Quantifying the hydrological services of wetlands with respect to the Strahler order of their river segments

• Sequential assessment allows estimating the marginal contribution of each Strahler order to hydrological services. • Cumulative and normalized analyses reveal the compound upstream–downstream asymmetry in wetland services. • Low flow indicators (e.g. 7Q2) exhibit exponential declines emphasizing the disproportionate impact of wetland loss on drought resilience. • High flow indicators (e.g., Q2, Q20) show a near-linear increase with wetland area loss. • Normalized hydrological impacts shows a consistent 0.05–0.08 m 3 s −1 km −2 attenuation per km 2 of wetland lost. Hydrological services associated with wetlands are critical for water resource management, particularly in mitigating extreme flows and maintaining hydrological stability. This study quantifies these services by examining the spatial distribution of wetlands relative to the Strahler order of their associated river segments within the USA-Canada transboundary Lake Champlain-Richelieu River (LCRR) watershed. A semi-distributed hydrological model (PHYSITEL/HYDROTEL) was employed to simulate the effects of wetland loss across 20 subwatersheds, spanning diverse sizes and hydrographic configurations. Three assessment methods (cumulative upstream-to-downstream, sequential, and cumulative downstream-to-upstream) were used to evaluate changes in key hydrological indicators, including high flows (Q2, Q10, Q50) and low flows (7Q2, 7Q10, 30Q5), under various wetland scenarios. The results reveal that upstream wetlands, particularly those associated with Strahler order 1 segments, exert a disproportionate influence on hydrological regulation. Wetland loss was shown to amplify high flows linearly, with a 3.5% loss in wetland area corresponding to a 1% increase in high flow indicators. Conversely, low flows exhibited an exponential decline in response to wetland loss, highlighting the reduced resilience to drought conditions. By analyzing many subwatersheds with varying sizes and configurations, this study provides insights that extend beyond the LCRR, offering a framework applicable to other watersheds with heterogeneous characteristics. This research is novel in its use of 20 diverse subwatersheds to identify generalizable trends in wetland hydrological services, a scale and heterogeneity not previously addressed in similar studies. It underscores the necessity of preserving upstream wetlands to mitigate flooding and sustain baseflows, particularly in regions facing increasing hydrological variability. While an empirical rule for high flow regulation was identified, more work is needed to refine low flow relationships and incorporate typological wetland distinctions (e.g., riparian vs. isolated). These findings provide actionable insights for land management planning and wetland conservation, emphasizing their role in promoting hydrological stability at both local and regional scales