Productivity: Definition and Measurement

Productivity is the average rate of production of organic matter in a particular unit area at a given time, such as a day or a year. There are multiple factors in the natural system that can cause irregular changes in the rate of instantaneous rapid production. Therefore, in the case of normal research, only the average production rate is determined. In this case, the generation rate of the organism is taken into consideration. Aquatic ecosystems have different levels of productivity. Basic or primary productivity is divided into total and net productivity. Secondary productivity has different trophic levels. Basic productivity refers to the rate at which energy is stored in productive organisms (chlorophyll-containing organisms, mainly plants and phytoplankton) through the process of photosynthesis.

Gross primary productivity refers to the total rate of photosynthesis, including the organic matter used in respiration, when measured. It is also called total photosynthesis or total assimilation. Net primary productivity refers to the rate at which energy is stored as food, excluding energy used by plants for respiration. It is also called apparent photosynthesis or net assimilation. Generally, gross or total primary productivity is achieved by adding the value of respiration rate obtained from plants to the apparent photosynthesis. The rate of energy storage at decomposer and consumer trophic lavels is called secondary productivity. These energy storage rates gradually decrease at the trophic levels. In order to perfect the secondary productivity, only the food assimilation by the autotrophs is considered at each subsequent trophic level (parasitic). The term productivity is not associated with these trophic levels.

The term productivity always refers to the average production rate or average energy flow rate. It must be emphasized that productivity refers to the rate of production or the rate of energy flow and is called the richness of a reservoir or ecosystem. It cannot single-handedly consider the biomass of existing crops at different trophic levels.

Gross and net productivity rates fluctuate with the abundance of water bodies. Productivity can range from 1 gram carbon (C) / sqm / day in the open sea to more than 60 g carbon / sq m / day in natural and artificial systems.

Gross productivity of some reservoirs given by Odum (1959)

  • Open sea: 0.5 g / sqm / day
  • Shallow inshore water: 3.2 g / sq m / day
  • Tidal Bay Area: 4.4 g / sq m / day
  • Coral reefs: 16.2 g / sqm / day
  • Crude sewers or ponds: 26.0 g / sq m / day
  • Extensive algae cultivated water body: 43.0 g / sq m / day
  • Polluted river: 56 g / sq m / day

It has been observed that a large part of the land surface is low productivity. Some areas, such as the continental shelf, are high productivity areas like coral reefs in the arelle. Due to the rapid release of nutrients, coral reefs are highly productive due to the symbiosis of plants and animals.

Primary productivity in fish ponds has been measured through several types of studies. Among these research works, the research of Hepher (1982) is significant. He applied different levels of fertilizers to compare the primary production in the ponds and collected the rate of primary production at different depths of the fish ponds. Hepher noted that high primary productivity was not achieved by applying too much fertilizer at an early stage. However, good results are obtained by applying small amount of fertilizer every two weeks in the ponds. Even with double fertilizer application the surface gross productivity is higher but with moderate fertilizer application, the yield is higher at all depths.

This is an important aspect in the application of fertilizers in fish farming ponds. Ali (198) measured the gross productivity based on depth at different times before and after the application of fertilizer on Aluu. The quality of productivity obtained by Ali is not as high as that of Heper (1982), but the effect of fertilizer application time on gross productivity is obvious. These results are of local importance and can be re-applied. The ponds in Ali’s research were excavated which were not fully prepared resulting in low gross productivity.

Noriga-Curtis (1989) calculated the depth of compensation to measure the profile of net primary production based on depth at different times of the year.

Table: Changes in Primary Productivity in Israel and Compensation Depth of Fish Ponds with Existing Plankton Levels.

Net Production (PN g/cm2))

Respiration (R/day)



Existing crop of Plankton based on dry weight (mg/l)



bottom 100(100)














Note: The values inside and outside the bracket are of 2 separate ponds.

Compensation depth was 40-60 cm at a depth of 1 m in the ponds. According to Ozlimbai (1977), fish production is related to the existing stocks of phytoplankton from primary productivity.

From the above discussion it is clear that fish production (secondary production) of natural and artificial reservoirs is related to the primary productivity of the respective reservoirs (PG). Various initiatives have been taken to link PG with fisheries productivity. It has also been observed that dissolved solids in the respective reservoirs, such as conductivity, are well related to fish production. The Mospho-Edaphic Index (MEI) reflects the above phenomenon (the productivity of a reservoir is directly related to conductivity and inversely related to the depth of water). The following relationship was established with MEI (Henderson and Ellcome, 1974; Melack, 1976) by comparing the fish production of 8 African lakes.

log FY=0.113 PG +0.91;r=0.05

Here FY = fish production per kg per hectare per year.PG = Gross photosynthesis for the production of oxygen expressed in grams per square meter per day.

Milak established the relationship between FY and PG in the case of some of the tropical lakes of Madras, india.

FY=0.122 PG+0.95;r=0.82

It can be observed that this relationship is more evident in the production of all the lakes where herbivorous fish are stored in Madras (Srinivasan, 1972).

In the case of African lakes (r = 0.004) the MEI relationship was very low but in the case of Madras Lake the correlation was good.

FY=4.1(K/Z)0.80; r=0.60

Here K is conductivity and Z is depth.

In the case of Israeli fertilizer-applied ponds, fish production in ponds is related to primary productivity (Noreiga-Curtis, 1979). The results of his research are given below-


Fish Yield: gC/sqm/90 days


Primary productivity(gC/sqm/90 days)

Efficiency FY×100



A (composite culture)




B (composite culture)





 (Hapher, 1962)

10.3 gC/240 days

694.0gC/240 days


Productivity Measurement

Numerous strategies have been devised to determine the rate of production. Most of these techniques are used to measure the organism of a particular group. In the case of aquatic macrophytes and some algae, primary production can be obtained by calculating the change in organisms over a period of time. Finding the rate of production of planktonic microflora from changing biomass is more complex (Vollenweider, 1969).

Net productivity cannot be measured in the measurement of multiple species at the same time (one set) due to depletion, death, accumulation in sediments, migration through streams, and depletion due to grazing by animals. All of these parameters are rarely used in the analysis of production rates due to changes in organisms. In limonology, more attention has to be paid to get the primary production of phytoplankton. Primary production of phytoplankton is widely measured in numerous aquatic ecosystems.

The following methods are used to measure productivity:

1. Harvest Method

This is the simplest method. This method can be used to measure the productivity of water bodies like fish ponds by extracting them at the end of the season. Secondary productivity is obtained through such productivity. It refers to net productivity.

2. Oxygen Measurement Method

Primary productivity can be measured by measuring the amount of oxygen dissolved in a certain volume of water at a given time. The water productivity needs to be determined by holding it in a white and a black bottle with a stopper. Light cannot enter inside the black bottle. Phytoplankton and other elements in water produce oxygen in water bottles. However, some oxygen disappears due to respiration. The oxygen in the black bottle was then measured. In this black bottle only respiration occurs. Thus the amount of oxygen produced by photosynthesis in a sealed bottle can be known. However, this oxygen production refers only to the net primary production.

The use / expenditure of oxygen in black bottles by confined organisms can be found in the variation of dissolved oxygen. Adding the respiration value to the production of oxygen in the white bottle gives a gross primary production. The phytoplankton sample is placed at the depth from which the sample is collected in a transparent and opaque bottle by the oxygen method. It is thought that the initial concentration of dissolved oxygen in an opaque or black bottle is C1, and it is thought that its oxygen content decreases to a lower level (C2) as a result of respiration.

Due to differences in photosynthetic production and respiratory use, the amount of oxygen in the transparent bottle increases to the maximum level (C3). This variation in oxygen levels (C1-C2) represents respiration in every unit volume at a given time of incubation. C3 -C1 means that the difference between the last oxygen level and the initial oxygen level in a transparent bottle is equal to the net light synthesis. The sum of C3 – C1 and C1 – C2 = C3 – C2 which is related to total light synthesis.

3. Diel Method

Primary productivity is measured by changing the oxygen during the day and night. In this case, bright transparent bottles are used especially during the day and black bottles are used at night. As the dissolved oxygen increases during the day, the net primary production increases, while respiration occurs at night, which reduces the amount of oxygen by about half as much as during the day. In this case, the amount of oxygen produced at night is added to the amount of oxygen produced during the day to get daily gross photosynthesis.

4. Measurement of Primary Productivity Using 14C Isotope

It is a more reliable method of determining productivity using radioactive carbon as a carbonate. Marked carbonates are added to bottled water, including phytoplankton and other organisms, and the plankton is separated and dried for a short time. Radioactive carbon mixed with radioactive carbonate is then measured. In this case, the carbon attached to the cell membrane is measured and productivity is measured by measuring the net primary productivity.

The primary productivity and potential production for fish farming in a selected reservoir is to be measured. Such measurements play an important role in fish farming planning. Such measurements are made to assess the quality of the reservoir (natural or man-made) for extensive farming methods and for fish farming in cages and ponds. In this case, the rate of primary production is measured by inserting 14C isotopes into the organic matter of phytoplankton during photosynthesis. If the amount of total CO2 present in the experimental water is known and the known amount of CO2 is added to the water, the amount of carbon (14C) marked in the phytoplankton is determined to find out the total amount of carbon assimilated to the incubation.

The use of 14C in light and dark techniques has led to numerous systemic and physiological problems. With caution, most technical problems can be overcome and errors can be identified. For example, respiratory damage of CO2 and the rate of photosynthesis of soluble organic matter can be determined. It is difficult to determine the respiratory rate directly by applying this technique. In many cases, the results obtained by the 14C method are close to the net photosynthesis rate. Comparison of oxygen and 14C methods in determining the rate of photosynthesis under moderate conditions gives close results.

It is extremely difficult to accurately calculate from primary productivity in freshwater to secondary productivity by invertebrates and vertebrates, Trophic relationships are extremely complex. This relationship can often change from one ecosystem to another ecosystem or in the life cycle of a species. Extensive variations in animal size are observed from adult to immature stage. Since most animals are mobile, they respond to environmental stimuli and actively expand. Therefore, it is more complicated to collect samples properly as uneven dispersion occurs.

The productivity of an animal is measured by its definition, biomass and growth rate. Changes in the accuracy of sampling result in a decrease in the size of the population of benthic organisms and fish from zooplankton. On the other hand, the growth rate of many temperate fish and long-lived invertebrates can be easily measured from many small and fast-breeding zooplankton and other invertebrates.

The population dynamics and productivity of an organism can be determined indirectly from food intake and consumption of ingested food. Assimilation refers to the absorption of food from the digestive tract and assimilation efficiency refers to the rate at which the percentage of food taken in is digested and absorbed by the body. Assimilation skills depend a lot on the quality of the food and the rate of food intake. Assimilation can be measured based on the following simple relationship.

Assimilation = food intake – indigestible part- (equation-I) orAssimilation = growth + respiration–(equation-II)

These equations are simple types. Proper measurement of zooplankton and larger organisms in a natural population is a difficult task. Although food intake can be easily measured, the rate of excretion of indigestible portions is difficult to determine by current methods. Growth in the general sense also includes the production of eggs and offspring. Like normal biochemical respiration, respiration and excretion and other damage or expense are included.

Assimilation and its efficiency can be roughly measured using the first equation by measuring the change in radioactivity by feeding the animal radioactive food followed by non-radioactive food. Growth and respiration can be calculated using the second equation by measuring the rate of food intake (e.g. calories consumed each time), growth rate and respiration. If the respiratory rate (CO2 production / use of O2) is known, respiration can be measured by changing the use of oxygen to a unit of energy.

Ratio Between Productivity and Biomass (P/B)

The productivity of an organism or group of organisms is in most cases related to the P / B ratio. The P / B ratio is used to measure the rate of biomass change. This gives a general indication of the rate of energy flow relative to a trophic organism. It is very important to determine the value of P / B to compare between different trophic levels like the same trophic level in different environmental conditions.

The annual average P / B ratio usually decreases with increasing trophic levels. It is thought that the P / B value of smaller organisms increases and the P / B ratio decreases as the size of the organism increases. As the active growth season lengthens, latitude in aquatic ecosystems decreases and production per unit organism generally increases. In lower latitudes, the number of generations increases with each growing season. Oligotrophic lakes have lower P / B values than eutrophic lakes.

Some Definitions About Productivity

Standing Crop

Standing crop refers to the weight of organic matter which can be sampled and extracted from a particular area at any time. In the sampling process, unaccounted for parts of the sampled species or some species are excluded. Therefore, the total population of an area is not included in the crop. In a normal extraction process, the weight of the total organic matter at a given time from a given area is called the crop. For example, wheat is a crop grown annually on soil or leaves. The term standing crop is widely used in limology. In the case of plankton, the term crop is used as a synonym  for an organism`s biomass.


Biomass refers to the mass of all living things in a single area at a given time. Standing crop refers only to the weight of the topsoil which is applied to aquatic macrophytes. Biomass includes the whole plant. Evaluation of any particular organism is vital in the dynamics of aquatic plant population or productivity.


Yield refers to the rate of production of a crop. The mass of new organic matter created at a particular time is called production. In this case, any loss / depreciation at that time will also be included in the production. Thus production refers to the increase in the mass of an organism observed at a given time, including the energy expended on the organism’s respiration, excretion, excretion, injury, death, and food intake.

Biomass and Productivity

Numerous criteria are used to measure the aquatic life mass and productivity such as calculus, volume, wet weight, dry weight, organic weight, amount of carbon and pigment, combustion heat and ATP as energy, carbon dioxide, and oxygen exchange rate, etc. In most cases productivity is compared using these criteria.

Organism Calculation and Volume Determination

The number of organisms per unit area is calculated. This method is used to calculate the number of microorganisms. There are several advantages to using this method to determine quantitative differences between species and organisms (Detritus). Since there is a wide variation in the size of the organisms, the actual mass of the organism cannot be assessed by calculation.

Larger organisms such as zooplankton, benthic fauna and fish mass are determined using special allometric relationships. Due to the large number of air chambers, the size of freshwater macrophytes is rarely determined. As a result, there is a huge difference in mass and size.


With proper care, the weight of a water-free organism is fresh weight which is equal to the wet weight. Moist weights are not taken because of the wide variations in almost all types of aquatic organisms. With proper precautions, the wet weight of a species can be converted from a particular environment to dry weight by analysis. Since dry weight can vary below 1050C, it is recommended to take dry weight at that temperature. The fridge drawing (lyophilization) method was chosen because some volatile substances were lost in the analysis of food ingredients at a temperature of 1050 C.

Weight loss after combustion at room temperature can in most cases accurately determine dry weight (ash-free). This method is used to measure the biomass of larger organisms.

The complexity of separating bacteria, algae, and other microorganisms from dead,  rotten organic matter makes it difficult to apply this method to measure the ash-free weight of larger organisms.

Method of Measuring Biomass Through Measurement of Molecular Elements

This method is used in the measurement of biomass of photosynthetic organisms. In this case, carbon dioxide (CO2) is produced by oxidizing the organic plant material. This organic matter (carbon) is created by photosynthetic disintegration. Organic carbon is one of the mutable structural elements of plants and its amounts are to 40-60% of the ash-free dry weight of plants.

Algae contain 53±5% carbon and aquatic macrophytes have an average ash-free dry weight of 47% carbon. At present external dead, rotten organic particles are not excluded. Similar conditions exist in the case of particulate organic carbon analysis in pelagic samples with highly inorganic organic matter.

The amount of carbon in algae is usually calculated based on the average species’ carbon holding capacity. The relationship between the volume of carbon and organic matter is called allometric (Mullit, 1966). By measuring the size of the known population, the mass of the unknown natural population can be measured. Other cell components are also used in different ways to measure the change in the mass of a population.

Measurement of organisms by elements other than carbon is more complex. Their use in specialized physiological analysis is limited due to differences in the response of cellular components to changes in the environment. Significant variations in the pigment matter of plants are accompanied by variations in the levels of environmental parameters that are capable of producing pigment degradation products for the measurement of pigment matter active in plants. As a result the mixed population dynamics in algae can be effectively analyzed.

There are several conversion factors that can be used to measure the mass of a cellular component from another cellular component. Such factors are used with greater caution, even in the most favorable conditions. Otherwise in most cases they cannot be evaluated.