Periphyton carbon and nitrogen stable isotopes detect agricultural stressors in low-order streams

Shifts in the stable isotope signatures of carbon (C) and nitrogen (N) in ecological materials have the potential to indicate environmental disturbances. This study examined the δ13C‰ and δ15N‰ ratios of stream water and periphyton from low-order streams in a landscape influenced by agricultural activities. Our key purpose was to assess the influence of best management practice (BMP) presence and age on C and N isotope values as a potential water-quality assessment. We collected stream water and periphyton from 19 streams within the Upper Delaware River watershed in New York, USA, in each of 4 management categories: 1) recently applied BMP treatments, 2) long-standing BMPs, 3) streams lacking BMPs, and 4) minimally disturbed reference streams. We sampled and analyzed water and periphyton for δ13C‰ and δ15N‰ in a repeated-measures design (BMP category ´ time) from April to November 2013. There were large seasonal differences in stream water δ13C-dissolved organic C (DIC)‰ and δ15NO3-N‰, ...