Emerging Issue Summary
COASTAL SALINIZATION

Highlights:

  • Coastal salinization will change plant and animal species composition and may reduce water available for ice road construction.
  • Little is known about this phenomenon on the North Slope and current data are as yet inadequate to fully assess trends. However, with additional field measurements, it may be possible to model future coastal salinization.
  • Research is needed on the salinity tolerances of local plant species, site-specific conditions for trapping water and salt from melting ice, and the use of snow trapping to mitigate salt content of meltwater.
  • Although coastal salinization is not known to have impacted large areas, it is known to occur in areas where native communities, subsistence fishing and hunting activities, and the oil industry are concentrated.
Salinization
Coastal areas are threatened with salt water spray from increased storm activity. (BLM)

Overview and Management Relevance:

Coastal salinization of terrestrial or freshwater environments may be an issue to land managers for at least two reasons. First, it will cause changes in habitat structure, such as plant species composition, which in turn may cause changes in how or which animals use the land or waters. This in turn could impact subsistence use of those resources. Second, large quantities of freshwater are often necessary for ice road/pad construction during oil and gas exploration drilling, development, and maintenance. Coastal salinization could reduce the availability of or access to such waters.

There are at least six pathways, the first five of which are sensitive to climate change, for introduction of marine salts into the terrestrial environment:

  1. Certain wind conditions, such as winds from the west on the North Slope or onshore winds in general, push seawater into freshwater systems. The frequency and strength of storm systems during the open water season, and the resulting storm surges, have increased in recent years. Sea level rise of 0.3-1 m during the next century will increase the extent of coastal flooding and extend the areas affected during storms.
  2. Increased wave action during storms, related to decreased extent of sea ice, can result in increased airborne salts moving onto the land and into freshwaters.
  3. Coastal erosion can result in the breaching of freshwater lakes by the ocean. By moving the shoreline position further inland, coastal erosion moves the effects of processes in pathways 1, 2, 4 and 5 further inland.
  4. Increased active layer/permafrost thawing may allow ocean water to percolate through the upper substrate (i.e., active layer) and reach nearby freshwater lakes.
  5. Plumes of ocean water may move upriver during periods of reduced stream flow, an effect that may be enhanced by sea level rise. This plume is a natural event each winter and is sensitive to periodic drought conditions during summer, and could thus be altered by any changes in seasonal weather pattern affected by climate change.
  6. In the oil fields, spills from pipelines carrying seawater or produced water and leaching from marine sediments used in gravel pads and roads may introduce salts to the environment. However, this is a localized phenomenon and is not considered further in this summary.

The extent of coastal saline habitats and salt-killed tundra along the Arctic coast is poorly known. On the Colville and Fish Creek deltas, coastal habitats (salt marsh, coastal dwarf shrub) cover approximately 24 km2 (Jorgenson, pers. comm.). However, no data are yet available to assess trends in the extent of these habitats across the North Slope.

In addition, there currently exists about 26 km2 of recently (i.e., within the past few decades) salt-killed vegetation on the Colville and Fish Creek deltas due to storm surges in tapped lake basins, and there may be as much as 100 km2 of salt-killed vegetation along the entire coast (Jorgenson, pers. comm.). This phenomenon is sensitive to climate change (e.g., through sea level rise or changing weather patterns) and increasing rates of shoreline erosion. Coastal salinization, where it occurs, changes plant species composition and may subsequently impact some birds and mammals.

The studies needed to assess the trade-offs that would be involved in allowing saline water for ice road construction have not been done. Such studies would include the effects on vegetation of differing levels of salinity, the potential for melt water from ice roads to be trapped and concentrated through evapotranspiration, and the potential for diluting salinity during the spring thaw by trapping additional snow in the immediate vicinity throughout winter.

Coastal salinization would not affect groundwater in the sense the latter term is normally used. Due to the extent and depth of permafrost on Alaska’s arctic coastal plain, there is no hydraulic connection from the surface through permafrost to any groundwater below. Salinization would affect only the “groundwater” in the active layer, normally only tens of centimeters deep. This is important, however, because this is where most biological activity occurs.

In addition to these broad concerns, the NSSI Senior Staff Committee provided the STAP with specific questions relevant to coastal salinization. STAP responses to these questions are presented below:

  1. What is currently known about the level of coastal salinization on the North Slope; who’s measuring it; where; is it being measured adequately?

    Some measurements have been taken in lakes north and east of Teshekpuk Lake, as well as in the vicinity of Barrow (e.g., through the NSSI-funded water quality study). Many lakes already contain some salt, likely from storm surges that allow seawater into lakes or from deposition of airborne salts. Pond salinity is low in spring when water levels are recharged from runoff, but salinity increases throughout summer as water evaporates, suggesting that the salt is functionally trapped. If salt is repeatedly introduced into closed systems, it will remain trapped and become increasingly concentrated. In summary, little is known about coastal salinization, and while some sampling has occurred, no one is yet actively measuring it on a Slope-wide scale. Current data are thus inadequate to assess trends.

  2. Can we predict or model coastal salinization for the future? What is the geographic variability?

    Components of such a model would have to include:

    • surface topography and near shore bathymetry (both of which are currently poorly quantified at sufficient resolution),
    • lake geography (location and elevation above sea level, which for the most part is known),
    • current salinity of lakes (known for relatively few lakes),
    • the extent of future sea ice during the fall storm season (can be modeled),
    • predictions of sea-level rise and storm surge (can be modeled), and
    • rates of permafrost melting (uncertain).

    To the extent that this information is either available or can be projected, models of future coastal salinization could be produced, with model confidence constrained by the accuracy of the data and the other models incorporated. Such an effort could benefit from USGS efforts to acquire new LIDAR digital elevation model (DEM) data along the U.S. Beaufort Sea and northern U.S. Chukchi Sea coasts in 2009 and 2010, although this effort may not adequately measure river deltas. Complete DEMs for the coastal plain of the North Slope could greatly extend the utility of these models.

  3. How will increasing salinity in near shore waters affect fish species? How will it affect fish in areas that are currently freshwater habitats? What species of freshwater fish and fish predators are more/less tolerant of salt intrusion?

    Near shore marine waters currently maintain a relatively low salinity due to river input being kept near the coast by prevailing winds. Not much effect on fish is expected in this area unless climate change produces significant shifts in either wind regime or freshwater outflow. Salinity-tolerant freshwater fish species include arctic cisco, dolly varden, and the stickleback species group. The fall fishery for arctic cisco at Nuiqsut is dependent on a saltwater wedge moving up the Colville River’s delta; the farther upriver it goes, the closer to town arctic cisco can be caught. Alternatively, salt-sensitive fish in rivers would move upstream (down the salinity gradient) until finding suitable levels. For lakes that overflow during breakup, the salt can be flushed out. For lakes that do not overflow during breakup, any salt that enters is functionally trapped. Thus, the issue may not be what fish species can tolerate various levels of salinity, but what fish are present in salinized lakes near the coast. Least cisco are the freshwater species most frequently associated with near shore fresh waters, but most lakes near the coast are shallow and contain sticklebacks or no fish at all. Not much, if any, coastal salinization effect on fish is expected in rivers or lakes beyond the immediate coastal areas.

  4. How does increasing coastal salinization influence plant species composition and forage plant nutrient composition?

    In some areas of obviously salt-killed tundra, there are dense stands of salt-tolerant plant species (e.g. Carex subspathacea, Puccinellia phryganodes). These salt-tolerant species may be preferred forage for some birds and mammals in certain seasons. These shifts in plant communities may be responsible for an observed shift in brant (geese) molting distributions.

  5. To what extent may ice road construction need to rely on the use of saltwater?

    Currently, the only ocean water used for ice road construction is for roads located on the sea ice, and we assume this question refers to construction of ice roads on land. Therefore, the answer to this depends on where on land oil and gas exploration may occur in the future, and the amount and distribution of water of varying salinity in that area. The answer also depends on the level of salinity in the “saltwater.” Ocean water kills terrestrial vegetation, and the impacts are long lasting. Use of ocean water for ice road construction on land is not currently justified or reasonable. Water in coastal plain lakes varies in salinity, and some lake water may be saline enough to impact terrestrial vegetation. The extent to which lake water with elevated salinities is likely to be used for ice roads and ice pads is not known.

  6. How will the use of saltwater for ice roads impact vegetation over time?

    Depending on the salinity of the water, the effect could be immediate (i.e., plant mortality during the first summer), or the impacts could take years to develop. Even low levels of salt trapped annually in closed lake basins would tend to concentrate over time and could reach levels toxic to the vegetation present.

Recommendations:

  1. Explore the potential to develop a predictive model of coastal salinization on the North Slope over the next few decades. The model should include the timing, extent and geographic variability of this change, and should incorporate local knowledge on coastal salinization.
  2. Use of ocean water for ice road construction on land is not currently justified or reasonable.
  3. In areas where freshwater resources are limited, first consider alternatives other than the onshore use of saline water for ice road construction (e.g., use of snow roads). Before the use of ocean water or even brackish water can be seriously considered for ice roads, studies are needed to assess the potential impacts on the plant community and related impacts on thermal stability, as well as the potential for mitigating those impacts through dilution with snow or other means.

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