Notes on Dissolved Oxygen for Bluff Lake Nature Center and Achieve Academy 5th Grade
5/5/14 – Donny Roush, Earth Force
This is my summary about dissolved (DO) oxygen data from on and near Bluff Lake Nature Center, from
samples collected between November 2012 to May 2014. After reviewing the data collected by Achieve
Academy students and comparing it to other student-generated data from the last two years (from
Fletcher Intermediate and the Westerly Creek Corps), I conclude that DO in Bluff Lake, Sand Creek, and
Westerly Creek typically runs at about 50% saturation – or equivalent to 4 ppm for 28°C water, and
approximately double to ppm for readings in typical cold season temperatures. Such levels stress most
aquatic organisms and are generally below the range for survival of preferred, native species of fish. (If
we consider altitude and atmospheric pressure, the news gets a little better…we start with 80% of
saturation as that at sea level.)
The World Water Monitoring Challenge (the organization behind the kits we use) provides this
statement and table:
Dissolved Oxygen
Dissolved Oxygen (DO) is important to
the health of aquatic ecosystems. All
aquatic animals need oxygen to survive.
Natural waters with consistently high
dissolved oxygen levels are most likely
healthy and stable environments, and
are capable of supporting a diversity
of aquatic organisms. The saturation
percentage of dissolved oxygen is also
an important measurement of water
quality. Cold water can hold more
dissolved oxygen than warm water. For
example, water at 28°C will be 100%
saturated with 8 ppm dissolved oxygen.
However, water at 8°C can hold up to 12
ppm of oxygen before it is 100%
saturated. High levels of bacteria or
large amounts of rotting plants can
cause the % saturation to decrease.
This can cause large fluctuations in
dissolved oxygen levels throughout the
day, which can affect the ability of
plants and animals to thrive.
W
Highest readings for DO are:

8 ppm on 2/21/13 by Fletcher Intermediate (water temp was 2°C, which is 58% saturation)


6.4 ppm on 7/19/13 by the Westerly Creek Corps (on Westerly Creek in Lowry; water temp was
27°C, which is 80% saturation; measured using titration method which is more precise and
accurate)
Please add Achieve’s data here. I am not recalling anything higher than 7 ppm, and most in the
4-5 ppm range.
Even being cautious considering the World Water Monitoring tests are not highly precise or accurate, I
feel confident in saying that DO is depressed in our waters. (As always in these situations, more data
would be helpful. More data collected using more accurate and precise methods, plus some sets of
hourly data for several days would help us better understand current conditions.)
What might be some plausible causes of oxygen depletion? What can we do about it?
The standard line for low DO is: “Organic pollutants come from the decomposition of once-living
organisms, either plants or animals, and their by-products. Grass clippings, leaves, human sewage, and
pet wastes are all examples of organic pollution.” (from Mitchell and Stapp [2008], Field Manual for
Water Quality Monitoring [13th ed.], p. 26) Across the Denver-Aurora metro, vertebrate fecal waste is
the largest putative contributor, with fertilizers also indicated.
Some management techniques, which might also be student action projects, that can positively affect
DO levels include:
 Conduct a more in-depth study of DO as well as biological oxygen demand, to get a better grip
on factors depleting the O2. Likewise, if you ever have the resources, getting a characterization
of the mud at the bottom of lake could show if it is serving as a storehouse for excess nutrients.
 Plant more (eventually) overhanging trees, willows, and, maybe, some emergent aquatic plants.
When you help lower temperature, DO usually improves as well. Similarly, if you get a pool
established in the lake that is perennial, you might consider inoculating it with some healthy
algae. They raise DO every time the sun shines and they photosynthesize.
 Removal of any algal blooms in the lake, before decomposition starts. (This would be a late
summer issue most likely.) Removal of accumulated plant material in the creek, before
decomposition really ramps up in summer. (This would be a reason to keep clearing the debris
from the floods.)
 Sharing information and coordinating efforts with Aurora Parks, Recreation and Open Space,
especially the Fitzsimons Golf Course grounds and turf managers, and Aurora Water’s
stormwater education efforts. An idea would be to produce a brochure for residents in the area
that drains into Bluff Lake, and distributing those along with, dog cleanup bags and/or a car
wash coupon.
Thinking about your lotic system (Sand Creek) and your lentic system (Bluff Lake), different approaches
might help more one than the other. As you make the dam repairs and become better able to keep a
pool of water in the lake, a portable aerator might be a good investment. Last summer with the
Westerly Creek Corps, we sampled a private stormwater retention pond (because an original sampling
site on the creek had been obliterated) and found it had consistently higher DO than the creek. There
was a portable aerator in the pond. (See picture…it is the blue thing on the shore behind the kids.)