Stoichiometry of carbon, nitrogen, and phosphorus through the freshwater pipe

The "freshwater pipe" concept has improved our understanding of freshwater carbon (C) cycling, however, it has rarely been applied to macronutrients such as nitrogen (N) or phosphorus (P). Here, we synthesize knowledge of the processing of C, N, and P together in freshwaters from land to the ocean. We compared flux estimates into and out of the N and P "pipes" and showed the net removal rates of N and P by inland waters were less than those for C. The C : N : P stoichiometry of inland water inputs vs. exports differed due to large respiratory C and N losses, and efficient P burial in inland waters. Residence time plays a critical role in the processing of these elements through the pipe, where higher water residence times from streams to lakes results in substantial increases in C : N, C : P, and N : P ratios.