Biomassa e composição elementar (C, N e P) da comunidade perifítica em diferentes gradientes fluviais tropical (alto rio Santa Maria da Vitória, Espírito Santo, Brasil)

Abstract

The research aimed to evaluate the influence of environmental variables into the biomass and elementary composition of the periphyton in Brachiaria mutica (Forsk) Stapf and inferences about the primary limiting nutrient to growth in different fluvials gradients of a tropical river (high course Santa Maria da Vitória, Espírito Santo, Brazil). Samples were taken at quarterly intervals of Oct./2004 the July/2005 in two sampling stations (E1 and E2), being E1 located in the preserved area and E2 subject to impacts anthropogenic. The biomass was evaluated trough’s of the dry weight (DW), organic matter (OM), ash (A) and chlorophyll a and the elementary composition trough’s the carbon, nitrogen and phosphorus concentration’s. Were determined also: precipitation, temperature (air and water), the electric conductivity, total dissolved solids, oxygen dissolved, pH, nitrite, nitrate, orthophosphate, total nitrogen and total phosphorus. In E1, dry weight, organic matter, ash and chlorophyll a varied, respectively, 5.4 - 36.3 g/cm², 32.7 - 79% DW, 21 – 67.3 % DW, 0.07 – 0.67 ug/cm², while phosphorus, nitrogen and carbon ranged from 0.06 – 0.14 % DW, 7.3 – 10.9 % DW e 17.3 - 42% OM. In E2, the variation of the biomass was 9.9 - 51 g / cm² (dry weight), 12.7 - 62.7% DW (organic matter), 37.3 - 87.3% DW (ash) and 0.16 – 0.21 ug/cm² (chlorophyll a), while the elementary composition ranged, respectively from 0.13 – 0.18 % DW (phosphorus), 7.8 – 12.3 % DW (nitrogen) e 6.7 – 33.2 % OM (carbon). The spatial variation was explained by different trofics degrees of the sampling stations, influencing the periphytic elementary composition (correlation between the water’s and periphyton’s nutrients) and biomass (larger average DW, OM and ash in E2). The periphyton suffered physics disturb effects, mainly on algae (low chlorophyll a concentration in both stations). Phosphorus was identified as primary limiting nutrient growth.