Streamwater nutrients stimulate respiration and breakdown of standardized detrital substrates across a landscape gradient: Effects of nitrogen, phosphorus, and carbon quality

AbstractElevated streamwater nitrogen (N) and phosphorus (P) concentrations can stimulate microbial activity on detrital C and accelerate its breakdown in stream ecosystems. Our study evaluated whether nutrient–detrital relationships are robust across a moderately altered land-use gradient and can be used to identify functional impairment of stream ecosystems. We tested the relative importance of N vs P as likely drivers of these responses, whether responses differed for labile or recalcitrant standardized substrates, and whether responses were detectable across streams with other stressors, which can potentially mask nutrient effects. Two studies were conducted in 23 sites in southeastern US streams. These streams differed in land use and exhibited low-to-moderate gradients in N and P. In study 1, we used 9 sites to compare the relationships between nutrient (N and P) concentrations and microbial respiration and breakdown of 2 standardized C substrates: recalcitrant oak wood veneer and labile cellulose s...