CE/NR797 Lab Report: Water
Chemistry
[Prepared by R.
Fortner for ˇ§Digital and Field Techniques for Coastal Environment
Studies,ˇ¨ 7/02]
You may work together to learn the techniques for the display of
data, but please submit an individual interpretation of your
results.
Results
1. One objective of the analysis is to compare the water
temperature and dissolved oxygen over time, and relate that to position in the
lake. Demonstrate as GIS layers with georeferenced points of data for the same
depth, say 1 m and 2m in the Bay and 1m, 2 m and bottom measure in the Lake.
The bottom one is important. Please find a way to use it or at least scatter
graph it by depth.
2. A second objective is to identify relationships between any of the
variables of secchi depths, conductivity, plankton density, and phosphate
concentration. This sounds like a spreadsheet task with graphs or relational
statistics. Common sense would suggest that some variables determine the
transparency of the water, and some determine the amount of photosynthesis.
See what you can find with statistical correlations, plots of two variables on
the two axes, or other creative manipulations. Attach your work. Does the
photometer reading relate to any of the changes you observed?
3. Plot the total depth of the stations on a map of the Bay and Lake areas
monitored. Draw isolines for depth as much as possible from your data
(Bathymetry lines are unlikely to be completed; just use the data you have or
can interpolate). How close do the class data points match the published
information on depth? Rank the sources of error in order of their impact size.
Analysis
and Discussion
General
Which data collection area (Bay or Lake) is likely to have the most
reliable readings? What is the basis of your answer?
Which variables have the greatest sources of error? Describe the main
sources, and evaluate their impact on the credibility of your measurements. In
light of the error sources, was this lab a waste of time? Explain.
Temperature
and DO
What would you tell someone who asks you if this section of Lake Erie is
developing a "dead zone" like the historic one in the Central Basin?
Describe the pattern of
- DO with depth
- Temperature with depth
- DO with temperature
What does the use of GIS contribute to your understanding of the depth
relationship of these variables? To what extent does the tool have value in
explaining the pattern or process you have observed?
Water transparency,
phosphate and plankton relationships
Make a chart or web that shows the relationship between incident light,
secchi readings, conductivity, phosphate concentration, and plankton density. It
can be a simple concept map, or a flowchart with correlation stats written on
the arrows, or other means of showing the strength and direction of the
connections.
Look at a map of land use in this section of Lake Erie. What are the main
locations and types of activity that are contributing phosphates to the lake?
Examine past phosphate concentrations in the region from the literature and
compare this summerˇ¦s measurements. What changes have occurred that may
account for the differences?
Nitrate concentration
Describe the pattern of nitrate change over time in samples from the city
dock. What would you expect to see as nitrate levels in water from other places
(such as the can buoy or Gibraltar dock) and at other times (such as early
spring or a different part of the day)?
Speculate on the source of nitrate in the samples. Nitrogen can enter the
lake in a number of forms. What was the probable form of this measured quantity
ˇV N2 gas, a nitrate salt, ammonia, or what?
Nitrate is not a limiting factor for the algae in Lake Erie but phosphate is.
Read about and discuss the relationship of algae types and nutrients in the
lake.