Total ammonia and coliform concentrations at the end of the Mississippi River from 1900 to 2019

Total ammonia (TA) concentrations (NH3 + NH4+) at four locations at the terminal end of the Mississippi River, the largest river on the North American continent, were assembled to examine trends and relationships with point and non-point loadings from 1980 to 2019 and compared to values in 1900 to 1901. TA concentrations were lowest in 1900 to 1901, highest in 1980 and then declined, and then rose slightly in the last 2 decades. Variations in individual measurements and in situ temperature are indirectly related because of the influence temperature has on ammonia solubility and protein degradation rates. Importantly, the average annual concentrations of TA were directly related to both total coliform and fecal coliform densities. The highest measured average annual TA concentrations in the river (15.5 +/- 1.5 SE mu mol in 1985) were below the currently recommended toxicity thresholds for fresh-water aquatic ecosystems. Sewerage loadings are implicated as controlling factors on TA concentrations, not nitrogen stabilizers added to fertilizers to reduce ammonia conversion to nitrate, nor the fertilizer loadings.

Automated summary

This study examines the trends and relationships of total ammonia (TA) concentrations in the terminal end of the Mississippi River from 1980 to 2019, compared to values in 1900 to 1901. TA concentrations were lowest in 1900 to 1901, peaked in 1980, declined, and slightly increased in the past two decades. The study suggests that sewerage loadings are the controlling factors on TA concentrations, rather than nitrogen stabilizers or fertilizer loadings.