Nutrients are chemical compounds that are used for growth and for maintaining life.  The three nutrients that are needed in the largest quantities for plant growth include nitrogen, phosphorous, and potassium.  They are referred to as primary macronutrients.  Other nutrients such as calcium, magnesium, sulfur, and zinc, are needed in smaller quantities and are usually referred to as secondary macronutrients or micronutrients. Plants get their nutrients from the soils that they grow in.  Some nutrients may be there naturally from the minerals found in the soil, rock, or decaying plants.  If there are not enough nutrients existing in the soil to meet plant growth goals, we can add nutrients with materials like synthetic fertilizers, manure, or compost.  Like people, plants can only consume a limited amount of nutrients at one time and will need to have nutrients available to feed them throughout their life.  Luckily, healthy soils can hold onto nutrients so that plants can use them throughout the growing season.  You can think of soil particles as tiny magnets that chemical compounds are attracted to so that they can be taken up by plant roots later on. 

Sometimes nutrients will not stay where you put them.  Nutrients can move off-site and end up in waterbodies in two major ways.  First, if we apply too many nutrients to the land, the soil will not be able to hold onto all of them, and the extra nutrients can be dissolved and carried away more easily by water – either in surface runoff or leaching.  The other major way nutrients can be lost is through erosion.  Erosion is the process of wearing away and moving soil by natural forces, like when there is a heavy rainfall and water runs off of and washes away the soil surface. This is especially the case for bare soil.  If soils are allowed to erode, they will carry adsorbed nutrients and deposit them into our waterways, resulting in both sediment and nutrient pollution.  According to the Pennsylvania Department of Environmental protection, erosion and sedimentation is the primary way that nutrients end up in our waterways.

Once nutrients get into our streams, rivers, lakes, and ponds they begin to cause problems.  Waterways with excess nutrients go through a process called eutrophication.  Eutrophication is initiated by excess levels of nitrogen or phosphorous.  Typically, phosphorous is the most limiting nutrient in our freshwater systems, meaning that there are plenty of other nutrients and the total amount of plant growth is controlled by the amount of phosphorous in the water.  If even a little extra phosphorous gets into our waterbodies, more plants can grow because they have everything else that they need.  The plant that tends to grow first is algae and one of the most obvious signs of eutrophication is the excessive growth of algae, referred to as an algae bloom.  Algae grows quickly, shading out and killing plants below.  Eventually, plants and algae die and decay, which uses up the dissolved oxygen in the water creating dead zones which can eventually lead to fish kills.  Another potential outcome from eutrophication are harmful algae blooms, which occur when specific types of cyanobacteria bloom and have the potential for producing toxins that threaten the health of humans and animals. 

There are many things we can do to prevent nutrient pollution in our waterways.  It is best to always soil test before applying fertilizer, manure, or compost and make sure not to apply more nutrients than the soil test recommends.  Extra fertilizer is not only a pollution problem but is also a waste of money.  To make sure you are applying the correct amount of an amendment, read the labels on synthetic fertilizers or have manure or compost tested by a lab so that you know the nutrient content of what you are applying and can apply it based on the soil test recommendations.  Preventing erosion by keeping soil covered with vegetation or mulch will protect it from washing away and carrying nutrients with it.  In settings with steeper slopes, additional erosion controls may be needed to prevent mulch from washing away.  Finally, reducing stormwater runoff in our communities can lessen the overall amount of nutrients being carried to our streams.

If you have additional questions about stormwater, or you are just interested in learning more, you can find a full series of videos and articles in the Penn State Extension Stormwater Basics series. Article compliments of PSU extension. Author: Danielle Rhea Extension Educator