Linking Hydrology to Nitrogen in Streams

Background for Teachers

The six samples that get submitted to the lab for total nitrogen analysis for this project must be collected between the time of maximum snowpack and the time of complete snow loss. One sample must come from the time of maximum snowpack and one must come from the time of complete snow loss. It is important that students not only understand the role of hydrology in nitrogen cycling, but also that they understand that they will need to capture the effects of hydrologic events with their sampling efforts.

In this two-part activity the students will be interpreting graphical data to understand better the seasonal changes in water movement through a watershed. They should use this information to being planning their field sampling “window”.

This activity will allow students to identify the watershed’s seasonal pattern by looking at how much water enters and leaves the watershed, and when. It uses online data sources for precipitation and stream flow from reliable sources.

The data—precipitation data and streamflow data—we are using come from two sources:

Precipitation data (including rain amounts, snow amounts and snowpack):

Comes from a database of precipitation data from the NOAA NCDC (National Oceanic and Atmospheric Administration - National Climatic Data Center)- the website is difficult to use. Use the existing data we’ve already downloaded and formatted, available below.

Streamflow data:

http://waterdata.usgs.gov/me/nwis/current/?type=flow You will access data for the stream-gaging site closest to your field site (see Lesson Resources for the instructions with screenshots:).

Look at your graph.

You can print or screen capture it.

  • See if you can see when big peaks in flow (discharge) were occurring.
  • Change the dates and look at least 2 other water years – do the peaks match up?
  • Can you see a big peak in spring, or are there lots of peaks in spring?
  • How different are the different years?
  • Now choose another site or two, and see if you can find times of the year that had big peaks in discharge.

Sites that are larger rivers tend to be shown on a logarithmic scale--be sure to have students take note when comparing to smaller streams.

There are example graphs in the Graph Packet in the supplemental materials.

You may need to explain some key terms to students before proceeding:

Hydrograph

A hydrograph is just what the word says: a graph of water flow rate. Specifically, it shows how much water is flowing past a point (called “discharge” and measured by the US Geological Survey in cubic feet per second-cfs).

You may want to have your students read:
http://ga.water.usgs.gov/edu/measureflow.html
http://ga.water.usgs.gov/edu/watercyclestreamflow.html
Water year

Why does our U.S. Calendar start on January 1? Not all calendars start there – the Chinese New Year is based on lunar cycles and is sometime in January-February; the Jewish New Year is usually in September. When thinking about yearly cycles in a watershed, it makes sense to pick a New Year that, well, has to do with water and not with human calendars. If you think about precipitation through the year, and streamflow that is related to that precipitation, you might realize that it’s usually driest in summer, and that there are wet periods in fall, winter, and spring. So, if we want to start the water “new” year at a time when the stream is likely to be at its lowest, so we can consider all the water that falls in a watershed within one year rather than having storms split across years, then our water year would probably start right after the summer dry period. Think about snowpack – if we had a water year start on January 1, it would probably mean that snow sitting on the ground from December, that stays put until it melts the next spring, wouldn’t be considered in the calendar year. So it’s logical to start the water year when it’s dry. By convention, USGS scientists begin the water year on October 1 each year. Water year 2012 runs from Oct. 1 2011 – Sept. 30 2012.

Snowpack

Snowpack is simply the accumulated snow that is sitting on the ground. Because it’s sitting there all winter, it can become compressed, some can melt, or some can blow away. It is useful for students to learn the difference between snowpack and snowfall (new snow from each storm) and begin to think about how snow changes as it sits on the ground – that it is temporary, and that changes in weather (like mid-winter thaws) will mean less stored snow in the watershed, and thus less of a streamflow spring pulse event. These types of changes in snow accumulation patterns are exactly what some climate scientists and water managers are worried about, particularly in places like California where most of the entire year’s drinking water comes from snow melting out of the mountains. What happens when the snow melts at different times – or simply doesn’t accumulate much but falls as rain? See: http://ga.water.usgs.gov/edu/watercyclestreamflow.html

Goals

  • Students will have a better understanding of the hydrological cycle of their watershed
  • Students will be familiar with snow and rainfall patterns in their area
  • Students will understand how precipitation that falls as snow is different from rainfall, specifically, that snow accumulates as snowpack and later melts, contributing water to a stream or lake in a pulse

Outcomes

  • Students will determine a target set of dates to collect stream water samples for their research, based on existing weather data

Where does this lesson happen in the Project?

This is the second activity in Unit 2: Watersheds in Winter. It follows Unit 1: The Nitrogen Cycle, and comes before designing a plan for sampling.

Getting Ready

To access and graph the data you will need computers and Internet access. You may want to download the snowfall and snowpack data (the .xlsx spreadsheet below) beforehand and put it in a class wiki, Moodle or Google docs spreadsheet. Review the nitrogen cycle (with seasonality) from Activity 1.

It is helpful to have identified a study stream, and to have either visited the site with the class or to have photos from the site. Students will need to understand what types of living and non-living things are within their study watershed.

Materials

  • Computers with Internet connectivity
  • Snowfall and snowpack data
  • Graph Packet
  • Question Sets

Handouts

If you do not have the time to explore the websites or make your own graphs you can use the Graph Packet in the Lesson Resources.
Question Sets

Student Prerequisites

  • Students should know that precipitation (rain, snow, sleet, hail) that falls in a watershed ultimately runs off and collects in a lake or stream
  • Students should be ready to look at datasets and work with data

Time Needed

1-2 class periods: One for Dataset 1: Reading a watershed’s ‘pulse’- inputs; one for Dataset 2: Reading a watershed’s ‘pulse’- outflow (hydrographs). You will find the data for “Taking the Watershed’s Pulse” at {site}.

* You may choose a few ways to approach the data acquisition, which will change how much time is needed, depending on your goals for the class.

Option 1 (more time) – teacher downloads data and prepares it for student use before class time.

Option 2 (less time) – use graphs we have already downloaded and formatted, at [Graph Packet web site], for 3 years at Bangor (precipitation, data table or pre-made graphs) and for the Bear Brook Watershed, Penobscot River and Narraguagus River (hydrograph).

You can move more quickly with these two dataset activities by breaking the class into groups and having some students work with precipitation data and others with streamflow data. At the end, have students come together to share results and see if having access to each others’ information gives a fuller picture of the water regime in local areas. Use the discussion questions to probe their understanding, or assign them as homework.

Doing the Activity

Dataset 1. Reading a watershed’s ‘pulse’- inputs

Download the dataset.

Using the columns DATE, SNOW, SNWD create a time series graph of snowfall (SNOW) and snowpack (SNWD) for water years 2008-2010.

Print your graph and answer the following questions:

  • Which year had the greatest snowpack? What was the biggest individual snowfall amount?
  • When was the snowpack peak in each year? How variable is the date of the peak?
  • If you had to bet on when the melt was going to happen this year based on these data, when would it be?
  • If you were the owner of a ski mountain, which year would probably have been the best for business? In which year did you have to close the earliest? Which year could you stay open the latest?
  • Which year had the earliest snowstorm? Which year had the latest snowstorm? Was the date of the earliest and latest storms as variable as the date of the snowpack peak?
  • If we assume that snowpack duration (the length of time it sticks around before melting) is mostly a function of temperature, then which winter do you think would have been the coldest? The warmest?
  • One of your samples for this project has to come from the time at or shortly after peak snowpack. If you were going to collect stream water samples at your site, and you wanted to collect the samples just after the time of peak snow pack, when snow is melting fast - when would you collect (it can be a range- a ‘sampling window’)?

Dataset 2. Reading a watershed’s ‘pulse’- outflow (hydrographs)

Go to: http://waterdata.usgs.gov/me/nwis/current/?type=flow

Choose a site near your study site, and a site that is a similar size river/stream to your site. Click on the site number you chose.

At the top, under the site name, choose “Time series: Daily data”. The screen will refresh.

Now scroll down – there is a blue box where you can change the graph you’re looking at, and a graph. The default graph shows discharge over the last year. In the blue box, leave the defaults EXCEPT change the dates to look at the last few water years – start with last year: Oct 1 2010 – Sept 30 2011

Look at the graph. You can print or screen capture it. See if you can see when big peaks in flow (discharge) were occurring.

Change the dates and look at least 2 other water years – do the peaks match up? Can you see a big peak in spring, or are there lots of peaks in spring? How different are the different years?

Now choose another site or two, and see if you can find times of the year that had big peaks in discharge. Sites that are larger rivers tend to be shown on a logarithmic scale. Be sure to have students take note when comparing to smaller streams.

 Print your graph and answer the following questions:

  • Based on the streamflow graph when do you think the big snowpack melt occurred? Was there a big snowpack melt event in each year?
  • If you had to bet on when the melt was going to happen this year based on these data, when would it be? Is that date similar or different from the date you chose using the precipitation data?
  • Looking at the snowfall and snowpack data, can you see any patterns that coincide with the runoff (discharge) events? Were they more closely matched in smaller streams or in larger streams?
  • What could be some of the factors that influence snowmelt timing at the different sites? If you use the examples given at the end, what could be different about the Narraguagus as compared to Bear Brook (note: they are in the same watershed) or about the North Branch of the Penobscot?
  • Knowing about the precipitation patterns in the same water years, what conclusions can you draw from the hydrographs? For example, how is the 2008 hydrograph different from 2009? Do the snowfall graphs explain any of the differences? What other information would you need?
  • One of your samples for this project has to come from the time at or shortly after peak stream flow. If you were going to collect stream samples at your site, and you wanted to collect the samples at the time of peak stream flow - when would you collect (it can be a range- a ‘sampling window’)?

Assessment

Formative

Pose the question: How will a rainy winter affect the spring pulse of nitrogen input into the streams?

Summary

Have students design a sampling plan to capture pre-snow through spring melt stream water samples to get a profile of nitrogen input to the stream throughout the winter.

Lesson Extensions and Supplements

Data literacy practice: Ice out data. Work with these time-series data to understand what time series can tell you.

Download USGS data and make graphs using data tables. Overlay precipitation and hydrographs, for more skilled graphing practice (coordinating the dates will the most challenging part).

Two snow-related activities for your students:

From Glacier National Park: How Much Water is in Snow? (pdf below)

From http://www.taiga.net/nce/schools/lessonplans/snowstudy.html: Conducting a Snow Pit study.
 

This Activity is included in: 

Handouts: 

Teacher Instructionals and Primers: