A CONNECTIVITY FRAMEWORK TO EXPLORE THE ROLE OF ANTHROPOGENIC ACTIVITY AND CLIMATE ON THE PROPAGATION OF WATER AND SEDIMENT AT THE CATCHMENT SCALE

Anthropogenic disturbance in intensively managed landscapes (IMLs) has dramatically altered critical zone processes, resulting in fundamental changes in material fluxes. Mitigating the negative effects of anthropogenic disturbance and making informed decisions for optimal placement and assessment of best management practices (BMPs) requires fundamental understanding of how different practices affect the connectivity or lack thereof of governing transport processes and resulting material fluxes across different landscape compartments within the hillslope-channel continuum of IMLs. However, there are no models operating at the event timescale that can accurately predict material flux transport from the hillslope to the catchment scale capturing the spatial and temporal heterogeneity of landscape features arising from anthropogenic disturbance.

The overarching goal of this research is to develop a landscape connectivity framework that encapsulates relevant hydrological and sediment transport processes occurring across different spatio-temporal scales and apply the framework to assess the role of anthropogenic activity and climate drivers on the propagation of water signals, with particular emphasis on understanding the degree to which humans have altered the connectivity of IMLs with respect to lower agroecosystem disturbance conditions.

The connectivity framework was developed, verified, and implemented within the context of a case study in South Amana Sub-Watershed (SASW), IA. The framework consists of a bottom-up geomorphic hydrological routing component for hillslope planes coupled with a diffusive wave channel routing component for channels that are interlinked and resolve timescales from seconds to days and spatial scales from the plot scale to the watershed scale. The framework was informed and verified based on an extensive collection of data, including in situ sampling, rainfall simulation experiments at the plot scale, literature/theoretically derived data, remote sensing data, instream dye tracing data, and watershed outlet data.

At the plot scale, key findings revealed the importance of accounting for the emergence and evolution of geomorphic micro-features. Hillslope scale findings indicated that an optimal resolution on the 0.1 m order of magnitude was sufficient for accurate representation of the structure of the hydrograph peak, as commonly used resolutions of 1 m and above were shown to introduce significant bias with regards to both hydrograph peak flow and the time-to-peak. Key findings at the watershed scale suggested that shifting from vegetated hillslope planes to grassed waterway best management practices will most likely lead to an increase in the overall peakiness of the hydrographs, will reduce their overall time to peak and will progressively increase the peakiness of the hydrographs along the drainage network. Also, a characteristic threshold drainage area on the order of ~1-10 km² was identified, beyond which the variability in the characteristic peak magnitude and timescale decreases significantly as a result of geomorphologic and hydrodynamic dispersion.