Câmara F R A, Rocha O, Pessoa E K R, Chellappa S, Chellappa N T
Unidade Acadêmica Especializada em Ciências Agrárias, Universidade Federal do Rio Grande do Norte, Macaíba, RN, BR.
Departamento de Ecologia e Biologia Evolutiva, Universidade Federal de São Carlos, São Carlos, SP, BR.
Braz J Biol. 2015 Aug;75(3):628-37. doi: 10.1590/1519-6984.19513. Epub 2015 Aug 25.
The present study focuses on the structure and function of phytoplankton community during periods of marked changes in hydrological traits, influenced by an atypical climatic event (La Niña) and its impact on Armando Ribeiro Gonçalves Reservoir of Rio Grande do Norte, situated in the Caatinga biome of northeastern Brazil. The main questions addressed were: What are the effects of environmental factors on the temporal variation of Morphologically Based Functional Group (MBFG) of phytoplankton community? How does the composition of cyanobacterial species shift in relation to high and low trends of phytoplankton diversity? The samples were collected monthly during 2008-2009 and analyzed for pH, temperature, electrical conductivity, dissolved oxygen content and the nutrients, such as, nitrate-nitrogen, ammoniacal nitrogen, total nitrogen and orthophosphate. Phytoplankton samples were collected for both qualitative and quantitative analyses to evaluate species richness index and species diversity index. The data was divided into two distinct hydrodynamic periods of instability and stability. The results demonstrate considerable changes in dissolved oxygen content, water transparency and nitrogen nutrients, which directly influenced the MBFG of phytoplankton community in space and time. The instability of reservoir water was caused by heavy rainfall, which exerts atypical external disturbances. The seasonal variation of MBFG demonstrates a change in cyanobacterial composition and their diversity during instability and stability periods. MBFG VII, composed by colonial cyanobacteria with mucilage, was associated with reduced values of electrical conductance and alterations in pH. The predominance of filamentous species with heterocyst (MBFG III) occurs only during the hydrodynamic stability period and did not show significant association with analyzed parameters. The co-dominance of MBGFs III, V and VII along with high species diversity of phytoplankton community occurred during the second hydrodynamic instability period which was associated with the reduction in water temperature. It is concluded that the decrease in cyanobacterial species dominance and the general increase in the diversity of phytoplankton community are influenced by pluvial anomaly. The higher water level during the period of pluvial anomaly resulted in nutrient pulse and the mixing of water column in the reservoir, which determined the MBPG phytoplankton community distribution.
本研究聚焦于水文特征发生显著变化期间浮游植物群落的结构和功能，这些变化受一次非典型气候事件（拉尼娜现象）及其对位于巴西东北部卡廷加生物群落的北里奥格兰德的阿曼多·里贝罗·贡萨尔维斯水库的影响。所探讨的主要问题是：环境因素对浮游植物群落基于形态的功能群（MBFG）的时间变化有何影响？蓝藻物种组成如何随浮游植物多样性的高低趋势而变化？在2008 - 2009年期间每月采集样本，分析其pH值、温度、电导率、溶解氧含量以及硝酸盐氮、氨氮、总氮和正磷酸盐等营养物质。采集浮游植物样本进行定性和定量分析，以评估物种丰富度指数和物种多样性指数。数据被分为两个不同的水动力不稳定期和稳定期。结果表明，溶解氧含量、水体透明度和氮营养物质发生了显著变化，这些变化直接在空间和时间上影响了浮游植物群落的MBFG。水库水的不稳定是由暴雨引起的，暴雨带来了非典型的外部干扰。MBFG的季节变化表明，在不稳定期和稳定期蓝藻的组成及其多样性发生了变化。由具黏液的群体蓝藻组成的MBFG VII与电导率降低和pH值变化有关。具异形胞的丝状物种（MBFG III）仅在水动力稳定期占优势，且与分析参数无显著关联。在第二个水动力不稳定期，MBGFs III、V和VII共同占优势，同时浮游植物群落具有较高的物种多样性，这与水温降低有关。研究得出结论，蓝藻物种优势度的降低和浮游植物群落多样性的普遍增加受降雨异常影响。降雨异常期间较高的水位导致了营养脉冲和水库水柱的混合，这决定了MBPG浮游植物群落的分布。
