Frequently asked questions from monitors:

Why does cold water hold more oxygen than warm water?

Warm water allows for larger spaces between water molecules where oxygen can readily escape. Where as, cold water is more closely packed together with smaller spaces between molecules holding oxygen tighter. (see illustration below)


Is the oily film in my stream pollution or natural?

Oily films can often be seen on the surface of stream water, almost always at the edges of the stream or in pools where the water is not flowing.  This film looks shiny, appears oily and may appear to have the colors of the rainbow.  Commonly this sheen is mistaken for petroleum products that may have entered the stream.  While petroleum can make a film on the surface of water, more often than not this film is composed of bacteria.  The bacteria may be from two causes; organic breakdown of decaying plant material or, from bacterial breakdown of iron and manganese present in soil or ground water.  Bacteria are part of the natural breakdown of organic matter and minerals in the water.  Often the bacterial film will overlay mats of decaying leaves in the water.

How to determine whether it is petroleum or bacteria

Take a stick and gently stir the film on the surface.  If the film breaks up into pieces and appears as islands of film, it is bacteria.  When passing a stick through petroleum products in water, they will not break up.  As the stick passes through, the sheen will stay together and will not break apart.   

When measuring stream discharge how close to my riffle should we be?

It is not necessary to be close to the riffle you monitor for macroinvertebrates. It is best to measure stream flow in a run, an area of flowing water that is relatively straight, free from obstructions such as fallen tree limbs and large boulders or gravel bars. You may measure stream flow outside of your 300 ft. monitoring area if necessary.

When measuring stream discharge what should we do when the wind is blowing the ball backwards?

When the wind is blowing a cross the surface of the stream it is difficult to get an accurate velocity measurement. Look for an area that is sheltered from the wind.  If none can be found, it may be necessary to wait to measure stream discharge on a calm day.


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