Biomass: what it is, how it is calculated, and how it is distributed

Bioelements, as their name suggests, are the chemical elements of the periodic table that make up the different living beings on the planet. Despite the fact that life is made up of about 30 elements, 96% of the cell mass of almost all taxa that you can think of is made up of only six of them: carbon, oxygen, nitrogen, hydrogen, phosphorus and sulfur. These elements give rise to proteins, vitamins, nucleic acids, lipids, carbohydrates and many other compounds, so conceiving life without them is an impossible task.

The organic matter present on Earth is not fixed, but is transformed through the use of energy. For example, a plant grows thanks to light energy and inorganic compounds present in the soil, transforming minerals into carbon. This mass is consumed by a herbivorous animal, then by a carnivore and then by a super predator, until it dies. At this point, all the accumulated matter decomposes in the soils and we start the cycle again.

Food chains in ecosystems modulate this energy flow, that is, "who eats who ”condition the functioning of environments and, therefore, of all life present in the environment. Anyway,

To understand the exchange of energy in different biological systems, it is necessary to describe extensively a term of great interest: biomass. Today we tell you all about her, so read on.

• Related article: "The 10 branches of Biology: their objectives and characteristics"

What is biomass?

Biomass is the mass of living biological organisms present in a given ecosystem at a given time. Weight can be determined at the level of a specific taxon or population (species biomass) or comprising all living elements that coexist in the environment (community or community biomass). Biomass is distributed in terrestrial ecosystems in a pyramidal way in the trophic chain, from the primary producers that are the base, to the super predators of the tip.

It should be noted that biomass is not used 100% at all ecosystem levels. We explain ourselves. On an ecological level, of all the biomass consumed by a cow in the form of grass (100% of the energy), only 10% will go to the next trophic level. The mammal must burn the organic matter it consumes to forage, reproduce, produce heat and in definitively live, so only a tiny part of the energy obtained by biomass passes from level to level in the chain. Fortunately, solar energy is "unlimited", so this loss should not be noticed in a healthy ecosystem as long as there are plants that carry out photosynthesis.

An interrelated term with biomass is bioenergy, as this refers to obtaining energy in a renewable way in the human sector, through the use of organic matter (either treated naturally in the ecosystem or mechanics). Biomass and bioenergy are two sides of the same coin, but the first term generally refers to a natural event, while the second has a clear anthropic applicability.

The biomass of the Earth, in raw data

In 2018, the research The biomass distribution on Earth was published on the PNAS scientific portal, which dealt with estimate the biomass throughout the Earth in the form of carbon (C), the organic component par excellence of living beings. A total of 550 gigatons of carbon were calculated, which are distributed among the different living taxa as follows:

• Plants were the dominant producing kingdom. These are responsible for storing 450 gigatons of carbon, that is, 80% of the total. They are the primary producers of all normal ecosystems.
• Behind them, you will be surprised to know that there are bacteria, which provide about 70 Gt, 15% of the total carbon. Although we cannot see them, these microorganisms are everywhere.
• Fungi, archaea, and protists rank third, fourth, and fifth, respectively, with 12, 7, and 4 Gt total.
• To the shame of the evolutionary pinnacle, we animals only assume 2 gigatons of carbon - only viruses contribute less than we do, at 0.2 Gt.

Furthermore, this study calculated that the amount of land biomass is two orders larger than the marine, but it is estimated that the biota in the aquatic environment contributes a total of 6 gigatons of carbon, a figure that is not negligible. As you can see, most of the organic matter on Earth is found in microorganisms and plants.

Calculation of biomass

Calculating the total biomass produced in an ecosystem is an extremely difficult task, although new technologies (such as Laser Vegetation Imaging Sensor) help researchers to make fairly reliable estimates, at least when it comes to quantifying the plant carbon in an environment. Due to the intrinsic complexity of taking into account all the living elements of the biome, It is necessary to resort to equations and regression methods, that is, to calculate the biomass produced by an individual and then extrapolate this value to the total population.

To give you an idea of ​​how biomass can be calculated, we will take a petri dish with microorganisms, the smallest scale that we can think of. To estimate carbon, the following equation is followed:

Biomass (in micrograms of carbon / milliliter of sample): N x Bv X F

In this equation, N represents the number of microorganisms counted in a milliliter of sample, Bv is the biovolume is what each microorganism occupies (in µm ^ 3 scale) and F is the carbon conversion factor, in µg of C per µm ^ 3. As you can see, quantifying the biomass in a sample is not easy, not even when we move on microscopic scales.

• You may be interested in: "The 8 types of biomes that exist in the world"

Productivity and biomass

A term completely linked to biomass is ecological productivity. This parameter is defined as the production of organic matter in a determined area per unit of time, that is, the amount of biomass that is generated in a natural ecosystem or artificial system human.

The most common unit used to quantify productivity in an ecosystem is kilograms / hectare per year, although they can be used other weight scales (tons, gigatons) surface (square meters, square centimeters, etc.) and even time (days, hours, decades). It all depends on the utility and focus of the study in question that is trying to obtain specific parameters.

Let's take an example. Suppose we have an area of ​​40 hectares that was empty at the beginning, but has been repopulated with plants that, on average, weigh 1 kilogram. In total we count about 1,000 plants of the species of interest at the end of the year, which consequently gives us 1,000 kilograms of total mass (species biomass). If we make the pertinent calculations (1,000 kg / 40 Ha), we will obtain that, in total, the productivity has been 25 kg / Ha / year.

This hypothetical model presents a high productivity rate, but things change a lot if we talk about animals. Now think of a population of cows that, for example, need a land area of ​​20,000 hectares to thrive. However much these livestock mammals weigh, they will be fewer total individuals than plants and, In addition, the foraging ground is larger, which gives us a total biomass produced a lot less.

In addition to this, it is necessary to take into account the previous point: the energy that jumps from link to link in the chain is only 10%. Cows use 90% of their energy to live, so a primarily plant ecosystem is always more productive than one with abundant animals. However, natural selection does not "seek" to maximize productivity, but to maintain a stable long-term balance between all components. Therefore, when alien species are introduced into an ecosystem, the outcome is often disastrous.

Resume

To put everything you have learned into perspective, we compare two specific cases: plant productivity (primary) in a desert is less than 0.5 grams / square meter / day, while in a cultivated field the value oscillates 10 grams / meter square / day. The more plants present in an ecosystem, the more biomass there will be and, therefore, the higher the productivity rate.

In summary, biomass reflects the amount of organic matter in a particular place and site, while the productivity refers to the speed and effectiveness with which this organic matter is produces. These parameters help us to understand the functioning of natural ecosystems, but they also help us allow to maximize the material and economic benefits when exploiting the land for purposes humans.

Bibliographic references:

• Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences, 115 (25), 6506-6511.
• Brown, S. (1997). Estimating biomass and biomass change of tropical forests: a primer (Vol. 134). Food & Agriculture Org ..
• Cai, J., He, Y., Yu, X., Banks, S. W., Yang, Y., Zhang, X.,... & Bridgwater, A. V. (2017). Review of physicochemical properties and analytical characterization of lignocellulosic biomass. Renewable and Sustainable Energy Reviews, 76, 309-322.
• Macgregor, C. J., Williams, J. H., Bell, J. R., & Thomas, C. D. (2019). Moth biomass increases and decreases over 50 years in Britain. Nature Ecology & Evolution, 3 (12), 1645-1649.
• Parikka, M. (2004). Global biomass fuel resources. Biomass and bioenergy, 27 (6), 613-620.