Definition of Net Ecosystem Exchange

Ecologists have many ways to measure how an ecosystem is behaving. One of the most important factors in any ecosystem is what substances are entering the system, and what substances are leaving. Healthy ecosystems have a predictable amount of materials that enter and leave constantly as it exchanges them with other nearby environments, sometimes building up certain substances like carbon as the system grows and develops. Unhealthy environments lose too much of vital substances or cannot get rid of toxins effectively. Net ecosystem exchange is a concept used to judge these differences.

Net Ecosystem Exchange

• Net ecosystem exchange, commonly known as NEE, is a measurement of how much carbon is entering and leaving the ecosystem. While at first glance this may seem simple, carbon is a very common element and is found in all types of life. One of the most common sources of carbon change in net ecosystem exchange is CO2 or carbon dioxide, which as a gas can move more easily between environments.

GPP

• GPP stands for gross primary productivity, or the total amount of carbon materials created from carbon sources such as carbon dioxide. When plants and animals create these materials, they increase the GPP of the system, because this carbon now stays in the environment. GPP also includes other sources of carbon, such as respiration or natural fluxes which do not mean that the system has actually gained carbon, only that carbon is naturally moving from place to place. GPP directly affects NEE.

Positive Results

• In all ecosystems that ecologists have studied, NEE remains normal--in other words, these systems consistently gain carbon materials. There are several possibilities for this effect: it could be that ecologists have not yet fully studied the systems that are losing carbon. It could also be that ecosystems naturally accumulate carbon, especially when major changes occur. It could also be that carbon is naturally increasing in the biosphere due to higher levels of carbon dioxide.

Causes for Change

• NEE takes into account all vertical exchanges of carbon. This includes natural gas fluxes as gases move in and out of the ecosystem due to atmospheric conditions and respiration. Some events, like a fire, can easily remove a large amount of carbon vertically. NEE also takes into account advection and drainage of carbon via temperature changes, habitat movements and flowing water.

Lateral Fluxes

• NEE does not take into account lateral transfer of carbon. This refers to the transfer of carbon through the soil as soil elements slowly change. It also does not take into account the fluxes that occur as materials are leaching up or down from deep underground.