title: Nutrient availability and phytoplankton nutrient limitation across a gradient of atmospheric nitrogen deposition.
abstract: Atmospheric nitrogen (N) deposition to lakes and watersheds has been increasing steadily due to various anthropogenic activities. Because such anthropogenic N is widely distributed, even lakes relatively removed from direct human disturbance are potentially impacted. However, the effects of increased atmospheric N deposition on lakes are not well documented. We examined phytoplankton biomass, the absolute and relative abundance of limiting nutrients (N and phosphorus [P]), and phytoplankton nutrient limitation in alpine lakes of the Rocky Mountains of Colorado (USA) receiving elevated (> 6 kg N x ha(-1) x yr(-1)) or low (< 2 kg N x ha(-1) x yr(-1)) levels of atmospheric N deposition. High-deposition lakes had higher NO3-N and total N concentrations and higher total N : total P ratios. Concentrations of chlorophyll and seston carbon (C) were 2-2.5 times higher in high-deposition relative to low-deposition lakes, while high-deposition lakes also had higher seston C:N and C:P (but not N:P) ratios. Short-term enrichment bioassays indicated a qualitative shift in the nature of phytoplankton nutrient limitation due to N deposition, as high-deposition lakes had an increased frequency of primary P limitation and a decreased frequency and magnitude of response to N and to combined N and P enrichment. Thus elevated atmospheric N deposition appears to have shifted nutrient supply from a relatively balanced but predominantly N-deficient regime to a more consistently P-limited regime in Colorado alpine lakes. This adds to accumulating evidence that sustained N deposition may have important effects on lake phytoplankton communities and plankton-based food webs by shifting the quantitative and qualitative nature of nutrient limitation.
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA. j.elser@asu.edu
authors.forename: James J
authors.initials: JJ
authors.lastname: Elser
authors.forename: Marcia
authors.initials: M
authors.lastname: Kyle
authors.forename: Laura
authors.initials: L
authors.lastname: Steger
authors.forename: Koren R
authors.initials: KR
authors.lastname: Nydick
authors.forename: Jill S
authors.initials: JS
authors.lastname: Baron
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D017753:Ecosystem; D005618:Fresh Water / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry* / Q000494:pharmacology*; D010758:Phosphorus / Q000737:chemistry; D010839:Phytoplankton / Q000187:drug effects / Q000254:growth & development*; D014872:Water Movements
chemical_list: D010758:Phosphorus; D009584:Nitrogen