Nutrients in estuaries

Nedwell, D.B.; Jickells, T.D.; Trimmer, M.; Sanders, R. ORCID: 1999 Nutrients in estuaries. Advances in Ecological Research, 29. 43-92.

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Nitrogen and phosphorus loading in rivers has increased considerably as a result of human activity. Silicon loads have been less impacted. However, extrapolating these increased loads in rivers through to coastal waters is not straightforward because of the intense nutrient cycling that can take place in estuaries. In this article we review the inputs to estuaries, methods of calculating fluxes through estuaries to coastal waters, and the processes that give rise to the intense cycling within estuaries. Although all the nutrients are intimately linked through their role in primary production, their cycling processes within estuaries are markedly different and hence estuarine cycling can not only change total nutrient loads, but also modify the ratios of one nutrient to another. These modifications of nutrient ratios may have important implications for both the extent and the number of species involved in primary productivity in coastal waters. Many estuaries are rather turbid, which limits the extent of primary productivity and hence the impact of this process on nutrient cycling. Primary productivity is probably the dominant process affecting dissolved silicon (Si) fluxes, and hence the modification of Si fluxes may be limited. The high turbidity will promote particle–water exchange reactions, which are particularly important for phosphorus (P) cycling. The high turbidity is also associated with net sedimentation in most estuaries and the sedimented material is rich in organic matter derived from riverine, marine and estuarine sources. The bacterial degradation of this organic matter drives a series of redox reactions which have a major impact on nitrogen (N) and P cycling. Denitrification can be a major sink for nitrate in estuaries, helping to attenuate its impact on coastal ecology, but the concomitant production of nitrous oxide may have a deleterious effect on the atmosphere. Iron(III) reduction in sediments can mobilize P bound to ferric oxyhydroxides in sediments and release this back into the water column. Considerable progress has been made on understanding nutrient cycling processes in individual estuaries, but we are still some time away from being able to generalize these results for other estuaries and hence effectively predict the present and future nutrient cycling in unstudied systems.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 00652504
Date made live: 06 Oct 2020 14:43 +0 (UTC)

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