1- Temperature

     All living plants and animals are affected by their surrounding temperature; they can exist and function within a preferred range. Of course weather and time of year strongly influence temperature. 

     In shallow streams like Yellow Creek, the summer sun can lead to stressfully high temperatures for some fish and macroinvertebrates.  Riparian vegetation, plants and especially trees, improves the habitat by shading the stream, leading to lower temperatures during the day and less day / night variation in temperature. 

     Temperature is also important for us because it influences other chemical and physical measures. 

2- Dissolved Oxygen

     All animals require elemental oxygen (O2) for respiration; therefore dissolved oxygen may be the most important of our tests. The mixing associated with moving water increases levels dissolved O2.  With its several hundred foot drop, Yellow Creek is an actively running stream. 

     As the temperature rises water can hold less oxygen.  Decomposition of organic matter can dramatically lower O2 values. 

     Our measured O2 values are close to saturation (their maximum values) and considerably higher than 5mg/l EPA minimum recommended value.

3- Turbidity

     Turbidity makes water cloudy; it is the opposite of clarity.  Because higher stream velocities are associated with higher turbidity, it tends to be high during and after storms as particles from the stream bed, runoff, and erosion mix with the water. Turbidity can also be caused by organic matter – algae and plankton. 

     Consistently high turbidity prevents sunlight from reaching deep into the stream, thus reducing the biodegradability of waste matter. Suspended particles causing turbidity can provide attachment points for some pollutants including metals and bacteria. Additionally, turbidity reduces the aesthetic value of the stream. 

     There are no national standards for acceptable levels of turbidity.  During a dry period in the summer, turbidity can be very low – less than 5 ntu units.  Under normal conditions Yellow Creek tends to be in the 0 to 15 range indicating good water clarity.

4- pH Level

     pH is a measurement of acidity and alkalinity of aqueous systems. A pH of 7 is neutral. A pH of 4 or lower is very acidic and a pH of 9 and higher is very alkaline; neither can support plants or animals.  pH affects solubility and biological availability of nutrients and heavy metals. 

     pH of a stream is strongly affected by the composition of the surrounding soil.  pH is lowered by rain, which has a pH of 5 – 5.5 in our area.  

     The EPA suggested stream pH range is 6.5 - 9; the optimal range for most species (and maximum biological diversity) is 6.5 - 8.  Our measurements show Yellow Creek to be at the high (alkaline) end of the normal range.

5- Conductivity

     The ability of water to conduct electricity is determined by the concentration of charged particles or ions it contains. Dissolved inorganic solids are the source of the ions. Dissolved organic materials do not ionize, and thus fail to contribute to conductivity. Conductivity in natural streams is primarily affected by the geology of the area. Granite bed rock is inert and leads to low conductivity. On the other hand, streams that run through clay soil have higher conductivity because components of the clay ionize when in contact with water.      

     Dissolved solids from pollutants such as road salt can greatly increase conductivity. Higher temperatures lead to increases in conductivity, as well. 

     Conductivity in US Rivers and streams usually runs between 50 and 1500 µs/cm. Streams supporting good fisheries range between 150-500 µs/cm.  EPA maximum conductance value is 2400 µs/cm @ 25°C.

     Our conductivity results show Yellow Creek to be in the mid-range of US streams, with values in the 600 to 1000 µs/cm range.  The stream bed composition is likely the main factor determining these values.