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Concern over rising water temperatures for freshwater ectotherms has led to application of experimentally derived thermal thresholds to stream temperature models for estimation of streams at high risk of exceeding thermal thresholds under current and future climate conditions. We optimised an approach that links field‐relevant thermal maxima experiments to corresponding stream temperature models and identifies opportunities to reduce stream temperatures through riparian tree growth.We conducted a thermal maxima experiment on cold‐water adapted juvenile Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) that reflected natural temperatures by using incremental temperature ramping with diel fluctuations (IT‐Dmax) and refit a regionally specific stream temperature model for British Columbia, Canada to directly relate to lab‐derived thresholds. Salmon‐bearing streams across British Columbia were categorised by threshold exceedance risk (i.e., low, moderate, high, severe) based on risk tolerance scenarios for management decision making (i.e., considering a range of prediction intervals [PIs] and stream thermal sensitivities to air temperature). We linked these results directly to riparian management and restoration actions by estimating the potential for riparian tree growth to reduce threshold exceedance risk.Lab‐derived IT‐Dmax endpoints were consistently 24°C (based on the median value between the 7‐day average of the daily maximum and the mean weekly average temperature) across acclimation treatments for both species. Under current conditions, most stream reaches (99.6% using an intermediate risk tolerance scenario) were below the thermal threshold; streams with moderate to high risk of threshold exceedance were projected to increase from 0.4% to 1.5% (total linear stream length of 6,929 km) by end of century. The risk‐averse (high sensitivity, 75% PI) and risk‐tolerant (low sensitivity, 95% PI) scenarios differed by 1,107 km of streams predicted to have a moderate to severe risk of exceeding thresholds by end of century. Maximal riparian tree growth was predicted to shift 670 km of streams from moderate to low exceedance risk under end‐of‐century conditions and intermediate risk tolerance, showing the potential for mitigation from thermal impacts.Our integrative approach tackled several key considerations in identifying streams at high temperature risk for freshwater ectotherms that to date have not been addressed. Furthermore, we showcased the delineation of spatially comprehensive estimates that identify where management mitigation and a specific restoration activity may be most needed to reduce impacts of rising temperatures on rearing salmonids across an extensive region. [ABSTRACT FROM AUTHOR]

It is a widely discussed topic in restoration ecology to use organic carbon (OC) management to increase nutrient uptake in chronically loaded agricultural streams. However, although nitrate uptake has been shown to correlated closely with the availability of dissolved OC, this relationship is less clear for phosphate. Likewise, the role of particulate OC (POC) on stimulating nutrient uptake has to be clarified. We aimed at investigating the effects of leaf additions on the net uptake of soluble reactive phosphorus and nitrate‐nitrogen from the water column by benthic biofilms in combined laboratory flume and batch experiments.Fine sediments were colonised under nutrient‐enriched conditions in the dark (dark‐grown heterotrophic biofilms) and under a 12/12‐hr dark/light cycle (light‐grown photoautotrophic biofilms) in flumes. In each light treatment, half of the biofilms were grown under strong OC‐limitation, the other half under near‐optimal C:N:P ratios. For the uptake experiments, the colonised sediments were incubated in nutrient‐enriched water to which (1) fresh alder leaves, (2) pre‐leached leaves, or (3) no leaves were added. Net nutrient uptake (or release) rates were determined via the change in nutrient concentrations in the water column over time.Net phosphorus uptake by dark‐grown biofilms was significantly increased by the addition of leaves. Despite their high initial nutrient leaching, fresh leaves showed stronger stimulating effects on the net P uptake than leached leaves over the entire experiment. Furthermore, biofilms grown under near‐optimum C:N:P ratios responded stronger to the POC supply than biofilms grown under C‐limited conditions. In contrast to dark‐grown biofilms, leaf additions had no significant effects on the net P uptake by light‐grown biofilms. We also found no effects of leaf additions on net nitrate uptake.Our study shows that an increased POC supply in nutrient‐impacted streams may boost heterotrophic phosphate uptake. However, the stimulating effect of the POC addition depends on a variety of POC‐dependent (e.g. respiration, heterotrophic assimilation, denitrification) and independent (e.g. adsorption, photoautotrophic assimilation) processes, making nutrient control via POC management challenging. We suggest application of management approaches that focus on restoration of riparian areas and wetlands to increase the amount of natural, complex POC with a moderate degradability, thus keeping the heterotrophic metabolism low but potentially stimulating in‐stream N and P retention. [ABSTRACT FROM AUTHOR]

Worldwide, riparian zones of many intermittent rivers and ephemeral streams (IRES) have been severely degraded. However, compared with perennially flowing waters, there have been few restoration efforts (e.g., revegetation, livestock removal) to halt or reverse this degradation. Even rarer are assessments of whether desired responses occurred and, if so, their underlying mechanisms, especially where flow extremes such as drying and flooding in IRES might alter or delay ecological responses to restoration.In order to assess how aquatic invertebrate communities responded to riparian replanting and livestock removal in three degraded lowland IRES in southeastern Australia, we conducted an eight‐year experiment (2004–2013), sampling paired control (unrestored) and treatment (restored, between 2005 and 2007 across creeks) sites twice yearly before and after restoration. To evaluate likely mechanisms underlying invertebrate responses to riparian restoration, we used a range of structural (e.g., richness) and functional (e.g., trait‐based) metrics. We also monitored environmental variables predicted to be likely drivers of aquatic invertebrate responses such as macrophyte and canopy cover, water quality, instream organic matter and instream wood. The study coincided with the last few years of a decade‐long drought that broke with severe floods (in 2010–2012), so we opportunistically examined how these hydrological extremes affected invertebrate responses to riparian restoration.At all three sites, macrophyte and canopy cover, water quality, organic matter and instream wood were comparable at treatment and control sites throughout the eight‐year experiment. There were also no significant differences in structural or functional metrics to indicate aquatic invertebrate responses to restoration after 6–8 years. This lack of predicted invertebrate responses apparently reflected how severely the drought impeded the riparian restoration, delaying even short‐term responses. Pervasive effects of catchment‐scale degradation may have further diminished the predicted benefits of the reach‐scale restoration efforts.By contrast, invertebrate metrics responded strongly to flow extremes, especially the brief floods that occurred as drought broke. These responses were evident for functional groups and individual families (especially rheophilic ones), but were not detected by a commonly used integrative measure of stream condition. This highlights the importance of selecting appropriate indicators in restoration monitoring programs and recognising their variability in responsiveness to restoration versus flow extremes.IRES are abundant and, in many parts of the world, increasingly common. Understanding how their inherent hydrological extremes may delay, modify and even overwhelm predicted responses to riparian restoration is crucial to setting realistic goals for IRES in the Anthropocene. Furthermore, assessing the success of riparian restoration in IRES requires a long‐term view given the extended time frames over which responses may occur, especially when expectations are often based on results of riparian restoration of perennial streams and rivers. [ABSTRACT FROM AUTHOR]

The response of riparian vegetation to flow regulation has been a research focus for decades. Several studies have shed light on the effects of flow stabilisation on riparian woody species, but other life forms exposed to intensified inundation have been overlooked. Furthermore, studies from a functional perspective are scarce.We evaluated the functional response of riparian vegetation along the shores of the Three Gorges Reservoir on the Yangtze River in China to unnaturally long annual flooding (>7 months) after the first year of filling. We aimed to answer the following: (1) can we derive well‐defined flow‐response guilds from the riparian zones of the Yangtze River? and (2) which plant traits and guilds are favoured or disfavoured by the unnaturally long flooding environment?Woody and herbaceous species were inventoried in 12 reaches along the shorelines of the Three Gorges Reservoir and another 12 reaches along the free‐flowing Yangtze River. We performed a cluster analysis to derive riparian guilds using abundance data (projective coverage) from 40 riparian plant species and 13 responsive traits. Structural composition and functional diversity of the unnaturally and naturally flooded riparian vegetation were compared.Unnaturally long flooding substantially reduced species richness, but it did not change the riparian vegetation cover. This novel flooding reduced functional diversity, mostly owing to the loss of stress‐tolerant woody species and competitive perennial herbs. However, competitive annual herbs and flood‐tolerant riparian herbs, as the most abundant functional guilds, were favoured even under such long‐term hypoxic conditions.These guilds under regulation revealed a high functional resilience to prolonged flooding along the upstream reaches of the Yangtze River. Flooding tolerance and the capacity to synchronise germination and growth with short‐exposure periods underlie the plant species changes. Our findings are useful for anticipating the effects of long‐lasting inundation on riparian areas triggered by flow regulation or warmer climates. The functional perspective lends confidence that our conclusions can be generalised to other geographical regions despite not sharing the same species pool. Finally, the plant species that showed a high flooding tolerance should be considered for the restoration of riparian areas affected by the Three Gorges Reservoir. [ABSTRACT FROM AUTHOR]

1. Tallgrass prairies and their streams are highly endangered ecosystems, and many remaining streams are threatened by the encroachment of woody riparian vegetation. An increase in riparian vegetation converts the naturally open-canopy prairie streams to closed-canopy systems. The effects of a change in canopy cover on stream metabolism are unknown. 2. Our goal was to determine the effects of canopy cover on prairie stream metabolism during a 4-year period in Kings Creek, KS, U.S.A. Metabolic rates from forested reaches were compared to rates in naturally open-canopy reaches and restoration reaches, the latter having closed canopies in 2006 and 2007 and open canopies in 2008 and 2009. Whole-stream metabolism was estimated using the two-station diurnal method. Chlorophyll a concentrations and mass of filamentous algae were measured after riparian removal to assess potential differences in algal biomass between reaches with open or closed canopies. 3. Metabolic rates were spatially and temporally variable even though the sites were on very similar streams or adjacent to each other within streams. Before riparian vegetation removal, whole-stream community respiration (CR) and net ecosystem production were greater with greater canopy cover. In the vegetation removal reaches, gross primary production was slightly greater after removal. 4. Chlorophyll a concentrations were marginally significantly greater in open (naturally open and removal reaches) than in closed canopy and differed significantly between seasons. Filamentous algal biomass was greater in open than in closed-canopy reaches. 5. Overall, the restoration allowed recovery of some features of open-canopy prairie streams. Woody expansion apparently increases CR and moves prairie stream metabolism towards a more net heterotrophic state. An increase in canopy cover decreases benthic chlorophyll, decreases dominance of filamentous algae and potentially alters resources available to the stream food web. The results of this study provide insights for land managers and conservationists interested in preserving prairie streams in their native open-canopy state. [ABSTRACT FROM AUTHOR]

1. Management of stream biodiversity is often tightly linked with the restoration and protection of riparian and catchment vegetation. Despite that, there are no established guidelines on how much forest should be retained or replanted in riparian zones and surrounding catchments to maintain or re-establish instream ecological integrity. In this study, we assess relationships between vegetation cover at multiple spatial scales (reach, segment and catchment) and macroinvertebrate metrics that reflect community structure, ecological condition and biodiversity at 138 Waikato, New Zealand, stream sites sampled in 2006. 2. Percentage of catchment vegetation in native forest had stronger relationships with measured diversity and condition metrics than segment or reach scale measures of riparian vegetation. Functional feeding group metrics were weakly associated with upstream catchment vegetation cover. 3. Of the macroinvertebrate metrics tested, the RIVPAC O/E and an organic pollution tolerance metric based on species presence–absence (Macroinvertebrate Community Index; MCI) had the strongest relationships with percentage native riparian vegetation, followed by the quantitative MCI and measures of the richness and relative abundance of Ephemeroptera, Plecoptera and Trichoptera faunas. The O/E and MCI indicated that catchments with 80–90% in native forest or scrub (low-growing trees) were associated with faunas indicative of “clean” water quality. 4. Of the biodiversity indices considered Fisher’s α Index of species richness had the strongest relationship with percent native riparian vegetation in the upstream catchment. There are no established thresholds for measuring biodiversity loss in New Zealand streams, but this analysis indicates that on average streams draining catchments with 40–60% upstream native vegetation cover retain 80% of the mean biodiversity present in pristine forest streams. 5. This research indicates that riparian management aimed at enhancing macroinvertebrate biodiversity and the ecological condition of streams is likely to be more successful when focused on protecting and/or restoring headwater catchments rather than short stretches of stream. [ABSTRACT FROM AUTHOR]

1. The articles in this Special Issue on pressure-response relationships in stream ecology cover a range of pressures including acidification, excess loading of metals, nutrients and organic matter to stream ecosystems and changes in riparian and catchment land use. Impacts on the biota (macroinvertebrates), ranging from single species to community responses, are addressed over a multitude of spatial scales using large data sets. 2. The majority of articles are based on monitoring data compiled as part of the EU-funded project REBECCA, but the Special Issue also includes articles from outside Europe (US and New Zealand) as well of studies using other data sources. 3. Results from the six articles gave new insights of relevance to water managers and documented that large-scale monitoring can be an asset to freshwater science. The large data sets enable a range of analytical approaches that single out important patterns in highly variable data.: importance of humic substances in reducing the negative impact of low pH; impact of very low levels of BOD (<2 mg L−1); higher sensitivity of trait-based metrics compared with identity-based metrics and importance of catchment and riparian vegetation for the ecological quality of streams. 3. We advocate an increased use of monitoring and survey data in addressing questions relevant to scientist and end-users, but issues relating to especially data quality should be considered. In future, the use of these data could increase knowledge exchange between the scientific community and managers with the ultimate aim of improving our freshwater resources. [ABSTRACT FROM AUTHOR]

1. Riparian vegetation in dry regions is influenced by low-flow and high-flow components of the surface and groundwater flow regimes. The duration of no-flow periods in the surface stream controls vegetation structure along the low-flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow-regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low-flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees ( Populus, Salix) to more drought-tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient-holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood-dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood-suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south-western United States, some focus on re-establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment. [ABSTRACT FROM AUTHOR]

1. The restoration of native, forested riparian habitats is a widely accepted method for improving degraded streams. Little is known, however, about how the width, extent and continuity of forested vegetation along stream networks affect stream ecosystems. 2. To increase the likelihood of achieving restoration goals, restoration practitioners require quantitative tools to guide the development of restoration strategies in different catchment settings. We present an empirically based model that establishes a relationship between a ‘stress’ imposed at different locations along a stream by the spatial pattern of land cover within catchments, and the response of biologically determined ecosystem characteristics to this stress. The model provides a spatially explicit, quantitative framework for predicting the effects of changes in catchment land cover composition and spatial configuration on specific characteristics of stream ecosystems. 3. We used geospatial datasets and biological data for attached algae and benthic macroinvertebrates in streams to estimate model parameters for 40 sites in 33 distinct catchments within the mid-Atlantic Piedmont region of the eastern U.S. Model parameters were estimated using a genetic optimisation algorithm. R2 values for the resulting relationships between catchment land cover and biological characteristics of streams were substantially improved over R2 values for spatially aggregated regression models based on whole-catchment land cover. 4. Using model parameters estimated for the mid-Atlantic Piedmont, we show how the model can be used to guide restoration planning in a case study of a small catchment. The model predicts the quantitative change in biological characteristics of the stream, such as indices of species diversity and species composition, that would occur with the implementation of a hypothetical restoration project. [ABSTRACT FROM AUTHOR]