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CHAPTER TWO
2. LINEAR REGRESSION
Anderson (1998) established that the denitrification rate could be predicted by using one
of the most important factor in denitrification, i.e, organic carbon (OC %). Otis (2007)
has used organic carbon and WFP to determine denitrification rates in the Wekivia river
basin. Following the approach used by Anderson (1998) and Otis (2007) approach a
hierarchal linear regression analysis is conducted on the dataset. Initially all data are
clumped together and the relationship between the denitrification rate and organic carbon
is investigated, this yields a very weak correlation (r 2 = 0.1). The same relationship is
investigated using data from similar studies. While there is an improvement in the
coefficient of determination, is it still below the targeted coefficient of determination
value of 0.6. This section describes in detail the hierarchal linear regression analysis.
2.1. All Available data
Using all the available literature values the denitrification rate is plotted against organic
carbon (Figure 2.1). While Anderson’s (1998) linear regression is a reasonable estimation
based on the data used by him and helped account for loss of nitrogen due to
denitrification, it may not necessarily be applicable in a universal setting Based on
literature studies an increase in the organic carbon should result in an increase in the
denitrification rate. The results obtained do show that the denitrification rate increases
with an increase in organic carbon content, however the coefficient of determination is
extremely low (r 2 = 0.1).
There are several factors that may account for the low correlation value. It is likely that
this erroneous result may be caused by the conversion of units to a common unit of kg N
ha − 1 d − 1 or from the clumping together of data from different studies, many of which have
used different methods. Some of the methods within the dataset estimate and measure the
potential denitrification rate i.e. the maximum possible rate under ideal conditions; others
are field experiments that report the actual rate of denitrification. Even within the same
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