Quality of water in different periods of growth of flooded rice

Este trabalho teve como objetivo avaliar a qualidade da água utilizada para a rizicultura, em diferentes estádios de desenvolvimento da planta, no sistema de plantio pré-germinado. Foram analisadas as águas de irrigação e de drenagem no processo de cultivo. Foram escolhidas três áreas de amostragens, localizadas no Município de Gaspar, SC, que apresentam técnicas de cultivo semelhantes. A água utilizada para irrigação é retirada de um curso de água e devolvida após o uso no quarteirão, para o mesmo curso. Neste sistema não existem aportes de poluentes externos intermediários. Para avaliar a qualidade da água, foi utilizado o Índice de Qualidade de Água de Bascarán (IQAb). De acordo com os resultados, a água utilizada para irrigação apresenta qualidade imprópria (IQAb−4050). A água de drenagem foi classificada, de modo geral, como desagradável (IQAb−3040). Os parâmetros que mais influenciaram a diminuição do IQAb na água de drenagem foram a turbidez, fosfatos e DQO. Constatou-se que a fase de preparo do solo é a que provoca maior degradação da qualidade da água, na cultura orizícola.The objective of this study was to evaluate the quality of the water used for rice irrigation, considering different periods of the plants growth, using the pre-germinated seeds planting technique. Irrigation and drainage water were analyzed during the process of tillage. Three sites of sampling located around the City of Gaspar SC, Brazil were chosen. All three sites presented similar techniques of tillage. The water used for the irrigation was collected from a watercourse and returned after it passed through the tillage. In this system there are no external or intermediary pollutant conductors. To evaluate the quality of water it was used the Quality of Water Index from Bascarán (IQAb). The results demonstrate that the water used for irrigation, enters in the tillage area with an improper quality (IQAb 40−50). Drainage water was classified as disagreable (IQAb 30−40). The parameters that influenced the decrease of IQAb in drainage water were the turbidity, phosphates and QOD. The decrease of drainage water quality was influenced by the vegetative period. This study determined that the major degradation of the quality of the water is due to the preparation of the soil

Variation of Chironomidae (Insecta: Diptera) trophic guilds and their relation with trophic state in reservoirs in the semiarid

The Chironomidae larvae are sensitive to variations in aquatic ecosystem conditions. We aim to analyze the variation of Chironomidae trophic guilds and their relation to the trophic state index in reservoirs in the semiarid. The study was conducted from 66 sites, distributed in the littoral zone of three reservoirs of Piranhas-Assu river, during June and December of 2014. The larvae were collected, and after identification, were classified in functional trophic groups. We applied the Trophic Status Index of Carlson, modified by Toledo for trophic classification. Sabugí reservoir was the only classified as mesotrophic (52,60±3,64) in June, where the greatest levels of diversity also occurred in the trophic guilds: gatherer-gollector (9 genera), predator (6 genera) and filterer-collector (1 genus). Higher levels of eutrophication occurred in Passagem das Traíras reservoir (84,99±6,19), the same with the smallest diversity in the guilds: gatherer-collector (3 genera) and 1 genus in the other categories. The variation of trophic guilds has been associated with trophy levels, because higher levels of degradation eliminate sensitive species, reducing the number of taxa. Thus, the Chironomidae trophic guilds demonstrate potential capacity for indicating the degree of impact to which the reservoirs are submitted

Leaching of carbon from native and non-native leaf litter of subtropical riparian forests

We evaluated the leaching of dissolved organic and inorganic carbon (DOC and DIC, respectively) from leaf litter of plant species of the native Atlantic Forest and of Pinus elliottii (Engelm.) and Eucalyptus grandis (Hill ex Maiden) forests. We carried out experiments in which leaves from each forest system (native, E. grandis, and P. elliottii) were placed in reactors with sterile water. After 1/4 h, 1 h, 4 h, 12 h, 24 h, and 48 h of incubation, we quantified the concentrations of DIC and DOC of each leachate. The greatest quantity of DIC was leached in the native forest system, whereas the greatest quantity of DOC was leached in the E. grandis forest system. With respect to the period of year, the greatest quantity of DIC was leached in autumn, whereas that of DOC was leached in the summer. Our results demonstrated that the replacement of native species in riparian zones, by non-native forest monocultures, could alter the chemical composition of the water. Finally, the results presented in this paper reinforce the need for a more careful look at ecological processes

Leaf traits of Brazilian semiarid species as regulatory factors for associated aquatic invertebrates

The input of leaf litter is an important energy source for the riparian vegetation of aquatic ecosystems, and the chemical composition of leaf litter is decisive for colonization by invertebrates in streams. Plant species of the semiarid regions present different morphophysiological characteristics to combat the effects of drought, including tough leaves that have less nutritional quality. However, although concern regarding the decomposition of organic matter in aquatic ecosystems in semiarid regions is increasing, no information exists on the influence of leaf traits (e.g., N, C:N ratio and toughness) before the colonization of invertebrates and the decomposition of leaf litter. We hypothesized that: i) leaves with greater toughness, higher C:N ratio and lower amount of N present low density and biomass of associated invertebrates; ii) greater density and biomass of associated invertebrates results in increased decomposition rates; and iii) leaf traits influences the structure and composition of functional feeding groups of associated invertebrates. We incubated senescent leaves of Tabebuia aurea and Aspidosperma pyrifolium in a Brazilian semiarid stream using litter bags, and after 3, 7, 15 and 30 days, four litter bags were withdrawn for laboratory washing of the remaining leaf sediment and for collection of associated invertebrates. A. pyrifolium leaves presented higher nutritional quality (low C:N ratio, lower toughness), and the decomposition rate was higher than T. aurea leaves. Invertebrate density and biomass varied among litter, being higher in T. aurea and A. pyrifolium, respectively. The leaf litter quality also altered the composition of functional feeding groups. We observed a higher density of filters on T. aurea and collectors on A. pyrifolium. Both T. aurea and A. pyrifolium presented higher biomass of collectors, however T. aurea showed higher biomass of filters than A. pyrifolium. In the absence of shredders, leaf litter may have been used by invertebrates as a substrate, for shelter against predators and current, and sporadically as a food resource. Thus, differences in the leaf traits were important structures of the streams invertebrate. These are the first results of the influence of leaf traits on invertebrate colonization in the streams of semiarid regions, and reinforce the need for studies to verify the contribution of organic matter as well as the feeding preferences of invertebrates

First record of Corbicula largillierti (Philippi 1844) in the Paraíba River Basin and potential implications from water diversion of the São Francisco River

) em sedimentos grossos (cascalho, 2-4 mm). A transposição das águas do Rio São Francisco pode ocasionar a introdução de novas espécies exó ticas potencializando problemas ecoló gicos na bacia do Rio Paraíba

Size-mass relationships of Melanoides tuberculatus (Thiaridae: Gastropoda) in a eutrophic reservoir

This study evaluated the relationships of certain allometric measurements in Melanoides tuberculatus Muller, 1774, in order to develop a statistical model to estimate the biomass of this mollusc species. We measured the total length and aperture of 70 shells. These measurements were correlated with the biomass values to construct exponential and power-function models, and both models showed high coefficients of determination. The exponential model was the better biomass predictor, with a coefficient of determination over 93%. These proposed models may be an effective tool to determine the biomass of M. tuberculatus in eutrophic Brazilian reservoirs