Waterfowl populations decline with nutrient reduction and increase with nutrient restoration: 20 years of adaptive management at a Ramsar-listed wastewater treatment plant

Abstract Nutrients such as nitrogen and phosphorus are typically considered detrimental to wetland values, but waterfowl can be numerous on nutrient-rich wetlands. Waterfowl were counted three six times per year nine treatment lagoons associated wetlands (2,025 ha) at the Western Treatment Plant (south-east Australia) from 2000, help maintain ecological values of this Ramsar-listed well treating sewage for a large city (Melbourne). Up 185,000 counted, varying with season, continental rainfall lagoon operation. Nutrient levels reduced Lake Borrie in 2005 (as part an Environmental Improvement Program) restored 2015. declined when it received treated effluent not raw sewage, increased 2015 partially sewage. This pattern was highly significant total most species guilds replicated other lagoons. Modelling revealed positive relationships between numbers nutrient concentrations, including ammonia nitrite, moderate levels. shows that careful management enrichment have benefits, allowing artificial wastewater plants support high densities waterbirds food webs sustain them.