Water Quality Parameters & Standards

Alkalinity is a measure of the acid buffering ability of a water sample. The main chemical agents responsible for buffering are carbonate (CO32-) and bicarbonate (HCO3-). If acid (H+) is put into the sample, the following buffering reactions occur:

H+ + CO32- = HCO3-

Then when all of the carbonate is gone (pH will be below 6 at this point):

H+ + HCO3- = H2CO3

Other negatively charged compounds can act as buffers, such as borate, nitrate, organic acids, but are present at such low concentrations as to be relatively insignificant.

As mentioned above in the pH section, alkalinity is important to measure as it quantifies the ability of a water body to resist acidification. Alkalinity is measured by measuring the amount of acid required to lower the pH of a water sample to a value of 4.5, the point at which all of the carbonate and bicarbonate buffers have been exhausted. The concentration units are mg Calcium Carbonate (CaCO3) per liter of water or ppm CaCO3. Typical river water values range from 5 to 15. Values above 15 indicate high total dissolved solids levels associated with stormwater runoff.

The US EPA uses the following categories to classify water bodies by their alkalinity:

Classification Alkalinity (ppm CaCO3)
Acidified Less than or equal to 0 and a pH lower than 5.0
Critical Greater than 0 and up to 2
Endangered Greater than 2 and up to 5
Highly Sensitive Greater than 5 and up to 10
Sensitive Greater than 10 and up to 20
Not Sensitive Greater than 20

Chlorophyll is a measure of the concentration of suspended phytoplankton. Phytoplankton can be used as an indicator organism for the health of a body of water. Monitoring chlorophyll levels is a direct way of tracking algal growth.

Surface waters that have high chlorophyll conditions are typically high in nutrients, generally Phosphorus and Nitrogen. These nutrients can cause the algae to grow (bloom). When algal populations bloom, then crash and die in response to environmental conditions, dissolved Oxygen levels may be depleted, a primary cause of most fish kills. High levels of nutrients can be indicators of pollution from man-made sources (e.g., septic system leaks, inefficient wastewater treatment plants, fertilizer runoff). Thus, chlorophyll measurement can also be used as an indirect indicator of nutrient levels.

Color is a measure of the natural absorbance or color of a water sample. Natural color is usually the result of high concentration of relatively large molecules of dissolved organic matter usually referred to as humic material. Our rivers have high concentrations of these compounds and thus are highly colored. Color is measured relative to a platinum-cobalt standard and the reporting units are “PtCo units”. Typical river water ranges from 180 to 250 PtCo units. Values below 180 are observed immediately after large rain events which dilute the river water. Values greater than 250 are observed following floods or high enough water so as to submerge adjacent swamps. This water leaches organic matter out of the swamps and the water eventually drains back into the river.

Conductivity is a measure of the amount of dissolved solids which are primarily ions. Meter detects the amount of electricity that is conducted by the water sample. The larger the amount of ions the greater the amount of electricity conducted and hence conductivity of the sample. Units are µΩ⁄/cm or µS⁄cm. Values typically range from 40 to 140 in the river. Sites greatly impacted by stormwater (runoff which contains high levels of dissolved solids) have values as high as 600.

Dissolved Oxygen (DO) is a measure of the amount of elemental oxygen which is the form required by animals and aerobic bacteria. The meter uses an oxidation-reduction reaction to detect the presence and quantity of oxygen. Units are parts per million (ppm) of O2 or milligrams of O2 per liter of sample.

Dissolved oxygen values are extremely temperature dependent as solubility increases with decreasing temperature. Since the atmosphere is about 21% O2, atmospheric O2 is available to dissolve into surface waters to a level dictated by the temperature-controlled solubility. O2 concentrations less than this are observed when animals and aerobic bacteria are utilizing O2 in large amounts during aerobic respiration of organic matter (and ammonium for nitrifying bacteria). O2 concentrations greater than the solubility values are observed when plants are producing O2 via photosynthesis. The concentration of O2 relative to its solubility value is expressed as a percent saturation (O2 concentration observed/O2 solubility concentration x 100).

In the Waccamaw River, water values vary from 40% (4 ppm) in the summer to 80% (8 ppm) in the winter, reflecting the high concentration of dissolved organic matter which supports a lot of bacterial respiration year round. Waters with heavy algal growth (usually related to nutrient pollution) can have percent saturations as high as 200%! The state’s DO limit is 5 ppm for the Waccamaw River. Values less than this are observed for most of the summer. Fish are said to experience stress at DO levels less than 6 ppm.

Coliform bacteria are always present in the digestive tracts of animals, including humans, and are found in their wastes. They are also found in plant and soil materials. The most basic test for bacterial contamination in water is the test for total coliform bacteria. Total coliforms include bacteria that are found in the soil, in water that has been influenced by surface water, and in human or animal waste.

Total coliform counts give a general indication of the sanitary condition of a water supply. Fecal coliforms are the group of the total coliforms that are considered to be present specifically in the gut and feces of warm-blooded animals. Because the origins of fecal coliforms are more specific than the origins of the more general total coliform group of bacteria, fecal coliforms are considered a more accurate indication of animal or human waste than the total coliforms.

Escherichia coli (E. coli) is the major species in the fecal coliform group. Of the five general groups of bacteria that comprise the total coliforms, only E. coli is generally not found growing and reproducing in the environment. Consequently, E. coli is considered to be the species of coliform bacteria that is the best indicator of fecal pollution and the possible presence of pathogens.

The US EPA recommends measurement of E. coli as an indicator of pathogen presence in freshwaters and a water quality standard of 235 CFU/100 mL for single samples. Waters that have values greater than this are considered to be polluted, with swimmers being at increased risk of contracting gastroenteritis.

Typical Waccamaw River water nitrate (NO3-) values range from 0 to 0.2 mg N per liter of sample (or ppm N). Concentrations greater than 1 ppm N are usually the result of stormwater runoff associated with sewage or fertilizers. The degradation of sewage generates dissolved nitrogen as nitrate and fertilizers contain nitrogen as nitrate. High nitrate levels can stimulate algal growth and lead to eutrophication. Ammonium and nitrite are the other products of the nitrification.

The simplest way to denote nitrification would be as follows: Dissolved organic matter nitrogen ==> Ammonium ==> Nitrite ==> Nitrate. Nitrite is the most unstable as compared to the other forms of nitrogen and therefore, reads zero in almost all of our field measurements.

pH is a measure of the acid content of the water sample.

Typical river water values range from 5 to 7. Sites with high conductivity often have a pH as high as 8.2.

Acidification of natural waters is a result of acid rain entering waters with little buffering ability (see Alkalinity). Local industries and the power plant contribute to this as well. Fish experience stress at a pH below 5.

Phosphorus is an essential nutrient for the plants and animals that make up the aquatic food web. Since phosphorus is a nutrient in short supply in most fresh waters, even a modest increase can, under the right conditions, cause undesirable consequences including algal blooms and low dissolved oxygen.

There are many sources of phosphorus, including soil and rocks, wastewater treatment plants, and runoff from lawns and agricultural lands. Monitoring phosphorus is challenging because it involves measuring very low concentrations down to 0.01 milligram per liter (mg/L) or even lower.

TDS is a measure of the total dissolved solids that are present in the water. Most of these solids are dissolved salts, such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, and sulfate. It is computed from the conductivity measurement. High values are indicative of the presence of groundwater or mine drainage. Low values typically occur after rain flows freshwater into the river. There is no water quality standard for TDS.

Temperature is a measure of the heat content of the water sample. Typical river values range from 5 to 28 oC. High temperatures are stressful to aquatic life and can be caused when water bodies are partially filled making them shallow and when shading vegetation is removed. The conductivity, pH and DO meters all have temperature sensors because of the need to make temperature corrections during the measurement of these parameters.

Turbidity is a measure of the particle content of the water sample. The turbidity meter used for the measurement detects the amount of light reflected by the particles. Results are reported as nephelometric turbidity units or NTUs. 

Typical river water values range from 5 to 10. Values in excess of 10 indicate a soil erosion event. High particle concentrations stress fish and filter-feeding microorganisms because they clog their gills. High particle concentrations also affect the bottom-dwelling organisms as the particles settle out and blanket the river bottom.