Summer Low-flow Period Research Articles

How and when glacial runoff is important: Tracing dynamics of meltwater and rainfall contribution to river runoff from headwaters to lowland in the Caucasus Mountains

As glacier degradation is intensifying worldwide, understanding how and when glacial runoff is important becomes imperative for economic planning and societal adaptation in response to climate change. This research highlights a probable emergence of new low-flow periods, ranging from one to several weeks, with an anticipated 50–90 % reduction in runoff even in major rivers originating in glacierized mountains by the mid to late 21th century. While the predicted decline in annual and monthly runoff appears moderate for most glaciated regions globally, the emergence of new deglaciation-induced summer low flow periods could create critical “bottle necks” constraining effective water resources management.In this study, a nested catchment approach (7.6–2259 km2) in conjunction with an isotopic tracer method (D, 18O), was employed to quantify the seasonal dynamics of snow and glacial meltwater and rainfall contribution to runoff across various scales of river catchments for the underreported Caucasus Mountains. Although the contribution of meltwater was predictably dominant in the headwaters (75–100 %), it still constituted a substantial 50–60 % of river runoff in the lower reaches most of the time from June to September. While the relative capacity for rainwater storage was found to significantly increase with watershed scale, during weeks devoid of noteworthy rainfall, the runoff in river basins with a mere 7 % glaciation basically entirely consists of what is formed in the glacierized headwaters. The glacial runoff was prevalent in the melt component from late July/early August to mid-September: not less than 30–60 % to the total runoff in the headwaters and 30–40 % in the lower reaches.An approach is proposed to account for the spatial heterogeneity of stable water isotopic content within snow cover and glacier ice. Sources of uncertainties and soundness of assumptions typically used for isotopic hydrograph separation are discussed with particular consideration given to the study objectives.

Towards ecological flows: status of the benthic macroinvertebrate community during summer low-flow periods in a regulated lowland river

Climate change along with the increasing exploitation of water resources exacerbates low-flow periods, causing detrimental effects on riverine communities. The main mitigation measure currently adopted to counteract hydrological alterations induced by off-stream diversion is the release of minimum flows (MFs), even if within the European Union Water Framework Directive an upgrade towards ecological flows is urgently required to achieve good ecological status (GES). In this study, we investigated the temporal evolution of the benthic macroinvertebrate community in an Italian-regulated lowland river (Ticino River) to clarify the ecological effects of summer low flows, and we evaluated the current MFs in the perspective of meeting GES standard. Biomonitoring was carried out for four consecutive years (2019-2022), in a river site immediately below a large off-stream diversion. The four study years were characterized by different streamflow patterns, thus allowing us to compare the temporal trajectories of the community under different flow conditions. Moreover, the interruption of the low-flow periods due to overflow spilled by the upstream dam gave us the opportunity to assess the effects of experimental flow peaks. Contrary to the expectation, the macroinvertebrate assemblage kept almost unvaried across the years, showing great resistance and resilience to hydrological changes. Even in extraordinarily dry 2022, the community composition varied only slightly, with a reduction of mayflies and an increase of mollusks. However, a deterioration of the ecological status below GES standard was recorded that summer, indicating the need for an upgrading of the current MFs. This upgrade would include experimental flow peaks in critical periods, which act as intermediate disturbances, enhancing community richness, diversity, and overall quality, as well as compliance with a threshold of an index specifically developed for the hydrological pressure.

Optical signatures of dissolved organic matter in the Siberian Rivers during summer season

Rivers are the main way of mobilizing, transforming and transporting of dissolved organic carbon to the ocean, thus largely determining the features of the carbon cycle on the Arctic shelf and in the Arctic Ocean as a whole. Seasonal variations in dissolved organic matter (DOM) fluxes from land to sea have been well documented in the Siberian river’s deltas, yet remarkably little is known about how DOM varies with hydrograph within the rivers main stems. The distribution of DOM and its optical characteristics as well as the CO2 fluxes between river water and the atmosphere in the main channel and tributaries of Siberian rivers such as the Lena, the Ob and the Anadyr in summer (July) were studied. The aim of this study was to investigate spatial changes in dissolved organic carbon (DOC) concentrations and DOM composition based on its absorption properties along the riverine main stem, to compare the dynamics of DOC concentration and DOM properties in different Siberian rivers and to reveal the main factors determining its variability, to evaluate the relationship of DOM with carbonate chemistry of riverine waters. The observed spatial variability of the investigated parameters in the river channel was strongly influenced by the river hydrograph along with landscape and geographical features of its catchment area. The phase of river runoff differed significantly in the same time period in different river sections, thus largely determining the quantitative and qualitative variations in the composition of DOM. In the Ob River the inflow of water from its largest tributary, the Irtysh River, is also an important factor of spatial variations. During the summer low-flow period, less aromatic DOM was found in river waters; it was more photodegraded with a relatively low molecular weight of compounds, compared to the high-water period. Such dynamics is one of the factors that alter the carbonate chemistry of waters as well as the magnitude and direction of CO2 fluxes between river water and the atmosphere.Higher DOC concentrations and higher aromatic DOM were found in the Ob River waters compared to the waters of ‘permafrost’ rivers – the Lena and the Anadyr rivers, which was caused by higher soil organic carbon content and its greater availability determined by the state of permafrost located in the river’s watersheds. A strong correlation between DOC concentrations and the colored fraction of DOM was established, thus confirming the possibility of using the latter as a proxy of DOC concentrations in Siberian rivers. The unique information obtained on the properties and variability DOM, which enters the rivers in different flow phases along the main stem, allows a more accurate evaluation of the effect of changing climate on biogeochemical cycles in the Arctic.

Seasonal variation and release of soluble reactive phosphorus in an agricultural upland headwater in central Germany

Abstract. Soluble reactive phosphorus (SRP) concentrations in agricultural headwaters can display pronounced seasonal variability at low flow, often with the highest concentrations occurring in summer. These SRP concentrations often exceed eutrophication levels, but their main sources, spatial distribution, and temporal dynamics are often unknown. The purpose of this study is therefore to differentiate between potential SRP losses and releases from soil drainage, anoxic riparian wetlands, and stream sediments in an agricultural headwater catchment. To identify the dominant SRP sources, we carried out three longitudinal stream sampling campaigns for SRP concentrations and fluxes. We used salt dilution tests and natural 222Rn to determine water fluxes in different sections of the stream, and we sampled for SRP, Fe, and 14C dissolved organic carbon (DOC) to examine possible redox-mediated mobilization from riparian wetlands and stream sediments. The results indicate that a single short section in the upper headwater reach was responsible for most of the SRP fluxes to the stream. Analysis of samples taken under summer low-flow conditions revealed that the stream water SRP concentrations, the fraction of SRP within total dissolved P (TDP), and DOC radiocarbon ages matched those in the groundwater entering the gaining section. Pore water from the stream sediment showed evidence of reductive mobilization of SRP, but the exchange fluxes were probably too small to contribute substantially to SRP stream concentrations. We also found no evidence that shallow flow paths from riparian wetlands contributed to the observed SRP loads in the stream. Combined, the results of this campaign and previous monitoring suggest that groundwater is the main long-term contributor of SRP at low flow, and agricultural phosphorus is largely buffered in the soil zone. We argue that the seasonal variation of SRP concentrations was mainly caused by variations in the proportion of groundwater present in the streamflow, which was highest during summer low-flow periods. Accurate knowledge of the various input pathways is important for choosing effective management measures in a given catchment, as it is also possible that observations of seasonal SRP dilution patterns stem from increased mobilization in riparian zones or from point sources.

Climate change impacts on native cutthroat trout habitat in Colorado streams

AbstractHeadwater streams support vital aquatic habitat yet are vulnerable to changing climate due to their high elevation and small size. Coldwater fish are especially sensitive to the altered streamflow and water temperature regimes during summer low flow periods. Though previous studies have provided insights on how changes in climate and alterations in stream discharge may affect habitat availability for various native cutthroat trout species, suitable physical habitats have not been evaluated under future climate projections for the threatened Greenback Cutthroat Trout (GBCT) native to headwater regions of Colorado, USA. Thus, this study used field data collected from selected headwater streams across the current distribution of GBCT to construct one‐dimensional hydraulic models to evaluate streamflow and physical habitat under four future climate projections. Results illustrate reductions in both predicted streamflow and physical habitat for all future climate projections across study sites. The projected mean summer streamflow shows greater decline (−52% on average) compared to the projected decline in mean August flow (−21% on average). Moreover, sites located at a relative higher elevation with larger substrate and steeper slope were projected to experience more reductions in physical habitat due to streamflow reductions. Specifically, streams with step‐pool morphologies may experience grater changes in available habitat compared to pool‐riffle streams. Future climate change studies related to coldwater fish that examine spatial variation in flow alteration could provide novel data to complement the existing literature on the thermal characteristics. Tailoring reintroduction and management efforts for GBCT to the individual headwater stream with adequate on‐site monitoring could provide a more holistic conservation approach.

Augmenting environmental flow information with water temperature: case study in Eastern Canada

The increasing global water demand and climate change put freshwater resources and riverine ecosystems at risk of increasing scarcity and conflict in water usage. Stream biota may be confronted with increasing stressful aquatic habitat conditions due in part to increasing water temperatures. In response to these issues, environmental flows play a crucial role in flow assessment, water resource management and the protection of aquatic biota. Environmental flows (eflows), also known as instream flow requirements, refer to the amount of water needed in rivers to maintain a balanced aquatic ecosystem. Recently, the inclusion of river temperature in the assessment of eflows has raised interest, especially in the context of climate change and dam operations, which are altering the river thermal regimes and affecting aquatic habitat. This study focuses on hydrological metrics that can be used to prescribe eflows in Atlantic Canada and Quebec (Eastern Canada). Eflow analyses were conducted jointly with the analyses of river temperatures at 61 sites. The results show that summer environmental flow metrics can be associated with relatively high water temperatures during a period when water withdrawals may be important. Classifying rivers according to their thermal regime during summer low flow periods prior to prescribing an eflow target is therefore recommended.

An empirical test of groundwater pumping effects on river flow and temperature: Chemainus River case study

Groundwater abstraction from pumping wells can reduce the flows and water levels of hydraulically connected surface waters, which can affect aquatic communities and water rights of other users. Four pump tests were implemented in the 2016 summer low-flow period to measure groundwater pumping effects to Chemainus River surface water flow and temperature. The effect of pumping on surface flow was estimated using four metrics based on differences between measured and predicted flow at a hydrometric gauge located 340 m from the groundwater wells. Differences were estimated as residuals from a regression model relating flow at this gauge to flow at a gauge 1.3 km upstream of the wells. The effect of pumping on surface water temperature was assessed using daily maximum and daily average water temperature at gauges located 340 m and 1.4 km downstream of the wells. An effect of pumping on river flow was measurable when the pumps were turned on and shut off. The consistency of measured effects across all tests and the absence of discernable trends within and across tests indicate that the average effect of pumping across a broader period is equivalent to the average of all before and after comparisons, which was estimated as 9.9 L/s ± 12.1 L/s, or 5.5% of river discharge at the time of the tests. Groundwater pumping did not result in a detectable shift in water temperature. The results indicate that changes in water temperature in relation to the pump tests were smaller in magnitude or spatial scale than the detection limits of the implemented experimental design. This case study provides an example of quantification of pumping effects on stream flow and temperature, as required by the Water Sustainability Act for licensing of groundwater abstraction. We suggest this approach could be used elsewhere to quantify effects of groundwater abstraction.

Climate change impacts on snow and streamflow drought regimes in four ecoregions of British Columbia

In many regions with seasonal snow cover, summer streamflow is primarily sustained by groundwater that is recharged during the snowmelt period. Therefore, below-normal snowpack (snow drought) may lead to below-normal summer streamflow (streamflow drought). Summer streamflow is important for supplying human needs and sustaining ecosystems. Climate change impacts on snow have been widely studied, but the relationship between snow drought and streamflow drought is not well understood. In this study, a combined investigation of climate change impacts on snow drought and streamflow drought was completed using generic groundwater – surface water models for four headwater catchments in different ecoregions of British Columbia. Results show that, in response to increased precipitation and temperature, the snow drought regime changes substantially for all four catchments. Warm snow droughts, which are caused by above-normal winter temperatures, increase in frequency, and dry snow droughts, which are caused by below-normal winter precipitation, decrease in frequency. The shift toward more frequent and severe temperature-related snow droughts leads to decreased summer streamflow, decreased summer groundwater storage, and longer, more severe summer low flow periods. Moreover, snow droughts propagate into summer streamflow droughts more frequently in the future time periods (2050s, 2080s) as compared to the baseline 1980s period. Thus, warm snow droughts not only become more frequent and severe in the future but also more likely to result in summer streamflow drought conditions.

Quantitative modelling of fish habitat in a large regulated river in a changing climate

AbstractThe expansion of hydropower in combination with the already existing infrastructure and a changing climate are significantly influencing the world's rivers. The resulting alteration in flow regimes is expected to strongly affect fish habitat and associated fish communities both spatially and temporally. Using habitat modelling, this study identified habitat bottlenecks during the critical summer low flow period and fish assemblages that will be most susceptible to regulated and predicted future flow regimes in the Saint John River downstream the Mactaquac Generating Station. Expert knowledge‐based habitat models were applied at the meso‐scale to evaluate the influence of alternative future flow regimes on habitat suitability indices of fish assemblages. Dam renewal and removal scenarios predicted low habitat suitability for rheophilic fish species, particularly during prolonged low flow periods in dry years. Limnophilic and eurytopic fish assemblages were not expected to be limited in habitat conditions. Overall, the proposed modelling approach represents a promising tool to support the development of environmental flows in large regulated rivers that face challenges with ageing infrastructure and a changing climate.

How Are Greenhouse Gases Coupled Across Seasons in a Large Temperate River with Differential Land Use?

Rivers are known to emit large amounts of greenhouse gases globally, however, few studies have evaluated the interacting influence of land use, within river features (for example, sites of major confluence, changes in shape), and hydrology on the coupled dynamics of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Here, we measured CO2, CH4 and N2O concentrations and fluxes at 15 sites along a 146.6 km stretch of the main stem of a large north temperate river: the Riviere du Nord, which experiences an abrupt change in geology and land use and winter ice cover. Each site along the river was sampled once per season, at targeted low flow and high flow moments, for three consecutive years. Overall, highest concentrations of all gases were found in the lower reaches where urban and agricultural activity are most intensive. CO2 and N2O were highest overall under ice during winter, whereas CH4 was highest during summer. The river was always supersaturated in CH4 whereas surface water was occasionally undersaturated in N2O and CO2, particularly during the summer low flow period in pristine upper reaches. Spatial variability was, however, minimized during periods of high flow. Emissions varied along the continuum, with peaks occurring at turbulent sites of major confluence. Although land use influenced the spatial variability in concentrations along the river, seasonal changes in temperature influenced the relative importance of the different gases to global warming potential, and hydrology mediated where they were produced as well as their overall concentrations and emissions.

River management response to multi‐decade changes in timing of reservoir inflows, Columbia River Basin, USA

AbstractAround the world, long‐term changes in the timing and magnitude of streamflow are testing the ability of large managed water resource systems constructed in the 20th century to continue to meet objectives in the 21st century. Streamflow records for unregulated rivers upstream of reservoirs can be combined with records downstream of reservoirs using a paired‐watershed framework and concepts of water resource system performance to assess how reservoir management has responded to long‐term change. Using publicly available data, this study quantified how the intra‐annual timing of inflows and outflows of 25 major reservoirs has shifted, how management has responded, and how this has influenced reliability and vulnerability of the water resource system in the 668,000 km2 Columbia River basin from 1950 to 2012. Reservoir inflows increased slightly in early spring and declined in late spring to early fall, but reservoir outflows increased in late summer from 1950 to 2012. Average inflows to reservoirs in the low flow period exceeded outflows in the1950s, but inflows are now less than outflows. Reservoirs have increased hedging, that is, they have stored more water during the spring, in order to meet the widening gap between inflows and outflows during the summer low flow period. For a given level of reliability (the fraction of time flow targets were met), vulnerability (the maximum departure from the flow target) was greater during periods with lower than average inflows. Thus, the water management system in this large river basin has adjusted to multi‐decade trends of declining inflows, but vulnerability, that is, the potential for excess releases in spring and shortfalls in summer, has increased. This study demonstrates the value of combining publicly available historical data on streamflow with concepts from paired‐watershed analyses and metrics of water resource performance to detect, evaluate, and manage water resource systems in large river basins.

Streamflow permanence in headwater streams across four geomorphic provinces in Northern California

AbstractMountainous headwater streams represent a substantial proportion of the global stream network. These small streams may flow episodically, seasonally, or perennially, providing diverse values and services. Given their broad importance and growing pressures on terrestrial and aquatic resources, we must improve our understanding of the drivers of flow permanence to facilitate informed land and water management decisions. We used field observations from >10 cross‐sections in each of 101 non‐fish bearing, headwater streams across four geomorphic provinces in Northern California to quantify flow permanence and network connectivity during the summer low flow period in 2018. At each stream cross‐section, we noted the presence or absence of streamflow and used this information to classify streams as perennial (continuous streamflow in all cross‐sections) or non‐perennial and connected (surface water in the most downstream cross‐section) or disconnected. At each cross‐section, we also quantified channel size (width and depth) and grain size. We coupled field observations with geospatial data of catchment physiography, hydrology, and climate in random forest models to investigate controls of flow permanence and network connectivity. Potential drivers of flow permanence or network connectivity included in our models were channel geometry, grain size, slope, aspect, elevation, annual and seasonal precipitation, air temperature, and topographic wetness index. We found more perennial streams in the Klamath Mountains and Sierra Nevada than in the Cascades and N. Coast regions. Streams in the Klamath were the most connected followed by streams in the N. Coast, Sierra Nevada, and Cascades. The most important variables for predicting flow permanence were channel grain size, winter 2018 precipitation, and drainage area. Comparatively, the most important variables for predicting network connectivity were winter and spring 2018 precipitation, grain size, and bankfull depth. Our study illustrated the complexity of the processes that drive flow permanence and highlighted the uncertainty in projecting the precense of water in streams across diverse regions.

Import, export, and recycling of dissolved nutrients in the Ogeechee River estuary (Georgia, USA)

We constructed an empirical mass balance model of nutrient fluxes in the Ogeechee River estuary (Georgia, USA) from eight surveys of seasonal estuarine nutrient concentrations during 2015 and 2016. The model results indicated a net removal of dissolved phosphorus and a net production of dissolved nitrogen (N) within the estuary over an annual cycle. During summer and autumn low flow periods, much of the dissolved N discharged to the ocean seems to be recycled into the estuary in the form of phytoplankton biomass. As a result, the outwelled N is not new nitrogen fueling coastal production but is nitrogen trapped within a recycling loop across the ocean–estuarine boundary. Higher flows in the fall and winter lead to direct discharge of nutrients with minimal recycling. A balanced N budget for the Ogeechee River estuary requires that estuarine N-fixation must exceed burial and denitrification losses within the estuary.

A data-driven modeling approach for simulating algal blooms in the tidal freshwater of James River in response to riverine nutrient loading

Algal blooms often occur in the tidal freshwater (TF) of the James River estuary, a tributary of the Chesapeake Bay. The timing of algal blooms correlates highly to a summer low-flow period when residence time is long and nutrients are available. Because of complex interactions between physical transport and algal dynamics, it is challenging to predict interannual variations of bloom correctly using a complex eutrophication model without having a high-resolution model grid to resolve complex geometry and an accurate estimate of nutrient loading to drive the model. In this study, an approach using long-term observational data (from 1990 to 2013) and the Support vector machine (LS-SVM) for simulating algal blooms was applied. The Empirical Orthogonal Function was used to reduce the data dimension that enables the algal bloom dynamics for the entire TF to be modeled by one model. The model results indicate that the data-driven model is capable of simulating interannual algal blooms with good predictive skills and is capable of forecasting algal blooms responding to the change of nutrient loadings and environmental conditions. This study provides a link between a conceptual model and a dynamic model, and demonstrates that the data-driven model is a good approach for simulating algal blooms in this complex environment of the James River. The method is very efficient and can be applied to other estuaries as well.

Non-domestic phosphorus release in rivers during low-flow: Mechanisms and implications for sources identification

A common assumption in phosphorus (P) load apportionment studies is that P loads in rivers consist of flow independent point source emissions (mainly from domestic and industrial origins) and flow dependent diffuse source emissions (mainly from agricultural origin). Hence, rivers dominated by point sources will exhibit highest P concentration during low-flow, when flow dilution capacity is minimal, whereas rivers dominated by diffuse sources will exhibit highest P concentration during high-flow, when land-to-river hydrological connectivity is maximal. Here, we show that Soluble Reactive P (SRP) concentrations in three forested catchments free of point sources exhibited seasonal maxima during the summer low-flow period, i.e. a pattern expected in point source dominated areas. A load apportionment model (LAM) is used to show how point sources contribution may have been overestimated in previous studies, because of a biogeochemical process mimicking a point source signal. Almost twenty-two years (March 1995–September 2016) of monthly monitoring data of SRP, dissolved iron (Fe) and nitrate-N (NO3) were used to investigate the underlying mechanisms: SRP and Fe exhibited similar seasonal patterns and opposite to that of NO3. We hypothesise that Fe oxyhydroxide reductive dissolution might be the cause of SRP release during the summer period, and that NO3 might act as a redox buffer, controlling the seasonality of SRP release. We conclude that LAMs may overestimate the contribution of P point sources, especially during the summer low-flow period, when eutrophication risk is maximal.

Trends and seasonality of river nutrients in agricultural catchments: 18 years of weekly citizen science in France

Agriculture and urbanization have disturbed three-quarters of global ice-free land surface, delivering huge amounts of nitrogen and phosphorus to freshwater ecosystems. These excess nutrients degrade habitat and threaten human food and water security at a global scale. Because most catchments are either currently subjected to, or recovering from anthropogenic nutrient loading, understanding the short- and long-term responses of river nutrients to changes in land use is essential for effective management. We analyzed a never-published, 18-year time series of anthropogenic (NO3− and PO43−) and naturally derived (dissolved silica) riverine nutrients in 13 catchments recovering from agricultural pollution in western France. In a citizen science initiative, high-school students sampled catchments weekly, which ranged from 26 to 1489km2. Nutrient concentrations decreased substantially over the period of record (19 to 50% for NO3− and 14 to 80% for PO43−), attributable to regional, national, and international investment and regulation, which started immediately prior to monitoring. For the majority of catchments, water quality during the summer low-flow period improved faster than during winter high-flow conditions, and annual minimum concentrations improved relatively faster than annual maximum concentrations. These patterns suggest that water-quality improvements were primarily due to elimination of discrete nutrient sources with seasonally-constant discharge (e.g. human and livestock wastewater), agreeing with available land-use and municipal records. Surprisingly, long-term nutrient decreases were not accompanied by changes in nutrient seasonality in most catchments, attributable to persistent, diffuse nutrient stocks. Despite decreases, nutrient concentrations in almost all catchments remained well above eutrophication thresholds, and because additional improvements will depend on decreasing diffuse nutrient sources, future gains may be much slower than initial rate of recovery. These findings demonstrate the value of citizen science initiatives in quantifying long-term and seasonal consequences of changes in land management, which are necessary to identify sustainable limits and predict recovery timeframes.

Associating metrics of hydrologic variability with benthic macroinvertebrate communities in regulated and unregulated snowmelt‐dominated rivers

Abstract Dams and diversions in rivers often alter flow regimes, which in turn can affect stream biota, particularly when the novel conditions are dramatically different from those under which native species evolved. Management of regulated rivers can include development of environmental flows that seek to restore ecological integrity. However, designing a flow regime that adequately supports aquatic biodiversity requires quantifiable metrics of hydrologic variability that directly relate to aquatic species diversity. This study examined both regulated and unregulated montane rivers over 3 years within the marked seasonality of California's Mediterranean climate to determine which quantifiable elements of a flow regime were most correlated with changes in the biologic community, using stream invertebrates during the summer low flow period as an indicator. Boosted regression trees were used to assess relationships between quantifiable metrics of flow regimes and the invertebrate community. Non‐metric multidimensional scaling and a multi‐response permutation procedure were used to analyze general trends in invertebrate assemblage patterns between rivers and years. Results indicated that hydrologic alteration corresponded to differences in invertebrate community composition, and that metrics related to the spring snowmelt recession and variability in summer water temperature had the greatest relative influence on invertebrate community diversity. Rivers exhibiting longer duration spring recessions, lower daily rates of change during the spring recession, and stable water temperatures during summer supported relatively higher invertebrate community diversity. These relationships suggest that quantifiable metrics associated with seasonal flow variability and predictability should be an integral part of environmental flow design and monitoring.

Backpack electrofishing effort and imperfect detection: Influence on riverine fish inventories and monitoring

Summary An increased electrofishing sampling effort will increase detection probabilities of riverine fishes. In this study, a repeat-sampling approach was used in small to medium-sized Ontario (Canada) rivers to estimate: (i) species-specific detection probabilities of freshwater fishes, (ii) the number of sampling events required to confidently detect species, and (iii) the power of timed-search surveys to detect future distribution (or occupancy) declines. Wadeable habitats at 36 sites were sampled with a backpack electrofisher on four separate dates during the summer low-flow period in 2013 and 2014. Forty-two species were collected, including three species of conservation concern (American eel Anguilla rostrata Lacepede, 1802, channel darter Percina copelandi Jordan, 1877, northern sunfish Lepomis peltastes Cope, 1870), and two recreationally important species (largemouth bass Micropterus salmoides Lacepede, 1802 and smallmouth bass Micropterus dolomieu Lacepede, 1802). A hierarchical Bayesian modelling approach was used to estimate detection probabilities and site occupancy for 18 species at four levels of effort: 250, 500, 750 and 1,000 s. In all cases, species detection was imperfect. Search effort had a positive effect on estimates of detection probability and site occupancy and the power to detect declines in future distribution. Detection probabilities ranged from 0.11 to 0.66 with an effort of 250 s, and 0.27 to 0.92 with an effort of 1,000 s. For 13 species, detection and power to detect changes in distribution were significantly improved by increasing sampling effort from 250 to 750 s or 1,000 s. For the channel darter and northern sunfish, three replicate sampling visits (of 750 or 1,000 s duration) are recommended for confident detection.

Small differences in riparian vegetation significantly reduce land use impacts on stream flow and water quality in small agricultural watersheds

Fluvial ecosystem integrity is intimately tied to agricultural intensity in most rural landscapes. Row crop agriculture in particular can elicit a range of deleterious effects on hydrology, surface water quality, and fluvial ecology. Riparian vegetation represents a critical defence of stream systems against environmental perturbations. Vegetation filters surface runoff and encourages infiltration. Furthermore, riparian forests shade streams and are thus able to stabilize in-stream temperature and dissolved oxygen (O). In northwest New Brunswick9s potato (Solanum tuberosum L.) growing region, once densely forested riparian corridors now often contain only scattered, irregular patches of residual vegetation, and national water quality standards for streams are regularly exceeded. The objective of this study was to ascertain whether relatively small differences in riparian forest cover are of any significant benefit to stream environments. Specifically, we assessed the capacity of riparian forests to reduce the effects of row crop agriculture on stream flow, water quality, and benthic macroinvertebrate communities of streams draining small subwatersheds near Grand Falls, New Brunswick. The subwatersheds ranged in agricultural intensity from 0.5% to 97% crop cover, which predominantly consisted of potato. Riparian cover and agricultural intensity were highly collinear; hence, riparian forest cover was converted to a binomial categorical predictor (i.e., high and low), with agricultural intensity treated as a continuous covariate. Higher intensity of row-crop agriculture in small subwatersheds corresponded to base flow decline; greater flow pulse frequency; higher dissolved nitrate-nitrogen (NO3-N), conductivity, pH, and temperature; lower dissolved O; and prevalence of pollution-tolerant macroinvertebrate taxa and grazers. With less than 20% increase in riparian forest cover relative to agricultural intensity, we observed reduced severity of summer low flow periods, significantly lower dissolved phosphate (PO4) concentrations, lower temperatures, and higher dissolved O. Macroinvertebrate assemblage structure of the riparian cover categories diverged with increasing agriculture, demonstrating the value of even minor amounts of riparian vegetation to benthic community condition. Our results conclusively show that relatively small increases in riparian forest cover will lead to statistically detectable and ecologically meaningful improvements to stream health.

Climate and land cover effects on the temperature of Puget Sound streams

AbstractWe apply an integrated hydrology‐stream temperature modeling system, DHSVM‐RBM, to examine the response of the temperature of the major streams draining to Puget Sound to land cover and climate change. We first show that the model construct is able to reconstruct observed historic streamflow and stream temperature variations at a range of time scales. We then explore the relative effect of projected future climate and land cover change, including riparian vegetation, on streamflow and stream temperature. Streamflow in summer is likely to decrease as the climate warms especially in snowmelt‐dominated and transient river basins despite increased streamflow in their lower reaches associated with urbanization. Changes in streamflow also result from changes in land cover, and changes in stream shading result from changes in riparian vegetation, both of which influence stream temperature. However, we find that the effect of riparian vegetation changes on stream temperature is much greater than land cover change over the entire basin especially during summer low flow periods. Furthermore, while future projected precipitation change will have relatively modest effects on stream temperature, projected future air temperature increases will result in substantial increases in stream temperature especially in summer. These summer stream temperature increases will be associated both with increasing air temperature, and projected decreases in low flows. We find that restoration of riparian vegetation could mitigate much of the projected summer stream temperature increases. We also explore the contribution of riverine thermal loadings to the heat balance of Puget Sound, and find that the riverine contribution is greatest in winter, when streams account for up to 1/8 of total thermal inputs (averaged from December through February), with larger effects in some sub‐basins. We project that the riverine impact on thermal inputs to Puget Sound will become greater with both urbanization and climate change in winter but become smaller in summer due to climate change. Copyright © 2016 John Wiley & Sons, Ltd.