Effects of eucalyptus afforestation on leaf litter dynamics and macroinvertebrate community structure of streams in Central Portugal

To test the hypothesis whether afforestation with Eucalyptus globulus affects litter dynamics in streams and the structure of macroinvertebrate aquatic communities, we compared streams flowing through eucalyptus and deciduous forests, paying attention to: (i) litterfall dynamics, (ii) accumulation of organic matter, (iii) processing rates of two dominant leaf species: eucalyptus and chestnut, and (iv) macroinvertebrate community structure. The amount of allochthonous inputs was similar in both vegetation types, but the seasonality of litter inputs differed between eucalyptus and natural deciduous forests. Eucalyptus forest streams accumulated more organic matter than deciduous forest streams. Decomposition of both eucalyptus and chestnut leaf litter was higher in streams flowing through deciduous forests. The eucalyptus forest soils were highly hydrophobic resulting in strong seasonal fluctuations in discharge. In autumn the communities of benthic macroinvertebrates of the two stream types were significantly different. Deciduous forest streams contained higher numbers of invertebrates and more taxa than eucalyptus forest streams. Mixed forest streams (streams flowing through eucalyptus forests but bordered by deciduous vegetation) were intermediate between the two other vegetation types in all studied characteristics (accumulation of benthic organic matter, density and diversity of aquatic invertebrates). These results suggest that monocultures of eucalyptus affect low order stream communities. However, the impact may be attenuated if riparian corridors of original vegetation are kept in plantation forestry.     

Similar breakdown rates and benthic macroinvertebrate assemblages on native and Eucalyptus globulus leaf litter in Californian streams

1. Eucalyptus globulus, a tree species planted worldwide in many riparian zones, has been reported to affect benthic macroinvertebrates negatively. Although there is no consensus about the effects of Eucalyptus on aquatic macrobenthos, its removal is sometimes proposed as a means of ecological restoration. 2. We combined the sampling of macroinvertebrates with measurement of the colonisation of leaf packs in mesh bags, to examine the effects of riparian Eucalyptus and its litter on benthic macroinvertebrates in three small streams in California, U.S.A. Each stream included one reach bordered by Eucalyptus (E‐site) and a second bordered by native vegetation (N‐site). 3. The macrobenthos was sampled and two sets of litter bags were deployed at each site: one set with Eucalyptus litter (Euc‐bags) and one with mixed native tree litter (Nat‐bags) containing Quercus, Umbellularia, Acer and Alnus. Bags were exposed for 28, 56 and 90 days and this experiment was repeated in the autumn, winter and spring to account for effects of changing stream flow and insect phenology. 4. Litter input (average dry mass: 950 g m^?2 year^?1 in E‐sites versus 669 g m^?2 year^?1 in N‐sites) was similar, although in‐stream litter composition differed between E‐ and N‐sites. Litter broke down at similar rates in Euc‐bags and Nat‐bags (0.0193 day^?1 versus 0.0134 day^?1), perhaps reflecting the refractory nature of some of the leaves of the native trees (Quercus agrifolia). 5. Summary metrics for macroinvertebrates (taxon richness, Shannon diversity, pollution tolerance index) did not differ significantly between the E and N sites, or between Euc‐bags and Nat‐bags. No effect of exposure time or site was detected by ordination of the taxa sampled. However, distinct seasonal ordination clusters were observed in winter, spring and autumn, and one of the three streams formed a separate cluster. 6. The presence of Eucalyptus was less important in explaining the taxonomic composition of the macrobenthos than either ‘season’ or ‘stream’. Similarly, these same two factors (but not litter species) also helped explain the variation in leaf breakdown. We conclude that patches of riparian Eucalyptus and its litter have little effect on stream macrobenthos in this region.     

Effects of organic matter and season on leaf litter colonisation and breakdown in cave streams

1. Low organic matter availability is thought to be a primary factor influencing evolutionary and ecological processes in cave ecosystems. We examined links among organic matter abundance, macroinvertebrate community structure and breakdown rates of red maple (Acer rubrum) and corn litter (Zea mays) in coarse‐ (10 × 8 mm) and fine‐mesh (500‐μm) litter bags over two seasonal periods in four cave streams in the south‐eastern U.S.A. 2. Organic matter abundance differed among cave streams, averaging from near zero to 850 g ash‐free dry mass m^?2. Each cave system harboured a different macroinvertebrate community. However, trophic structure was similar among caves, with low shredder biomass (2–17% of total biomass). 3. Corn litter breakdown rates (mean k = 0.005 day^?1) were faster than red maple (mean k = 0.003 day^?1). Breakdown rates in coarse‐mesh bags (k = 0.001–0.012 day^?1) were up to three times faster than in fine‐mesh bags (k = 0.001–0.004 day^?1). Neither invertebrate biomass in litter bags nor breakdown rates were correlated with the ambient abundance of organic matter. Litter breakdown rates showed no significant temporal variation. Epigean (surface‐adapted) invertebrates dominated biomass in litter bags, suggesting that their effects on cave ecosystem processes may be greater than hypogean (cave‐adapted) taxa, the traditional focus of cave studies. 4. The functional diversity of our cave communities and litter breakdown rates are comparable to those found in previous litter breakdown studies in cave streams, suggesting that the factors that control organic matter processing (e.g. trophic structure of communities) may be broadly similar across geographically diverse areas.     

Effects of local and regional factors on the fish assemblage structure in Meridional Amazonian streams

The aim of this study was to evaluate the effects of local, regional and temporal factors structuring fish assemblages in Meridional Amazonian streams during the months of May (rainy season) and August (dry season) of 2008. To accomplish this task, 14 streams located in Serra do Expedito (Aripuanã River basin) were sampled along 30-m stretches. A total of 3,212 specimens distributed among five orders, 18 families, and 55 species were recorded. The fish assemblage structure in the streams presented variation among types of riparian vegetation (local factor) and watersheds (regional factor), but did not present variation between seasons (temporal factor) and stream order (regional factor). Larger streams with margins covered with pasture presented higher species richness and abundance than smaller streams with margins covered with forest.     

Across-reach consistency in macroinvertebrate distributions among litter patch types in Japanese headwater streams

Different types of litter patches with contrasting macroinvertebrate assemblages have been observed within a stream reach. This study examined whether distributions of macroinvertebrates among three litter patch types (riffle, middle, edge) were consistent between reaches with different channel characteristics in headwater streams in central Japan. Mass of leaves per unit area was significantly higher in riffle and edge patches than in middle patches, which was consistent between reaches, while no consistent pattern was evident between reaches for mass of either woody material or small litter fragments. Distribution among the patch types was consistent between reaches for 11 out of 13 dominant macroinvertebrate taxa; density was highest in riffle patches for 5 taxa and in middle patches for 5 taxa. Although we previously related densities of some taxa to mass of woody material or small litter fragments, hydraulic characteristics (water depth, current velocity), which were consistent between reaches, may be more important determinants of macroinvertebrate distributions among the patch types, even within pools (i.e. middle and edge patches) where current is uniformly low. The results of this study indicate that a reach-scale macroinvertebrate community structure associated with litter is likely to vary according to litter patch type composition, which would be affected by channel characteristics of the reaches.     

Hot spots of leaf breakdown within a headwater stream reach: comparing breakdown rates among litter patch types with different macroinvertebrate assemblages

1. Detecting hot spots of litter decomposition will promote understanding of litter processing in a heterogeneous system. To identify hot spots of leaf breakdown within a headwater stream reach, we examined the difference in leaf breakdown rate among four types of litter patches, one that formed in riffles and three that formed in pools (middle, alcove, edge), in different seasons. 2. Middle patches showed the highest breakdown rate in some seasons; the rate in middle patches was 1.5–4 times higher than in the other patches. Thus middle patches can be regarded as hot spots of leaf breakdown in the study reach. This result contrasted with other studies showing higher breakdown rate in riffles than in pools. 3. Significant relationships between abundance of caddisfly shredders and breakdown rate were observed in seasons when the rate differed among patch types. Greater abundance of Lepidostoma seems to be responsible for middle patches being hot spots of leaf breakdown. 4. It is expected that when the proportion of leaves retained in middle patches within a reach is higher, the breakdown rate of the entire reach will be increased. Clarifying how the proportion of leaves retained on middle patches within a reach varies temporally and spatially would improve our understanding of leaf breakdown in headwater streams.     

Fish determine macroinvertebrate food webs and assemblage structure in Greenland subarctic streams

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Colonization and processing of leaf litter by macroinvertebrate shredders in streams of contrasting pH

• 1 Leaf litter processing rates and macroinvertebrate shredder assemblages in leaf packs were compared in four streams on the Allegheny plateau in the central Appalachian Mountains, U.S.A.; these streams were characterized by different bedrock geology and streamwater pH.
• 2 Leaf litter processing rates were fastest in the neutral streams, slowest in the acidic stream, and intermediate in the most alkaline stream.
• 3 Slower processing rates in the acidic stream were associated with lower total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies.
• 4 The differences in processing rates between the more alkaline stream and the neutral streams were not associated with differences in shredder biomass, but appeared to be related to taxonomic differences in the shredder assembiages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.

     

Small dams decrease leaf litter breakdown rates in Mediterranean mountain streams

The damming of rivers and streams alters downstream habitat characteristics and biotic assemblages, and might thus alter stream functioning, although there is not much direct evidence of this impact. In this study we compared breakdown of alder leaves upstream and downstream from 4 small (<1 hm³) dams in 4 Mediterranean mountain streams with no appreciable impact on water temperature and nutrient concentrations. Despite no effect on water characteristics, dams decreased leaf litter breakdown rates. Abundance and biomass of invertebrates and shredders and hyphomycete sporulation rates did not differ between upstream and downstream bags. However, the structure of invertebrate and hyphomycete assemblages did. Especially evident was a drop in limnephilids, which might explain the slower breakdown of leaf litter below dams. These results may help to explain some of the variability found in the literature on the effects of dams on decomposition rates. If dams increase water temperature and nutrient concentrations they may promote faster decomposition, but if dams do not change water characteristics, their impact on detritivore communities may cause slower decomposition rates.     

Global synthesis of the temperature sensitivity of leaf litter breakdown in streams and rivers

Streams and rivers are important conduits of terrestrially derived carbon (C) to atmospheric and marine reservoirs. Leaf litter breakdown rates are expected to increase as water temperatures rise in response to climate change. The magnitude of increase in breakdown rates is uncertain, given differences in litter quality and microbial and detritivore community responses to temperature, factors that can influence the apparent temperature sensitivity of breakdown and the relative proportion of C lost to the atmosphere vs. stored or transported downstream. Here, we synthesized 1025 records of litter breakdown in streams and rivers to quantify its temperature sensitivity, as measured by the activation energy (E_a, in eV). Temperature sensitivity of litter breakdown varied among twelve plant genera for which E_a could be calculated. Higher values of E_a were correlated with lower‐quality litter, but these correlations were influenced by a single, N‐fixing genus (Alnus). E_a values converged when genera were classified into three breakdown rate categories, potentially due to continual water availability in streams and rivers modulating the influence of leaf chemistry on breakdown. Across all data representing 85 plant genera, the E_a was 0.34 ± 0.04 eV, or approximately half the value (0.65 eV) predicted by metabolic theory. Our results indicate that average breakdown rates may increase by 5–21% with a 1–4 °C rise in water temperature, rather than a 10–45% increase expected, according to metabolic theory. Differential warming of tropical and temperate biomes could result in a similar proportional increase in breakdown rates, despite variation in E_a values for these regions (0.75 ± 0.13 eV and 0.27 ± 0.05 eV, respectively). The relative proportions of gaseous C loss and organic matter transport downstream should not change with rising temperature given that E_a values for breakdown mediated by microbes alone and microbes plus detritivores were similar at the global scale.     

Experimental shading alters leaf litter breakdown in streams of contrasting riparian canopy cover

1. Headwater stream ecosystems are primarily heterotrophic, with allochthonous organic matter being the dominant energy. However, sunlight indirectly influences ecosystem structure and functioning, affecting microbial and invertebrate consumers and, ultimately, leaf litter breakdown. We tested the effects of artificial shading on litter breakdown rates in an open‐canopy stream (high ambient light) and a closed‐canopy stream (low ambient light). We further examined the responses of invertebrate shredders and aquatic hyphomycetes to shading to disentangle the underlying effects of light availability on litter breakdown. 2. Litter breakdown was substantially slower for both fast‐decomposing (alder, Alnus glutinosa) and slow‐decomposing (beech, Fagus sylvatica) leaf litters in artificially shaded stream reaches relative to control (no artificial shading) reaches, regardless of stream type (open or closed canopy). 3. Shredder densities were higher on A. glutinosa than on F. sylvatica litter, and shading had a greater effect on reducing shredder densities associated with A. glutinosa than those associated with F. sylvatica litter in both stream types. Fungal biomass was also negatively affected by shading. Results suggest that the effects of light availability on litter breakdown rates are mediated by resource quality and consumer density. 4. Results from feeding experiments, where A. glutinosa litter incubated under ambient light or artificial shade was offered to the shredder Gammarus fossarum, suggest that experimental shading and riparian canopy openness influenced litter palatability interactively. Rates of litter consumption by G. fossarum were decreased by experimental shading in the open‐canopy stream only. 5. The results suggest that even small variations in light availability in streams can mediate substantial within‐stream heterogeneity in litter breakdown. This study provides further evidence that changes in riparian vegetation, and thus light availability, influence organic matter processing in heterotrophic stream ecosystems through multiple trophic levels.     

Catchment land cover as a proxy for macroinvertebrate assemblage structure in Carpathian Mountain streams

We compared land cover, riparian vegetation, and instream habitat characteristics with stream macroinvertebrate assemblages in 25 catchments in the Carpathian Mountains in Central Europe. This study area was particularly selected because of its diverse history of forest and agricultural ecosystems linked to geopolitical dynamic, which provide a suite of unique landscape scale, land cover settings in one ecoregion. Canonical Correspondence Analysis (CCA) showed that variation in composition and structure of macroinvertebrate assemblages was primarily related to four land cover types, and not to riparian or instream habitat. These were the portions in the catchment areas of (1) broadleaved forest, (2) fine-grained agricultural landscape mosaic with scattered trees (e.g., pre-industrial cultural landscape), (3) mixed forest, and (4) natural grassland without trees. Principal Component Analysis (PCA) suggested that land cover types and stream channel substrates co-varied. The PCA also showed that chemical variables, including organic carbon, had higher values in the agricultural landscape compared to natural forests. The major source of variation among taxa in streams was higher abundance of Diptera in agricultural landscapes and of Plecoptera, Coleoptera, Trichoptera, and Amphipoda in forests. Gastropoda and Oligochaeta were more abundant in open, fine-grained agricultural landscape mosaics with scattered trees. Ephemeroptera taxa were quite indifferent to these gradients in catchment land cover, but showed a tendency of being more abundant in the pre-industrial cultural landscape. Our findings suggest that land cover can be used as a proxy of the composition and structure of macroinvertebrate assemblages. This means that land use management at the catchment scale is needed for efficient conservation and recovery of stream invertebrate communities.     

Scales of spatiotemporal variation in macroinvertebrate assemblage structure in monsoonal streams: the importance of season

1. We assessed the relative importance of different scales of spatial and temporal variability on benthic macroinvertebrate assemblage structure in six unpolluted streams in monsoonal Hong Kong using ordination and complementary multivariate analyses. The spatial scales were regions, sites (streams) and sections (riffles) within sites. The temporal scales were years (three, including one with unusually high rainfall), seasons (dry versus wet) and days within seasons. 2. Significant differences in assemblage structure were manifested at all temporal scales. Those at the site scale were most obvious, whereas demarcation of assemblage structure at the section (riffle) scale was smaller, and there was no significant regional differentiation in assemblage structure. Seasonal variability in assemblage structure was greater than that among years or days. 3. Inter‐year differences in assemblage structure were recorded at all sites, and were noted among all years at some sites but not at others. They were recorded more frequently during the dry season, although their occurrence (in pair‐wise comparisons between years) appeared to be related to differences in the monsoonal (wet season) rainfall. 4. Seasonal differences in assemblage structure were strongly evident at all sites. Inter‐site differences were more apparent during the dry season when local (site‐scale) influences on assemblages were stronger. By contrast, wet‐season samples were more variable because of spate‐induced disturbance, and inter‐site differentiation was less distinct. 5. Differences among days at all sites were relatively minor, but shifts attributable to repeated spate‐induced disturbance were evident at some sites during the wet season. 6. Differences at the section scale were recorded more frequently during the dry season, when the extent of within‐site variability among sections was higher, reflecting increased patchiness within sections resulting from increased substratum heterogeneity and/or greater intensity of biotic interactions. 7. Seasonal shifts in macroinvertebrate assemblage structure at a variety of scales in Hong Kong streams are likely to be attributable to monsoonal rains affecting the relative intensity of abiotic disturbance and biotic interactions in accordance with the harsh‐benign hypothesis.     

Variability in the response of amphipods and macroinvertebrate assemblage structure to prolonged drought in forested upland streams

With climate change set to increase the frequency and severity of drought in many parts of the world, there is a need to better understand the effects of drying on stream ecosystems. We investigated the long-term effects of drought on two amphipod taxa Paramoera fontana (Pontogeneiidae) and Austrogammarus australis (Paramelitidae) and macroinvertebrate assemblage structure through an analysis of 13 years of data collected from four forested stream reaches (Victoria, Australia). Abundances of A. australis and P. fontana in the lower reach of Lyrebird Creek declined to zero following surficial streambed drying. Similar declines in abundances were not observed in Sassafras Creek or the two headwater springs, which continued to flow throughout the drought. P. fontana was detected again in the lower reach of Lyrebird Creek 12 months after the final cease-to-flow, however A. australis remained undetected 5 years later, despite an upstream source population within 2 km. Both the entire and shredder macroinvertebrate assemblage structure in Sassafras Creek and the lower reach of Lyrebird Creek shifted significantly pre- and post-surficial streambed drying in the lower reach of Lyrebird Creek. Despite signs of recovery following a return to more average flows, assemblage composition remained considerably different. The substantial differences in the recovery of the two species indicates varying resistance and resilience traits. The failure of A. australis to recolonize after 5 years indicates an absence of any significant resistance or resilience traits. In contrast, the rapid re-colonization of P. fontana may indicate poor resistance traits, but strong resilience traits. The sensitivity of A. australis to cease-to-flow events points to the need to carefully manage water extraction to protect this threatened species. The effective management of macroinvertebrate assemblages in the face of drought requires a clear understanding of their response to drying, the conservation of refugia and the minimization of additional stressors which reduce ecosystem resilience.     

Interaction of water temperature and shredders on leaf litter breakdown: a comparison of streams in Canada and Norway

Litter decomposition in running water sometimes proceeds faster in small, cool tributaries than in warm, wide rivers because stenothermal, leaf-shredding invertebrates are more abundant in the cool streams. Evidence from eastern Canada suggests that the cold-stenothermal stonefly Leuctra has a disproportionate influence on rapid mass loss in upstream reaches of soft-water river systems, but is not replaced by an effective, warm-water shredder downstream. To test the generality of this observation, we compared litter decomposition rates in upstream (second or third order) and downstream (fourth or fifth order) reaches of a medium-size river system in Nova Scotia (Canada) and three river systems in Nordland (Norway). In all river systems, mass loss of nitrogen-rich speckled alder (Alnus incana) leaves and nitrogen-poor red maple (Acer rubrum) leaves proceeded faster at the upstream site only if water temperature there was significantly cooler than downstream. Decomposition rates in all systems were strongly correlated with abundance of Leuctra, and to a lesser extent the caddisfly Lepidostoma. The distribution of Leuctra seems to be driven primarily by water temperature, with a strong peak of abundance at 14°C, but may also be influenced by competition from other shredding species.     

Tropical shift in decomposers’ relative contribution to leaf litter breakdown in two Guinean streams

The hypothesis that leaf litter breakdown in Guinean streams is governed by microorganisms was confirmed, supporting the reported latitudinal shift in decomposers’ contribution to this process. The large body size of dominant macroinvertebrate decomposers (shrimps) only partially compensated for their very low densities. In contrast with other tropical regions mostly dominated by insect larvae, the functional consequences of global warming on these stream ecosystems may be less severe due to the lower sensitivity of crustaceans to temperature increase.     

大型底栖无脊椎动物对溪流中三角枫落叶分解的影响

采用复合网袋法,研究了冬季南京紫金山三角枫落叶在无干扰溪流和生态恢复溪流中的分解过程.结果表明：112 d后,三角枫落叶无灰干质量剩余率为31％～62％,分解速率符合指数衰减模型(P<0.05).在生态恢复溪流和无干扰溪流的流水生境中, 三角枫落叶的分解速率分别为0.0030 d^-1和0.0064 d^-1,静水生境中分别为0.0018 d^-1和0.0016 d^-1.流水生境中,无干扰溪流网袋内的大型底栖动物多度和生物量显著高于恢复溪流(P<0.05),而静水中无显著差异(P>0.05).无干扰溪流中的撕食者多度比例最高(70.4%),以栉水虱为主;生态恢复溪流中滤食者的多度比例最高(37.8%),以长跗摇蚊属为主.流水生境中三角枫落叶的分解速率与撕食者物种丰富度和多度相关性显著(P<0.01),而与生物量的相关性不显著(P>0.05).说明冬季溪流中撕食者的物种丰富度和多度决定三角枫落叶的分解速率.     

Effects of leaf litter species on macroinvertebrate community properties and mosquito yield in Neotropical tree hole microcosms

Detritus quality and quantity affect macroinvertebrate productivity and distribution in many freshwater ecosystems. This study experimentally investigated the effects of leaf litter from Ceiba pentandra, Dipteryx panamensis, Ficus yoponensis, and Platypodium elegans on macroinvertebrate species composition, richness, and abundance in artificial water-filled tree holes in a lowland moist forest of Panama. Species composition was similar among treatments, but species richness and longevity differed among litter types and were consistently highest with Platypodium litter. Similar patterns were observed in natural tree holes of the focal tree species. The mosquito Culex mollis was the most abundant species in the field experiment. Average conductivity and dissolved oxygen concentration differed among leaf species, but pH did not. Leaf toughness was positively correlated with mean macroinvertebrate abundance and cumulative species richness. A laboratory experiment measured C. mollis yield and pupation time in tree hole microcosms containing the four litter species. Cumulative mosquito mass and time to pupation differed among leaf litter species, with Platypodium litter supporting the greatest yield. Pupation was slowest on Ceiba litter. Grazing by mosquito larvae facilitated leaf decomposition in all treatments. Results suggest that differences in macroinvertebrate species richness and mosquito yield can be attributed to differences in nutritional quality among litter species. Received: 14 October 1998 / Accepted: 21 February 1999     

Primate assemblage structure in Amazonian flooded and unflooded forests

There is considerable variation in primate species richness across neotropical forest sites, and the richest assemblages are found in western Amazonia. Forest type is an important determinant of the patterns of platyrrhine primate diversity, abundance, and biomass. Here we present data on the assemblage structure of primates in adjacent unflooded (terra firme) and seasonally inundated (várzea and igapó) forests in the lower Purús region of central-western Brazilian Amazonia. A line-transect census of 2,026 km in terra firme, 2,309 km in várzea, and 277 km in igapó was conducted. Twelve primate species were recorded from 2,059 primate group sightings. Although terra firme was found to be consistently more species-rich than várzea, the aggregate primate density in terra firme forest was considerably lower than that in the species-poor várzea. Consequently, the total biomass estimate was much higher in várzea compared to either terra firme or igapó forest. Brown capuchin monkeys (Cebus apella) were the most abundant species in terra firme, but were outnumbered by squirrel monkeys (Saimiri cf. ustus) in the várzea. The results suggest that floodplain forest is a crucial complement to terra firme in terms of primate conservation in Amazonian forests.