This paper was written as part of the 2010 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.

Possible Effects of Freshwater Inputs from Melting Icefields on the Marine Ecosystem of Petersburg, Alaska

Authors

Kristin Neuneker
Sharece Randrup
Bynum Jackson
Patricia Jackson
Shelton Brett
Joe Zarlengo

Team W.O.A.A.

Petersburg High School
PO Box 289
Petersburg, Alaska 99833

Abstract

Our community of Petersburg, Alaska is dependant upon fishing to sustain our way of life. With the decrease of sea ice in Alaska, both here and in other areas there could be seen some major changes. Ocean freshening, or the addition of freshwater into our saltwater oceans, may occur. This may cause lower salinity levels and stronger currents due to the difference in densities. There will be more rainfall leading to stronger stream flows and outburst flooding, washing out the salmon spawning streams and causing massive erosion. Isostatic rebound may occur, causing the ground level to rise. Also the sea level will rise due to more water. There will be more nutrients available because of extra runoff. This may make the phytoplankton blooms occur earlier and on a different schedule. Sport fishing, commercial fishing, and charter fishing could all be in danger because of the impacts on the salmon species from ocean freshening. All of these factors would drastically change our way of life here. We propose that an effort should be made to reduce the production of greenhouse gasses, both here and other places. We should also be studying the biological and physical effects of glacial melting, on salmon populations especially since we rely on them so much.

Introduction

Globally, the cryosphere contains 75% of the freshwater on Earth (Bates et al. 2008), of which roughly three percent is made up of mountain glaciers (Arendt 2002). In Alaska there is an abundance of glaciers, and together with icefields of neighboring Canada, they make up approximately 13% of the mountain glacial area (Arendt 2002). These glaciers have been steadily retreating, leaving behind them a wave of change. The retreat of glaciers is due to the warming of our earth. The predicted temperature (Figure 1a) shows an average monthly increase of 6°C by the year 2041 and 10°C by the year 2091 (SNRAS 2009). Greenhouse gasses in our atmosphere are causing our earth to warm up and this causes the glaciers and colder regions to warm and thaw. When glaciers thaw they produce large amounts of freshwater that flow through the streams into our oceans. The distribution of freshwater, larger volumes of water, and more erosion into the ocean may cause damaging effects to the ecosystem. In this research paper we are addressing the possible outcomes of increased freshwater inputs and the effects it could have on the marine ecosystem of Petersburg, Alaska and surrounding waters.

Some glaciers are seen retreating at a rapid pace while some retreat and advance interchangeably throughout time. The precipitation modeled for Petersburg suggests a 1mm average monthly increase (Figure 1b) by 2041 and a 2mm average monthly increase by 2091 (SNRAS 2009). Some of this additional precipitation may fall in the winter months somewhat offsetting summer melt. The LeConte Glacier is the southernmost tidewater glacier in Alaska. Since 1983, Petersburg High School students have been surveying the terminus to determine whether the glacier is advancing or retreating. To date, the galloping glacier has slowed down and maintained its current terminus (Figure 2) (Petersburg High School 2009). However, this says nothing about the mass balance of this particular glacier in the Stikine Icefield. Some glaciers, such as ones in Glacier Bay, Alaska, have had the most rapid glacial retreat in the world; a total of 2500km2 since 1750. The entire basin of what is now Glacier Bay remains after this retreat (Fastie 1995). These glaciers we value not only for their beauty but also for their help in regulating our natural environment as a storehouse for water and nutrients and as a habitat for many marine and terrestrial organisms.

Here in Petersburg, Alaska we rely heavily on fishing to sustain our economy. Fishing provides jobs and money directly and indirectly to everyone in town. With the rising temperatures and receding glaciers we may see a change in that way of life. Fish may have to move around to find food and better living conditions, forcing fishermen to spend more money and time to locate and catch them. This would unsettle our community's way of life. As we look at the possible effects of increased freshwater inputs into the marine environment, we begin by looking at the way in which the freshwater would change circulation in the near shore waters.

Physical Oceanography

According to Garrison (2005), the density of the water, which is determined by salinity and temperature, drives ocean water circulation. The circulation due to these densities is called thermohaline circulation. Generally, the more dense the water, the deeper it sinks. Each mass of ocean water has its own salinity and temperature characteristics. When two masses meet, they do not mix. Instead, one tends to flow above or beneath the other. Water masses near the surface are usually warmer and less saline because they may have formed in warmer areas where the precipitation was greater than the evaporation. Currents traveling along the western margins of ocean basins transport warm tropical surface waters towards the North and South Poles. In some places, the water's heat is lost to the atmosphere and the water itself sinks and becomes deep water and bottom water. This now cold, dense water moves southward and wells up in the Indian and Pacific Oceans. The water may take up to 1,000 years to make this trip (Garrison 2005).

Freshwater input is a major factor in the water properties of a fjord estuarine environment, such as in southeastern Alaska. These environments are characterized by large amounts of precipitation. The freshwater runoff in fjords can influence important water properties, such as the stability of water columns and the flow dynamics, as well as the addition of suspended and dissolved minerals that can greatly affect the water column properties. These patterns of freshwater entering fjords can influence the well-being of the animals in the habitat, as it may affect the availability of prey, spreading of species, and the dispersal of planktonic organisms (Hill et al. 2009).

As discussed by Weingartner et al. (2009), not only does the freshwater runoff affect the fjord estuarine environment, but it also has an influence on regional coastal circulation and oceanographic properties. To understand this, the Alaska Coastal Current (ACC) must first be explained. This current is important to the Gulf of Alaska's marine ecosystem. The ACC begins on the British Columbian shelf and flows through southeastern Alaska, continuing north until it reaches the Bering Sea and through Unimak Pass. Due to the buoyant freshwater runoff added to the coastal waters, the more saline, surface water is forced to downwell, or sink. Downwelling, aided by strong winds and cooling, induces vertical mixing. By midwinter, the water is well mixed (Weingartner et al. 2009). Because the denser water is forced down by the runoff, the circulation of the ACC could potentially increase. If the output from freshwater, which is currently the source of 4% of the current's transport, was to double, the transport would also double, given a lag of about one month (Tomczak 2000).

In addition to the circulation patterns caused by winds and the freshwater input, tides play a major role in oceanographic conditions in southeastern Alaska according to Weingartner et al. (2009). The combination of the ACC and tidal surges around the islands create eddies that contribute to the vertical mixing (Weingartner et al. 2009). Vertical mixing can enhance the nutrient transport into the photic zone because it would decrease stratification caused by freshwater inputs (Weingartner et al. 2009).

Geological

As global warming occurs around us the effects become more apparent, and with each passing year the warming becomes more evident in our glaciers. Scientists know that the glaciers are receding, thinning, and getting smaller. With the glaciers getting smaller and more freshwater getting into the oceans it could have effects in and possibly change the ecosystem of coastal Alaska as we know it today. A group of scientists used airborne lasers to estimate the volume change of 67 glaciers in Alaska from the mid-1950's to the mid-1990's. There was and average of -.52 m/year change in the thickness of 67 Alaskan glacier (Arendt 2002). They also found that there was enough water being put into the ocean to raise sea level +.14 mm/year (Arendt 2002). Repeated measurements were done in the mid-1990's to 2001 from 28 glaciers and suggested that there was an increase average thinning of -1.8 m/year (Arendt 2002).

Glaciers have been creating runoff for thousands of years and that runoff created streams that run to the ocean. The freshwater from these streams mixes with the salt water. The streams can handle the same amount of water coming off of the glacier each year and do not have any major effects on them. However, if the glacier puts off more water than normal into the stream, the stream may be unable to handle it and a result may be erosion along the streambed, putting additional sediment into the water. If the bank of a streambed erodes away it makes the stream become more vulnerable to wind erosion. With both these factors working together to erode the stream bank, this eroded area is more likely to get to enlarge and move inland, which could eventually affect someone's home, major highway, or even a whole community. With glaciers melting off quicker, the water from the glaciers erodes away the stream bank and then could cause further erosion and could eventually leave it with little or no vegetation around the stream. For example Madagascar's high plateau area, which is around ten percent of the country's land mass, has become devegetated because the soil has eroded away leaving the area looking barren and empty (Butler 2006).

Outburst flooding is an example of how this could occur here in southeast Alaska. When water melts it is possible for it to get dammed up between the glacier and the ground. Now with earthquakes and avalanches being a frequent thing here in Alaska it is very likely that this dam could break and have all this water come rushing out of the dam into the stream causing erosion and maybe even a small tsunami that blows out the stream channel. This is known as a "glacial lake outburst flood" (Björnsson 2002).

Glaciers are a major part of Alaska. As described by Mayo and Post, glaciers cover approximately 73,800km2 and are concentrated near the Pacific coast. Most Alaskan communities and transportation routes are located along rivers from glacial runoff and because of this, glacier dammed lakes may be hazardous to Alaskans. When ice dams fail, outburst flooding occurs. However, large amounts of water stored under glaciers can also lead to outburst flooding. There are many different ways that glacier dammed lakes form. The largest lakes, which present the greatest amount of danger, generally occur when glaciers block valleys that receive input from rivers. When water is trapped in a niche or recess in the wall of a valley, a small lake is formed. Once a depression is blocked by a glacier, a small lake is formed by runoff from the glacier as well as rainwater. Eventually, the trapped water makes its way down to the bedrock and pours into an ice dam. Most large ice dammed lakes fill until they reach the point at which they are no longer stable (Mayo and Post 1971).

According to Mayo and Post, the release of an ice-dammed lake is usually initiated by a channel through, under, or over the ice dam. After the leak has opened, it will continue to expand though the process of melting. The rate of discharge slowly increases until it reaches extremely high values. As the lake drains, it becomes more lacking in the energy and water that is needed to flow and the drainage stops abruptly. Sometimes the lake will drain completely before it has to stop. Although a lake may not be very large, it can still produce an extremely large flood. "For example, Summit Lake, British Columbia dammed by Salmon Glacier has a maximum size of only 4.2km2. On November 30, 1965, it released and produced a flood peak of 3,100 cubic meters per second (Mayo and Post 1971)." Areas in the path of these hazardous floods are subject to serious damage. These floods can result in a high rate of erosion, deposition, and they can greatly change stream channel paths (Mayo and Post 1971).

If a streambed has eroded away and left the area above the stream open to the sun's heat it causes the water to warm up. Salmon need the water to be a certain temperature for them to be able to spawn and have the larva hatch. If there is less vegetation that is covering the stream and keeping the water temperature low the salmon population could decrease, causing a fall in salmon sales throughout Alaska.

When glaciers are formed they cause the land to change and to reform. One of the reasons is because as the glacier moves over the land it erodes away parts of the landmass it is moving over. It could move boulders as big as cars over a period of a few years. The weight of these glaciers can also cause the land underneath it to compress and get smaller. When a glacier then recedes, isostatic rebound occurs. Isostatic rebound is the reformation of the land after a glacier has left the area. (See Figure 3.)Where the earth's surface is scraped away by the glacier, wide-spread erosion is likely to occur. Also, since some weight has been taken off of the surface of the earth as the glacier melts, the earth will then de-compress itself causing that region to actually rise up. It would not cause for the whole earth to rise up but rather just the area with the glacier around it would rise significantly. As we can see in Figure 4 the areas with little or no glaciers in the area would only rise up 4 mm/year (Motyka 2009). An area with large amounts of glaciers could rise up anywhere from 10-28 mm/year (Motyka 2009). GPS data can show uplifts in 30 mm/year in areas like Glacier Bay and 32 mm/year east of the Yakutat area (Motyka 2009).

With glaciers melting and isostatic rebound happening this would still cause for this area to be a factor of rising sea levels. It is estimated that seas worldwide have risen at an average rate of 1.5 mm/year for the past century (Douglas 1991). It is estimated that in the year of the 1990's the sea level rose and average of 2.5 mm/year (Cazenave 2006).

Ocean Freshening

About 77% of the earth's surface is covered in water. The seawater is about 96.5% water and the 3.5% is dissolved substances (Garrison 2005). Most of the dissolved substances are various types of salts. With freshwater flowing into the ocean it will decrease the various salts in the water. The salinity in the ocean varies between 3.3% and 3.7% (Garrison 2005). Ocean freshening is when freshwater from streams or rivers flows into the ocean causing the salinity to decrease. The salinity of the ocean changes throughout the year. In warmer months the salinity is lower due to the melting of the ice and glaciers, and in colder months the salinity is greater because there is less freshwater runoff into the ocean. The University of Alaska Fairbanks currently has a study going on that maps the temperature and salinity versus depth of the oceans outside Seward, Alaska (Weingartner 2009). GAK1, as it is called, has been an ongoing project since 1970. They determined that salinity, not temperature, is the driving force behind seawater density. They use buoys that take certain salinity readings and found that there is a pattern to it. During the warmer summer months the salinity is lower, with the most variance being within the first 50 meters (Figure 4). In winter and colder months the salinity is greater, again with the most variance being within the first 50 meters. Most biological happenings, such as phytoplankton blooms also occur within the first 50 meters.

Salinity Changes in Estuaries

Estuaries are zones where mixing between rivers and the sea occurs (Boesch 2002), and they are one of the richest ecosystems on the planet. Inputs from both freshwater and marine sources provide the typical features of estuarine ecosystems (Boesch 2002). Changing the amount of freshwater input could have a number of effects, such as shifting the estuarine gradient, affecting the dispersion of organisms, and changing the transportation of sediments and nutrients (Boesch 2002). Organisms that tolerate only a narrow salinity range could be restricted to lower reaches because of the fluctuations in salinity that would occur (Boesch 2002) if a greater extent of the stream was exposed to freshwater only for a longer period of time. Conversely, if the sea level does rise then organisms that typically occur in the lower reaches would be able to move further upstream. Either way, changes in plant and animal communities are likely to occur.

Biological/Ecosystem

Fishing is a major resource for our community. They supply jobs and food for many families in Petersburg. Our community is a primarily fishing based community with most people owning boats that help them make a living. We rely on salmon and other fisheries to supply us with jobs and money. The melting of the nearby ice fields could cause a higher freshwater content in the marine environment. This could cause damaging affects to our local salmon population. From a biological prospective this process could disrupt the food chain or alter existing communities and be detrimental to our community.

Due to rising temperatures there may be a great number of changes that occur. These changes would all affect life in the oceans. The glaciers will shrink and coastal erosion could increase. This could add a large amount of freshwater into saltwater communities, and also erosion would send higher levels of nutrients into the water. This would cause shifts in biological events, such as phytoplankton bloom timing, species distributions and community structure (Rosenzweig 2008).

Salmon in the Pacific are dependant upon a variety of factors to survive, one of the central dependencies being their diet. In the wild, juvenile salmon consume zooplankton as a main food source. These zooplankton consume phytoplankton to survive. Phytoplankton are the primary producers of the oceanic food web, and all animals depend on them for the reliability of their food source.

Here in southeastern Alaska and Petersburg, the diatom is the most dominant among primary producers (Weingartner et al. 2009). Diatoms are single celled, algae-like phytoplankton that are contained within a hard outer shell ("Diatoms: Ever Wonder?" 2000). They are very prevalent in all waters of the world and as a primary producer they are a major foundation of the food web. When there are enough nutrients and sunlight diatoms will bloom, or reproduce at a fast rate. This creates a large food resource for marine animals.

In southeastern Alaska, nutrient runoffs, in conjunction with temperature, control the timing of when these diatoms and other primary producers bloom. When there are enough nutrients to sustain them, they will reproduce quickly, or bloom. This creates a huge food source for marine animals. They rely on the success and timing of this food source to survive. If the blooms were to start at different times then the fish that rely on them could possibly miss the bloom and their major nutrient source. With increased temperatures there may be increased rainfall, washing more nutrients into the ocean. This would cause the diatom blooms to occur more often, creating a variable time period for the blooms to occur, disrupting the pattern of zooplankton and fish and possibly causing a difference in their success of living (Wiengartner et al. 2009).

Due to the major erosion of the coast there will be more nutrients in the water. For example silica, referring to any composition that contains both silicon and oxygen, is a major limiting nutrient for diatoms. Diatoms rely on this as a component of their hard outer casing. Silica minerals may be found in the water but also in many rocks along the shore ("Diatoms: Ever Wonder?" 2000). These rocks displace some of their nutrients into the water when they erode due to weathering. With more rainfall and runoff from shore there will be more nutrients available to the phytoplankton. This would cause them to have a greater bloom and possibly change the community structure.

Zooplanktons are the primary consumers of the marine world. Copepods for example, feed on diatoms or other phytoplankton, to survive. This very small and abundant plankton is a major link for many organisms between the primary producers and what they can consume. Herring, a major food source for the salmon population, feed on copepods. Some salmon also eat copepods as a main food source for their diet (Cooney and Willette 1998, Sturdevant 2005). Some eat mainly these zooplankton while others mix with fish. These zooplankton are a key food source for many of the fish that we rely on in our community.

Fish populations rely on the stability and consistency of the phytoplankton blooms, as do many other organisms in the marine ecosystem. If these populations were to change, as is projected, the salmon population may suffer. There would be a lower level of fish that could survive due to the disruption caused by the irregular blooming periods. Another marine organism that is vital to our Petersburg economy, which would be disrupted by the increasing freshwater, would be Dungeness crab. Dungeness crab cannot survive in freshwater and are moderately sensitive to salinity (Stratman and Bishop). With ocean freshening happening the crab could be subjected to lower salinity levels, which could damage their populations.

If increased precipitation were to fall it would cause higher stream flow in salmon spawning streams. This could wash out the salmon who are trying to swim up the stream to spawn. It also might go through the stream and cause massive erosion and flooding, changing the whole landscape and making it more difficult for fish to swim upstream. If the flooding were to happen during the period of spawning the excess amount of water would damage the eggs and spawning fish.

This flooding could also cause major changes to the shoreline. Erosion would wear away at the shore and take away soil, rocks, and any plants that were in the way. In Glacier Bay there is a great deal of rapid succession that is taking place due to the retreating of the many glaciers. Trees colonize the most recently exposed surfaces of the bay within the first 15-25 years (Fastie 1995). Any surfaces that have been exposed for 35-45 years are have 100% cover of shrubs and young trees (Fastie 1995). These trees and shrubs could possibly contribute more nutrients into the streams and rivers by which they grow. This could help sustain the food source that salmon fry depend on (Piccolo and Wipfli 2002). Because of the ever-receding glaciers there are major changes occurring, which could happen to the glaciers near Petersburg. There are changes that could cause a difference in landscape and structure for the ecosystem.

Changes in community structure will also occur because of increased freshwater in the marine environment. Many animals are sensitive to salinity levels and live in certain areas of the ocean due to those levels. If the ocean's salinity were to decrease some organisms would have to move to places where they could live. These vacated areas would leave room for new species that could handle the decreased salinity. This moving of animals would change the organisms moving into these areas and change the makeup of that specific region. Due to the rising temperatures affect on the ice and climate of Alaska there could be some major biological impacts. Ocean freshening would occur due to the rising temperatures causing the melting of glaciers, and increased rainfall in southeastern Alaska. Increased rainfall would also cause outburst flooding, disturbing salmon spawning and rearing habitat in streams (Gillikin 1993).

In summary, our Petersburg economy relies on fishing to survive. With fluctuations in nutrients, diatom blooms would occur more frequently, adding more food to the ecosystem but also more disorder for the time period that the diatoms bloom. Decreased salinity would drive out species from some regions while bringing in a different array from others. And the area left from the retreating glaciers will be grown over with trees and shrubs. Some of these effects could be positive while some negative, but they will all affect us in Petersburg, Alaska.

Human Impacts

Commercial fishing is very important to the Petersburg economy. According to the State of Alaska (2009), in 2008 we had a total of 336 permits for salmon, and for all fisheries combined we had a total of 473 permit holders. The number of permits issued for salmon was 415, and for all other fisheries was 1,145 permits. For the salmon group we had a total of 232 fishermen and 252 permits fished. There was a total of 23,665,395 pounds of fish brought in and an estimated gross earning of $16,441,621. With all fisheries combined we had a total of 378 fishermen who fished and 784 permits fished. We landed 46,725,487 pounds and had an estimated gross earning of $55,395,235. For the herring industry in Petersburg in the year of 2008, a total of 11,065,020 pounds of herring was landed, making a total gross estimate of $5,581,390 (State of Alaska 2009).

Subsistence fishing is whenever fish is taken and is used to feed people's families. With global warming, some bodies of water will have less salt some will have more because of evaporation. This effect will cause a decrease in the abundance of some species and an increase in the abundance of others (Human Effects of Climate-Related Changes in Alaska Commercial Fisheries). November 1998 an annual "Fish Expo" industry trade show in Seattle was advertised in the show brochure as follows: "We have much at stake with respect to potential climate change impacts on fresh-water and marine fisheries. Projected changes in water temperatures, water quality, salinity, and currents will affect the growth, survival, reproduction, and geographic location of fish species. Climate change will cause fish habitat gains in some locations and losses in others. This session will help you learn how different weather patterns can affect your catch." With Petersburg Alaska being a "rural" town , fishing plays a big role in our small community and how we survive. If certain fish were to leave people couldn't sell that fish for a fair price or afford to find them.

With fish leaving certain towns and different types coming in it will affect sport fishing. This will be because there will be a greater need for the fish people catch just sport fishing. There will be less tourism because some tourists come to sport fish while they stay in our small communities and the less and less there is left for them to catch the less likely they will come back for more.

Outside of fishing, there are possible effects on communities within southeastern Alaska. Not many communities are located along glacial outwash rivers in southeastern Alaska and possible direct effects on communities are minimal. Hyder is located at the outlet of the Salmon River, yet has not been at risk to date from any major outburst flood events. As for the affects outburst flooding would have on the people of Yakutat, the Situk river could be potentially dangerous if it flooded. Any cabins in that area would be lost, and there would be a minor threat to the Yakutat airport (Gubernick and Paustian 2007).

Policy

We really do not know about how much freshwater is contributed from the icecap and glaciers in southeastern Alaska, nor do scientists really understand what the effects of increased freshwater inputs might be in the coastal ecosystem. We recommend that we research and monitor the changes. It would be possible to monitor the amount of freshwater runoff from surrounding glaciers by installing additional stage gauges. To go further, we could examine the impact of varied peak flows and the timing of flows on salmon runs. In order to fix the problem, we must first know what the effects might be, how significant of an effect it will have on our marine ecosystems, and what we could do to prevent or slow its progression.

Every human and animal will die, or global warming is no big deal. No matter where in this spectrum of thinking one lies, it is true that every human being has a carbon footprint. A carbon footprint is how many pounds of the green house gas CO2 is released by every day civilians. Many web sites suggest ways to decrease carbon footprints such as lowering thermostats by two degrees, adjusting water heater settings, or running a dishwasher full. Even with the participation of millions of people in the effort of decreasing their carbon footprint it would only amount to a miniscule difference in the temperature of the earth. In order to find big climate change impact solutions governments are meeting to discuss policies such as carbon taxes and CO2 restrictions. These policies are an attempt to bring nations to an agreement on industrial activities, which will hopefully slow global warming in the long run. Although the planetary temperature is the primary indicator of global warming, the more pressing issue is decreasing the negative effects of global warming. Danish academic Bjorn Lomborg suggests putting our resources into new technologies that would give us the biggest bang for our buck "He proposes that nations cease the bureaucratic morass of reducing emissions and start investing in whatever low-carbon-emitting technologies or techniques they consider prudent-conservation, renewable energies, fusion, fission, carbon capture, or some novel ideas yet unknown" (Bergin 2007).

We should also examine the effects of increased freshwater inputs have on estuarine communities. To help out with the research we could follow the example of GAK1 in Seward to monitor the changes in salinity and temperature of the ocean water (Weingartner 2009).

Conclusion

In the end, it all comes back to global warming. Because of the rising temperatures of the earth's atmosphere, our glaciers are receding at an alarming rate. These beautiful works of nature are important to the environments around them and the freshwater melt off from these glaciers will most likely have an effect on the ecosystem of Petersburg, Alaska and surrounding waters.

As we have stated, water currents are powered mostly by density (though other factors go into this as well). Increasing the amount of freshwater that is added to the ocean may cause the saline, denser water to sink farther down than it normally does. A possible effect would be the increase of the transport in the ACC.

When the meltwater comes off of a glacier, it usually forms a stream. With an increase in the melting rate of the glacier the stream may be flooded and eroded, leaving the normally covered water exposed to sunlight. This contributes to increased absorption of infrared or heat energy creating a positive feedback loop that further melts glaciers. This would destroy the habitat for any animals living in the stream and the stream itself would be more susceptible to wind erosion. If the stream was to move further inland, it could become a problem for homes, highways, and/or towns. Also, if there was an outburst flood from a glacier that proceeded down a stream near which cabins were located, the cabins could be destroyed, along with anyone who was inside them. Retreating glaciers could have a positive affect, because the land they no longer occupy would be open for vegetation and animals. However, we cannot ignore where the freshwater from the glaciers ends up. The freshwater is eventually added to the ocean, and too much of it can result in ocean freshening. When the freshwater enters estuaries, too much of it can reduce the salinity and creatures that have a narrow range of habitat will be forced to move, opening the space for creatures that had generally resided farther upstream.

Without a doubt, salmon is one of the main sources of income for Petersburg, Alaska. In southeast Alaska, the phytoplankton diatom is the main producer and increased amounts of freshwater entering the ocean may proliferate the nutrients that are available to the diatoms, affecting the rate at which they bloom (Weingartner et al. 2009). The possible increase of their blooming would affect the success of living for fish and other marine life (Weingartner et al. 2009). However, increased freshwater in streams may cause the stream to be more powerful, making the trip upriver more difficult for salmon. It could also potentially wash away salmon eggs, having a damaging effect on the ecosystem not only for people in Petersburg, but for other communities as well.

Figures

chart of Petersburg temperature projections
chart of Petersburg precipitation projections

Figure 1. Predicted temperature (1a) and precipitation (1b) change for Petersburg, AK. Yellow and lavender indicate 1961-1990; Orange and dark blue indicate years 2041-2050 and red and light blue indicate years 2091-2100 (SNRAS 2009).


LeConte Glacier terminus location

Figure 2. LeConte Glacier terminus location (Petersburg High School 2009)


projected isostatic rebound in Glacier Bay

Figure 3. Projected isostatic rebound projected in tenths of centimeters per year. Note the knobs of high rebound around Glacier Bay (Larsen 2000).


monthly salinity readings in Prince William Sound

Figure 4. GAK1 monitoring of monthly salinity at varying depths in Prince William Sound (Weingartner 2009b).


References