One of the most ominous predictions related to recent climatic warming is that low-lying coastal environments will be inundated by higher sea levels. The threat is especially acute in polar regions because reductions in extent and duration of sea ice cover increase the risk of storm surge occurrence. The Mackenzie Delta of northwest Canada is an ecologically significant ecosystem adapted to freshwater flooding during spring breakup. Marine storm surges during the open-water season, which move saltwater into the delta, can have major impacts on terrestrial and aquatic systems. We examined growth rings of alder shrubs (Alnus viridis subsp. fruticosa) and diatoms preserved in dated lake sediment cores to show that a recent marine storm surge in 1999 caused widespread ecological changes across a broad extent of the outer Mackenzie Delta. For example, diatom assemblages record a striking shift from freshwater to brackish species following the inundation event.What is of particular significance is that the magnitude of this recent ecological impact is unmatched over the >1,000-year history of this lake ecosystem. We infer that no biological recovery has occurred in this lake, while large areas of terrestrial vegetation remain dramatically altered over a decade later, suggesting that these systems may be on a new ecological trajectory. As climate continues to warm and sea ice declines, similar changes will likely be repeated in other coastal areas of the circumpolar Arctic. Given the magnitude of ecological changes recorded in this study, such impacts may prove to be long lasting or possibly irreversible.paleoecology | paleolimnology | dendrochronology | limnology | salinization

While it is widely recognized that financial stock portfolios can be stabilized through diverse investments, it is also possible that certain habitats can function as natural portfolios that stabilize ecosystem processes. Here we propose and examine the hypothesis that free-flowing river networks act as such portfolios and confer stability through their integration of upstream geological, hydrological, and biological diversity. We compiled a spatially (142 sites) and temporally (1980-present) extensive data set on fisheries, water flows, and temperatures, from sites within one of the largest watersheds in the world that remains without dams on its mainstem, the Fraser River, British Columbia, Canada. We found that larger catchments had more stable fisheries catches, water flows, and water temperatures than smaller catchments. These data provide evidence that free-flowing river networks function as hierarchically nested portfolios with stability as an emergent property. Thus, free-flowing river networks can represent a natural system for buffering variation and extreme events.

1. Indigenous people are considered to be among the most vulnerable to food insecurity and biodiversity loss. Biodiversity is cited as a key component of indigenous food security; however, quantitative examples of this linkage are limited. 2. We examined how species and population diversity influence the food security of indigenous fisheries for Pacific salmon (Oncorhynchus species). We compared two dimensions of food securitycatch stability (interannual variability) and access (season length)across a salmon diversity gradient for 21 fisheries on the Fraser River, Canada, over 30 years, using linear regression models. We used population diversity proxies derived from a range of existing measures because population-specific data were unavailable. 3. While both population and species diversity were generally associated with higher catch stability and temporal access, population diversity had a stronger signal. Fisheries with access to high species diversity had up to 1Á4 times more stable catch than predicted by the portfolio effect and up to 1Á2 times longer fishing seasons than fisheries with access to fewer species. Fisheries with access to high population diversity had up to 3Á8 times more stable catch and three times longer seasons than fisheries with access to fewer populations. 4. Catch stability of Chinook Oncorhynchus tshawytscha and sockeye Oncorhynchus nerka fisheries was best explained by the number of populations and conservation units, respectively, that migrate past a fishery en route to spawning grounds. Similar population diversity metrics were important explanatory variables for season length of sockeye, pink Oncorhynchus gorbuscha, coho Oncorhynchus kisutch and chum Oncorhynchus keta fisheries. 5. Synthesis and applications. We show an empirical example of how multiple scales of biodiversity support food security across a large watershed and suggest that protecting fine-scale salmon diversity will help promote food security for indigenous people. The scales of environmental assessments need to match the scales of the socio-ecological processes that will be affected by development. We illustrate that upstream projects that damage salmon habitat could degrade the food security of downstream indigenous fisheries, with implications to Canadian indigenous people and to watersheds around the world where migratory fishes support local fisheries.

Identifying habitat that is essential to the recovery of species at risk, known as critical habitat, is a major focus of species at risk legislation, yet there has been little research on the degree to which these areas are protected. Here, we first review the provisions for protecting critical habitat on non-federal lands within Canada's Species at Risk Act (SARA). Next, we use the declining southern mountain population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada as a case study to show that identification of critical habitat does not guarantee its protection on non-federal lands. Our analyses show that 909 km 2 of critical habitat identified on provincial lands were logged in 5 years after it was legally identified under SARA. Existing provincial legislation and policies have provided incomplete protection of caribou critical habitat, and Canada's federal government has yet to exercise authority under SARA that could protect these areas. In the absence of nondiscretionary protection under provincial legislation, a combination of alternative mechanisms, involving all levels of government, Indigenous people, and industry, will be essential to protect critical habitat and help recover species at risk.

Because of decreasing sea-ice extent and increasingly frequent Arctic storms, low-lying coastal ecosystems are at heightened risk from marine storm surges. A major Arctic storm event originating in the Beaufort Sea in September 1999 resulted in the flooding of a large area of the outer alluvial plain of the Mackenzie Delta (Northwest Territories, Canada), and has been previously shown to have caused unprecedented impacts on the terrestrial ecosystems on a regional scale. We use diatoms preserved in lake sediment cores to gain a landscape perspective on the impact of the storm on freshwater systems, and to determine if other such events have occurred in the recent past. Our results indicate that five lakes located at the coastal edge of the low-lying Mackenzie Delta show strong, synchronous, and previously unobserved increases in the relative abundance of brackish-water diatom taxa coincident with the timing of the 1999 storm surge. These changes were not observed at a control site located farther inland. The degree to which the storm surge impacted the chemical and biological limnology of the lakes varied, and was not explained by measured physical variables, suggesting the degree of impact is likely related to a combination of factors including distance from the coast, the size:volume ratio of the lake and its catchment, and water residence time. We show that the 1999 storm surge resulted in unmatched broadscale impacts on the freshwater ecosystems of the outer Mackenzie Delta, and that while minimal recovery may be occurring in some of the systems, the lakes studied remain chemically and biologically impacted more than a decade after the inundation event.