Leaf Litter Breakdown In Streams Research Articles

Intraspecific variation in crayfish behavioral traits affects leaf litter breakdown in streams.

Although intraspecific trait variation is increasingly recognized as affecting ecosystem processes, few studies have examined the ecological significance of among-population variation in behavioral traits in natural ecosystems. In freshwater habitats, crayfish are consumers that can influence ecosystem structure (e.g., macroinvertebrate communities) and function (e.g., leaf litter breakdown). To test whether crayfish behavioral traits (activity, boldness, and foraging voracity) are major contributors of leaf litter breakdown rates in the field, we collected rusty crayfish (Faxonius rusticus) from eight streams across the midwestern USA and measured behaviors using laboratory assays. At the same streams, we measured breakdown rates of leaf packs that were accessible or inaccessible to crayfish. Our results provide evidence that among-population variation in crayfish boldness and foraging voracity was a strong predictor of leaf litter breakdown rates, even after accounting for commonly appreciated environmental drivers (water temperature and human land use). Our results suggest that less bold rusty populations (i.e., emerged from shelter more slowly) had greater direct impacts on leaf litter breakdown than bold populations (P = 0.001, r2 = 0.85), potentially because leaf packs can be both a shelter and food resource to crayfish. Additionally, we found that foraging voracity was negatively related to breakdown rates in leaf packs that were inaccessible to crayfish (P = 0.025, r2 = 0.60), potentially due to a trophic cascade from crayfish preying on other invertebrates that consume leaf litter. Overall, our results add to the growing evidence that trait variation in animals may be important for understanding freshwater ecosystem functioning.

Land-use effects on leaf-litter breakdown in streams in a tropical lowland catchment

The expansion of oil palm and cattle grazing in the tropics continues to alter numerous ecosystem functions. The generated land-use change is potentially impacting stream leaf-litter breakdown, a fundamental process for freshwater ecosystems. To assess the effect of land-use change, we studied breakdown rates of forest (Pachira aquatica, Pouroma aspera, Sloanea ampla, and Hippocratea volubilis) and oil palm (Elaeis guineensis) leaves after a 26-day immersion in streams surrounded by rainforests, grazing lands, or oil palm plantations with and without riparian buffers. In addition, we assessed breakdown drivers by deploying litter bags (248) of two mesh sizes (15 mm and 0.5 mm) allowing or restricting macroinvertebrates’ access (134 coarse-mesh bags and 114 fine-mesh bags). Forest leaf breakdown by microbes (fine-mesh) was lower by 55% in the plantations compared to forests; while microbial oil palm-leaf breakdown was lower by 32% in the unbuffered plantations compared to forests (p < 0.05). Total litter breakdown was lower (p > 0.05) in the plantations but not when these preserved riparian buffers. Litter breakdown was driven primarily by microbes in all land uses except in the buffered plantations, possibly due to increased shredder biomass. These results suggest that oil palm agriculture may decrease microbial stream leaf-litter breakdown, especially in streams with no riparian buffers.

Anthropogenic Carrion Subsidy and Herbicide Glyphosate Depressed Leaf-Litter Breakdown: Effects on Environmental Health in Streams

Terrestrial leaf-litter (LL) inputs impose great bottom-up effects on freshwater ecosystems by fueling detritus-based food webs, affecting macroinvertebrate and microbial communities, and influencing ecosystem functioning. However, increasing intensive anthropogenic activities including the inputs of herbicide glyphosate disturb the breakdown of LL in streams. In this study, an anthropogenic carrion subsidy (chicken meat) and glyphosate (a stressor) were used to investigate their individual and combined effects on LL breakdown in urban streams and forest streams in China. We found that: 1) carrion subsidy decreased LL breakdown rate in both urban and forest streams and increased total and predator richness in forest streams, the reduced LL breakdown rates may be attributed to the foraging shift of macroinvertebrates from LL to carrion subsidy; 2) glyphosate depressed LL breakdown rate in forest but not in urban streams, the reduced LL breakdown rate may be caused by the negative effects on microbes; 3) forest streams showed significantly higher LL breakdown rates in both coarse and fine mesh bags than urban streams which were induced by the high dissolved oxygen (DO) and collector-gatherer richness. Our results provide evidence that LL breakdown in streams is sensitive to inputs of anthropogenic carrion subsidy and glyphosate through the impacts on macroinvertebrates and microbes, respectively. Furthermore, this study underscores the importance of local macroinvertebrate and microbial communities when assessing the responses of stream ecosystem functioning and macroinvertebrate communities to multiple stressors, as the individual and combined effects of stressors can be site-specific in streams with different physical characteristics and biological communities.

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 (Ea , in eV). Temperature sensitivity of litter breakdown varied among twelve plant genera for which Ea could be calculated. Higher values of Ea were correlated with lower-quality litter, but these correlations were influenced by a single, N-fixing genus (Alnus). Ea 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 Ea 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 Ea values for these regions (0.75±0.13eV and 0.27±0.05eV, respectively). The relative proportions of gaseous C loss and organic matter transport downstream should not change with rising temperature given that Ea values for breakdown mediated by microbes alone and microbes plus detritivores were similar at the global scale.

Effects of Land Use on the Composition and Structure of Aquatic Invertebrate Community and Leaf Breakdown Process in Neotropical Streams

Different land uses directly affect the characteristics of a river basin and influence the aquatic biota and ecosystem processes. This study aimed to analyse the community structure and composition of aquatic invertebrates and the role of these organisms in the process of leaf litter breakdown in streams with different land uses. The study was conducted from September to December 2013 in five streams in the Neotropical region. At each stream, we placed 18 bags containing litter for colonization by aquatic invertebrates, and the bags were collected at different exposure times (5, 30, 45, 60, 75 and 90 days). We registered spatial differences in the aquatic invertebrate community structure and composition. There were no significant differences in the activity of invertebrates in the leaf litter breakdown process among streams with different land uses. However, the variability in mass decay rate was lower for the reference stream. This result may have been influenced by habitat quality, availability of organic matter and the structure and composition of benthic community present in the reference stream, which differs significantly among locations with different types of land use. The results of this study shows that human activities, particularly agriculture and urbanization, modify the structure and composition of the benthic community and acts on ecosystem processes, especially in the variability of the processing of allochthonous material invertebrates. However, we reject the hypothesis that land use negatively influences the decomposition of litter, measured by weight loss. Copyright © 2016 John Wiley & Sons, Ltd.

Leaf-litter breakdown in urban streams of Central Amazonia: direct and indirect effects of physical, chemical, and biological factors

AbstractUrbanization alters water physical and chemical variables and may affect leaf-litter breakdown in streams. Higher temperature and nutrient inputs in urban streams can stimulate microbial biomass, which can increase leaf-litter breakdown rates over rates in nonurban streams. On the other hand, urbanization can reduce leaf-litter breakdown rates by eliminating shredders. We evaluated physical, chemical, and biological factors that may directly and indirectly affect leaf-litter breakdown of Coussapoa trinervia and Mabea speciosa in 42 urban streams in Central Amazonia. We used structural equation modeling to assess whether: 1) shredder activity is more important than microbes for leaf-litter breakdown of plant species with softer tissues, 2) microbes (as adenosine triphosphate [ATP] concentration) and fungi (as ergosterol concentration) positively influence leaf-litter breakdown rate, 3) water velocity positively affects leaf-litter breakdown rate, and 4) effects of shredders and microbes, including ...

Leaf-litter breakdown in streams of East Malaysia (Borneo) along an altitudinal gradient: initial nitrogen content of litter limits shredder feeding

AbstractBreakdown of litter in streams is an important terrestrial–aquatic C pathway in forests. Macroinvertebrate detritivore shredders that feed on litter may be more abundant in temperate than tropical streams because the feeding guild is generally restricted to cool waters and because temperate streams may have more high-quality resources. However, rich shredder communities have been found in some high-altitude tropical streams. We investigated litter breakdown and the variation in resource quality of native riparian vegetation in tropical streams at different altitudes (86–3393 m) in eastern Malaysia (Borneo). At each stream, we collected 3 native local leaf species, analyzed their initial resource quality, and incubated them for 56 d in coarse- (shredder and microbial colonization) and fine- (only microbial colonization) mesh bags. We incubated Macaranga tanarius litter in all streams to compare breakdown rates directly. Shredder-mediated breakdown of native litter was detected in only 5 of 24 cases...

The role of the freshwater shrimp Atyaephyra desmarestii in leaf litter breakdown in streams

In aquatic ecosystems, microorganisms and invertebrates provide critical links between plant detritus and higher trophic levels. Atyaephyra desmarestii is an omnivorous decapod that inhabits freshwaters and exhibits high tolerance to temperature oscillations and high ability to colonize new habitats. Although A. desmarestii is able to ingest a variety of foods, few studies have been conducted to elucidate the role of this freshwater shrimp on detritus breakdown in streams. In this study, A. desmarestii was allowed to feed on conditioned or unconditioned alder and eucalyptus leaves in microcosms with or without access to its fecal pellets. At the end of the experiment, total body length of the animals was measured, and the remaining leaves and fecal pellets were used for dry mass quantification and assessment of bacterial and fungal diversity by denaturing gradient gel electrophoresis (DGGE). Cluster analyses of DGGE fingerprints indicated that the major differences in microbial communities on leaves were between leaf types, while on fecal pellets were between conditioned and unconditioned leaves. However, the consumption rate by the shrimp did not differ between leaf types, and was significantly higher on leaves conditioned by microorganisms and in treatments without access to feces. In treatments without access to feces, the production of feces and fine particulate organic matter was also significantly higher for conditioned leaves. Overall, our results support the feeding plasticity of A. desmarestii and its potential role in plant litter breakdown in streams. This might have implications for maintaining stream ecosystem functioning, particularly if more vulnerable shredders decline.

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

Summary 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.

Biodiversity and ecosystem function in species-poor communities: community structure and leaf litter breakdown in a Pacific island stream

Pacific island stream communities are species-poor because of the effects of extreme geographic isolation on colonization rates of taxa common to continental regions. The effects of such low species richness on stream ecosystem function are not well understood. Here, we provide data on community structure and leaf litter breakdown rate in a virtually pristine stream on a remote island in the eastern Caroline Islands of Micronesia. The Yela River catchment on Kosrae, Federated States of Micronesia, is uninhabited, completely forested, and not traversed by any road. At each of 5 sampling stations along the Yela River we measured physical and chemical variables, characterized the benthic invertebrate community, and estimated the relative abundance of macroconsumers (fishes, shrimps, and snails) using snorkeling surveys and trapping. Benthic invertebrate biomass decreased with stream size and was dominated by macroconsumers (i.e., decapods and gastropods). Benthic insect species richness and density were extremely low, characterized by the complete absence of Ephemeroptera, Trichoptera, and Plecoptera, with nonshredding larval Chironomidae making up ∼85% of the exceptionally low insect biomass (∼0.6 mg dry mass/m2). Six species each of fishes and shrimps and 4 snail species were found. We examined the functional role of these noninsect macroconsumers in organic matter processing by comparing litter breakdown rates inside and outside electrified macroconsumer-excluding quadrats at a single site in the lower Yela River. Breakdown rates were slow relative to those reported in most tropical litter decay studies (k = 0.004–0.018 among quadrats). Despite differences in macroconsumer density (p = 0.01), the leaf breakdown rate was not significantly different between reference and electrified treatments (p = 0.77). Thus, macroconsumers at this site had neither a direct role in shredding nor an indirect effect on leaf breakdown through their interactions with any nonexcluded taxa. In the absence of a significant role played by insect or macroconsumer shredders, leaf litter breakdown in streams of remote Pacific oceanic islands might be driven purely by physical and microbial processes. Our results suggest that biogeographic processes have placed some Pacific island streams at the extreme low end of a continuum of shredder biodiversity and biomass, restricting the ecosystem function of their species-poor communities.

Role of fungi, bacteria, and invertebrates in leaf litter breakdown in a polluted river

The effects of water-quality degradation caused by urbanization, agricultural, and industrial activities on leaf litter breakdown and associated communities of invertebrates and microorganisms were examined at 1 reference and 2 downstream polluted sites in the Ave River (northwestern Portugal). Conductivity, concentrations of NH4+-N, NO3−-N, and PO43−-P, and density of culturable microorganisms were high at the polluted sites. Rates of leaf breakdown also were high, and the highest value was found at the most-downstream, nutrient-enriched polluted site. However, the other polluted site had low current velocity and sedimentation, and nutrient enrichment did not lead to rapid leaf breakdown. Shredders were scarce or absent at all sampling sites, and low shredder density probably explained the lack of differences in leaf breakdown rates between fine-mesh and coarse-mesh bags. High fungal and bacterial production on leaves supported high leaf breakdown rates. Bacterial production was greater at both polluted sites than at the reference site, but it did not exceed 11% of the total microbial production. Fungal biomass and production were markedly different between polluted sites, with the highest values corresponding to the fastest leaf breakdown. Our findings indicate that fungi were the major decomposers in this polluted river. We encourage further research on the effects of multiple stressors on the activity of fungal decomposers to help us better understand the mechanisms underlying leaf litter breakdown in streams under stress.

Ecosystem Linkages between Southern Appalachian Headwater Streams and Their Banks: Leaf Litter Breakdown and Invertebrate Assemblages

We examined red maple (Acer rubrum L.) leaf litter breakdown in streams and riparian zones at two sites in the southern Appalachian Mountains to understand how differences in abiotic and biotic factors influence leaf breakdown rates. Litterbags were placed in three riparian habitats differing in litter layer moisture: stream > bank > upland. Invertebrates colonizing litterbags at one site were also examined to determine how variations in community and functional structure affect breakdown rates. Leaves broke down fastest in streams and slowest in upland habitats, whereas bank habitats were intermediate and characterized by high variability. Faster leaf breakdown rates in streams appeared to be a function of greater moisture availability, a more stable thermal regime, and a higher biomass of leaf-shredding invertebrates, especially the stonefly Tallaperla. In addition, patterns of leaf breakdown and invertebrate community structure provided evidence for a stronger than expected ecological connection between the stream and the bank. Overall, detritus processing within this narrow riparian ecosystem varied considerably depending on the availability of moisture. Results from this study show that stream channel–floodplain interactions in riparian ecosystems of steep forested mountains are analogous to ones in larger downstream or low-gradient systems. Riparian zones throughout a river network display a remarkable heterogeneity in their ability to process organic matter, which is ultimately driven by changes in hydrological conditions.

A Perspective on Leaf Litter Breakdown in Streams

Leaf litter breakdown, a critical ecosystem level process in streams and other aquatic environments , has been conceptualized using models borrowed from terrestrial systems. We argue that current views of the process in fresh waters need to be conceptually improved. Specifically, we think the idea that breakdown proceeds in three distinct temporal stages (leaching, conditioning, fragmentation) has been over emphasized. Leaching, the massive loss of soluble leaf components within 24 h after immersion, is generally considered to constitute a well-defined first stage. Recent evidence suggests, however, that the initial solute losses are largely an effect of the un natural drying procedures to which experimental leaves are normally subjected. Fresh leaf litter does lose solutes when immersed,but gradually throughout the breakdown process rather than instantly upon wetting. Conditioning, the second breakdown stage, describes the enhancement of leaf palatability for detritivores by microbial colonization, and is thus ultimately targeted towards a group of organisms (which contribute to litter degradation) rather than addressing the breakdown process per se. Furthermore,conditioning implies a key role for detritivorous invertebrates and underrates the established direct degradative activity of microbial decomposers. If, thus, leaching and conditioning are not generally useful operators to describe portions of the litter breakdown process in freshwaters, the traditional concept, which emphasises leaching, conditioning and fragmentation as three sequential stages, loses much of its appeal. Consequently, we propose a new conceptual model, in which the coincidence and interplay of various subprocesses of litter breakdown is more strongly recognized. In this model, we propose to view the process in terms of the products of litter breakdown-as a complement to the usual perspective which focuses on litter mass loss. Six primary breakdown products are considered : bacterial, fungal and shredder biomass; dissolved organic matter; fine-particulate organic matter; and inorganic mineralization products such as CO2, NH+ and PO3-. We present a scheme illustrating the hypothesized formation of these products throughout breakdown. However, to improve understanding of the process, application of the proposed conceptual framework in experimental work is necessary.

Leaf breakdown along an altitudinal stream gradient

Breakdown of alder (Alnus glutinosa) leaf litter was followed in fourteen sampling stations along a 1400 m altitudinal gradient of a 1st to 3rd-order undisturbed stream. Altitudinal patterns of leaf mass loss, nitrogen concentration in the leaves, fungal biomass determined as ergosterol content, and numbers and biomass of shredders and total macroinvertebrates associated with the decomposing leaf litter were analysed using rank and linear correlations. The breakdown rate (0.020-0.041d -1 ) almost doubled from the upper to the lower sites and exhibited a significant correlation with altitude. The abundance of shredders, which largely dominated invertebrate assemblages on leaf litter, was negatively correlated both with altitude and percentage of leaf mass remaining after 13 days. Similarly, fungal biomass on leaf litter showed a negative linear correlation with altitude after 37 days. These results, which contrast with those of other studies, suggest that the increasing role of shredders and micro-fungi as one goes downstream can explain the altitudinal pattern of leaf litter breakdown in streams.

Leaf litter breakdown in streams receiving treated and untreated metal mine drainage

Rates of alder leaf decomposition were used as an ecosystem-level measure of effects of untreated and treated acid mine drainage on two Colorado mountain streams. Untreated mine effluents had low pH and high concentrations of metals, particularly iron. Deposition of ferric hydroxide on leaf surfaces inhibited colonization by decomposers, such as fungi and aquatic insects, and thus little leaf breakdown occurred. Treated effluents had improved water quality (basic pH, low metal concentrations), but suspended flocs released by the treatment process buried leaves and reduced consumer activity. The rate of leaf breakdown was not significantly different from the rate with untreated effluents; thus improvement in water quality alone was insufficient to restore this important pathway of energy flow in headwater streams.

Environmental Patchiness and the Breakdown of Leaf Litter in a Woodland Stream

The breakdown of allochthonous leaf litter in woodland streams occurs at the community level process which is patchily distributed. Two kinds of environmental patches were tested: types of bottom sediment and sizes of leaf pack. Four sediments, aligned along parallel environmental gradients (velocity and sediment complexity), were studied: rock, gravel, sand, and silt. Five pack sizes were studied: 1, 5, 10, 20, and 40 g. Preweighed packs of white ash (Fraxinus americana) leaflets were tied to bricks and set on the sediments. These were sampled weekly for 6 wk, and the percent dry weight lost was determined. This design was followed in each of the four seasons to test the seasonal variability in leaf litter breakdown. Analysis of variance and comparison of means show that, in all seasons, sediment and pack—size effects are highly significant (P &lt; .001). Leaf packs of all sizes were broken down less in the silt than in the other sediments. The sediment patterns are consistent with the community level effects of physical heterogeneity and stability. Though the pack—size effects were highly variable from season to season, the degree of breakdown differentiated the leaf—pack sizes in every season, at least one size displaying major differences from the others. The seasonal patterns in breakdown reflect its temperature dependence, the breakdown increasing with increasing temperature. The community level process of leaf litter breakdown in streams is patchily distributed in space. This suggests a level of organization between the population and the community, namely the patch—specific component community.