Conde, D., Bonilla, S., Aubriot, L., de León, R., & W. Pintos. 1998
Abstract
The
relative chlorophyll a content of Tthree microalgal communities wasere
studied between August 1996 and September 1997 in a brackish lagoon, Laguna
de Rocha (Uruguay), located on the south-eastern coast of South America.
The system is shallow and periodically connected to the Atlantic Ocean
and the anthropogenic influence is scarce. The freshwater and marine water
inflows cause an extreme hhorizontal gradient in water level (range = 0.25
to 1.2 m), conductivity (range = 0.2 to 48.9 mS cm-1), nutrient concentration
and sediment characteristics (sandy to muddy). At the northern station,
dominated by freshwater, and at the southern one, dominated by the marine
influence, the chlorophyll a concentration amount of phytoplankton, microphytobenthos
and epiphyton was measured on a monthly basis. Relating to lake surface,
Cchlorophyll a ranged from 0.7 to 9.0 mg m-2 for phytoplankton, from 2.7
to 162.7 mg m-2 for microphytobenthos. and The epiphyton reached chlorophyll
amounts from 2.7 to 536.0 mg m-2 for epiphyton relating to the surface
of the colonized macrophytes. The contribution of the epiphyton to the
total algal biomass of the system was negligible however, since the development
of the macrophyte substrate was scarce during the whole study period. Phytoplankton
biomass was similar at both stations whereas, however, microphytobenthos
biomass was significantly higher (p<0.05) at the freshwater station
North, probably due to better nutrient availability. Considering the relative
microalgal biomass estimated through the chlorophyll a content of the three
communities, the system was dominated by the epipelon in freshwater area
and by epipsammon in the marine one. The benthic dominance classifies the
system in theas a “dry state” (sensu Goldsborough & Robinson), favoured
by the extreme shallowness, the high nutrient content and light availability
at the bottom.
