Availability Of Detritus Research Articles

Flow velocity determines detritus availability and microbial food web patterns in a river confluence

Detritus is the vital support for the microbial food web, which would further affect river ecological conditions. Determining the effects of detritus availability on microbial food webs in rivers is critical for protecting river ecological functions. However, the detritus availability was difficult to estimate directly, since the detritus transformation processes (i.e. detritus availability) and flow-induced transport processes are interdependent in rivers. Therefore, this study quantified the detritus transformation processes in a natural river and further identified the impacts of detritus availability on microbial food web patterns. Results revealed that the flow velocity was the main physical driver determining the detritus availability. The decreased velocity would promote detritus availability. Moreover, the increased detritus availability significantly promoted the diversity of bacteria, protozoan and metazoan (p < 0.05). The responses of low trophic levels to detritus availability were significantly greater than those of higher trophic levels, emphasizing the bottom-up cascading effect of detritus availability on microbial food web composition (p < 0.05). From microbial food web perspectives, the detritus availability was amplified with flow velocity decreased, promoting trophic transfer efficiency between different trophic levels. Results and findings revealed the ecological effect of detritus transformation processes on multi-trophic levels in rivers and provided advantageous information for river management.

Upper‐flow‐regime deposits related to glacio‐volcanic interactions in Patagonia: Insights from the Pleistocene record in Southern Andes

AbstractSupercritical flows and their associated upper‐flow‐regime bedforms have been increasingly recognized in several contrasting depositional environments around the world, including volcano‐sedimentary settings. In recent years, there have been significant advances in flow modelling, architecture and depositional dynamics in upper‐flow‐regime bedforms related to glacio‐volcanic interaction, however most of these works come from specific volcanic landscapes. Examples of other regions with different tectonic and volcanic settings are needed in order to gain a more global perspective regarding the generation and preservation of upper‐flow‐regime glacio‐volcanic bedforms. This study presents a detailed analysis of Pleistocene volcaniclastic deposits accumulated in alluvial to lacustrine deltaic environments in the Southern Andes within the Southern Volcanic Zone. Six facies were defined and related to distinctive bedforms by examining sedimentary features, including textural characteristics, sedimentary structures, architecture and composition. Among these facies, five are distinguished by deposition from supercritical flows and upper‐flow‐regime bedforms, such as cyclic steps, chutes and pools, and antidunes. The stratigraphic succession reveals a predominance of repeated supercritical flows, which appear to be influenced by the availability of detritus for removal along with sudden water discharges. Compositional analyses indicate that explosive volcanism was the primary source of detritus, occurring synchronously with sedimentation. Additionally, the widespread occurrence of Pleistocene glacial conditions in this region suggests that volcanic‐induced melting ice or snow may have been an important source of water supply. Regarding the Southern Andes, the presence of local depressions, such as volcano‐tectonic calderas plays an essential role in the generation and preservation of the upper‐flow‐regime bedforms related to glacio‐volcanism. Furthermore, the importance of carrying out detailed and multidisciplinary studies seems to be critical for the recognition of these deposits in the record of the Andes.

Submerged macrophytes enhance carbon emission (CO2 and CH4) from the freshwater wetland in Keibul Lamjao National Park, Manipur, India

Worldwide, the exacerbation of global warming has accelerated the growth of submerged macrophytes in wetlands, thereby substantiating the supply of labile substrates for carbon (CH4 and CO2) emissions. Nevertheless, limited studies have been conducted on carbon emission from tropical wetlands with submerged macrophytes. In the current study an attempt has been made to reveal the role of submerged macrophytes in influencing carbon flux from a natural wetland in the Indo-Burma Biodiversity hotspots. The submerged macrophytes colonising the shallow freshwater wetland of Keibul Lamjao comprise of Hydrilla verticillata, Ceratophyllum demersum, and Potamogeton crispus, with primary productivity at community level ranging between 20.72 and 152.53 g m-2 d-1 (mean, 95.6 ± 54.66 g m-2 d-1). This study gives a comparative analysis of the carbon gases (CH4 and CO2) emission in two distinct zones of the wetland: areas with profuse submerged macrophytic growth and water free of macrophytes. The mean CO2 and CH4 emissions from the zone with submerged macrophytes were 8362.64 ± 2935.57 and 227.90 ± 73.50 mg m-2 d-1, respectively, compared to 5558.07 ± 1222.05 and 149.72 ± 20.44 mg m-2 d-1 from those without macrophytes. The CO2 and CH4 emissions peak during the summer and wane in the following seasons, with minimum emissions occurring during the winter. It is apparent from the results that the generation of the gases in the wetland was temperature dependent, plus the macrophytic detritus availability. The carbon emissions were significantly correlated with the physicochemical properties of the water and the lake bottom sediment. A significantly positive correlation between carbon emission and dissolved organic carbon (DOC) and organic matter (OM) was established in the zone with macrophytes, thereby revealing that the growth of submerged macrophytes in the wetland enhances atmospheric carbon emissions.

Larval Competition Between Aedes albopictus and Aedes aegypti (Diptera: Culicidae) in Argentina: Coexistence and Implications in the Distribution of the Asian Tiger Mosquito.

Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) are worldwide vectors of dengue and yellow fever viruses. These species coexist in many countries and the biotic interactions between them can influence their abundances and distributions. In Argentina, Ae. aegypti is widely distributed in the north and center regions of the country, with temperate and subtropical climate, while both are sympatric only in the northeastern area of the subtropical region. Interspecific and intraspecific larval competition for food was evaluated to assess if their interaction influences on patterns of abundance and distribution. Finite rates of increase and survivorship for each species were estimated and the effects of mosquito density ratio and detritus availability were determined. The Lambda (λ´) index of population performance of both showed there is no competitive exclusion pattern. However, survival of Ae. albopictus was negatively affected by the presence of Ae. aegypti. These results suggest one possible explanation for the codominance pattern of both species display in rural regions of the southernmost distribution of Ae. albopictus in South America. They also show Ae. aegypti as a potential biotic barrier for the expansion of Ae. albopictus as was reported in regions of the United States.

Carbon Regulating Services of A 30-year-old Reclaimed Limestone Mine Area in Foothills of Himalaya

The study aims to assess various carbon regulating services of a limestone mine site, reclaimed 30 years back, compared to its adjoining natural forest. The natural forest is dominated by broad leaf species ( Quercus leucotricophora ) whereas, the reclaimed sites have Cupressus torulosa as the dominant species. Though there was no significant difference in the number of species of various life forms (trees, shrubs, herbs and grasses), total basal cover (TBC) estimated for the natural forest (2513.36cm 2 /100m 2 ) was much higher compared to the reclaimed site (584.30 to 997.07 cm 2 /100m 2 ). The difference is much higher in TBC of trees compared to shrubs. Annual litter production was also higher in the natural forest. Microbial activity in the top soil layer was found to have increased substantially in the reclaimed mine site. Soil respiration rate and soil microbial biomass in the reclaimed mine site was on a par with that of natural forest. It indicates a significant level of organic matter and detritus availability in the reclaimed sites' top soils since the soil's degradable organic carbon is the main fuel responsible for the CO emission during soil 2 respiration. Though the carbon assimilation rate recorded in the vegetation of the reclaimed area is on a par with that of vegetation of natural forest at the species level, at the community level, the reclaimed site may have lower assimilation owing to lower TBC. Therefore, the difference in vegetation structure and composition in the reclaimed site compared to the natural forest might significantly impact the overall carbon regulating services in the study area.

Integrated mineralogical and geochemical study of the Rapel fluvial system, central Chile: An application of multidimensional analysis to river sedimentation

The mineralogical and chemical composition of the <180 μm fraction of 90 stream sediments collected along the Rapel, Cachapoal and Tinguiririca rivers were studied in order to assess the influence of natural and anthropogenic factors. In order to distinguish major and secondary chemical patterns the data was analyzed using an unsupervised artificial neural network technique. The studied rivers present different chemical signatures, which are associated with geological formations and anthropogenic factors such as mining, agro-industry and urbanization. The upper-middle reaches of the Cachapoal River are characterized by elevated Cu–Mo–As–Sb concentrations that reflect input of mining-derived material. This signature, which is further amplified in the middle reaches of this river due to the influence of the city of Rancagua, masks other signatures such as organic matter-related high B concentrations. The sediments of the Tinguiririca River are strongly depleted in heavy metals, but present high P2O5 concentrations, which reflects the extensive use of phosphates in its floodplain. At the upper reaches of the Rapel River the transition from granitic to sedimentary-dominated bedrock coincides with a marked decrease in P2O5–La–Ce–Y abundances. Similarly, the lower reaches of this river coincide with a marked CaO–MgO increase, which reflects an increase in the availability of CaO-rich detritus associated to a lithological transition. Enrichment of strongly correlated Fe2O3–TiO2–MnO–P2O5–Pb–V–Ni–Cr–Y–Ce–La in the middle-lower reaches of this river is interpreted as reflecting heavy mineral accumulation in point-bar deposits. This is further supported by the mineralogy of the associated samples. Most of the suspended load of the Cachapoal and Tinguiririca rivers settles in the Rapel Lake. Thus the quantity of metals and P2O5 contained in the sediments of this lake is considerable and, together with the very high Cu–Mo–As–Sb concentration of the sediments of the Cachapoal River constitute a potential hazard to the catchment environment.

Implications of micro-plankton and micro-detritus on the food web in the largest monsoonal estuary along the west coast of India

This study presents how seasonal hydrographical changes affect the size structure of the micro-plankton community and thereby the availability of micro-detritus in the Kochi backwaters (KBW). Advanced quantification of plankton and detritus has been conducted using a FlowCAM, and we tested here the hypothesis that floodwater considerably increases the detritus availability in the KBW. Fortnightly time-series sampling was carried out over a year (2013–14) in a downstream location of the KBW. The water column in the study region was moderately rich in nutrients throughout the year (NO3: >1.4 μM; PO4: >0.3 μM; SiO4: >3 μM), showing the maximum levels during the Southwest Monsoon (SWM; June to September) followed by the Northeast Monsoon (NEM; November to February) and the Pre-Southwest Monsoon (PSWM; March–May). Following the above, the abundance and biomass of micro-autotrophs increased from the SWM (av. 1827 ± 1056 L−1 and av. 8 ± 2.53 μgC L−1) and peaked during the PSWM (av. 23963 ± 17142 L−1 and av. 16 ± 9.49 μgC L−1, respectively). The micro-heterotrophs (mean size and abundance) also remained high during the PSWM, followed by NEM. However, the micro-autotroph mean size was minimum during the PSWM (av. 20883 ± 2239 μm³), which increased during the SWM (av. 43510 ± 3611 μm³) and NEM (av. 35245 ± 8655 μm³). The micro-detritus was found highly abundant during both the PSWM and the NEM following the temporal trend in the abundance and biomass of micro-autotrophs and micro-heterotrophs in the study region, suggesting the active transfer of energy to the next trophic levels through smaller plankton as well as detritus. Also, the positive interrelationship of these components indicates that the primary source of micro-detritus is the dead plankton materials, which is an apparent deviation from the traditional belief that KBW possibly gets loaded with more detritus during the SWM due to the floodwaters.

Community structure of deep fjord and shelf benthic fauna receiving different detrital kelp inputs in northern Norway

Kelp forests produce large amounts of macroalgal detritus, ranging from whole plants to small particles (1 mm). The role of this kelp detritus in fueling deep-sea communities adjacent to healthy kelp forests was investigated in a region in the north of Norway by comparing the community structure and biodiversity of meio-, macro-, and megafauna in two deep (450 m) areas with different expected input of kelp detritus: a deep fjord basin surrounded by kelp forests and the adjacent continental shelf 15 km offshore from the kelp forests. The results showed that, although the fjord received a significantly higher amount of large kelp detritus (i.e. blades) than the shelf area, the amount of small kelp detritus available on the sediment was similar in both areas. There were significant differences in the multidimensional scaling analyses on the community structure for meio-, macro-, and megafauna between the fjord and the shelf. Significant differences were also found in biomass, abundance and biodiversity indices for some groups. However, no clear pattern emerged in the community structure and biodiversity between the fjord and the shelf, and the observed differences could not be linked directly to kelp detritus availability. The similar amounts of small particles of kelp detritus in the fjord and shelf area suggest that kelp detritus can provide organic matter to ecosystems further away than initially hypothesized, thus potentially shaping the structure and functioning of deep benthic communities distant from the kelp forests. Yet, the direct (trophic) links of kelp detritus and the studied benthic fauna need to be further analysed. The results are discussed in relation to current global changes in kelp forest, including regime shifts from healthy kelp reefs to turfs or barren areas, which reduce drastically the amount of macroalgal detritus produced and exported.

Giant Reed (Arundo donax) wrack as sink for plastic beach litter: First evidence and implication

In order to maintain the hydraulic outflow in land reclaimed canalizations, the competent agencies provide to mechanically mow the Giant Reed (Arundo donax, L. 1753) along the aquatic ecosystem banks. Nevertheless, the reeds mowed can be transported away from the waters following storm surges and can be deposited in large quantities along the sandy beaches. We carried out a stratified study in a Mediterranean sandy beach to test the hypothesis that Giant Reed wrack may act as a sink and barrier for plastic beach litter. We observed a large amount of plastic litter entrapped in the Arundo donax wrack (density of 0.868 items/m2), with a higher density when compared to both the inner and the shoreline belts. Density of litter is significantly higher considering the categories of meso- and micro-plastics. Organic macrophyte wrack is useful for dunal macrodetritivorous invertebrates and generally for fauna communities, which use this litter as refuge and trophic pabulum. Significant accumulations of organic wrack can mitigate coastal erosion; nevertheless, for its structural characteristics, Arundo wrack can also act as a barrier for litter towards the inner vegetated dunes, so entrapping a large amount of anthropogenic litter. In this regard, Arundo wrack can represent a sink habitat, first attracting (due to large availability of detritus with a relative high rate of decomposition) and then, entrapping many organisms in anthropogenic litter. We suggest that, once mechanically mowed, the land reclaimed agencies should periodically remove from the channel banks the Arundo donax reeds, impeding the accumulation of incoherent vegetated matter along the aquatic ecosystem banks.

Community structure of algae epiphytic in different leaf litter of mangroves

Mangrove is a plant that has the morphological and physiological adaptations to habitats which influenced by a tide. This plant can grow and develop in an environment of high salinity and its soil conditions are less stable and aerobic. Litter mangrove is the main source for the availability of detritus and is the largest component constituent of a food web in a mangrove ecosystem environment. Algae epiphytic microalgae is a group that lives attached to the plant, including the mangrove litter. The study aims to assess the abundance and diversity of epiphytic algae on different types of mangrove leaf litter. The observed mangroves leaf litter were Avicennia alba, Sonneratia sp. and Rhizophora sp. Epiphytic algae were brushed on mangrove leaf litter covering an area of 6.25 cm2 and diluted with distilled water. Samples were observed under a microscope with a magnification of 400 x. Water quality parameters were measured in situ and the organic ingredients, total N and P were analyzed. The results showed that epiphytic algae on each type of mangrove leaf litter were not different. Rhizophora sp is the most abundant and the richest species compared with other types of litter that are equal to 622 individuals / cm2 and 26 species of epiphytic algae. While the abundance of Avicennia alba and Sonneratia sp were 459 ind/cm2 and 321 ind /cm2, in the coastal mangrove areas of Morodemak was found 28 species of epiphytic algae. The common epiphytic algae species found in all types of mangrove litter were Cymbella sp., Coscinodiscus sp., and Synedra ulna. In general, the group of Bacillariophyta (diatoms) is the dominant species in some mangrove leaf.

Detrital dolomite: characterization and characteristics

Investigating dolomite fragments derived from pre-existing dolomite-containing sediments or rocks, that is detrital dolomites, constitutes a challenge in carbonate sedimentology. Detrital dolomites are generally difficult to recognize and their presence can have profound consequences, even in small quantities, on the interpretation of the tectonosedimentary evolution and palaeoenvironmental conditions of the enclosing basin. In addition, identification and quantification of detrital dolomites may provide insight into provenance and sediment transportation, quality of hydrocarbon reservoirs, and some aspects of the dolomite problem. Typically, detrital dolomites are recognized by their clastic behaviour, such as 1) their wide range of grain sizes and shapes, 2) evidence for transportation and weathering, and 3) their association with other detrital grains. Detrital dolomite can be derived from dolomite-containing sediments (by reworking) or dolomite-containing rocks (by disintegration) and can be transported by various means including wind, water, glaciers and sediment gravity flows. Detrital dolomite can be found in a variety of lithofacies confirming that they are controlled by availability of dolomite detritus and not by depositional environment. The role of detrital dolomite in promoting diagenetic dolomitisation is examined whereby they have provided nucleation sites, for syntaxial overgrowth, or a source of Mg, through dissolution.

The impact of primary and export production on the formation of the secondary nitrite maximum: A model study

The so-called secondary nitrite maximum (SNM) is a pronounced subsurface feature in many oxygen deficient zones of the ocean. A nitrite layer of up to several hundred meters thickness indicates high microbial activity and nitrogen loss from the system. To study the effects of primary and export production on the SNM, we have developed a one-dimensional ecosystem model for oxygen deficient zones. Our model couples the marine nitrogen and oxygen cycles with physical water column processes, includes euphotic, aphotic, aerobic and anaerobic processes and thereby dynamically describes source and sink processes for nitrite. The model is able to reproduce a number of typical SNM features found in observations from several oxygen deficient zones. Sensitivity experiments indicate that the SNM is particularly sensitive to the amount of labile dead organic matter sinking out of the euphotic zone but rather insensitive to the strength of regenerated primary production. The absence or presence of SNMs in oxygen deficient zones may be explained by the (non-)availability of labile detritus. Our model is applicable to different ocean regions and can be used to quantify sinks of bioavailable nitrogen due to potential changes in oxygen levels and/or detritus composition.

Stream power as a predictor of aquatic macroinvertebrate assemblages in the Yarlung Tsangpo River Basin (Tibetan Plateau)

Assemblage structures and distribution patterns of aquatic macroinvertebrates are influenced by riverine environmental variables. The relationship between environmental variables and macroinvertebrate assemblages, however, has rarely been examined quantitatively for rivers with high stream power at high altitude. In this study, stream power was analyzed in relation to macroinvertebrate distributions in the Yarlung Tsangpo River Basin on the Tibetan Plateau. Field investigations were carried out at 22 sites in April, 2014 and 2015. Stream power, substrate size and evenness, discharge, bedload transport, and organic detritus availability varied greatly among these sites. In total, 125 taxa of macroinvertebrates belonging to 48 families and 104 genera were identified. The macroinvertebrate density was negatively and significantly correlated with the stream power (D = 3.30, P < 0.001). Both the assemblage indices (taxa richness, density, biomass, and the Improved Shannon–Wiener Index) and the environmental variables (elevation, substrate size, and discharge) differed among the sites with different levels of stream power. An adaptability analysis showed contrasting adaptive strengths of typical taxa. Orthocladius, Baetis, and Simulium adapted to wide ranges of stream power and their most optimal stream powers were relatively high, while Bethbilbeckia and Natarsia were only well-adapted to fairly narrow ranges in stream power. Some macroinvertebrates have evolved specific strategies to adapt to high stream power: Baetidae and Heptageniidae have developed specialized body shapes, and Epoicocladius has altered its host preference. The stream power has been shown to be significantly correlated with and could be used to predict macroinvertebrate density in the Yarlung Tsangpo River Basin.

Phenological response of a key ecosystem function to biological invasion.

Although climate warming has been widely demonstrated to induce shifts in the timing of many biological events, the phenological consequences of other prominent global change drivers remain largely unknown. Here, we investigated the effects of biological invasions on the seasonality of leaf litter decomposition, a crucial freshwater ecosystem function. Decomposition rates were quantified in 18 temperate shallow lakes distributed along a gradient of crayfish invasion and a temperature-based model was constructed to predict yearly patterns of decomposition. We found that, through direct detritus consumption, omnivorous invasive crayfish accelerated decomposition rates up to fivefold in spring, enhancing temperature dependence of the process and shortening the period of major detritus availability in the ecosystem by up to 39days (95% CI: 15-61). The fact that our estimates are an order of magnitude higher than any previously reported climate-driven phenological shifts indicates that some powerful drivers of phenological change have been largely overlooked.

Sedentary urchins influence benthic community composition below the macroalgal zone

AbstractSea urchins are important ecosystem engineers in subtidal ecosystems worldwide, providing biogenic structure and altering nutrient dynamics through intensive grazing and drift algal capture. The current work evaluates red urchin (Strongylocentrotus franciscanus) density on fixed transects through time, individual displacement, and urchin‐associated benthic community composition using a field‐based approach at multiple depths (in and outside of the macroalgal zone) and replicated across sites in the San Juan Archipelago, Washington. Urchins exhibited no large‐scale, temporal or directional changes in density among depths. Furthermore, 87% of individual urchins observed in repeated small‐scale surveys over 3 weeks exhibited no change in position. Individual displacement was negatively correlated to drift algal capture. Evidence of sedentary behavior from the displacement surveys was supported by the sessile and mobile community composition in areas directly under versus adjacent to (control) urchins. The benthos under urchins had a higher percentage of bare space, crustose coralline algae, and increased density of snails, crabs and shrimp relative to associated control plots. Abundance of mobile organisms associating with urchins increased relative to control plots at the deepest survey depth (30 m), indicating a greater strength of interaction with distance from macroalgal production. This work presents evidence of food availability‐related behavior in red urchins and indicates that even when sedentary, urchins have a strong influence on ecosystem structure through increasing availability of shelter and macroalgal detritus to the benthos.

Compositional controls on early diagenetic pathways in fine-grained sedimentary rocks: Implications for predicting unconventional reservoir attributes of mudstones

Diagenesis significantly impacts mudstone lithofacies. Processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks. Selected organic-carbon-rich mudstones, from the Kimmeridge Clay and Monterey Formations, have been investigated to determine how varying starting compositions influence diagenesis. The sampled Kimmeridge Clay Formation mudstones are organized into thin homogenous beds, composed mainly of siliciclastic detritus, with some constituents derived from water-column production (e.g., coccoliths, S-depleted type-II kerogen, as much as 52.6% total organic carbon [TOC]) and others from diagenesis (e.g., pyrite, carbonate, and kaolinite). The sampled Monterey Formation mudstones are organized into thin beds that exhibit pelleted wavy lamination, and are predominantly composed of production-derived components including diatoms, coccoliths, and foraminifera, in addition to type-IIS kerogen (as much as 16.5% TOC), and apatite and silica cements. During early burial of the studied Kimmeridge Clay Formation mudstones, the availability of detrital Fe(III) and reactive clay minerals caused carbonate- and silicate-buffering reactions to operate effectively and the pore waters to be Fe(II) rich. These conditions led to pyrite, iron-poor carbonates, and kaolinite cements precipitating, preserved organic carbon being S-depleted, and sweet hydrocarbons being generated. In contrast, during the diagenesis of the sampled Monterey Formation mudstones, sulfide oxidation, coupled with opal dissolution and the reduced availability of both Fe(III) and reactive siliciclastic detritus, meant that the pore waters were poorly buffered and locally acidic. These conditions resulted in local carbonate dissolution, apatite and silica cements precipitation, natural kerogen sulfurization, and sour hydrocarbons generation. Differences in mud composition at deposition significantly influence subsequent diagenesis. These differences impact their source rock attributes and mechanical properties.

Contrasting Effects of Sand Burial and Exposure on Invertebrate Colonization of Leaves

Leaf detritus in streams fills dual resource roles as habitat and as food. Unless retained by some structural component, detritus gets transported to downstream reaches out of the local system. Low gradient sandy-bottomed streams retain leaf detritus via burial in sand, but this mechanism of retention limits the availability of detritus as a resource for the benthic community. We hypothesized that burial of leaf litter in sand would impact invertebrate colonization by reducing density and richness on leaf litter. We conducted a short-term experiment (i.e., 2 wk) in a sandy-bottom stream in which leaves were subject to either burial in sandy substrate, exposure to the water column, or a sequential combination of both. Results showed that 2 wk burial of leaf litter significantly impacted the colonization of benthic invertebrates. Burial or exposure status of leaves at the time of collection represented the major factor influencing invertebrate abundances on leaf litter. Leaves exposed to the water column had the highest abundance of invertebrates, dominated by collector-gatherers, that suggests the primary role of leaf litter as refugia in this system. Burial of leaf litter in sand had a significantly negative effect on invertebrate colonization of leaf litter. Furthermore, no difference existed in invertebrate colonization on leaf litter that had never been buried versus leaf litter that had been buried for 1 wk and then exposed and collected after a week in the water column. This suggests short-term burial of leaf litter does not influence colonization by invertebrates once leaf litter is exposed to the water column. The results of this study suggest that the benthic colonization on newly exposed leaf litter is rapid, potentially due to a lack of habitat structure availability in the sandy-bottomed stream.

Within-year temporal variation and life-cycle seasonality affect stream macroinvertebrate community structure and biotic metrics

Seasonal changes in macroinvertebrate taxon abundances that are related to life history introduce temporal variation into macroinvertebrate community structure that can potentially confound bioassessments. In this study, macroinvertebrates from three rural and three urban streams were sampled monthly to assess temporal variability in community structure, determine how taxon life-cycle seasonality affects this variability, and determine if this temporal variability confounds biotic index interpretations. Temporal variation in taxon abundances was higher in the rural streams than in the urban streams, and 17 of 23 indicator taxa from rural streams exhibited, or are known to exhibit, either fast- or slow-seasonal life cycles. Conversely, five taxa were identified as indicators for urban streams, but only two of these taxa exhibited seasonal life cycles. Further, the life-cycle seasonality of many rural stream indicator taxa appeared to be linked to the seasonality of environmental conditions such as hydrologic permanence and benthic leaf detritus availability. Macroinvertebrate bioassessment index (MBI) scores were higher in the rural streams than in the urban streams during all months except June, July, and October when no difference was detected. We attribute the reduced discriminatory power of the MBI in the summer and early autumn to the life-cycle of a single taxon ( Stenelmis sp.), and its effects on % Clingers – a component metric of the MBI. Stenelmis sp. exhibited a non-seasonal life cycle with a larval development time of approximately 12 months with considerable overlapping of cohorts present during the summer and early autumn when an extended first instar recruitment period was evident. During this overlap period, urban stream MBI values increased resulting in no statistical difference in the MBI between urban and rural streams in June, July, and October. Analyses of temporal variability in taxon abundances and life-history characteristics, as completed in this study, can greatly contribute to the creation and/or validation of bioassessment protocols.

Contrasting Zooplankton Assemblages in Two Oxbow Lakes with Low Transparencies and Narrow Emergent Macrophyte Belts (Krapina River, Croatia)

AbstractThe aim of this study was to examine the combined effect of water transparency and narrow macrophyte belts on zooplankton assemblages in two oxbow lakes (Krapina River, Croatia). Samples were collected in open water and among helophytes in the littoral zone from April until September 2008. Rotifers were the most abundant group of zooplankton in both lakes, and dominated in the Krapina oxbow lake 1 (KO1). Lake KO1 had significantly lower transparency, lower percentage macrophyte cover and higher chlorophyll a concentration than Krapina oxbow lake 2 (KO2). In lake KO1, variation in the horizontal distribution of cladocerans and rotifers in terms of their abundance seemed to be determined by competition between Bosmina longirostris and Keratella cochlearis, initiated by oscillation in transparency and detritus availability. In lake KO2, with higher transparency and higher percentage macrophyte cover, the abundance of small‐ and large‐bodied cladocerans increased in the littoral zone simultaneously with higher transparency, suggesting fish predation. Results of this study indicated that small differences in transparencies between the two lakes caused significant differences in horizontal distribution of the zooplankton assemblage. Even narrow helophyte belts offered a refuge to zooplankton, although lower transparencies reduced the effectiveness of macrophytes as a refuge from predators. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Status assessment of raptors in Cape Verde confirms a major crisis for scavengers

AbstractScavenging raptors have been postulated to be declining at a rate far higher than predatory raptors. To test this hypothesis we reviewed the historical and present status of the seven raptor species—three scavengers (two kites and a vulture), one partial scavenger (a buzzard) and three species (osprey and two falcons) that take live prey—that breed on the Cape Verde islands. Scavenging raptors have experienced steeper declines and more local extinctions than non-scavengers in Cape Verde, with the partial scavenger midway between the two groups. Causes of scavenger decline include incidental poisoning, direct persecution and declines in the availability of carcasses and other detritus. These findings, which highlight the conservation importance of the island of Santo Antão, indicate the priority that needs to be accorded to scavengers, particularly in Europe where many insular populations are reaching unsustainable levels.