Nutrients Cycling @2

What are the 3 main ways humans impact biogeochemical cycles?

• Agriculture, including forestry

• Fossil fuel combustion

• Urbanization

What is eutrophication?

A large input of a limiting nutrient (N or P) that can occur in terrestrial or aquatic ecosystems

• typically focuses on aquatic impacts

What can eutrophication result in?

Increased plant/algae growth, which increases the amount of decomposition, and oxygen depletion in aquatic or wet environments

What has happened to nitrogen fixation due to humans?

Human N fixation now rivals or exceeds natural fixation

What are the major anthropogenetic sources of phosphorus?

• Phosphate rock (fertilizers, main source)

• Manure

• Human Waste

• Guano

How do fertilizers affect ecosystems?

By releasing N, P, K (and others) into the soil and water, which can increase productivity 

Why do different plants affect nitrogen cycling differently?

Because some plants use N and other plants fix N at different rates

How do pesticides affect ecosystems?

killing organisms (including decomposers), which can alter a communities structure and nutrient cycling

How do monocultures affect nutrient cycles?

By reducing diversity and making nutrient cycling less stable

How does deforestation affect decomposition?

Because it increases dead organic matter, which increases decomposer activity and decomposition rates

What happens after a clear cut?

mineralization and leaching increases in nitrogen cycling

What happened after clear-cutting at hubbard brook?

The nitrate level in the streams drastically increased as mineralization increased

What happened after clear-cutting and scarification in Murtopuro basin?

There was a large spike in nitrogen export

What causes dead zones, such as those in lake erie and the Gulf of Mexico?

By excess nutrients and leads to algal blooms, which increases decomposition and reduced oxygen levels

Why does urbanization affect nutrient cycling?

It increases N and P leaching due to runoff from impervious surfaces (roads or sidewalks)

What is point source pollution?

Pollution that comes from a single, identifiable source

• Industrial sources

• Wastewater treatment

What is non-point source pollution?

Pollution that comes from diffuse, widespread sources; where no single source can be specifically identified

• Runoff from rainfall

• Atmospheric deposition

How does acid rain affect soil pH?

By lowering the pH and making the soil more acidic, resulting in the mobilization of toxic metals like Al and Mn and reduced solubility of others

How does acid rain affect microbe activity?

By reducing microbial activity, which can slow decomposition

What is acid rain able to alter in soil?

N forms in soil, nitrifying or denitrifying which can vary, with ammonia being the most common and available

How does acid rain affect plants?

• Reducing plant growth

• Lowering chlorophyll content

• Lowering photosynthetic efficiency

What do indirect losses, such as leaching of N and erosion of P result in?

An increase in mineralization of dead OM, but reduced immobilization due to tree removal

How do humans directly add nutrients into the environment?

primarily through the mining of phosphate and industrial fixation of N2 into chemicals and fertilizers