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Suspended sediment transport in montane headwaters is important to water quality and nutrient balances. However, predictions of sediment source and transport can be difficult, in part, because of a changing climate and increasing frequencies of disturbances. We used observations from 10 headwater streams in water year (WY; starting on 1st October ending on 30th September) 2007–2009 and 2013–2018 to determine the potential impacts of climate and forest management on suspended sediment delivery. We analysed hysteretic responses of suspended sediment for 76 events in five headwater catchments within a snow‐dominated site and another five within a lower‐elevation, rain‐snow transition site, in the mixed‐conifer zone of California's Sierra Nevada. Hysteresis patterns were predominantly clockwise at both sites, suggesting localized sediment sources such as streambeds and banks. The warmer, transition site exhibited a lower proportion of clockwise‐loop events, faster transport speed and higher peak sediment concentrations than the snow‐dominated site. This suggests extended sediment sources and increases in transport can occur as currently snow‐dominated areas become rain‐snow transitional. Over the nine water years, we observed similar hysteresis effects amongst years under drought, near‐average, and extremely wet conditions. Hence, fluctuations in precipitation amounts across years may not influence sediment source area substantially. Furthermore, we compared hysteresis metrics between the control, thin only, burn only and thin combined with burn catchments during the posttreatment period (WY 2013–2018). Hysteresis effects remained unchanged amongst treatments, which may be attributed to the combinations of low‐intensity operations implemented with best management practises combined with a four‐year drought (WY 2013–2016). Taken together, sediment sources in small headwater catchments will probably remain localized with changing precipitation levels and low‐intensity management operations, but it may be extended and potentially lead to higher sediment yields as the main hydrologic input shifts from primarily snow to a mix of rain and snow. [ABSTRACT FROM AUTHOR]

Suspended sediment transport in montane headwaters is important to water quality and nutrient balances. However, predictions of sediment source and transport can be difficult, in part, because of a changing climate and increasing frequencies of disturbances. We used observations from 10 headwater streams in water year (WY; starting on 1st October ending on 30th September) 2007–2009 and 2013–2018 to determine the potential impacts of climate and forest management on suspended sediment delivery. We analysed hysteretic responses of suspended sediment for 76 events in five headwater catchments within a snow‐dominated site and another five within a lower‐elevation, rain‐snow transition site, in the mixed‐conifer zone of California's Sierra Nevada. Hysteresis patterns were predominantly clockwise at both sites, suggesting localized sediment sources such as streambeds and banks. The warmer, transition site exhibited a lower proportion of clockwise‐loop events, faster transport speed and higher peak sediment concentrations than the snow‐dominated site. This suggests extended sediment sources and increases in transport can occur as currently snow‐dominated areas become rain‐snow transitional. Over the nine water years, we observed similar hysteresis effects amongst years under drought, near‐average, and extremely wet conditions. Hence, fluctuations in precipitation amounts across years may not influence sediment source area substantially. Furthermore, we compared hysteresis metrics between the control, thin only, burn only and thin combined with burn catchments during the posttreatment period (WY 2013–2018). Hysteresis effects remained unchanged amongst treatments, which may be attributed to the combinations of low‐intensity operations implemented with best management practises combined with a four‐year drought (WY 2013–2016). Taken together, sediment sources in small headwater catchments will probably remain localized with changing precipitation levels and low‐intensity management operations, but it may be extended and potentially lead to higher sediment yields as the main hydrologic input shifts from primarily snow to a mix of rain and snow. [ABSTRACT FROM AUTHOR]

We present here a method to integrate geologic, topographic, and land-cover data in a geographic information system to provide a fine-scale, spatially explicit prediction of sediment yield to support management applications. The method is fundamentally qualitative but can be quantified using preexisting sediment-yield data, where available, to verify predictions using other independent data sets. In the 674-km Sespe Creek watershed of southern California, 30 unique 'geomorphic landscape units' (GLUs, defined by relatively homogenous areas of geology, hillslope gradient, and land cover) provide a framework for discriminating relative rates of sediment yield across this landscape. Field observations define three broad groupings of GLUs that are well-associated with types, relative magnitudes, and rates of erosion processes. These relative rates were then quantified using sediment-removal data from nearby debris basins, which allow relatively low-precision but robust calculations of both local and whole-watershed sediment yields, based on the key assumption that minimal sediment storage throughout most of the watershed supports near-equivalency of long-term rates of hillslope sediment production and watershed sediment yield. The accuracy of these calculations can be independently assessed using geologically inferred uplift rates and integrated suspended sediment measurements from mainstem Sespe Creek, which indicate watershed-averaged erosion rates between about 0.6-1.0 mm year and corresponding sediment yields of about 2 × 10 t km year. A spatially explicit representation of sediment production is particularly useful in a region where wildfires, rapid urban development, and the downstream delivery of upstream sediment loads are critical drivers of both geomorphic processes and land-use management. [ABSTRACT FROM AUTHOR]