Were there differences between the water surrounding the rooted plants and water in the open part ...

You would expect the shallow water near the rooted plants to be warmer than the
water of the open areas unless you live in a part of North America where the air
temperature is warm during most of the year. In southern Florida, California, and
Texas, the air temperature tends to produce lakes that are permanently stratified
(warmer water on the top and cooler water on the bottom). Thermal stratification
can produce very warm open water areas in a lake. The fish in such a lake will be
confined to the cooler water, which holds more oxygen. The dissolved oxygen and
pH of the water will also vary according to the time of day the samples were taken
(see Figure 17-3 in the lab manual). The dissolved oxygen will vary in different
portions of the lake or pond in relation to the number of aquatic plants, including
algae. Plants tend to increase the oxygen content of the water. The exception arises
when the concentration of algae is so great that they use all the available dissolved
oxygen as rapidly as they produce it.

The optimal water for fish production varies according to the species of fish. Trout
and salmon need cold water in contrast to Tilapia and catfish, which prefer warmer
water. Trout and salmon prefer water with a higher dissolved oxygen content
warmer water holds less oxygen than cooler water. Good light penetration indicates
a lower level of suspended solids in the water than poor light penetration. Fish do
not grow well in silty water. Suggest that your students work in small groups. Assign
each group a commercial species of fish to consider when answering the questions
in this lab exercise. Hopefully, your students will come to the conclusion that the two
sites that you have selected might be each suited for the production of a different
species of commercial fish.

All things considered, light should penetrate farther in the sunny areas unless there
is a floating algal mat or other floating aquatic vegetation in the sunny locations. In
the shaded areas, the amount and intensity of the light striking the surface of the
pond or lake are greatly reduced. The water may have greater clarity because algae
will tend to congregate in areas with enough light to support photosynthesis. If the
area that you selected for your students to sample is close to the place where a
stream, creek, or river enters the pond or lake, the results you obtain may be highly
variable. Streams with a high velocity may be carrying a high sediment load, which
will reduce the depth to which light penetrates in the area where the water enters
the lake.