Marcos Paulo Figueiredo-Barros

Stoichiometry of benthic invertebrate nutrient recycling: interspecific variation and the role of body mass

Ecological stoichiometry (ES) and allometry offer frameworks for predicting how nutrient recycling varies within and among animal species. Despite the importance of benthic-derived nutrients in most aquatic systems, predictions based on ES and allometry have been poorly tested among benthic invertebrate consumers. Here, we show that the rates and ratios at which three freshwater benthic invertebrate species (a crustacean, an insect, and a polychaeta) recycled nitrogen (N) and phosphorus (P) can be partially predicted by ES and allometry depending on whether data are analyzed intra- or interspecifically. Mass-specific N and P excretion rates were negatively correlated with invertebrate body size both among and within taxa, supporting allometric predictions. However, mass-specific N and P excretion rates were positively and negatively correlated to invertebrate body N and P, respectively, but only when data were analyzed intraspecifically. As a corollary, the mass-specific N:P excretion ratio was positively related to body N:P ratio. Such a contrasting pattern on excretion-mediated N and P recycling suggests that stoichiometric constraints regarding consumer-resource imbalances for the three species utilized in this study may be stronger for P than for N. Our results indicate that the variation in nutrient recycling, which is mediated by taxonomic constraints on stoichiometry and allometry, may substantially help us to understand the importance of benthic detritivorous species to the functioning of aquatic ecosystems.

Benthic bioturbator enhances CH4 fluxes among aquatic compartments and atmosphere in experimental microcosms

We utilized laboratory microcosms to evaluate the effects of a benthic sediment bioturbator (Heteromastus similis; Polychaeta; conveyor-belt deposit feeder) on vertical distributions of CH4 in sediment and net CH4 fluxes across sediment-water-air interfaces. The effect of H. similis on sediment CH4 concentration ((CH4)) varied depending on sediment depth and was strongest at higher animal densities. In comparison with defaunated controls, microcosms with the highest density of H. similis exhibited an increase in (CH4) of 3.7-fold, on average, at the sediment surface (0- 2 cm), but these concentrations decreased by ~2-fold in deeper sediment layers (2-8 cm). However, irrespective of sediment depth, the density of H. similis resulted in an overall nonlinear reduction of bulk sediment (CH4). Most of the observed CH4 losses from the sediment were due to CH4 oxidation, but the bioturbatory activities of H. similis also promoted significant increases in (CH4) in both the water column and the microcosm headspace. These results suggest that benthic invertebrates can mediate CH4 turnover between compartments in aquatic ecosystems, with further consequences for the coupling between benthic-pelagic food chains via the methanotrophic-mediated microbial loop, as well as increase CH4 emissions to the atmosphere.

The role of Campsurus notatus (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

About 30% of the total area of Lake Batata (Amazon) was impacted by the disposal of bauxite tailings originated from the process of washing bauxite. This effluent, composed by fine particles of clay and water, settled on top of the natural sediment, originating a new substratum with a different physical and chemical composition. This phenomenon created a new distinct habitat (impacted sediment) influencing the benthic community. The aim of this study was to evaluate the impact of bioturbation by Campsurus notatus (Ephemeroptera: Polymitarcytidae) on potential gas fluxes in the sediment of natural and impacted areas of the lake. The natural sediment had a significantly higher methane concentration when compared to the impacted one. In incubated sediment cores, the presence of C. notatus nymphs resulted in a significant increase in oxygen consumption and methane and carbon dioxide release to the water column. The effect of the presence of nymphs on methane was ambiguous. The C. notatus nymphs strongly decreased methane concentration in natural sediment samples, probably because of the enhancement of the oxic sediment area. However, this effect was not observed in impacted samples. Finally, the new substratum of Lake Batata decreased methane concentration in sediment and water column. C. notatus nymphs demonstrated to have a significant role on gas flux (methane and CO2) from sediment to water column as well as on oxygen consumption in Lake Batata, consequently influencing the carbon cycle in this lake.

Community structure of resting egg banks and concordance patterns between dormant and active zooplankters in tropical lakes

Little effort has been devoted to characterizing the resting egg banks in tropical lakes. In this study, we evaluated the structure of egg banks across 26 Brazilian lakes located in four geographical regions. We also evaluated cross-taxon concordance in species richness and community similarity between dormant rotifers and dormant cladocerans, and searched for concordant patterns between dormant and active communities. We observed 88 taxa among all the hatchlings that belonged mainly to rotifers and cladocerans. Lakes located in the same geographical region displayed more similar dormant communities. Overall, no concordance was observed between dormant rotifers and dormant cladocerans. Concordance in community similarity was observed between dormant and active organisms but only for rotifers and the entire zooplankton community. Resting egg banks were not associated to a set of environmental variables. Our results demonstrate the occurrence of resting egg banks in several tropical lakes. Due to the weak concordant patterns, rotifers or cladocerans found in egg banks should be used cautiously as a surrogate of the other group in zooplankton surveys. Finally, the lack of strong concordance between the active and dormant stages of cladocerans suggests that some species may not receive appropriate cues to induce diapause.

Twenty-Five Years of Restoration of an Igapó Forest in Central Amazonia, Brazil

This chapter describes a 25-year experience of restoration of a vast area impacted by a bauxite tailings spill over Lake Batata and its marginal igapo vegetation in Central Amazonia. It reviews papers and theses produced during this period and aims to provide a view of the restoration process from the past into the future. The main conclusions of this long-term restoration effort are: (1) Despite the sterility and difficult penetrability of the consolidated tailings substrate, igapo plants have been capable to establish and grow spontaneously in these areas, reaching reproductive stage and completing full life cycles; (2) Wherever natural regeneration was not possible, either due to topographic reasons or to water movements, human intervention by planting seedlings was also viable; (3) In areas subjected to longer term flooding (>8–9 months a year), planting is either physically not possible or, whenever possible, saplings die; (4) Natural regeneration and planting, altogether, were responsible for returning species richness and diversity to impacted areas, but floristic similarity with native, nonimpacted sites was moderate to low; this established vegetation produces shade, litter, organic matter and thus create new habitats and organic substrate for other species to establish naturally; (5) Recuperation is variable depending on site characteristics (annual length of flooding, species introduced, etc.) but often slow and in worse case scenarios new forests may take more than 75 years to converge to similarity with native nonimpacted igapo; thus, additional interventions are necessary to further forest growth, structure and diversity; (6) Despite the challenges posed by the scale of this enterprise, relevant actions to speed up successional trajectory are feasible, necessary and include continuous monitoring and evaluation, litter and seed addition, and selection of framework species for replacements.

Interactive effects of climate change and biodiversity loss on ecosystem functioning

Climate change and biodiversity loss are expected to simultaneously affect ecosystems, however research on how each driver mediates the effect of the other has been limited in scope. The multiple stressor framework emphasizes non-additive effects, but biodiversity may also buffer the effects of climate change, and climate change may alter which mechanisms underlie biodiversity-function relationships. Here, we performed an experiment using tank bromeliad ecosystems to test the various ways that rainfall changes and litter diversity may jointly determine ecological processes. Litter diversity and rainfall changes interactively affected multiple functions, but how depends on the process measured. High litter diversity buffered the effects of altered rainfall on detritivore communities, evidence of insurance against impacts of climate change. Altered rainfall affected the mechanisms by which litter diversity influenced decomposition, reducing the importance of complementary attributes of species (complementarity effects), and resulting in an increasing dependence on the maintenance of specific species (dominance effects). Finally, altered rainfall conditions prevented litter diversity from fueling methanogenesis, because such changes in rainfall reduced microbial activity by 58%. Together, these results demonstrate that the effects of climate change and biodiversity loss on ecosystems cannot be understood in isolation and interactions between these stressors can be multifaceted.