Leaf Bags Research Articles

Taxonomic and functional diversity of stream invertebrates along an environmental stress gradient

Anthropogenic stress has been identified as main driver of freshwater biodiversity loss. Adverse effects on the biodiversity of freshwater organisms, such as macroinvertebrates, may propagate to associated ecosystem functions, such as organic matter breakdown (OMB). In this context, the functional diversity (FD) of communities has been suggested to be a more suitable predictor of changes in ecosystem functions than taxonomic diversity (TD). We investigated the response of TD and FD of invertebrate communities to an environmental stress gradient and the relation of both metrics to the rate of organic matter breakdown. For this, we sampled macroinvertebrates and determined OMB using leaf bags along an environmental stress gradient (i.e. changes in physicochemical and hydromorphological conditions) in 29 low-order streams. Taxonomic richness decreased with increasing environmental stress (r=−0.55) but was not related to OMB. Conversely, the Simpson diversity of communities was not associated with the gradient but correlated moderately (r=0.41) with OMB. Of three functional diversity indices (functional richness, evenness and divergence), only functional richness correlated moderately with the stress gradient (r=−0.41) and any of the indices correlated with OMB. Nevertheless, functional metrics such as specific trait modalities and the total abundance of the dominant shredders correlated higher (r=0.46 and 0.48) with OMB than the TD indices. Given a relatively small species pool in our study and methodical constraints such as the limited resolution of autecological information, the FD might perform better in other contexts and if focusing on response and effect traits for the stressor and ecosystem function under scrutiny, respectively.

Top predator absence enhances leaf breakdown in an intermittent stream

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

Bagworm bags as portable armour against invertebrate predators

Some animals have evolved the use of environmental materials as “portable armour” against natural enemies. Portable bags that bagworm larvae (Lepidoptera: Psychidae) construct using their own silk and plant parts are generally believed to play an important role as a physical barrier against natural enemies. However, no experimental studies have tested the importance of bags as portable armour against predators. To clarify the defensive function, I studied the bagworm Eumeta minuscula and a potential predator Calosoma maximoviczi (Coleoptera: Carabidae). Under laboratory conditions, all bagworm larvae were attacked by carabid adults, but successfully defended themselves against the predators’ mandibles using their own bags. The portable bags, which are composed mainly of host plant twigs, may function as a physical barrier against predator mandibles. To test this hypothesis, I removed the twig bags and replaced some with herb leaf bags; all bag-removed larvae were easily caught and predated by carabids, while all bag-replaced larvae could successfully defend themselves against carabid attacks. Therefore, various types of portable bags can protect bagworm larvae from carabid attacks. This is the first study to test the defensive function of bagworm portable bags against invertebrate predators.

Seasonal and multi-annual patterns ofPhragmites australisdecomposition in a wetland of the Adriatic area (Northeast Italy): a three-years analysis

Wetlands are one of the most biologically productive ecosystems, in which reedbeds of Phragmites australis are an essentially detritus-based system where litter decomposition is a fundamental process. This study represents a three year dataset describing cyclic trends of Phragmites australis leaf litter breakdown in a temporary and managed environment. For three years, 45 days field experiments were seasonally performed, using leaf bag technique within a large managed temporary pond (Natural Reserve of the Isonzo River Mouth, Northeast Italy), in order to analyze spatial and temporal variation in decomposition processes, to search for patterns on seasonal and inter-annual time scale and to infer the relevance of the main environmental features (physical and chemical) on decomposition dynamic. During the three years of analysis, decay rates (k ) ranges were 0.0066–0.0075 days-1 in autumn, 0.0108–0.0158 days-1 in spring and k = 0.0168 days-1 in summer. Average mass loss per day % range was 0.97–1.31% in autumn, 1.12–2.04% in spring and 1.79–2.06% in summer. A well-defined seasonal cycle was observed through the study years as result of the drought-reflooding dynamic and the highest percentage (91.1%) of the average mass loss per day % variability was explained above all by rainfall, temperature and conductivity.

Organic matter breakdown in streams in a region of contrasting anthropogenic land use

Streams provide ecosystem services to humans that depend on ecosystem functions, such as organic matter breakdown (OMB). OMB can be affected by land use-related disturbance. We measured OMB in 29 low-order streams in a region of contrasting land use in south-west Germany to quantify land use effects on OMB. We deployed fine and coarse mesh leaf bags in streams of forest, agricultural, vinicultural and urban catchments to determine the microbial and invertebrate-mediated OMB, respectively. Furthermore, we monitored physicochemical, geographical and habitat parameters to explain potential differences in OMB among land use types and sites. Only microbial OMB differed between land use types. Microbial OMB was negatively correlated with pH and invertebrate-mediated OMB was positively correlated with tree cover. Generally, OMB responded to stressor gradients rather than directly to land use. Therefore, the monitoring of specific stressors may be more relevant than land use to detect effects on ecosystem functions, and to extrapolate effects on functions, e.g. in the context of assessing ecosystem services.

Experimental manipulation of leaf litter colonization by aquatic invertebrates in a third order tropical stream.

Through a manipulative experiment, the colonization of leaf litter by invertebrates was investigated in two sections of a tropical stream (spatial scale) that differed in function of the canopy cover, one with the presence (closed area) and another without riparian vegetation (open area), during one month of the dry and one of the wet season (temporal scale). The work aimed to verify differences related to four variables: season, canopy cover, leaf type and leaf condition. Litter bags containing arboreal and herbaceous leaves (leaf type variable), non-conditioned and preconditioned (leaf condition variable) were placed at the bottom of the stream in each area (canopy cover variable) and season (dry and wet), and removed after 13-day colonization. The analysis of the remaining litter dry mass per leaf bag emphasizes differences related mainly to seasonality, canopy cover and leaf type, although leaf condition was also important when combined with those three factors. Comparing the abundance of invertebrates per treatment, there was a tendency of high predominance of Chironomidae during the dry season and greater taxa diversity and evenness during the wet season, when the water flow increase could alter the availability of microhabitats for local fauna. Even though canopy cover alone was not a significant source of variation in the abundance of invertebrates, the results showed a tendency of a combined effect of canopy cover with seasonality and leaf condition.

Food, substrate or both? Decomposition of reed leaves (Phragmites australis) by aquatic macroinvertebrates in a large shallow lake (Lake Balaton, Hungary)

The aim of this study was to investigate the use and decomposition of reed leaves (Phragmites australis) by aquatic macroinvertebrates in a lake environment (Lake Balaton, Hungary). Natural and artificial leaves were exposed to separate the use of leaves as substrate and as food at different vertical positions. Although we recorded a low density of macroinvertebrates, mixed-effect models showed that natural leaves were colonized by a higher number of taxa and individuals than artificial leaves. Moreover, indicator species analysis identified two detritivorous species (Dikerogammarus villosus and Asellus aquaticus) as indicators of natural leaves. The obtained results suggest that macroinvertebrates use the leaves of reed not only as substrate but also as food. Leaf decay experiment showed that macroinvertebrates contribute to 87.5% of the total leaf litter decay. Leaf bags positioned at the surface were found to host less individuals but the decay rate was faster. The vertical position did not have an impact on the number of taxa or taxa composition. According to these results, macroinvertebrates represent an important component of detritus-based food webs in reed-vegetated littoral areas of the lake.

Leaf Litter Decomposition and Invertebrate Colonization in Alpine Environments Above the Tree Line: an Experimental Study

ABSTRACT: Recent studies suggested a general warming trend in the Alps, resulting in a significant migration of forests to altitudes higher than the usual, regional tree line. As a consequence, some headwater streams will likely receive more allochthonous organic matter. For this reason, the dynamics of decomposition of terrestrial leaf detritus in stream reaches that naturally lacked this resource represents a subject of considerable interest, on which no information is currently available. The aim of this study was to analyse breakdown and macroinvertebrate colonisation of leaf bags in an Alpine headwater stream above the tree line. Results of this study indicate that decomposition of terrestrial leaves in a lotic alpine environment above the tree line takes place through a process similar to what happens at lower altitudes, but with some differences. The reduced rate of decomposition observed may be due to lower temperatures. At lower altitudes, tree cover provides a supply of organic material sufficie...

Colonisation of leaf litter by lotic macroinvertebrates in a headwater stream of the Phachi River (western Thailand)

Leaf litter decomposition has been widely studied during the last 60 years. However, the relative im- portance of various processes, such as physical abrasion, microbial activity and macroinvertebrates consumption, remains unclear in tropical streams. The aim of this study was to gain insights into the ecological processes leading to the decomposition of leaf litter in headwater streams of Thailand, with a particular focus on the role played by macroinvertebrates. The breakdown rate of two leaf species, Bambusa bambos and Lagerstroemia floribunda, was investigated in a 1 st order tropical stream of Ratchaburi province (western Thailand) using litter bags submerged over an 8-week period. Litter bags were retrieved after 2, 14, 28, 42 and 56 days of immersion and characterised by two metrics, remaining AFDM and faunal composition of macroinvertebrates. Most rapidly decomposed leaves were those of B. bambos placed in riffles and most slowly decomposed were those of L. floribunda placed in pools (k = 0.030 and 0.006 d -1 , respectively). The highest amount of invertebrates per leaf bag were found after 14 days of immersion for B. bambos (174 individuals, SE = 10.0, n = 4) and after 28 days of immersion for L. floribunda (174 individuals, SE = 15.8, n = 5). Faunal composition of invertebrates differed between pools and riffles but not within leaf species. The low influence of shredders (accounting for maximum 5 % of total invertebrate abundance in leaf bags) is in accordance with previous findings in tropical zones, while there is a new thought that physical abrasion may play an important role in leaf decay. Nevertheless, non-shredder invertebrates may indirectly contribute to the decomposition of leaf material. In both pools and riffles, macroinvertebrate communities varied with time, showing a diminution of stream habitability, correlated with progressive water withdrawal.

The influence of water quality and macroinvertebrate colonization on the breakdown process of native and exotic leaf types in sub-alpine stream

Most of the energy input of low-order lotic food webs derives from non-living sources of terrestrial organic matter. For this reason, many studies have examined patterns of leaf breakdown; most recently, interest has focused on the importance of water quality or the nature (native versus exotic) of plant material. In this study, we combined both aspects by analyzing the breakdown process and macroinvertebrate colonization of leaf bags containing leaves of different plant types in two nearby sites with different levels of water quality. We exposed a total of 600 leaf bags made of five leaf types (three native: Alnus incana, Populus alba and Quercus robur; and two exotic: Reynoutria japonica and Robinia pseudoacacia) at two sites of the Pellice River (northwestern Italy). Leaf bags were retrieved after 10, 20, 30, 40, 50 and 60 days, leaf mass loss determined and the associated macroinvertebrates quantified. Significant differences were found in the mass loss and in the colonization of leaf bags between sites but not between native and exotic species. Dry mass loss was different among species but without any evident relation with exotic or native origin of plants. In our study sites, geographical origin of plant detritus is not per se central in shaping macroinvertebrate colonization and mass loss because the impact of wastewater treatment plant effluent seems to be much more important than plant origin in the breakdown process.

Macrofauna in Mediterranean and Black Sea transitional aquatic ecosystems: A comparative study of the benthic populations sampled by box corer and leaf bags

This study compares the ethic macrofauna sampled with a box corer and the leaf bag technique, widely used to study plant detritus decomposition processes. The study was carried out in 10 transitional aquatic ecosystems located in the Mediterranean and the Black Sea, covering a wide salinity range.A total of 171 taxa were sampled, 49 only in the sediment samples, 50 only in the leaf bags and 72 common to both. The macroinvertebrate assemblages sampled by the two techniques were different in terms of taxonomic and functional composition; annelids characterized mainly the corer samples, whereas arthropods were a dominant component in the leaf bags. Concerning functional groups, collectors and shredders were dominant respectively in the corer and the leaf bag samples. The taxonomic and the functional dominant composition also varied in relation to water salinity, mainly in the corer samples but less in the leaf bags. The sediment and leaf bag assemblages were significantly different at the scale of the lagoon and in most of the sampling sites. Primary biological variables and diversity indices showed a common trend with both sampling devices across the salinity gradient, but were also highly variable within each lagoon. The results indicated that the assemblages inhabiting the superficial sediment and colonizing litter detritus in transitional waters were distinct, but also highlighted the heterogeneity among these ecosystems.

Colonisation of low- and high-quality detritus by benthic macroinvertebrates during leaf breakdown in a subtropical stream

Abstract Leaf litter in streams is exploited by benthic macroinvertebrates, and leaf traits may influence colonisation by this group. This study aimed to compare the leaf decomposition rates, structure, and composition of the macroinvertebrate fauna colonising the litter of plant species with contrasting leaf traits. Litter bags from two native plant species ( Sebastiania brasiliensis and Campomanesia xanthocarpa ) and two non-natives ( Hovenia dulcis and Platanus × acerifolia ) were incubated in a subtropical stream. After 7, 14, 21, and 28 days, four leaf bags for each species were removed, and the leaf decomposition rates, density of organisms and trophic guilds, taxonomic richness, and functional composition of the macroinvertebrates were compared. The decomposition rates and densities of organisms, shredders, and collector–gatherers were higher for the leaves considered to be better quality, with lower C:N and Lignin:N ratios (from S. brasiliensis and H. dulcis ). Additionally, the taxonomic and functional compositions of the macroinvertebrates were different for these leaves. In contrast, the species richness and density of the other guilds showed no significant difference between species. This study shows that detritivorous groups prefer leaves of better quality, and most results may be influenced by the high nutritional content and low amount of compounds that complicate fragmentation, such as tannins, lignin, and cellulose. Therefore, the effects of the replacement of riparian plant species on the local macrofauna depend of the traits of the introduced and replaced plant, regardless of their origin.

Predators and Resources Influence Phosphorus Transfer along an Invertebrate Food Web through Changes in Prey Behaviour

Predators play a fundamental role in prey trophic behaviour, with indirect consequences for species coexistence and ecosystem functioning. Resource quality and availability also influence prey trophic behaviour, with potential effects on predator-prey dynamics. Although many studies have addressed these topics, little attention has been paid to the combined effects of predators and resources on prey species coexistence and nutrient transfer along food chains, especially in detritus-based systems. To determine the influence of predators and resource quality on the movement and P uptake of detritivores, we carried out a field experiment on the River Kelvin (Scotland) using 32P to test the hypothesis of reduced prey vagility among resource patches as a strategy to avoid predation. Thirty leaf sacks containing alder leaves and two detritivore prey populations (Asellus aquaticus and Lymnaea peregra) were placed in cages, half of them with two predator species (Dendrocoelum lacteum and Erpobdella octoculata) and the other half without predators. Five alder leaf bags, each individually inoculated with a different fungus strain to simulate a patchy habitat, were placed inside each leaf sack. One bag in each sack was labelled with 32P, in order to assess the proportion of detritivores using it as food and thus their movement among the five resource patches. Three replicates for each labelled fungus and each predation treatment (i.e. with and without predators) were left on the riverbed for 7 days. The presence of predators had negligible effects on the number of detritivores in the leaf bags, but it did reduce the proportion of 32P-labelled detritivores and their P uptake. The most strongly affected species was A. aquaticus, whose vagility, trophic overlap with L. peregra and P uptake were all reduced. The results confirm the importance of bottom-up and top-down forces acting simultaneously to regulate nutrient transfer along food chains in patchy habitats.

Leaf quality influences invertebrate colonization and drift in a temperate rainforest stream

Changes in riparian forest composition and diversity, such as plantations of exotic species, may alter resource quality, detritivore assemblages, and litter breakdown rates in streams. We hypothesized that different litter resources may influence colonization and drift of invertebrates inhabiting small, temperate rainforest streams in southwestern British Columbia, Canada. Leaves of different quality and origin were incubated in stream-side channels to test this hypothesis. The sequence of leaf decomposition rates was as follows: alder > alder + cedar > cedar ≥ eucalyptus. Cedar litter decayed faster when mixed with alder than when alone. Invertebrates colonizing leaf bags were predominantly collector–gatherers and shredders, particularly on alder leaves. Drift density varied over the incubation period and seemed to be controlled by leaf quality, since there were more individuals drifting from channels with alder leaves than from channels with cedar or eucalyptus. However, we observed different species-specific invertebrate responses controlled by leaf traits, particularly by numerically dominant chironomid species. Indeed, invertebrate drift from channels incubated with alder bags was mostly due to pupation and emergence of orthoclad midges, whereas this was not observed in the other channels. This differential response in colonization and drift has the potential to modify the transfer rates of organic matter to higher trophic levels and thus ecosystem functioning.

Experimental wood addition in streams: effects on organic matter storage and breakdown

Summary 1. Channel complexity affects the physical structure, biotic communities and functioning of stream ecosystems. Large wood (LW) is a key element in the creation and maintenance of physically complex stream channels in forested areas. 2. In an attempt to enhance stream habitat quality and ecosystem functioning and to reduce inputs of organic matter to a downstream reservoir, LW was experimentally introduced into four mountain streams in the Basque Country (northern Spain), ranging in channel width from 3 to 13 m. Following a before–after/control–impact (BACI) design, streams were monitored during 1 year prior to wood addition and during 2 years after addition in one control and one experimental reach per stream. 3. Areal cover of benthic organic matter in the entire channel was measured from regular transects and the mass of stored organic matter from random Surber samples. Breakdown of organic matter was assessed in litter bag experiments performed with black alder leaves. When 50% of the initial mass in the bags remained, invertebrates associated with leaf bags were collected. 4. Wood placement produced a 2- to 70-fold increase in the storage of organic matter, especially in thick deposits upstream from wood jams, with values in excess of 2 kg AFDM per m2 in the small streams. The accumulation of organic matter produced by wood introduction decreased with increasing stream size. 5. Despite the large increase in the availability of organic matter, litter breakdown rates were unaffected by the experimental reaches, suggesting large increases in the total amount of organic matter consumed at the reach scale. 6. Numbers of invertebrates and shredders per gram of leaf litter did not respond to wood addition. Average body mass of invertebrates associated with leaf litter showed a non-significant decreasing trend, which might reflect increased recruitment. 7. Although the effects of wood addition can depend on wood stability and stream size, adding LW to restore channel complexity can improve environmental conditions for invertebrate communities and affect stream ecosystem functioning, enhancing the efficiency to use organic matter inputs on a reach scale.

Phosphorus Enrichment Affects Immobilization but not Litter Decomposition or Exoenzymatic Activities in a Pampean Stream

AbstractThe effect of phosphorous enrichment on decomposition rate, exoenzymatic activities (β‐glucosidase, cellobiohydrolase and alkaline phosphatase), and macroinvertebrate abundance in Typha latifolia leaves were assessed in a 2nd order Pampean stream (Central Argentina). Phosphorous was added to a downstream reach while another reach located upstream was kept intact and, once significant differences in phosphorus concentration in water were attained, leaf bags were attached to each reach bottom. T. latifolia leaves lost 77% of their initial weight along 154 days and decomposition rates were not significantly different between reaches. Besides, neither exoenzymatic activities nor macroinvertebrate abundances differed between reaches. However, an increment in leaf phosphorus content, attributed to immobilization by decomposer microorganisms, was detected in the enriched reach. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Leaf Litter Decomposition of Three Riparian Tree Species and Associated Macroinvertebrates of Eswathu Oya, a Low Order Tropical Stream in Sri Lanka

AbstractLeaf decomposition, an important component of the organic matter dynamics in streams, has been widely examined in temperate regions but much less documented in tropical regions. We report here the first study of leaf decomposition in a Sri Lankan stream. The litterbag technique was used. Coarse (8 mm) and fine (100 µm) litterbags, that included or excluded macroinvertebrates respectively, were used to enclose leaves of three dominant riparian tree species: native Ochlandra stridula (bamboo), and the introduced Alstonia macrophylla and Hevea brasiliensis (rubber). A fourth set of litterbags contained a mixture of these three species. Leaf colonization by macroinvertebrates was highest in the early stages of the decomposition process on Hevea leaves but invertebrate densities declined later. The opposite colonization effect was observed on the native Ochlandra leaves: slow colonization with continuing low densities from the beginning to the end of the process. Decomposition of all three species was significantly faster in the coarse than in the fine mesh bags. Alstonia, which has the softest leaf tissue, was most rapidly decomposed while Ochlandra, with its tough structure, was the slowest. Among the invertebrates, insects were the most important leaf colonizing animals, with Diptera, Coleoptera and Trichoptera the most dominant. The invertebrate variety in the mixed bags was higher than in the single‐species leaf bags, where Chironomidae dominated the colonizing assemblages. This study has shown that toughness, indicated by the ‘specific weight of leaf tissue’, and the quality of the leaves was more important in determining breakdown rates than their origin. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Decomposition of native leaf litter by aquatic hyphomycetes in an alpine stream

Despite the recognised significance of hyphomycetes in the degradation of leaf litter in streams, few studies have been carried out in alpine environments and none in Australian alpine streams. We hypothesised that the fungal communities responsible for leaf decomposition would change over immersion time, and would respond differently at different sites and on different types of vegetation. Leaf bags containing Epacris glacialis (F. Muell.), Eucalyptus pauciflora (Sieber ex. Spreng) and Eucalyptus delegatensis (R.T. Baker) were deployed at different sites in a stream in the Victorian Alpine National Park, south-eastern Australia. Leaf colonisation was delayed for 2 weeks and decay constants for E. pauciflora and E. delegatensis were 0.004–0.005 and 0.006 respectively. Maximum fungal biomass on leaves was similar to that in previous published studies, whereas sporulation rates were two or three orders of magnitude lower, indicating a reduced reproductive effort. Sporulation and DNA-based studies combined showed that fungal communities on the decomposing leaf material changed over time and exhibited significant preferences for leaf type and study site. We have shown that aquatic hyphomycetes can degrade physically tough leaves of Australian alpine plant species, potentially contributing to pathways for particulate carbon to enter alpine-stream food webs.

Nutrient addition does not enhance leaf decomposition in a Southeastern Brazilian stream (Espinhaço mountain range)

A decomposition experiment using eucalyptus leaves was carried out in a Southeastern Brazilian mountain stream located at the transition between the Cerrado and the Atlantic Forest to test whether nutrient addition increases microbial and invertebrate colonisation and accelerates breakdown rates. The results show that none of the tested variables was significantly affected by nutrient addition, despite the average increase in ATP concentrations and invertebrate colonisation observed in the fertilised leaf bags. This could mean that breakdown in the stream was already at its maximum due to the relatively high water temperature and nutrient content, or that the breakdown rate of eucalyptus leaves was too fast to allow the detection of any effects of nutrient addition. Breakdown rates of eucalyptus leaves were much faster than the values reported in literature for most species in Brazilian Cerrado streams, suggesting that the replacement of the natural vegetation by eucalyptus may affect nutrient dynamics in the region.

How can habitat size influence leaf litter decomposition in five mid-Appalachian springs (USA)? The importance of the structure of the detritivorous guild

Although habitat size is known to influence both structural and functional properties of ecosystems, there have been few attempts to assess the influence of habitat size on ecosystem processes. Here we investigated the relationships between leaf litter decomposition and ecosystem surface area, macroinvertebrates and physico-chemical factors in five freshwater springs located in Huntingdon County (Pennsylvania, U.S.A.). Leaves of Ulmus americana L. were used to study leaf litter breakdown with the litter-bag technique. Field work was carried out at one sampling station per spring, each with eight replicates per sampling time (3, 20, 40 days), from April to May 2004. American elm leaves decomposed at different rates in the different springs, varying inversely with the spring area. The leaf bags were colonized by 16 taxa of benthic macrofauna, amongst which scrapers and shredders were the most common guild. Macroinvertebrate species richness co-varied with spring area, but not with other physico-chemical variables. Moreover, a significant inverse relationship was observed between American elm leaf decay rate and taxonomic richness. In the studied springs, habitat area was an ecosystem feature indirectly affecting detritus processing by influencing the structure of the detrital food web within the systems.