Macroinvertebrate Colonization Research Articles

Effects of substrate on the benthic macroinvertebrate community: An experimental approach

Wood and concrete are used in restoration projects in streams and rivers worldwide. Although the goal of such projects is often related to geomorphology or fish habitat, there may also be differences between wood and concrete materials in regards to colonization by macroinvertebrates. Similarly, installed structures with smooth surface textures may host different macroinvertebrate communities than those with complex surfaces (e.g., pitted or grooved). In the current study, a multiple-factor experimental setting was used to test the effect of wood and concrete and of their surface complexity in structuring stream macroinvertebrate assemblages. Forty uniform-sized substrates were placed in the Cedar River in northeast Iowa, USA and macroinvertebrate colonization was examined after one and two months. Using distance-based redundancy analysis, it was determined that (1) after one month community differences were only related to underlying streambed composition, (2) after two months differences were only related to smooth versus complex surfaces, and (3) at neither time did communities differ between wood and concrete. These results highlight the importance of colonization time in studies of introduced substrates; within the first month communities may have been related to local streambed inhabitants crawling onto the substrates, by the second month structural differences supported different communities on smooth versus complex surfaces, and over longer time periods it remains possible that communities would have responded to more subtle differences between wood and concrete. We suggest that restorationists should consider macroinvertebrates when installing structures in aquatic environments, and either use structures with both smooth and complex areas to promote different assemblages or conduct studies like this one to determine preferences for taxa of concern.

Empty native and invasive bivalve shells as benthic habitat modifiers in a large river

Bivalves are remarkable ecosystem engineers and their long-lasting shells may provide important physical structures for benthic organisms. In the last decades the Danube River has experienced great changes in the bivalve fauna, i.e. several native species have been declining and several invasive species have been introduced. The invasive Corbicula fluminea and Sinanodonta woodiana are now widespread and produce large amounts of shells. In this study, we investigated empty shells of native (Anodonta anatina, Unio tumidus) and invasive (C. fluminea, S. woodiana) bivalves (including their mixtures) as benthic substrates and compared them to clay granules (control), which mimics the natural hard substrates in the Danube River (Hungary). Macroinvertebrate colonization was compared between (i) empty shells and control substrate; (ii) different bivalve species (native and invasive) and (iii) three scenarios (before invasion, and short and long time after invasion) by using a mix of empty shells (native, native plus invasive, and invasive species). In comparison to control treatments the empty shells facilitated the presence of amphipods, caddis larvae and isopods, which contributed to a shift in the trophic structure by decreasing the proportion of gathering collectors while increasing the presence of shredders and predators. Several shell traits such as size, outer-shell surface roughness, hardness, thickness, 3D shape and chemical composition may be important attributes in the habitat modifying effects; however, this study could not disentangle which contribute most for the differences found. Given the capability of invasive C. fluminea and S. woodiana to accumulate large amounts of empty shells on several sites of the Danube, its habitat modifying effects can be particularly important, especially on the macroinvertebrate community structure. Moreover, these effects may increase in near future due to the predicted more frequent and severe extreme climatic conditions, which have been responsible for massive mortalities in both species.

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...

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.

Analyses of benthic macroinvertebrate colonization during the early successional phases of created wetlands in temperate Asia

Analyses of benthic macroinvertebrate colonization during the early successional phases of created wetlands in temperate Asia

Macroinvertebrate colonization dynamics on artificial substrates along an algal resource gradient

Riparian canopy removal and land use may introduce multiple stressors that can alter food and habitat for stream organisms, but the influence of these alterations on macroinvertebrate colonization dynamics is less well known. A field study involving the simultaneous placement and removal of artificial substrates was performed to examine how macroinvertebrate colonization rates might vary with algal accumulation within a perennial stream segment in eastern Ohio, USA. The study was conducted over a 60-day summer colonization period in three reaches that were selected to represent an algal resource gradient according to canopy cover and agricultural nutrient sources in the riparian corridor. Total nitrogen, water temperatures, and mean algal biomass from substrates increased along the resource gradient represented by the study sites. Total macroinvertebrate biomass and the abundance and biomass of scrapers also increased according to the gradient. Correlation results indicated that chlorophyll a biomass, rather than time or temperature, was better related to the abundance and biomass of most primary consumers on substrates. These results suggest that the combined effects of elevated temperatures and nutrients can result in relatively rapid algal accrual that may alter the colonization and establishment of macroinvertebrate communities in streams subjected to gradients of riparian disturbances.

Aquatic oligochaetes associated with bryophytes in an Atlantic Forest stream

There are few reports in the literature about the colonization of benthic macroinvertebrates on bryophytes. The aim of the present study was to analyzed the oligochaetes established on bryophytes adhered to stones in a first-order stream. The collections were carried out in an Atlantic Forest fragment area during the dry and rainy seasons. We identified 15 taxa from a total of 422 oligochaetes specimens, of which the most abundant were Pristina sp.1, Enchytraeidae and Pristina jenkinae. Unlike other habitats, where the abundance of macroinvertebrates tends to be greater in the dry season, we did not find any significant differences in the abundance, richness, composition and diversity between the two periods. The results of this study indicate that bryophytes are possible areas of refuge for oligochaetes in periods of faster water flow.

Macroinvertebrate colonization of a nature-like fishway: The effects of adding habitat heterogeneity

Nature-like fishways are designed to imitate the characteristics of natural streams, thereby providing both fish passage and habitat for a variety of aquatic organisms. To date, however, the potential for habitat rehabilitation of nature-like fishways has not been fully realized. To develop the concept of how to design a nature-like fishway, a 500-m long nature-like fishway, termed the biocanal, was constructed at the Eldforsen hydroelectric facility, Sweden. It included four habitat types: riffle, pool, floodplain and braided (i.e. with islands), each replicated three times. The riffle sections were considered controls for typical Swedish nature-like fishways. Thus the biocanal had a more varied in-stream environment than those of conventional fishways. To test the prediction that the biocanal had a positive effect on biodiversity, we compared the physical habitat and benthic fauna composition of the more diverse habitat types in the biocanal to the riffle habitats. We also made comparisons between the biocanal and six natural reference streams in the area. After two years, 63% of the benthic fauna families found in the reference streams had colonized the biocanal. Families present in the reference streams, but not in the biocanal, were predominantly slow colonizers or taxa linked to riparian vegetation, which was scarce and in an early successional stage along the biocanal. In the biocanal, pool and floodplain habitats contained the highest number of families, the highest family diversity (Shannon–Weaver) and the highest densities of Ephemeroptera, Plecoptera and Trichoptera. Since these habitats contained more families and had higher diversities than the riffle habitats which are typical of conventional nature-like fishways, we suggest that the construction of biocanals indeed possesses the potential for high biodiversity.

Rapid colonisation of artificial substrates by macroinvertebrates in a South African lentic environment

Macroinvertebrate colonisation patterns on artificial substrates were investigated in a small reservoir in the Eastern Cape, South Africa. Semi-closed 1 000 cm3 polythene netting cages filled with either brick, gravel, shredded plastic, or equal proportions of these three materials, were suspended above the benthic substrate. Gravel was preferred by caenid mayflies and chironomids, plastic by odonates, and brick by potamonautid crabs. Colonisation rates were rapid, with half the substrate-specific asymptotic diversity and richness being attained within a week. Overall, taxon richness on the substrates was similar to that in samples collected with a sweep net, but diversity was almost half. Taxon richness was found to be highest on the gravel and brick substrates, and lowest on plastic. By contrast, macroinvertebrate communities on the plastic and mixed substrates were the most diverse and the most even. All substrates, with the exception of gravel, showed that the number of odonates was significantly positively correlated with the number of potential prey that included chironomid midges, caenid mayflies and caddisfly larvae. It is recommended that plastic be used to construct artificial substrates if a high macroinvertebrate diversity is required for monitoring purposes within lentic environments.

Current velocity as a factor in determining macroinvertebrate assemblages on wood surfaces

The velocity of moving water near submerged wood surfaces may be an important factor for shaping benthic communities in sandy-bottomed streams. As wood can be suspended above the streambed and be kept free of inundating sediments, wood substrates may provide the primary hard surface for macroinvertebrate colonization. To examine this, we sampled macroinvertebrate assemblages from the surface of 20 pieces of submerged wood in a sandy-bottomed stream in the west-central Wisconsin. Near-surface velocity was characterized at the wood surface and the streambed macroinvertebrate assemblage was sampled near each wood piece for comparison. We found that the density of macroinvertebrates was five times greater on wood than the sandy streambed and the average richness on wood was twice as great. Macroinvertebrate abundance and richness on wood surfaces increased with velocity; however, abundance increased as a consequence of adding taxa rather than adding individuals of the dominant taxa. These data suggest that near-surface current velocity on wood may be an important determinant of benthic community composition when the availability of other hard surfaces is limited.

Spacial and Temporal Variation of Degradation of Organic Matter by Benthic Macroinvertebrates

Leaf litter input from riparian landscapes has been identified as both a major energy flow to stream ecosystems and as a food source for stream macroinvertebrates. In this study the benthic macroinvertebrate community was used to evaluate the decomposition of organic matter in river systems. The aim of this work was to study the decomposition of organic matter using the benthic macroinvertebrate colonization. The research was developed over five months (January 2011 to May 2011) in four different sites, distributed along the River Ferreira terminal area, northern Portugal. A litter bag experiment was used to examine the role of macroinvertebrate communities in the processing of organic material on the river. Litter bags were placed in the water and collected every 7, 15, 30, 60, 90 and 120 days. In litter bags was observed a high abundance of Oligochaeta and Chironomidae, which are characterized by being detritivorous-herbivores and filtering collectors, respectively, indicating the benthic macroinvertebrate more involved on the decomposition of organic matter. These results contributed to increase current knowledge about benthic macroinvertebrate communities and may serve as incentive for future research works.

Episodic acidification affects the breakdown and invertebrate colonisation of oak litter

Summary1. Although European streams are now recovering chemically from acidification, biological recovery is limited. One hypothesis is that continuing acid episodes restrict acid‐sensitive species in recovering locations either through direct toxicity or by affecting ecological processes. Here, we test this hypothesis by assessing the effects of episodic acid exposure on the breakdown and macroinvertebrate colonisation of oak (Quercus robur) litter.2. Over 83 days, acid episodes of 4 days’ duration were simulated by repeatedly transplanting litter bags of contrasting mesh size between replicate acidic and circumneutral streams around Llyn Brianne (Wales, U.K.). Results were compared against controls from circumneutral streams and circumneutral transplants, while invertebrates colonising litter were compared with adjacent assemblages.3. Breakdown was retarded significantly by repeated acid exposure in comparison with circumneutral transplants, but only in litter to which invertebrates had access. Overall breakdown was also significantly slower in fine‐mesh than in coarse‐mesh bags.4. Plecopteran shredders were the major invertebrate colonists of litter, along with smaller numbers of grazers and predators. However, acid exposure eliminated or suppressed acid‐sensitive families, resulting in an overall composition converging on that in acid streams.5. The rapid loss of sensitive invertebrates from acid‐exposed litter supports the hypothesis that acid episodes suppress biological recovery from acidification through direct physiological effects. However, our litter breakdown data indicate that (i) some effects of acid episodes could be mediated through litter processing; and (ii) episodic acidification could disrupt litter breakdown through effects on invertebrate composition or activity. These data suggest that delayed biological recovery from acidification can reflect a combination of direct toxic and indirect ecological effects.

Influence of riparian habitat on aquatic macroinvertebrate community colonization within riparian zones of agricultural headwater streams

Little is known about aquatic macroinvertebrate colonization of aquatic habitats within riparian zones of headwater streams in the midwestern United States. Many headwater streams and their riparian habitats in this region have been modified for agricultural drainage. Riparian habitat modifications caused by agricultural drainage may influence aquatic macroinvertebrate colonization within the riparian zones of headwater streams. However, the effects of agricultural drainage-induced riparian modifications have not been evaluated because others have focused on the impact of agricultural drainage on aquatic macroinvertebrates within the streams. We placed water-filled mesocosms in the riparian zones of two channelized and two unchannelized streams in central Ohio and sampled them from June to August 2009 to determine if differences in physical habitat, water chemistry, and aquatic macroinvertebrate colonization occurred between riparian zone types and among sampling dates. Canopy cover was greater in unchannelized than channelized riparian zones. Dissolved oxygen was greater in channelized than unchannelized riparian zones only during the latter half of the study. Turbidity and nutrients progressively increased throughout the study. Taxa richness was greater in unchannelized than channelized riparian zones. Copepod relative abundance, zooplankton relative abundance, and Shannon diversity index was greater in unchannelized than channelized riparian zones only during the latter half of the study. Abundance, taxa richness, culicid relative abundance, and dipteran relative abundance increased from the beginning of the study to the end. Our results indicate aquatic community colonization in the riparian zones of headwater streams is influenced by riparian habitat type and nutrients.

Distribution and species composition of macroinvertebrates in the hyporheic zone of bed sediment

The hyporheic zone is a layer of substrate on a river bed where benthic animals normally live, grow, feed, reproduce, and exist for any portion of their life cycle. The hyporheic zone was studied by sampling and experiment in mountain streams. Macroinvertebrates in hyporheic zone were sampled from the Juma, Xizhi, Songhua, Yanghe, and Guishui Rivers from May 2008 to August 2009. An experiment of colonization of macroinvertebrates at different depths of gravel or cobble beds was conducted in the Juma River. Results revealed that thickness of the hyporheic zone with living macroinvertebrates varied within a large range. The hyporheic zone is only several centimeters thick in sand bed, but up to 60 cm in cobble bed. The number of taxa increased with increasing median diameter of bed material. Numerous taxa were found in gravel and cobble beds, but few were observed in silt and fine sand beds. The experiment showed that macroinvertebrates colonized in a new habitat in about 6 weeks; predator species took longer to colonize than did other species. Macroinvertebrate abundance varied with bed depth and sediment size. The highest abundance was found at a bed depth of 0–30 cm. More macroinvertebrates were found in the gravel bed with median diameter of 2 cm than in the cobble bed with median diameter of 5–10 cm. Different taxa exhibited different bed depth preferences. Larvae of Dytiscidae, Haliplidae, and Atyidae lived only in upper layers near the bed surface, and taxa with hard covers or shells, such as larvae of Corydalidae, Naucoridae, and Corbiculidae preferred the lower layers with bed depths larger than 30 cm.

Riparian forest invasion by a terrestrial shrub (Lonicera maackii) impacts aquatic biota and organic matter processing in headwater streams

Lonicera maackii, a highly invasive species of riparian habitats, has the potential to substantially alter aquatic ecosystems. We investigated effects of this terrestrial invader on aquatic biota and ecosystem processes in three 3rd order headwater streams in southwestern Ohio. We assessed (1) in situ leaf breakdown and (2) aquatic macroinvertebrate colonization of leaf packs containing senesced foliage from either a) invasive (L. maackii), b) native (Fraxinus spp. and Platanus occidentalis), and c) a native-invasive species mix. Leaf breakdown rates and macroinvertebrate density, richness, and functional feeding group (FFG) relative abundances were measured for leaf packs deployed in the autumn of 2009. Invasive leaf breakdown rates were up to 4× faster than native leaves (F = 20.46, df = 2, P < 0.001), resulting in significantly less organic matter remaining compared to the other leaf pack types throughout the study (Friedman’s test = 8.00, P < 0.05). The gathering-collector FFG, represented by Chironomidae and Hydropsychidae, dominated the macroinvertebrate community in the invasive and mixed species leaf packs (F = 73, df = 4, P < 0.01) in all streams but were only dominant in native packs in one stream (F = 41.91, df = 4, P < 0.05). In summary, L. maackii leaf breakdown was significantly faster than native leaves in headwater streams, and colonization of macroinvertebrates was variable depending on leaf pack species composition. These results support the hypothesis that L. maackii can have direct and significant impacts on aquatic ecosystems by influencing organic matter availability and macroinvertebrate community dynamics.

Macroinvertebrate Communities Differences on Riverine Parts and Reservoirs of Zarrineh River

This study was conducted to identify present macro invertebrate's fauna in reverine and reservoir parts of the Zarrinehrood River for fishe ries purposes. The abundance and species composition of macro invertebrate were analyzed and compared in various parts of the Zarrinehrood River (west Azerbaijan, Iran) during November 2008-February 2009 to evaluate the rivers benthic fauna as a resource of fish and fowl feeding. Total ly 67 macro invertebrate species were found in Zarrinehrood River. Concerning the macro invertebrate density, a high-density was detected on the summer thanks to the development of bacteria and moderate meta zooplanktons on the rivers bed. The density of Oligochaeta was higher on the polluted s ites and dipper zone of the reservoirs but the population of chironomidae larvae increased on the heterotrophic shallow areas. Patchy distribution of Gastropod, Amphipod and Trichoptera occurred in the reverie stations with high water speed and dissolved oxygen. It was concluded that different e nvironmental characteristics and eutrophication degrees of the sampled stations seem to be the main factors that determined the macro invertebrate's colonization and abundance. Therefore, preserving better trophy cond ition can guarantee biodiversity richness in various parts of the Zarrinehrood River .

Leaf Decay Processes during and after a Supra‐Seasonal Hydrological Drought in a Temperate Lowland Stream

AbstractClimate change models for Central Europe predict hydrological drought with fragmentation into pools during periods of high litter input in numerous lowland streams, presumably affecting in‐stream leaf decay processes. To investigate this assumption, we measured physicochemical parameters, macro‐invertebrate colonization, microbial activity, and decay rates of exposed leaves during and after a supra‐seasonal drought in a German lowland stream. Microbial activity, shredder colonization and leaf decay rates during fragmentation were low, presumably caused by drought‐related environmental conditions. Microbial activity and temperature‐corrected decay rates increased after the flow resumption but not leaf mass loss and shredder colonization. During both periods, exposed leaves appeared physically unaffected suggesting strongly reduced shredder‐mediated leaf decay despite shredder presence. Our results indicate that hydrological drought can affect organisms and processes in temperate lowland streams even after flow resumption, and should be considered in climate change scenarios. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Macroinvertebrate colonization of two different tree species leaf packs (native vs. introduced) in a Mediterranean stream

Allochthonous leaf litter from riparian vegetation represents the main energy source in small lotic systems, where canopy limits autochthonous primary production. In this study, leaf packs of two tree species (the native Salix neotrichia and the introduced Populus x canadensis) were positioned in the Fardes Stream (southern Spain) to analyze the macroinvertebrate colonization. On two dates, leaf packs were removed, and colonizing macroinvertebrates were collected and identified; at the same time, Surber samples were collected to characterize the riverbed macroinvertebrate coenosis. Leaf packs attracted rich and varied communities of benthic macroinvertebrates, with an increase of the abundance of most taxa over time. No significant differences were found between the colonizing communities of the two leaf types. Some macroinvertebrate species showed a preference for leaf packs, probably due to trophic or hydrologic factors. Considering functional feeding groups, increases in shredders and scrapers and decreases in predators and filterers were detected over time, while collector-gatherers almost did not change in abundance.

Evolution of a stream ecosystem in recently deglaciated terrain

Climate change and associated glacial recession create new stream habitat that leads to the assembly of new riverine communities through primary succession. However, there are still very few studies of the patterns and processes of community assembly during primary succession for stream ecosystems. We illustrate the rapidity with which biotic communities can colonize and establish in recently formed streams by examining Stonefly Creek in Glacier Bay, Alaska (USA), which began to emerge from a remnant glacial ice mass between 1976 and 1979. By 2002, 57 macroinvertebrate and 27 microcrustacea species had become established. Within 10 years of the stream's formation, pink salmon and Dolly Varden charr colonized, followed by other fish species, including juvenile red and silver salmon, Coast Range sculpin, and sticklebacks. Stable-isotope analyses indicate that marine-derived nitrogen from the decay of salmon carcasses was substantially assimilated within the aquatic food web by 2004. The findings from Stonefly Creek are compared with those from a long-term study of a similarly formed but older stream (12 km to the northeast) to examine possible similarities in macroinvertebrate community and biological trait composition between streams at similar stages of development. Macroinvertebrate community assembly appears to have been initially strongly deterministic owing to low water temperature associated with remnant ice masses. In contrast, microcrustacean community assembly appears to have been more stochastic. However, as stream age and water temperature increased, macroinvertebrate colonization was also more stochastic, and taxonomic similarity between Stonefly Creek and a stream at the same stage of development was <50%. However the most abundant taxa were similar, and functional diversity of the two communities was almost identical. Tolerance is suggested as the major mechanism of community assembly. The rapidity with which salmonids and invertebrate communities have become established across an entire watershed has implications for the conservation of biodiversity in freshwater habitats.

Breakdown rates, nutrient concentrations, and macroinvertebrate colonization of bluejoint grass litter in headwater streams of the Kenai Peninsula, Alaska

Grass litter can be a dominant detritus type in many streams. However, use of this C source in stream food webs often is viewed as insignificant because of its relatively slow breakdown rates and low nutritional quality. We deployed leaf packs containing senesced bluejoint grass (Calamagrostis canadensis) across a natural nutrient gradient of 6 salmon-rearing headwater streams on the lower Kenai Peninsula, Alaska. We hypothesized that litter-colonizing microbes would use dissolved stream nutrients and enhance breakdown rates, litter nutrient concentrations, and densities of macroinvertebrates across streams. Leaf-pack mass and nutrient concentrations were measured on the material at 0 (predeployment), 2, 4, 6, and 8 wk in all streams. Breakdown rates were calculated from the mass measurements with an exponential decay model. Macroinvertebrate composition and abundance were measured at 8 wk in all streams and every 2 wk in 1 stream. Breakdown rates of bluejoint litter were relatively low (20–30% mass loss over 2 mo), but similar to rates found in previous studies of senesced grass litter. Weighted regressions showed that bluejoint breakdown rates in the 6 streams were significantly (p < 0.05) related to dissolved stream nutrient concentrations (r2 = 0.94 and 0.67 for dissolved inorganic N and PO4-P, respectively), litter nutrient concentration (r2 = 0.72 and 0.96 for leaf % N and % P, respectively), total macroinvertebrates/g (r2 = 0.73), and nonmetric multidimensional scaling-axis-1 scores of macroinvertebrate community structure (r2 = 0.80). Litter nutrients changed after just 2 wk and were increasingly and significantly related to stream nutrient concentrations over time. NMS ordination showed that succession of macroinvertebrates on leaf packs from one stream followed a distinct direction over time, and a large shift in macroinvertebrate community structure occurred between weeks 6 and 8, a result potentially indicating a consumer response to microbial conditioning. The abundance and diversity of macroinvertebrate taxa using bluejoint litter provide evidence that it is an important habitat and energy pathway for consumers in headwater streams of the Kenai Peninsula. In addition, climate change has the potential to change terrestrial vegetation assemblages, which drive differences in stream nutrient concentrations in this region. If N-fixing shrubs become more abundant in the future, litter-decomposition rates will be positively affected by increases in both stream and leaf-litter nutrient concentrations.