242
and indirect effects on food production. Changes in wind velocity and timing due to
climate change may also affect seed production for wind-pollinated plants that
produce cereal grains.
9.2.1.2 Biogeochemical Cycles
Biogeochemical cycles in ecosystems influence the availability of the nutrients
organisms require to live, grow, and reproduce. In nexus studies the phosphorus,
nitrogen, carbon, and sulfur cycles are most commonly of interest; other chemical
elements are important in smaller amounts dependent on the ecosystem. These
cycles are driven by both biotic and abiotic factors.
Nutrients in ecosystems cycle repeatedly move through various states and forms,
with the potential to return to the same or other consumers in the food web. For
example, the carbon exhaled by animals as CO 2 may be stored in plant leaves that
are consumed by those animals; or the plant leaves may fall off and decompose,
making the component nutrients available for uptake by the roots of that plant or
other organisms. The biological unavailability of atmospheric nitrogen (N 2 ) to
plants and animals illustrates the importance of this biological decomposition activity in the nitrogen cycle; it is the activity of microorganisms that break down organic
matter in the soil that provides much of the nitrogen (nitrate NO 3
−
and ammonium
NH 4
+
) available to plant and animal life. As more research occurs into the role of
microbial processes in biogeochemical cycles, we are finding that soil microbes also
influence storage of other nutrients such as carbon and phosphorus that are applicable for agricultural crop growth and sustainability.
The sulfur cycle is of interest in nexus studies because sulfur is an essential element for the formation of plant and animal proteins and it is also a by-product of
fossil fuel consumption, in addition to being produced naturally, such as in volcanic
eruptions. The atmospheric reaction of sulfur emissions (as sulfur dioxide SO 2 and
hydrogen sulfide H 2 S) with air and water may result in acid deposition (as sulfuric
acid, the primary component of acid rain H 2 SO 4 ) that pollutes land and water, in
some cases making inland lakes devoid of fish and other aquatic life. Conversely,
sulfur deposited on land through the biogeochemical cycle (as sulfate SO 4
2−
) may
support agricultural production, when it occurs at less-than-toxic concentrations. As
with nitrate, sulfate does not bind readily to mineral soil that typically is composed
of negatively charged anions; this means that positively charged particles in soils
such as organic materials are essential for nutrient retention.
9.2.1.3 Energy Flow
Primary energy originates from the sun and flows through ecosystems, with various
ecosystem components storing energy. For example: through photosynthesis, plants
convert sunlight and nutrients into sugars and complex molecules that are stored as
N. Matthews et al.
and indirect effects on food production. Changes in wind velocity and timing due to
climate change may also affect seed production for wind-pollinated plants that
produce cereal grains.
9.2.1.2 Biogeochemical Cycles
Biogeochemical cycles in ecosystems influence the availability of the nutrients
organisms require to live, grow, and reproduce. In nexus studies the phosphorus,
nitrogen, carbon, and sulfur cycles are most commonly of interest; other chemical
elements are important in smaller amounts dependent on the ecosystem. These
cycles are driven by both biotic and abiotic factors.
Nutrients in ecosystems cycle repeatedly move through various states and forms,
with the potential to return to the same or other consumers in the food web. For
example, the carbon exhaled by animals as CO 2 may be stored in plant leaves that
are consumed by those animals; or the plant leaves may fall off and decompose,
making the component nutrients available for uptake by the roots of that plant or
other organisms. The biological unavailability of atmospheric nitrogen (N 2 ) to
plants and animals illustrates the importance of this biological decomposition activity in the nitrogen cycle; it is the activity of microorganisms that break down organic
matter in the soil that provides much of the nitrogen (nitrate NO 3
−
and ammonium
NH 4
+
) available to plant and animal life. As more research occurs into the role of
microbial processes in biogeochemical cycles, we are finding that soil microbes also
influence storage of other nutrients such as carbon and phosphorus that are applicable for agricultural crop growth and sustainability.
The sulfur cycle is of interest in nexus studies because sulfur is an essential element for the formation of plant and animal proteins and it is also a by-product of
fossil fuel consumption, in addition to being produced naturally, such as in volcanic
eruptions. The atmospheric reaction of sulfur emissions (as sulfur dioxide SO 2 and
hydrogen sulfide H 2 S) with air and water may result in acid deposition (as sulfuric
acid, the primary component of acid rain H 2 SO 4 ) that pollutes land and water, in
some cases making inland lakes devoid of fish and other aquatic life. Conversely,
sulfur deposited on land through the biogeochemical cycle (as sulfate SO 4
2−
) may
support agricultural production, when it occurs at less-than-toxic concentrations. As
with nitrate, sulfate does not bind readily to mineral soil that typically is composed
of negatively charged anions; this means that positively charged particles in soils
such as organic materials are essential for nutrient retention.
9.2.1.3 Energy Flow
Primary energy originates from the sun and flows through ecosystems, with various
ecosystem components storing energy. For example: through photosynthesis, plants
convert sunlight and nutrients into sugars and complex molecules that are stored as
N. Matthews et al.