THE TROPHIC SIGNIFICANCE OF EPILITHIC ALGAL PRODUCTION IN A FERTILIZED TUNDRA RIVER ECOSYSTEM

Fertilization of a pristine tundra river with phosphorus and nitrogen changed the nitrogen and carbon stable isotope ratios in epilithic alg ae. Determination of deltaN-15 and deltaC-13 values in consumers allow ed this algal organic matter to be traced in the food web for several kilometers downstream of the fertilizer addition sites. Changes in the isotopic composition of consumers documented the tight coupling algal production in response to fertilization and measured increases in the growth of insects and fish.