different years (20, 30, and 40 years) in China [80]. The authors reported that longterm wastewaters irrigation does not constitute heavy metals pollution in soil and
groundwater; however, they suggested that the monitoring of Hg, Pb, and Cu
concentrations should be evaluated in areas that use treated wastewater irrigation
to avoid health risks.
4.2 Effects on Soil Microbiological Characteristics
The soil microbiota is an essential component of the soil system, interacting with
inorganic components, the atmosphere, soil organic matter, and with other organisms of the soil ecosystem, including plant crops. Microorganisms provide many
functions in the soil ecosystems that are essential for the quality and productivity of
agricultural products, including plant growth promotion, organic matter turnover,
availability of nutrients, and plant pathogen suppression. The application of treated
wastewater to agricultural soil can affect the structure and functions of the soil
microbiome in two primary ways: first, through the introduction of exogenous
microorganisms (with repeated events following each irrigation treatment) leading
to changes in microbial diversity and dynamics; and second, through changes in the
physicochemical properties of soil due to the composition of the wastewater and the
consequent intake of salts, inorganic nitrogen and phosphorous, metals, and micropollutants, with unavoidable impacts on the properties of the soil and on cultivated
crops.
There is still a lack of information regarding the stability of exogenous microbial
communities from wastewater. One study [3] found that short-term applications of
treated industrial wastewater could cause a shift in soil microbial communities
during a single tomato crop season. More recently, Dang et al. [81] found that
irrigation with treated industrial wastewater had a greater impact on microbial
community structures than domestic wastewater; irrigation significantly affected
the composition of indigenous soil microbial communities at different soil depths
and might therefore introduce exogenous microbes into the soil environment.
The composition of wastewater can effect of the degree to which its application
modifies the physicochemical properties of the soil; generally, any deviation from
the native soil structure and composition (pH, salinity, etc.) tends to reduce microbial
diversity, and bacteria are particularly sensitive to soil perturbations. However, an
increase in microbial diversity does not necessarily imply an increase in functional
diversity, in terms of microbial metabolic activity within the soil. As an example,
Cheng et al. [82] found that aquaculture wastewater irrigation of agricultural soil
reduced the functional activity of microbial communities (primarily due to increased
salinity) but induced a higher richness of microbial taxa.
Wastewater Reuse in Agriculture: Effects on Soil-Plant System Properties
93
groundwater; however, they suggested that the monitoring of Hg, Pb, and Cu
concentrations should be evaluated in areas that use treated wastewater irrigation
to avoid health risks.
4.2 Effects on Soil Microbiological Characteristics
The soil microbiota is an essential component of the soil system, interacting with
inorganic components, the atmosphere, soil organic matter, and with other organisms of the soil ecosystem, including plant crops. Microorganisms provide many
functions in the soil ecosystems that are essential for the quality and productivity of
agricultural products, including plant growth promotion, organic matter turnover,
availability of nutrients, and plant pathogen suppression. The application of treated
wastewater to agricultural soil can affect the structure and functions of the soil
microbiome in two primary ways: first, through the introduction of exogenous
microorganisms (with repeated events following each irrigation treatment) leading
to changes in microbial diversity and dynamics; and second, through changes in the
physicochemical properties of soil due to the composition of the wastewater and the
consequent intake of salts, inorganic nitrogen and phosphorous, metals, and micropollutants, with unavoidable impacts on the properties of the soil and on cultivated
crops.
There is still a lack of information regarding the stability of exogenous microbial
communities from wastewater. One study [3] found that short-term applications of
treated industrial wastewater could cause a shift in soil microbial communities
during a single tomato crop season. More recently, Dang et al. [81] found that
irrigation with treated industrial wastewater had a greater impact on microbial
community structures than domestic wastewater; irrigation significantly affected
the composition of indigenous soil microbial communities at different soil depths
and might therefore introduce exogenous microbes into the soil environment.
The composition of wastewater can effect of the degree to which its application
modifies the physicochemical properties of the soil; generally, any deviation from
the native soil structure and composition (pH, salinity, etc.) tends to reduce microbial
diversity, and bacteria are particularly sensitive to soil perturbations. However, an
increase in microbial diversity does not necessarily imply an increase in functional
diversity, in terms of microbial metabolic activity within the soil. As an example,
Cheng et al. [82] found that aquaculture wastewater irrigation of agricultural soil
reduced the functional activity of microbial communities (primarily due to increased
salinity) but induced a higher richness of microbial taxa.
Wastewater Reuse in Agriculture: Effects on Soil-Plant System Properties
93