Nitrifying Kinetics and the Persistence of Nitrite in the Seine River, France

Abstract

Although a higher oxidation rate for nitrite than for ammonia generally prevents nitrite accumulation in oxic waters, nitrite concentrations in the Seine River (1-31 μM) exceed European norms. We investigated the kinetics of in situ ammonia- and nitrite-oxidizing communities in river water and wastewater treatment plant (WWTP) effluents to determine the role of pelagic nitrification in the origin and persistence of nitrite downstream of Paris. The main source of nitrite is the major Parisian WWTP, and its persistence, up to tens of kilometers downstream of the plant, is explained by low ammonia and nitrite oxidation rates and high river flow. Furthermore, similar nitrite and ammonia oxidation rates preclude a rapid consumption of both preexisting nitrite and nitrite produced by ammonia oxidation. Maximum ammonia oxidation rates are two to three times higher downstream than upstream of the WWTP, indicating the input of ammonia oxidizers and ammonia from the WWTP. In both river water and WWTP effluents, nitrite oxidizers were unable to oxidize all available nitrite. In the human-impacted Seine River, this phenomenon might be due to mixotrophy. This study highlights the low resilience of the river to nitrite contamination as well as the importance of managing nitrite, nitrifiers, and organic matter concentrations in WWTP effluents to avoid nitrite persistence in rivers.

Landward Perspective of Coastal Eutrophication Potential Under Future Climate Change: The Seine River Case (France)

“…Simultaneously, nitrate and phosphate concentrations increases during low flow, particularly in the 7th stream order, are most likely related to the lower dilution of point sources in the urbanized river basin, as commonly observed downstream of large sewage treatment plant effluents. In addition, the increase in nitrate is also related to higher nitrification rates resulting from higher ammonium concentrations and higher water residence time, as already observed in the Seine River Aissa-Grouz et al, 2015;Raimonet et al, 2017a). The biogeochemical impacts of river flow decrease are thus expected to be greater downstream of conurbations with major sewage treatment plant effluents.…”

Influence of organic ammonium derivatives on the equilibria between NH4+, NO2− and NO3− ions in the Nistru River water

“…If the concentrations of 1-NA exceed the MAC values, the breaking ammonium oxidation is more pronounced. In other words, the NO 2 − oxidation into NO 3 − proceeds more slowly than the formation of NO 2 − by NH 4 + oxidation leading to the increase of NO 2 − concentration 59 , 60 . At the same time, the NO 2 − accumulation becomes gradually more pronounced as the concentration of 1-NA increases.…”