Water temperature is one of the most important parameters in natural surface water systems. It is a measure of the amount of heat present in water. Temperature controls the metabolism of aquatic plants and animals and is largely responsible for biochemical reactions and many other processes. All aquatic organisms have preferred temperature ranges in which they can survive and reproduce optimally. High water temperatures can be caused by high ambient air temperatures and by industrial discharges. Water temperatures vary on a seasonal basis, on a daily basis and even throughout the day, warming in the daytime with cooling trends in the evening and overnight.
pH is the measure of hydrogen ion activity of a system. It is a major factor affecting the availability of nutrients to plants and animals. It partially controls the concentration of many biochemically active substances dissolved in water. The greater the hydrogen ion concentration, the lower the pH on a scale of 0-14 units. Typically the more pure the water the more neutral the pH (pH 7 @ 25 oC). Rainwater is slightly acidic (pH 6.5) while seawater is usually slightly basic (pH 8.5). The pH is influenced on a daily basis by the biological and geological processes occurring in the water body. These processes are strongly affected by the water temperature.
Conductivity is a measure of the ability of water to pass an electrical current. Conductivity measured at or corrected to 25 oC is called “Specific Conductance”. Specific Conductance is an indirect measure of the amount of dissolved substances (salts). The Specific Conductance may influence the toxicity of many substances. Typically the more pure the water the lower the Specific Conductance. Low Specific Conductance (0 to 200 µS/cm) is an indicator of pristine or background conditions. Mid range conductance (200 to 1000 µS/cm) is the normal background for most major rivers. High conductance (1000 to 10,000 µS/cm) is an indicator of saline conditions. Conductivity is temperature sensitive and follows the same trend as water temperature.
DO is probably the most important parameter in natural surface water systems for determining the health of aquatic ecosystems. It is a measure of the amount of oxygen dissolved in water. The concentration of DO is controlled by consumption by aquatic organisms, consumption by plants during darkness, production by plants during daylight, exposure (or lack of) by natural re-aeration (waterfalls, riffles) and water temperature, flow and depth. DO is strongly influenced by water temperature and varies throughout the day. Low DO levels (0-8 mg/L) are an indicator of high oxygen demand on the water and can result in fish kills (0-4 mg/L). High DO levels (12 to 20 mg/L) can be caused by excessive algal and macrophyte growth. Mid range DO levels (8-12 mg/L) are usually an indicator of a healthy system.
Turbidity is a measure of the extent to which light is either absorbed or scattered in water. It is a measure of the amount of suspended material in water. High levels of turbidity are aesthetically displeasing and can change the diversity of aquatic systems by affecting light penetration and photosynthetic reactions in streams and lakes. Increased turbidity can also affect water temperature and distribution of heat through the water column. It also negatively affects the disinfection of drinking water. Turbidity values are often 0 NTU for some pristine waterbodies.
Percent Saturation is the amount of Dissolved Oxygen (DO) in the water sample compared to the maximum amount that could be present at the same temperature. It is possible for water to be supersaturated and thus to have a DO percent saturation greater than 100 % due to excessive aeration of water (e.g. at waterfalls). Supersaturation and low percent saturation can both be harmful to aquatic life. Values less than 60% or over 125% are undesirable. DO percent saturation values in the range of 80-120% are desirable. The probe does not directly measure Percent Saturation, it calculates this from the measured DO.
TDS is a measure of all the dissolved solids in the water, organic and inorganic. It is an indication of the potential buffering capacity of water and water hardness. The probe does not directly measure TDS, it calculates TDS using the following algorithm equation from the conductance and temperature measurements:
TDS (g/L) = Specific Cond (µS/cm)*0.00064
Oxidation-Reduction Potential (ORP)
Oxidation-Reduction Potential (ORP) is a measure of the ability of the water to oxidize or reduce other substances in the water. Expressed in millivolts (mV), a positive ORP value signifies that the water has the potential to oxidize other substances, while a negative ORP value indicates the water’s ability to reduce or donate electrons. In essence, ORP measures the overall electron activity within the water, providing insight into its potential to support or undergo oxidation (loss of electrons) or reduction (gain of electrons) reactions. This measurement is significant in assessing water quality, understanding its ability to support life, and evaluating the presence of certain substances or contaminants that influence its redox state.