SPATIAL AND TEMPORAL VARIABILITY IN THE LOWER FOOD-WEB OF THE TIDAL FRESH-WATER HUDSON RIVER

The mid Hudson River is a heterotrophic system where allochthonous inp uts apparently iud the largest proportion of secondary production and ecosystem metabolism. We have analyzed a 6-yr dataset collected quarte rly at six stations spanning a 150-km reach to assess variability at i nter- and intra-annual time scales and regional spatial scales. The ma jor components of the lower food web: bacterial biomass, detrital part iculate organic carbon (POC), and dissolved organic carbon (DOC), show surprisingly discordant patterns in temporal and spatial variability. Bacterial abundance shows significant variability at all three scales , but the interannual variability is by far the greatest. DOC concentr ations showed greatest variability among years, with intra-annual and spatial variability roughly equal. Freshwater flow is commonly conside red a major driving force in river-estuarine variability but simple di scharge was not a strong predictor of any component of suspended matte r or DOC. For organisms in the Hudson River food web, these multiple s cales of variability indicate highly unpredictable food resources in t ime and space, and these fluctuations may contribute to the variabilit y In higher trophic levels.