A coupled model of zebra mussels and chlorine in collective pressurized irrigation networks

Abstract

Zebra mussel infestation has become a serious problem affecting pressurized networks. Larvae settle in pipeline walls creating relevant obstructions to flow as they grow and develop shells. Oxidant injections in the stream are commonly used to control the infestation. A model is proposed for simulating the transportation, settlement and death of mussels in pressurized networks. This model is coupled to a solute transport, diffusion, and decay model of oxidant chemicals. During the analyzed irrigation campaigns, the larvae entry was monitored at various intervals. These data, showing high variability, were used as input to the model using different scenarios averaging and modifying the time distribution of larvae concentration. Simulations predicted similar mussel settlement patterns across all scenarios, suggesting that network morphology and total larval abundance primarily influence settlement distribution. We compared the effectiveness of continuous and intermittent oxidant applications. Continuous treatments were the most effective (up to 99%), but required up to 3.5 kg ha⁻¹ of chlorine. Reasonable control could also be attained with short injections (1 to 3 h) just before the peak irrigation service discharge, leading to up to 93% of chlorine savings and reaching similar mortality rates. The model was also used to estimate the larvae and chlorine export to on-farm irrigation systems through hydrants and to evaluate strategies for mitigating the risks of on-farm infestation and environmental impact. The protection of on-farm irrigation systems required additional chlorine input. The model can be parametrized to simulate similar species in different types of pressurized networks, using different chemicals for treatment.