Nghiên cứu sự biến động sinh khối phiêu sinh thực vật và hàm lượng ôxy hòa tan để quản lý đàn cá trên kênh Nhiêu Lộc - Thị Nghè, Thành phố Hồ Chí Minh

Abstract

The study was conducted during one-year cycle, with six sampling periods in January, March, July, September and November 2015 to identify the phytoplankton and dissolved oxyen (DO) fluctuations at the Nhieu Loc - Thi Nghe (NL-TN) canal in spatial, temporal and tidal scales, thereby proposing solutions to manage the fish stock in the canal. The NL-TN canal is devided into three sections including downstream, midstream and upstream, with nine sampling stations. The collected samples represented the highest and lowest tide periods of the month. The results showed that the phytoplankton biomass reached highest value in upstream (5,2-6,1 gDW/m3) and lowest in downstream (4,4-4,9 gDW/m3); however, there is no correlation between high biomass phytoplankton and low DO in early morning in spatial scale. In terms of temporal aspect, phytoplankton biomass reached the highest in July (6.9 gDW/m3) and the lowest in September (3.5 gDW/m3); however, there is no correlation between phytoplankton and DO biomass over time. Therefore, the monitoring of phytoplankton biomass with the frequency of 2 months/time is not effective in predicting correlative fluctuations of phytoplankton indicator with DO deficiency for fish stock management. Considering tidal fluctuations, high and low tide levels had significant influence on the annual average phytoplankton biomass difference. Considering the DO aspect, DO shows the lowest level in the early morning of May at the low tide period, which coincides with the high mortality of fish stock in the canal at the beginning of the rainy season, posing a requirement for DO monitoring and management at the risky times with DO deficiency for fish stock management.