Do microbial nitrogen transformations confuse marine nitrogen signal as indicated by N-15?
Nitrification and dentrification within the hyporheic zone may create false apparent marine signals in isotopic ratios. Gilles Pinay (Centre National de la Recherche Scientifique, Rennes, France) was on site for three weeks during the summer of 1999 and 2000 to collaborate on experiments using co-injections of tracer and acetylene to estimate in situ denitrification rates. His preliminary results indicate that denitrificaiton does occur in the hyporheic zone and must be considered when interpreting N-15 data. Gilles Pinay conducting denitrification studies Broader questions: Are other sources of nutrients present? Yes, our data indicate that the steep alder-dominated slopes are an important source of nitrogen. What is relative importance of marine versus other nutrient sources? Making a “back of the envelope” calculation, a single fish brings approximately 73 g of nitrogen into the system. We estimate a return of no more than 4000 fish for the sytem in 1999. This would correspond to 29
