Environmental and Low-Temperature Geochemistry by Peter Ryan;

Author:Peter Ryan;
Language: eng
Format: epub
ISBN: 9781119568612
Publisher: John Wiley & Sons, Inc.
Published: 2019-10-16T19:50:39+00:00

6.2.2.2 The global phosphorus cycle

The largest reservoir of P at and near the Earth's surface is sedimentary rock and sediments, and the main means by which P is transported at the Earth's surface is by stream flow. Given that P is largely insoluble, the majority is transported as particulate material. Approximately 22 TgP yr−1 are transported by rivers to lakes and to the global ocean, and ∼90% is carried as adsorbed P or as P minerals (e.g. phosphates) – this component is mainly deposited in deltas and other types of marine sediments near continents. To reiterate a point made above, the main particulates responsible for P transport in the solid state are iron hydroxides and particulate organic matter (Ruttenberg 2003). The dissolved P carried by rivers is ultimately transported by currents into the open ocean, where it can be taken up as a nutrient or can circulate at the surface or to deeper levels.

Physical and chemical weathering of rock and sediment plus decomposition and erosion of organic matter yields ∼20 TgP yr−1 to biota and soils, and this flux is matched by erosion of soil P and biologically bound P into streams and, ultimately, the ocean. The cycle is closed by burial of marine P into marine sediments and the eventual transformation of these sediments in rock. In general, the flux of P between the main reservoirs (sediment/rock → soils/biota → streams → ocean → sediment/rock) is ∼20 TgP yr−1, although as is indicated on Figure 6.11, the riverine flux is about 10% greater, reflecting increased erosion due to anthropogenic activities, including road building, construction, logging, agriculture, and application of mined phosphorus as fertilizer. The increased fluvially transported P is responsible for much eutrophication.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.