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Here is the dissolved
oxygen profile for Site 1. On
the Y-axis again is the depth down in the water column, starting with the
surface of the water at the top of the image. The darker blue corresponds to more dissolved oxygen, the
lighter blue corresponding to less Dissolved Oxygen. We are concerned with dissolved
oxygen for several reasons. One
is fish in are dependent on dissolved oxygen in the water to survive. Furthermore, anoxic conditions are
defined as less than 1 part-per-million oxygen, and once water reaches this
level, phosphorus, which I will talk about in a minute, is released from
sediments, which can have a large impact on water quality. For this profile we again see the
stratification of the water during with summer [Click to show box 1], and
then mixing in the fall causes the dissolved oxygen to become uniform in the
water column [Click for second box].
Another trend to notice for the dissolved oxygen is that as the
summer progresses, in the deepest parts of the lake, light cannot penetrate,
so there is no photosynthesis occurring, but respiration and decomposition
still occur, both of which deplete the oxygen further. And because of these conditions, we
can see anoxic conditions rising in the water column as seen here [Click to
show arrows]. One final point
is that anoxic conditions are seen as shallow as 6 meters down in the water
column, and I would like to show the area of the lake that could potentially
go anoxic during stratification of the water column. [Click for next slide].
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