Coastal Impacts, Adaptation, and Vulnerabilities - Climate ...

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Vulnerability and Impacts on Natural Resources 63Delta survival requires equilibrium between sediment supply and rising sea levels.Deltas naturally degrade as sediments subside and get reworked by storms, and, overthe longer term, deltas, like barrier islands, are generally self-sustaining systems undernatural conditions given an adequate supply of sediment. However, the constructionof levees and dams, and navigation activities along major U.S. rivers have alterednatural sediment flows and, in some cases, starved the natural environment of the sedimentsupply necessary to keep pace with changing water levels. Deltas world-wide areexperiencing land-loss due to the combined effects of increased human development,subsidence, and rising sea levels (Nicholls et al., 2007; Syvitski et al., 2009). The Bird’s-Foot Delta of the Mississippi River provides one of the more striking examples of thesecompounding impacts. Here, sea levels are rising at three times the rate of sedimentaccumulation on the delta, which portends the inevitable drowning of this delta system(Blum & Roberts, 2009).Mudflats: Mudflats are susceptible to threshold changes due to the combinedeffects of sea-level rise, temperature, land use, altered flows, and increasednutrient runoff.Sea-level rise is already reducing the intertidal area of mudflat feeding habitat for wadingbirds within estuaries, especially in locations constrained by coastal protective barriers(Galbraith et al., 2005). In a recent assessment of the sensitivities of mudflat communitiesto climate change in the San Francisco Bay estuary (EPA, 2012a), local experts identifiedthe potential for nonlinear losses within benthic communities due to a combination ofnutrient runoff and increased temperatures that drive dissolved oxygen levels below athreshold. They also anticipated precipitous losses of wading bird populations due toreduced prey densities and shrinking feeding habitat resulting from sea-level rise andsediment starvation. Although the potential for such thresholds may be high, patternsof disturbance and recovery in mudflats are extremely patchy and context-dependentand larger-scale behavioral responses of bird populations are unknown, which makespredictions of exactly when and where a threshold change may occur difficult to offer(EPA, 2012a; Norkko et al., 2010).Rocky Shores: Complex interactions between physical and biological factorshave been demonstrated in rocky-shore communities, which makes responses toclimate change difficult to predict.Although the impacts of sea-level rise are obvious for rocky-shore intertidal communities,temperature and ocean acidity are also potentially important. Hawkins et al. (2008)have noted general changes in abundance and range of rocky-shore species that can beattributed to climate warming. Although most of these changes involve range expansions,investigators caution that this may simply reflect the preponderance of studies atthe northern limits of species ranges compared to studies in lower latitudes. At a regionalscale, long-term recruitment records for mussels and barnacles showed a relationshipto large-scale climate and upwelling patterns along the U.S. West Coast (Menge et al.,2011a). The relationship explained approximately 40 percent of the variance in the recruitmentrecord. At the local scale, Harley (2011) determined that climate warming hadthe potential to drive changes in the community structure of rocky shores as it limited
64 Coastal Impacts, Adaptation, and Vulnerabilitieshabitat suitability in the high intertidal zone for barnacles and mussels. Temperaturetolerances could force these keystone species to live in lower, cooler zones where theyare more vulnerable to predatory sea stars.Increasing ocean acidity may make building and maintaining calcium carbonateshells more difficult, and this may be detrimental to key shellfish species in rocky shorecommunities (Gaylord et al., 2011). In addition to the loss of structural diversity thismight cause, diminished populations of filter feeders and rock-cleaning invertebratescould lead to increased algal populations on rocky shores.Although these findings suggest rocky intertidal communities are affected by climate,the complexity of key species’ individual and interactive responses to many otherenvironmental drivers make predicting community responses difficult (Menges et al.,2001b).Sea-ice systems: Sea-ice ecosystems are already being adversely affected by theloss of summer sea ice and further changes are expected.Perhaps most vulnerable of all to the impacts of warming are Arctic ecosystems such asthe Bering Sea. This area off the western coast of Alaska produces our nation’s largestcommercial fish harvests as well as providing food for many Native Alaskan peoples.Sea ice, a critical component of this ecosystem, is vanishing more rapidly than earlierprojections and may disappear entirely in summertime within this century (ACIA, 2005;Janetos et al., 2008; Royal Society, 2005). Fish populations depend on plankton bloomsthat are regulated by the extent and location of the ice edge in spring. As sea ice continuesto decline, the location, timing, and species composition of the blooms is changing.The spring melt of sea ice in the Bering Sea has long provided material that feeds clams,shrimp, and other life forms on the ocean floor that, in turn, provide food for walruses,gray whales, bearded seals, eider ducks, and many fish; however, the earlier ice meltresulting from warming leads to phytoplankton blooms that are largely consumed bymicroscopic animals near the sea surface, which vastly decreases the amount of foodreaching the living things on the ocean floor. This will radically change the species compositionof the fish and other creatures with significant repercussions for both subsistenceand commercial fishing (Janetos et al., 2008).Ringed seals give birth in snow caves on the sea ice, which protect their pups fromextreme cold and predators. Warming leads to earlier snow melt, which causes the snowcaves to collapse before the pups are weaned. The small, exposed pups may die of hypothermiaor be vulnerable to predation by arctic foxes, polar bears, gulls, and ravens.Gulls and ravens are also arriving earlier in the Arctic as springs become warmer, whichincreases the birds’ opportunity to prey on the seal pups (Janetos et al., 2008).Polar bears are the top predators of the sea-ice ecosystem and they use the ice as aplatform from which to hunt seals, their primary prey. Polar bears take advantage of thefact that seals must surface to breathe in limited openings in the ice cover. In the openocean, successful hunting is rare because bears lack a hunting platform and seals are notrestricted in where they can surface. In addition, the rapid rate of warming in Alaskaand the rest of the Arctic is sharply reducing the snow cover in which polar bears builddens. Female polar bears hibernate in dens for four to five months each year and, whilethere, give birth to their cubs. Born weighing only about 1 pound, the tiny cubs depend
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National Climate Assessment Regiona
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© 2012 The National Oceanic and At
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Coastal Impacts, Adaptation,and Vul
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Chapter 3Lead Author: Carlton H. He
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ContentsKey TermsAcronymsCommunicat
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4.4 Human Health Impacts and Implic
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Key TermsxixExposure 3 - The nature
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AcronymsxxiNAO - North Atlantic Osc
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Executive Summaryxxvffffffffffffffo
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Executive Summaryxxviiweakened by v
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Executive SummaryxxixAdaptation and
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Introduction and Context 3irrigatio
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Introduction and Context 9coastal w
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Physical Climate Forces 11fffffffff
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ReferencesAbuodha, P. & Woodroffe,
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Coastal Impacts, Adaptation, and Vu
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