Nutrient Load Module

Thomas Meixner, The University of Arizona
Author Profile


Estimating nutrient loads is a critical concept for students studying water quality in a variety of environmental settings. Many of these students will be asked to assess the impacts of a proposed anthropogenic activities on human water resources and/or ecosystems as part of their future careers. This module has students explore factors contributing to the actual loads of nitrogen that are transmitted down streams. Nitrogen is a key water quality contaminant contributing to surface water quality issues in fresh, salt and estuarine environments. Students will utilize real-time nitrate data from the US Geological Survey to calculate nitrate loads for several locations and investigate the interplay of concentration and discharge that contributes to the calculated loads.

Intended Audience

This module is intended for introductory to mid-level, Earth Science, Biological Science and Environmental Science students. It is helpful if students have a little knowledge of chemistry. It will also be useful for the students to understand the fundamentals of the hydrological cycle prior to this module as runoff plays a key role in the interpretation of the results. The Excel skills used in this activity involve using equations, summations and averages.

Conceptual Learning Outcomes

● Analyze and interpret data to deepen knowledge and increase understanding of hydrogeological concepts and nitrogen cycling in aquatic systems in the context of increased nutrient availability.
● Explore advantages and disadvantages of different ways to investigate, sample, and quantify nutrients in aquatic systems.
● Develop skills for critical data analysis, graphing, and statistics.

Practical Learning Outcomes

Student will develop a pragmatic understanding of dealing with large water quality data sets to calculate means and loads.

Student Time Required

3-5 hours

Supporting Reference Documents and Files

Teacher Handout (Microsoft Word 2007 (.docx) 18kB Jun30 16)
Student Handout (Microsoft Word 2007 (.docx) 2.4MB Jun30 16)


Part A (Lecture and background - 1 hour)
Students will learn background of nutrient issues in surface waters and learn about concentration, discharge, their relationship and the calculation of load from their multiplication.

Part B (Calculations and Graphing - Concentration Discharge -1 hour)
Students will learn to access USGS data sets using either NWIS or CUAHSI's Hydro Client and learn to combine concentration and discharge data to investigate nutrients loads from agricultural systems in Iowa. They will learn to graph the data as time -series and X-Y plots as well as investigate calculations that can be made with these data.

Part C (Calculations and Graphing - Concentration Discharge - 1 hour)
Students will learn to quantify correlations between the two variables at different time scales and in different ways using both graphs and statistical correlations.

Part D (Calculations of load - 1 hour)
Students will learn to calculate loads of nutrients exported from a catchment and compare an upstream and a downstream catchment to see how concentration and discharge change along with nutrient load with distance downstream.

Part E (Sample Frequency- 1 hour)
Students will learn to calculate loads of nutrients exported from a catchment with varying sample frequency. It is rare to have high frequency data like the ones used in the earlier parts of this module. In this exercise students will work with desampled data to investigate the effects of sample frequency on the calculation of nutrient loads.

Steps within this lesson


    Assignment should be graded on an equal basis across the parts. Assessment should focus more on students grasp of fundamental concepts versus specific correct calculations.