Risk Management/Agricultural Water Pollution Management

Surface runoff: The hydrological dilemma
Surface runoff increases disproportionally to rainfall.

Artificial surface waters
Characteristics:
 * artificial
 * drainage channels
 * channelized
 * cleared

Differences to natural surface waters:
 * lower plant density
 * higher flow velocity / lower retention time
 * higher flood potential (in downstream regions)
 * reduced self purification

Surface waters do not fulfil their full range of ecosystem services to humans and society!

Characteristics

 * artificial wetland containing vegetation
 * created for treating anthropogenic
 * discharge (municipal or industrial wastewater)
 * storm-water runoff (urban or agriculture)
 * decrease of flow velocity / longer residence time
 * higher sedimentation rate
 * higher metabolisation rates: photodegradation and microbial processes
 * integration of nutrients in biomass
 * adsorption of chemicals to organic surfaces (e.g., plants or sediment)

Important factors

 * size
 * flow length
 * hydraulic loading rate
 * hydraulic retention time

Retention
The retention of a chemical or suspended solids can be calculated:

$$Retention[\%]=\frac{C_{i}-C_{o}}{C_{i}}$$

with

$$C_{i}: Inlet \, concentration$$

$$C_{o}: Outlet \, concentration$$

Study Concept

 * Application of Azinphos-methyl (AZP) to orchards
 * Measurement of AZP at inlet and outlet before and after application events
 * Calculation of AZP retention

Results

 * 90% AZP retention in the CW
 * Sorption of AZP to aquatic macrophytes
 * Retention of > 90% of measured insecticide substances observed
 * Sorption of AZP to aquatic macrophytes

Conclusion
Constructed wetlands are a good option for agricultural water management
 * A case study showed that pesticide retentions ≥ 90% are possible within a CW
 * Mortality of aquatic invertebrates was 90% lower at concentrations measured at the CW outlet compared to concentrations measured at the inlet
 * Plants play an important role in the retention of pesticides as shown in a meta analysis of literature data