Environmental Engineering Reference
In-Depth Information
Consumers
Heat
Heat
Sun
Heat
Producers
Decomposers
Heat
Heat
Nutrients
Figure 2.5
Schematic of a natural ecosystem. Solid lines represent the flow of materials in a closed loop.
Dotted lines represent the flow of energy in an open loop.
factors are deeply interconnected and generally a disturbance in one of them results in a
change on the other.
Ecosystems constantly cycle materials in a process powered by the sun. Photosynthetic
organisms, which are primary producers, take nutrients and water from the soil and produce
biomass by transforming carbon dioxide into carbohydrates. Primary consumers (herbivores)
eat the biomass and then serve as food for secondary and higher-level consumers. At each step
of the chain, organisms generate waste and eventually die; thus, decomposers close the cycle
of matter by returning chemicals into the abiotic environment. This dynamic cycle repeats
indefinitely unless a major disturbance takes place in the ecosystem.
When undisturbed by external factors, natural ecosystems remain in balance by self-
regulatory mechanisms, including food availability, predators, and waste. In terms of mass,
untouched ecosystems behave like closed systems (Fig. 2.5); but it does not happen the same
for energy. Energy is taken from the sun by the producers and then lost as heat at each step of
the cycle.
When ecosystems are altered (e.g., transformation of grassland into agricultural land) the
balance and self-regulation is lost and the recycling of matter is disrupted. So to keep up with
the mass retrieved from the system, there is a need for constant inputs of material (e.g.,
fertilizers) to make up for loses and the introduction of some regulation by eliminating predators.
Services provided by natural ecosystems
Natural ecosystems are not only important because they can be visually attractive, but also
because they provide important services to humans without even having a market value.
Natural ecosystems provide habitats for wildlife and diversity, act as carbon storage sites,
produce oxygen, and perform water cycling. Evapotranspiration from forests is important in
the hydrologic cycle and consequently in regional weather patterns. Healthy wetlands
provide water filtration, flood control, costal protection, habitats for aquatic and nonaquatic
animals, treatment of wastes, and nutrients cycling through the execution of biogeochemical
cycles.
Ecosystems are vital players in regulating services, including pest and disease control,
resistance to invasive species, pollination, seed dispersion, climate regulation, and human
disease regulation (Díaz et al., 2005) (See Table 2.3.).
