Delivery of marine-derived nutrients to streambeds by Pacific salmon

doi:doi:10.1038/ngeo364

Nature Geoscience 1, 840 - 843 (2008)
Published online: 30 November 2008 | doi:10.1038/ngeo364

Subject Category: Biogeochemistry

Delivery of marine-derived nutrients to streambeds by Pacific salmon

John F. Rex & Ellen L. Petticrew

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Marine fish that migrate to freshwater rivers to spawn deliver substantial quantities of marine-derived nutrients to terrestrial and freshwater environments^1,². These nutrients support riparian vegetation³, terrestrial organisms⁴, benthic macroinvertebrates⁵, algae⁶ and other fish populations¹. Although it is known that the quantity of nutrients delivered to these environments is influenced by the number of spawning salmon⁷, little is known about the mechanisms of nutrient delivery. Here, we present a pathway for nutrient delivery and retention in a Pacific salmon stream, which depends on the aggregation of inorganic and organic particulate matter⁸. We verify the existence of this pathway in the controlled environment conditions of a recirculating flume, replicating the hydrologic conditions of a stream environment. We show that the addition of salmon organic matter and clay to the flume increases the formation of organic–inorganic aggregates in the water column, and the transfer of these aggregates to the stream bed. We find that the formation of these aggregates is associated with an increase in the concentration of bacteria in the stream bed. We suggest that bacterial aggregation of salmon organic matter and inorganic particulate matter delivers nutrients to streambeds, and thus plays an integral role in nutrient cycling in Pacific salmon streams.