An Ecological Assessment of the Louisiana Tensas River Basin Chapter 4 
Chapter 4: Water Quality 
Perceived problems with water quality have been an 
issue in the Tensas River Basin. The approach taken 
here to examining water quality was to first gather all the 
stream water quality data available and then to analyze it 
both temporally and spatially. Initially the hope was to 
gather enough data to be able to associate water quality 
with some of the landscape metrics discussed previously. 
The major source of the data was STORET, the EPA 
water quality data base. Not only is the EPA data stored 
in this data base but so is data from the USGS and 
various states including Louisiana. All of the existing 
water quality data for the Tensas River Basin was re¬ 
quested. It was then verified with Louisiana Department 
of Environmental Quality (LDEQ) and USGS that all 
existing water quality data for the basin were contained in 
the storet data base. 
The water quality data search yielded a data set that 
included stream water quality data from 17 stations. 
However many of these stations included only data from 
a one-time sampling effort often dating back to the 1970s 
or the station ceased to operate in the 1970s or early 
1980s. The criterion for using a station’s water quality data 
required that it have data from the 1990s or it be located 
close to a station that had data from the 1990s. This 
criteria was selected as these would be the most relevant 
data to current conditions in the Tensas River Basin. This 
criteria limited the data available for analysis to three sites; 
Tendal, Winnsboro, and Clayton. The locations of these 
stations are shown in Figure 4.1. Both Louisiana state 
and the USGS collect samples from Tendal and Clayton. 
Unfortunately, with a sample number of only three water 
quality monitoring stations, it is impossible to make valid 
associations between the water quality data and any of the 
landscape metrics that was previously presented. In 
addition to the three stream monitoring stations, water 
quality data from Lake Providence were also retrieved. 
This lake in the Tensas Bayou serves as the headwaters 
of the Tensas River. 
This analysis focused on two variables: total phosphorus 
and total nitrogen as nitrite and nitrate. In the analysis of 
the data, significant differences between the three stations 
were examined as well as seasonal differences and trends 
over many years. 
Figure 4.2 shows the seasonal distribution of the 
nitrogen and phosphorus data from 1990 through 1996 
for all three LDEQ water quality monitoring stations. This 
type of display is known as a box and whisker plot. The 
top and bottom edges of the blue box represent the 25th 
and 75th percentiles of the distribution of the data (i.e., 
50% of the data values fall within this range). The vertical 
lines extend from the blue box down to the 10th and up 
to the 90th percentile (i.e., 80% of the data values fall 
within this range). 
Figure 4.1 
Location of Tensas River Basin Water Quality Monitoring Stations. 
