Watersheds in Winter

By the end of this Unit your students will understand how seasons affect nitrogen cycling.

Unit Overview

Now that students have a general sense of the nitrogen cycle, they will begin to think about how nitrogen moves in a watershed like their study site(s) and will begin to consider how changes in season can result in different patterns of nitrogen in a stream.

How does the nitrogen cycle fit with the seasonal cycle? Scientists have begun studying how the cycles of different elements and nutrients – like nitrogen – might be affected by changes in climate that we observe in hydrologic measurements. For example, scientists at Hubbard Brook Experimental Forest have studied how the lack of snow might affect freezing of soil (see: http://www.springerlink.com/content/r2x28228u41424p3/).

In the case of this project we are interested in the seasonal timing of snow-related hydrology events- first snowfall, deepest snowpack, snowmelt, and the spring freshet—snowmelt running off into streams and lakes. The research you are doing will help scientists begin to understand how changes in snow accumulation and the timing of snowmelt will affect nitrogen patterns in streams, a topic that has only recently been studied in a few sites.

What is hydrology?

Simply put, hydrology is the study of water – how it moves, where it is, and its quantity and quality (See http://ga.water.usgs.gov/edu/hydrology.html).

Activity 1 is a general opening up of the topic of seasonal changes in a nutrient cycle. In Activity 2 we will look at two aspects of how water moves- precipitation and stream flow.


Weather and climate affect more than just air temperature. Weather and climate-related changes in precipitation, snow, and temperature can affect how nutrients, like nitrogen, move through a watershed. Students need to think of a watershed as a system with connections among living and non-living components and feedbacks, and that the watershed as a system affects the movement of nitrogen through its cycle—and vice versa.

This unit introduces seasonally related hydrology and logically includes a frequently overlooked dimension – time – which adds to the system view by highlighting the idea that biogeochemical inputs and outflows are not static.  Students should think of a stream as an expression of all the processes that happen within the watershed – put simply, what happens in the watershed affects the stream.


Students understand that:

  • There are seasonal elements to the N cycle
  • Location and weather are important drivers in the N cycle
  • Nitrogen cycles globally, but also locally

Additionally, students read information from graphs

Instructional Strategies

Activity 1: ‘A watershed for all seasons’ is a discussion

Activity 2: ‘Linking hydrology to nitrogen in streams’ involves making and interpreting graphical data (time series).

You may want to practice interpreting time series with your students.