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!

Constructed Wetland (CW)

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: a real constructed wetland

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