Nutrients: Enough, but not too much

During the monthly Carpenter Creek monitoring, “citizen scientists” volunteer their time to take measurements of two of the main nutrients in the stream, nitrogen and phosphorus. Just like our gardens, or our bodies, the aquatic plants and animals need nutrients as building blocks for their cells and tissues.

The three main nutrients are carbon, nitrogen and phosphorus. These three, together with small amounts of micronutrients, make up the proteins, sugars and carbohydrates all life requires. However, just like our diets, it is possible for the amount of nutrients to be out of balance in the stream. So we measure nitrogen and phosphorous to keep tabs on whether there is an overabundance of nutrients in our stream.

The chemical form in which nitrogen and phosphorous will be found depend on other water quality parameters like pH, temperature and oxygen supply. Each can be found in several different forms in water. These chemicals can be bound up or released into the water depending on the water chemistry around them.

Typically nitrogen will be found as nitrate, nitrite, or ammonia. If there is too much ammonia it can be acutely toxic to fish or other organisms. Ammonia is the only nutrient for which the state has set a water-quality standard. The most useful forms of these nutrients for aquatic plants are soluble nitrate and phosphate. Most naturally occurring nitrogen and phosphorous come from the breakdown of plant or animal materials.

Salmon spawning in rivers are an important source of nitrogen. Most anthropogenic (man-introduced) nitrogen and phosphorous come from septic tanks, fertilizers, or other runoff from our lawns.

Nutrients are measured in all the freshwater sites (1, 2, 3, and 4 in the figure at left). Nitrate and phosphate measurements are done performing a chemical test where chemical reagents are mixed with the creek water in a test tube and the mixture is compared with a color chart. We do not measure these nutrients in the salt and brackish water sites (A, B, C, and D) at this time.

All the freshwater monitoring sites in Carpenter Creek currently exhibit healthy nutrient concentrations. They all appear to have some, but not too much. The measurements at all four monitoring sites typically exhibit approximately 0.25 part per million (ppm) of nitrate.

Phosphate has been measured to be between 0-1.75 ppm at Site 1, 0-1.5 ppm at Site 2 and approximately 1.0 ppm at Sites 3 and 4. While we have seen little change in phosphate measurements at Sites 3 and 4 over the measuring period, we have seen some change in phosphate at Site 1 over time.

In the early years (2001, 2002) phosphate measurements were typically 1.0 ppm. Since 2006, they tend to be greater than 1.0 ppm. While this value is not in itself of concern, we will need to watch this trend and see if we begin to see other changes in vegetation or land use near the stream that might be contributing to phosphorus loading.

Betsy Cooper is a board member and stream monitor at Stillwaters Environmental Education Center. She also serves on the Kingston Citizens’ Advisory Council.

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