Why are nutrients (nitrogen and phosphorus) important?
Just as nutrients are important for land based plants and animals, phytoplankton and algae need nitrogen and phosphorus to grow. Aquatic organisms, such as menhaden eat only phytoplankton/algae for food. However, too much of a good thing is bad. If you overfertilize your garden, it dies. The same is true for the South River; too many nutrients cause an over production of phytoplankton and algae. The phytoplankton and algae uptake the nutrients, causing them to grow, and as they grow, they expand into a giant bloom, and the plants consume oxygen. Then when the phytoplankton and algae die, the biological decay consumes oxygen.
What causes high levels of nutrients?
Nitrogen comes from atmospheric sources, such as burning coal and other fossil fuels, as well as from human and animal waste, fertilizer, and the breakdown of organic material. Phosphorus is found in fertilizer, but it is also bound to sediment, so erosion of soil from construction sites or stream banks can often result in both sediment and phosphorus pollution.
Where do nutrients come from?
The nutrients in the South River watershed mostly come from stormwater runoff, leaky septic
and sewer systems, eroding stream banks, and fertilizers. Some nutrients are also recycled from
bottom sediments during low oxygen events.
When does this occur?
Rain events “wash” the nutrients into the streams and into the South River. Conventional septic systems are designed to “leak” nutrient into the groundwater, which eventually makes their way to the river. In some cases, sewer lines are antiquated and eventually break and leak, discharging nutrients into the groundwater as well.