Increasing riparian vegetation cover to improve water quality: the importance of considering land use

Riparian vegetation plays a crucial role in regulating sediment dynamics, reducing surface runoff, mobilising sediment and stabilising streambanks. Despite extensive research on sediment loads and riparian vegetation individually, there remains a gap in understanding their interrelationship, particularly within the context of water quality and catchment management. This study investigates the statistical association between water quality and riparian vegetation cover within the Herbert catchment, Far North Queensland, Australia. Over one million total suspended sediment equivalent (TSSeq) data points were collected from 14 monitoring sites between December 2020 and December 2023, averaged into 361 monthly samples and paired with site-specific total cover (TC) values. Using Spearman's rank correlation across land use disturbance classes (minimal, moderate, high) and seasonal subsets, results revealed a significant overall negative correlation between TSSeq and TC (ρ = -0.431, p < 0.0001). The strength of this relationship declined with increasing disturbance: minimal disturbance sites showed the strongest correlation (ρ = -0.530, p < 0.0001), while at high disturbance sites the correlation was not significant (ρ = 0.075, p > 0.05). Seasonal analysis showed stronger correlations during the wet season, except in high disturbance areas, where the dry season correlation was higher but still not statistically significant. Limitations in TC's ability to distinguish vegetation types and capture dynamic cover changes in disturbed areas are discussed. These findings highlight the importance of riparian vegetation in improving water quality and underscore the need for refined remote sensing methods when integrating high-resolution temporal water quality datasets.