Refractory dissolved organic nitrogen accumulation in high-elevation lakes

Area of Science:

• Environmental Chemistry
• Aquatic Ecology
• Biogeochemistry

Background:

• Dissolved organic matter (DOM) plays a critical, yet often overlooked, role in aquatic nutrient cycling.
• Atmospheric nitrogen (N) deposition has altered nutrient limitation in Sierra Nevada lakes, shifting them towards phosphorus (P)-limitation.
• Understanding DOM's role in nutrient storage is crucial for accurate aquatic ecosystem management.

Purpose of the Study:

• To investigate the function of DOM in storing reactive nitrogen (N) within Sierra Nevada lakes.
• To determine the origin and characteristics of DOM in Lake Tahoe and surrounding smaller lakes.
• To assess DOM's potential impact on inorganic nutrient stoichiometry in these P-limited systems.

Main Methods:

• Isolation and characterization of DOM from Lake Tahoe and smaller watershed lakes.
• Utilized Nuclear Magnetic Resonance (NMR) spectroscopy for molecular analysis of DOM.
• Employed isotope analyses to trace the origin and residence time of DOM components.

Main Results:

• Accumulation of refractory, proteinaceous DOM with a long residence time (100-200 years) was identified in Lake Tahoe.
• DOM in smaller lakes within the same watershed exhibited characteristics typical of terrestrial sources.
• Autochthonous production of proteinaceous DOM in Lake Tahoe was inferred, contrasting with allochthonous inputs in smaller lakes.

Conclusions:

• DOM functions as a significant sink for reactive nitrogen (N) in these lake ecosystems.
• The accumulation of autochthonous proteinaceous DOM in Lake Tahoe influences N storage and ecosystem dynamics.
• DOM's role in nutrient cycling and stoichiometry is a key factor in understanding the response of these lakes to environmental change.