Forested Stream Ecosystems Research Articles

Catchment-scale deer exclusion changes longitudinal patterns of macroinvertebrate communities through soil runoff mitigation

Deer overpopulation is occurring worldwide, and deer-induced soil runoff into streams increases levels of suspended sediment and fine sedimentation. While deer-induced fine sedimentation in depositional habitats including first- and fourth-order streams is known to alter macroinvertebrate communities, effects of drifting suspended sediment in erosional habitats between the stream orders are poorly understood. Here, habitat and macroinvertebrate community structures in first- to third-order streams were compared between deer-excluded and grazed catchments of a Japanese headwater system. Fine sediment cover on the streambed was significantly greater in the grazed catchments than the deer-excluded catchment only for first-order streams, while macroinvertebrate community structure differed distinctly between the deer-excluded and grazed catchments at all stream orders. Burrowing collector-gatherers, which inhabit fine streambed sediments, were less abundant in first-order streams in the deer-excluded catchment than the grazed catchments, while clinging collector-filterers, which are vulnerable to suspended sediment inputs, were more abundant in second- and third-order streams of the deer-excluded catchment than the grazed catchments. These results suggest that the effect of deer exclusion on stream ecosystems varies with longitudinal changes in sediment deposition and transport capacity. Hydro-geomorphological processes are thus fundamental to assessing the restoration of forest-stream ecosystems, particularly in spatiotemporally dynamic headwater systems.

Pathways of productivity and influences on top consumers in forested streams

Forested stream ecosystems involve complex physical and biotic pathways that can influence fish in numerous ways. Consequently, the responses of fish communities to disturbance can be difficult to understand. In this study, we employed a food web model that links biotic (e.g., physiology, predator–prey interactions) and abiotic (e.g., temperature, sunlight) attributes to address fish responses to changes in stream-riparian ecosystems. We modeled responses to food web dynamics in four streams, using scenarios that included responses to riparian disturbance, climate change, and shifts in top consumers. The two consumers we focused on were coastal cutthroat trout (Oncorhynchus clarkii clarkii) and sculpin (Cottus spp., collectively treated as a functional group). We found the responses to environmental changes varied by fish species and among streams, and that responses were not independent due to exploitative interspecific competition. Simulations based on long-term data indicated that coastal cutthroat trout were responsive to changes in allochthonous resources including terrestrial detritus and invertebrates, whereas sculpin were more responsive to changes to autochthonous resources that included, periphyton and aquatic invertebrates. These results may be, in part, a consequence of species-specific foraging behavior. Trout have a higher propensity to drift feed and therefore receive a substantial subsidy from terrestrial invertebrates, whereas sculpin feed mostly on aquatic insects on the streambed. Simulations of changes in summer temperature and stream discharge suggest decreased biomass of both fish species because of physiological constraints on invertebrate prey which reduce fish foraging opportunities. Exploitative competition also may be important in fish responses: when one fish taxon was removed, the other showed increased biomass. Although the pattern of simulation results was consistent across the four streams, the magnitude of change varied among streams. Streams with food webs fueled by multiple energy sources may be more resilient to changes to riparian forests and climate. Through application of a systems model, we gained insights into pathways of productivity for fish in forested stream ecosystems that provide understanding of processes that influence fish and streams, as well as implications for management of both.

Explorando o impacto da presença de detritos exóticos na comunidade de invertebrados aquáticos e no processo de decomposição foliar em um riacho na Mata Atlântica

Abstract: Aim In this study, we examined the effects of non-native leaf litter on the functioning of an Atlantic Forest stream ecosystem. Methods Were tested two predictions: (i) Leaf litter from the native trees with high nutritional quality will have higher decomposer’s activity and faster litter decomposition; (ii) Given the presence of anti-grazing defenses, we also hypothesized that non-native leaf litter would be colonized by fewer invertebrates and that native species would be more species-rich. For this, in a forest stream (Florianópolis, SC, Brazil) we conduct the experiment to understand the decomposition and biological colonization of leaf litter among two non-native (Eucalyptus sp. and Pinus radiata D. Don) and two native trees (Ficus eximia Schott and Alchornea triplinervia (Spreng) Mull. Arg). Results Our predictions were partially corroborated. The percentage of dry mass remaining was lower for the native leaf litter. The invertebrate abundance and richness, and functional feeding groups vary between native and non-native leaf litter. Invertebrate abundance was higher in non-native Eucalyptus detritus, largely due to the high larval abundance of Chironomidae (Diptera). Conclusions Our results indicate that the presence of non-native riparian species can modify leaf decomposition and aquatic invertebrate communities in subtropical streams, with potential consequences for ecosystem functioning.

The dark side of rocks: An underestimated high‐quality food resource in river ecosystems

Abstract Algae are generally a high‐quality diet source because they provide essential compounds to aquatic consumers. In forested stream ecosystems, the availability of high‐quality algae is low compared to terrestrial organic matter, which may constrain the dietary transfer of essential compounds to consumers. However, there could be other overlooked high‐quality resource pools that provide essential compounds to consumers in river ecosystems. We conducted a field study along a subalpine river continuum in Austria to identify the nutritional role of a ‘hidden’ food resource for aquatic consumers; the biofilms growing on the underside of rocks (dark biofilms). Dark and light (i.e. upper surface of rocks) biofilms and invertebrates were collected, and their fatty acid (FA) composition was analysed. Compared with light biofilms, dark biofilms contained greater proportions of bacterial FA, long‐chain saturated FA (biomarkers of terrestrial plants) and oleic acid (18:1ω9; a fungal biomarker), but a lower proportion of algal FA, especially omega‐3 polyunsaturated FA (ω3 PUFA). The ω3 PUFA composition in dark biofilms was strongly correlated with that in light biofilms. Furthermore, the overall FA profiles of dark biofilms were significantly associated with invertebrate FA profiles. Strong correlations were also observed between invertebrates and dark biofilms for bacterial FA and the ω3 PUFA eicosapentaenoic acid (EPA, 20:5ω3). Synthesis. This field study demonstrates that dark biofilms are a high‐quality resource pool for invertebrates in river ecosystems that is often overlooked. Similar to light biofilms, dark biofilms provide physiologically important FA and bacterial FA for stream invertebrates. However, these high‐quality resources are threatened by increasing human disturbances to river ecosystems. Future research is required to better understand how the quality of both dark and light biofilms changes in response to human disturbance, and how this affects dietary energy transfer to upper trophic consumers, including fish and humans.

Combined carbon flows through detritus, microbes, and animals in reference and experimentally enriched stream ecosystems.

Tracking carbon (C) flow through ecosystems requires quantification of myriad biophysical processes, including C routing through microbial and metazoan food webs. Yet detailed organic matter budgets are rarely combined with simultaneous measurement of C flows supporting microbial and animal production. Here, we synthesize concurrent data sets on organic matter, microbes, and macroinvertebrates from two detritus-based stream ecosystems, one of which was subject to experimental nitrogen (N) and phosphorus (P) enrichment. Our synthesis provides new insights into C flow through forest stream ecosystems. Over 3 yr, the reference stream showed a striking balance of inputs and outputs, with a mean surplus of only 7g C·m-2 ·yr-1 (~1% of annual inputs), presumably stored in sediments as fine particulate organic matter (FPOM). In contrast, N and P enrichment over 2 yr resulted in severe deficits of C (-576g C·m-2 ·yr-1 or~170% of annual inputs), a shortfall presumably met by stored C. Our data set provides an ecosystem-based estimate of the fate of forest litter C at ambient nutrient concentrations: 6.2% was leached as dissolved organic C, 40.6% and 8.5% flowed to litter-associated fungi and bacteria, respectively, 7.5% was consumed by macroinvertebrates, 1.8% was exported as coarse particles, and the remainder (35.4%) was presumably fragmented by biophysical processes. Our calculations also allowed an estimate of inputs into the heterogeneous FPOM pool, which is otherwise difficult to obtain. At naturally low nutrient concentrations, 50.7% was derived from fragmented litter, 39.1% from microbial biomass (mostly fungal), and 10.2% from macroinvertebrate egesta. Nutrient addition drove large changes in C fluxes in the experimental stream, especially in flows of leaf litter to fungi (×1.7 pretreatment) and macroinvertebrates (×2.7), and of FPOM to hydrologic export (×2.6). Our results underscore the key roles of both microbes and metazoans in controlling C flow through detritus-based ecosystems, as well as how release from persistent nutrient limitation may perturb steady-state conditions of C inputs vs. outputs. Our analysis also suggests areas for future research, including assessing the relative importance of stored vs. recycled C in fueling detrital food webs subject to altered nutrient regimes and other global-change drivers.

Multi-Scale Assessment of Relationships between Fragmentation of Riparian Forests and Biological Conditions in Streams

Due to anthropogenic activities within watersheds and riparian areas, stream water quality and ecological communities have been significantly affected by degradation of watershed and stream environments. One critical indicator of anthropogenic activities within watersheds and riparian areas is forest fragmentation, which has been directly linked to poor water quality and ecosystem health in streams. However, the true nature of the relationship between forest fragmentation and stream ecosystem health has not been fully elucidated due to its complex underlying mechanism. The purpose of this study was to examine the relationships of riparian fragmented forest with biological indicators including diatoms, macroinvertebrates, and fish. In addition, we investigated variations in these relationships over multiple riparian scales. Fragmentation metrics, including the number of forest patches (NP), proportion of riparian forest (PLAND), largest riparian forest patch ratio (LPI), and spatial proximity of riparian forest patches (DIVISION), were used to quantify the degree of fragmentation of riparian forests, and the trophic diatom index (TDI), benthic macroinvertebrates index (BMI), and fish assessment index (FAI) were used to represent the biological condition of diatoms, macroinvertebrates, and fish in streams. PLAND and LPI showed positive relationships with TDI, BMI, and FAI, whereas NP and DIVISION were negatively associated with biological indicators at multiple scales. Biological conditions in streams were clearly better when riparian forests were less fragmented. The relationships of NP and PLAND with biological indicators were stronger at a larger riparian scale, whereas relationships of LPI and DIVISION with biological indicators were weaker at a large scale. These results suggest that a much larger spatial range of riparian forests should be considered in forest management and restoration to enhance the biological condition of streams.

Towards a simple global-standard bioassay for a key ecosystem process: organic-matter decomposition using cotton strips

Abstract Cotton-strip bioassays are increasingly used to assess ecosystem integrity because they provide a standardized measure of organic-matter decomposition – a fundamental ecosystem process. However, several different cotton-strip assays are routinely used, complicating the interpretation of results across studies, and hindering broader synthesis. Here, we compare the decay rates and assemblages of bacteria and fungi colonizing the three most commonly used cotton materials: Artist’s canvas, Calico cloth, and Empa fabric. Cotton strips from each material type were incubated in 10 streams that span a wide range of physicochemical properties across five ecoregions. Additionally, to evaluate responses to environmental stress without potentially confounding biogeographical effects, we deployed identical bioassays in five streams across an acidification gradient within a single ecoregion. Across all streams decomposition rates (as tensile strength loss [TSL]) differed among the three cotton materials; Calico cloth decomposed fastest (time to 50% TSL [T50] = 16.7 d), followed by the Empa fabric (T50 = 18.3 d) and then Artist’s canvas (T50 = 21.4 d). Despite these differences, rates of TSL of the three cotton materials responded consistently to variation in environmental conditions; TSL of each fabric increased with stream temperature, dissolved-nutrient concentrations and acid-neutralizing capacity, although Artist’s canvas and Calico cloth were more sensitive than Empa fabric. Microbial communities were similar among the materials, and values of community structure (e.g., phylotype richness and diversity) were comparable to those reported for decaying leaves in streams from the same region, the major natural basal carbon resource in forested-stream ecosystems. We present linear calibrations among pairs of assays so that past and future studies can be expressed in a “common currency” (e.g., Artist’s-fabric equivalents) ‘past and future studies’ repeated two times in the sentence. Lastly, given its relatively low within-site variability, and the large number of streams where it has been used (>700 across the globe), we recommend Artist’s fabric for future work. These results show that cotton provides an effective and realistic standardized substrate for studying heterotrophic microbial assemblages, and acts as a reasonable proxy for more chemically complex forms of detritus. These findings add to growing evidence that cotton-strip bioassays are simple, effective and easily standardized indicators of heterotrophic microbial activity and the ecosystem processes that result.

Effects of plant species on stream bacterial communities via leachate from leaf litter

Leaf litter provides an important resource to forested stream ecosystems. During leaf fall a significant amount of dissolved organic carbon (DOC) enters streams as leaf leachate. We compared the effects of plant species and leaf leachate bioavailability on the composition of stream bacterial communities and rates of DOC decomposition. We used four common riparian tree species that varied in foliar chemistry, leachate optical properties, and litter decomposition rate. We used laboratory microcosms from two streams and amended with a standard concentration of DOC derived from leaf leachate of the four tree species. After 24 h, we measured rates of DOC biodegradation and determined the composition of the bacterial communities via bar-coded pyrosequencing of the 16S rRNA gene. The composition, diversity, and abundance of the bacterial community differed significantly among plant species from both streams. The phylogenetic distance of the different bacterial communities correlated with species-specific leachate optical properties and rates of DOC biodegradation. Highest rates of DOC decomposition were associated with high tannin and lignin leaf types. Results demonstrate that riparian plant species strongly influences stream bacterial communities via their leachate suggesting that alterations to the presence or abundance of riparian plant taxa may influence these communities and associated ecosystem processes.

特集「シカの採食圧による植生被害防除と回復」 シカの過採食による森林と渓流生態系の相互作用の変化

近年，シカの過採食によって劇的に森林の下層植生が衰退している。本来ならば夏期には渓流を覆うように繁茂する渓畔植生も，シカ高密度地域では壊滅状態に追いやられている。河畔植生は，林床を覆って土壌の流出を抑制したり，訪花昆虫，食植性昆虫などを渓流に供給したりすることで，森林と渓流生態系をつなぐ重要な役割を果たしている。土壌侵食の活発化は，無機物的な側面では，土砂流入による河床改変を引き起こし，底生動物群集の多様性低下を招く。一方有機物的な側面では，森林由来の他生性有機物が渓流に過剰に流入することで渓流生態系内の栄養循環に変化をもたらす可能性がある。前者のような土砂の堆積プロセスは河川地形に応じて空間的に不均質であるため，シカによる土砂流出が渓流生態系に及ぼす影響の評価には，河川地形学や森林水文学など生態学に囚われない学際的な視点が重要である。一方，渓畔植生から渓流への陸生動物の供給がシカの過採食によって変化すると，森林-渓流生態系のつながりを通して魚類も含めた生態系内の栄養循環のバランスが崩れることが示唆された。

Responses of benthic invertebrate assemblages to shifts in the acidity of subtropical mountain streams

Recent economic development in China has been remarkable and so has the scale of associated atmospheric pollutant loading. Forest soil acidification resulting from atmospheric pollutant deposition has become a major concern, particularly in tropical and subtropical forests. Nutrient saturation in southeastern Chinese forest ecosystems has been reported, and soil pH is now in the range of 3.8–4.0. This acidification in forest soil undoubtedly affects water chemistry, and hence forest stream ecosystems. There have been few studies of these impacts on streams. In order to better understand the risks of nitrogen (N) saturation on stream ecosystem in warm and humid climate, where seasonal tropical and subtropical forests are located, we undertook a comparative study of stream faunas in two regions of Dinghushan (DHS) where stream acidification has already occurred and in Heishiding (HSD) where stream acidification has not yet begun, but where forest soils are already acidified. Abundance and species richness o...

Leaf litter from insect‐resistant transgenic trees causes changes in aquatic insect community composition

Summary1. Recent research has addressed how transgenic residues from arable crops may influence adjacent waterways, aquatic consumers and important ecosystem processes such as litter breakdown rates. With future applications of transgenic plants in forestry, such concerns may apply to forest stream ecosystems. Before any large‐scale release of genetically modified (GM) trees, it is therefore imperative to evaluate the effects of genetic modifications in trees on such ecosystems.2. We conducted decomposition experiments under natural stream conditions using leaf litter from greenhouse grown GM trees (Populus tremula × Populus tremuloides) that express Bacillus thuringiensis (Bt) toxins (cry3Aa; targeting coleopteran leaf‐feeding beetles) to examine the hypothesis that GM trees would affect litter decomposition rates and/or the aquatic arthropod community that colonizes and feeds on leaf litter in streams.3. We show that two independent transformations of isogenic Populus trees to express Bt toxins caused similar changes to the composition of aquatic insects colonizing the leaf litter, ultimately manifested in a 25% and 33% increases in average insect abundance.4. Measurements of 24 phenolic compounds as well as nitrogen (N) and carbon (C) in the litter did not significantly differ among modified and wild‐type trees and were thus not sufficient to explain these differences in the insect assemblage.5. Decomposition rates were comparable among litter treatments suggesting that the normal suite of leaf traits influencing decomposition was similar among litter treatments and that the shredding functions of the community were maintained despite the changes in insect community composition.6. Synthesis and applications. We report that leaf litter from GM trees affected the composition of aquatic insect communities that colonized litter under natural stream conditions. This suggests that forest management using GM trees may affect adjacent waterways in unanticipated ways, which should be considered in future commercial applications of GM trees. We also argue that studies at different scales (e.g. species, communities and ecosystems) will be needed for a full understanding of the environmental effects of Bt plants.

Biogeochemical properties of fine particulate organic matter as an indicator of local and catchment impacts on forested streams

Summary1. The magnitude and spatial scales of human effects on stream habitats need to be correctly measured to achieve sound ecosystem management. We investigated whether the biogeochemical properties of fine particulate organic matter (FPOM) might be indicative of reach‐scale vs. catchment‐scale effects on forested stream ecosystems.2. Along each of three forested streams, we established 4–5 sampling stations at 0·6–2·0‐km intervals, which represent a range of local riparian forest conditions (e.g. vegetation types and forestry practices). At each station, rock biofilm (considered as a representative of stream‐origin POM), FPOM in sediment (FPOMS) and suspended in water (FPOMW) and three species of benthic macroinvertebrates were collected during a summer low‐flow period.3. Measures of δ13C, C:N and chlorophyll a:C for FPOMW, FPOMS and biofilm were longitudinally heterogeneous, reflecting the reach‐scale, local environment. δ13C, C:N and chlorophyll a:C of FPOMS were significantly related to irradiance and streambed coarse particulate organic matter (CPOM) abundance, suggesting that the relative contribution of in‐stream primary production and CPOM breakdown are dominant controls of FPOM properties.4. In redundancy analysis, variations in FPOM properties were principally explained by local environmental factors correlated with stream size and/or longitudinal position of the sampling stations (irradiance, streambed CPOM, stream gradient, discharge, riparian vegetation). No significant effect of riparian forestry activities (logged, riparian reserve or no harvest in the past 75 years) was found on FPOM properties.5. Resource use by primary consumers was species dependent. δ13C of larval Lepidostoma roafi depended on the relative abundance of stream‐origin POM in pools of stored FPOM. Selective intake/assimilation of stream‐origin POM by this species was probably enhanced when stream‐origin POM was abundant. δ13C of larval Despaxia augusta or larval Paraleptophlebia spp. were not related to FPOMSδ13C, suggesting no linkage with FPOM composition.6. Synthesis and applications. The tight linkages between biogeochemical properties of FPOM, resource use by primary consumers, and reach‐scale environment indicate that local effects were greater than signals transmitted from upstream in this study. The use of in‐stream FPOM properties can help managers to measure reach‐scale effects of environmental changes on forested stream habitats.

Riparian canopy type, management history, and successional stage control fluxes of plant litter to streams

The food webs of forest stream ecosystems are based primarily on cross-boundary flows of terrestrial plant litter (PL). As such, changes in the composition of riparian forest canopies can alter flows of PL, affecting the ecosystem functioning of adjacent streams. We measured seasonal changes in PL fluxes to 20 small streams flowing through temperate rain forests in southwestern British Columbia to determine how riparian forest type and riparian management history influence resource availability in these systems. Differences in PL fluxes among the four riparian forest types studied were most pronounced in the summer, when PL fluxes from clearcuts < riparian reserve strips and coniferous forests, and PL fluxes from deciduous-dominated forests < riparian reserve strips. PL fluxes also varied among seasons (spring < summer < autumn). Fluxes were similar in riparian reserve strips and coniferous forests of similar age, indicating that reserve strips maintain this crucial ecosystem process. Clearcutting of riparian forests dramatically increased light availability while reducing leaf litter inputs; these effects, however, lasted only a few years. As riparian forest stand age increased, inputs shifted from broadleaf to coniferous inputs, indicating a possible long-term decrease in the lability of the leaf litter resources available to stream consumers.

Nematomorph parasites drive energy flow through a riparian ecosystem

Parasites are ubiquitous in natural systems and ecosystem-level effects should be proportional to the amount of biomass or energy flow altered by the parasites. Here we quantified the extent to which a manipulative parasite altered the flow of energy through a forest-stream ecosystem. In a Japanese headwater stream, camel crickets and grasshoppers (Orthoptera) were 20 times more likely to enter a stream if infected by a nematomorph parasite (Gordionus spp.), corroborating evidence that nematomorphs manipulate their hosts to seek water where the parasites emerge as free-living adults. Endangered Japanese trout (Salvelinus leucomaenis japonicus) readily ate these infected orthopterans, which due to their abundance, accounted for 60% of the annual energy intake of the trout population. Trout grew fastest in the fall, when nematomorphs were driving energy-rich orthopterans into the stream. When infected orthopterans were available, trout did not eat benthic invertebrates in proportion to their abundance, leading to the potential for cascading, indirect effects through the forest-stream ecosystem. These results provide the first quantitative evidence that a manipulative parasite can dramatically alter the flow of energy through and across ecosystems.

Analysis of cellulolytic and hemicellulolytic enzyme activity within the Tipula abdominalis (Diptera: Tipulidae) larval gut and characterization of Crocebacterium ilecola gen. nov., sp. nov., isolated from the Tipula abdominalis larval hindgut

Abstract In forested stream ecosystems of the north and eastern United States, larvae of the aquatic crane fly Tipula abdominalis are important shredders of leaf litter detritus. T. abdominalis larvae harbor a dense and diverse microbial community in their hindgut that may aide in the degradation of lignocellulose. In this study, the activities of cellulolytic and hemicellulolytic enzymes were demonstrated from hindgut extracts and from bacterial isolates using model sugar substrates. One of the bacterial isolates was further characterized as a member of the family Microbacteriaceae. Taxonomic position of the isolate within this family was determined by a polyphasic approach, as is commonly employed for the separation of genera within the family Microbacteriaceae. The bacterial isolate is Gram‐type positive, motile, non‐sporulating, and rod‐shaped. The G + C content of the DNA is 64.9 mol%. The cell wall contains B2γ type peptidoglycan, D‐ and L‐diaminobutyric acid as the diamino acid, and rhamnose as the predominant sugar. The predominant fatty acids are 12‐methyltetradecanoic acid (ai‐C15:0) and 14‐methylhexadecanoic acid (ai‐C17:0). The isolate forms a distinct lineage within the family Microbacteriaceae, as determined by 16S rRNA sequence analysis. We propose the name Crocebacterium ilecola gen. nov., sp. nov., to accommodate this bacterial isolate. The type species is T202T (ATCC BAA‐1359; GenBank Accession DQ826511).

Multiple stressors in north temperate streams: lessons from linked forest–stream ecosystems in northern Japan

Summary1. Streams are highly connected to their landscapes and so are easily altered by multiple stressors that affect both uplands and riparian zones, and the streams themselves. These include dams and diversions, channelisation, deforestation, water pollution, biological invasions and climate change.2. We review research conducted in Hokkaido Island, northern Japan, which measured the effects of many of these stressors on both stream food webs and fluxes of invertebrates to and from the riparian zone that feed aquatic and terrestrial consumers. About half the energy that sustains fish falls directly into streams as terrestrial invertebrates, and a quarter of the energy needs for riparian birds is supplied by adult aquatic insects emerging from the stream.3. Single stressors in these Hokkaido streams, including deforestation, channelisation, erosion‐control dams, biological invasions and climate change, have drastic effects on stream food webs, the fishes they support and riparian predators (spiders, birds, and bats). Most stressors caused 30–90% declines in foraging, growth, or abundance of aquatic or terrestrial predators. Indirect effects of stressors also cascaded throughout stream food webs and across the aquatic–terrestrial boundary.4. Effects of individual stressors were largely concordant across spatial scale, through time during years of different productivity and among different food web components.5. Two studies of multiple stressors revealed that each stressor alone reduced food web components like abundance of stream benthos or riparian spiders to low levels (35–83% reduction; mean 59%), beyond which an additional stressor had little effect. Synergism and antagonism are less relevant when individual stressors have such large effects.6. Thematic implications: small streams in Hokkaido are highly sensitive to many individual stressors and have little resistance or resilience to their effects. Moreover, each stressor alone can reduce biota strongly, indicating that restoration will need to consider all simultaneously to protect biotic diversity.

Dynamics of wood recruitment in streams of the northeastern US

Wood is an important component of forested stream ecosystems, and stream restoration efforts often incorporate large wood. In most cases, however, stream restoration projects are implemented without information regarding the amount of wood that historically occurred or the natural rates of wood recruitment. This study uses a space-for-time analysis to quantify large wood loading to 28 streams in the northeastern US with a range of in-stream and riparian forest characteristics. We document the current volume and frequency of occurrence of large wood in streams with riparian forests varying in their stage of stand development as well as stream size and gradient. Linear models relating stream wood characteristics to stream geomorphic and forest characteristics were compared using Akaike's Information Criterion (AIC) model selection. The AIC analysis indicated that the volume and frequency of large wood and wood accumulations (wood jams) in streams was most closely associated with the age of the dominant canopy trees in the riparian forest (best models: log10(large wood volume (m3100m−1))=(0.0036×stand age)−0.2281, p<0.001, r2=0.80; and large wood frequency (number per 100m)=(0.1326×stand age)+7.3952, p<001, r2=0.63). Bankfull width was an important factor accounting for wood volume per unit area (m3ha−1) but not the volume of wood per length of stream (100m−1). The empirical models developed in this study were unsuccessful in predicting wood loading in other regions, most likely due to difference in forest characteristics and the legacy of forest disturbance. However, these models may be applicable in other streams in the northeastern US or in streams with comparable riparian forests, underlying geology, and disturbance regimes—factors that could alter long-term wood loading dynamics. Our results highlight the importance of understanding region-specific processes when planning stream restoration and stream management projects.

“Livewood”: Geomorphic and Ecological Functions of Living Trees in River Channels

Although the geomorphic and ecological importance of large wood in streams and rivers is well recognized, most studies consider only dead wood in channels. However, we have observed that living parts of trees are often found within active channels and that this “livewood” shares functions with both instream dead wood and live riparian trees, while also providing some functions unique to living woody material within a channel. We describe the mechanisms that produce livewood and illustrate its characteristics and influences on riparian and stream ecosystems with examples from Europe, North America, and New Zealand. We hypothesize that, compared with dead wood in channels, livewood (a) persists longer because of greater stability and greater resistance to decay, and (b) imparts greater structural complexity (with associated hydraulic roughness and retentiveness). The phenomenon of livewood implies that a broader range of tree species and sizes than previously considered may contribute functionally important wood to channels. We encourage the study of livewood in a range of forest-stream ecosystems to test our hypotheses and further our understanding of how forests interact with rivers and streams.

A watershed scale assessment of in-stream large woody debris patterns in the southern interior of British Columbia

In-stream large woody debris (LWD) is a structurally and functionally important component of forested stream ecosystems. To assess the role played by LWD in sustaining aquatic ecosystems at the watershed scale, the amount, distribution, dynamics and function of LWD within channel networks have to be determined. We surveyed 35 sites in first- through fifth-order streams within forested watersheds in the southern interior of British Columbia, and the spatial variation and distribution of LWD characteristics (frequency, density, volume, biomass, orientation, submersion, and decay state) were quantified based on four stream size categories. We found that the average diameter, length, volume and biomass of individual LWD pieces increased as a function of increasing bankfull width. However, LWD density (piece per 100 m 2 of the stream area) decreased with an increase in bankfull width. LWD volume ranged from 0.78 to 1.58 m 3/100 m 2 of stream area, with intermediate sized streams (sizes II and III) having the largest value and large sized streams (size IV) having the lowest values. Results showed that LWD biomass averaged 383 kg/100 m 2 (range 265–651 kg/100 m 2) in stream size I, increased to 491 kg/100 m 2 (range 81–1254 kg/100 m 2) in stream size II, and slightly decreased to 465 kg/100 m 2 (range 247–938 kg/100 m 2) in stream size III and further decreased to 250 kg/100 m 2 (range 88–533 kg/100 m 2) in stream size IV. The large majority of LWD pieces in the smallest sized streams was orientated perpendicular to streamflow and was located in spanning the channel. Conversely, most LWD pieces in intermediate sized streams were orientated parallel to the direction of flow and were situated below the bankfull height of the channel. With a difference in the orientation and position, LWD pieces within different sized streams are expected to have varying potentials to affect streamflow and channel habitats. These results highlight the need to recognize spatial variation of in-stream LWD loading and function through channel networks when maintaining suitable LWD pieces and making riparian management decisions at watershed scales.

Biodegradable dissolved organic matter in a temperate and a tropical stream determined from ultra-high resolution mass spectrometry

We investigated dissolved organic matter (DOM) metabolism by employing plug-flow biofilm reactors and ultra‐ high resolution mass spectrometry of DOM isolated by C18 extraction in two forested stream ecosystems, a low DOM tropical stream sampled at baseflow and a higher DOM temperate stream sampled during a storm. On passage through the bioreactors, DOM concentrations in the tropical stream sample declined by 22%, whereas they declined by 42% in the temperate stream sample. The extracted DOM was subjected to electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry to obtain information on molecular weight distributions and elemental compositions for the thousands of compounds whose masses are calculated with sufficient accuracy to allow calculation of unique elemental formulas. In both streams, metabolism modifies DOM to lower molecular weight molecules, and oxygen-rich molecules are selectively biodegraded. Applying van Krevelen analyses for the unique elemental formulas of DOM constituents revealed that hydrogen-deficient molecules with low H : C ratios (assigned to black carbon‐derived molecules) are present and generally not metabolized. Black carbon molecules are refractory to biodegradation compared with other components of DOM, supporting the suggestion that black carbon molecules in DOM flow to the ocean without experiencing significant microbial degradation.