Detrital processing in streams exposed to acidic precipitation in the Central Appalachian Mountains

Continuing high rates of acidic deposition in the eastern United States may lead to long-term effects on stream communities, because sensitive catchments are continuing to lose anions and cations. We conducted a two-year study of the effects of pH and associated water chemistry variables on detrital processing in three streams with different bedrock geology in the Monongahela National Forest, West Virginia. We compared leaf pack processing rates and macroinvertebrate colonization and microbial biomass (ATP concentration) on the packs in the three streams. Breakdown rates of red maple and white oak leaf packs were significantly lower in the most acidic stream. The acidic stream also had significantly lower microbial and shredder biomass than two more circumneutral streams. Shredder composition differed among streams; large-particle detritivores dominated the shredder assemblages of the two circumneutral streams, and smaller shredders dominated in the acidic stream. Within streams, processing rates for three leaf species were not significantly different between the two years of the study even though invertebrate and microbial communities were different in the two years. Thus, macroinvertebrate and microbial communities differed both among streams that differed in their capacity to buffer the effects of acidic precipitation and among years in the same stream; these differences in biotic communities were not large enough to affect rates of leaf processing between the two years of the study, but they did significantly affect processing rates between acidic and circumneutral streams.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.     

Assessing the influence of wildfire on leaf decomposition and macroinvertebrate communities in boreal streams using mixed-species leaf packs

1. We investigated how compositional differences in riparian leaf litter derived from burned and undisturbed forests influenced leaf breakdown and macroinvertebrate communities using experimental mixed-species leaf packs in boreal headwater streams. Leaf pack mixtures simulating leaf litter from dominant riparian woody-stem species in burned and undisturbed riparian zones were incubated in two references and two fire-disturbed streams for 5 weeks prior to measuring temperature-corrected breakdown rates and macroinvertebrate community composition, richness, and functional metrics associated with decomposers such as shredder abundance and % shredders.
2. Leaf litter breakdown rates were higher and had greater variability in streams bordered by reference riparian forests than in streams where riparian forests had been burned during a wildfire. Streams bordered by fire disturbance showed significant effects of litter mixture on decomposition rates, observed as significantly higher decomposition rates of a fire-simulated leaf mixture compared to all other mixtures.
3. Variation among sites was higher than variation among litter mixtures, especially for macroinvertebrate community composition. In general, fire-simulated leaf mixtures had greater shredder abundances and proportions, but lower overall macroinvertebrate abundance; however, the shredder abundance trend was not consistent across all leaf mixtures at each stream.
4. These results show that disturbance-driven riparian forest condition and resulting composition of leaf subsidies to streams can influence aquatic invertebrate community composition and their function as decomposers. Therefore, if one of the primary goals of modern forest management is to emulate natural disturbance patterns, boreal forest managers should adapt silvicultural practices to promote leaf litter input that would arise post-fire, thereby supporting stream invertebrate communities and their function.

     

Litter retention in Tasmanian headwater streams after clear-fell logging

Clear-fell logging around small headwater streams in Tasmanian wet eucalypt forests was predicted to affect both the retention of leaf litter and the composition and size of leaf packs. Retention structures were surveyed in six natural streams and six streams in forest regenerated 3–5 years after clear-fell and burn logging. Logged streams had more wood, but retained less leaves than natural streams, and consequently had fewer and smaller leaf packs. Leaf packs from natural streams contained 200% more leaves, bark and twigs than packs from logged streams. The effect of buoyancy on leaf retention was assessed with release and recapture of marked Eucalyptus obliqua and Nothofagus cunninghamii leaves. Eucalypt leaves were more likely to be trapped by retention structures on the bed of the stream, while smaller, more buoyant N. cunninghamii leaves were mainly trapped by leaf packs. Leaf packs in natural streams were formed on a matrix of small twigs and long strips of bark, shed from the upper branches of mature stringybark eucalypts, while leaf retention was reduced in logged streams because there are no mature trees to provide effective retention structures. Changes to the channel form increase both discharge and sedimentation. These factors have strong implications for downstream nutrient processing and riverine food webs.     

Effects of agricultural development on processing of tussock leaf litter in high country New Zealand streams

1. We compare the rates and mechanisms of processing of tussock (Chionochloa spp.) leaf litter in six New Zealand streams draining grassland catchments that contrast in the extent to which they have been developed for pasture. 2. Rates of processing, measured as rate of weight loss of leaf packs and rate of leaf softening, were at the slow end of the spectrum for vascular plant processing. Processing was faster at developed sites, mediated mainly through the influence of oxidized nitrogen concentration on microbial activity. 3. Few invertebrate shredders colonized leaf packs and it is unlikely that invertebrates had an appreciable effect on leaf processing in our study streams, which do not effectively retain leaf litter. Very small headwater tributaries appear to retain leaf litter and possess a more abundant shredder community. 4. Measures of leaf processing in our six streams were significantly correlated with Petersen's (1992) RCE score of stream condition. We discuss the potential for using rate of leaf litter processing as a method of bioassessment. 5. Even the most degraded stream in our study is classed as ‘good’ using the RCE inventory system. Human impact in the Taieri River is relatively small compared with the degradation observed in some parts of the world.     

Bioturbation by a dominant detritivore in a headwater stream: litter excavation and effects on community structure

Bioturbation can affect community structure by influencing resource distribution and habitat heterogeneity. Bioturbation by detritivores in small headwater streams could affect community structure by reintroducing buried detrital resources into the food web and could also affect the distribution of various taxa on detritus. We evaluated the ability of the caddisfly Pycnopsyche gentilis to uncover experimentally buried leaves in a headwater stream. Packs of leaves were placed in enclosures and covered with a known volume of sediment. We added 0, 3 or 6 large Pycnopsyche to the enclosures which were permeable to most other invertebrate taxa. Leaf packs were sampled after 23 days and leaf pack mass, the amount of sediment covering the leaf packs, and macro‐ and microinvertebrate densities on leaf packs were quantified. There was a significant negative relationship between Pycnopsyche density and leaf pack mass. Pycnopsyche also reduced the volume of sediment covering leaf packs. Pycnopsyche had complex effects on the abundance of invertebrate taxa associated with the leaves. Some taxa exhibited their highest abundance in the 3 Pycnopsyche treatment while others exhibited non‐significant increases as Pycnopsyche density increased. These results suggest that the beneficial effects of Pycnopsyche (e.g. uncovering leaves which increases the availability of habitat and food) outweigh any negative effects (e.g. disturbance, encounter competition) of the caddisfly when it is present at lower densities. However, the negative impacts of Pycnopsyche appear to outweigh the positive effects via sediment removal at higher caddisfly densities for some taxa. Our results suggest that bioturbating organisms in streams have the potential to reintroduce organic matter to detrital food webs and affect the distribution and abundance of benthic taxa associated with organic matter.     

An assessment of the sources of error in estimations of bulk sedimentary pigment concentrations and its implications for trophic status assessment

Rates of leaf litter processing and densities of macroinvertebrates in leaf packs were compared at two sites that differed in catchment logging history. The processing rate of leaves of sugar maple (Acer saccharum Marsh.) was significantly faster in a stream draining a catchment that had been logged about 20 years ago than in one that had been undisturbed for 80 years. The faster processing rate was accompanied by significantly higher leaf pack densities of total macroinvertebrates, shredders, and collector-gatherers. The higher densities of leaf pack macroinvertebrates were apparently a result of differences in tree species between the two catchments. These differences resulted in greater inputs of fast-decomposing leaf litter to the stream draining the disturbed catchment and in smaller amounts of leaf litter remaining in the stream draining the disturbed catchment by spring when this study was conducted. The Unit is jointly sponsored by the West Virginia Department of Natural Resources, West Virginia University, the U.S. Fish and Wildlife Service, and the Wildlife Management Institute. The Unit is jointly sponsored by the West Virginia Department of Natural Resources, West Virginia University, the U.S. Fish and Wildlife Service, and the Wildlife Management Institute.     

Over-winter decomposition and associated macroinvertebrate communities of three deciduous leaf species in forest streams on the Canadian Boreal Shield

The decomposition of deciduous leaf material provides a critical source of energy to aquatic food webs. Changes to riparian forests through harvesting practices may alter the species composition of deciduous leaf material entering streams. We compared over-winter decomposition of three different riparian leaf species (speckled alder (Alnus incana ssp. rugosa (Du Roi) J. Clausen), white birch (Betula papyrifera Marsh.), and trembling aspen (Populus tremuloides Michx.)) to determine their importance as a food resource for macroinvertebrate communities within Boreal Shield streams in northeastern Ontario, Canada. Leaf pack decomposition of the three leaf species formed a processing continuum throughout winter, where alder and birch leaf packs decomposed at a medium rate (k = 0.0065/day and 0.0053/day, respectively) and aspen leaf packs decomposed more slowly (k = 0.0035/day). Macroinvertebrate community colonization on leaf packs changed through time regardless of leaf species. Alder leaf packs supported higher abundances of macroinvertebrates in the fall while aspen leaf packs supported greater shredder abundances in the following spring. The study shows that leaf diversity may be important for providing a sustained food resource for aquatic macroinvertebrates throughout the relatively long over-winter period in Canadian Boreal Shield streams. Riparian forest management strategies should ensure that deciduous plant species richness is sustained in riparian areas.     

A comparison of streams in logged and unlogged areas of Great Smoky Mountains National Park

Second order streams draining areas of virgin forest in Great Smoky Mountains National Park, Tennessee and North Carolina, U.S.A., are compared to those which drain forests logged before the establishment of the park in the 1930's. Water quality of two main study streams (one unlogged and one formerly logged) was compared and the unlogged stream had generally higher levels of dissolved solids and lower levels of suspended particulates than the logged stream. Stream channel characteristics were compared on four logged and four unlogged streams. The unlogged streams had over four times more (by volume) of woody debris and 10 times more material in debris dams than the logged streams. Only minor differences in substrate composition were observed. Macroinvertebrate samples from the four logged and four unlogged streams showed that the logged streams contained greater numbers of organisms and more taxa. More detailed sampling on the two main study streams showed similar patterns of more individuals and more taxa in the logged stream, as well as differences in the composition of five functional groups. These differences in invertebrate fauna may be due to differences in quantity and quality of leaf litter inputs, although other explanations are also possible.     

Effects of upland clearcutting and riparian partial harvesting on leaf pack breakdown and aquatic invertebrates in boreal forest streams

1. Leaf litter breakdown and associated invertebrates were compared among three logged and three reference stream reaches 2–3 years before and 3–4 years after logging to assess the environmental impacts of partial‐harvest logging as a novel riparian management strategy for boreal forest streams. 2. Partial‐harvest logging at three sites resulted in 10, 21 and 28% average basal area removal from riparian buffers adjacent to upland clear‐cut areas. 3. Leaf litter breakdown rates were not significantly different between reference and logged sites after logging, but litter breakdown was significantly different from year to year at all sites. 4. Significant post‐logging differences in aquatic invertebrate communities were detected at only one of the three logged sites. These differences were largely the result of increases in some leaf‐shredding stoneflies and a detritivorous mayfly and a decrease in a chironomid group 2–4 years after logging. This site where significant change was detected had the lowest intensity of riparian logging (average 10% removal) but the highest proportion of the catchment area that was clear cut (85%). 5.The post‐logging differences in invertebrate communities at this site were more related to catchment‐wide influences (e.g. weather patterns, water yield, possibly upland clearcutting) than to reach‐level disturbances from riparian logging. 6.The study indicates that partial‐harvest logging in riparian buffers at up to 50% removal should pose little risk of harm to leaf litter breakdown processes or aquatic invertebrate communities beyond any impacts that might arise from upland logging disturbance or catchment‐wide influences. However, the results should be viewed in the context of the natural disturbance (summer drought conditions) through the post‐logging assessment period of this study. Post‐logging summer drought conditions may have masked or confounded logging impacts on streams.     

Patterns of macroinvertebrate colonization on fresh and senescent alder leaves in two Michigan streams

SUMMARY.

• 1 Communities of invertebrates colonizing senescent autumn and fresh summer alder leaves (Alnus rugosa) were compared. Leaf packs for each treatment were placed in two hardwater streams in the Upper Peninsula of Michigan in late summer and early autumn. One stream has a cobble-bottom and the other a sand-bottom and both receive fresh leaf inputs by beaver fellings.
• 2 Fresh leaf packs remained intact after 26 days immersion, but thereafter were processed faster than were the autumn leaf packs in both streams.
• 3 In the cobble-bottom stream taxon richness (S), numbers of individuals and biomass were higher on fresh than on autumn leaves.
• 4 Fresh leaves in the sand-bottom stream supported a more diverse (H'), richer (S) and more equitably distributed (J') insect fauna than did the autumn leaves.
• 5 We discuss the simultaneous lack of fresh leaf loss and the presence of more complex insect communities on those leaves during the first 26 days of the study. Invertebrates in both mid-latitude heterotrophic streams and in tropical lowland wet forest streams may rely on fresh leaf inputs, which have received little attention.

     

Calcium concentration in leaf litter affects the abundance and survival of crustaceans in streams draining warm–temperate forests

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Leaf-pack dynamics in a southern African mountain stream

SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally-occurring leaf packs were studied over 24 months in Langrivier, a second-order mountain stream in the south-western Cape, South Africa. Langrivier is shallow and fast-flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year. 2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10^?5 m³) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10^?3 m³) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m^?2 of stream bed. They were ephemeral, lasting on average <1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year. 3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December). 4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,     

Habitat structure and fish predation: effects on invertebrate colonisation and breakdown of stream leaf packs

1. We investigated the effects of two features of leaf‐pack habitat structure (i.e. mass of a leaf pack and surface area of leaves comprising a leaf pack) and fish predation on colonisation of shredders and leaf breakdown rates in a coldwater stream. Packs were constructed of red maple (Acer rubrum) leaves. 2. A 2 × 3 × 3 factorial experiment was used to manipulate fish predation (exclusion and control cage), leaf‐pack mass (1, 3 and 5 g dry mass) and leaf surface area (small: approx. 17.9 cm², medium: approx. 34.6 cm², large: approx. 65.6 cm²). Exclusion cages had mesh on all sides, whereas control cages lacked mesh on two sides to provide access to fish. 3. Common shredders were Gammarus pseudolimnaeus, Pycnopsyche and Lepidostoma. Shredder biomass per leaf pack increased with the mass of a leaf pack (P < 0.001), but biomass per unit mass of leaf pack did not differ with leaf‐pack mass (P = 0.506). Shredder densities did not respond to the exclusion of fish (P > 0.7) or leaf surface area (P > 0.7), and interactions among treatment factors were not significant (P > 0.2). 4. Breakdown rates were lower for leaf packs comprised of small leaves (P < 0.001) and leaf packs with high mass (P = 0.001). Excluding fish did not significantly affect leaf breakdown rates (P = 0.293), and interactions among treatment factors were not significant (P > 0.3). Breakdown rates were highest when packs consisted of few leaves (i.e. leaf packs with large leaves and low mass) and were colonised by many shredders. 5. Fish predation was not an important factor controlling shredder densities in leaf packs over the spatiotemporal scale of our experiment. Nevertheless, we found shredder colonisation was proportional to leaf‐pack mass and breakdown rates were affected by leaf‐pack size (i.e. number of leaves in a pack). We suspect that fragmentation is the primary mechanism causing the breakdown rates to be dependent on leaf‐pack size.     

Do tadpoles affect leaf decomposition in neotropical streams?

1. Of the relatively few studies that have examined consequences of amphibian declines on stream ecosystems, virtually all have focused on changes in algae (or algal‐based food webs) and little is known about the potential effects of tadpoles on leaf decomposition. We compared leaf litter decomposition dynamics in two neotropical streams: one with an intact community of tadpoles (with frogs) and one where tadpoles were absent (frogless) as a result of a fungal pathogen that had driven amphibians locally extinct. The stream with tadpoles contained a diverse assemblage (23 species) of larval anurans, and we identified five species of glass frog (Centrolenidae) tadpoles that were patchily distributed but commonly associated with leaf detritus and organic sediments in pools. The latter reached total densities of 0–318 tadpoles m^?2. 2. We experimentally excluded tadpoles from single‐species leaf packs incubated over a 40‐day period in streams with and without frogs. We predicted that decomposition rates would be higher in control (allowing access of tadpoles) treatments in the study stream with frogs than in the frogless stream and, in the stream with frogs, in the control than in the tadpole exclusion treatment. 3. In the stream with frogs, Centrolene prosoblepon and Cochranella albomaculata tadpoles were patchily distributed in leaf packs (0.0–33.3 m^?2). In contrast to our predictions, leaf mass loss and temperature‐corrected leaf decomposition rates in control treatments were almost identical in our stream with frogs (41.01% AFDM lost, k_{degree day} = ?0.028 day^?1) and in the frogless stream (41.81% AFDM lost, k_{degree day} = ?0.027 day^?1) and between control and tadpole exclusion treatments within each stream. Similarly, there were no significant differences in leaf pack bacterial biomass, microbial respiration rates or macroinvertebrate abundance between treatments or streams. Invertebrate assemblages on leaf packs were similar between treatments (SIMI = 0.97) and streams (SIMI = 0.95) and were dominated by larval Chironomidae, Simuliidae (Diptera) and larval Anchytarsus spp. (Coleoptera). 4. In contrast to dramatic effects of grazing tadpoles on algal communities observed previously, tadpoles had no major effects on decomposition. While centrolenid tadpoles were common in the stream with frogs, their patchy distribution in both experimental and natural leaf packs suggests that their effects on detrital dynamics and microbes are probably more localised than those of grazing tadpoles on algae.     

Invertebrate colonization and processing of maple leaf litter in a forested and an agricultural reach of a stream

Processing of maple leaf (Acer saccharum Marsh) packs, their colonization by invertebrates and nutrient dynamics in leaves were investigated in a forested reach and agricultural reach of Canagagigue Creek, Ontario. Shredders, Pycnopsyche, and collectors, Ephemerella subvaria, Stenonema vicarium and Baetis were significantly more numerous in packs at the forest site than in packs at the agricultural site, whereas filter feeders, especially blackflies, were significantly more numerous in packs at the agricultural site. Weight loss of litter packs was nearly equivalent at the two sites. However, there were major differences in the mechanism of processing between the sites. Physical abrasion and microbial activity governed weight loss of maple leaf packs at the agricultural site, whereas processing was governed mainly by microbial and invertebrate activity and, to a much lesser extent, by physical abrasion at the forest site. Both shredders and collector species played an important role in the processing of leaf material at the forest site. Greater uptake of N and P (P<0.05 in spring) and higher C concentrations were observed in leaf packs at the forest site than the agricultural site. Therefore, the results support the concept of retention of nutrients in forested areas and their export in deforested (agricultural) areas. Findings also indicated that the processing of leaf litter is not an efficient means of monitoring changes in stream ecosystems since leaf processing is affected by many factors, particularly physical abrasion.     

Leaf breakdown in streams differing in catchment land use

1. The impact of changes in land use on stream ecosystem function is poorly understood. We studied leaf breakdown, a fundamental process of stream ecosystems, in streams that represent a range of catchment land use in the Piedmont physiographic province of the south‐eastern United States. 2. We placed bags of chalk maple (Acer barbatum) leaves in similar‐sized streams in 12 catchments of differing dominant land use: four forested, three agricultural, two suburban and three urban catchments. We measured leaf mass, invertebrate abundance and fungal biomass in leaf bags over time. 3. Leaves decayed significantly faster in agricultural (0.0465 day^?1) and urban (0.0474 day^?1) streams than in suburban (0.0173 day^?1) and forested (0.0100 day^?1) streams. Additionally, breakdown rates in the agricultural and urban streams were among the fastest reported for deciduous leaves in any stream. Nutrient concentrations in agricultural streams were significantly higher than in any other land‐use type. Fungal biomass associated with leaves was significantly lower in urban streams; while shredder abundance in leaf bags was significantly higher in forested and agricultural streams than in suburban and urban streams. Storm runoff was significantly higher in urban and suburban catchments that had higher impervious surface cover than forested or agricultural catchments. 4. We propose that processes accelerating leaf breakdown in agricultural and urban streams were not the same: faster breakdown in agricultural streams was due to increased biological activity as a result of nutrient enrichment, whereas faster breakdown in urban streams was a result of physical fragmentation resulting from higher storm runoff.     

Estimating the biomass of freshwater mussels (Bivalvia: Unionidae) from shell dimensions

Packs of autumn-shed maple leaves were placed at coal ash effluent-exposed and reference sites in streams on December 5, 1977 and removed after 27 and 96 days. Leaf surface area (cm²/leaf) and disc weight (ash-free dry wt/15 mm disc) were greater at the effluent-exposed site than at the reference site after 96 days (p < .001). ATP content of leaves from the reference stream quadrupled between 27 and 96 days while ATP content of effluent-exposed leaves remained low. Macroinvertebrates colonized the leaf packs in the reference site but were not found on or in effluent-exposed packs. We concluded that leaf processing beyond the leaching of soluble organics did not occur in the effluent-exposed packs owing to reduced colonization and decomposition by fungi. Since stream invertebrates prefer decomposed leaf material and animals grow faster on leaves colonized by microbes, the ash effuent appears to indirectly affect macroinvertebrates by interfering with leaf decomposition and thus reducing the quality of their food.     

Leaf processing in a woodland stream*

Detritus processing by a small woodland stream is analysed by following the loss of weight of 10 g, single species accumulations of riparian leaves. The daily loss rates are expressed as exponential coefficients after the data are fitted by least squares. Comparisons are made between two sites on a small hardwater trout stream during two seasons. Leaf processing rates form a continuum from a low of 0.5%/day to a high of 2.0%/day. Differences between species of leaf are observed, but significant differences between fall and winter processing and between the two sites are not. The response of the invertebrate community to differences in leaf species is investigated using controlled, artificial streams where significant differences in the effect of the invertebrates are related to the ability ofthe leaf to be processed. Evidence suggests that differential invertebrate colonization of leaf packs is a function of microbial colonization and conditioning. The data are used to develop a general scheme of leaf pack processing.     

Resource–consumer diversity: testing the effects of leaf litter species diversity on stream macroinvertebrate communities

1. Understanding relationships between resource and consumer diversity is essential to predicting how changes in resource diversity might affect several trophic levels and overall ecosystem functioning. 2. We tested for the effects of leaf litter species diversity (i.e. litter mixing) on litter mass remaining and macroinvertebrate communities (taxon diversity, abundance and biomass) during breakdown in a detritus‐based headwater stream (North Carolina, U.S.A.). We used full‐factorial analyses of single‐ and mixed‐species litter from dominant riparian tree species with distinct leaf chemistries [red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera), chestnut oak (Quercus prinus) and rhododendron (Rhododendron maximum)] to test for additivity (single‐species litter presence/absence effects) and non‐additivity (emergent effects of litter species interactions). 3. Significant non‐additive effects of litter mixing on litter mass remaining were explained by species composition, but not richness, and litter‐mixing effects were variable throughout breakdown. Specifically, small differences in observed versus expected litter mass remaining were measured on day 14; whereas observed litter mass remaining in mixed‐species leaf packs was significantly higher on day 70 and lower on day 118 than expected from data for single‐species leaf packs. 4. Litter mixing had non‐additive effects on macroinvertebrate community structure. The number of species in litter mixtures (two to four), but not litter species composition, was a significant predictor of the dominance of particular macroinvertebrates (i.e. indicator taxa) within mixed‐species packs. 5. In addition, the presence/absence of high‐ (L. tulipifera) and low‐quality (R. maximum) litter had additive effects on macroinvertebrate taxon richness, abundance and biomass. The presence of L. tulipifera litter had both positive (synergistic) and negative (antagonistic) effects on invertebrate taxon richness, that varied during breakdown but were not related to litter chemistry. In contrast, the presence/absence of L. tulipifera had a negative relationship with total macroinvertebrate biomass (due to low leaf mass remaining when L. tulipifera was present and higher condensed and hydrolysable tannins associated with leaf packs lacking L. tulipifera). Macroinvertebrate abundance was consistently lower when R. maximum was present, which was partially explained by litter chemistry [e.g., high concentrations of lignin, condensed tannins, hydrolysable tannins and total phenolics and high carbon to nutrient (N and P) ratios]. 6. The bottom‐up effects of litter species diversity on stream macroinvertebrates and litter breakdown are different, which suggests that structural attributes of macroinvertebrate communities may only partially explain the effects of litter‐mixing on organic matter processing in streams. In addition, stream macroinvertebrates colonising decomposing litter are influenced by resource diversity as well as resource availability. Broad‐scale shifts in riparian tree species composition will alter litter inputs to streams, and our results suggest that changes in the diversity and availability of terrestrial litter may alter stream food webs and organic matter processing.