Detecting shifts in ecosystem functioning: The decoupling of fundamental relationships with increased pollutant stress on sandflats

► Stress on estuarine biota from sediment heavy metals altered ecosystem functioning. ► The strength of coupling between key processes on sandflats was used as an indicator. ► Strength of coupling between processes was more indicative than process magnitudes. ► A decoupling of key processes occurred at low sediment contaminant concentrations. ► Contaminated sites were less responsive to additional stress of organic enrichment.