Enzymatic Assessment of Nitrogen and Phosphorus Bioavailability to Stream Periphyton Communities at Different Velocity Regimes

Abstract

ABSTRACT Phosphatase (Pase) and glutamine synthetase (GS) activities were used as physiological indicators of P and N bioavailability, respectively, to study the effect of velocity regime on nutrient supply dynamics in periphyton of East Branch Codorus Creek, a cold-water stream in an agricultural watershed of the Northern Piedmont Region of Pennsylvania, USA. To validate this dual enzyme approach, chlorophyll weighted activities of Pase and GS were measured on periphyton amended with ammonium and phosphate in vitro by post-colonization incubations of artificial substrates and in situ by difisive substrate periphytometers. As expected the chlorophyll weighted activity of GS decreased with N enrichment relative to the control and phosphate treatments, and that of Pase decreased with phosphate enrichment relative to the control and ammonium treatments. Both bacteria and algae were limited by P based on nutrient amendment experiments performed in situ at a pool and riffle site. Pool periphyton had higher mineral sediment content, less relative organic content, and greater N bioavailability (less GS activity) but was more P deficient than periphyton at higher velocities (runs and riffles), especially during warmer seasons. A benthic source of ammonium associated with fine sediment accumulation at low velocity can explain repressed GS activity and low GS:Pase ratios in pools during all seasons sampled.