Effects of small rivers on chemical properties of sediment and diets for primary consumers in estuarine tidal flats

• Published in: Marine ecology. Progress series (Halstenbek) 2008-05, Vol.360, p.13-24
• Main Authors: Sakamaki, Takashi, Richardson, John S.
• Format: Article
• Language: English
• Subjects: Brackish; Carbon; Diet; Estuaries; Food; Microalgae; Nitrogen; River water; Sediments; Tidal flats; Watersheds
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps07388

We compared effects of particulate organic matter (POM) transported from small rivers (POMR) on chemical properties of sediment and diets of primary consumers in 3 estuarine tidal flats with different watershed characteristics in southwestern British Columbia, Canada. The source rivers (0.1 to 1.9 m³ s–1, annual mean) flowed through forested and urbanized areas (FR) or through agricultural areas (AG1 and AG2). The C:N ratio of POMRwas significantly higher in FR (8.6 to 10.1) than in AG1 and AG2 (6.7 to 7.0). The chlorophyllaconcentration of river water was significantly lower in FR (0.4 μg l–1) than in AG1 and AG2 (9.4 to 10.3 μg l–1). In the tidal flat of FR, organic matter of sediment (SPOM) had relatively higher C:N ratios (FR, 17.9; AG1, 9.6 and AG2, 8.2), suggesting the accumulation of terrestrial organic matter. Mixing model (IsoSource) calculations based on stable isotope measurements showed that in the tidal flat of FR, POMRwas dominant in SPOM (~70%), also suggesting POMRwas an important food source for some primary consumers (37 to 48%) as were benthic microalgae (35 to 45%). In AG1 and AG2, POMRdid not dominate SPOM, and there was no evidence of significant incorporation of POMRinto macrobenthos diets. In the present study, POMRfrom the watershed with substantial forest areas appeared to be more influential on the chemical properties of sediment and macrobenthos diets in the tidal flat. This could be attributed to the low degradability and long retention of POMRin the tidal flat sediments.