Document
Metadata
Title
application des diatomees benthiques comme indicateur de la qualite biologique des rejets des eaux usees de toliara (madagascar) – recherche d’un indice diatomique
Authors
RASOAMANANTO Irène
Research Topic
Abstract
The study of the water physico-chemical parameter and benthic diatoms community in the sewer
networks were performed in 5 stations during 14 months from October 2009 to November 2010.
The sampling data were conducted monthly. Among these 5 stations, there is one station which is
located around thirty kilometers from the Toliara is considered as a control Belaza station or (BLZ).
For the pilot constructed wetland of wastewater treatment from the public toilette, the
physicochemical parameters and the community of benthic diatoms were monitored at 3 times a
week for 6-weeks. There is no monthly variation of physico-chemical parameters such as dissolved
oxygen, pH, salinity, conductivity, rates of total suspended solids and nutrients. But, they change
between stations from one station to another and from one time to another. It is noted that the
monthly change was observed with the temperature. In support of the national standards value and
guidelines in the drainage systems of domestic wastewater and urban, dissolved oxygen, pH,
volatile suspended solid was used to indicate the degree of organic pollution from the wastewater
on the one hand and pollution by nutrients such as phosphate and nitrite on the other. This pollution
from the phosphate and nitrite was not detected throughout the year. The phosphate pollution was
observed especially during the hot and rainy season and for the nitrite its pollution was detected for
the dry season Environmental factors in the sewer networks present variations while those at the
control site in Belaza are slightly unstable during the study period. When the design constructed
wetland, the rates of nutrients, organic matter content decreased by an average almost more than
50% against the increase of dissolved oxygen and pH gradually tends towards alkaline. In the total,
131 species of benthic diatoms were identified. It is noted that, species of centric diatoms were
rarely detected in the drainage wastewater stations. While Pennatea diatoms belonging to the family
of Naviculaceae and Nitzschiaceae are abundant both in terms of quality and quantity in all study
sites. The Shannon diversity index and evenness indicated heterogeneity in taxonomic richness of
benthic diatoms. The environmental factors complexity in the area study explain the important
difference in development and spatio-temporal fluctuations of species or taxa of benthic diatom
study where there is the mixture of three types of water such as: the sea water, the underground
water and domestic wastewater. This density was resulted by outbreaks of certain species belonging
to the genus Nitzschia, with the contribution of species Nitzscha sp10, Nitzschia cf palea, Nitzscha
sp4 and small unidentified diatom. For the genus Navicula, the species are Navicula sp1, Navicula
sp4 and the species Thalassiosira sp1 which is belong to the order of Centraceae. According to their
dominance and their distribution within the five study sites, these results allow concluding that four
species including two species Navicula sp1, Amphora sp1 were present in the sewer networks and
the control station throughout the study period. They have more than 1% of dominance and two
other species namely Nitszchia cf palea and Gomphonema parvulum are presented during the study
period and their dominance was more than 1% at the stations in the sewer networks. Among these
four species, three of these namely Navicula sp1, Nitszchia cf palea, Gomphonema parvulum are
encluded in the five species observed in pond of the constructed wetland with high cell densities
especially at the exit of the basin. These four species with their particularity supporting organic
pollution and the role as filter are interest to open up a new research in the laboratory about
microcosm biochemical study and in large geographic area for the universal indicator of organic
pollution in brackish as it was in the running freshwater or lake.
Volume
1
Date of publication
October 5, 2012
Institution (University)
Institut Halieutique et des Sciences Marines
Page numbers (pp)
224