José Francisco Gonçalves Júnior

Temporal dynamics of allochthonous coarse particulate organic matter in a subtropical Atlantic rainforest Brazilian stream

Allochthonous organic matter is a major energy source for headwater stream ecosystems. Therefore, examinations of how energy flows throughout these streams requires knowledge of mechanisms driving leaf input, retention and export. In this study we quantified the major input pathways and retention dynamics of coarse particulate organic matter (CPOM) in an Atlantic Rainforest stream in southern Brazil. We hypothesised that much of the temporal variability in the CPOM budget would be driven by precipitation, and thus we focus especially on the importance of vertical v. lateral input pathways, precipitation-driven inputs v. stocks, and composition of CPOM throughout 1 year. Most leaf litter entered the stream by the lateral input pathway (70.5gm–2month–1±108s.d.) compared with the vertical (32.4gm–2 month–1 ±17.5s.d.), and lateral input was correlated with precipitation and bank slope. In addition, torrential rainfall caused a net decrease in CPOM by reduction in the benthic stocks. Finally, six species represented 52.9% of total leaf input, where the most important (~25% of total input) was Schizolobium parahyba. Overall, this research confirms our prediction that the CPOM budget of this Atlantic Rainforest stream is driven in large part by precipitation.

Experimental assessment of temperature increase and presence of predator carcass changing the response of invertebrate shredders

The role of the invertebrate shredders in leaf decomposition process in tropical lotic ecosystems has been explored only recently. In addition to the influence of the quality of litter and the temperature, the risk of predation generally results in changes on the survival and behavior of invertebrate shredders. The aim of this study was to observe the responses of the invertebrate shredders to different species of leaf litters (Experiment 1: Talauma ovata and Inga laurina ; Experiment 2: Talauma ovata, Inga laurina and Richeria grandis ) under gradual temperature rise (24 °C, 26 °C, 28 °C, 30 °C, 32 °C), in the presence (Experiment 2) and absence (Experiment1) of fish (Astyanax sp.) carcasses, as well as to observe the possible consequences of the leaf mass loss (LML). The results from the first experiment suggest that the quality of the litter was capable of changing the feeding preference of the invertebrate shredders, regardless of temperature. In the second experiment, the leaf mass loss was faster in litter with higher quality (Talauma ovate and Richeria grandis ); in addition, we observed that the exploration of these resources resulted in the case-building in the presence of fish carcass. The negative correlation of leaf mass loss of Inga laurina in relation to temperature in the presence of fish carcass probably occurred due to an accelerated metabolic, respiratory and cardiac rates. Apparently, this process may have led to an increased shredding activity on the litters of better quality in relation to the Inga laurina. This fact may be related to less energy consumption, so as to meet their energy demands more efficiently.

Future ecological studies of Brazilian headwater streams under global-changes

Este artigo resulta de discussoes ocorridas durante o Simposio de Ecologia de Riachos que aconteceu durante o XIII Congresso da Sociedade Brasileira de Limnologia em setembro de 2011 em Natal, Brasil. Baseados em nossa experiencia, propomos algumas perguntas sobre ecologia de riachos na perspectiva de mudancas globais e sugerimos alguns aspectos a serem abordados em futuros estudos no pais. Esses estudos estao relacionados a necessidade de se conhecer a biologia das especies; a elaboracao de modelos para avaliar as mudancas (o que implica a necessidade de um grande volume de dados em larga escala temporal e espacial); a ecologia das zonas ribeirinhas e o intercâmbio de materiais e energia atraves das interfaces terra-agua; as alteracoes na cobertura florestal e estrategias de amostragem e tratamento de dados padronizados para avaliar as mudancas globais.

Microbial effects in leaf breakdown in tropical reservoirs of different trophic status

Abstract.  The objective of our study was to compare leaf breakdown rates (k) and the influence of microorganisms and aquatic invertebrates on mass loss of Eichhornia crassipes (Mart.) Solms and Typha domingensis Pers in 2 reservoirs (eutrophic and oligotrophic). We hypothesized that k would be higher in eutrophic than in oligotrophic conditions because of increased microbial activity in eutrophic conditions. We collected green leaves, which we air-dried, weighed, placed in litter bags, and incubated in each reservoir. We calculated k (negative exponential model) for each species in each reservoir. We characterized initial leaf chemistry, estimated total microbial biomass (as adenosine triphosphate [ATP]) and fungal biomass (as ergosterol), and evaluated invertebrate community composition and structure. Both species decomposed faster in the eutrophic reservoir. During leaf breakdown, bacteria were more important in the eutrophic reservoir, whereas fungi were more important in the oligotrophic reservoir. Invertebrate communities differed between reservoirs, but invertebrates did not affect k in either reservoir. Our results indicate that leaf breakdown may have been accelerated by greater nutrient availability and variations in O2 concentration and water temperature that increased microbial community metabolism in the eutrophic reservoir. Typha domingensis held nutrients in its tissues for longer than E. crassipes, and might be useful for management of nutrients in reservoirs, whereas E. crassipes decomposed rapidly and would not be useful for controlling eutrophication.

Leaf litter input and electrical conductivity may change density of Phylloicus sp. (Trichoptera: Calamoceratidae) in a Brazilian savannah stream

Objetivo Invertebrados fragmentadores sao geralmente escassos em riachos tropicais, com evidencias consideraveis sugerindo que a disponibilidade de recursos alimentares possa determinar esse padrao em riachos de cabeceira. O objetivo desse estudo foi avaliar os efeitos de variacoes na disponibilidade de recursos alimentares durante um ano na densidade Phylloicus sp. (Trichoptera: Calamoceratidae), o qual esta entre os principais invertebrados fragmentadores em riachos de cabeceira neotropicais. Metodos Medimos a importância relativa da materia orgânica vegetal aloctone em termos de entrada vertical (EV) e estoque bentico (EB) na densidade de Phylloicus sp., entre outubro de 2012 e setembro de 2013, em um riacho preservado de terceira ordem no Cerrado, Distrito Federal, Brasil. Resultados Folhas foi a fracao mais abundante na EV e EB (~70%). A biomassa de folhas foi alta durante todo o ano (biomassa mensal de 24,2 g.m–2 ±23,1 SD na EV e 46,1 g.m–2 ±76,7 SD no EB), aumentando ao final da estacao seca (agosto a outubro). Phylloicus sp. Teve baixa densidade durante o ano (2,4 ± 4,9 ind.m–2 media±DP) e seu pico foi associado a maior biomassa de folhas na EV e maior condutividade eletrica no riacho. O pico bem definido de Phylloicus sp. em outubro sugere uma interacao entre o aumento densidade de Phylloicus sp. e a entrada de folhas no final da estacao seca. A condutividade eletrica tambem foi maior em outubro, refletindo um aumento nas concentracoes de nutrientes na agua durante esse periodo. Conclusoes A disponibilidade de detritos foliares pode ser um fator determinante para a densidade sazonal de Phylloicus sp., sugerindo um efeito bottom-up em riachos tropicais. Mudancas no suprimento de recursos aloctones em riachos podem afetar as populacoes de fragmentadores como Phylloicus sp. e influencias antropogenicas na vegetacao riparia podem afetar processos ecologicos de grande importância para riachos de cabeceira.

Top-down and bottom-up control of epilithic periphyton in a tropical stream

Tropical forests are characterized by high tree biomass that forms a dense canopy, thereby reducing the amount of light that reaches forest streams. Forest streams are likely to receive large amounts of organic matter in the form of leaf litter and also have low primary production relative to more open forested systems. Forest clearing can, therefore, affect the in-stream carbon cycle by increasing carbon immobilization and decreasing mineralization. We addressed the question of whether heavily shaded streams are bottom-up limited by light and nutrients or top-down limited by grazers. To answer these questions, we experimentally manipulated nutrients and grazers in enclosures established in either a shaded or a partially open stretch of an Atlantic Forest stream in Brazil. Algal biomass in this stream was low (51.5 to 367.2 mg Chl a /m2). Prior tree removal resulted in a 58% increase in light in the semi-open stream area, and enclosures in this area had a 2.7× increase in algal biomass and a 4× increase in primary production (from 10–40 mg C m−2 d−1) relative to enclosures in shaded areas. Nutrient (P) addition had no effect on algal standing crop. Grazing by the caddisfly Helicopsyche caused a ∼50% reduction in algal biomass. The addition of the most abundant predator, the stonefly Anacroneuria, to the enclosures did not reduce feeding by Helicopsyche. Substrates in the shaded and semi-open stretches differed in the dominance of some algal taxa, and grazing appeared to favor the cyanobacteria Dolichospermum sp. over diatoms. We conclude that algae in forested, low-order streams in the Atlantic Forest are limited by both top-down (herbivory) and bottom-up (light) factors. These findings suggest that tree removal in riparian areas can cause small changes to light availability in streams, but that even small changes can have profound effects on primary producers and, therefore, energy supply for stream consumers.

Effects of increasing temperature and, CO2 on quality of litter, shredders, and microorganisms in Amazonian aquatic systems

Climate change may affect the chemical composition of riparian leaf litter and, aquatic organisms and, consequently, leaf breakdown. We evaluated the effects of different scenarios combining increased temperature and carbon dioxide (CO2) on leaf detritus of Hevea spruceana (Benth) Müll. and decomposers (insect shredders and microorganisms). We hypothesized that simulated climate change (warming and elevated CO2) would: i) decrease leaf-litter quality, ii) decrease survival and leaf breakdown by shredders, and iii) increase microbial leaf breakdown and fungal biomass. We performed the experiment in four microcosm chambers that simulated air temperature and CO2 changes in relation to a real-time control tracking current conditions in Manaus, Amazonas, Brazil. The experiment lasted seven days. During the experiment mean air temperature and CO2 concentration ranged from 26.96 ± 0.98ºC and 537.86 ± 18.36 ppmv in the control to 31.75 ± 0.50ºC and 1636.96 ± 17.99 ppmv in the extreme chamber, respectively. However, phosphorus concentration in the leaf litter decreased with warming and elevated CO2. Leaf quality (percentage of carbon, nitrogen, phosphorus, cellulose and lignin) was not influenced by soil flooding. Fungal biomass and microbial leaf breakdown were positively influenced by temperature and CO2 increase and reached their highest values in the intermediate condition. Both total and shredder leaf breakdown, and shredder survival rate were similar among all climatic conditions. Thus, low leaf-litter quality due to climate change and higher leaf breakdown under intermediate conditions may indicate an increase of riparian metabolism due to temperature and CO2 increase, highlighting the risk (e.g., decreased productivity) of global warming for tropical streams.

Connecting the litterfall temporal dynamics and processing of coarse particulate organic matter in a tropical stream

We collected leaf litter monthly and analysed how the temporal dynamics of litterfall affect the breakdown rates, microbial and fungal biomass and aquatic invertebrate community in a tropical stream in southern Brazil. The results showed that total annual litterfall varied over time and was negatively associated with rainfall. Litter fell mostly in the spring months, but other peaks occurred throughout the year. In all, 122 tree species were identified; however, only seven represented >70% of the total of leaf litter vertical input. Leaf decomposition was higher in February and April (wet, warm months) than during the wet season. Fungal biomass was high in decomposing leaves (460±28μgg–1 of ash-free dry mass, AFDM), with a maximum of 655μgg–1 AFDM in July. Microbial biomass in decomposing leaves was lower (326±27 nmol g–1 AFDM), with a maximum of 504 nmol g–1 AFDM in October. Monthly variability in the fungal and microbial biomass and aquatic invertebrate colonisation were associated with litter quality. The results suggested that litterfall is the result of regional environmental factors and characteristics of the riparian vegetation and that modifications in the quality, quantity and timing of the delivery of litter input to the stream affect activity in the decomposer community, which then affects monthly litter-breakdown rates.