The role of dissolved organic matter (DOM) as either a sink for inorganic nutrients or an
additional nutrient source is an often-neglected component of nutrient budgets in aquatic
environments. Here, we examined the role of DOM in reactive nitrogen (N) storage in Sierra
Nevada (California, USA) lakes where atmospheric deposition of N has shifted the lakes
toward seasonal phosphorus (P)-limitation. Nuclear magnetic resonance (NMR) spectroscopy
and isotope analyses performed on DOM isolated from Lake Tahoe reveal the accumulation
of refractory proteinaceous material with a 100–200-year residence time. In
contrast, smaller lakes in the same watershed contain DOM with typical terrestrial characteristics,
indicating that proteins in Lake Tahoe are autochthonously produced. These data
support the role of DOM as a possible sink for reactive N in these lake ecosystems and
identify a potential role for DOM in affecting the inorganic nutrient stoichiometry of these
environments.