Eleocharis mutata (L.) Roem. et Schult. subject to drawdowns in a tropicalcoastal lagoon, State of Rio de Janeiro, Brazil

This investigation of the aquatic macrophyte Eleocharis mutata (L.) Roem. E t Schult. was carried out in Imboassica lagoon, a coastal lagoon in Macae ( 22 degrees 50'S; 44 degrees 42'W), in the northern part of Rio de Janeiro, Brazil. The sandbar separating this lagoon from the ocean has been opened s everal times for flood control and to allow the entrance of marine species of commercial interest. The barrier bar has been breached without appropria te planning, and the consequences of breaching for the lagoon ecosystem are poorly understood. These openings drastically affect the structure and fun ctioning of the lagoon, but there are no data on possible effects on macrop hyte communities. In this project, we obtained data on the increase of the distribution, biomass accumulation and production rates of E. mutata in the establishment of a new stand, in an effort to relate effects of sandbar br each events to the expansion of this species. During 22 months of sampling, 4 breachings of the sandbar occurred, and E. mutata increased its area of coverage by about 8.10(4) m(2), or 2.5% of the total area of the lagoon. Th e total aerial biomass reached a maximum of 1515 g DW m(-2), and the underg round biomass reached 583 g DW m(-2). During the establishment and developm ent of the stand, both dead and live aerial biomass and underground biomass tended to accumulate. Aerial net primary production (ANPP) was quite varia ble, reaching a maximum of 18.9 g DW m(-2) d(-1). We conclude that the sudd en variations in water level caused by breaches in the sandbar were benefic ial to the expansion of this species in Imboassica lagoon.