Contribution of bedrock nitrogen to high nitrate concentrations in stream water

• Published in: Nature (London) Vol. 395; no. 6704; pp. 785 - 788
• Main Authors: Dahlgren, R. A, Holloway, J. M, Hansen, B, Casey, W. H
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 22.10.1998; Nature Publishing Group
• Subjects: Agricultural runoff; Anthropogenic factors; Bedrock; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Freshwater; Geology; Hydrology; Hydrology. Hydrogeology; Industrial effluents; Industrial wastewater; Infants; Livestock; Nitrates; Nitrogen; Pollution, environment geology; Rivers; Rocks; Streams; Surface water; Wastewater discharges; Water quality; United States; California; USA, California; California, United States; eutrophication; nitrogen; streams; nitrates; saprolite; North America; drainage basins; sedimentary rocks; bedrock; water quality; rocks; soils; clastic rocks
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/27410

Concentrations of nitrate in stream water throughout the world are reported to be elevated relative to natural background levels. This enrichment is commonly attributed to anthropogenic activities such as atmospheric emissions, livestock feeding, agricultural runoff,, timber harvesting practices and domestic/industrial effluent discharge,. Here we show that bedrock containing appreciable concentrations of fixed nitrogen contribute a surprisingly large amount of nitrate to surface waters in certain California watersheds,o an extent that even small areas of these rocks have a profound influence on water quality. As 75% of the rocks now exposed at the Earth's surface are sedimentary in origin, and as these rocks contain about 20% of the global nitrogen inventory, 'geological' nitrogen may be a large and hitherto unappreciated source of nitrate to surface waters. Such a natural nitrate source may be especially significant given that nitrate contamination at very low levels can contribute to surface water eutrophication, may cause infant methaemoglobinaemia ('blue baby' syndrome) and has been implicated in certain cancers. In addition, geological nitrogen may be a source of the 'missing' nitrogen noted in several biogeochemical studies of ecosystem nitrogen budgets.