RESUMO
The Lerma-Chapala Basin, in Central Mexico, is geologically heterogeneous, climatically diverse and boasts high biodiversity, lying within two Biodiversity Hotspots, namely Mesoamerica and the Madrean Pine-Oak Woodlands. Epilithon and water samples were collected in the basin from 14 sampling sites three times each, two sampling campaigns during the rainy season and one in the dry season. A total of 274 infrageneric taxa in 48 genera were recorded. The taxonomic composition observed was dominated by taxa from the genera Nitzschia, Gomphonema, Pinnularia, Navicula, Sellaphora and Eunotia. About a third of the taxa found could not be identified to the species level. From those unidentified morphodemes, two are described as new species, namely Brachysira altepetlensis and Sellaphora queretana. Furthermore, Eolimna rhombica is transferred to Sellaphora. Canonical Correspondence Analysis (CCA) revealed that specific conductivity and pH were the main environmental factors driving the community composition observed. Three groups of samples were identified after the CCA: 1) characterized by acidic waters and low conductivity; 2) with circumneutral waters, low specific conductivity and high temperature and phosphorous concentrations; and 3) characterized by circumneutral waters, high conductivity and low nitrogen concentrations. The indicator value method (IndVal), based on the relative abundance and relative frequency of the most abundant taxa was calculated based on the groups observed in the CCA, identifying the characteristic taxa for each of the three groups.
RESUMO
Benthic microalgae sampling in lotic systems is carried out using either artificial or natural substrate. Natural substrate is more suitable for biomass and productivity estimates as well as biodiversity assessment because it contains the communities that are typical of the environment. We present a new gadget for epilithic microalgae sampling (GEMS) that allows sampling in situ when it is impossible to remove the substrate from the river bed. The sampler consists of an acrylic box with a 25 cm diameter opening on its base that allows access to the substrate. This gadget can be used in shallow plan bedrock streams and it keeps the sample area isolated as much as possible minimising losses and contamination. It is also easy to construct and handle.
As amostragens de microalgas bênticas em sistemas lóticos são realizadas através do uso de substrato natural ou artificial. Substratos naturais são mais adequados para a estimativa de biomassa e produtividade, assim como, para a avaliação de biodiversidade, porque eles contêm as comunidades que são típicas de um determinado ambiente. Nós apresentamos um novo dispositivo para amostragem de microalgas epilíticas (GEMS) que permite a amostragem in situ, quando é impossível remover o substrato do leito do rio. O amostrador consiste em uma caixa de acrílico com uma abertura de 25 cm de diâmetro em sua base que permite acesso ao substrato. O amostrador pode ser usado em riachos rasos e de leito rochoso e plano, e mantém a área amostral o mais isolada possível, minimizando perdas e contaminação, além de ser fácil de construir e manusear.
Assuntos
Eucariotos , Monitoramento Ambiental/instrumentação , Água Doce , Densidade DemográficaRESUMO
Benthic microalgae sampling in lotic systems is carried out using either artificial or natural substrate. Natural substrate is more suitable for biomass and productivity estimates as well as biodiversity assessment because it contains the communities that are typical of the environment. We present a new gadget for epilithic microalgae sampling (GEMS) that allows sampling in situ when it is impossible to remove the substrate from the river bed. The sampler consists of an acrylic box with a 25 cm diameter opening on its base that allows access to the substrate. This gadget can be used in shallow plan bedrock streams and it keeps the sample area isolated as much as possible minimising losses and contamination. It is also easy to construct and handle.(AU)
As amostragens de microalgas bênticas em sistemas lóticos são realizadas através do uso de substrato natural ou artificial. Substratos naturais são mais adequados para a estimativa de biomassa e produtividade, assim como, para a avaliação de biodiversidade, porque eles contêm as comunidades que são típicas de um determinado ambiente. Nós apresentamos um novo dispositivo para amostragem de microalgas epilíticas (GEMS) que permite a amostragem in situ, quando é impossível remover o substrato do leito do rio. O amostrador consiste em uma caixa de acrílico com uma abertura de 25 cm de diâmetro em sua base que permite acesso ao substrato. O amostrador pode ser usado em riachos rasos e de leito rochoso e plano, e mantém a área amostral o mais isolada possível, minimizando perdas e contaminação, além de ser fácil de construir e manusear.(AU)