The ratio between total nitrogen and total phosphorus in relation to eutrophoication

TN: TP relation to eutrophication :

 The TN concentration enhances the release of P from sediment which leads to eutrophication. Downing J.A. and McCauley E. established a relation between the ratio of both TN and TP and eutrophication. Their study showed that the eutrophication of lakes can be predicted using TN: TP ratio. The ratio of TN: TP usually high for oligotrophic lakes (ratio ranged between 21 and 240), the higher TN: TP comes from runoff forests (N and P come from natural sources only). 

Lower ratios were reported for mesotrophic, eutrophic and hypereutrophic lakes (17-96, 4-71 and 0.5-9 respectively) (Downing, 1992). Nevertheless, Guildford found a relation between TN: TP ratios and the limiting nutrient, the N showed to be a limiting factor when TN: TP ratios were less than 20. Where P acted as a limiting factor for TN: TP ratios ˃50 (Guildford, 2000). Xie L. study investigated the effect of TN: TP ratios on the blooming of Microcystis in Lake Donghu (China). The study argued that, at high eutrophic state, even if the TN: TP ratio increased above 29, still the Microcystis blooms. This means, TN: TP ratio is not a cause of eutrophication but rather a result. This would strengthen the belief that nitrogen acts as a limiting nutrient when TN: TP ratio is less than 10 (Canfield Jr, 1984).

References

Canfield Jr, D. S. J. C. D. H. W. W. I. C. a. M. M., 1984. Prediction of chlorophyll a concentrations in Florida lakes: importance of aquatic macrophytes. Canadian Journal of Fisheries and Aquatic Sciences, 41(3), pp. 497-501.

Downing, J. a. M. E., 1992. The nitrogen: phosphorus relationship in lakes. Limnology and Oceanography, 37(5), pp. 936-945.

Guildford, S. a. H. R., 2000. Total nitrogen, total phosphorus, and nutrient limitation in lakes and oceans: Is there a common relationship?. Limnology and Oceanography, 45(6), pp. 1213-1223.