PHYTOPLANKTON AND WATER QUALITY CHARACTERIZATION: SEASONAL AND MEDIUM TERM MONITORING IN NORTHERN TUNISIA

Mohamed Salah Romdhane, Amel Ben Rejeb Jenhani, University of Carthage Tunisia

Abstract

Monitoring of 5 years of monthly biological water quality data was performed throw 35 sampling sites covering 4 lakes (reservoirs) and 5 fresh water networks (river and channels) in northern Tunisia.
The aim of this study was the possible use of phytoplankton as a monitoring variable to detect water-quality changes and to outline an assessment criterion.During the period 2007-2011, the results showed that the species richness, composition and cell densities of algae were changed considerably throughout sites, seasons’ and years. A maximum of 47 taxa of algae were observed, belong to 6 phyla. Chlorophycae, Cyanobacteria, Diatoms, Dinophycae, Chrysophycae and Euglenophycae, The percentage of Chlorophycae diatoms, and Cyanobacteria was 40.4%, 29.8% and 19.2% to the algae flora, respectively. The other 3 phyla were only representing 10.6%.
The cell densities of algae fluctuate from 0.011x106 ind/l to 0.53x106 ind/l in the most productive lake; the values were decreased to less than 0.005×106 ind./l throw major distribution network.
The species richness was decreased, from lakes to channels and distribution networks, but that of some Cyanobacteria was increased.
The chlorophyll A concentrations were particularly dynamic and spatially heterogeneous varying from 0 to 15µg/l. Chlorophyll a biomass seems to be good indicator of the algae concentration across network sites (rivers and channels); but It is no match  significant in the largest water plan (lakes and reservoirs).
The data base which have been compiled during this monitoring will be tested by models to expect phytoplankton species assemblages and seasonal biomasses concentrations under a set of environmental conditions such models make phytoplankton suitable as an early warning indicator

Keywords:  water networks, water quality, monitoring, phytoplankton