Sam's Nenana River Project
Sam and his science fair project in Healy, AK.
Sam has been studying the water quality of the Nenana River for two years. He has measured the water temperature and conductivity and determined the suspended sediment load of the Neanana River on a weekly basis for the years 2008 and 2009. He has had several sampling sites on the river. You can see his data from the Denali Education Center (or McKinley Village) (2008 and 2009), Riley Creek (2009) and the "Glitter Gulch" bridge (2009).
Sam presented his research project at the Denali Borough School District Science Fair which was held on February 26 at the Tri-Valley School in Healy. He received a General Science Excellence coin from Clear Air Force Station and one of the science fair grand prizes. This qualified him for the science fair in Fairbanks in March.
At the Interior Alaska Science Fair, held March 25-28 at the Pioneer Park Civic Center in Fairbanks, Sam received a first place ribbon, a Northern Chapter Alaska Library Association certificate and the Alaska Science Teachers Association Award of Excellence for a project related to the Alaskan Environment.
Sam says, "I have had alot of fun doing this project! I want to keep studying the Nenana River. I want to continue the project for next summer."
Introduction
The Nenana River is 140 miles long. Its sources are the Nenana Glacier in the Alaska Range and the 31 mile long Yanert Fork. It begins at Yanert Glacier and flows NW to the Nenana River,
14 miles south east of Healy.
What Kinds of Material Can We Find in River Water?
Water carries materials in two ways. They can either be dissolved or suspended.
- •Solids can dissolve in water because water (H2O) is a polar molecule. This means that the oxygen atom has a slightly excess negative charge and hydrogen atoms have a slightly more positive charge. This allows water to “pull apart” some kinds of solids. A dissolved solid is called an ionic substance (salt). It breaks up into individual cations (+) and anions (-) that become surrounded by water molecules.
- •Suspended materials are small particles like silt or sand that are carried by the water. The faster the water moves, the more energy it has, and the more material it can carry. The faster the water moves the larger the particles it can carry. Water usually moves more quickly because the ground it is flowing over is steep. Water moving over a level surface usually moves more slowly and can only carry very small particles.
Sources of Solids in the Nenana River
Materials get into the Nenana River in several different ways:
- •Precipitation Runoff – When it rains or the snow pack melts the water can pick up particles as it runs downhill to the river. The water can pick up dissolved particles by chemical erosion or it can pick up solid particles by physical erosion.
- •Glacial Melt – Glaciers pick up rocks and dirt at their base as they move down the mountain valley. Rocks and dirt can fall onto a glacier by landslides or avalanches. Fine particles can be blown onto the glacier’s surface and become frozen into the glacier when the winter’s snow covers it and becomes ice. All of this material is released into the glacier’s river when it melts. The glacier melts faster the higher the air temperatures are.
Some Research Questions
During the summers of 2008 and 2009, Sam made measurements at several sites along the Nenana River (see the satellite image and table at right). Some of the questions he was interested in were:
Is the water quality of the Nenana River, as determined by dissolved and suspended load, the same from in the same place from year to year?
Is the water quality of the Nenana River, as determined by dissolved and suspended load, the same from place to place along the river in the same year?
Do weather conditions have an impact on the water quality, as determined by dissolved and suspended load? If yes, which ones and how?
Does the water quality change after a precipitation event? Does the water quality change with the air temperatures?
A satellite image of Sam's study area. "Confluence" is the place where the Yanert Fork flows into the Nenana River. The Yanert Fork originates at the Yanert Glacier.
Sam's Sampling Sites
Denali Education Foundation (McKinley Village) - 63° 44.234’N, 148° 53.219’W
Riley Creek - 63°43.624’N, 148° 53.008’W
Glitter Gulch Bridge - 63°44.234’N, 148° 53.219’W
Weather Stations (airstrips)
Cantwell (PATW) - 63° 23.472’N, 148° 57.337’W
Denali (PAIN) - 63° 43.9556’N, 148° 54.638’W
Healy (PAHV) - 63° 52.055’N, 148° 58.139’W
Important Local Geography
Nenana Glacier - 63°29.717’N, 147°48.017’W
Yanert Glacier - 63°35.617’N, 147°52.483’W
Confluence: Yanert Fork - Nenana River 63°40.917’N, 148°46.783’W
Comparison of water data from 2008 and 2009 at the Denali Educations Center (McKinley Village)
Sam measured and recorded an number of variables at his sites along the Nenana River:
- • Dissolved Ion Concentration - is the quantity of dissolved chemical compounds in the water.For example, when table salt (NaCl) is dissolved in water it breaks into two parts Na, which has a positive charge, and Cl, which has a negative charge, (when you add + and – you get no charge because they cancel out). This is why water with dissolved particles in it has a charge and you can measure its conductivity (its ability to conduct an electrical charge). It can do this because there are particles with + and – charges and the more charged particle there are the easier it is for the water to conduct electricity and the higher the measured conductivity will be. This is measured with a Conductivity/TDS meter in milliSiemens (mS).
- • Water Conductivity - is directly related to the concentration of dissolved ionized solids in the water (the higher the dissolved ion concentration the higher the conductivity). The ions allow the water to conduct an electrical current. This is measured with a Conductivity/TDS meter in milliSiemens (mS).
- • Water Temperature - This is measured with a Conductivity/TDS meter in milliSiemens (mS) when the water conductivity and dissolved ion load are determined.
- • Total Suspended Solids (TSS) - the concentration of solid-phase material suspended in a water-sediment mixture measured in milligrams per liter (mg/L). This values is determined by filtering a known volume of a well-mixed water sample.
In addition, he measured the air temperature at each site at the time of sampling. He also documented the weekly precipitation at each site. This was done with a rain gauge that was set out at each site. Although the precipitation measured may not have represented the total precipitation between sampling dates (some evaporation may have occurred), it gave Sam some idea of the magnitude of the rainfall.
Sam had two years of data from the Denali Education Center (McKinley Village). The graphs at right are a time series of these data. They are called "time series" because time is the variable on the X axis.
— What do you see in these graphs?
— Are there any trends in these data?
— Are there any similarities between graphs?
— What might explain your observations?
Nenana River water data from 2008 and 2009
In 2009, Sam made measurements at three different sites along the Nenana River: the Denali Education Center, where Riley Creek enters Nenana River and under the bridge at "Glitter Gulch". The time series graphs at the far right show the 2009 data. The near right graphs are of the 2008 data.
— What do you see in the 2009 graphs?
— Are there any trends in these data?
— Are there any similarities between graphs?
— Are there any similarities between sampling sites?
— Are there any similarities between the 2008 and 2009 graphs?
— Are there any relationships between the 2009 variables in these graphs?
— What might explain your observations?
The central tendencies and variation of the Nenana River water data
These graphs show the box and whiskers plots and mean ± standard deviation (sd) for all of Sam's data. The box and whisker plots show the full spread of the data (minimum and maximum) and where most of the data are (in the boxed area). The mean and standard deviation show a more central location of the data. Remember: the longer the whiskers and the wider the standard deviation, the more spread out the data are.
— What can you say about these data?
— Are there any similarities between graphs?
— Are there any similarities between sampling sites?
— Are there any similarities between the 2008 and 2009 graphs?
— What might explain your observations?
This graph shows the mean ± standard deviation for conductivity and Total Suspended Sediment (TSS) for all of the data.
— What can you say about these data?
— Does the conductivity vary as much as the TSS?
— What does this mean?
— How do the box and whisker plots compare to the mean ± sd?
— What might this mean?
A comparison of the 2008 and 2009 summer air temperatures in the study area
The 2008 and 2009 mean daily air temperatures are graphed for the Cantwell, Denali and Healy airstrips (left hand graphs, below). These sites are selected because they cover the whole area of sampling. The Cantwell airstrip is south of the sampling sites, the Denali airstrip is in the middle of the sampling area and the Healy airstrip is north of the sampling area (see the table in Introduction).
The graphs on the right side (below) show the 2008 data subtracted from the 2009 data. If the values are positive, this means that day in 2009 was warmer than in 2008 and if the values are negative this means that that day in 2009 was colder than 2008.
— What can you say about these data?
— What might this mean for the Nenana River water?
Summary of the weekly measured precipitation and measured water variables
The measured weekly rain values are plotted with the water conductivity (top) and total suspended sediment (TSS). This was done because Sam was interested in knowing if rainfall had an impact on the TSS.
— What can you say about these data?
— How do the measured weekly precipitation values from the three sites compare?
— How do the water conductivity values from the three sites compare?
— How do the TSS values from the three sites compare?
— Are there any relationships between the measured weekly precipitation and the water conductivity and TSS?
Looking at the Data
Look at the satellite data in the Introduction. Notice that the Denali Education Center (DEC) samping site (McKinley Village) is located south of the confluence of the Nenana River and the Yanert Fork while the Riley Creek and Glitter Gulch Bridge sites are north of the confluence of these waterbodies. Recall that the Yanert Fork is fed by the Yanert Glacier which is one of the sources of suspended sediment load in the Nenana River.
Do you think this could make a difference between the measured values at DEC, Riley Creek and the Glitter Gulch Bridge? What might that be?
Now let's look at the two years of DEC site data. Notice that although the two sets of data are not exactly the same they are very similar. The river water temperature is above freezing during the summer and begins to decrease in mid-August reaching freezing in October. The water conductivity and the dissolved ions slowly increase from June to freeze-up in October/November. The total suspended sediment (TSS) vauies slightly during the open water season. It varies more in 2009 than in 2008. However, in both years the TSS is quite low.
Can we say that the two years of data at this site are similar or different?
Now let's look at all of the 2009 water data. The river water temperatures follow a similar pattern, although the DEC values are slightly higher in July and August than at the other two sites. The water conductivity and dissolved ion graphs look similar with the DEC values being somewhat lower than the other two sites. Similarly, the pattern in the TSS graph for each site looks much the same but the values for DEC are much lower than for Riley Creek or Glitter Gulch bridge.
Can we say that the data from these three sites are similar or different? Are any data sets more similar or different to each other than they are to the third data set?
The graphs showing the central tendencies and variation can tell us something about these data. The water conductivity and total dissolved ions graphs show us that the median and means, and their associated variation, of the DEC data (2008 and 2009) are lower than those at the other two sites. The extreme values for all of these data are arranged symmetrically around the "middle" value. The DEC TSS variability at DEC is smaller than at the other sites in both years although the variability is much higher in 2009 than in 2008. The extreme values for all of the 2009 data are well above the median/mean. Looking at the mean and standard deviation for the water conductivity and TSS, we see that the means for both variables is lower at DEC in both years that at Riley Creek and Glitter Gulch Bridge. The variability of the TSS is very large at the two most northern sites.
What can these graphs and the time series graphs tell us about the water conductivity, total dissolved ions and the TSS?
Now let's look at the two most important environmental factors that might influence the water quality of the Nenana River. A comparison of the daily mean temperatures at three sites , in the Nenana River valley, indicate that, on average, the summer of 2009 was warmer than 2008 all along the river.
How might this influence the water quality of the river?
The precipitation data that Sam measured are graphed with the water conductivity and TSS. This was done because Sam was interested to know if the TSS changed with rain events.
What do these data tell us about the relationship between rain events and TSS?
Putting It All Together
First of all, let's recall a few important facts:
— The Nenana River flows north to the Tanana River.
— There are two main sources for sediment in the Nenana River. These are loose surface sediment washed into the river by precipitation runoff and glacial sediment that is released into the river from the Nenana and Yanert glaciers by melting. The Yanert Glacier is much larger than the Nenana Glacier: from this, we might infer that the Yanert Glacier contributes more sediment to the river than the Nenana Glaicer.
Looking at Sam's data, we see that:
— The measured water variables are much the same at DEC in 2008 and 2009, although there is more variation in the TSS in 2009 than in 2008.
— The 2009 data from Riley Creek and Glitter Gulch Bridge, while similar to each other, are noticably different from the data acquired at DEC.
— There appears to be a relationship between the water conductivity (dissolved ions) and TSS. For example, when the TSS is high at the end of July the water conductivity is low and when the TSS is low at the end of June the water conductivity is relativiely high.
— The summer or 2009 was warmer than the summer of 2008.
— There does not appear to be a relationship between rain events and TSS. For example, the highest TSS value at the end of July is paired with very low measured precipitation while a very high measured precipitation value at the end of September is paired with a very low TSS.
Sometimes it helps to consult an expert in your field of research. According to a member of the Glaciology Group at the Geophysical Institute, University of Alaska Fairbanks:
"The Nenana River headwaters have large sections of flat water so it carries very little sediment compared to the Yanert Fork that is much closer to the glacier with sustained gradient. On cool, cloudy days, the Yanert Glacier doesn't contribute much (hence the water stays relatively clear), but on hot days the Yanert Fork turns the Nenana River muddy."
This seems to indicate that on warm days, the Yanert Glacier melts more and contributes more sediment to the Nenana River.
Overall, we can say that the Yanert Glacier is a significant sediment contributor to the Nenana River and, as a consequence, the TSS values north of the Yanert Fork-Nenana River confluence are consistently higher than those from south of the confluence in any year. The changes in TSS during 2009 appear to be the consequence of high air temperatures melting the glaciers rather than from rain events. It is possible that the glacial meltwater is low in dissolved ions and so has a low conductivity. This accounts for the inverse relationship between TSS and water conductivity and the increasing water conductivity later in the open water season when the glacial meltwater contribution to the Nenana River decreases as the air temperatures decrease and the rate of glacial melting decreases.
What do you think?
Project Details
Nenana River Project
Monitoring the freeze-thaw cycle of the Nenana River
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