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March 1, 2020

Water Quality Measurements

Thanks to the virtual environmental club from Friends of Atwater Park in Los Angeles, CA, we have this link to more terms about water. Thank you Mariah!


Oxygen is a critical necessity for life. In aquatic systems oxygen is found in the form of dissolved oxygen (DO) and without it, the fish, crabs, and oysters cannot survive. Low dissolved oxygen concentrations can lead to reduced growth, reproduction rates, a change of the distribution and behavior patterns of the aquatic organisms, as well as death. For more information, click here.


Water Clarity is the measurement of how far sunlight can pass through the water column. Sunlight is one of the key elements needed for underwater grass to grow. When the water column’s clarity is reduced, the underwater grasses do not receive the sunlight necessary for growth. Excess sediment is the leading factor for the South River’s poor health. For more information, click here.


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 Rivers; 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 Rivers 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 Rivers. 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.


Salinity measures the amount of dissolved salts in the water. The Chesapeake Bay has a wide range of salinity. Up north where the Bay is fed by freshwater rivers like the Susquehanna, the salinity is as low as 0.5. By the time you reach the mouth of the Bay down in Virginia, the salinity can be as high as 30. The middle of the bay is considered brackish which is used to describe waters that are a mixture of fresh and salt water.

Salinity not only varies by location, but by time of year and depth as well. The Bay has a higher salinity during drier months and a lower salinity during the wetter months, especially after the winter snow melts and the spring rains. Salinity also increases with depth because the less dense fresh water remains on the surface.

Many plant and animal species are limited by the different salinity ranges so depending where you are in the Bay, you will be able to see different flora and fauna.


Temperature is more than just a number! Temperature is an important water quality parameter because it influences both biological and chemical characteristics of the water. Temperature impacts dissolved oxygen levels, rates at which algae and other plants photosynthesize, metabolic rates of organisms, and bacterial growth. Warmer temperatures tend to be associated with the most problems which is why summer often brings a decline in water quality.

Temperature directly affects dissolved oxygen levels. The relationship is inverse; as temperature goes up, dissolved oxygen goes down. Chances are you have heard the term “dead zone.” Dead zones occur when the dissolved oxygen levels become too low to sustain life. These occur most frequently in the summer because warmer water is less capable of holding dissolved oxygen than cooler water.

The metabolic rate of aquatic organisms is also increased when temperature increased. As their metabolic rate increases, their bodies need more oxygen. At the same time, the increased temperatures are decreasing the water’s capability to hold dissolved oxygen creating stress on the organisms. Additionally, temperatures that are too low or too high can make an organism more susceptible to pollutants and diseases caused by bacteria, parasites, and viruses.

In addition to the changing seasons, other factors can influence temperature. Turbidity increases the amount of heat that is absorbed from sunlight which is one of the reasons we care so much about water clarity. Thermal pollution also influences temperatures. In the South River watershed, most of the thermal pollution comes from stormwater runoff whereas other rivers may be impacted by thermal pollution from power plants. On hot days, stormwater heated up by impervious surfaces such as roads and roof tops before being carried directly into our waterways.


Why is pH important?
This year’s new indicator is pH. Measuring pH and alkalinity in the South River and throughout the South River watershed are important to understanding its overall health. Since the pH of water is critical to the survival of most aquatic plants and animals and alkalinity is a measurement of the water’s capacity to neutralize acids, monitoring pH is vitally important. Substances with a pH of less than 7 are acidic, and those with a pH greater than 7 are basic.

What causes pH changes?
Biological activity can significantly alter pH in the South River. Through a process called photosynthesis, plants remove carbon dioxide (CO2) from the water and expel oxygen (O2). Since CO2 becomes carbonic acid when it dissolves in water, the removal of CO2 results in a higher pH, and the water becomes more alkaline, or basic. When algae naturally begin to increase in estuaries during the spring, pH levels tend to rise. An overabundance of algae (called an algal bloom) may cause pH levels in the river to rise significantly, and this can be lethal to aquatic animals

Where has this been occurring?
The increase in pH peaks shortly after the chlorophyll and/or blue-green algae blooms.

When does this occur?
These increases in pH have generally been occurring in the late spring through the summer, however due to the high nutrient concentrations and climatic events, blooms have also been occurring in the fall and early winter. The impact is that aquatic animals which can only live in a narrow pH range are stressed or killed by the fluctuations.