Benjamin Abban

From soilscapes to landscapes: A landscape‐oriented approach to simulate soil organic carbon dynamics in intensively managed landscapes

Most available biogeochemical models focus within a soil profile and cannot adequately resolve contributions of the lighter size fractions of organic rich soils for enrichment ratio (ER) estimates, thereby causing unintended errors in soil organic carbon (SOC) storage predictions. These models set ER as constant, usually equal to unity. The goal of this study is to provide spatiotemporal predictions of SOC stocks at the hillslope scale that account for the selective entrainment and deposition of lighter size fractions. It is hypothesized herein that ER values may vary depending on hillslope location, Land Use/Land Cover (LULC) conditions, and magnitude of the hydrologic event. An ER module interlinked with two established models, CENTURY and Watershed Erosion Prediction Project, is developed that considers the effects of changing runoff coefficients, bare soil coverage, tillage depth, fertilization, and soil roughness on SOC redistribution and storage. In this study, a representative hillslope is partitioned into two control volumes (CVs): a net erosional upslope zone and a net depositional downslope zone. We first estimate ER values for both CVs I and II for different hydrologic and LULC conditions. Second, using the improved ER estimates for the two CVs, we evaluate the effects that management practices have on SOC redistribution during different crop rotations. Overall, LULC promoting less runoff generally yielded higher ER values, which ranged between 0.97 and 3.25. Eroded soils in the upland CV were up to 4% more enriched in SOC than eroded soils in the downslope CV due to larger interrill contributions, which were found to be of equal importance to rill contributions. The chronosequence in SOC storage for the erosional zone revealed that conservation tillage and enhanced crop yields begun in the 1980s reversed the downward trend in SOC losses, causing nearly 26% of the lost SOC to be regained.

Quantifying Sediment Sources to the Suspended Load of an Agricultural Stream Using Radioisotopes

The goal of this study was to understand better the delivery of sediment to streams in small, intensively agricultural watersheds of the U.S. Midwest by determining the amount of sediment coming from the fields and stream banks during three consecutive runoff events. The natural activities of Beryllium-7 and Lead-210 in different source soils were compared with the corresponding activities of the suspended sediment collected in the stream during these events. Both a simple two end-member mixing model and a Bayesian model were used to determine the relative contributions from the source areas to the suspended load of each event. The two end-member approach suggested that ~60% of the sediment carried in the stream during the first event was eroded upland soils and was attributed to a “first flush” of readily available material from past events. For the second and third events, the amounts of eroded upland soils were ~34% and ~26%, respectively, because less material was readily available for mobilization. The two end-member model results compared favorably with the Bayesian model, which also incorporated Cesium-137 as a third tracer. Additionally, these results were confirmed with the clockwise hysteresis observed in the different events. During the third event, a flash flood, stream bank collapse was observed and bank retreat estimates from multiple methods compared favorably with the partitioning results. Quantifying sediment sources in watersheds will allow land managers to target more accurately areas where Best Management Practices (BMPs) are most needed to control sediment-related problems. INTRODUCTION Quantifying erosion and sediment delivery at the watershed scale has proven difficult due to high temporal and spatial variability of the different erosion processes occurring over a landscape (Church 2006), despite recent progress in understanding the mechanisms of erosion (e.g., Romkens et al. 2002; Govers et al. 2007). This problem is further exacerbated in agricultural areas where anthropogenic activities, including tillage (e.g., Van Oost et al. 2006) and channel straightening (e.g., Urban and Rhoads 2003) are added stressors. The need still exists to identify and quantify 1243 World Environmental and Water Resources Congress 2014: Water without Borders

The coupling of WEPP and 3ST1D numerical models for improved estimation of runoff and sediment yield at watershed scales

One of the major problems in watershed hydrology and sedimentology is to accurately simulate the transport of water and sediment from their sources to the watershed outlet. Current numerical models have been extensively used to determine upland erosion, but their application is primarily limited to the field/hillslope scale without providing an estimation for the sediment delivery to the main channels. Along the same lines, hydrodynamic and sediment transport models of the in-stream channel processes have been developed assuming that the channel system is isolated from its surrounding hills. This lack of connectivity between the upland erosion and the in-stream channel processes introduces significant error in the water and sediment yield estimates along the channel network. The main objective of our study is to provide a modeling framework to evaluate transport of water and sediment from the fields to the main channels. To meet this objective, two numerical models will be coupled; the well established WEPP model, which is a continuous process-based upland erosion simulation model capable of accounting for the effects of crop rotation, and the one-dimensional 3ST1D model which is used to calculate flow and sediment transport within the channels. The main advantage of 3ST1D is that it can handle transcritical flows without violating the flow continuity equation, it is applicable for both cohesive and non-cohesive sediments and includes various formulas for determining the sediment transport capacity as well as incipient motion criteria. It is envisaged that the coupled model will improve water and sediment yield estimates at the watershed scale, thus making it possible to evaluate the efficiency of various erosion prevention Best Management Practices, currently being evaluated primarily at the hillslope scale.

Coupling flow with nutrient dynamics via BioChemFOAM in the Mississippi River

An enhanced three-dimensional unsteady hydrodynamic, multispecies transport fate model called BioChemFOAM was developed in OpenFOAM-free computational fluid dynamic platform for understanding and predicting nutrient dynamics, namely, transport and transformation, in aquatic ecosystems. The study motivation was to better quantify transport and distribution of nutrient species in the Upper Mississippi River Basin (UMRB), a major source of nutrient contributor from intense agriculture. The study is unique in examining the transport and reactivity rates under complex hydrologic conditions where main conveyance channels and backwaters co-exist. The model has two main components: a new coupling of turbulent flow processes with multiple species to modulate transport and reaction rates simulations at channel/backwater areas and a complex chemical and biological transformation module suited for species reaction rates in backwaters. The coupled model was first tested for an idealistic domain/case borrowed from the literature. The final model was calibrated, tested and verified in the UMRB.

Framework for Bridge Scour Measurement Using Radio Frequency IDentification (RFID)

Scour around bridge piers can undermine the bridge integrity and cause catastrophic bridge failures. The goal of this coupled experimental and theoretical study is to set a framework for applying Radio Frequency IDentification (RFID) technology to develop a bridge scour remote monitoring system. RFID involves the wireless exchange of information between a base station (reader) and a transponder via an antenna. The proposed bridge scour monitoring system utilizes the Return Signal Strength Indicator (RSSI) of a transponder buried in the vicinity of the pier to determine the transponder distance from the antenna and thus the scour depth. In this study we present a novel methodology for experimentally determining the RSSI voltage for a low frequency (134.2 kHz), passive RFID system.