Nymphoides indica (L.) O. Kuntze (Menyanthaceae) em um pequeno lago raso subtropical (Rio Grande, RS)

Shallow freshwater ecosystems are typical in the Rio Grande do Sul coastal plain, and the aquatic macrophyte Nymphoides indica is found in lakes and wetland shore zones. This study was carried out at a small lake in Rio Grande (RS). Biomass variation and primary productivity estimatives (Smalley method) were done from monthly samplings between October 2000 and September 2001. The abiotic variables of the water column (temperature, electric conductivity, dissolved oxygen and pH) were measured. In the laboratory, total nitrogen, phosphorous, and carbon of plant biomass and at water column were determined. The maximum biomass was recorded in November (220.8 g DW m-2). The greatest primary productivity was measured in October (5.9 gDW m-2 d-1). Results indicated that N. indica has a seasonal growth, with highest biomass and primary productivity in spring months, when these plants accumulate great amounts of nutrients.