Presentation Title GROUP #1: Gerardo Carrasco; Kryssia Mairena; Italo Palazzese; Maria Fernanda Suazo

Human activity often intrudes in nutrient cycles by removing nutrients from one part of the biosphere and adding them to another. Humans have intruded on nutrient cycles to such an extent that it is no longer possible to understand any cycle without taking human effects into account.

Examples of how humans are impacting the biosphere’s chemical cycle: Agricultural Effects on Nutrient Cycling Critical Load and Nutrient Cycles Accelerated Eutrophication of Lakes

Agricultural Effects on Nutrient Cycling

Agriculture has a great impact on the nitrogen cycle. Cultivation; breaking up and mixing the soil, increases the rate of decomposition of organic matter, releasing usable nitrogen that is removed from the ecosystem. Eventually, in any area under intensive agriculture, the natural store of nutrients becomes exhausted. When this happens, fertilizer must be added.

Industrially synthesized fertilizer is used to make up for the loss of usable nitrogen from agricultural ecosystems. Recent studies indicate that human activities have approximately doubled the globe’s supply of fixed nitrogen available to primary producers.

Nitrogen oxides can contribute to atmospheric warming, to the depletion of atmospheric ozone, and in some ecosystems to acid precipitation.

Critical Load and Nutrient Cycles:

The ecological effects of elevated atmospheric nitrogen (N) deposition on high-elevation lakes of the western and northeastern United States include nutrient enrichment and acidification. The nutrient enrichment critical load for northeastern lakes ranged from 3.5 to 6.0 kg N per year.

There are present critical loads for N deposition for headwater lakes in regions of the United States where the primary environmental impacts come from N deposition and climate change as opposed to land use or water pollution discharges.

Rocky Mountains, and the Sierra Nevada are lake-rich regions where atmospheric deposition is the dominant—if not the sole—source of inorganic N. Rocky Mountain Sierra Nevada

The key issue seems to be Critical Load, the amount of added nitrogen that can be absorbed by plants without damaging ecosystem integrity. Nitrogen is one of a handful of major elements that sustain life on Earth. Elevated amounts of reactive, available N are now evident in many parts of the world.

Accelerated Eutrophication of Lakes:

Lakes are classified on a scale of increasing nutrient availability: Oligotrophic Mesotrophic Eutrophic

Oligotrophic: Oligotrophic means full of lots of oxygen and less nutrients, since the nutrients are consumed by Diatom Algae and diatoms by zooplankton and fish. The most common example for oligotrophic lakes are glacial lakes. They are found where glaciers once were and have now retreated. This includes much of Canada and the Northern United States, as well as Iceland, Greenland, and Alaska

Mesotrophic: Mesotrophic lakes contain a narrow range of nutrients, principally phosphate and nitrate, the concentrations of which are considered to be neither high nor low. Mesotrophic lakes potentially have the highest diversity of plants and animals of any lake type. Relative to other types of lake they contain a higher proportion of nationally scarce and rare aquatic plants.

Mesotrophic lakes are found mainly in the margins of upland areas in the north and west. Several of the largest and most important lakes in the UK were once mesotrophic but have become eutrophic because of pollution.

Eurotrophic: Eutrophic means having lots of mineral and organic nutrients. This means it has a lot of plants and algae and less amount of Diatoms. Other algae are not consumed by fish, so they die and decompose, so there is very little oxygen in the water and other organic life dies.

Eutrophication of lakes and rivers is caused primarily by inputs of phosphorus and nitrogen. Accelerated eutrophication can render a water body unusable for many uses, from fishing to swimming to drinking water.

Types of Eutrophication: Natural EutrophicCultural Eutrophic

Natural eutrophication, where the basin gradually fills in from nutrient and sediment inputs, occurs over long time periods – on the order of centuries. Human-induced, or cultural eutrophication, occurs on a much shorter time scale (decades) as a result of human disturbance and nutrient inputs.