Annual primary production: Patterns and mechanisms of change in a nutrient-rich tidal ecosystem

Limnology and Oceanography
By: , and 

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Abstract

Although nutrient supply often underlies long-term changes in aquatic primary production, other regulatory processes can be important. The Sacramento-San Joaquin River Delta, a complex of tidal waterways forming the landward portion of the San Francisco Estuary, has ample nutrient supplies, enabling us to examine alternate regulatory mechanisms over a 21-yr period. Delta-wide primary productivity was reconstructed from historical water quality data for 1975–1995. Annual primary production averaged 70 g C m−2, but it varied by over a factor of five among years. At least four processes contributed to this variability: (1) invasion of the clam Potamocorbula amurensis led to a persistent decrease in phytoplankton biomass (chlorophyll a) after 1986; (2) a long-term decline in total suspended solids—probably at least partly because of upstream dam construction—increased water transparency and phytoplankton growth rate; (3) river inflow, reflecting climate variability, affected biomass through fluctuations in flushing and growth rates through fluctuations in total suspended solids; and (4) an additional pathway manifesting as a long-term decline in winter phytoplankton biomass has been identified, but its genesis is uncertain. Overall, the Delta lost 43% in annual primary production during the period. Given the evidence for food limitation of primary consumers, these findings provide a partial explanation for widespread Delta species declines over the past few decades. Turbid nutrient-rich systems such as the Delta may be inherently more variable than other tidal systems because certain compensatory processes are absent. Comparisons among systems, however, can be tenuous because conclusions about the magnitude and mechanisms of variability are dependent on length of data record.

 

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Annual primary production: Patterns and mechanisms of change in a nutrient-rich tidal ecosystem
Series title Limnology and Oceanography
DOI 10.4319/lo.2002.47.3.0698
Volume 47
Issue 3
Year Published 2002
Language English
Publisher Association for the Sciences of Limnology and Oceanography
Contributing office(s) Toxic Substances Hydrology Program
Description 15 p.
First page 698
Last page 712
Country United States
State California
Other Geospatial Sacramento-San Joaquin River Delta
Online Only (Y/N) N
Additional Online Files (Y/N) N