tide, the average floc size D50 was lowest (42.66 ± 11.55 µm). It reached the highest value in the ebb tide (62.87 ± 23.34 µm) and then decreased to intermediate values in the flood tide (48.75 ± 15.72 µm). The coefficient of variation of the mean floc size D50 was lowest in the high tide (27.05%), highest in ebb tide (37.13%), then intermediate in the flood tide (32.12%).


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