The use of integrative tools and multiple models for aquatic environmental quality assessment: a case study of the Mirim Lagoon, Southern Brazil.

This study performed toxicity assays with microalgae, microcrustaceans, and fish as well as evaluated biochemical and behavioral biomarkers in fish and microcrustaceans to assess the quality of the surface water of Mirim Lagoon, which belongs to one of the largest hydrographic basins in the world, located in southern Brazil. Three distinct sampling periods were chosen (January, March, and June 2022) based on the rice plantation dynamics which is the main activity surrounding the lagoon. In January, the plantation is irrigated; in March, the water is drained into the Mirim Lagoon, and July is the off-season. Concerning toxicity tests, there was significant inhibition in microalgae growth when exposed to water collected in March, but no mortality was observed for Ceriodaphia dubia, Daphnia magna, and Danio rerio. Regarding biomarkers, behavioral variables contributed more to the higher values of the Integrated Biomarker Response (IBR) index for both D. magna and D. rerio, in March. The Redundancy Analysis (RDA) indicated a correlation between the biomarkers for both organisms and abiotic parameters, mainly nutrients (total phosphorus and total nitrogen), thermotolerant coliforms, total solids, and turbidity. Spatially, there was no difference during monitoring, but the most significant ecotoxicological effects were observed in March. Multivariate analysis and the IBR index proved to be useful tools for monitoring of water bodies such as Mirim Lagoon.

Compactação superficial de Latossolos sob integração lavoura: pecuária de leite no noroeste do Rio Grande do Sul / Surface compaction of oxisols with crops: dairy cattle production in northwest of Rio Grande do Sul, Brazil

Em sistemas de integração lavoura-pecuária, o solo sofre pressões pelo pisoteio animal e tráfego de máquinas, alterando sua estrutura. Neste trabalho, avaliaram-se a densidade, a porosidade e a resistência do solo à penetração em cinco propriedades rurais que adotam o sistema de integração lavoura-pecuária. Os resultados indicaram um aumento da compactação pelo pisoteio animal na camada superficial do solo (0,10m). Os valores de densidade estavam acima de 1,4Mg m-3, a macroporosidade abaixo de 0,10m³ m-3 e a resistência à penetração acima de 2MPa na umidade de 0,26kg kg-1, o que indica degradação física do solo. Assim, é necessário adotar práticas de manejo adequadas para a recuperação desses solos e evitar o aumento da compactação.

In crop and livestock integration system, pressure applied by animal trampling and farm-machinery wheeling changes soil structure. In this study soil bulk density, porosity and soil penetration resistance were evaluated in five farms which adopt the crop and livestock integration system. The results indicated an increase in soil compaction by cattle trampling in the surface soil layer (0.10m). The bulk density was above 1.4Mg m-3, the porosity is below 0,10m³m-3 and soil penetration resistance is above 2MPa at 0.26kg kg-1 soil moisture, which characterize soil physical degradation. Thus, adoption of management practices suitable for the soil physical amelioration and prevent further increase in the state of compaction is necessary.