Nitrate in polluted mountainous catchments with Mediterranean climates.

Area of Science:

• Environmental Science
• Ecology
• Hydrology

Background:

• Southern California mountains experience high atmospheric nitrogen (N) deposition, leading to elevated nitrate (NO3-) in some streams.
• A significant difference in NO3- concentrations exists between perennial (approx. 200 µmol L−1) and ephemeral (approx. 20 µmol L−1) streams.

Purpose of the Study:

• To investigate the source of high NO3- in San Bernardino Mountain streams.
• To understand the differential impact of N deposition on terrestrial and aquatic ecosystems in Mediterranean climates.
• To assess the applicability of the N saturation concept in semiarid Mediterranean systems.

Main Methods:

• Comparative analysis of NO3- concentrations in perennial and ephemeral streams.
• Evaluation of N deposition rates and their correlation with stream chemistry.
• Assessment of temporal asynchrony between N deposition, soil availability, and plant uptake.

Main Results:

• Groundwater is identified as the primary source of NO3- in streams.
• Aquatic systems show a faster response to N deposition compared to terrestrial systems.
• Temporal asynchrony between N deposition, soil NO3- leaching, and plant N demand influences ecosystem response.

Conclusions:

• Mediterranean aquatic ecosystems are impacted more rapidly by N deposition than terrestrial ones.
• Extrapolation of N impacts from humid to Mediterranean climates is unreliable.
• The concept of N saturation may require re-evaluation for semiarid, seasonally dry ecosystems.