NUTRIENT DYNAMICS
Melanie D. Harrison
Water Quality Specialist, National Oceanic and
Atmospheric Administration, Santa Rosa, CA, USA
Definition
Nutrient dynamics is broadly defined as the way nutrients
are taken up, retained, transferred, and cycled over time
and distance, in an ecosystem (Hauer and Lamberti,
2006; Allan and Castillo, 2007).
Description
Nutrients are defined in the broad sense as all chemical
elements vital to biological functions (e.g., survival and
reproduction) (DeAngelis et al., 1989). Organisms require
macronutrients in large quantities such as carbon (C),
hydrogen (H), nitrogen (N), phosphorus (P), potassium
(K), sulfur (S), and calcium (Ca); other nutrients such as
silicone (Si) are used for critical cellular processes.
Micronutrients, such as copper (Cu) and zinc (Zn), are
needed in lesser quantities (Smith and Smith, 1998). In
nature, various elements can limit primary productivity
of an ecosystem at a given place and time. The productivity of most aquatic ecosystems is controlled by the concentration, molecular form, and stoichiometry of the
macronutrients N and P (Officer and Ryther, 1980).
Nutrient limitation
The German agricultural chemist, Justus von Liebig theorized that the yield of plants can be limited by the nutrient
that is present in the environment in the least quantity relative to plant demands for growth (von Liebig, 1855); this
theory has come to be known as Liebig’s Law of the Minimum. The concept is the cornerstone of nutrient dynamics. It implies (1) that one key nutrient should be the
primary limiting factor for plant growth in a given ecosystem, (2) that the growth of plants in a given ecosystem
should be proportional to the rate of supply of this nutrient, and (3) that the control of eutrophication should be
accomplished by restricting the loading of this key nutrient to the ecosystem (Smith et al., 1999).
Nutrient uptake
Nutrients are taken up by plant organisms and are affected
by a number of abiotic (nonliving) and biotic (living) environmental interactions. Conditions that affect nutrient
uptake in soil include soil texture, soil organic matter, soil
water content, and soil temperature. Nutrient uptake is
a function of plants and soils and is influenced by two
main processes: (1) mass flow and (2) diffusion. Mass
flow in soils is a rapid process, whereas diffusion is only
measured in mm per day. Mass flow is insufficient to
satisfy plant demand, but zones of nutrient depletion create concentration gradients that drive nutrient diffusional
process in the soil.
Nutrient cycling
Ecosystems that receive chronically low inputs of limiting
nutrients are characterized by mechanisms and structures
that result in a high degree of nutrient recycling in relation
to the amount of nutrient input. If there is no loss of nutrients to the ecosystem, the cycle is said to be a “perfect
cycle,” and if loss does occur, the cycle is said to be
“imperfect.” The decomposers play an important role in
these cycles because they break down dead organisms
and make the nutrient components available once more
to other organisms. Microorganisms play an important
role in the cycling of nutrients because they assimilate
(take up) and mineralize nutrients and return them back
to the nutrient pool.
For example Denitrification is an anaerobic microbial
process that reduces nitrogen oxides (NO 3
À
) to nitrogenous gases (N 2 ).
Controlling factors
The primary abiotic factors that control nutrient dynamics
in ecosystems at a larger scale include the atmosphere, climate and water, soil structure and chemistry, water chemistry, and seasonality. Hydrologic processes control how
much (amount or load), when (storm events), and where
(estuaries) nutrients are deposited on the land and seascape. The hydrology, ecology, and biogeochemical
processing are strongly coupled. In river basins, soils,
groundwater, riparian zones and floodplains, streams, rivers, lakes, and reservoirs act as successive filters to retain
a significant fraction of the nutrients transported
(Bouwman et al., 2013). At smaller scales, components
of abiotic factors, such as pH, salinity, redox conditions,
nutrient availability, dissolved oxygen, and temperature,
also play an important role in regulating the transfer, retention, and cycling of nutrients in an ecosystem. Biotic components such as microorganisms, plants, and animals take
up (assimilate) and mineralize, retain, and cycle nutrients.
Their role as producers, consumers, detritivores, decomposers, parasite, host, predator, competitor, herbivore,
symbiant, and pathogens is an integral part in how nutrients flow through an ecosystem.
Nutrients sources
The sources of nutrient inputs are important to how elements are used and cycled in a biological system. Soil is
composed primarily of weathered materials, along with
water, oxygen, and organic materials. Most elements are
released on land and transported to the ocean where they
are eventually buried in marine sediments. Prior to
reaching the ocean, nutrients are filtered through soils,
groundwater, riparian zones, floodplains, rivers, lakes,
estuaries, and coastal marine areas. Many of the nutrients
are retained in these systems. Changes in land use and
human activities have dramatically increased nutrients in
terrestrial and aquatic ecosystems from sources such as fertilizer, animal manure, atmospheric deposition of nutrients,
and wastewater flows (Stumm, 1973; Valiela et al., 1992;
462
NUTRIENT DYNAMICS
Melanie D. Harrison
Water Quality Specialist, National Oceanic and
Atmospheric Administration, Santa Rosa, CA, USA
Definition
Nutrient dynamics is broadly defined as the way nutrients
are taken up, retained, transferred, and cycled over time
and distance, in an ecosystem (Hauer and Lamberti,
2006; Allan and Castillo, 2007).
Description
Nutrients are defined in the broad sense as all chemical
elements vital to biological functions (e.g., survival and
reproduction) (DeAngelis et al., 1989). Organisms require
macronutrients in large quantities such as carbon (C),
hydrogen (H), nitrogen (N), phosphorus (P), potassium
(K), sulfur (S), and calcium (Ca); other nutrients such as
silicone (Si) are used for critical cellular processes.
Micronutrients, such as copper (Cu) and zinc (Zn), are
needed in lesser quantities (Smith and Smith, 1998). In
nature, various elements can limit primary productivity
of an ecosystem at a given place and time. The productivity of most aquatic ecosystems is controlled by the concentration, molecular form, and stoichiometry of the
macronutrients N and P (Officer and Ryther, 1980).
Nutrient limitation
The German agricultural chemist, Justus von Liebig theorized that the yield of plants can be limited by the nutrient
that is present in the environment in the least quantity relative to plant demands for growth (von Liebig, 1855); this
theory has come to be known as Liebig’s Law of the Minimum. The concept is the cornerstone of nutrient dynamics. It implies (1) that one key nutrient should be the
primary limiting factor for plant growth in a given ecosystem, (2) that the growth of plants in a given ecosystem
should be proportional to the rate of supply of this nutrient, and (3) that the control of eutrophication should be
accomplished by restricting the loading of this key nutrient to the ecosystem (Smith et al., 1999).
Nutrient uptake
Nutrients are taken up by plant organisms and are affected
by a number of abiotic (nonliving) and biotic (living) environmental interactions. Conditions that affect nutrient
uptake in soil include soil texture, soil organic matter, soil
water content, and soil temperature. Nutrient uptake is
a function of plants and soils and is influenced by two
main processes: (1) mass flow and (2) diffusion. Mass
flow in soils is a rapid process, whereas diffusion is only
measured in mm per day. Mass flow is insufficient to
satisfy plant demand, but zones of nutrient depletion create concentration gradients that drive nutrient diffusional
process in the soil.
Nutrient cycling
Ecosystems that receive chronically low inputs of limiting
nutrients are characterized by mechanisms and structures
that result in a high degree of nutrient recycling in relation
to the amount of nutrient input. If there is no loss of nutrients to the ecosystem, the cycle is said to be a “perfect
cycle,” and if loss does occur, the cycle is said to be
“imperfect.” The decomposers play an important role in
these cycles because they break down dead organisms
and make the nutrient components available once more
to other organisms. Microorganisms play an important
role in the cycling of nutrients because they assimilate
(take up) and mineralize nutrients and return them back
to the nutrient pool.
For example Denitrification is an anaerobic microbial
process that reduces nitrogen oxides (NO 3
À
) to nitrogenous gases (N 2 ).
Controlling factors
The primary abiotic factors that control nutrient dynamics
in ecosystems at a larger scale include the atmosphere, climate and water, soil structure and chemistry, water chemistry, and seasonality. Hydrologic processes control how
much (amount or load), when (storm events), and where
(estuaries) nutrients are deposited on the land and seascape. The hydrology, ecology, and biogeochemical
processing are strongly coupled. In river basins, soils,
groundwater, riparian zones and floodplains, streams, rivers, lakes, and reservoirs act as successive filters to retain
a significant fraction of the nutrients transported
(Bouwman et al., 2013). At smaller scales, components
of abiotic factors, such as pH, salinity, redox conditions,
nutrient availability, dissolved oxygen, and temperature,
also play an important role in regulating the transfer, retention, and cycling of nutrients in an ecosystem. Biotic components such as microorganisms, plants, and animals take
up (assimilate) and mineralize, retain, and cycle nutrients.
Their role as producers, consumers, detritivores, decomposers, parasite, host, predator, competitor, herbivore,
symbiant, and pathogens is an integral part in how nutrients flow through an ecosystem.
Nutrients sources
The sources of nutrient inputs are important to how elements are used and cycled in a biological system. Soil is
composed primarily of weathered materials, along with
water, oxygen, and organic materials. Most elements are
released on land and transported to the ocean where they
are eventually buried in marine sediments. Prior to
reaching the ocean, nutrients are filtered through soils,
groundwater, riparian zones, floodplains, rivers, lakes,
estuaries, and coastal marine areas. Many of the nutrients
are retained in these systems. Changes in land use and
human activities have dramatically increased nutrients in
terrestrial and aquatic ecosystems from sources such as fertilizer, animal manure, atmospheric deposition of nutrients,
and wastewater flows (Stumm, 1973; Valiela et al., 1992;
462
NUTRIENT DYNAMICS