Management effectiveness in a freshwater protected area: Long-term water quality response to catchment-scale land use changes

As freshwater environments become increasingly threatened, the need for efficient and effective protection grows more urgent. Yet quantitative evidence of management effectiveness within freshwater protected areas is limited, inhibiting our ability to infer the practicality and efficacy of practices. Herein, we employ linear mixed-effects models and time series models to evaluate the connection between catchment-scale management actions and surface water quality within a freshwater protected area, over the past three decades. Within the study area, all croplands were restored to traditional grasslands resulting in a landscape dominated by meadows and forests. The extent of land use change and time frame needed for water quality improvements were investigated and management effectiveness appraised. Results indicate that the complete grassing of croplands was approximately three times more effective at reducing concentrations of nitrate than electrical conductivity and calcium. Significant improvements in water quality occurred within nine years of management implementation, with mean annual nitrate concentrations decreasing from 5.5 to 1.9 mg/L following the grassing of all croplands covering 3.1% of the study area, whereas gradual improvements continued over the next 20 years, ultimately resulting in nitrate concentrations below 1.0 mg/L. The results of this study provide valuable insights on how land use conversions in small headwater catchments can influence stream water quality and helps to establish expectations for outcomes when planning conservation strategies.