NEW AND RECYCLED PRIMARY PRODUCTION IN AN OLIGOTROPHIC LAKE - INSIGHTS FOR SUMMER PHOSPHORUS DYNAMICS

Primary production that is supported by new inputs of nutrients from outside the system is distinct from production that is supported by remineralization of nutrients within the system. We applied the concept of new production to Mirror Lake, New Hampshire, and our view of P dynamics in this lake was altered dramatically. New production during midsummer put a large demand on P in surface waters, removing 37-mu-mol P m-2 d-1. Without new inputs of P, the P content of surface waters would drop to zero in < 1 month. There is, however, a slight increase, not a decrease, in P content of surface waters during summer stratification. Inputs to surface waters during summer months must, therefore, be large. We now believe that higher than average P loading to the lake occurs in summer, despite low runoff inputs.