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pyrifolium in a Brazilian semiarid stream using litter bags, and after 3, 7, 15 and 30 days, four litter bags were withdrawn for laboratory washing of the remaining leaf sediment and for collection of associated invertebrates.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

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

Latitude dictates plant diversity effects on instream decomposition

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113 degrees of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes

Global Patterns and Controls of Nutrient Immobilization On Decomposing Cellulose In Riverine Ecosystems

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature

Intra- and inter-annual variations in Chironomidae (Insecta: Diptera) communities in subtropical streams

The structure and composition of stream benthic communities are strongly influenced by spatial and temporal factors. This study evaluated the intra and inter-annual variations in Chironomidae communities in subtropical streams. The organisms were sampled from 10 small-order streams during the summer and winter of 2010-2012. The number of chironomid specimens sampled was 7,568, distributed in 49 genera. Chironomid abundance and richness varied intra and inter-annually and community composition varied intra-annually (2010 and 2011). Water temperature, total organic carbon, nitrogen, and rainfall were correlated with chironomid community composition. The intra-annual variation of the community was dependent on climatic variations (temperature and rainfall) and changes caused by intensive agricultural use. We conclude that the temporal variation observed in the Chironomidae community correlates with climatic variations (rainfall) and changes in the total organic carbon and total nitrogen, caused by intensive agricultural land use

Experimental assessment of the effects of environmental factors and longitudinal position on alpha and beta diversities of aquatic insects in a neotropical stream

v. 97,n. 2, p. 157-167, mai., 2012.Submitted by Luanna Matias ([email protected]) on 2015-07-29T18:23:03Z No. of bitstreams: 1 Experimental assessment of the effects of environmental factors - 2012.pdf: 311687 bytes, checksum: 962ced8b3e67f9818b27594457af4966 (MD5)Approved for entry into archive by Claudia Moura ([email protected]) on 2015-10-08T20:44:48Z (GMT) No. of bitstreams: 1 Experimental assessment of the effects of environmental factors - 2012.pdf: 311687 bytes, checksum: 962ced8b3e67f9818b27594457af4966 (MD5)Approved for entry into archive by Claudia Moura ([email protected]) on 2015-10-08T20:50:35Z (GMT) No. of bitstreams: 1 Experimental assessment of the effects of environmental factors - 2012.pdf: 311687 bytes, checksum: 962ced8b3e67f9818b27594457af4966 (MD5)Made available in DSpace on 2015-10-08T20:50:51Z (GMT). No. of bitstreams: 1 Experimental assessment of the effects of environmental factors - 2012.pdf: 311687 bytes, checksum: 962ced8b3e67f9818b27594457af4966 (MD5) Previous issue date: 2012-04-26We evaluated the effect of environmental factors on the abundance and genera richness of aquatic insects colonizing artificial substrates. We also assessed the relative effects of environmental factors on assemblage variation (beta diversity), and contrasted its magnitude with the variation associated with the spatial position of reaches in a Neotropical stream. Homogeneous and heterogeneous bricks were installed in seven stream reaches and removed after 60d. Substrate type and organic matter showed significant effects on abundance. For observed richness, substrate type was the only important variable. For rarefied richness, no explanatory variable was important. A NMDS ordination of bricks revealed the effect of spatial position and substrate type. A partial Redundancy Analysis (pRDA) indicated that the environmental matrix explained 12.44% of the total variation, while reach position explained 7.41%. We conclude that at local scale (reaches 430–920 m apart), environmental factors, especially substrate heterogeneity, were important in determining the alpha and beta diversities of the insect assemblage in the stream

Distribution and additive partitioning of diversity in freshwater mollusk communities in Southern Brazilian streams

La partición aditiva de la diversidad de especies es un enfoque prometedor para el análisis de los patrones de diversidad en las comunidades de moluscos, especialmente su distribución espacial. Nuestros objetivos fueron evaluar la distribución de las comunidades de moluscos en los arroyos en el Sur de Brasil, y evaluar la partición de diversidad de la comunidad en diferentes escalas espaciales. El muestreo se llevó a cabo en cuatro cuencas del curso inferior del río Toropi, Brasil. Todas las especies encontradas, y también la comunidad en su conjunto mostraron una distribución agregada. La partición aditiva de la riqueza de especies mostró que la riqueza observada en menor escala (α=dentro de los arroyos) representó el 20.7%, y entre los arroyos (β1) representó el 10.5% de la riqueza total. La riqueza y diversidad de Shannon observadas en escala alfa (α=dentro de los arroyos) fueron mayores que las observadas en el primer nivel de escala de la diversidad beta (β1=entre los arroyos). La mayor variación en las grandes escalas de análisis, con la participación de los componentes entre-órdenes y entre-microcuencas (β2 y β3, respectivamente) fue la esperada, ya que el aumento de la distancia conduce a mayores diferencias de riqueza (mayor diversidad beta). En conclusión, nuestros resultados muestran que la dispersión agregada tuvo influencia en la partición de la diversidad de las comunidades de moluscos en los arroyos estudiados. Los métodos de dispersión y tolerancia a las variaciones de los factores abióticos también juegan un papel importante para determinar la diversidad alfa. Así, la conservación de los arroyos a nivel local contribuirá a la conservación de la cuenca y al mantenimiento de la diversidad regional (gamma).Additive partitioning of species diversity is a promising approach for analyzing patterns of diversity in mollusk communities, especially their spatial distribution. Our aims were to assess the distribution of mollusk communities in Southern Brazilian streams, and to evaluate the partitioning of community diversity at different spatial scales. The study was carried out in the lower course of the Toropi River, one of the main tributaries of the Ibicuí River Basin, in Southern Brazil. Four microbasins were considered: Sertão da Mata, Ribeirão, Tororaipi and Chiniquá, and sampling were undertaken in autumn, April and May 2009. Six sites were sampled in each stream: two in 1st-order segments, two in 2nd-order segments, and two in 3rd-order segments. All species found and the community as a whole, exhibited a clumped distribution. However, the variance-to-mean ratios for the Drepanotrema kermatoides and Heleobia bertoniana were higher than those of other species, suggesting a higher degree of aggregation. The additive partitioning of the species richness showed that the observed richness at smallest scale (α=within streams) represented 20.7%, and among-streams (β1) represented 10.5% of the total richness. The richness and Shannon diversity index observed at the alpha scale, were higher than those observed at the first level of beta diversity scale (β1=among-streams). The interaction between passive dispersal, tolerance to changes in some environmental variables, abiotic factors, and clumped distribution might have determined the spatial distribution of the communities studied. The greatest variation at the larger scales of analysis, involving among-orders and among-microbasins (β2 and β3, respectively) components, was expected, considering that the increase in distance leads to greater differences in richness (higher beta diversity). In conclusion, our results showed that the clumped distribution influenced the partition of the diversity of the mollusk communities in the streams studied. Dispersal methods and tolerance to variations in abiotic factors also have important roles in determining high alpha diversity. The partitioning of diversity showed that to preserve limnetic mollusks, it is important to preserve local areas, i.e., streams. Accordingly, conservation of streams on a local scale will contribute to conservation of the entire basin and maintenance of regional diversity (gamma)

The effects of heavy metals on the incidence of morphological deformities in Chironomidae (Diptera)

ABSTRACT Streams in urban areas are strongly impacted by the input of organic matter and metals, for instance copper (Cu) and zinc (Zn). These metals are essential for the aquatic biota, but when absorbed in excess they are toxic. In Chiro nomidae larvae, the deleterious effects of heavy metals can be ascertained by analyzing the morphological deformities of the larval mentum, a structure of the oral cavity. In this study, we evaluated I) the bioavailability of Cu and Zn in urban stream sediments and II) the relationship between Cu and Zn concentrations and the incidence of deformities in the mentum of Chironomus larvae. Chironomid flies were collected from four locations in two streams at an urban area in southern Brazil. They were identified and the incidence of deformities in the mentum was quantified. Sediment samples were collected at the same locations where larvae were collected, to quantify the bioavailable fractions of Cu and Zn. The concentrations of Cu in the sediment were similar between the collection sites. However, Zn concentrations varied among sites, being greater in the stretch directly influenced by the input of the organic waste. In total, 2,895 Chironomid larvae were collected. The incidence of deformities in the mentum was above 30% and was correlated with the concentrations of Cu (r = 0.68) and Zn (r = 0.87). This correlation indicates that the municipal waste that is thrown into the city’s streams has influenced the occurrence of deformities

A Global Assessment of the Effects of Eucalyptus Plantations on Stream Ecosystem Functioning

Forest change is a major environmental problem worldwide. Forest streams, with their large aquatic-terrestrial interface and strong dependence on terrestrially derived organic matter, are highly sensitive to forest changes. Fast-wood plantations can be particularly threatening if they markedly differ from native forests. Eucalyptus plantations, in particular, cover large areas worldwide (>20 million ha, mostly from 35 degrees S to 35 degrees N), but their effects on stream functioning have been addressed mostly in the Iberian Peninsula, which limits generalization to other regions. We assessed the effect of eucalyptus plantations on total (microbial decomposers and macroinvertebrates; in coarse mesh bags) and microbial-driven (in fine mesh bags) leaf litter decomposition by comparing streams flowing through native forests and eucalyptus plantations in seven regions in the Iberian Peninsula, Central Africa and South America. We found an overall significant inhibition of total litter decomposition by 23%. The effect did not significantly differ across regions, although a significant inhibition was found for Spain (-41%), South Brazil (-31%) and Uruguay (-36%) (Portugal had a marginally nonsignificant inhibition by 50%) but not for other regions, suggesting that the effects of plantations in temperate climates are mediated through effects on macroinvertebrate communities. Contrarily, the overall effect for microbial-driven litter decomposition was non-significant, but it significantly differed across regions with a significant stimulation in Central Brazil (110%) and Uruguay (32%), and nonsignificant effects for other regions (Kenya had a marginally nonsignificant inhibition by 48%), suggesting that functional redundancy among microbial communities is not general and effects can occur if plantations induce changes in nutrient availability, solar irradiation or litter characteristics