|Team Members:||Rosemary K. Le1,
Christopher V. Rackauckas2,
Anne S. Ross3,
and Nehemias Ulloa4 |
|Graduate Assistant:||Sai K. Popuri5 |
|Faculty Mentor:||Dr. Nagaraj K. Neerchal5 |
|Client:||Dr. Brian R. Smith6 |
The Chesapeake Bay and its surrounding tributaries house over 3,600 species of plants and animals. As the largest estuary in the United States, the Chesapeake Bay serves as a valuable commercial and recreational resource for the people who live in its basin. In order to assess its health, the Maryland Department of Natural Resources monitors various parameters such as dissolved oxygen, turbidity (a measure of water clarity) and chlorophyll (a measurement to estimate algae growth) in monitoring stations located throughout the bay and its associated tributaries.
While percent failure is one indicator of a station's performance, statistical tests take inaccuracies and missed readings into account. We employed the Wilcoxon Signed-Rank Test to classify each continuous monitoring station as "Good," "Bad," or "Borderline." The Wilcoxon Signed-Rank Test is a non-parametric test that compares the median of two populations (in this case, the readings of one station against the failure threshold). When using the test, one assumes that the population from which samples are drawn is symmetric. If this is not the case, i.e. the data is skewed, the true Type I Error may be inflated. Our simulation study (using Γ(α,β) to cover a wide range of skewness values) shows that log-transformation substantially reduces the Type I Error.
Oxygen (5mg) | Ranks of monitoring stations with respect to percent failure:
the Tukey Test (TT), the Bonferroni Test (Bonf),
Benjamini Hochberg Method (BH), the Bayesian Ranking Method (BRM).
|Station Name||% Fail||TT||Bonf||BH||BRM|
|Havre de Grace||0||2||1||1||2||2|
This table is an example of the results of running our various ranking methods for all parameters. It is a portion of the dissolved oxygen with the 5mg/L threshold ranking table. The stations are listed in order of increasing percent failure in dissolved oxygen, that is listed from fairing best to fairing worst. The second column gives this percent failure. The following columns show a segment of the rankings assigned, each column being a different method. From this and similar tables we created, we can see that the Benjamini-Hochberg was most useful because it shows ties in the ranking without being too conservative. The Bonferoni method was too conservative and thus resulted in many ties whereas Tukey's Test was quite the opposite and had little to no ties. Although the Bayesian Ranking method does not have any ties, it is still useful because the probabilities of the rankings are not uniform. This means that the posterior probabilities between rank 1 and rank 2 are not necessarily the same as the posterior probabilities between rank 2 and rank 3.
This project also included creation of GUI to make graphs of the data easily accessible, providing scientific researchers and the general public a powerful tool to aid in understanding Maryland's tidal waterways. The GUI was developed using the R statistical package. However, there is no installation of R required in order to run this GUI, one must simply unpack the compressed folder and then there will be an executable able to run the specifed GUI. The GUI has three modes: