FRACTIONATION OF PHOSPHORUS AND NITROGEN LOADINGS FROM A NORTHERN-IRELAND FISH FARM

Over a 1-year period, the composition of the total phosphorus loading from a N. Ireland fish farm was as follows: soluble reactive phosphorus (SRP) 60.0%, soluble unreactive phosphorus (SUP) 10.0% and particulate phosphorus (PP) 30.0%. By comparison, the fractions of the total nitrogen loading were: ammonium nitrogen (NH4N) 62.1%, soluble organic nitrogen (SON) 26.6%, particulate organic nitrogen (PON) 8.9% and nitrite + nitrate nitrogen (NO2/3N) 2.4%. In comparison with surface waters in N. Ireland, it was shown that the proportion of SRP in the fish farm effluent was higher than found in the inflows to Lough Neagh (54.6%) and Upper Lough Erne (43.2%) or in three rural catchments (30.6-39.3%). The ratio of PP to total soluble phosphorus was shown to increase with temperature over the temperature range 4-13-degrees-C. Over the entire temperature range measured (4-22-degrees-C), the proportion of SON in the effluent tended to increase with temperature. Negative NO2/3N loss rates occurred during the period February to April, inclusive, and a weak relationship, R2 = 0.12, between temperature and daily NO2/3N loss rates was established. Significant non-linear relationships between loss rates of the remaining soluble fractions with temperature were observed, but they tended to produce low R2 values (< 0.12) with the exception of NH4N loss rates (R2 = 0.40). No significant relationships between temperature and PON and PP loss rates were observed.