Leaf Bags Research Articles

Present Effects of Past Wildfires on Leaf Litter Breakdown in Stream Ecosystems

We investigated the present effects from a 10-year-old wildfire on leaf litter breakdown rates in 3 head-water streams in central Idaho. These systems experienced a massive debris flow one year after the fire. Based on soil instability and burn patterns, we identified 3 stream conditions; unburned, burned only, and burned/scoured. We placed leaf bags containing willow leaves (Salix sp.) in each stream type and removed bags at various time intervals until all bags were collected 100 days after their introduction. Leaf material was dried and weighed, and decay rate coefficients were calculated. Macroinvertebrates colonizing the bags were enumerated and identified, and selected taxa were placed into trophic groups. We found that the unburned stream had the fastest leaf litter breakdown rate, the lowest level of incident light reaching the stream, and the largest amount of benthic organic matter. The burned/scoured stream was nearly opposite in all respects. Numbers of 2 detritivore invertebrate taxa, Serratella tibialis and Zapada oregonensis, were highest in the unburned stream but lowest in the burned/scoured stream. A third taxon, Baetis sp., showed the opposite relationship. Presence of predatory invertebrates did not affect detritivore abundance or leaf decay rate in the bags, Our research suggests that recovery response variables of some stream systems may not have returned to prefire levels even a decade after the initial wildfire. In this study, the recovery of our streams appears to be connected to the return of the riparian zone, though fire-induced debris flows may slow or alter final recovery of the stream system.

Decomposition of reed swamp detritus in the Danube Delta: a case study of four eutrophic systems

Leaf litter decomposition rates in aquatic ecosystems are known to be related to many abiotic and biotic factors. Here, field experiments were carried out during fall 2005 in four sites of the Danube Delta system, differing mainly in terms of type and characterised by euthrophycation. The litter bag technique was used to study reed decomposition and evaluate the relevance of ecosystem characteristics to reed leaf decay rates. Trophic conditions were very high in all sites (TRIX > 8.0), indicating poor water quality. Overall, the processing rate k of Phragmites australis in the Danube Delta was equal to 0.016 days-1. The mass remaining in the leaf bags differed among ecosystems (ANOVA, P A high percentage (>60%) of leaf breakdown variability was related to differences in phosphorus compound concentrations in the water.

In situ experimental study of reed leaf decomposition along a full salinity gradient

An experimental study on Phragmites australis leaf litter decomposition was conducted in the estuarine environment, Ria de Aveiro, Western Portugal, using the leaf-bag technique, with fine- (1 mm) and coarse-mesh (5 mm) bags. The leaf bags were placed in the field sites at day 0, covering a complete salinity gradient, and replicates were collected over time, at days 3 (leaching), 7, 15, 30 and 60. The biomass loss through the leaching phase, about 20% of the initial leaf mass, was independent of both the salinity and the bag mesh size. The biomass decay pattern along the salinity gradient varied through time and presented strong similarities between the two mesh sizes, with the remaining biomass always lower in the 5 mm mesh-size bags. At days 7 and 15, the lowest remaining biomass was observed at the head of the estuary, the preferential distribution area of P. australis. At day 30, the remaining biomass was higher in the marine area and diminished under a direct relationship with salinity, reaching the lowest value in the freshwater environment, with values ranging from 66% to 44% of the initial weight in 5 mm bags, and from 79% to 51% in 1 mm bags. The largest heterogeneity in the remaining biomass among the study areas positioned along the salinity gradient was found close to days 30 (5 mm) and 40 (1 mm). The overall results indicate that the relationship between leaf decay rate and salinity depends on the decay time considered ( k 15, k 30 or k 60) and, for the later stages ( k 60), also on the leaf-bag mesh size. This implies that the use of leaf litter decay rates as a functional indicator in transitional waters will need to take into consideration the factor location in the salinity gradient and leaf litter stage at which the decay rate is determined. The differences between the decay rates with the mesh size acted mainly at the level of the absolute k value and not at the level of the pattern along the salinity gradient. Even so, the data obtained at the mouth of the estuary, in the area closest to a fully marine environment, indicated that after the initial biomass loss through leaching, P. australis decayed either very slowly, in the 5 mm, or not at all, in the 1 mm mesh bags.

Relationships between structure and function in streams contrasting in temperature

Summary1. We studied 10 first‐order Icelandic streams differing in geothermal influence in separate catchments. Summer temperature (August–September) ranged between 6 and 23 °C.2. Macroinvertebrate evenness and species overlap decreased significantly with temperature whereas taxon richness showed no response. In total, 35 macroinvertebrate species were found with Chironomidae the dominant taxonomic group. Macroinvertebrate density increased significantly with temperature. Dominant species in the warm streams wereLymnaea peregraandSimulium vittatum. Algal biomass, macrophyte cover and richness were unrelated to temperature. Densities of trout (Salmo trutta), the only fish species present, reflected habitat conditions and to a lesser degree temperature.3. Density of filter‐feeders increased significantly with temperature whereas scraper density, the other dominant functional feeding group, was unrelated to temperature. Stable isotope analysis revealed a positive relationship between δ15N and temperature across several trophic levels. No pattern was found with regard to δ13C and temperature.4. Leaf litter decomposition in both fine and coarse mesh leaf bags were significantly correlated to temperature. In coarse mesh leaf packs breakdown rates were almost doubled compared with fine mesh, ranging between 0.5 and 1.3 g DW 28 days−1. Nutrient diffusion substrates showed that the streams were primarily nitrogen limited across the temperature gradient while a significant additional effect of phosphorous was found with increasing temperature.5. Structural and functional attributes gave complementary information which all indicated a change with temperature similar to what is found in moderately polluted streams. Our results therefore suggest that lotic ecosystems could be degraded by global warming.

Leaf‐Litter Mixtures Affect Breakdown and Macroinvertebrate Colonization Rates in a Stream Ecosystem

AbstractPrevious work in terrestrial and aquatic ecosystems has suggested that the relationship between breakdown rates of leaf litter and plant species richness may change unpredictability due to non‐additive effects mediated by the presence of key‐species. By using single‐ and mixed‐species leaf bags (7 possible combinations of three litter species differing in toughness; common alder [Alnus glutinosa ], sweet chestnut [Castanea sativa ], and Spanish oak [Quercus ilex ilex ]), I tested whether leaf species diversity, measured as richness and composition, affects breakdown dynamics and macroinvertebrate colonization (abundance, richness and composition) during 90 days incubation in a stream. Decomposition rates were additive, i.e., observed decomposition rates were not different from expected ones. However, decomposition rates of individual leaf species were affected by the mixture, i.e., there were species‐specific responses to mixing litter. The invertebrate communities colonizing the mixtures were not richer and more diverse in mixtures than in single‐species leaf bags. On the opposite, mixing leaf species had a negative, non‐additive effect on rates of shredder and taxa colonization and on macroinvertebrate diversity. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Leaf diversity influences in‐stream litter decomposition through effects on shredders

Summary1. The functioning of many aquatic ecosystems is controlled by surrounding terrestrial ecosystems. In a view of growing interest in linking biodiversity to ecosystem‐level processes, we examined whether and how leaf diversity influences litter decomposition and consumers in streams.2. We tested experimentally the hypothesis that the effects of leaf diversity on decomposition are determined by the responses of leaf consumers to resource–habitat heterogeneity. Leaves from three common riparian trees, beech (Fagus sylvatica), hazel (Corylus avellana) and ash (Fraxinus excelsior), were exposed alone and in all possible mixtures of two and three species in a stream. We analysed individual leaf species for decomposition rate, microbial respiration and mycelial biomass, and we determined the species composition, abundance and biomass of shredders in leaf bags.3. We found that the decomposition of the fastest decomposing leaves (hazel and ash) was substantially stimulated (up to twofold higher than single species leaf packs) in mixtures containing beech leaves, which are refractory. In contrast, the decomposition of beech leaves was not affected by leaf mixing. Such species‐specific behaviour of leaves in species mixtures has been overlooked in previous studies that examined the overall decomposition of litter mixtures.4. The effects of leaf diversity on decomposition varied with the abundance and biomass of shredders but not with microbial parameters. Beech leaves alone were less attractive to shredders than leaf packs made of hazel, ash or any mixture of species. Moreover, the presence of beech leaves in mixtures led to higher shredder abundance and biomass than we had expected from data from single species exposed alone. Lastly, we found that early instars of the caddisfly Potamophylax (the dominant shredder in terms of biomass) almost exclusively used the toughest material (i.e. beech leaves) to construct their cases.5. Leaf pack heterogeneity may have altered shredder‐mediated decomposition. Shredders colonising diverse leaf packs benefited from the stable substratum provided by beech leaves, whereas ash and hazel leaves were primarily used as food. Thus, our findings provide strong evidence for an intimate linkage between the diversity of riparian vegetation and aquatic communities.

Responses in organic matter accumulation and processing to an experimental wood addition in three headwater streams

Summary1. Additions of large wood are being used to restore streams that have been subjected to channelization, wood removal or riparian timber harvest. This added wood potentially increases channel stability, habitat complexity and organic matter retention and improves habitat and productivity of higher trophic levels. However, few stream restorations monitor restoration effectiveness after project completion.2. We added 25 aspen logs (each 2.5 m length × 0.5 m diameter) to 100‐m reaches of each of three forested headwater streams in the Upper Peninsula of Michigan, U.S.A. These wood‐poor streams drain forests that were completely harvested of timber over a century ago and have been selectively logged for the past 50–60 years. An upstream unmanipulateds 100‐m reach in each stream served as the control.3. We evaluated responses in organic matter processing by measuring red maple leaf decomposition 1 year before and 2 years after wood addition. We also quantified coarse organic matter standing stocks in the main channel and in debris accumulations associated with large wood. In response to wood addition, we predicted both organic matter standing stocks and leaf decomposition rates would increase, thereby enhancing resource availability to higher trophic levels.4. Leaf decomposition rates did not change following wood addition. Temporal variation in rates among streams was mostly explained by differences in degree days, water velocity, scour/burial and water column inorganic nitrogen concentrations, but not large wood. Variation within streams across years was explained by differences in degree days, water velocity and shredder biomass.5. Contrary to our prediction, organic matter standing stocks did not increase significantly at the reach scale. However, the experimentally added wood retained c. 4% of total annual coarse benthic organic matter (CBOM) in the first year and an additional c. 15% in the second year, suggesting accumulation over time in the manipulated reaches. The CBOM held by the new logs may be more biologically available because it is less susceptible to burial and transport than material in the streambed.6. Some shredding macroinvertebrates responded to changes caused by the wood additions. In particular, the common caddisfly shredder, Lepidostoma sp., increased in abundance in leaf bags following wood addition, whereas the biomass of the winter stoneflies, Capniidae, declined in the first year.7. Considerable funds are spent to restore in‐stream habitat, but few restorations are monitored, particularly over long periods (>5 years). Our results show that longer‐term monitoring is needed to determine the efficacy of these restorations on ecosystem function; organic matter decomposition in our low‐gradient streams did not respond to a substantial increase in large wood after 2 years.

A Decade after Invasion: Evaluating the Continuing Effects of Rusty Crayfish on a Michigan River

In 2004, we revisited a Michigan stream invaded by rusty crayfish ( Orconectes rusticus) to determine if this species continued to expand its downstream range and negatively impact the stream food web. Compared to a 1992 study, we predicted that rusty crayfish would increase in density and downstream distribution from a small lake, resulting in further reduction of in-stream resources such as organic matter, benthic invertebrates, and periphyton. To determine current crayfish distributions and impacts, we conducted a longitudinal survey of crayfish abundance, ran a 28-d leaf breakdown experiment, and sampled benthic substrates. Leaf packs of sugar maple ( Acer saccharum) leaves were placed at three sites with differing crayfish densities (high, intermediate, and none). Breakdown rates were compared across the three sites and for two treatments (closed leaf bags excluding crayfish and open bags allowing crayfish access). Benthic invertebrates were sampled from leaf bags and invertebrates and periphyton were sampled from cobbles. In contrast to 1992, we found that the maximum downstream distance of rusty crayfish declined from 4 km to less than 3 km downstream from the lake. Leaves in open bags decayed significantly faster (k = 0.143) than did leaves in closed bags at all sites (k = 0.079) (p = 0.0005). The site lacking crayfish had significantly higher densities of invertebrates compared to both high and intermediate crayfish density sites (p = 0.005). Although we found that rusty crayfish reduced standing stocks of leaves and invertebrates, we did not detect measurable changes in periphyton biomass. Therefore, rusty crayfish have not dispersed further downstream since 1992, but where present, these omnivores significantly reduce resource availability via the consumption of leaf material and benthic invertebrates.

A Comparative Study of Leaf Breakdown of Three Native Tree Species in a Slowly‐Flowing Headwater Stream in the Colombian Andes

AbstractThe dynamics of leaf breakdown in a headwater Colombian stream were evaluated for the native tree species Myrsine guianensis, Cupania latifolia and Nectandra lineatifolia using coarse and fine mesh litter bags. Ten bags of each species (five of each mesh size) were retrieved from the stream at 1, 8, 15, 30, 60 and 120 days. k values ranged from 0.0008 to 0.0058 day–1 and density of macroinvertebrates from 35 to 55 individuals per leaf bag, peaking at day 8. Myrsine guianensis degraded more rapidly than the other species for both coarse and fine mesh bags. This species and Nectandra lineatifolia presented differences in k values between coarse and fine mesh bags, suggesting that macroinvertebrates influenced the decay rate. Despite the low densities of macroinvertebrates found, shredders represented 12.7% of individuals and 50 to 68% of the invertebrate biomass in bags, indicating that this functional feeding group was an important component of fauna associated with litter breakdown in this first order tropical stream. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Leaf breakdown in streams differing in catchment land use

Summary1. 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.

Leaf Litter Decomposition in Aquatic and Terrestrial Realms of a Second-Order Forested Stream System

ABSTRACT We conducted a leaf decomposition experiment by placing leaf litter bags in pool and riffle zone in a second-order forested stream, the Yanase River. Identical leaf bags were also placed in the adjacent floodplain and the surrounding forest habitat. Leaves from sakura (Prunus lannesiana) and keyaki (Zelkova serrata) trees from the surrounding forest were placed in multiple mesh bags, which were then sampled regularly from November 13, 2002 to May 20, 2003. The average rate of decomposition was greatest in the riffle habitat, followed by pool, floodplain, and forest floor. Sakura leaves decayed more readily than keyaki leaves.

Effects of Nutrient Enrichment on Decomposition and Fungal Colonization of Sweet Chestnut Leaves in an Iberian Stream (Central Portugal)

This study assessed the effect of nutrient enrichment on rates of decomposition, ergosterol concentrations (as a measure of fungal biomass), and rates of fungal sporulation of sweet chestnut (Castanea sativa Miller) leaves in a 3rd order stream (Central Portugal), with medium to high background values of nutrients. Coarse and fine mesh leaf bags were attached to nutrient diffusing substrata containing NaNO3, KH2PO4, both nutrients, or no additions. Leaf breakdown rates were similar in the four treatments and in the two mesh sizes (k=−0.0155 to −0.0219 day−1). Phosphorus content of P or N + P enriched leaves was higher than in the other treatments after 28 days, but there were no differences in N concentrations. Ergosterol concentrations associated with decomposing leaves were similar among treatments. The peak sporulation rates of aquatic hyphomycetes were stimulated by the addition of N + P and N but not by P alone. Results from the experiment provide evidence that leaf breakdown in the study stream, as a model for streams with naturally medium to high level of nutrients, was not nutrient-limited, and that fungal reproductive activity was limited by dissolved N but not by dissolved P in stream water.

Aggregation among resource patches can promote coexistence in stream‐living shredders

Summary1. We conducted a new single‐site study and a meta‐analysis of pre‐existing studies from multiple streams to assess whether intraspecific aggregation among leaf packs promotes coexistence among leaf‐eating invertebrates (shredders) in Swedish streams.2. In the single‐site study, 48 standardised leaf bags were exposed for 1 month for shredder colonisation in a homogeneous glide of a forested stream. Current velocity, water depth and substratum composition were additionally assessed to investigate how these factors affected shredder distributions.3. The meta‐analysis included information on shredder colonisation of leaf packs from seven other studies of detritus decomposition to assess patterns of aggregation. Intra‐ and interspecific aggregation and their relative strength were assessed using indices (J, C and A respectively) originally developed for terrestrial insects also dependent on patchy and ephemeral resources.4. In both parts of the study, intraspecific aggregation was much stronger than interspecific aggregation, which was weak overall, indicating that the conditions under which aggregation is expected to facilitate coexistence were fulfilled in our shredder assemblages.5. In the single‐site study, shredder abundances were weakly associated with environmental variables suggesting that habitat heterogeneity only partly explains aggregation patterns.6. Our results strongly suggest that shredder diversity in streams, particularly during periods of leaf limitation (such as might occur in spring), is promoted by the aggregation of individual species among patches of resource.

Microbial Biomass, Respiration, and Decomposition of Hura crepitans L. (Euphorbiaceae) Leaves in a Tropical Stream1

ABSTRACTThe processing of leaves in temperate streams has been the subject of numerous studies but equivalent tropical ecosystems have received little attention. We investigated leaf breakdown of a tropical tree species (Hura crepitans, Euphorbiaceae), in a tropical stream using leaf bags (0.5 mm mesh) over a period of 24 days. We followed the loss of mass and the changes in adenosine triphosphate (ATP) concentrations and respiration rates associated with the decomposing leaves. The breakdown rate was fast (k=−0.0672/d, kd=−0.0031/degree‐day), with 81 percent loss of the initial mass within 24 days. This high rate was probably related to the stable and high water temperature (22°C) favoring strong biological activity. Respiration rates increased until day 16 (1.1 mg O2/h/g AFDM), but maximum ATP concentrations were attained at day 9 (725 nmol ATP/g AFDM) when leaf mass remaining was 52 percent. To determine the relative importance of fungi and bacteria during leaf decomposition, ATP concentrations, and respiration rates were determined in samples treated with antibiotics, after incubation in the stream. The results of the samples treated with the antifungal or the bacterial antibiotic suggest a higher contribution of the fungal community for total microbial biomass and a higher contribution of the bacterial community for microbial respiration rates, especially during the later stages of leaf decomposition. However, these results should be analyzed with caution since both antibacterial and antifungal agents did not totally eliminate microbial activity and biomass.

Stream macroinvertebrate communities in leaf bags versus benthos: does leaf type matter?

Stream macroinvertebrate communities in leaf bags versus benthos: does leaf type matter?

Breakdown of leaf litter in a neotropical stream

We investigated the breakdown of 2 leaf species, Croton gossypifolius (Euphorbiaceae) and Clidemia sp. (Melastomataceae), in a 4th-order neotropical stream (Andean Mountains, southwestern Colombia) using leaf bags over a 6-wk period. We determined the initial leaf chemical composition and followed the change in content of organic matter, C, N, and ergosterol, the sporulation activity of aquatic hyphomy cetes, and the structure and composition of leaf-associated aquatic hy phomy cetes and macroinvertebrates. Both leaf species decomposed rapidly ( k 5 0.0651 and 0.0235/d, respec- tively); Croton lost 95% of its initial mass within 4 wk compared to 54% for Clidemia . These high rates were probably related to the stable and moderately high water tempera ture (19 8 C), favoring strong biological a ctivity. Up to 2300 and 1500 invertebrates per leaf bag were found on Croton and Clidemia leaves after 10 and 16 d, respectively. Shredders accounted for , 5% of the total numbers and biomass. F ungal biomass peaked at 8.4 and 9.6% of the detrital mass of the 2 leaf species, suggesting that fungi contributed cons iderably to leaf mass l oss. The difference in breakdown rates between leaf species was consistent with the earlier peaks in ergosterol and sporulation rate in Croton (10 d vs 16 d in Clidemia ) and the faster colonization of Croton by macroinvertebrates. The softer texture, lower tannin content, and hi gher N content were partly responsible for the faster breakdown of Croton leaves. The rapid breakdown of leaf litter, combined with a low infl uence by shredders, is in accordance with previous findings. The high fungal activity associated with rapid leaf breakdown appears to be characteristic of leaf processing in tropical streams.

Macroinvertebrates colonising leaf litter of contrasting quality in a travertine Mediterranean stream

We investigated the invertebrate assemblages that colonised two types of leaf litter bags, which differed considerably in quality: (1) Mixed-species bags made of leaves from indigenous tree and shrub species (Populus nigra L., Rubus ulmifolius SCHOTT, and Salix atrocinerea BROT.); (2) and bags made of the recalcitrant leaves from the exotic species Platanus orientalis L. The study was conducted at two sites differing in riparian canopy located in the Mediterranean stream Rio Vicario, characterised by massive travertine precipitation. The overall density and biomass of invertebrates that colonised the mixed-species bags did not differ significantly from those that colonised the Platanus leaf bags. The same was observed, in general, for the density and biomass of functional feeding groups. The gut content of Leuctra franzi AUB., the most abundant and frequent shredder, showed that only a few individuals (ca. 10 %) had recently consumed leaf litter and only in limited amounts (<15 % leaf remains). Furthermore, the mean percentage of leaf remains in the gut of L. franzi from mixed-species bags did not differ significantly from those colonising Platanus-bags, at the more incrusted site. These results suggest that the travertine crust precipitated on decomposing leaves in Rio Vicario attenuate the effect of leaf litter quality on the macro-invertebrate assemblages colonising leaf bags.

Leaf Bags and Natural Leaf Packs: Two Approaches to Evaluate River Functional Characteristics

An extensive knowledge of the functional characteristics of rivers is of basic importance to develop precise management plans with specific aims, e.g. to rehabilitate riparian ecotones or increase the retention capacity of streams. In this study man-made leaf bags (LB) and natural leaf accumulations (NLP) were used. The first method was useful in calculating breakdown rates and the second one in understanding the effective litter composition, which does not always reflect the composition of the riparian canopy. The assemblages of macroinvertebrate colonizing both LB and NLP were divided into functional feeding groups and compared. Are both methods (Leaf Bags and Natural Leaf Packs) necessary and complementary to analyse the functional characteristics of an upland river? The study was carried out in three different sites on the upper reaches of the Adige River. The breakdown rates were very similar in all three study sites but litter quality and quantity were very different. Although, in the two upper sites, the composition of invertebrates colonizing LB and NLP was the same, abundance and biomass values coincided only in the first stage of the colonization process of LBs. In the third site no invertebrates using litter as a trophic resource were found. Both NLP and LB methods are needed in the evaluation of rehabilitation programs as they take account of the different aspects of the dynamics and the composition of CPOM.

Comparison of Leaf Decomposition in Two Mediterranean Rivers: a Large Eutrophic River and an Oligotrophic Stream (S Catalonia, NE Spain)

The litter bag technique was used to study leaf decomposition in the large forested eutrophic (160.9 μmol l -1 DIN, 1.7 μmol l -1 SRP) Ebro river and in the forested Senia (12.8 μmol l -1 DIN, 0.7 μmol l -1 RSP), Air dried leaves (3g) of Phragmites australis were used in both watercourses while Populus alba leaves were studied in the Ebro river only, and Populus nigra leaves and a submerged rooted macrophyte (stems and leaves), Potamogeton coloratus, were studied only in the Senia stream. Litter bags of 100 μm and 1 mm mesh size were collected on days 0, 3, 15, 30, 90 and 120 and 5 mm mesh bags were sampled once after 30 days. Macroinvertebrates inside the leaf bags were retrieved and ash free dry weight and carbon and nitrogen contents of the remaining detritus were determined. Litter decomposition rates, k, were estimated using a simple exponential model. No significant differences in decomposition rates were observed between 100 μm and I mm mesh bags. In 100 μm litter bags, decomposition of P. nigra leaves from the Senia stream (0.0104 day -1 ) was faster than that of P. alba leaves from the Ebro river (0.0049 day -1 ) (ANCOVA, p < 10 -5 ). The decomposition rate of P. australis was higher in the Ebro river (0.009 ± 0.002 day -1 ) than in the Senia stream (0.0056 ± 0.0004 day -1 ) for the first 30 days of decomposition, but no differences were observed from day 30 onwards. The number of macroinvertebrates increased over time and were mainly collectors-gatherers of the genus Chironomus. Percentage of detritus nitrogen increased in litter that had initially high C/N ratios (28.7 in P. alba and 64.7 in P. nigra) and decreased when initial C/N ratios were low (12.6 and 14.6 for P. australis from the Senia and Ebro river respectively).

III. Methods in Litter Breakdown Leaf Bags and Natural Leaf Packs: Two Approaches to Evaluate River Functional Characteristics

III. Methods in Litter Breakdown Leaf Bags and Natural Leaf Packs: Two Approaches to Evaluate River Functional Characteristics