Claudio Rossano Trindade

Seasonal dynamics of methane in the water column of two subtropical lakes differing in trophic status

Alterations in methane concentration in the water column of aquatic systems is closely linked to the processes of production and consumption of this gas, i.e., methanogenesis and methanotrophy respectively. The aim of this research is to evaluate methane dynamics through diurnal variation in the concentration of this gas in the water column of two lakes differing in trophic status at the campus of Fundação Universidade do Rio Grande (FURG). In two sampling periods (November 2001 and July 2002) methane concentrations in the water column were significantly higher (3.66 and 0.41 micromoles.L-1, respectively) at Lago dos Biguás, with mesoeutrophic features when related to Lago Polegar (1.43 and 0.19 micromoles.L-1, respectively) which has oligotrophic features. The higher methane concentrations were detected in November 2001 when higher temperature was also detected. The results highlighted the importance of trophic status as well as seasonality for the methane dynamics in these ecosystems.

Macrófitas aquáticas como indicadores da qualidade da água em pequenos lagos rasos subtropicais, Sul do Brasil

Abstract: Aims: We evaluated the potential of aquatic macrophyte communities as bioindicators in six small shallow lakes. Methods: The sampling was conducted monthly for one year, during which all macrophytes were surveyed, and the water temperature, dissolved oxygen, pH, conductivity, total alkalinity, chlorophyll- a , suspended matter, total nitrogen (Nt) and total phosphorus (Pt) were measured. Results: In total, forty-three species were recorded, and there were significant differences in the species richness and limnological conditions among the lakes studied. A canonical correspondence analysis showed that the concentration of nutrients (Nt and Pt), chlorophyll- a , suspended matter, dissolved oxygen and pH were the most important predictors of the distribution of macrophytes. Some emergents were related to the high concentration of nutrients, chlorophyll- a , and suspended matter. Moreover, the most submersed species were associated with environments with low nutrient concentrations and the lowest values chlorophyll-

Temporal variation in the biomass and nutrient status of Azolla filiculoides Lam. (Salviniaceae) in a small shallow dystrophic lake

AIM: This study determined the temporal variation of the biomass and the concentrations of carbon, nitrogen and phosphorus in Azolla filiculoides Lam. in a small (0.5 ha) shallow dystrophic lake located in the city of Rio Grande (Rio Grande do Sul State, Brazil). METHOD: Sampling was conducted monthly between November 2000 and October 2001. The macrophytes were collected randomly in three replicates with a circular collector 0.3 m in diameter and subsequently washed with tap water and oven-dried at 60 oC for determination of the dry weight and the nutrient status (i.e., carbon, nitrogen and phosphorus). Primary productivity was estimated by the variation in biomass among successive samples. RESULTS: A. filiculoides was present in the lake throughout the year and occupied between 50 and 80% of the surface area. The biomass values ranged from 34.2 g DW.m-2, recorded in May (autumn), to 170.9 g DW.m-2 in January (summer). The highest rate of primary productivity was 3.3 g DW.m-2.d-1, observed in June. The concentrations of carbon, nitrogen and phosphorus in the plant ranged between 403 and 551 g.kg-1, 13.4 and 25.7 g.kg-1 and 0.5 and 1.9 g.kg-1, respectively. The water N:P ratio ranged between 19:1 and 368:1. CONCLUSION: The coverage of the surface of the lake by A. filiculoides throughout the study period and the nutritional status of the plant demonstrate the importance of the cycling of nutrients by macrophytes in this aquatic environment. The higher N:P ratio in the water column, compared with other neighboring environments without macrophytes, shows that the enrichment of the lake may result from the biological N-fixation activity produced by A. filiculoides.

Aquatic macrophytes of six subtropical shallow lakes, Rio Grande, Rio Grande do Sul, Brazil

The aim of this study was to document the richness of aquatic macrophytes in six shallow lakes at Federal University of Rio Grande - FURG, Rio Grande, Rio Grande do Sul, Brazil. Qualitative surveys were carried out during 2008. Specimens were deposited at the university herbarium (HURG). We recorded 44 species belonging to 35 genera and 21 families. The majority of species were present all year. The family with highest diversity was Cyperaceae (eight species). Other studies have reported approximately 170 species for wetlands in the south of Brazil. This study documented approximately 25% of these species. The flora of the area should be preserved and monitored.

Macrophyte functional groups elucidate the relative role of environmental and spatial factors on species richness and assemblage structure

We evaluated the relative importance of environmental and spatial factors on species richness and assemblage structure of macrophytes in 29 coastal wetlands in southern Brazil. We used variation partitioning on total assemblage and three functional groups (emergent, floating, and submerged) and predicted that the relative importance of environment would be greater than that of space for all groups. Further, we predicted that both environment and space would show greater relative importance for floating and submerged than for emergent species, since the first ones depend more on local characteristics and on hydrocoric and zoocoric dispersal, while emergent species are less dependent on local characteristics and disperse mostly by wind. Variation in species richness was partly explained only for floating macrophytes by the environmental fraction. Regarding assemblage structure, environmental variables were more important for floating species and spatial variables for submerged species than for emergent ones and total assemblage. Further, while floating species were structured only by local environmental variables, emergent species were influenced by climatic environmental variables. These results revealed different patterns among macrophyte functional groups in wetlands, highlighting the importance of accounting for ecological differences to further advance the understanding of the relative role of predictors to metacommunity structure.

Water quality of the São Gonçalo channel, urban and agricultural water supply in southern Brazil

O canal Sao Goncalo liga as lagoas dos Patos e Mirim, no sul do Brasil, possuindo um comprimento de cerca de 70 Km. E importante manancial agricola para a cultura do arroz irrigado, e urbano, para o municipio de Rio Grande, com cerca de 250 mil habitantes. Este trabalho visou obter um diagnostico da qualidade das aguas deste manancial, utilizando metricas da comunidade de invertebrados bentonicos (indice de Shannon-Wiener, abundância e riqueza de taxons), e o indice biotico BMWP, avaliacao de caracteristicas fisicas e quimicas, e aplicacao do indice de estado trofico. O indice BMWP geral para o periodo indicou aguas contaminadas ou poluidas, com maiores valores de riqueza e densidade de grupos indicadores de condicoes alteradas (Sarcodina e Hydracarina). As variaveis analisadas indicam aguas eutrofizadas, com valores de clorofila-a caracteristicos de ambientes eutroficos (> 2,9 µg. L-1), baixas taxas N:P tanto na agua como no sedimento, indicando limitacao por nitrogenio na maioria dos periodos. Estes valores sao corroborados pelos escores de indices de estado trofico, que em sua maioria indicaram condicoes de mesotrofia e eutrofia, atingindo periodos de hipertrofia. Os valores de IET mais elevados ocorreram a jusante do rio Piratini, nas coletas de abril/2009 e fevereiro/2011, atingindo valores de super e hipereutrofico, respectivamente, em periodos coincidentes com drenagem das culturas de arroz irrigado no entorno. Os resultados encontrados relativos as concentracoes de nutrientes, estequiometria de nitrogenio e fosforo e indice biotico reforcam a necessidade de avaliacoes de usos do entorno deste manancial.