The Great Stour Project - River Pollution

Analyses

WORKED EXAMPLE OF DATA ANALYSIS

(Graphing data for downstream changes in Biological Oxygen Demand).

The data for BOD figures have been plotted on a nominal Y-axis to illustrate five equal bands of General Quality Assessment.  Five points on the X-axis locate downstream sites, with Canterbury STW falling between Vauxhall Bridge and Blackmill Bridge.

This could be our starting hypothesis: BOD biological oxygen demand (as a sensitive indicator of overall river pollution) will increase downstream, as the combined effect of all point and diffuse sources accumulates through the Canterbury area.  In particular, the discharge of final effluent from the STW will seriously reduce river water quality.  Does the graph bear this out?

Evaluation:  The line graph shows clearly, and contrary to expectations, that water quality remains in the ‘good’ to ‘very good’ bands of the General Quality Assessment.  Potential pollution sources are closely monitored by the Environment Agency and consent agreements are being successfully adhered to.  Final effluent from the Canterbury STW is of ‘good’ quality, well within the consent guidelines, and makes no serious impact on the overall character of the river.

We can therefore reject our hypothesis.

Explore another downstream change in river water quality in this way, plotting the four main sites first and adding Canterbury STW as a 5^th and separate point on your graph.  Suggest an hypothesis to test.  Evaluate the result, explaining the various sources of pollution which may be contributory.  Accept or reject your hypothesis.  Explore other downstream trends in the pattern of  pollution through Canterbury.