Conclusions
As discussed above, the present investigation reveals that:
-
(1)
Almost a steady state of dissolved oxygen (6.0 to 6.2 mg/l) was found at Digha water. The highest dissolved oxygen was recorded at Diamond Harbour with the gradual lowering of values at all points from the mouth to the head of the estuary.
-
(2)
Average pH at Digha was 8.4, whereas at other centres it was about 8.1. The bicarbonate alkalinity (reserved) of the estuarine water give a good buffering action.
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(3)
The chlorinity conflict at Fuleshwar was maximum and it was minimum at Calcutta. Diamond Harbour occupies an intermediate position in so far as chlorinity conflict is concerned. Digha typified a marine condition.
-
(4)
Average air temperature was higher at all stations than the average water temperature. Sudden variations in temperatures were few, an exception in one case was observed when temperature dropped suddenly by 2.5°C at midnight. The overall condition of the estuary during a 24-hour period did not exhibit any adverse condition owing to factors causative to diurnal variations. The public health hazards from the chemical and bacteriological point of view have not been accounted in this study, as such there is a great need to undertake a detailed study on this aspect.
Résumé
Dans le présent travail, les variations diurnes dans quelques tronçons choisis de l'estuaire du fleuve Hooghly aux Indes sont décrites.
Si. l'effectif en poissons a, depuis quelques années, sérieusement diminué dans l'estuaire du flueve Hooghly, c'est certainement en partie à cause de la pollution due aux décharges d'eaux usées brutes ou insuffisamment traitées. Mais il y a aussi d'autres raisons dont les principales sont d'une part la réduction des apports d'eau fraîche et d'autre part l'intrusion progressive de la zone marine. L'étude des eaux de l'estuaire a révélé ce qui suit:
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1)
Teneur presque constante en oxygéne dissous à Digha Water (6,0 à 6,2 mg/l). Teneur maximum à Diamond Harbour, puis diminution graduelle des valuers à tous les points de mesure de la bouche à la tête de l'estuaire.
-
2)
A Digha, la valeur pH moyenne était de 8,4, alors qu'elle atteignait environ 8,1 aux autres points de mesure. L'alcalinité bicarbonatée (réservée) de l'eau de l'estuaire procure on bon effettampon.
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3)
Les divergences entre les teneurs en chlore étaient à leur maximum à Fuleshwar et à leur minimum à Calcutta. A ce point de vue, Diamond Harbour occupe une position intermédiaire. A Digha, les conditions marines sont en prépondérance.
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4)
A toutes les stations, la température moyenne de l'air était plus élevée que celle de l'eau. Il y eut peu de variations subites, sauf en un cas où la température diminua très rapidement de 2,5 °C à minuit. L'ensemble des conditions régnant dans l'estuaire au cours d'une période de 24 heures n'a subi aucune influence défavorable de la part de facteurs responsables des variations diurnes. Il n'a pas été tenu compte dans cette étude d'éventuels risques pour la santé publique pouvant être causés des facteurs chimiques et bactériologiques. Il y aurait lieu d'entreprendre une étude spéciale de cet aspect du problème.
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Basu, A.K., Ghosh, B.B. Observations on diurnal variations in some selected stretch of the hooghly estuary (India). Schweiz. Z. Hydrologie 32, 271–283 (1970). https://doi.org/10.1007/BF02502407
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DOI: https://doi.org/10.1007/BF02502407