The role of riparian buffers in protecting stream water quality and habitat integrity: thresholds for freshwater management

Freshwater ecosystems face multiple stressors from agriculture, dispersed urbanization, and forestry plantations (eucalyptus, coniferous), which degrade water quality and habitat integrity. To assess the effectiveness of riparian strips as ecological buffers, we selected 168 sites in Galicia (NW Iberian Peninsula). We applied a methodological approach to identify impacts at different spatial scales (basin, riparian and reach), along multiple pressure intensification gradients. Generalized Additive Models (GAMs) were fitted to compare different models including basin and riparian predictors alone, and combined models to predict water quality and habitat integrity variables. The combined models showed high significant predictive capacity for water quality, while performance was lower for habitat integrity variables. Relevant quantitative ecological thresholds concerning basin and riparian management practises were also identified: agriculture cover exceeding 15% and urban higher than 6% increased nitrogen and phosphorus exports to streams, while extensive agricultural over 8% seem to partially limit these inputs. Moreover, wider native riparian forest (> 7 m) generally showed lower nutrient concentrations and better habitat conditions compared to those with exotic riparian trees presence. However, higher tree density and steeper riparian slopes increased nitrogen inputs to streams while simultaneously benefiting in-stream habitat structure. We conclude that riparian forests can act as effective ecological buffers mitigating multiple pressures impact to streams, although basin-scale management remains essential. These results provide fundamental support for the ecological protection of rivers, as establishing limitations for basin scale activities and defining appropriate riparian characteristics are critical to maintaining good water quality and habitat integrity.