Structure: Ecosystem, soil organisms

Terrestrial mediation processes are regulated by the microbiological qualities (e.g. strains of bacteria and fungi), amount of organic matter, temperature, moisture and currents of water (rain), soil type, acidity and redox potential. In Finland, the most important factor regulating activity of microbes is temperature, because soil is frozen approximately 110–130 days in Southern Finland and in the north even longer. Besides most of the soil in Finland are dominated by moraine and gravel, so the habitat of bacteria and fungi can be harsh, which may slow down gradation of organic matter. In other words, decomposition of organic matter is slower in Finland than compared to countries with warmer climate.

In 2013 there were 23 900 land areas registered as contaminated in Finland, and the number is increasing while surveys proceed. Most of the contaminated areas are located in Southern Finland, where most of the industrial activities and centers of population are located. Approximately 20 % of the contaminated areas locate in ground water areas, 20 % in settled areas and 10 % in conservation areas.  

Terrestrial ecosystems have often great biodiversity of species, which regulates circulation of nutrients from dead organic matter back to producers and shapes soil both mechanically and biochemically. The most important groups of organisms that decompose dead organic matter are fungi and bacteria and decomposer animals, which are grouped by size as microfauna (< 200 μm, e.g. Protozoa, Nemata), mesofauna (100 μm-2 mm, e.g. Collembola, Enchytraeidae, Acari) and macrofauna (> 2 mm, e.g. Oligochaeta, Diplopoda, Isopoda, Gastropoda.

Bacteria and fungi decompose most of the dead organic matter it has been observed that gradation speed increases with biodiversity of soil ecosystem. Microbes decompose around 90 % of dead organic matter and they have most of the enzymes needed for the process. According the estimates there may be millions of fungi and bacteria per hectare in the first layer of 2,5cm in fertile soil bacteria.

Protozoa and Nematoda feed on microbes releasing nutrients to soil. By the number of species and inviduals Nematoda is the most abundant group of animals living in soil. Collembola (mesofauna) are the biggest group of invertebrate by the number of inviduals in most of the soil ecosystems. They constitute 1–5% of the biomass in soil and they feed on decomposing organic matter, parts of plants and fungi and bacteria. Mesostigmata are the predators of soil ecosystems and they prey on small plant feeding insects.

Macrofauna (e.g. Oligochaeta) decreases mechanically surface area of dead organic matter making it easier for microbes to decompose it and help microbes to spread on new habitats. Microbes also feed on excrement of macrofauna. As the top predators of soil ecosystems bigger animals like birds and mammals prey on macrofauna.

  

References:

Leona Matsoff (2005): Torjunta-aineiden maaperän eliöille aiheuttamien riskien arviointi. Suomen ympäristö 804.

Syke 2013: Tiedote 19.11.2013 http://www.ymparisto.fi/fi-FI/Kulutus_ja_tuotanto/Pilaantuneet_maaalueet/Suomesta_kartoitettu_yli_23_000_pilaantu%2827302%29

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