Key controls on nutrient retention efficiency in vegetated buffer strips: A global meta-analysis
Vegetated buffer strips (VBS) are widely used to mitigate agricultural non-point source pollution yet reported retention efficiencies vary considerably across different landscapes. We synthesized 409 observations extracted from 91 peer-reviewed publications to evaluate critical determinants of VBS retention efficiency for agricultural runoff, focusing specifically on total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS). Our analysis indicated that warmer conditions (mean annual temperature > 13 ◦ C) correlated with increased TN and TP retention, likely due to enhanced microbial processing, plant nutrient uptake, and denitrification kinetics. Conversely, wetter climates (precipitation ≥ 900 mm yr 1 ) improved TN retention but diminished runoff retention, revealing a critical trade-off wherein higher moisture availability supports biogeochemical processes yet reduces hydraulic residence time, increasing bypass potential. Retention efficiency peaked at moderate hydraulic loading rates (5–10 m 3 h 1 ) and higher inflow concentrations, emphasizing the balance between sufficient residence time and optimal reaction rates. Wider buffer strips (>10 m), gentler slopes (<5 ◦ ), and silt- textured soils consistently enhanced retention through improved infiltration and sedimentation processes. Additionally, the effects of vegetation richness on TSS and runoff underscore the importance of structural complexity. Integrated path analysis and regression modeling (TN: R 2 = 0.76; TP: R 2 = 0.73) further identified inflow concentration, buffer width, and slope as primary direct influences on retention efficiency, with climate exerting indirect effects via hydrology. We propose a constraint–modulation conceptual framework, wherein inherent site characteristics define retention potential, while adjustable design factors modulate actual performance. Our findings advocate for climate-adaptive, resource-efficient VBS designs: buffer sizing tailored to local runoff and inflow conditions, prioritization of adequate widths on gentle slopes, and strategic management of retention trade-offs in high-precipitation environments.
Keywords: Nonpoint source pollution, Buffer strips, Nutrient retention, Hydraulic properties, Site constraints
