“…Samples were filtered through a 0.2 µm pore-size inorganic membrane filter (Whatman, Anotop 10 IC) before chemical analysis. The main digestion methods available and in current use for total nitrogen determination in aqueous samples are: Kjeldahl digestion (Doval et al, 1997, Nozawa et al, 2005, Yasuhara and Nokihara, 2001, alkaline persulphate oxidation (Cape et al, 2001, Cornell et al, 2003, Scudlark et al, 1998 and high-temperature catalytic oxidation (Cape et al, 2001, Cornell et al, 2003, Keene et al, 2002.…”