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Lake deltas (LDs) receive nutrient and energy subsidies from upstream habitats. These inputs can support LD benthic production. However, LDs may also receive impacts from upstream disturbance. Small lakes in coastal British Columbia often have inflow streams from areas with forest harvesting, which is pervasive in this region. Forest harvesting impacts can alter stream production, although downstream impacts on lakes, compared to streams, are less studied and understood. We aimed to test whether benthic LD communities (biofilm and invertebrates) are more productive and (or) diverse compared to other communities along the lakeshore (LS) (non-LDs), and whether there are differences in LD communities associated with upstream harvesting. We compared LD communities with upstream riparian areas that were harvested (HLD) or relatively undisturbed (ULD), and LS sites. We found that while community structure was similar across sites, ULDs had higher biofilm and invertebrate standing stocks (1.5- and 2-times higher, respectively) than HLDs and LS sites. Our results suggest subsidies and benthic production were higher at ULDs. These results advance our understanding of forest harvesting disturbance and stream-lake connectivity.

Small lakes (2) are physically, chemically, and biologically linked to their watersheds through hydrologic, terrestrial, and aerial delivery of materials. Inputs affecting lake function and structure, such as nutrient, energy, sediment, and large wood subsidies, arrive at the lake on three spatial scales, that is, the lake watershed, lake-inflow streams, and lake riparian areas. Lakes are sinks in the waterscape and integrate cumulative inputs from the landscape. Lakes can, therefore, react to landscape disturbances such as forest harvesting. Forest harvesting and associated activities can induce changes in watershed water yields, inputs of organic and inorganic materials to lakes, and in lake temperatures and wind. These changes result in stressors that can alter the lake’s physical habitat, water quality, and food webs. Here we review the reported impacts of forest harvesting on small, temperate zone lakes. The magnitude of the lake response to harvesting can depend on factors such as the proportion of the watershed harvested, the intensity of this harvesting, silvicultural practices and other activities, and road construction and density. Other additional factors include the proximity of the lake to harvesting and its impact on hydrological pathways connecting perturbed areas to stream and lake systems. The majority of surveyed studies reported short-term increases in nutrient and energy inputs, increased sedimentation due to harvesting, and increases in wind speeds, where about half reported increases in primary production or decreases in zooplankton biomass. Results on benthic macroinvertebrate, fish, and amphibians were less frequently reported and were geographically variable. Variation in the direction and magnitude of a lake’s food web response is likely due to studies of lakes with differences in watershed characteristics and forestry activities that can affect the magnitude of the lake response (i.e., proportion of watershed harvesting, forestry operations methods, hydrological connections to the lake, and site-specific attributes). We also discuss watershed forestry management and the implementation of lakeshore riparian buffers in the context of reducing forestry impacts on lakes. Most studies have been short-term, and the long-term, cumulative effects of forest harvesting on lake ecosystems remain unclear.

Increasing concentrations of atmospheric greenhouse gases (GHGs; CO2, CH4, N2O) cause climate change. Depending on the conditions, soils have the potential to store carbon or to be a source of GHGs to the atmosphere. Riparian soils in particular have high potential to store carbon, but also to be sources of CH4 and N2O. Headwater streams make up a large proportion of stream length in a drainage network, and their riparian zones have valuable ecosystem functions. In parallel, the riparian zones of headwater streams are particularly vulnerable to forest harvest. Studies of GHG fluxes from these unique ecosystems remain limited. Our objective was to quantify the effects of forestry practices and groundwater discharge (DIS) areas on GHG emissions from riparian forest soils in coastal British Columbia. We compared nine sites with three different forest management protocols: (1) harvesting with a riparian buffer, (2) no buffer, and (3) reference sites without harvesting. We measured gas fluxes, soil temperature, soil moisture and depth to the groundwater table alongside headwater streams monthly over one growing season. We found that CH4 uptake rates were 65% lower at the no buffer sites, and N2O emission rates were 52% lower at the no buffer sites, when compared to the reference sites. Additionally, CH4 uptake was 54% lower at DIS areas than in non-DIS areas. The results of our research help inform forest management by demonstrating that maintaining riparian buffers can be effective in protecting the ecosystem functions contributing to soil GHG fluxes.

Western red cedar (Thuja plicata Donn ex D.Don) is a dominant species in forests of the Pacific Northwest in North America, but little is known about its decomposition in riparian habitat. We experimentally tested how early-stage mass loss of cedar leaf litter varied with distance from the stream (five distances from 1 to 40 m away) and responded to nutrient and water additions near four headwater streams in southwestern British Columbia. We ran three coarse-mesh litterbag trials in durations between five months to one year from January 2013 and January 2014. Litterbags were either untreated or given the following treatments: water additions during dry summer months, nitrogen and phosphorus additions, or additions of both. Control litterbags lost 21% initial mass over 12 months (January 2013 – January 2014), 20% over five months (January 2013 – June 2013), and 15% over eight months (June 2013 – January 2014). Rates of mass loss did not increase with water in any trial but did increase with nutrients in the 12-month trial. Litter located 40 m from the stream lost 7% more mass than that located 1 m away in this same trial. Our study indicates that cedar leaf litter mass loss responded primarily to nutrient additions.

Tributary junctions are regarded as ecologically important due to unique habitat present; however, there is limited understanding of the drivers of habitat attributes at these locations. Using six sites across two mainstem rivers, we tested whether tributary size relative to main stem governs the strength and direction of response of substrate size, stream temperature, and nutrient and coarse particulate organic matter (CPOM) concentration. We found that only phosphorus and CPOM concentration showed a significant relationship with relative tributary size. Small tributaries contributed high concentrations, whereas concentrations in larger tributaries resembled the main stem. Often, tributary exports were enough to increase the resource concentration in the main stem by 40%. Substrate coarsened by ∼60% downstream of tributaries. Temperature asynchrony was observed, where tributaries contributed water between 2.8 °C cooler to 1.9 °C warmer than the main stem within one diel period. Our results highlight the importance of small tributaries for whole network functioning. However, large spatiotemporal variability revealed how habitat attributes are highly context-dependent in these locations and may be difficult to predict in both scientific and management settings.

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter. Key Points • Nitrogen (N) and phosphorus (P) immobilization was measured on organic matter (cotton) in 100 rivers and riparian zones representing 11 biomes • Elevated temperature in riparian zones and phosphate in rivers increased immobilization, and consequently accelerated decomposition • N and P immobilization was strongly linked by microbial stoichiometry despite widely varied surface-water nutrient ratios Plain Language Summary Bacteria and fungi contribute to the breakdown of leaf litter in rivers and floodplains. To break down leaf litter, these microbes need the nutrients nitrogen and phosphorus (P), and microbes can get nutrients either from the leaf litter itself or from the environment. Most leaf litter has low nutrient content and microbes must rely on the environment to supply nutrients. We studied microbial nutrient uptake from the environment during litter breakdown to determine whether it varies predictably across the globe and how it is influenced by changing climate and nutrient pollution. In 100 rivers and floodplains in 11 of Earth's major biomes we placed small strips of cotton as stand-ins for leaf litter. Nutrient uptake was consistently greater on cotton strips that were submerged in the river compared to cotton on the floodplain. For microbes in the river, nutrient uptake was faster in instances where there was more P in the water. For microbes in the floodplain, nutrient uptake was faster where temperatures were warmer. Faster nutrient uptake by microbes was linked with faster cotton breakdown in rivers and floodplains. Our study shows that climate change and nutrient pollution can alter the activity of microbes in rivers and floodplains.

Forest regeneration has increased in many tropical abandoned lands and current restoration commitments in this region aim to restore over 1,400,000 km

Pesticides are important contributors to the global freshwater biodiversity crisis. Among pesticides, neonicotinoids are the best-selling class of agricultural insecticides and are suspected to represent significant risks to freshwater and terrestrial ecosystems worldwide. Despite growing recognition that neonicotinoid impacts may be modified by the presence of additional stressors, there is limited information about their interactions with other agricultural stressors in freshwater ecosystems. We conducted an outdoor pond-mesocosm experiment to investigate the individual and interactive effects of nutrients, fine sediment, and imidacloprid (a neonicotinoid insecticide) inputs on freshwater community structure (density, diversity, and composition of zooplankton and benthic invertebrates) and ecosystem functioning (ecosystem metabolism, primary production, and organic matter decomposition). We hypothesized antagonistic nutrient-imidacloprid, and synergistic sediment-imidacloprid interactions, affecting aquatic invertebrate communities. The three stressors had significant individual and interactive effects on pond ecosystems. The insecticide neutralized the positive effects of nutrient additions on benthic invertebrate richness and mitigated the negative effects of sediment on zooplankton communities (antagonistic interactions). Moreover, we observed compensatory responses of tolerant benthic invertebrates, which resulted in reversal interactions between sediment and imidacloprid. Furthermore, our observations suggest that imidacloprid has the potential to increase net ecosystem production at environmentally relevant concentrations. Our findings support the hypothesis that the impacts of imidacloprid may be modified by other agricultural stressors. This has important implications on a global scale, given the widespread use of these pesticides in intensive agricultural landscapes and the growing body of literature suggesting that traditional pesticide assessment frameworks, based on laboratory toxicity tests alone, may be insufficient to adequately predict effects to complex freshwater ecosystems.

Ecological shifts that enhance the efficiency of resource acquisition by consumers can affect the fate of resource subsidies in recipient ecosystems. To date, findings have been mixed about whether plant litter breakdown by stream decomposers is faster in locations where the litter originates from (i.e. home region) compared with other locations (away region). This phenomenon, known as home‐field advantage (HFA), may be influenced by litter quality and particularly decomposer groups (shredders versus microbes), rather than being an inherent consequence of the breakdown of locally native litter. We studied the effects of HFA on litter breakdown and litter‐associated communities in streams within mid‐ to late‐successional forests. Two pairs of riparian broadleaf and one pair of conifer litter species with contrasting chemical quality were reciprocally incubated across two temperate regions (˜3,000 km apart). Species in each pair are congeneric and allopatric. The HFA was assessed using within‐pair litter comparisons in home and away regions. Coarse‐ and fine‐mesh litterbags were used to separate the contributions to litter breakdown by microbial decomposition and shredder feeding. Conifer litter species used in this study were more recalcitrant than broadleaf litter species. Consequently, there was a significant positive HFA for the microbial decomposition of conifer litter. In contrast, there was no HFA for either microbial or shredder‐mediated breakdown of broadleaf litter, which might have been overridden by catchment‐scale differences in biophysical variables affecting breakdown. The effects of HFA on shredder colonisation and feeding on broadleaf litter were more variable among streams. Numerically abundant shredder taxa tended to have higher rates of colonisation and consumption on higher‐quality litter than on low‐quality litter, irrespective of litter origin. Our results suggest that prior (evolutionary and/or contemporary) litter exposure could strongly influence the litter‐processing capacity of microbial decomposers, but not shredders, at the community level. In particular, microbial decomposers specialised in degrading conifer litter probably had lower resource‐use plasticity than those processing broadleaf litter. Inter‐stream differences in riparian vegetation and habitat conditions could influence the HFA through altering the litter exposure history of decomposer communities. Our findings highlight the importance of prior litter–microbe interactions in determining the rates of microbial decomposition of native and exotic litter species.

he relationship between detritivore diversity and decomposition can provide information on how biogeochemical cycles are affected by ongoing rates of extinction, but such evidence has come mostly from local studies and microcosm experiments. We conducted a globally distributed experiment (38 streams across 23 countries in 6 continents) using standardised methods to test the hypothesis that detritivore diversity enhances litter decomposition in streams, to establish the role of other characteristics of detritivore assemblages (abundance, biomass and body size), and to determine how patterns vary across realms, biomes and climates. We observed a positive relationship between diversity and decomposition, strongest in tropical areas, and a key role of abundance and biomass at higher latitudes. Our results suggest that litter decomposition might be altered by detritivore extinctions, particularly in tropical areas, where detritivore diversity is already relatively low and some environmental stressors particularly prevalent., This study was part of the DecoDiv project conducted by the GLoBE network (www.globenetwork.es), which is coordinated by L. B. Most research was based on crowdfunding (details on specific funding sources at each region are given in Supplementary Information). Project coordination was funded by Basque Government funds (Ref. IT951-16) to the Stream Ecology Group (UPV/EHU, Spain).

Riparian zones of headwater streams have valuable ecosystem functions and are prevalent across many landscapes. Nevertheless, studies of greenhouse gas (GHG; CO 2 , CH 4 , N 2 O) fluxes from these unique ecosystems, with fluctuating water tables and high soil organic matter, remain limited. Our objectives were to (1) to quantify the effects of local riparian groundwater conditions on soil GHG flux rates, namely to determine if groundwater discharge (DIS) areas in the riparian zone would have higher soil moisture than adjacent non-discharge (ND) areas in the riparian zone, impacting GHG fluxes; and (2) to examine the relationship between GHG fluxes, soil moisture, soil temperature, and groundwater depth. We measured gas fluxes in situ alongside two relatively undisturbed headwater streams over one year, using closed static chambers and gas chromatography. We found that, although not significant, DIS areas had on average lower CH 4 uptake and lower CO 2 emissions than ND areas. We further found that soil temperature explained 30.0% and 26.2% of variation in CO 2 and N 2 O fluxes, respectively, and soil moisture explained 9.8% of variation in CH 4 fluxes. Our results provide information on the magnitude and drivers of GHG fluxes in riparian zones to help inform GHG budgets and forest management.

Leaf litter decomposition supports the provision of numerous ecosystem services—that is, the benefits nature provides to humans—through its contribution to the reduction and storage of organic materials that could negatively impact water supplies, and its support of the productivity of freshwater ecosystems. The magnitude of these services varies spatially, and with land use. Leaf litter decomposition contributes a large fraction of energy supporting production in small streams, and to downstream production through supplies of finer particles produced by consumers. Decomposition results in storage of carbon as biomass in biological communities, and reduces the amounts of organic materials that could impact water quality downstream. Changes in water quality that result from decomposition can also influence the aesthetic and recreational value of waterways. Land use can influence decomposition, for instance elevated nutrient concentrations can result in higher decomposition rates, but high temperatures and sediment loads may diminish those rates. Changes in the rates of such ecosystem functions may be proportional to changes in the associated benefits provided to humans. While decomposition is a key ecosystem function that can contribute to the provision of numerous services, there are few estimates of the human value of this process in freshwaters.

Plant litter functional diversity effects on instream decomposition change across latitudes., Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113° of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes.

Throughout history, humans have settled in areas of high biodiversity. Today these areas are home to our biggest urban centers with biodiversity at increasing risk from escalating cumulative threats. Identifying the management strategies to conserve species within such regions, and ensuring effective governance to oversee their implementation, presents enormous challenges. Using a novel Priority Threat Management (PTM) approach that calculates the cost‐effectiveness of conservation action and co‐governance, we discover that the 102 species at risk of local extinction within Canada's most diverse, heavily urbanized coastal region, the Fraser River estuary, require urgent investment in management strategies costing an estimated CAD$381 M over 25 years. Our study also suggests that co‐governance underpins conservation success in urban areas, by increasing the feasibility of management strategies. This study underscores that biodiversity conservation in heavily urbanized areas is not a lost cause but does require strategic planning, attention to governance, and large‐scale investment.

Purpose To estimate health and economic outcomes associated with newborn screening (NBS) for infantile-onset Pompe disease in the United States. Methods A decision analytic microsimulation model simulated health and economic outcomes of a birth cohort of 4 million children in the United States. Universal NBS and treatment was compared with clinical identification and treatment of infantile-onset Pompe disease. Main outcomes were projected cases identified, costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) over the life course. Results Universal NBS for Pompe disease and confirmatory testing was estimated to cost an additional $26 million annually. Additional medication costs associated with earlier treatment initiation were $181 million; however, $8 million in medical care costs for other services were averted due to delayed disease progression. Infants with screened and treated infantile-onset Pompe disease experienced an average lifetime increase of 11.66 QALYs compared with clinical detection. The ICER was $379,000/QALY from a societal perspective and $408,000/QALY from the health-care perspective. Results were sensitive to the cost of enzyme replacement therapy. Conclusion Newborn screening for Pompe disease results in substantial health gains for individuals with infantile-onset Pompe disease, but with additional costs.

PurposeTo estimate health and economic outcomes associated with NBS for infantile-onset Pompe disease in the United States.MethodsA decision analytic microsimulation model simulated health and economic outcomes of a birth cohort of 4 million children in the United States. Universal NBS and treatment was compared to clinical identification and treatment of infantile-onset Pompe disease. Main outcomes were projected cases identified, costs, quality adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) over the life course.ResultsUniversal NBS for Pompe disease and confirmatory testing was estimated to cost an additional $26 million annually. Additional medication costs associated with earlier treatment initiation were $181 million; however, $8 million in medical care costs for other services were averted due to delayed disease progression. Infants with screened and treated infantile-onset Pompe disease experienced an average lifetime increase of 11.66 QALYs compared to clinical detection. The ICER was $408,000/QALY from the health care perspective and $379,000/QALY from a societal perspective. Results were sensitive to the cost of enzyme replacement therapy.ConclusionsNewborn screening for Pompe disease results in substantial health gains for individuals with infantile-onset Pompe disease, but with additional costs.

Riparian forests along urban streams are affected by flashy hydrological regimes and adjacent upland land‐use, and their downstream dynamics are altered by forest fragmentation and by frequent river network truncation. This can lead to lower riparian habitat quality, decreased dispersal along the river network and increased recruitment of novel plant communities including non‐native species. Compared to forested landscapes, our understanding of riparian plant community diversity and composition along urban river networks is poor. We investigated riparian plant communities and riparian habitat variables along seven river networks situated along an urban gradient in the Greater Toronto Area, Canada. Six land‐use metrics classifying the intensity of urbanisation on three spatial scales (sub‐catchment, upstream riparian buffer, site buffer) were tested to explain the variation in riparian plant communities along the river networks and to describe the differences in riparian habitat. Riparian plant diversity peaked at sites which had between 40% and 70% of built‐up land cover within sub‐catchments; however, these communities contained a large number of non‐native species compared to the forested streams. While total species richness and native species richness were more related to river network factors (catchment area), non‐native richness was also affected by land‐use within a site. Community composition was more related to local land‐use than catchment area. Geographical distance between sites (both overland and hydrological) was increasingly more important for community heterogeneity along the urbanisation gradient. Riparian habitat worsened along the urbanisation gradient, with higher disturbance and soil pH and lower soil organic content and bryophyte cover in the more urban catchments. Riparian habitat variables were also related to the position along the river networks. Our results provide important insights into how riparian plant communities and riparian habitat differ along a gradient of urbanisation. Compared to previous studies we investigated the patterns in riparian vegetation in the context of river networks, including a variety of land‐use metrics, and analysed data across different spatial scales. This revealed important trends in plant diversity, demonstrated that urban land‐use increases the occurrence of non‐native species, and showed that the land‐use at the local scale is a stronger determinant of plant assemblages compared to land‐use at broader scales. These novel findings can be applied to land management in order to mitigate the effects of urbanisation on riparian ecosystems and the functions they provide for adjacent streams and rivers.

Background Measurement of health utilities is required for economic evaluations. Few studies have evaluated health utilities for rare conditions; even fewer have incorporated disutility that may be experienced by caregivers. This study aimed to (1) estimate health utilities for three rare conditions currently recommended for newborn screening at the state or federal level, and (2) estimate the disutility, or spillover, experienced by parents of patients diagnosed with a rare, heritable disorder. Methods A stated-preference survey using a time trade-off approach elicited health utilities for Krabbe disease, phenylketonuria, and Pompe disease at varying stages (mild, moderate, severe) and onset of disease symptoms (infancy, childhood, and adulthood). We recruited respondents from a nationally representative community sample (n = 862). Respondents valued disease specific health states in three consecutive question frames: (1) adult health state (> = 18 years of age), (2) child health state (

OBJECTIVE: Single-site studies indicate irregular hospital discharges are associated with elevated suicide risk. As part of ongoing analytics in the Veterans Affairs (VA) health system, the authors evaluated associations between irregular discharge and suicide over a 15-year period. METHODS: All inpatient discharges and discharge types from 2001 through 2014 were identified using VA administrative data. Mortality and cause-of-death data were drawn from comprehensive VA searches of the Centers for Disease Control and Prevention National Death Index. Suicide risk following regular versus irregular discharge was compared by using survival analysis and adjusting for age, gender, and VA facility. RESULTS: Among 5,051,051 discharges, 2.1% (103,995) were irregular. Adjusted suicide risk was higher following irregular discharge compared with regular discharge (hazard ratio [HR]=2.02, 95% confidence interval [CI]=1.78–2.29). Stratified analyses by unit type showed that the association was nonsignificant for psychiatric discharges but significant for general medical discharges (HR=3.01, CI=2.54–3.57). CONCLUSIONS: Patients were at increased suicide risk after irregular hospital discharges.

OBJECTIVE To explore the impact of problem-solving treatment (PST) for mild traumatic brain injury in active duty service members on the use of medical and psychological services. PARTICIPANTS Service members who had a mild traumatic brain injury during their last deployment and enrolled in the CONcussion Treatment After Combat Trauma (CONTACT) study. DESIGN Secondary analysis of a randomized clinical trial. Participants were assigned to telephone-based PST, or e-mailed or mailed education only over the course of 6 months. MAIN MEASURE Self-reported health service utilization from months 4 through 6 and 10 through 12 after initiation of treatment, using the Cornell Service Index. RESULTS In months 4 to 6, participants receiving PST had 6.17 times the odds of an emergency department visit or hospitalization than those receiving education only (95% confidence interval = 1.92-19.8; P value = .0023). These estimates, however, were not significant using a conservative Bonferroni correction (P value threshold < .0014). There were no other significant differences for other medical or psychological services received in months 4 to 6 or 10 to 12. CONCLUSION Telephone-based PST was designed to complement clinical care, and this study showed that it may increase emergency department utilization. Future evaluations of PST with more accurate and complete measures of health service utilization are needed.

Human population growth and development have degraded freshwater ecosystems through direct negative effects on basal resources and higher trophic levels. Knowledge of how basal resources are influenced by anthropogenic activities is needed to examine foodweb responses and to evaluate negative effects of human disturbance. We combined quantitative sampling of all putative resources and consumers and naturally occurring stable isotopes of resource C and N to investigate how land use influences characteristics of basal resources (leaf litter, fine particulate organic matter [FPOM] suspended in water, FPOM deposited in pools, and epilithon) and the invertebrate communities in 9 streams of British Columbia (Canada) on a seasonal basis. Study streams were grouped as forest, cropland, and urban, based on percentages of land use in their catchments. We tested for seasonal and spatial differences in biomass, isotopic variability, and overlap of different basal resources and their relationships with inverte...

Management perspectives on Aqua incognita : Connectivity and cumulative effects of small natural and artificial streams in boreal forests

The influence of stream channel structure on the production of prey for drift-feeding fish is not well understood. We quantified drift production, the entry rate per streambed area, and drift flux, the total export rate per channel unit, in three second-order, forested streams in southwest British Columbia, Canada. We tested whether (1) drift production was higher in riffles than in pools, (2) drift flux increased with riffle length, and (3) prey body size was larger from riffles relative to pools and from terrestrial drop relative to aquatic drift. Total and aquatic-derived drift production (mg·m−2·h−1) was ∼3.5 times higher in riffles relative to pools; however, terrestrial drift did not differ between channel types. Total drift flux (mg·h−1) was positively related to riffle length. Terrestrial invertebrates were approximately three times larger than aquatics, and invertebrates from riffles were approximately three times larger on average than those from pools. These results suggest that channel structure directly affects prey availability and prey quality for drift-feeding fish and that long riffles may be key areas of prey generation.

We manipulated nutrient concentrations in 14 channels adjacent to a forested headwater stream to examine the influence of nutrient enrichment on detrital and algal pathways. Our fertilization experiment increased the average water concentration of N up to a maximum of ~2 times and of P up to ~7 times relative to control channels, levels considered as moderate enrichment. We measured algal biomass and leaf mass loss as a proxy measure of primary production and leaf decomposition, respectively. We determined the effects of nutrients on the quantity and quality of food resources and tested whether these effects influenced biotic structure and stoichiometry. Our results indicate that algal pathways showed significant and consistent responses across treatments by increasing epilithon quantity and quality. Moreover, despite an increase in quality of leaves, its quantity and loss rate were unaltered. Importantly, changes to detritivore densities were subtle, but they showed a hump-shaped response along the induced nutrient gradient. This trend suggests the existence of nutrient limitation at low nutrient concentrations and the existence of negative biotic interactions and/or sublethal toxic effects at higher concentrations, while enhancing detritivore densities at intermediated enriched conditions (threshold at ~10 µg/l of P–PO4 in water and 0.10% of leaf-P). This study reveals the complexity of connections between algal and detritus pathways with implications in the study of transfer of matter and energy in oligotrophic, forested headwater streams.

Terrestrial leaf litter provides a key resource for freshwater food webs, and invertebrates are, in turn, major agents in leaf litter decomposition. Understanding the roles of invertebrates in the decomposition process requires assessment of the relative abundances, timing of colonization, and species composition. This chapter describes how to separate and collect invertebrates associated with decomposing leaves in freshwaters, along with suggestions for statistical analysis of the data. Leaves from a litter sample collected in the field are individually rinsed with running water and the dislodged invertebrates retained on a sieve are preserved for analysis. The specimens are identified, counted, and, if necessary, measured (size or body mass). Abundances (or biomass) of the invertebrates are often expressed as number (or mass) per unit dry mass or ash-free dry mass of leaf litter. Given that leaf litter is an important basal resource in freshwater ecosystems, analyses of consumer resource dynamics on decomposing litter can provide information on both detritivore nutritional ecology and litter decomposition.

Forested riparian buffers are recommended to mitigate negative effects of forest harvesting on recipient freshwater ecosystems. Most of the current best practices of riparian buffer retention aim at larger streams. Riparian protection along small streams is thought to be lacking; however, it is not well documented. We surveyed 286 small streams flowing through recent clearcuts in three timber-producing jurisdictions-British Columbia, Canada (BC), Finland, and Sweden. The three jurisdictions differed in riparian buffer implementation. In BC, forested buffers are not required on the smallest streams, and 45% of the sites in BC had no buffer. The average (+/- SE) width of voluntarily retained buffers was 15.9 m (+/- 2.1) on each side of the stream. An operation-free zone is mandatory around the smallest streams in BC, and 90% of the sites fulfilled these criteria. Finland and Sweden had buffers allocated to most of the surveyed streams, with average buffer width of 15.3 m (+/- 1.4) in Finland and 4 m (+/- 0.4) in Sweden. Most of the streams in the two Nordic countries had additional forestry-associated impairments such as machine tracks, or soil preparation within the riparian zone. Riparian buffer width somewhat increased with stream size and slope of the riparian area, however, not in all investigated regions. We concluded that the majority of the streams surveyed in this study are insufficiently protected. We suggest that a monitoring of forestry practices and revising present forestry guidelines is needed in order to increase the protection of our smallest water courses.

International audience; In this overview (introductory article to a special issue including 14 papers), we consider all main types of natural and artificial inland freshwater habitas (fwh). For each type, we identify the main biodiversity patterns and ecological features, human impacts on the system and environmental issues, and discuss ways to use this information to improve stewardship. Examples of selected key biodiversity/ecological features (habitat type): narrow endemics, sensitive (groundwater and GDEs); crenobionts, LIHRes (springs); unidirectional flow, nutrient spiraling (streams); naturally turbid, floodplains, large-bodied species (large rivers); depth-variation in benthic communities (lakes); endemism and diversity (ancient lakes); threatened, sensitive species (oxbow lakes, SWE); diverse, reduced littoral (reservoirs); cold-adapted species (Boreal and Arctic fwh); endemism, depauperate (Antarctic fwh); flood pulse, intermittent wetlands, biggest river basins (tropical fwh); variable hydrologic regime—periods of drying, flash floods (arid-climate fwh). Selected impacts: eutrophication and other pollution, hydrologic modifications, overexploitation, habitat destruction, invasive species, salinization. Climate change is a threat multiplier, and it is important to quantify resistance, resilience, and recovery to assess the strategic role of the different types of freshwater ecosystems and their value for biodiversity conservation. Effective conservation solutions are dependent on an understanding of connectivity between different freshwater ecosystems (including related terrestrial, coastal and marine systems).

International audience; Accumulations of leaf litter in freshwaters can vary from individual leaves to large leaf packs. Past studies have demonstrated that decomposition rates decrease as leaf pack size increases. We considered a set of hypotheses that lower breakdown in larger leaf packs occurs as a consequence of diffusion gradients of oxygen and nutrients, or lower accessibility to larger detritivores to leaf tissue in the middle of these leaf packs. We manipulated leaf pack size in a stream to quantify decomposition rates and the abundances of consumers relative to the amount of detrital mass available. Mass loss rates of beech leaves were lower as leaf pack size increased. We found no differences in fungal biomass across our treatment gradients, or when comparing leaves in the middle of the leaf pack versus those on the outside. The lower decomposition of larger leaf packs would thus not result from a lower quality of the resource based on fungal biomass. Invertebrates per unit mass of leaf packs declined exponentially with size of leaf pack. Smaller invertebrates were less abundant per unit of resource as leaf pack size increased, but abundances of larger invertebrates declined even more dramatically than that of smaller ones. The results are consistent with accessibility within leaf packs decreasing as leaf pack size increases, a factor that is important for the estimation of consumer-resource functions for this patchy resource.

We studied how multiple-stresssors in tributaries affect function, diversity, and physical habitat of recipient downstream ecosystems. Using a mesocosm model of a stream network, we manipulated sediment and nutrients individually and in combination in tributaries of second-order channels, to test the effect of complex stressor interactions within tributaries on recipient channels. Sedimentation in second-order channels increased with the level of disturbance of the tributaries. Moreover, Ephemeroptera, Plecoptera, and Trichoptera (EPT) density and EPT richness were higher in second-order channels fed by tributaries where the stressors were applied separately, compared to those fed by tributaries where the stressors were applied simultaneously. Our observations suggest this result was due to the combination of the two stressors within the same tributary reducing EPT drift from the tributaries further than the addition of the stressors in separate tributaries. These results support the hypothesis that cumulative upstream disturbance can influence downstream recipient ecosystems in stream networks. However, contrary to our expectations, most observed effects were due to impacts on dispersal patterns of EPT taxa, rather than downstream accumulation of disturbances throughout the network. Our results underscore the importance of metacommunity frameworks to understand how tributary disturbance may influence population dynamics in downstream ecosystems.

Our understanding of how effective forestry Best Management Practices (BMPs) can mitigate logging impacts on the structure and functioning of temperate headwater streams tends to be based upon studies conducted within the first few years post-harvest. Little is known about how the affected biological parameters of streams change during riparian and upland forest regeneration, particularly the time taken to return to pre-harvest levels, or to within the range of reference conditions. By following up on an earlier study in southwestern British Columbia, Canada, we examined the post-logging recovery trajectories of stream attributes under multiple forest treatments. These treatments provided a gradient of riparian protection, including streamside clear-cutting with no reserves, and with fixed-width reserves (10 m and 30 m), and thinning with 50% basal area removal of riparian trees, which were compared with unharvested control sites. About 15 years after clear-cutting and 9 years after thinning, slower decomposition of red alder leaves (Alnus rubra) was reported in streams affected by forest harvesting, which was attributed to lower density of shredder invertebrates. Thinned reaches had lower litter decomposition rate than, but similar shredder density and richness to, unharvested reference sites. After a further 7 years of forest regrowth (time elapsed between the previous and present study), we found that litter decomposition rate and shredder density in logging-affected reaches converged with values in reference reaches. Stream functional integrity, as reflected by litter decomposition, increased across all forest treatments. Some differences in rarefied shredder richness among forest treatments emerged in this study. The legacy effects of thinning on some biotic variables likely diminished more quickly (2–9 years post-harvest) than those of clear-cutting with and without riparian reserves (8–15 years). Stream recovery from thinning to reference conditions should continue to warrant attention, as wider, larger-scale partial harvesting practices are recommended within emerging paradigms of forest management. Overall, our findings indicate time scales towards recovery of an important ecological process of streams under common forestry practices, which could be longer than other stream properties, such as water quality. Such differences in recovery time frames should be considered for the planning of forestry operations and monitoring of harvesting legacies.

Sedimentation is a pervasive cause of biological impairment in streams, and predation exerts strong control over lower trophic levels. However, studies combining these two factors are lacking. In a factorial experiment in flow-through channels, addition of sand (

Summary Pulsed flow disturbances strongly influence invertebrate drift in lotic ecosystems. However, drift-flow relationships are often context dependent and non-intuitive, suggesting that local abiotic and biotic conditions mediate the impacts of flow on the physical and behavioural drivers of drift entry. Two factors may be particularly important: physical channel architecture, which modulates how flow influences velocity and habitat area; and species traits, which determine behavioural responses to flow and susceptibility to passive entrainment. We examined how channel architecture and species traits (e.g. mobility, body size, and dislodgement susceptibility) mediated the effects of flow on bulk drift abundance and taxa-specific per capita drift rates (the rate of emigration from the benthos). In complementary experiments, we reduced and increased flows in stream mesocosms with contrasting cross-sectional channel profiles: concave channels, where habitat area contracted and expanded with altered flow but velocity remained relatively constant; and flat channels, which maintained constant habitat area but experienced greater changes in velocity. Total drift concentration increased following flow reductions and decreased following flow increases whereas drift flux (the total number drifting) showed the opposite pattern. Channel architecture did not influence drift during flow reductions, but during flow increases drift flux and concentration were amplified in flat channels that experienced larger increases in velocity and shear stress. Contrasting responses among individual taxa to flow manipulation were explained by variation in mobility (swimming and crawling ability) and body shape (susceptibility to drag). Per capita drift rates for the most mobile taxa increased c. 10% under flow reduction, indicating a behavioural response, whereas drift of other taxa declined. Per capita drift increased for all taxa following elevated flow but by the largest magnitude in taxa with body shapes that experience more drag, suggesting passive dislodgement. Our results imply that: (i) stream channel architecture can modify the impacts of flow increases on stream invertebrates; and (ii) invertebrate taxa vary in their vulnerability and behavioural responses to flow disturbance. Together these inferences clarify some of the previously unexplained context-dependent responses of drift to flow disturbances.

Most studies of cross-ecosystem resource subsidies have demonstrated positive effects on recipient consumer populations, often with very large effect sizes. However, it is important to move beyond these initial addition–exclusion experiments to consider the quantitative consequences for populations across gradients in the rates and quality of resource inputs. In our introduction to this special issue, we describe at least four potential models that describe functional relationships between subsidy input rates and consumer responses, most of them asymptotic. Here we aim to advance our quantitative understanding of how subsidy inputs influence recipient consumers and their communities. In the papers following, fish were either the recipient consumers or the subsidy as carcasses of anadromous species. Advancing general, predictive models will enable us to further consider what other factors are potentially co-limiting (e.g., nutrients, other population interactions, physical habitat, etc.) and better integrate resource subsidies into consumer–resource, biophysical dynamics models.