M. Goni-urriza et al., Impact of an urban effluent on the bacterial community structure in the Arga River (Spain), with special reference to culturable Gram-negative rods, CAN J MICRO, 45(10), 1999, pp. 826-832
The Arga River is an interesting system in which to study the impact of urb
an effluent pollution because it receives a single effluent in the form of
wastewater discharge from the city of Pamplona. To analyze the extent of th
is discharge, total bacteria, culturable heterotrophic bacteria, and Gram-n
egative heterotrophic bacteria were enumerated and 409 isolates of the latt
er were identified. One sampling station was located upstream from the infl
ow, while five were located up to 30 km downstream. Bacterial counts increa
sed drastically downstream from the wastewater inflow. Total bacterial numb
ers decreased along the 30 km downstream, the last station attaining simila
r values to those recorded upstream from the discharge. However culturable
heterotrophic and Gram-negative heterotrophic bacteria levels generally rem
ained significantly higher within the 30 km zone investigated. Among the 40
9 isolates identified, Aeromonas spp, were the most frequent both upstream
and downstream from the discharge. In contrast, although strains belonging
to different genera of Enterobacteriaceae were found in all stations, their
occurrence was significantly higher just downstream from the polluted disc
harge. Acinetobacter spp., which were never found upstream, were detected i
n all stations below the discharge. Our results clearly show that the bacte
rial community structure changes definitively downstream from the discharge
and that Aeromonas were common throughout the sampling zone. Thus they can
not be considered good indicators of pollution in this setting compared to
some genera of Enterobacteriaceae or some species of Acinetobacter: the dis
tribution of which correlated better with the distance from the wastewater
discharge.