Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

Salmon Nutrients: Closing the Circle

John G. Stockner and Kenneth I. Ashley


The consequences of nutrient loss (oligotrophication) and attendant low productivity on ecosystem biodiversity and fish production have only recently perked the interest of researchers in aquatic science (Ney 1996; Ashley and Slaney 1997; Stockner et al. 2000). Conversely, research on the ecological consequences of ‘excess’ nutrients (eutrophication) has been a major focus of limnological research for several decades (Forsberg 1998; Vollenweider 1968). Inputs of phosphorus (P) and nitrogen (N) from anthropogenic interventions on the landscape were identified as primary causal factors of eutrophication (Edmondson 1969; Vallentyne 1974). Over the last century, the impact of man, mediated by overfishing, dam construction, and habitat destruction in both coastal and interior regions of the Pacific Rim nations (United States, Canada, Japan, Russia), has led to a marked decline and, in some cases, total loss of adult salmon spawners, which has had a profound impact on the productivity and biodiversity of salmonid ecosystems (Mathisen 1972; Stockner 1987; Larkin and Slaney 1997; Cederholm et al. 2000a; Gresh et al. 2000). Further, the construction of some dams within the Columbia River basin has not only markedly reduced and/or eliminated anadromous salmon runs, but also, in the upper basin within Canada, has had an equally devastating impact on kokanee salmon Oncorhynchus nerka stocks, due both to reservoir oligotrophication and introductions of exotic species, for example, mysids (Northcote 1973; Ashley et al. 1997; Pieters et al., this volume).