Week 14 v2024 12 03

A Deeper Dive into Macronutrients N and P

Overview of Content

  • The presentation focuses on macronutrients, specifically Nitrogen (N) and Phosphorus (P).

  • Case study regarding the impact of these nutrients on Lake Erie.

  • Upcoming review and final test, with reminders that there are no labs scheduled for Weeks 14 and 15.

Nitrogen

Nitrogen in the Atmosphere

  • Constitutes 78% of our atmosphere in the form of nitrogen gas (N2).

Common Forms of Nitrogen

  • Various forms present include:

    • N2 - Nitrogen gas

    • NO2 - Nitrite

    • NO3 - Nitrate

    • NH3 - Ammonia (toxic at concentration above 0.3 mg/L)

    • NH4+ - Ammonium ion

Nitrogen Cycle

Key Processes

  • Nitrogen Fixation: Conversion of nitrogen gas into usable forms.

  • Consumption: Organisms use nitrogen for growth.

  • Denitrification: Process by which nitrate is converted back to nitrogen gas.

  • Nitrification: Conversion of ammonia to nitrite and then to nitrate.

  • Ammonification: Conversion of organic nitrogen back into ammonia during decomposition.

Bacteria Involvement

  • Diazotrophs: Nitrogen-fixing bacteria.

  • Various bacteria contribute to nitrification, denitrification, and other processes in the cycle.

Seasonal Variation of Nitrogen

  • Different forms of nitrogen vary seasonally, affecting ecosystems in distinct ways.

  • Measurements include total nitrogen and specific nitrogen forms like nitrate (NO3-) and ammonium (NH4+).

Phosphorus

Role of Phosphorus

  • Often a limiting nutrient for production in aquatic ecosystems.

  • Sources include:

    • Natural (bedrock and soils) and anthropogenic (sewage, fertilizers, soaps/detergents, industrial processes).

Biologically Active Phosphorus (BAP)

  • Only about 10% of phosphorus entering lakes is biologically available (primarily as phosphate, PO4-3).

  • About 90% is in non-active forms, often bound to sediments.

Phosphorus Cycle

  • Phosphorus does not have a gaseous phase and cycles through various biological and geological systems.

  • Key inputs include both natural and human activities, leading to variations in biological availability.

Effects of Dissolved Oxygen and pH on BAP

  • Decreasing dissolved oxygen levels result in increased BAP availability for plants.

  • Acidic environments facilitate the absorption of phosphate.

Lake Simcoe: A Case Study

Phosphorus Dynamics

  • Addresses historical phosphorus loads and their impact on Lake Simcoe’s ecosystem.

  • Eutrophication: Increased nutrient inputs lead to reduced oxygen levels and changes in fish habitat, particularly for coldwater species.

Management Strategies

  • Includes reducing phosphorus inputs at the source (fertilizers), improving sewage treatment, controlling stormwater runoff, and other habitat rehabilitation measures.

Current Status and Future Directions

  • Monitoring and action plans are in place to manage phosphorus loads and preserve aquatic life in the lake.

  • Emphasis on the importance of maintaining low phosphorus concentrations to avoid harmful algal blooms and eutrophication.