Multivariate water quality analysis of Lake Cajititlán, Mexico.

Lake Cajititlán is a shallow body of water located in an endorheic basin in western Mexico. This lake receives excess fertilizer runoff from agriculture and approximately 2.3 Hm3 per year of poorly treated wastewater from three municipal treatment plants. Thirteen water quality parameters were monitored at five sampling points within the lake over 9 years. The objective of this work was to characterize the spatial and temporal variations of the water quality and to identify the sources of data variability in order to assess the influence and the impact of different natural and anthropogenic processes. One-way ANOVA tests, principal component analysis (PCA), cluster analysis (CA), and discriminant analysis (DA) were implemented. The one-way ANOVA showed that biochemical oxygen demand and pH present statistically significant spatial variations and that alkalinity, total chloride, conductivity, chemical oxygen demand, total hardness, ammonia, pH, total dissolved solids, and temperature present statistically significant temporal variations. PCA results explained both natural and anthropogenic processes and their relationship with water quality data. The CA results suggested there is no significant spatial variation in the water quality of the lake because of lake mixing caused by wind. The most significant parameters for spatial variations were pH, NO3-, and NO2-, consistent with the configuration of point and nonpoint sources that affect the lake's water quality. The temporal DA results suggested that conductivity, hardness, NO2-, pH, and temperature were the most significant parameters to discriminate between seasons. The temporal behavior of these parameters was associated with the transport pathways of seasonal contaminants.

Assessment of heavy metals in the surface sediments and sediment-water interface of Lake Cajititlán, Mexico.

Lake Cajititlán is an endorheic tropical lake located in the state of Jalisco, Mexico, which has suffered the consequences of high levels of eutrophication. This study assessed the presence of heavy metals and metalloids in Lake Cajititlán to ascertain possible risks to its aquatic biota and the environment. Eleven monitoring sites were selected throughout the lake; from each site, one sample was taken from the sediments and another from the sediment-water interface by using an Ekman dredger and a Van Dorn bottle, respectively. The measured metals in each sample were As, Cd, Cr, Hg, Pb, Zn, Cu, Ni, Fe, Mn, and Al. The results showed the following sequence of heavy metal concentrations Al > Fe > Mn > Zn > Cu > Cr, wherein Al had the highest average concentration and Cr had the lowest. As, Cd, Hg, and Pb were practically undetectable. Because the predominant rock in the lake basin is volcanic tuff and the soil is vertisol, the high quantities of Al and Fe suggest the weathering of the basin's minerals. The analyses of the sediment-water samples contained small amounts of dissolved Al, Fe, and Mn. According to the Håkanson equations with Hg, Cd, As, Cu, Pb, Cr, and Zn, the calculations of the contamination degree and ecological risk revealed that the presence of metals and metalloids does not present a potential risk to the aquatic biota; nonetheless, the water is not suitable for local human consumption due to an unrelated factor associated with nutrient and bacteriological contamination. The results show that heavy metals in the sediments were dispersed throughout the lake mostly because of the weathering of minerals from the local basin and not because of the punctual discharges of the pollutants from the municipal wastewater treatment plants (WWTPs). However, to ensure that the small amounts of dissolved metals (Al, Fe, and Mn) do not affect the aquatic biota, the fish species and phytoplankton need to be internally analyzed.

Seasonal dynamics of methane in the water column of two subtropical lakes differing in trophic status / Dinâmica sazonal do metano na coluna d'água de dois lagos subtropicais em diferentes estados tróficos

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 μmoles.L-1, respectively) at Lago dos Biguás, with mesoeutrophic features when related to Lago Polegar (1.43 and 0.19 μmoles.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.

As alterações na concentração de metano na coluna d'água nos ecossistemas aquáticos estão intimamente ligadas aos processos de produção e consumo deste gás, ou seja, à metanogênese e metanotrofia, respectivamente. Esta pesquisa tem como objetivo determinar a dinâmica do metano através da variação diurna da concentração deste gás na coluna d'água em dois lagos de diferentes estados tróficos do Campus da Fundação da Universidade do Rio Grande (FURG). Nos dois períodos de coleta (novembro de 2001 e julho de 2002), as concentrações de metano foram significativamente maiores no lago dos Biguás (3,66 e 0,41 μmoles.L-1, respectivamente) de caráter mesoeutrófico em relação ao lago Polegar (1,43 e 0,19 μmoles.L-1, respectivamente), de característica oligotrófica. Os maiores valores da concentração de metano na coluna d'água nos dois lagos foram observados no período de novembro de 2001, quando foram registrados também os maiores valores de temperatura. Estes resultados evidenciam tanto a importância do caráter trófico dos lagos quanto a sazonalidade em relação à dinâmica do metano nestes ecossistemas.

Macroinvertebrate fauna associated with Pistia stratiotes and Nymphoides indica in subtropical lakes (south Brazil)

This study was carried out at the Biguás and Polegar lakes, both small environments but at different successional stages. The main objective was to characterize the macroinvertebrate community associated to the aquatic macrophyte stand in each lake in order for this community, the environmental conditions and their water quality to interact. The samples were taken in 2003. The abiotic variables of N and P totals, the temperature, electrical conductivity, pH and dissolved oxygen, as well as the determined clorophyll a concentration were measured. Macroinvertebrates were sampled with a 500 µ mesh size net, separated under a stereomicroscope and identified at the lowest possible taxonomic level, and their densities were shown as the number of individuals per 100 g of macrophyte dry weight. The Shannon-Wiener Diversity Index (H'), Pielou evenness (J), frequency of occurrence, abundance and taxa richness were calculated for each invertebrate community. The Lago dos Biguás is undergoing a process of eutrophication and during the study presented a large Pistia stratiotes stand. The Lago Polegar is oligotrophic and had only a small Nymphoides indica bankwe. The macrophyte associated invertebrate communities in each lake were considered significantly different (p < 0.05). Sixty seven taxa were found for the Lago dos Biguás and 32 for the Lago Polegar. For both lakes, most of the taxa were considered rare, with a low dominance in a few months. The taxa with highest densities at Lago dos Biguás were Chironomidae, Daphniidae and Cyclopidae, and Oligochaeta, Chironomidae and Coenagrionidae for Lago Polegar.

Este estudo foi realizado nos lagos dos Biguás e Polegar, ambientes de pequenas dimensões que se encontram em diferentes estágios sucessionais. O objetivo principal foi caracterizar a comunidade de macroinvertebrados, que vive associada ao estande de macrófitas aquáticas encontrado em cada um dos lagos, na tentativa de obter relações entre a comunidade, a saúde dos ambientes e a qualidade de água. As coletas foram feitas durante o ano de 2003. Em cada lago, foram avaliadas as concentrações de N e o P totais, o pH, temperatura, oxigênio dissolvido, condutividade elétrica, e determinadas as concentrações de clorofila a na água. A malha utilizada para a separação dos macroinvertebrados foi de 500 µ e os resultados de densidade foram expressos em 100 gramas de peso seco de macrófita. A triagem foi realizada sob estereomicroscópio e os organismos identificados até o menor nível taxonômico possível. Para cada comunidade foram calculados o Índice de Diversidade de Shannon-Wiener (H'), a homogeneidade de Pielou (J), a freqüência de ocorrência, a abundância e a riqueza de taxa. O Lago dos Biguás, em processo de eutrofização, apresentou durante o período estudado um grande estande de Pistia stratiotes. O Lago Polegar, oligotrófico, abrigou apenas pequenos bancos de Nymphoides indica. As comunidades de macroinvertebrados associados às macrófitas em cada lago foram consideradas significativamente diferentes (p < 0,05). Foram encontrados 67 taxa no Lago dos Biguás e 32 no Lago Polegar. Nos dois ambientes, a maior parte dos taxa foi considerada rara, com pouca dominância em poucos meses. As maiores densidades foram de Chironomidae, Daphniidae e Cyclopidae no Lago dos Biguás, e de Oligochaeta, Chironomidae e Coenagrionidae no Lago Polegar.