Nechako River Research Articles

Water Budget Input Linked to Atmospheric Rivers in British Columbia's Nechako River Basin

ABSTRACTThis study explores the contribution of atmospheric rivers (ARs) to the water budget input of the Nechako River Basin (NRB) in British Columbia (BC), western Canada. The study quantifies the fraction of precipitation, rainfall, snowfall, and snow water equivalent (SWE) associated with ARs at multiple scales and tests for trends using the Mann–Kendall (MK) test. AR‐related totals for 1950–2021 were created by linking AR events to water budget input variables of the ERA5‐Land reanalysis product on a daily scale. Associations with different phases of the El Niño‐Southern Oscillation (ENSO) climate pattern and AR‐related contributions to the NRB are also investigated. Results indicate an increasing fractional contribution of rain in ARs landfalling in the NRB in the last two decades (2000–2019). Moreover, 21% of the total annual precipitation in the NRB is associated with ARs, with decreasing contributions from west to east. October has higher AR‐related total precipitation than other months, while March, May and June are the least affected. ARs contribute disproportionately more to mid‐ and high‐intensity daily precipitation totals, and provide up to 45% and 24% of the seasonal rainfall and snowfall, respectively. AR‐related SWE is relatively higher in autumn due to the increased frequency and intensity of ARs, resulting in a greater fractional contribution of ARs to the snowpack compared to winter. ARs influence snowpack accumulation during fall (18%) and winter (13%) but also increase the risk of natural hazards. The MK test for AR‐related water budget variables on the annual scale identified no significant trends. However, AR‐related snowfall shows decreasing trends in the NRB, more specifically in the Upper Nechako, Lower Nechako and Stellako sub‐basins during the summer. Over the study period, ARs consistently contribute up to one‐fifth of the annual input to the NRB's water budget. This study provides the first quantitative assessment and trend analyses of AR contributions to the water budget input of a reservoir‐regulated watershed in north‐central BC, yielding valuable information for hydropower production, ecological flows, irrigation, domestic and industrial water use.

Long life spans can mitigate the genetic effects of strays from temporary conservation hatchery programs.

While conservation fish hatchery programs can be a valuable tool providing demographic support, they can also cause domestication, risking unintended fitness consequences to both target and connected populations. When conservation hatcheries are used over a fixed amount of time, the interaction between program duration and species life history might determine the scale of fitness effects and the effectiveness of mitigation measures. We develop a mathematical model to quantify the effectiveness of approaches to mitigate unintended fitness consequences in such temporary conservation hatchery programs. We parameterize our model to represent a conservation aquaculture-based recovery program for white sturgeon (Acipenser transmontatus) in the Nechako River (British Columbia), which might impose genetic risks on the adjacent populations within the Fraser River. We find that, over a period spanning 50-200 years of hatchery operation, the life history characteristics of white sturgeon, particularly late age of maturity and longevity, reduce the genetic risks of conservation hatcheries when compared to shorter-lived species. The genetic impacts of the hatchery accumulate slowly providing increasing the potential for adaptive management in this system.

Towards an integrative understanding of British Columbia’s Nechako Watershed: Connecting knowledge systems to strengthen understanding of climate change, watershed security, health and well-being

Understanding of upstream and downstream dynamics of continental river basins demands attention to the influence of important tributaries and watersheds. This is exemplified by the 47,200 km2 Nechako Watershed, the second largest sub-watershed of British Columbia’s Fraser River Basin. Although the Nechako (derived from the Indigenous Dakelh word meaning “big river”) is recognised for its ecological, societal and cultural importance, attention to this sub-watershed has often been overshadowed by a focus on the iconic Fraser River. This paper examines insights from a purposeful response to this gap, whereby a team of researchers has worked together to strengthen understanding of cumulative stressors and changes in the Nechako, focusing on climate change and water security, sediment sources and quality, and health and well-being dynamics within the Nechako Watershed. Lessons learned from a decade of this collaboration are presented, reflecting on the Nechako Watershed’s past, present, and future through the lens of a unique case study of interdisciplinary research. Emerging research and knowledge exchange partnerships are highlighted along with growing concerns for the Nechako’s keystone aquatic species including three species of Pacific salmon and the endangered Nechako white sturgeon. Drawing on the natural, social and health sciences, we examine strengths and challenges of connecting research across interrelated watershed security issues ranging from climate change, landcover disturbances (e.g., wildfires, mountain pine beetle outbreaks and forest harvesting), land use changes (e.g., expansion of Vanderhoof’s agricultural belt), and the far-reaching impacts of the damming of the Nechako River mainstem in the 1950’s. Our paper brings necessary attention to these and other influences on waterways, landscapes and communities of the Nechako Watershed, highlighting new research opportunities arising among diverse knowledges and disciplines, and the ongoing collaborative effort required to address emerging challenges for the Nechako and wider Fraser River Basin, with consequences for current and future generations.

The carryover effects of embryonic incubation temperature on subsequent growth and thermal tolerance in white sturgeon

Environmental variation experienced during early periods of development can lead to persistent phenotypic alteration, known as carryover effects. Such effects increase concern for threatened or endangered species such as the white sturgeon (Acipenser transmontanus), particularly considering expected thermal changes due to climate change. We evaluated how temperature during embryonic development affects physiological parameters such as larval and early juvenile growth and thermal tolerance. Nechako River white sturgeon embryos were incubated at different environmental temperatures (Te) of 12 °C (the natural spawning temperature of this population), 15 °C (the hatchery incubation temperature), and 18 °C (representing potential increases in river temperatures given global climate change). After hatch, fish were reared at a common 15 °C for 80 days post-hatch (dph). Individuals from each temperature treatment were tested for thermal tolerance using the critical thermal maximum method (CTmax), euthanized, and measured. Fish were examined at regular intervals from 13 to 80 dph, which bridged the time from the start of exogenous feeding through the transition into early juveniles. We found carryover effects of high embryonic Te in the short term for both thermal tolerance and growth. Fish that developed at 18 °C had the lowest thermal tolerance during the start of exogenous feeding. However, differences in thermal tolerance were small for early juveniles and were unlikely to be ecologically relevant in the longer term. Fish that developed at 18 °C were smallest over the observation period, indicating a possible cost for survival from increasing environmental temperatures during embryonic development. This research represents a window into a critical period of development during which fish are particularly vulnerable to climatic variation, and shows that cooler temperatures (12 °C) during incubation are optimal for this population. The results can inform environmental managers on the best strategies to help conserve current white sturgeon populations across their range.

Evaluating the effects of climate change on river water temperature downstream of a hydropower reservoir in western Canada

This paper evaluates the impact of climate change on the water temperature of the Nechako River near the town of Vanderhoof (British Columbia, Canada). To do so, the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) hydraulic and water temperature model was used with data from 10 climate models representing two Shared Socioeconomic Pathways (SSP 2-4.5 and SSP 5-8.5) over two future time periods (2041-2070 and 2071-2100). The results showed an upward trend in projected water temperatures for all tested discharge rates from the impounding reservoir during the warmest periods of the year. The study found that water temperatures are expected to increase by up to 2.57 °C for the near future (2041-2070) and up to 3.56 °C on average for all flow scenarios studied for a far future (2071-2100) when using SSP5-8.5. The timing of the peak water temperature during the summer is also expected to shift, with maximum water temperatures occurring up to 10 days later than in the reference period. In 10.3% of the far future SSP5-8.5 scenarios, at least one day per summer had a mean daily temperature of at least 24 °C, which exceeds limits of 20 °C for sockeye salmon and 21 °C for white sturgeon which are considered detrimental for the fish. It has been shown that over 50% of sockeye salmon will stop their sustained swimming at water temperatures of 24 °C due to cardiac limitations.

Diagnosing the ability of reservoir operations to meet hydropower production and fisheries needs under climate change in a western cordillera drainage basin

Water regulation has contributed to the decline in Pacific salmon in British Columbia (Canada) despite attempts to manage reservoir operations to achieve operational requirements while meeting environmental needs to limit fish thermal stress. The ability of reservoir managers to meet these trade-offs in a changing climate is unknown. Here, we examine the reliability and vulnerability of the Nechako Reservoir to meet hydropower production commitments and fisheries needs under two projected Shared Socioeconomic Pathway scenarios (SSP2-4.5 and SSP5-8.5). While our findings are specific to the operation of the Nechako Reservoir, the issues that emerge are likely common to many reservoirs in areas where reservoir inflow regimes are currently snow-storage dominated. We found that projected changes in the timing of water availability have little to no influence on hydropower generation commitments. However, larger water releases will be required to avoid compromising reservoir safety, possibly endangering downstream fish habitat through scouring. Furthermore, the temperature of water released from the reservoir is projected to more frequently exceed a level, 20°C, that is detrimental to migrating sockeye salmon. Water released is subject to further warming as it travels towards the lower reaches of the Nechako River used by migrating salmon. Hence, there is a need to adapt reservoir operations to ensure reservoir safety and mitigate adverse effects on salmon habitat.

Spatiotemporal distribution and trend analyses of atmospheric rivers affecting British Columbia's Nechako Watershed

AbstractResearch and shared interest in atmospheric rivers (ARs) have increased significantly in recent years, alongside technological improvements that allow better comprehension of these storms. The Nechako River Basin (NRB) in British Columbia, Canada, is significantly affected by ARs originating in the Pacific Ocean. This work analyses the frequency, intensity, duration and trends of ARs in two regions (South and North) near the NRB. Analyses are based on data provided by an updated AR catalogue. The AR catalogue is matched on a daily scale to an adaptation of the AR scale to compile so‐called AR‐Days (ARDs). In the South region, ARDs exhibit stronger associations with hydroclimatic variables total precipitation, rain, snow and snow depth water equivalent (SWE). The Mann–Kendall (MK) trend test was applied to 364 time series created by combining the two closest AR‐monitored regions to the NRB with the annual and seasonal scales of climate data and the adapted AR scale (ARD0‐ARD5). Results show higher AR frequency of mainly beneficial ARDs during fall and a significant reduction of ARD1‐ARD3 in both analysed regions. Rain and total precipitation related to ARD2‐ARD3 also present significant decreasing trends for most sub‐basins of the NRB. The MK test shows a shift in water contribution from total precipitation and rainfall linked to more potentially dangerous ARDs to short‐duration, beneficial ARDs (ARD0). Rain from non‐AR‐related meteorological systems presents an increasing trend for the Upper Nechako sub‐basin, where the Nechako Reservoir is located. Trends are mainly for AR‐related total precipitation and rainfall, and in the northern part of the NRB, results point to the increase of AR‐related SWE.

Hydrothermal impacts of water release on early life stages of white sturgeon in the Nechako river, B.C. Canada

Water temperature plays a crucial role in the physiology of aquatic species, particularly in their survival and development. Thus, resource programs are commonly used to manage water quality conditions for endemic species. In a river system like the Nechako River system, central British Columbia, a water management program was established in the 1980s to alter water release in the summer months to prevent water temperatures from exceeding a 20 °C threshold downstream during the spawning season of Sockeye salmon (Oncorhynchus nerka). Such a management regime could have consequences for other resident species like the white sturgeon (Acipenser transmontanus). Here, we use a hydrothermal model and white sturgeon life stage-specific experimental thermal tolerance data to evaluate water releases and potential hydrothermal impacts based on the Nechako water management plan (1980–2019). Our analysis focused mainly on the warmest five-month period of the year (May to September), which includes the water release management period (July–August). Our results show that the thermal exposure risk, an index that measures temperature impact on species physiology of Nechako white sturgeon across all early life stages (embryo, yolk-sac larvae, larvae, and juvenile) has increased substantially, especially in the 2010s relative to the management program implementations’ first decade (the 1980s). The embryonic life stage was the most impacted, with a continuous increase in potential adverse thermal exposure in all months examined in the study. We also recorded major impacts of increased thermal exposure on the critical habitats necessary for Nechako white sturgeon recovery. Our study highlights the importance of a holistic management program with consideration for all species of the Nechako River system and the merit of possibly reviewing the current management plan, particularly with the current concerns about climate change impacts on the Nechako River.

Determination of sediment sources following a major wildfire and evaluation of the use of color properties and polycyclic aromatic hydrocarbons (PAHs) as tracers

PurposeThis research aimed to determine if a severe wildfire caused changes in the source of sediment being delivered to downstream aquatic systems and evaluate the use of polycyclic aromatic hydrocarbons (PAHs) and color properties as tracers.MethodsSediment samples were collected from 2018 to 2021 in three tributaries impacted by the 2018 Shovel Lake wildfire and from two sites on the mainstem of the Nechako River, British Columbia. Source samples were collected from burned and unburned soils as well as from channel banks and road-deposited sediment. Samples were analyzed for color properties and for the 16 US Environmental Protection Agency priority PAHs. After statistical tests to determine the conservatism and ability to discriminate between sources by the tracers, the MixSIAR unmixing model was used, and its outputs were tested using virtual mixtures.ResultIn the tributaries, burned topsoil was an important contributor to sediment (up to 50%). The mainstem Nechako River was not influenced as significantly by the fires as the greatest contributor was banks (up to 89%). The color properties provided more realistic results than those based on PAHs.ConclusionIn smaller watersheds, the wildfire had a noticeable impact on sediment sources, though the impacts of the fire seemed to be diluted in the distal mainstem Nechako River. Color tracers behaved conservatively and discriminated between contrasting sources. Due to their low cost and reliability, they should be considered more widely. While PAHs did not work in this study, there are reasons to believe they could be a useful tracer, but more needs to be understood about their behavior and degradation over time.

Investigating patterns and extent of predation of hatchery-reared juvenile Nechako white sturgeon (Acipenser transmontanus) by North American river otter (Lontra canadensis) in the Nechako River, British Columbia, Canada

Predation of fish released as part of conservation aquaculture programs may undermine conservation goals. Identification of factors influencing predation, therefore, can inform management decisions that minimize predation losses. For the endangered Nechako white sturgeon ( Acipenser transmontanus Richardson, 1836), the survival of individuals released as part of a conservation aquaculture program is threatened by river otter ( Lontra canadensis (Schreber, 1777)) predation. Through the recovery of sturgeon passive integrated transponder (PIT) tags from otter latrines, we set out to quantify the extent of predation, identify spatial patterns in predation including identifying predation hotspots, and understand the timing of predation. The recovery of 3.9% of PIT tags from the hatchery-released sturgeon represents a minimum predation estimate based on several identified factors. The distribution of predation hotspots varied by release cohort, with some consistent hotspots among cohorts. An apparent decrease in predation in recent years was seen in conjunction with fewer live captures and lower release numbers, suggesting some level of density-dependent predation. Results from this study can be used to contribute to management decisions related to Nechako white sturgeon recovery efforts, inform further research needs, and contribute to a growing knowledge of sturgeon predation.

Identification of upper thermal thresholds during development in the endangered Nechako white sturgeon with management implications for a regulated river.

Climate change-induced warming effects are already evident in river ecosystems, and projected increases in temperature will continue to amplify stress on fish communities. In addition, many rivers globally are impacted by dams, which have many negative effects on fishes by altering flow, blocking fish passage, and changing sediment composition. However, in some systems, dams present an opportunity to manage river temperature through regulated releases of cooler water. For example, there is a government mandate for Kenney dam operators in the Nechako river, British Columbia, Canada, to maintain river temperature <20°C in July and August to protect migrating sockeye salmon (Oncorhynchus nerka). However, there is another endangered fish species inhabiting the same river, Nechako white sturgeon (Acipenser transmontanus), and it is unclear if these current temperature regulations, or timing of the regulations, are suitable for spawning and developing sturgeon. In this study, we aimed to identify upper thermal thresholds in white sturgeon embryos and larvae to investigate if exposure to current river temperatures are playing a role in recruitment failure. We incubated embryos and yolk-sac larvae in three environmentally relevant temperatures (14, 18 and 21°C) throughout development to identify thermal thresholds across different levels of biological organization. Our results demonstrate upper thermal thresholds at 21°C across physiological measurements in embryo and yolk-sac larvae white sturgeon. Before hatch, both embryo survival and metabolic rate were reduced at 21°C. After hatch, sublethal consequences continued at 21°C because larval sturgeon had decreased thermal plasticity and a dampened transcriptional response during development. In recent years, the Nechako river has reached 21°C by the end of June, and at this temperature, a decrease in sturgeon performance is evident in most of the traits measured. As such, the thermal thresholds identified here suggest current temperature regulations may not be suitable for developing white sturgeon and future recruitment.

Post-wildfire contamination of soils and sediments by polycyclic aromatic hydrocarbons in north-central British Columbia, Canada

Background The Nechako River Basin (NRB) is a large, regulated basin in north-central British Columbia, Canada that has been impacted by numerous landscape disturbances, including a severe wildfire in 2018. Aims The aims of this study were to quantify the post-wildfire temporal and spatial extent of contamination by polycyclic aromatic hydrocarbons (PAHs) of both soils and riverine sediments, and to identify the primary sources of PAHs in the watershed. Methods Soil samples were collected at burned and unburned sites in 2018 and at the burned sites in 2020 and 2021. Sediment samples were collected at three tributaries impacted by wildfire and three Nechako River mainstem (i.e. main channel) sites from 2018 to 2021. Samples were analysed for parent PAHs. Key results PAH concentrations decreased in soil samples from 2018 to 2021 but are not below the concentrations found in unburned samples. Tributary sediment samples showed higher concentrations immediately post-fire relative to the mainstem Nechako River, but in the years since, that trend has reversed. Conclusions PAHs persist in terrestrial and aquatic environments for years following wildfire, but at concentrations below various quality guidelines. PAHs were primarily derived from the wildfires, with some mixed sources at the downstream sites. Implications Wildfires are an important source of environmental contamination of terrestrial and aquatic environments.

Quantifying the evolution of ensemble water temperature forecasts as a function of weather forecast lead-time: case study on the Nechako River watershed

Producing and improving hydrological and hydrodynamic forecasts while accounting for uncertainty through a probabilistic approach is useful in various applications, such as for water temperature forecasting. To produce such ensembles, probabilistic meteorological forecasts can be fed into hydrological and water temperature models for different lead-times. This study aims to gauge the impact of the meteorological forecast quality on the accuracy and reliability of water temperature forecast ensembles generated through the HEC-RAS process-based hydrothermal model. The Nechako River, a managed river system in British Columbia, Canada, is used in this case study. The thermal forecasts were generated and evaluated from 2017 to 2020. The tested hypothesis is that improvements in the meteorological forecasts would result in reducing the uncertainty and improving the accuracy of the water temperature forecast ensembles at various lead-times. The results of this study show that the thermal forecasts were indeed improved in terms of their sharpness and their individual accuracy, but no significant impacts were noted over the accuracy of the ensembles. Reliability was also investigated, and it was revealed that water temperature forecast ensembles were initially under-dispersed over the Nechako River, and that this issue was exacerbated when the HEC-RAS model was forced with better quality ensemble weather forecasts. The presence of lakes along the river and the meteorological forecast’s reliability are considered and discussed as causes for this issue. Overall, it was concluded that a reduction of the meteorological inputs’ uncertainty did not improve the uncertainty representation of water temperature forecasts for this system.

A coupled streamflow and water temperature (VIC-RBM-CE-QUAL-W2) model for the Nechako Reservoir

Study regionNechako Reservoir, British Columbia, Canada. Study focusHydrological regulation affect both hydrological and thermal conditions in the reservoir and downstream reach, subsequently disrupting fish habitats. This paper aims at developing an integrated model simulating physical processes that govern the quantity and quality of inflow, reservoir, and outflow water of the Nechako Reservoir. Such a model would help stakeholders understand the response of in-reservoir water temperature stratification and downstream water temperature to changes in inflow and reservoir operation under future climate change. New hydrological insights for the regionThe model was calibrated against historical reservoir levels and in-reservoir and outlet water temperature field data. The integrated model simulated accurately the wide variation of reservoir levels as well as the in-reservoir water temperature at Kenney Dam and the outlet temperature. Sensitivity analysis shows that reservoir water temperature particularly the epilimnion is sensitive to changes in both meteorological and hydrological forcing. Forcing the model with different outflow scenarios shows the weak sensitivity of temperature of water released to outflow rates. Given epilimnion water releases at the spillway, the Summer Temperature Management Program could be inefficient to provide cool water in the Nechako River during the critical period of salmon migration in a warming climate. However, colder water remains available at depth at Kenney Dam to potentially mitigate and better control downstream water temperature.

River conversations: A confluence of lessons and emergence from the Taieri River and the Nechako River.

Drawing on ongoing patterns of learning and relationship, this paper offers a reflection and acknowledgement on the notable influence of two rivers and their role as respected and highly valued “eco‐social elders”: The Taieri River in Otago, New Zealand, and the Nechako River in northern British Columbia, Canada. The paper is motivated by the question: “If a river has ‘voice’, what can be learned from the emergence arising from rivers ‘in conversation’?”. At the heart of the reflection are the themes of confluence and emergence—ways in which we grasp the coming together of things, especially when that combination is more than the sum of their parts. The paper aims to explore a “conversation” between the river teachings of the Taieri River and the Nechako River, identifying examples of patterns and connections between distinct river “voices,” and how these may contribute to emergence and ongoing conversations among different rivers and their teachings. The paper commences with an introduction to both rivers, identifying points of direct comparison and contrast, then moving to explore themes of confluence, weaving and emergence, combining ecological, metaphorical, and personal perspectives. The conversation then progresses downstream to river–ocean relationships, reflecting on rivers as eco‐social elders that inspire conversations, provide a sense of home, and offer a point of reference to consider the wider influence on rivers and waterways on the health of diverse species within catchments and across the planet.

Microsatellite DNA analysis of overwintering bull trout (Salvelinus confluentus) and its implications for harvest regulation and habitat management

AbstractA mixed‐stock fishery occurs when multiple populations of a fish species are exploited together in a common area where they aggregate outside the breeding season (e.g. for feeding or overwintering), and the aggregation is known as a mixture. Recreational fishing often exploits such mixtures, and estimating the proportional contributions of populations to fisheries promotes more sustainable resource use. Ten DNA microsatellites were assayed in a mixture of bull trout Salvelinus confluentus Suckley overwintering in the Nechako River, upper Fraser River, British Columbia, and in baseline population samples from 14 tributaries putatively contributing to the overwintering mixture. A DNA microsatellite‐based mixed‐stock fishery analysis suggested that five populations together contributed 0.80 to the mixture. Most of the errors associated with the mixture estimates were attributable to uncertainty in baseline allele frequencies. Radiotracking data confirmed that tributary populations contributing to the mixture estimated by genetic analysis also contained individuals that moved between spawning tributaries and overwintering sites. The results better resolve habitat use by potadromous bull trout in the upper Fraser River and, in combination with assessments of baseline population‐specific spawning abundances and productivity, will better inform a decision of whether or not allowing some harvest within the current catch‐and‐release fishery is biologically sustainable.

Determining contemporary and historical sediment sources in a large drainage basin impacted by cumulative effects: the regulated Nechako River, British Columbia, Canada

PurposeSediment dynamics in most large river basins are influenced by a variety of different natural and anthropogenic pressures, and disentangling these cumulative effects remains a challenge. This study determined the contemporary and historical sources of fine-grained (< 63-μm) sediment in a large, regulated river basin and linked changes in sources to activities in the basin. The river has seen declines in chinook salmon, sockeye salmon, and the endangered Nechako white sturgeon populations, and sediment (both fine-grained and sands) transport and deposition have been identified as potential causes of these declines.Materials and methodsSamples of suspended sediment and potential source materials were collected from numerous sites distributed throughout the upper Nechako River Basin in British Columbia, Canada. A floodplain sediment core was also collected in order to reconstruct sediment sources over the last ~ 70 years. Discriminating fingerprint properties were used within the MixSIAR model to apportion sources among sub-basins and land-use types. Results were compared to records of precipitation and Nechako River discharge trends, and to changes in landscape development.Results and discussionContributions from the erosion of channel banks dominated the suspended sediment load at most sites. Changes in sediment sources during the 2015 field season reflected snowmelt and patterns of water release from the Nechako Reservoir that affected the sediment-carrying capacity of tributaries and the Nechako River main stem. Spatial variations in 2015 also reflected the distribution of land use (e.g., forested or agricultural land) as well as topography (e.g., slope steepness). Over the last ~ 70 years, variations in sediment sources and the characteristics of the sediment (e.g., organic matter content and particle size composition) were linked to the construction of the Kenney Dam (operational in 1954) and the impacts of deforestation by the forestry and agricultural industries. Superimposed on these have been wildfires and a major mountain pine beetle infestation leading to higher erosion rates in the affected areas.ConclusionsThe sediment source fingerprinting technique, in combination with historical information on the hydrometeorology and the land use and river management in the basin, has provided valuable information with which to understand sediment dynamics in the Nechako River Basin. Such an approach can help to disentangle how large river systems respond to a combination of natural and anthropogenic pressures.

Sediment-associated organopollutants, metals and nutrients in the Nechako River, British Columbia: a current study with a synthesis of historical data

The flow-diverted Nechako River is the second largest tributary of the Fraser River which drains 25% of mainland British Columbia, Canada. The watershed provides critical reproductive habitats for anadromous chinook salmon (Oncorhynchus tshawytscha) and sockeye salmon (O. nerka) and year-round habitat for the endangered Nechako white sturgeon (Acipenser transmontanus) population. In this study, the chemical quality of sediment in the upper Nechako River and its major tributaries was examined for polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), legacy organochlorine (OC) pesticides, polycyclic aromatic hydrocarbons (PAHs), organophosphorus and phenoxy acid herbicides, polychlorinated dibenzo-p-dioxins (PCDDs) and furans (PCDFs), labile (exchangeable) metals/metalloids, and major nutrients (N and P). ΣPCB and ΣPBDE were detected in channel bottom sediments at all Nechako River and tributary sites; hexachlorobenzene (HCB) and 4,4′-DDE (dichlorodiphenyldichloroethylene) were also detected at most sites. Organophosphorus and phenoxy acid herbicides were not detected in any samples. While ΣPCB, ΣPBDE, HCB, and 4,4′-DDE concentrations in bottom sediments were always well below provincial and federal guidelines for the protection of aquatic life, concentrations of total labile As (AsT), CrT, CuT, FeT, MnT, NiT, and ZnT in suspended and/or bottom sediments often exceeded provincial threshold effect levels (TEL) and, in some cases, approached or exceeded probable effect levels. Distinct CuT, NiT, PbT and ZnT concentration maxima in suspended sediments were linked to road and urban densities. Historical PCDD, PCDF and PAH data show that concentrations in bottom sediment samples were highest at a site in the lower Nechako River between Miworth and the City of Prince George where PCDD and PCDF concentrations exceeded the interim federal TEL. Nitrogen and P concentrations in bottom sediments were negatively correlated with water velocity and sediment texture; the evidence suggests that reductions in velocity resulting from the 1952 diversion of the Nechako River have increased the nutrient content of bottom substrates.

Assimilation of water temperature and discharge data for ensemble water temperature forecasting

Recent work demonstrated the value of water temperature forecasts to improve water resources allocation and highlighted the importance of quantifying their uncertainty adequately. In this study, we perform a multisite cascading ensemble assimilation of discharge and water temperature on the Nechako River (Canada) using particle filters. Hydrological and thermal initial conditions were provided to a rainfall-runoff model, coupled to a thermal module, using ensemble meteorological forecasts as inputs to produce 5day ensemble thermal forecasts. Results show good performances of the particle filters with improvements of the accuracy of initial conditions by more than 65% compared to simulations without data assimilation for both the hydrological and the thermal component. All thermal forecasts returned continuous ranked probability scores under 0.8°C when using a set of 40 initial conditions and meteorological forecasts comprising 20 members. A greater contribution of the initial conditions to the total uncertainty of the system for 1-dayforecasts is observed (mean ensemble spread=1.1°C) compared to meteorological forcings (mean ensemble spread=0.6°C). The inclusion of meteorological uncertainty is critical to maintain reliable forecasts and proper ensemble spread for lead times of 2days and more. This work demonstrates the ability of the particle filters to properly update the initial conditions of a coupled hydrological and thermal model and offers insights regarding the contribution of two major sources of uncertainty to the overall uncertainty in thermal forecasts.

Climate change and resource development impacts in watersheds: Insights from the Nechako River Basin, Canada

Few studies to date examine the cumulative effects of climate change and resource development on social‐ecological systems, such as watersheds. In partnership with a watershed alliance we endeavoured to understand the interplay of climate change and resource exploitation impacts in the Nechako River Basin, which drains an area of 52,000 km2 in northwestern Canada as part of the Fraser River Basin. Existing regional climatic studies show a clear warming trend over the last century and a projected mean temperature increase of ∼2°C for the 2050s. Watershed stakeholders determined that hydroelectric development and forestry activities interrelate particularly closely with climate impacts related to ecosystem function, water supply, and (resultantly) community well‐being. Mining and oil and gas development do not currently represent a high level of concern, but will become problematic with future resource exploitation or climatic changes. The process was effective in grounding specific, day‐to‐day realities of climate change. The results illustrate the importance and challenge of considering both impact sources in tandem, and should inform ongoing regional planning and monitoring efforts. A major barrier to performing this type of assessment with regional stakeholders is communicating, cross‐referencing, and visualizing the interrelationships between climate change and resource development, which are independently highly complex.Les changements climatiques et le développement des ressources dans les bassins versants : leçons tirées du bassin de la rivière Nechako, CanadaÀ ce jour, peu d'études se sont intéressées aux effets cumulatifs des changements climatiques et du développement des ressources sur les systèmes socio‐écologiques, tels que les bassins versants. Nous avons entrepris, en partenariat avec un regroupement d'organismes de bassin versant, de comprendre l'interaction entre les effets des changements climatiques et du développement des ressources sur le bassin de la rivière Nechako qui draine les eaux d'un territoire couvrant 52 000 km2 et faisant partie du bassin de la rivière Fraser dans le nord‐ouest du Canada. Les études climatiques régionales réalisées à ce jour montrent une nette tendance au réchauffement au cours du siècle dernier et une augmentation de la température moyenne projetée de ∼ 2 °C à l'horizon 2050. Les parties prenantes du bassin versant ont établi que les activités de développement hydroélectrique et de foresterie sont intimement liées avec les effets du climat agissant sur la fonction écosystémique, l'approvisionnement en eau, et finalement le bien‐être communautaire. Les secteurs de l'extraction minière et de l'exploration pétrolière et gazière ne suscitent actuellement pas de fortes inquiétudes, bien qu'ils risquent de poser problème à l'avenir avec l'exploitation des ressources ou les changements climatiques. Le processus a permis d'identifier des réalités particulières liées aux changements climatiques. Les résultats font ressortir l'importance et le défi de tenir compte simultanément des deux sources d'effets. Ils sont également susceptibles d'éclairer les mesures prises en matière de planification régionale et de surveillance. Une difficulté de ce type d'évaluation faisant appel aux parties prenantes régionales est de communiquer, d'effectuer des recoupements, et d'identifier les liens réciproques entre les changements climatiques et le développement des ressources, lesquels sont déjà hautement complexes.