Allochthonous Energy Research Articles

First evidence of feeding on micromammals and fish by a cyprinid species (Squalius carolitertii) in lacustrine food webs

The consumption of resources at multiple trophic levels reflects the omnivorous behaviour of various species. Despite the importance of omnivory in food web structure and stability, there are still few observational data to assess the omnivorous role of species in food webs. We first assessed the feeding of two cyprinid [northern Iberian chub (Squalius carolitertii) and northern straight-mouth nase (Pseudochondrostoma duriense)] and one salmonid (brown trout Salmo trutta) species in a mountain lake of the Iberian Peninsula, and then we studied the omnivorous behaviour and niche partitioning of the cyprinid species. A noteworthy result was the consumption of micromammals by northern Iberian chub. This species showed a high trophic flexibility feeding on diverse food types (detritus, vegetal rests, zooplankton, aquatic insects, terrestrial insects, micromammals and small fish), whereas northern straight-mouth nase fed mostly on detritus. We observed that the consumption of zooplankton decreased with increasing fish length in northern Iberian chub, whereas no evidence for ontogenetic dietary shifts were observed for northern straight-mouth nase. Brown trout fed only on cyprinids, acting as top predator in the studied mountain lake. Despite high dietary overlap between omnivorous cyprinids, our analyses suggested that omnivorous behaviour and ontogenetic dietary shifts of northern Iberian chub can be an important adaptive feature that may reduce food competition and enable species coexistence in mountain lakes. Our study shows that endemic omnivorous cyprinids can exploit alternative energy pathways and underlines the importance of omnivorous species as promoters of stability in lacustrine food webs. We highlight that the importance of occasional pulses of allochthonous energy sources fueling lacustrine food webs, such as micromammals and terrestrial insects, represent a particularly promising area for future research.

Assessment of occurrence, diversity, and biomass of macroinvertebrates in Swiss groundwater systems using citizen science data

Groundwater is a vast ecosystem harboring a high diversity of specialized taxa. Despite its diversity, groundwater is a still relatively unexplored and threatened ecosystem. Especially the linkage of groundwater with other ecosystems remains largely unknown from the perspective of groundwater fauna. Here, we used citizen science data to get a first baseline knowledge of the occurrence, diversity, and biomass of major macroinvertebrate groups found in shallow groundwater systems of Switzerland. We investigated all organisms collected from the groundwater in 346 spring catchment boxes of municipal drinking water providers. We morphologically identified the organisms on a broad taxonomic level and estimated their biomass and pigmentation using automated image processing. Crustaceans, particularly Niphargus and groundwater isopods, were the most common taxa of obligate groundwater organisms. We also found a surprisingly high number of macroinvertebrates associated with surface and subsurface ecosystems. These taxa might be accidentally entering the groundwater or use it as temporary habitat. In both cases they possibly contribute essential allochthonous energy imports from the surface. We found a positive relationship between the estimated biomass of macroinvertebrates in the samples and the occurrence and abundance of Niphargus. Owing to the widespread occurrences of surface and subsurface macroinvertebrates in our groundwater samples, our study provides evidence for common interactions between groundwater, soil, and surface ecosystems.

The application of the River Continuum Concept (RCC) on the headwaters of the Sampolawa River in Southeast Sulawesi, Indonesia

Abstract. Erif, LOM, Djohan TS, Sudarmadji, Yasin A, Sudia LB, Kahirun. 2023. The application of the River Continuum Concept (RCC) on the headwaters of the Sampolawa River in Southeast Sulawesi, Indonesia. Biodiversitas 24: 290-299. Benthic aquatic insect communities in temperate regions have been used as bioindicators of a healthy forest in the stream headwaters.This research analyzes the abundance of benthic insects, the quality of water and nutrient sediment, and the response of the insect community in the Sampolawa River. The samples were collected using stratified random sampling methods with a Surber sampler 30 cm x 30 cm, 5 segmented streams, and 200 m with 4 replication. The results show that 19 species of 5 community feeding groups were found, including collector filters, gatherers, predators, scrapers, and shredders. However, the shredders community is very small, at about 2-4 %. The benthic insect aquatic dominance by collector filter with 29 % reflected that input from terrestrial vegetation is Fine Particulate Organic Matter (FPOM). Therefore, it can be deduced that Sampolawa headwaters do not fit with the prediction of the "River Continuum Concept (RCC)"for a typical headwater since the allochthonous energy supply from riparian vegetation is in the form of fine detritus.

A catastrophic coal mine spill in the Athabasca River watershed induces isotopic niche shifts in stream biota including an endangered rainbow trout ecotype

Freshwater biodiversity is declining from impacts associated with anthropogenic stressors. Here, we use carbon (δ13C) and nitrogen (δ15N) stable isotopes to assess food web effects following a coal mine spill that displaced biota and altered biophysical stream characteristics. We compared isotopic niche metrics of benthic macroinvertebrates and the fish community, including non-native brook trout (Salvelinus fontinalis) and endangered Athabasca rainbow trout (Oncorhynchus mykiss), to infer spatial differences in site-specific resource use along a habitat disturbance gradient. Predatory benthic macroinvertebrate trophic position was elevated where impacts from the spill were most pronounced. Autochthonous carbon contribution to consumer diets was lowest in biota sampled at the most highly impacted site from the mine spill, leading to an unexpected expansion of the isotopic niche size of rainbow trout and the aquatic invertebrate community. Collectively, our results suggest variation in trophic resource assimilation across multiple levels of the food web, fueled by the allochthonous energy pathway in highly impacted study sites. We conclude this reflects a biotic response to altered basal aquatic resources following a major industrial disturbance.

Litter decomposition of exotic and native plant species of agricultural importance in Amazonian streams

The conversion of riparian vegetation into monocultures alters the input of allochthonous energy and the heterotrophy of streams. Here, we aimed to assess the implication of leaf litter inputs from plant species of agricultural importance on decomposition in Amazonian streams. We hypothesized that decomposition is low in litter with high concentrations of lignin and cellulose, regardless of the origin of plant species (exotic or native). We incubated leaf litter from plant species of agricultural importance, such as cocoa (native) and oil palm (exotic), as a control, leaf litter of Hymenaea courbaril (native) in four streams for 60 days. Contrary to our initial expectations, the leaf litter from oil palm, which was of higher quality and had lower concentrations of structuring compounds (lignin and cellulose), did not differ in decomposition rates from the lower quality leaf litter of the control species, which presented higher concentrations of structuring compounds. We recorded higher decomposition rate in cocoa, which had intermediate concentrations of structural compounds. Our results indicate a negative effect of the conversion of riparian vegetation into oil palm monocultures (Elaeis guineensis) for the processing of organic matter in Amazonian streams, due to the slower decomposition rate of the leaf litter of this species.

Fatty acid stable isotopes add clarity, but also complexity, to tracing energy pathways in aquatic food webs.

Tracing the flow of dietary energy sources, especially in systems with a high degree of omnivory, is an ongoing challenge in ecology. In aquatic systems, one of the persistent challenges is in differentiating between autochthonous and allochthonous energy sources to top consumers. Bulk carbon stable isotope values of aquatic and terrestrial prey often overlap, making it difficult to delineate dietary energy pathways in food webs with high allochthonous prey subsidies, such as in many northern temperate waterbodies. We conducted a feeding experiment to explore how fatty acid stable isotopes may overcome the challenge of partitioning autochthonous and allochthonous energy pathways in aquatic consumers. We fed hatchery‐reared Arctic Char (Salvelinus alpinus) diets of either benthic invertebrates, terrestrial earthworms, or a mixture of both. We then compared how the stable carbon isotopes of fatty acids (δ13CFA) distinguished between diet items and respective treatments in S. alpinus liver and muscle tissues, relative to bulk stable isotopes and fatty acid profiles. Although a high degree of variability of fatty acid stable carbon isotope values was present in all three measures, our results suggest that the ability of this method to overcome the challenges of bulk stable isotopes may be overstated. Finally, our study highlights the importance of further experimental investigation, and consideration of physiological and biochemical processes when employing this emerging method.

Resource risk and stability in the zooarchaeological record: the case of Pueblo fishing in the Middle Rio Grande, New Mexico

Disarticulated fish remains are frequently recovered from late preHispanic and early historic archaeological sites in the Middle Rio Grande basin of central New Mexico, but they are rare during earlier time periods. Increased aquatic habitat quality brought on by wetter climatic conditions may have impacted Ancestral Pueblo foraging goals related to risk minimization, leading to an uptick in fish exploitation. Wetter stream conditions can increase the number of different energy channels that help support fish populations and increase ecological stability, which makes fish less risky to pursue for human foragers. Here, we illustrate how to identify stable ecological communities in the archaeological record using stable carbon and nitrogen isotope values of fish bones recovered from archaeological sites in the Middle Rio Grande. We find that energy derived from terrestrial C4 plants—a stabilizing “slow” allochthonous energy source—was important for the Middle Rio Grande aquatic food web during the late preHispanic/early historic period. This result suggests that fish populations were supported by a broader resource base and were thus more stable and less risky to pursue for Ancestral Pueblo people.

Grass species as a source of allochthonous energy for shredders and fungal decomposers in a subtropical stream

Grass species as a source of allochthonous energy for shredders and fungal decomposers in a subtropical stream

Declining glacier cover threatens the biodiversity of alpine river diatom assemblages.

Climate change poses a considerable threat to the biodiversity of high altitude ecosystems worldwide, including cold-water river systems that are responding rapidly to a shrinking cryosphere. Most recent research has demonstrated the severe vulnerability of river invertebrates to glacier retreat but effects upon other aquatic groups remain poorly quantified. Using new data sets from the European Alps, we show significant responses to declining glacier cover for diatoms, which play a critical functional role as freshwater primary producers. Specifically, diatom α-diversity and density in rivers presently fed by glaciers will increase with future deglaciation, yet β-diversity within and between sites will reduce because declining glacier influence will lower the spatiotemporal variability of glacier cover and its associated habitat heterogeneity. Changes in diatom assemblage composition as glacier cover declined were associated strongly with increasing riverbed stability and water temperature. At the species level, diatoms showed a gradation of responses; for example, Eunotia trinacria, found exclusively at river sites with high (≥52%) catchment glacier cover, may be affected negatively by ice loss. Conversely, seven taxa confined to sites with no glacier cover, including Gomphonema calcareum, stand to benefit. Nineteen (22%) taxa were noted as threatened, endangered, rare or decreasing on the Red List of Algae for Germany, with most at sites ≤26% glacier cover, meaning further ice loss may benefit these diatoms. However, six taxa found only in rivers ≥28% glacier cover may require reclassification of their Red List conservation status, as this habitat is threatened by deglaciation. Our identification of clear links between decreasing glacier cover and river diatom biodiversity suggests there could be significant reorganization of river ecosystems with deglaciation, for example, through alterations to primary production, biogeochemical cycles, and the shifting resource base of alpine freshwater food webs which lack significant allochthonous energy inputs.

Spatial and successional dynamics of microbial biofilm communities in a grassland stream ecosystem.

Biofilms represent a metabolically active and structurally complex component of freshwater ecosystems. Ephemeral prairie streams are hydrologically harsh and prone to frequent perturbation. Elucidating both functional and structural community changes over time within prairie streams provides a general understanding of microbial responses to environmental disturbance. We examined microbial succession of biofilm communities at three sites in a third-order stream at Konza Prairie over a 2- to 64-day period. Microbial abundance (bacterial abundance, chlorophyll a concentrations) increased and never plateaued during the experiment. Net primary productivity (net balance of oxygen consumption and production) of the developing biofilms did not differ statistically from zero until 64days suggesting a balance of the use of autochthonous and allochthonous energy sources until late succession. Bacterial communities (MiSeq analyses of the V4 region of 16S rRNA) established quickly. Bacterial richness, diversity and evenness were high after 2days and increased over time. Several dominant bacterial phyla (Beta-, Alphaproteobacteria, Bacteroidetes, Gemmatimonadetes, Acidobacteria, Chloroflexi) and genera (Luteolibacter, Flavobacterium, Gemmatimonas, Hydrogenophaga) differed in relative abundance over space and time. Bacterial community composition differed across both space and successional time. Pairwise comparisons of phylogenetic turnover in bacterial community composition indicated that early-stage succession (≤16days) was driven by stochastic processes, whereas later stages were driven by deterministic selection regardless of site. Our data suggest that microbial biofilms predictably develop both functionally and structurally indicating distinct successional trajectories of bacterial communities in this ecosystem.

Evidence for limited trophic transfer of allochthonous energy in temperate river food webs

The River Continuum Concept (RCC) predicts that riverine food webs shift from a reliance on allochthonous energy in headwaters to autochthonous production in lower reaches. However, estimates of resource reliance often fail to account for resource segregation within the food web. Stable-isotope biomarkers can be used to estimate the relative importance of allochthonous and autochthonous material to specific groups and within the food web. δ13C and δ15N isotope ratios were calculated for allochthonous (conditioned leaf litter) and autochthonous (biofilm and bryophytes) basal energy sources, macroinvertebrate functional feeding groups (shredder, grazer, collector–filterer, collector–gatherer, predator), and resident fish species at 17 locations spanning the headwaters to lower reaches of 2 river systems in eastern Canada. Stable-isotope mixing models and correlations were used to identify longitudinal trends in the food webs of both rivers. In headwater streams, allochthonous material was the predominant resource for shredders, whereas all other primary, secondary, and tertiary consumers predominantly used autochthonous basal resources. Stable-isotope ratios of allochthonous material varied minimally between sites. Both autochthonous basal sources were significantly 13C-enriched and 15N-depleted in lower-reach relative to headwater sites. Shredders displayed minimal variation across sites, whereas longitudinal variation in all other primary consumers, macroinvertebrate predators, and fishes was closely correlated with autochthonous basal sources. These results highlight the role of resource segregation within river food webs and indicate that the RCC may not predict energy pathways in all temperate river systems.

The importance of terrestrial subsidies in stream food webs varies along a stream size gradient

Cross system subsidies of energy and materials can be a substantial fraction of food web fluxes in ecosystems, especially when autochthonous production is strongly limited by light or nutrients. We explored whether assimilation of terrestrial energy varied in specific consumer taxa collected from streams of different sizes and resource availabilities. Since headwater streams are often unproductive, we expected that inputs from surrounding terrestrial systems (i.e. leaf litter, terrestrial invertebrates) would be a more important food source for consumers than in mid‐size rivers that have more open canopies and higher amounts of primary production available for consumers. We collected basal resources, invertebrates, and fish along a gradient in stream size in the Adirondack Mountains (NY, USA) and in Trinidad and Tobago and analyzed all samples for hydrogen isotopes as a means of differentiating biomass derived from allochthonous versus autochthonous sources. We found significant differences in allochthonous energy use within individual consumer taxa, showing that some taxa range from being entirely allochthonous to entirely autochthonous depending on where they were collected on the stream size gradient (grazers and collector–gatherer functional feeding groups), while other taxa are relatively fixed in the source of energy they assimilate (shredder and predator functional feeding groups). Consistent with expectations, allochthonous energy use was positively correlated with canopy cover in both regions for most feeding groups, with individuals from small, shaded streams having a more pronounced allochthonous signal than individuals collected from larger streams with less canopy cover. However, consumers in the shredder/detritivore feeding group did not vary among sites in their allochthonous energy use, and had a mostly allochthonous signal regardless of canopy cover and algal biomass. Our results demonstrate that the importance of energy from terrestrial subsidies can vary markedly but are similar in both temperate and tropical streams, suggesting a widely consistent pattern.

Adapting streams for climate change using riparian broadleaf trees and its consequences for stream salmonids

Summary The societal value, ecological importance and thermal sensitivity of stream‐dwelling salmonids have prompted interest in adaptive management strategies to limit the effects of climate change on their habitats. Additionally, in northern temperate regions, the management and restoration of riparian broadleaf forest is advocated increasingly to dampen variations in stream water temperature and discharge, but might have collateral effects on salmonids by changing allochthonous subsidies. Here, in a cross‐sectional analysis of 18 temperate headwaters with different riparian and catchment land use, we use classical fisheries data alongside stable isotope ratios in salmonids and their macroinvertebrate prey to examine whether increasing catchment cover of broadleaf trees could (i) increase the density, biomass and size of salmonids, (ii) increase brown trout (Salmo trutta) dietary reliance on production of terrestrial origin and (iii) mediate allochthonous energy flux between aquatic macroinvertebrates and brown trout. Contrary to expectation, catchment broadleaf cover had no systematic effect on salmonid density or individual size, although salmonid biomass was lowest in streams draining non‐native conifers. Moreover, there was no major effect of land use on the dependence of S. trutta on terrestrial production: averaged across all sites, trout used more production from in‐stream (62 ± 3%: mean ± 1 SE) than terrestrial (38 ± 3%) sources. Dependence on terrestrial production varied more substantially among individual streams than with riparian land use, mirroring site‐specific patterns observed in macroinvertebrates. Although increased broadleaf cover could benefit salmonids by offsetting the impacts of warming related to climate change, these results imply that broadleaf restoration along temperate, upland headwaters is neutral with respect to salmonid biomass, density and terrestrial subsidies. In contrast, the use of non‐native conifers for stream shading could have negative effects on salmonid production. Knowledge of the ecological implications of climate change adaptation remains rudimentary, and we advocate further evaluations like ours not only for fresh waters, but for ecosystems more generally.

Seasonal variation of allochthonous and autochthonous energy inputs in an alpine stream

Despite the enormous importance of alpine streams, information about many aspects of their ecology is still insufficient. Alpine lotic systems differ in many environmental characteristics from those lower down, for example because above tree line streams drain catchments where terrestrial vegetation is scarce and allochthonous organic input is expected to be small. The main objectives of this study were to examine seasonal variation of autochthonous and allochthonous energetic inputs and their relationship with macroinvertebrate communities in the Po river, an alpine non-glacial stream (NW Italy). For one year, samplings were monthly performed in a homogeneous 100 m stream reach for discharge, autochthonous energy input (benthic chlorophyll a ), allochthonous energy input (coarse particulate organic matter), abundance and structure of benthic macroinvertebrate community. Chlorophyll a concentrations were in the range of what reported for other alpine streams, but presented a time-lag with respect to what has been reported for glacial-fed mountain rivers. CPOM amounts were lower than those in lowland, forested streams of the same area but exhibited an intriguing, different seasonal variability, probably reported for the first time, with a maximum in spring and a minimum in winter. We collected 29,950 macroinvertebrates belonging to 13 families and 10 orders. Benthic communities were essentially dominated by Ephemeroptera, Plecoptera and Diptera. Scrapers was the most important FFG, but also Shredders were well represented. Relationships between chlorophyll a concentrations, CPOM availability and macroinvertebrate community characteristics were analysed and discussed considering the existence of different top-down or bottom-up regulation mechanisms. This study confirms that benthic algae constitute an essential resource for macroinvertebrates in alpine streams above the tree line but also underlines the importance of terrestrial organic input, a previously neglected input in environments above the tree line. The major forces shaping energetic inputs and invertebrate communities seemed to be related to the Alpine climate, and especially to snow accumulation and melting, with the consequent substantial discharge variations.

Rapid in-stream decomposition of leaves of common buckthorn (Rhamnus cathartica), an invasive tree species

Headwater streams derive a majority of their energy from allochthonous inputs; alteration of these inputs may lead to changes in stream communities and ecological function. Common buckthorn (Rhamnus cathartica) is invasive over much of the northern United States and southern Canada, and has the potential to become an ecosystem dominant and alter stream communities. However, while much is known of the effects of buckthorn on terrestrial ecosystems, little is known of its effects on aquatic ecosystems. Using leaf collection nets, we estimated that leaf fall to the stream consisted predominantly of green ash (69.0%) and common buckthorn (24.2%). Green ash leaves fell from September through mid-October, reaching its peak in early October, whereas common buckthorn contributed leaves for an additional month until mid-November. We placed leaf packs of common buckthorn and two native species, American elm and green ash, in a headwater stream to determine differences in leaf decomposition rates. Common buckthorn leaves decomposed more rapidly than the native species, with processing coefficients of 6.9 (ash) and 5.3 (elm) times greater. After 21 days of incubation, buckthorn leaf packs had less than half the initial biomass remaining, whereas ash and elm did not reach this point within this 84-day study. These results suggest that buckthorn has the potential to alter stream food webs by changing the timing of leaf fall and the duration of available allochthonous energy sources. Changes to riparian forests are likely to be exacerbated as common buckthorn alters soils to inhibit the growth of other trees and as the emerald ash borer, an invasive beetle, adversely affects native ash forests.

Trophic level determines levels of brominated flame-retardants in coastal herring gulls

Liver concentrations of eight polybrominated diphenyl ethers (ΣPBDEs: sum of brominated diphenyl ethers [BDE]-28, -47, -99, -100, -153, -154, -183, and -209) ranged from 135 to 985 ng g −1 lipid weight (lw) in coastal herring gulls ( Larus argentatus) from the marine Hvaler Archipelago (The Glomma River Estuary), Norway. Hexabromocyclododecane (HBCD) concentrations ranged from 10 to 698 ng g −1 lw. High range in δ 13C indicates that gulls were subject to a diversity of carbon sources, likely reflecting their mixed feeding on terrestrial and marine organisms, or diversity of autochthonous and allochthonous (watershed) energy sources at the bases of their marine/estuarial food chains. Inverse relationships of HBCD, and to somewhat lesser extent of BDE-209, with δ 13C values suggest higher abundance of these compounds in the land-derived energy-sources of the gulls. Inverse relationships of BDE-99, BDE-183 and BDE-209 with δ 15N suggest that trophic relationships affect bioaccumulation of these compounds in the herring gulls, with greater bioaccumulation from lower trophic level prey species. This may be because these PBDE congeners are subject of debromination in higher trophic levels prey species of the gulls (e.g., teleost fish). Levels of BDE-209 (up to 95 ng/g lipid) of these herring gulls from 1998 were in the higher range reported in European birds, and not matched by other reports in North Sea seabirds. The present study suggests that the currently used brominated flame-retardants (BFRs), BDE-209 and HBCD relate to changing nutrient allocation in the herring gulls, and represent a risk to seabirds exploiting near-shore and estuary ecosystems.

A nematomorph parasite explains variation in terrestrial subsidies to trout streams in Japan

Nematomorph parasites alter the behavior of their orthopteran hosts, driving them to water and creating a source of food for stream salmonids. We investigated whether nematomorphs could explain variation in terrestrial subsidies across several streams. In nine study streams, orthopterans comprise much of the stomach contents of trout (46 ± 31% on average). Total mass of ingested prey per trout biomass positively correlated with the mass of orthopterans ingested, suggesting that the orthopterans enhanced absolute mass of prey consumption by the trout population. The orthopterans ingested per trout biomass positively correlated with the abundance of nematomorphs in the stream, but not with the abundance of camel crickets (the dominant hosts) around the streams. Streams in conifer plantations had fewer nematomorphs than streams in natural deciduous forests. These results provide the first quantitative evidence that a manipulative parasite can explain variation in the allochthonous energy flow through and across ecosystems.

Decoupled conservatism of Grinnellian and Eltonian niches in an invasive arthropod

Whether a species niche is conserved or shifts across space and time is a question of heightened interest in ecology and evolution. Considerable scientific inquiry into this topic has used invasive species to evaluate conservatism of the Grinnellian climatic niche while generally neglecting the Eltonian functional niche. By contrast, we report here on the first simultaneous reciprocal comparison of both the Grinnellian and Eltonian niches for the globally invasive signal crayfish Pacifastacus leniusculus between its native (Pacific Northwest of North America) and non‐native ranges (Japan). Using multivariate statistics and the Maxent machine‐learning algorithm, we found strong evidence for a climatic niche shift between geographic regions for P. leniusculus. Pacifastacus leniusculus shifted from warmer temperatures with strong precipitation seasonality in western North America to cooler temperatures with less precipitation seasonality in Japan. However, analysis of stable isotopes of carbon and nitrogen revealed conservatism of the functional niche of P. leniusculus between multiple lakes in the native and non‐native ranges. We found that trophic position and niche width of P. leniusculus were equivalent between regions, and that niche attributes including reliance on autochthonous or allochthonous energy sources and ontogenetic shifts were comparable regardless of origin. Our finding of functional niche conservatism contrasts with the results of some recent studies evaluating the Grinnellian niche for invasive species, as well as our own climatic niche comparison, and raises the question of whether Grinnellian or Eltonian niches are more prone to shifts or conservatism. We hypothesize that the Grinnellian niche may be more labile than the Eltonian niche in general, but argue that resolving this question will require more reciprocal comparisons of Eltonian niches to keep pace with the recent increase in Grinnellian niche studies.

Catastrophic disturbances in headwater streams: the long-term ecological effects of debris flows and debris floods in the Klamath Mountains, northern California

Debris flows and debris floods are catastrophic disturbances in steep, mountainous landscapes throughout the world, but little is known about the long-term ecological effects of these events on headwater streams. In 10 basins (10–20 km2) in the Klamath Mountains, northern California, USA, we used a space-for-time substitution to infer the long-term (10–100 years) effects of debris flows on stream ecosystem structure. Debris flows mobilized sediment and wood and removed riparian vegetation from large portions of channel networks. Stream temperatures were significantly warmer in streams that had recent debris flows (<10 years ago). Large wood, benthic organic matter, and detritivorous stoneflies were all very sparse in recent debris flow streams, suggesting that allochthonous energy pathways took decades to recover. Rainbow trout ( Oncorhynchus mykiss ) were abundant in recent debris flow streams, but populations of other vertebrates such as coastal giant salamander ( Dicamptodon tenebrosus ) and coastal tailed frog ( Ascaphus truei ) were virtually absent. Increased frequencies of catastrophic debris flows associated with forest management practices can have significant negative impacts on aquatic biodiversity in forested, mountainous landscapes.

Do riparian zones qualify as critical habitat for endangered freshwater fishes?

Identification of critical habitat is a key step in conservation and recovery of endangered and threatened freshwater fish. Critical habitat under Canadian and US legislation may include habitat that is not directly used by listed fish, provided it is necessary for species conservation or recovery. Riparian habitat meets biological criteria for critical habitat because riparian zones are integral to aquatic ecosystem functions of importance to many fish species and other organisms. These functions include provision of shade for temperature-sensitive species, control of channel complexity and sediment inputs through bank stabilization, input of large wood and allochthonous energy sources, and filtering of nutrients and toxins from adjacent land. In response to decades of stream-riparian research, widespread implementation of regulations to protect riparian zones in most developed countries represent a de facto consensus that riparian buffers are essential for aquatic ecosystem health and the maintenance of populations of fish and other species. Consistent with widespread riparian regulations deemed necessary to protect not-at-risk species, riparian habitat adjacent to a body of water containing a listed freshwater species should be considered biologically critical unless the habitat requirements of individual taxa are demonstrated to be insensitive to the ecological functions associated with riparian habitat.