Data Collection

Barbed wire fencing was installed in 2001 on both sides of an 800 m reach of the subject watercourse to isolate the treatment area from cattle.  Two monitoring stations (one control, upstream, and one test, downstream) were established in 2004.  Grab samples of river water were collected weekly (for chemical analyses) and every two weeks (for bacterial analyses) from April until October, and then monthly during the winter, from May 2004 through to December 2007. Temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), turbidity, chlorophyll a were measured in the field using portable water quality meters and associated probes.

My population of interest is agricultural streams within cattle pastures in Southern Alberta.  However, due to cost limitations and availability of participating landowners, my population for this project is limited to only one stream within a cattle pasture in southern Alberta. To collect a sample representative of my broader population of interest, I would, ideally, have established replicates of my treatments on other agricultural streams within the region; the data set I utilized for this project was constrained to a comparison of a treatment reach and control reach on a single stream.

 

Figure 5.  Aerial photograph of the study site location.

Figure 6.  Relative location and layout of unfenced (upstream) and fenced
(downstream) treatments and sample collecion sites on the stream channel.

 

My sampling unit is my sample stream reach and my experimental units are a suite of physical, chemical and biological water quality parameters chosen to represent water quality.  My predictor variable is exposure to the riparian fencing treatment, which is a categorical variable (Control = no fence, Test = fenced).  My complete set of response variables include 31 water quality parameters, of which only E.coli concentration is discussed here.

The following data table represents a subset containing E.coli concentrations measured between June and the end of October - the period when cattle are expected to utilize adjacent pastures and when E.coli impacts to area watercourses are anticipated.  Selection of this time period also removed numerous low values observed through winter and reduced the data spread. Treatment 1 represents the fencing treatment, and Treatment 2, the background water quality without fencing. E.coli concentrations are given in Colony Forming Units per 100 milliliter (CFU/100mL).


Table 1. E.coli concentrations from the fencing (Treatment 1) and no-fencing (Treatment 2) treatments between the first week in June and last week in October, 2004 to 2007. 

 
Verification

Before detailed statistical analysis, graphical techniques, including scatterplots (Figure 7), histograms and boxplots (Figure 8), were used to check the complete, raw dataset for errors.  In a large dataset, random data entry keystroke errors can be present as can be systematic errors in rounding or the use of significant figures.  Some errors found in this step included:

     * Keystroke Errors: extreme values represented by a misplaced decimal or group of values multiplied by a factor of 10 or 100. 
     * Data Rounding: data recorded with unjustified significant figures (e.g., decimal places beyond the precision of the original measure).
     * Data Outliers: values that do not conform to the general pattern of a data set.
 
Extreme values of E.coli (as represented by outliers) are possible, biologically significant and of interest in the assessment of water quality; as a result, all values were included in my analysis.


 

 

Figure 7.  Example of scatterplot used to check for data errors in the complete water quality dataset, comparing dissolved oxygen measurements against recorded temperature.  Data points are labeled to assist with data corrections within the data set. Outliers are visible as points outside the dense collection of data (temperature < 30C, dissolved oxygen <15 mg/L).  



 

Figure 8.  Boxplots comparing E.coli concentrations between fenced and unfenced treatments across years, from 2004 to 2007.  Median values are indicated by the solid black bar and outliers are represented by open circles.