AbstractEutrophication is a serious phenomenon in shallow lakes in Hanoi. The most important effect is the change of dissolved oxygen (DO) in the water column. The value of DO in water changed over time, and the variation of DO proved to be more important than the absolute value. The research aimed to assess the role of daily DO variation in classifying the eutrophication status of shallow lakes in Hanoi. Data were collected in eight shallow eutrophicated lakes in Hanoi during 2015–2017 in relation to water quality parameters. A large variation of DO was observed with the maximum value achieved at 15–17 h (180% saturation DO) and the minimum value at 4–6 h (20% saturation DO). The lowest DO value reached 1.5 mg/L, which was much lower than the threshold of survival of some aquatic animals. The daily DO fluctuations correlated with phytoplankton density, the Trophic State Index (TSI), chlorophyll-a concentration and density, and the proportion of DIN:PO4, showing the close relationship between DO variation and eutrophication in the lakes. The decision trees were developed and also selected the ΔDO as the driving variable in classifying the eutrophication status in lakes. The daily DO variation could be an important indicator for eutrophication.
To investigate eutrophication in 31 freshwater lakes in Hanoi, Vietnam, water quality and Chlorophyll‐a content were monitored to calculate trophic indices. Twelve of the 15 urban lakes investigated were eutrophic, of which five were hypertrophic, while only seven of the 16 suburban lakes were eutrophic. The Trophic Index (TRIX) was the best predictive index to identify the eutrophication level of the lakes. Classification trees (CTs) were applied to study the trophic status of lakes and identify the driving variables. The results demonstrated that eutrophication in the lakes of Hanoi was driven by nutrients and organic enrichment, as well as by inappropriate management such as unplanned embankment and water uses. DIN, BOD, lake size and embankment were the key parameters controlling eutrophication in the lakes of Hanoi.
Climate is an important resource of tourism industry; climate indicators can be measured and assessed. The determination of the right time for tourism activities contributes to the orientation of making investment plans for managers and advising vacation time for visitors. To determine the right time, the authors used 7 climate parameters: total precipitation, monthly average temperature, relative humidity, average maximum temperature, average temperature of dark temperature minimum, average of relative humidity, daily average of sunshine hours and wind speed to calculate TCI model in Moc Chau. The TCI calculation results based on 10-year climate data (2008-2018) show that this is a place with favorable conditions for year-round tourism, from October to April next year.
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