Leaf Packs Research Articles

Decomposition and benthic macroinvertebrate communities of exotic Japanese knotweed (Fallopia japonica) and American sycamore (Platanus occidentalus) detritus within the Susquehanna River

ABSTRACTThe invasive shrub Japanese knotweed (Fallopia japonica) is spreading through riparian forests in Central Pennsylvania. There is concern that detritus from this species may impact adjacent aquatic ecosystems, as allocthonous material forms the basis for aquatic food webs and may impact benthic community structure. This study compares key ecosystem processes within Japanese knotweed leaf litter to leaf litter of a native riparian species, American sycamore (Platanus occidentalis). We assess benthic macroinvertebrate communities and decomposition rates within experimental Japanese knotweed and American sycamore leaf packs at three sites within the Susquehanna River. Japanese knotweed detritus hosted a similar macroinvertebrate community to American sycamore and their assemblages had similar representation of functional feeding groups. The similarity between the invertebrate communities occupying American sycamore and Japanese knotweed detritus indicates that macroinvertebrates are able to utilize non-native litter for habitat and potentially as an energy source. American sycamore decomposed at a faster rate than Japanese knotweed, lending support to the Novel Weapons Hypothesis, which suggests that non-native species like Japanese knotweed may inhibit microbial colonization and subsequent litter breakdown. Our results suggest that invasion of Japanese knotweed along riparian corridors of large river systems may not have severe ecological consequences on local ecosystem processes.

STUDY ON MACROZOOBENTHOS COMMUNITY IN THE WATERS OF THE RIVER AIR PERIKAN MUNICIPALITY OF PAGAR ALAM SOUTH SUMATRA

The research entitled “ Study on Macrozoobenthos Community in the Waters of the River Air Perikan Pagar Alam Municipality”, was conducted from November 2007 until March 2008. The aims of the research: to know about composition, density, diversity index, dominancy index, and similarity index, which based on the different microhabitat types. Sampling was carried out on November 2007. Five sampling stations were determined by survey method and the Purposive Sampling method was used at each sampling point to find stony, gravel, sandy and leaf pack area as a different microhabitat substrate. Twenty one orders (Ephemeroptera, Trichoptera, Diptera, Plecoptera, Collembola, Hemiptera, Odonata, Coleoptera, Lepidoptera, Megaloptera, Hymenoptera, Orthoptera, Decapoda, Plesiopora, Tricladida, Amphipoda, Isopoda, Mesogastropoda, Ctenobranchiata, Eulamellibranchiata, and Rhynchobdellida) which are consisted of 70 families and 151 genera were identified from four types of substrates on each sampling station. According to this research, station 4 has the highest in composition (80 genera), and the lowest one at station 1(33 genera). The highest abundance was 12589 ind./m2 found in the station 5, and the lowest one was in the station 1 approximately 880 ind./m2. For the diversity index value, station 3 was the highest (3.1) and the lowest one was station 5 (1.9). The Dominancy index was found in station 5 at the sandy substrates was approximately 0,8 index, which dominated by Tubifex sp. There were differences species composition on each station. Keywords : Macrozoobenthos, community, the river Air Perikan.

Leaf litter additions enhance stream metabolism, denitrification, and restoration prospects for agricultural catchments

AbstractGlobally intensive agriculture has both increased nitrogen pollution in adjacent waterways and decreased availability of terrestrially derived carbon frequently used by stream heterotrophs in nitrogen cycling. We tested the potential for carbon additions via leaf litter from riparian restoration plantings to act as a tool for enhancing denitrification in agricultural streams with relatively high concentrations of nitrate (1.3–8.1 mg/L) in Canterbury, New Zealand. Experimental additions of leaf packs (N = 200, mass = 350 g each) were carried out in 200‐m reaches of three randomly selected treatment streams and compared to three control streams receiving no additional leaf carbon. Litter additions increased ecosystem respiration in treatment streams compared to control streams but did not affect gross primary production, indicating the carbon addition boosted heterotrophic activity, a useful gauge of the activities of microbes involved in denitrification. Bench‐top assays with denitrifying enzymes using acetylene inhibition techniques also suggested that the coarse particulate organic matter added from leaf packs would have provided substrates suitable for high rates of denitrification. Quantifying denitrification directly in experimental reaches by open‐channel methods based on membrane inlet mass spectrophotometry indicated that denitrification was around three times higher in treatment streams where litter was added compared to control streams. We further assessed the potential for riparian plantings to reduce large‐scale downstream nitrogen losses through increasing in‐stream denitrification by modeling the effects of increasing riparian vegetation cover on nitrogen fluxes. Here, we combined estimates of in‐stream ecosystem processes derived from our experiment with a network model of catchment‐scale nitrogen retention and removal based on empirical measurements of nitrogen flux in this typical agricultural catchment. Our model indicated leaf inputs associated with increased riparian cover had the potential to double the catchment level rate of denitrification, offering a promising way to mitigate nitrate pollution in agricultural streams. Altogether, our study indicates that overcoming carbon limitation and boosting heterotrophic processes will be important for reducing nitrogen pollution in agricultural streams and that combining empirical approaches for predictions suggests there are large potential benefits from riparian re‐vegetation efforts at catchment scales.

Relationships of shredders, leaf processing and organic matter along a canopy cover gradient in tropical streams

Terrestrial allochthonous organic matter represents a structuring element and an important source of energy and carbon to fauna in small forested streams. However, the role of this matter as a food resource for benthic macroinvertebrates, and consequently, for shredders and their performance in riverine processes, is not clear in low-order tropical streams. Aiming to investigate the relationship between shredders and leaves, we analyzed along a gradient of 8-93% canopy cover biomass and abundance of shredders, accumulated leaves and breakdown rates of local leaves to verify if these parameters were related to shade conditions and to each other. Three hypotheses were tested: i) shredder biomass, accumulated leaves and breakdown rates are related to canopy cover and exhibit higher values in shaded sites; ii) shredder biomass is positively related to accumulated leaves and breakdown rates; and iii) due to the relatively large body size of the important shredders, the association of shredders with leaves and importance to leaf processing should be better expressed in terms of guild biomass than abundance. Shredder biomass varied between 846 and 1506 mg DM m‑2 and accumulated leaves varied between 479 and 1120 g AFDM m-2 across sites. Leaf breakdown rate (k), the only measured variable that varied significantly among sites, varied between -0.0015 and -0.0238 day-1. Neither shredder biomass nor leaf biomass were associated with the shading gradient. On the other hand, shredder abundance and biomass, mainly represented by Triplectides (Trichoptera, Leptoceridae), was positively related to accumulated leaves within sites and to breakdown rates assessed by leaf packs. Leaf breakdown, as assessed by the experimental leaf packs, was associated with shredder biomass, but not with shredder abundance. This result suggests that macroinvertebrates are important for leaf detritus processing and that their biomass reflects their activity, presumably because it is related to their secondary production and perhaps non-consumptive action. Their activity was observed at the scale of leaf packs and not at the scale of variation in canopy cover because apparently canopy did not modulate availability of leaves, which were apparently not limiting to the shredders.

Responses of aquatic food webs to the addition of structural complexity and basal resource diversity in degraded Neotropical streams

AbstractThe loss of riparian forests can disrupt the structure and function of lotic ecosystems through increased habitat homogenization and decreased resource diversity. We conducted a field experiment and manipulated structural complexity and basal resource diversity to determine their effect on multiple aspects of community and food‐web structure of degraded tropical streams. In‐stream manipulations included the addition of woody debris (WD) and the addition of wood and leaf packs (WLP). The addition of structural complexity to degraded streams promoted detritus retention and had a positive effect on stream taxonomic richness, abundance and biomass. At the conclusion of the experiment, abundance and richness in the WD‐treated reaches increased by over 110% and 80%, respectively, while abundance and richness in the WLP‐treated reaches increased by over 280% and 170% respectively. Wood debris and leaves were consumed only by few taxa. Detritivorous taxa were the most abundant trophic guild at the beginning and at the end of the experiment. Food webs in treated reaches were relatively more complex in terms of links and species at the conclusion of the experiment, with highest maximum food chain length in the WD treatments and highest number of trophic species, links, link density, predators and prey at the WLP treatment. Despite differences observed in diet‐based food webs, there was little variation in isotopic niche space, likely due to the high degree of omnivory and trophic redundancy, which was attributed to the importance of fine detritus that supported a broad range of consumers. Even in these degraded streams, aquatic taxa responded to the addition of increased complexity suggesting that these efforts may be an effective first step to restoring the structure and function of these food webs.

Impact of Macroconsumers on Leaf Breakdown and Detritivores in Wetlands on a Southeastern US Coastal Plain Floodplain during Drought

Interactions between macroconsumers (predators and large omnivores) and detritus breakdown on river floodplains are poorly understood, yet important to ecosystem function. We evaluated the impact of macroconsumers on leaf breakdown, macroinvertebrate abundance and biomass, and fungal biomass on a river floodplain using exclosures in 6 wetlands during a severe drought during which the floodplain was disconnected from the river. Sweetgum (Liquidambar styraciflua) leaves were held in both mesh bags and in leaf packs within each exclosure. After 301 days, breakdown rates (k) were slow and did not significantly differ between treatments. Fungal biomass and total macroinvertebrate abundance and biomass also did not significantly differ between treatments. Collector-gatherers were significantly more abundant in treatments open to macroconsumers in mesh bags. Shredders had significantly higher biomass in packs held in exclosures closed to macroconsumers, but were rare. A subsequent exclosure experiment in one flooded wetland mimicked stream-floodplain connectivity despite drought. Pre-conditioned leaves in mesh bags open to macroconsumers had significantly faster breakdown than those closed to macroconsumers. Abundance of total macroinvertebrates, scrapers and predators were higher in treatments open to macroconsumers. These results indicate that the role of macroconsumers on floodplains varies depending on river connectivity and water availability.

Regionalisation is key to establishing reference conditions for neotropical savanna streams

Areas with minimal anthropogenic influences are frequently used as reference sites and represent the best ecological state available in a region. Streams in such conditions are necessary for evaluating the conservation status of aquatic ecosystems of a region and to monitor them, taking natural environmental variability into consideration. Therefore, the aim of the present study was to analyse whether hydrological units are reliable regional units for aggregating reference sites. To this end, reference sites were studied in three different landscape units of the same hydrological unit. The study tested the hypothesis that water quality, physical habitat structure and the composition and structure of macroinvertebrate assemblages will be more similar for sites in the same landscape unit than for sites located in different landscape units in the same hydrological unit. The study showed that taxonomic richness and composition of the macroinvertebrate assemblages were negatively affected by site slope and positively affected by the presence of leaf packs on the streambed. The three landscape units supported significantly different macroinvertebrate assemblages and indicator taxa. Therefore, a hydrological unit does not constitute a homogeneous entity in terms of environmental variables and biological composition if it incorporates high landscape heterogeneity. These results should improve and facilitate the selection of reference sites for biomonitoring programs and for managing tropical headwater streams.

Long-term maintenance requirements of the riparian isopod, Lirceus sp.

Riparian isopods possess many traits that make them ideal candidates for a wide range of ecological and evolutionary studies, but they are under-utilized because long-term maintenance under laboratory conditions has been largely unsuccessful. We explored a variety of experimental conditions to determine those necessary to maintain captive populations. Our studies demonstrated that starting colonies with water from the natal stream, filtering the water in a way that causes agitation at the surface of the water, maintaining colonies in full-spectrum light at room temperature or colder, lining the bottom of containers with a coarse benthos, and providing a leaf pack that contains Norway maple leaves are important criteria for successful maintenance of individuals of Lirceus sp. colonies for periods of over 6 weeks in the laboratory. Water changes do not require addition of water from the natal stream, whether the containers are glass or plastic is inconsequential, aeration does not need to be high-powered, and refrigeration of colonies is not necessary for this species of riparian isopod. We expect identifying the minimum husbandry needs will facilitate research using these organisms.

Determination of food sources and trophic position in Malaysian tropical highland streams using carbon and nitrogen stable isotopes

Stable isotope analysis has been extensively used as an effective tool in determination of trophic relationship in ecosystems. In freshwater ecosystem, aquatic invertebrates represent main component of a river food web. This study was carried out to determine potential food sources of freshwater organism together with pattern of trophic position along the river food web. In this study, rivers of Belum-Temengor Forest Complex (BTFC) has been selected as sampling site as it is a pristine area that contains high diversity and abundance of organisms and can be a benchmark for other rivers in Malaysia. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were applied to estimate trophic position and food web paradigm. Analysis of stable isotopes based on organic material collected from the study area revealed that the highest δ13C value was reported from filamentous algae (−22.68±0.1260/00) and the lowest δ13C was in allocthonous leaf packs (−31.58±0.1870/00). Meanwhile the highest δ15N value was in fish (8.45±0.1770/00) and the lowest value of δ15N was in autochthonous aquatic macrophyte (2.00±1.2340/00). Based on the δ15N results, there are three trophic levels in the study river and it is suggested that the trophic chain begins with organic matter followed by group of insects and ends with fish (organic matter<insects<fish).

Wildfire in boreal forest catchments influences leaf litter subsidies and consumer communities in streams: Implications for riparian management strategies

Applying the emerging paradigm of emulation of natural disturbances (END) to forest management requires understanding of how the riparian-aquatic interface responds to natural forest disturbances. A comparison of riparian forest condition and stream function was conducted across boreal, headwater streams with wildfire, harvest with minimum 30m riparian buffers, and reference forested catchment histories. We assessed riparian vegetation characteristics, leaf litter inputs to streams, instream leaf litter decomposition rates using leaf packs, and aquatic macroinvertebrates that colonized the leaf packs. Riparian shrub and juvenile woody-stem community structure was significantly more taxonomically rich and compositionally different at fire than reference sites. Mature tree densities at reference sites were 1.7× and 4× higher than at harvested and fire, respectively. Leaf litter input from riparian forests to streams was significantly greater and compositionally dissimilar at fire compared to harvested and reference sites. Although decomposition of speckled alder (Alnus icana ssp. rugosa) in the leaf packs did not differ significantly among study reaches, the aquatic invertebrate communities found in the leaf packs at fire sites were characterized by significantly higher taxa richness and unique shredder taxa. Detectable differences in riparian forest condition and instream processes suggest that forest management under the END paradigm could sustain ecosystem services (the support of aquatic biodiversity) by inducing riparian forest succession, enhancing leaf litter inputs and organic matter processing, and promoting riparian habitat complexity.

Computational Fluid Dynamics and Thermal Analysis of Leaf Seals for Aero-engine Application

Aero-engine gas turbine performance and efficiency can be improved through the application of compliant shaft seal types to certain sealing locations within the secondary air system. Leaf seals offer better performance than traditional labyrinth seals, giving lower leakage flows at design duties. However, for aero-engine applications, seal designs must be able to cope with relatively large off-design seal closures and closure uncertainties. The two-way coupling between temperatures of seal components and seal closures, through the frictional heat generated at the leaf–rotor interface when in contact, represents an important challenge for leaf seal analysis and design. This coupling can lead to leaf wear and loss, rotor overheating, and possibly to unstable sealing system behavior (thermal runaway). In this paper, we use computational fluid dynamics (CFD), finite element (FE) thermal analysis, and experimental data to characterize the thermal behavior of leaf seals. This sets the basis for a study of the coupled thermomechanical behavior. CFD is used to understand the fluid-mechanics of a leaf pack. The leaf seal tested at the Oxford Osney Laboratory is used for the study. Simulations for four seal axial Reynolds number are conducted; for each value of the Reynolds number, leaf tip-rotor contact, and clearance are considered. Distribution of mass flow within the leaf pack, distribution of heat transfer coefficient (HTC) at the leaf surface, and swirl velocity pick-up across the pack predicted using CFD are discussed. The experimental data obtained from the Oxford rig is used to develop a set of thermal boundary conditions for the leaf pack. An FE thermal model of the rig is devised, informed by the aforementioned CFD study. Four experiments are simulated; thermal boundary conditions are calibrated to match the predicted metal temperatures to those measured on the rig. A sensitivity analysis of the rotor temperature predictions to the heat transfer assumptions is carried out. The calibrated set of thermal boundary conditions is shown to accurately predict the measured rotor temperatures.

Ephemeroptera, Plecoptera and Trichoptera (Insecta) Abundance, Diversity and Role in Leaf Litter Breakdown in Tropical Headwater River.

Leaf litter decomposition in a tropical stream was examined in two types of leaf packs; single species leaf packs of Pometia pinnata and two species leaf packs of equal combination of Pometia pinnata and Dolichandrone spathacea leaves. Both leaf packs were immersed in a river and weekly examined for remains of decomposed leaves and presence of EPT. In the control leaf packs, leaves in the two species leaf packs treatments decomposed within 35 days, faster than in single species leaf packs which decomposed after 42 days. In the presence of EPT, the leaf breakdown took 28 days in two species and 35 days for single species leaf packs. Higher abundance of EPT was observed in single species leaf packs but its diversity was higher in two species leaf packs. Litter breakdown in the stream was faster in the presence of EPT and softer leaves of D. spathacea with higher nitrogen content underwent faster decomposition and sustained higher numbers of EPT.

Shifts in shredder communities and leaf breakdown along a disrupted stream continuum

AbstractStream ecosystem functions are predicted to vary longitudinally along a stream network as a result of changes in physical and biotic processes. Conversion by headwater communities of allochthonous materials, such as leaves, into readily available sources of energy is an essential process for maintenance of downstream communities. We investigated how location along a stream continuum, the presence of a dam, and leaf type affected leaf breakdown. We placed yellow birch (Betula alleghaniensis), sugar maple (Acer saccharum), and white oak (Quercus alba) leaf packs in Sims Creek (North Carolina, USA), at a 1st-order site, a 2nd-order site above a dam, and a 2nd-order site immediately below this dam. Leaf breakdown rates of all species were slower at the above-dam than at the headwater site, and breakdown rates for birch and maple were lower at the below- than the above-dam site. Detritivore composition and abundance differed among sites. Leaf packs had lower detritivore abundance at the below- than the...

CO2-driven experimental acidification effects on aquatic macroinvertebrates in a tropical stream

ABSTRACTExperimental acidification of a tropical stream was conducted to measure the effects of declining pH on aquatic macroinvertebrates. The mechanisms by which anthropogenic acidification occur in a freshwater stream system are relatively well understood, while little is known about the natural phenomena of acidification or the corresponding effects on macroinvertebrate assemblages. Previous studies have attempted to model stream acidification using strong acids; however, this is one of the first studies which models stream acidification using the addition of gaseous CO2. This method is a more natural means of modeling stream acidification conditions arising from increased levels of dissolved CO2. We hypothesized that if experimental acidification was expressed most strongly at the injection site and produced a pH gradient downstream, macroinvertebrates should respond to the gradient and employ an escape mechanism to avoid the adverse conditions. Three macroinvertebrate sampling strategies were used: drift nets, leaf pack samples and benthic Surber samples. Samples were evaluated in the lab for macroinvertebrate abundance and taxonomic richness per m3 for drift net samples and benthic samples, and per g leaf material in the leaf pack samples. A maximum decline of 2 units in pH along a gradient was observed associated with the injection of CO2. Results obtained from drift net and benthic sample analysis were inconclusive, possibly because of low stream flow, although analysis of the leaf pack samples indicates lower macroinvertebrate composition at areas of lower pH. The leaf pack samples also show significant macroinvertebrate sensitivity to the most severe pH decline at the injection site.

Analytical Modeling and Experimental Validation of Heating at the Leaf Seal/Rotor Interface

The secondary air system of a modern gas or steam turbine is configured to satisfy a number of requirements, such as to purge cavities and maintain a sufficient flow of cooling air to key engine components, for a minimum penalty on engine cycle efficiency and specific fuel consumption. Advanced sealing technologies, such as brush seals and leaf seals, are designed to maintain pressures in cavities adjacent to rotating shafts. They offer significant reductions in secondary air parasitic leakage flows over the legacy sealing technology, the labyrinth seal. The leaf seal comprises a series of stacked sheet elements which are inclined relative to the radial direction, offering increased axial rigidity, reduced radial stiffness, and good leakage performance. Investigations into leaf seal mechanical and flow performance have been conducted by previous researchers. However, limited understanding of the thermal behavior of contacting leaf seals under sustained shaft contact has led to the development of an analytical model in this study, which can be used to predict the power split between the leaf and rotor from predicted temperature rises during operation. This enables the effects of seal and rotor thermal growth and, therefore, implications on seal endurance and rotor mechanical integrity to be quantified. Consideration is given to the heat transfer coefficient in the leaf pack. A dimensional analysis of the leaf seal problem using the method of extended dimensions is presented, yielding the expected form of the relationship between seal frictional power generation, leakage mass flow rate, and rotor temperature rise. An analytical model is derived which is in agreement. Using the derived leaf temperature distribution formula, the theoretical leaf tip temperature rise and temperature distributions are computed over a range of mass flow rates and frictional heat values. Experimental data were collected in high-speed tests of a leaf seal prototype using the Engine Seal Test Facility at Oxford University. These data were used to populate the analytical model and collapsed well to confirm the expected linear relationship. In this form, the thermal characteristic can be used with predictions of mass flow rate and frictional power generated to estimate the leaf tip and rotor temperature rise in engine operation.

Assessment of Decay Coefficients of Allochthonous Litter for Sustainable Riparian Forage Agriculture and Environmental Monitoring: A Study in River Nyangores, Kenya

Research on decay profiles of grass detritus in lotic systems has received little attention in preceding years. An investigation was conducted on in-situ processing coefficients for three dominant forage species grown by farmers along the banks of River Nyangores in 2013. The objectives of the study were; (i) to determine in-situ processing coefficients for Pennisetum purpureum, Panicum coloratum and Chloris gayana, and (ii) to estimate detrital total phosphorus trends during incubation. It was hypothesized that no significant differences existed among the decay rates of the three grass species. A total of 186 leaf packs were deployed in River Nyangores at upstream and downstream sections separated by Bomet urban settlement for ten weeks, with a two-week withdrawal interval. Temperature normalized decay rates were estimated using an aquatic decay model. Total phosphorus was analyzed using the molybdate-calorimetric procedure with ultraviolet spectrophotometry. Data was analyzed using XLSTAT-2014 computer program. The in-situ decay coefficients ranged from 6.70795 x 10-4 dd-1 to 9.12355 x 10-4 dd-1. Covariance analysis (p&lt;0.05) indicated significant differences for the decay rates among the three species, with higher in-situ processing coefficients recorded downstream than upstream for all the grasses. Litter phosphorus showed positive Pearson correlation with decay rates though not significant (p&gt;0.05). During incubation, detrital phosphorus build-up was lower upstream at 6.4% than downstream at 13.8%. Highest decay rate was recorded for Chloris gayana hence it appears to be the most agro-ecologically sustainable as a riparian forage for River Nyangores. Bomet urban settlement seemingly contributes to shifts in ecological functioning of the river.

Top predator absence enhances leaf breakdown in an intermittent stream

Current biodiversity loss is characterized by the extinction of top predators, but small-bodied freshwater fish are often overlooked in research and conservation management even when threatened because they usually lack commercial value. Therefore, the ecosystem impacts of their possible loss remain mostly unknown. We assessed whether the presence/absence of an endangered predatory fish (Barbus meridionalis (A. Risso, 1827)) in an intermittent stream affects leaf fungal biomass and leaf quality (i.e. leaf carbon:nitrogen ratio and leaf toughness), macroinvertebrate assemblages colonizing leaf packs, and leaf breakdown rates. We conducted a leaf bag experiment comparing a control reach with a population of B. meridionalis with an adjacent upstream fishless reach. In the fishless reach, leaf fungal biomass and microbially mediated breakdown rate were lower compared to the control reach. This was probably caused by the lack of the bottom-up stimulation through nutrient recycling by fish. Shredders and scrapers were found at higher abundance and biomass in the fishless compared to the control reach, and the whole macroinvertebrate community composition changed with fish absence. Consequently, macroinvertebrate mediated leaf breakdown was faster in the fishless than in the control reach, not only compensating for the lower microbially mediated leaf breakdown in the fishless reach, but accelerating the overall leaf breakdown rate. Our study contributes to understand the potential cascading effects produced by the extirpation of endangered small-bodied fish.

The Life History and Other Ecology ofCamelobaetidius variabilis(Ephemeroptera: Baetidae) From Honey Creek, Oklahoma

A study of the life history and ecology of Camelobaetidius variabilis was conducted in Honey Creek, Oklahoma, from February 2003–April 2004. C. variabilis exhibited a multivoltine life cycle with five overlapping generations. Ninety percent of lab-reared eggs hatched at 130 degree days (DD) (23 °C) while nymphs successfully emerged at 559 DD at 20.8 ± .38 °C. Microhabitat preference of C. variabilis nymphs was statistically significant for algae during the spring. Nonmetric multidimensional scaling analysis showed 90% similarity between spring algae, winter leaf packs, fall open bedrocks, and summer divets based on average number of nymphs by developmental stage. Winter leaf packs exposed to shade and sunlight were sampled and total number of nymphs counted. Leaf packs exposed to direct sunlight contained higher numbers of nymphs compared to those in shaded areas. Further internal temperature analysis of leaf packs exposed to sunlight showed an increase in internal leaf pack temperatures compared to ambient water temperature during the winter. C. variabilis nymphs have a varied microhabitat use depending upon season. Since they are scrapers, algae and periphyton are important food resources throughout the year.

Colonization by benthic macroinvertebrates in two artificial substrate types of a Riparian Forest

Abstract: Aim To analyze the efficiency of organic and inorganic substrates in samples of benthic macroinvertebrates of riparian forests from the Cerrado. Specific objectives (i) characterize the ecological succession and taxonomic richness of benthic macroinvertebrates in stream affluent of a riparian forest; (ii) analyze the influence of seasonality on the colonization of macroinvertebrates; and (iii) determine the effect of the types of artificial substrates on the richness, composition and abundance of the benthic community. Methods Sampling was carried out in the rainy and dry seasons, and we installed in the watercourse two types of substrates: organic (leaf packs) and inorganic (bricks), organized in pairs. Six samples per season were done to verify colonization, succession, richness and abundance of benthic community. The substrates were carefully sorted and the organisms were identified to the lowest possible taxonomic level. Results The ecological succession was clearly observed, with the initial occurrence of Chironomidae and Baetidae (considered early colonizers), and a late occurrence of organisms such as Helotrephidae and Trichoptera (considered late colonizers). No significant difference was found in the richness and abundance among the studied seasons (rainy and dry), but the organic substrate was significantly higher than the inorganic substrate for these parameters. Conclusion Organic artificial substrates are more efficient in characterizing the community of benthic macroinvertebrates in the study area, because they are more similar to the conditions of the substrate found naturally in the environment.

Impact of anti-inflammatories, beta-blockers and antibiotics on leaf litter breakdown in freshwaters.

Pharmaceuticals are now recognised as important pollutants in freshwater systems, but a shortcoming of effects studies is that they have focused on structural endpoints and impacts on ecosystem functioning are poorly understood. The decomposition of organic matter is an important functional process in aquatic systems, and it is known that this can be impacted by the presence of pollutants. Previous studies on leaf litter breakdown have only considered the effects of antibiotics and not other groups of drugs though. The current study investigated the effects of anti-inflammatories, a beta-blocker and an antibiotic on microbially mediated breakdown of leaf litter in the laboratory; colonisation of leaf packs by benthic macroinvertebrates when placed in a stream; and shredding of leaf litter by these organisms. Furthermore, the effects of single compounds relative to their mixture were assessed. It was found that exposure of leaf litter to the study compounds did not influence its breakdown by microbes in the laboratory or macroinvertebrates in a stream. Exposure of leaf litter to pharmaceuticals also had no effect on its colonisation by macroinvertebrates in this study. Many unknowns remain, however, and further studies of the effects of pharmaceuticals on structural and functional endpoints are needed to aid aquatic conservation.