Integrating environmental models and precision agriculture data to identify spatially explicit subfield opportunities for increased sustainability and economic return

From a general vantage point, mechanized agriculture cropping system fields such as those producing maize, wheat, and soybean appear to homogenous in terms of yield and economic return. However, the availability of precision agriculture data has revealed subfield variability in yield and economic performance as well as environmental impact. While subfield spatial and temporal variability of yields is known to exist and can be characterized using yield monitor or remote sensing technology, how to best use these data sources to better improve both economic and environmental performance remains challenging. The following dissertation describes the integration of environmental and economic modeling tools with precision agriculture data and public databases to identify subfield areas where the adoption of more sustainable practices is both environmentally impactful as well as cost-effective. Chapter 1 of the dissertation describes the development of a precision agro-economic and environmental performance tool. To assess the tool performance, modeled data was compared with empirical NO3--N leaching data obtained from a long-term experiment. Results of the comparison showed the model captured spatial variability of NO3--N leaching at the subfield spatial scale with an average RMSE of 21.5 kg ha-1 and an r2 of 0.19. A case study analysis of a cropping system field using the modeling framework revealed estimated NO3--N leaching and ROI were correlated, and high priority zones with low ROI and high NO3- leaching were found to represent approximately 6% of the total field area. Chapter 2 focuses on the application of the precision agro-economic and environmental modeling framework described in Chapter 1. Analysis of 15 fields showed a significant correlation between N-loss and economic return indicating a majority of fields contain areas susceptible to limited ROI and high NO3- leaching and/or N2O emissions. Simulating the targeted integration of switchgrass in these areas was estimated to reduce field-scale NO3--N leaching by up to 21.1% and , however the economic impacts were dependent on potential biomass prices which were predicted to approximately $93 t-1 yr-1 in order to reach relative break-even compared with maize and soybean cropping. Chapter 3 describes the novel use of the ApSIM agriculture system simulator and public data sources as a tool for estimating economically optimum seeding and N-fertilizer application rates at field to subfield scales. Maximum crop productivity typically corresponded with maximum seeding and N-fertilizer rates, however maximum ROI often corresponded with reduced input resources, particularly seeding density. Modeled crop production loss between maximum yield and maximum ROI seeding and N-management scenarios ranged from 313.2 to 538.7 kg ha-1 and corresponded with an ROI increases ranging from 5.5 to 11.0%. Results indicated yield-oriented seeding and N-fertilizer recommendations decrease potential ROI

Ecological modelling of a wetland for phytoremediating Cu, Zn and Mn in a gold–copper mine site using Typha domingensis (Poales: Typhaceae) near Orange, NSW, Australia

Abstract: An artificial wetland was computationally modelled using STELLA®, a graphical programming tool for an Au–Cu mine site in Central-west NSW, the aim of which was to offer a predictive analysis of a proposed wetland for Cu, Zn and Mn removal using Typha domingensis as the agent. The model considers the important factors that impact phytoremediation of Cu, Zn and Mn. Simulations were performed to optimise the area of the wetland; concentration of Cu, Zn and Mn released from mine (AMD); and flow rates of water for maximum absorption of the metals. A scenario analysis indicates that at AMD = 0.75mg/L for Cu, Zn and Mn, 12.5, 8.6, and 357.9 kg of Cu, Zn and Mn, respectively, will be assimilated by the wetland in 35 years, which would be equivalent to 61 mg of Cu/kg, 70 mg of Zn/kg and 2,886 mg of Mn/kg of T. domingensis, respectively. However, should Cu, Zn and Mn in AMD increase to 3 mg/L, then 18.6 kg of Cu and 11.8 kg of Zn, respectively, will be assimilated in 35 years, whereas no substantial increase in absorption for Mn would occur. This indicates that 91 mg of Cu, 96 mg of Zn and 2917 mg of Mn will be assimilated for every kg of T. domingensis in the wetland. The best option for Cu storage would be to construct a wetland of 50,000 m2 area (AMD = 0.367 mg/L of Cu), which would capture 14.1 kg of Cu in 43 years, eventually releasing only 3.9 kg of Cu downstream. Simulations performed for a WA of 30,000 m2 indicate that for AMD = 0.367 mg/L of Zn, the wetland captures 6.2 kg, releasing only 3.5 kg downstream after 43 years; the concentration of Zn in the leachate would be 10.2 kg, making this the most efficient wetland amongst the options considered for phytoremediating Zn. This work will help mine managers and environmental researchers in developing an effective environmental management plan by focusing on phytoremediation, with a view at extracting Cu, Zn and Mn from the contaminated sites

Soil redistribution and carbon dynamics in Mediterranean agroecosystems: Radioisotopic modelling at different spatial and temporal scales

66 Pags. Tesis elaborada en la EEAD-CSIC y presentada en la Univ. Zaragoza, Departamento de Ciencias de la Tierra. Incluye las referencias de los ocho artículos científicos realizados durante el período de la tesis, accesibles a texto completo a través de sus enlaces doi (versiones de los editores) y handle (versiones finales de autor en acceso abierto depositadas en repositorio Digital.CSIC) .The results of this thesis revealed that the spatial patterns of soil properties and soil nutrients are closely related to landscape position and topographie characteristies. Higher contents of finer soíl particles «0.05 mm soil fractíon) including magnetic minerals and 137cs, soil organic matter and SOC and SON were reeorded in the upper part of the field. On the contrary the contents of carbonate, coarse and sand fractions were inversely corrrelated with topographic characteristics. Spatial patterns of soil properties, 137Cs and soil nutrients indicated that their distribution was related to similar physical processes.This thesis contributes lo improve the knowledge of mechanisms that can explain why soil characteristics, land use and redistribution processcs are key factors that determine the current status of soil and can be used to identify suitable locations for implementing soil conservation strategies in Mediterranean mountain agroecosyslems.This doctoral project was funded by a pre-doctoral fellowship (Formación de Personal Investigador; FPI BES-2009-016976) of the Spanish Ministry of Economy and Competitiveness associated with the lnterministerial Commission for Science and Technology (CICYT) projects "Soil erosion and carbon dynamics in Mediterranean agroecosystems: radioisotopic modelling at different spatial and temporal scales" (MEDEROCAR; CGL2008-0831) and "Erosion and redistribution of soils and nutrients in Mediterranean agroecosystems: radioisotopic tracers of sources and sinks and modelling scenarios" (EROMED; CGL2011-25486) of the Spanish Ministry of Economy and Competitiveness.Peer reviewe

Modeling Nutrient Legacies and Time Lags in Agricultural Landscapes: A Midwestern Case Study

Land-use change and agricultural intensification have increased food production but at the cost of polluting surface and groundwater. Best management practices implemented to improve water quality have met with limited success. Such lack of success is increasingly attributed to legacy nutrient stores in the subsurface that may act as sources after reduction of external inputs. These legacy stores have built up over decades of fertilizer application and contribute to time lags between the implementation of best management practices and water quality improvement. However, current water quality models lack a framework to capture these legacy effects and corresponding lag times. The overall goal of this thesis is to use a combination of data synthesis and modeling to quantify legacy stores and time lags in intensively managed agricultural landscapes in the Midwestern US. The specific goals are to (1) quantify legacy nitrogen accumulation using a mass balance approach from 1949 - 2012 (2) develop a SWAT model for the basin and demonstrate the value of using crop yield information to increase model robustness (3) modify the SWAT (Soil Water Assessment Tool) model to capture the effect of nitrogen (N) legacies on water quality under multiple land-management scenarios, and (4) use a field-scale carbon-nitrogen cycling model (CENTURY) to quantify the role of climate and soil type on legacy accumulation and water quality. For objectives 1 and 2, the analysis was performed in the Iowa Cedar Basin (ICB), a 32,660 km2 watershed in Eastern Iowa, while for objective 3, the focus has been on the South Fork Iowa River Watershed (SFIRW), a 502 km2 sub-watershed of the ICB, and for objective 4 the focus was at the field scale. For the first objective, a nitrogen mass balance analysis was performed across the ICB to understand whether legacy N was accumulating in this watershed and if so, the magnitude of accumulation. The magnitude of N inputs, outputs, and storage in the watershed was quantified over 64 years (1949 – 2012) using the Net Anthropogenic Nitrogen Inputs (NANI) framework. The primary inputs to the system were atmospheric N deposition (9.2 ± 0.35 kg/ha/yr), fertilizer N application (48 ± 2 kg/ha/yr) and biological N fixation (49 ± 3 kg/ha/yr) and while the primary outputs from the system was net food and feed that was estimated as 42 ± 4.5 kg/ha/yr. The Net Anthropogenic Nitrogen Input (NANI) to the system was estimated to be 64 ± 6 kg/ha/yr. Finally, an estimated denitrification rate constant of 12.7 kg/ha/yr was used to estimate the subsurface legacy nitrogen storage as 33.3 kg/ha/yr. This is a significant component of the overall mass budget and represents 48% of the NANI and 31% of the fertilizer added to the watershed every year. For the second objective, the effect of crop yield calibration in increasing the robustness of the hydrologic model was analyzed. Using a 32,660 km2 agricultural watershed in Iowa as a case study, a stepwise model refinement was performed to show how the consideration of additional data sources can increase model consistency. As a first step, a hydrologic model was developed using the Soil and Water Assessment Tool (SWAT) that provided excellent monthly streamflow statistics at eight stations within the watershed. However, comparing spatially distributed crop yield measurements with modeled results revealed a strong underestimation in model estimates (PBIAS Corn = 26%, PBIAS soybean = 61%). To address this, the model was refined by first adding crop yield as an additional calibration target and then changing the potential evapotranspiration estimation method -- this significantly improved model predictions of crop yield (PBIAS Corn = 3%, PBIAS soybean = 4%), while only slightly improving streamflow statistics. As a final step, for better representation of tile flow, the flow partitioning method was modified. The final model was also able to (i) better capture variations in nitrate loads at the catchment outlet with no calibration and (ii) reduce parameter uncertainty, model prediction uncertainty, and equifinality. The findings highlight that using additional data sources to improve hydrological consistency of distributed models increases their robustness and predictive ability. For the third objective, the SWAT model was modified to capture the effects of nitrogen (N) legacies on water quality under multiple land-management scenarios. My new SWAT-LAG model includes (1) a modified carbon-nitrogen cycling module to capture the dynamics of soil N accumulation, and (2) a groundwater travel time distribution module to capture a range of subsurface travel times. Using a 502 km2 SFIR watershed as a case study, it was estimated that, between 1950 and 2016, 25% of the total watershed N surplus (N Deposition + Fertilizer + Manure + N Fixation – Crop N uptake) had accumulated within the root zone, 14% had accumulated in groundwater, while 27% was lost as riverine output, and 34% was denitrified. In future scenarios, a 100% reduction in fertilizer application led to a 79% reduction in stream N load, but the SWAT-LAG results suggest that it would take 84 years to achieve this reduction, in contrast to the two years predicted in the original SWAT model. The framework proposed here constitutes a first step towards modifying a widely used modeling approach to assess the effects of legacy N on time required to achieve water quality goals. The above research highlighted significant uncertainty in the prediction of biogeochemical legacies -- to address this uncertainty in the last objective the field scale CENTURY model was used to quantify SON accumulation and depletion trends using climate and soil type gradients characteristic of the Mississippi River Basin. The model was validated using field-scale data, from field sites in north-central Illinois that had SON data over 140 years (1875-2014). The study revealed that across the climate gradient typical of the Mississippi River Basin, SON accumulation was greater in warmer areas due to greater crop yield with an increase in temperature. The accumulation was also higher in drier areas due to less N lost by leaching. Finally, the analysis revealed an interesting hysteretic pattern, where the same levels of SON in the 1930s contributed to a lower mineralization flux compared to current

Modelling and simulating change in reforesting mountain landscapes using a social-ecological framework

Natural reforestation of European mountain landscapes raises major environmental and societal issues. With local stakeholders in the Pyrenees National Park area (France), we studied agricultural landscape colonisation by ash (Fraxinus excelsior) to enlighten its impacts on biodiversity and other landscape functions of importance for the valley socio-economics. The study comprised an integrated assessment of land-use and land-cover change (LUCC) since the 1950s, and a scenario analysis of alternative future policy. We combined knowledge and methods from landscape ecology, land change and agricultural sciences, and a set of coordinated field studies to capture interactions and feedback in the local landscape/land-use system. Our results elicited the hierarchically-nested relationships between social and ecological processes. Agricultural change played a preeminent role in the spatial and temporal patterns of LUCC. Landscape colonisation by ash at the parcel level of organisation was merely controlled by grassland management, and in fact depended on the farmer's land management at the whole-farm level. LUCC patterns at the landscape level depended to a great extent on interactions between farm household behaviours and the spatial arrangement of landholdings within the landscape mosaic. Our results stressed the need to represent the local SES function at a fine scale to adequately capture scenarios of change in landscape functions. These findings orientated our modelling choices in the building an agent-based model for LUCC simulation (SMASH - Spatialized Multi-Agent System of landscape colonization by ASH). We discuss our method and results with reference to topical issues in interdisciplinary research into the sustainability of multifunctional landscapes

Assessing monitoring and modeling approaches to improve water quality in the Hickory Grove Lake

Surface water quality regulated by agricultural pollution remains to be an important environmental concern around the world. Major contaminants from agriculture systems such as bacteria, sediment, and nutrients (nitrogen and phosphorus) continue to affect the designated use of a waterbody. As per the Clean Water Act legislation, water quality impairments must be addressed through the Total Maximum Daily Load (TMDL) approach. The TMDL program is a comprehensive and watershed-scale approach involving contaminant source identification and quantification, and conservation practice recommendation to reduce contaminant transport. The overall goal of this study was to improve the TMDL development process in achieving water quality goals and restoring impaired waterbodies. Specific objectives were to: (1) identify phosphorus transport pathways during rainfall-runoff events in a tile-dominated agricultural watershed; (2) demonstrate a novel approach in setting a bacteria TMDL for an impaired waterbody and; (3) determine potential locations for conservation practice placement at the watershed-scale to maximize reduction of sediment transport. The Hickory Grove Lake located in central Iowa, a waterbody impaired due to E. coli levels at the swimming beach was the focus of this study. Phosphorus (P) transport pathways in the tile drained agricultural watershed were determined through intensive monitoring during runoff events and a chemical hydrograph separation (CHS) method. Rainfall events in Spring 2013 were monitored for flow, Dissolved Reactive Phosphorus (DRP) and Total Phosphorus (TP) concentrations at the tile outlet (TO) and subwatershed outlet (SO) in the Hickory Grove Lake Watershed (HGLW). The drainage areas of TO and SO are 879 ha and 852 ha, respectively. The discharge at TO comprises runoff from surface intakes and flow from subsurface tile-drains, whereas discharge at SO comprises flow from TO and surface runoff during runoff events. The median TP concentrations during spring runoff events in 2013 at TO and SO were 0.89 mg/L and 1.13 mg/L, respectively. The TP and DRP levels at TO and SO during low flow and high flow conditions were similar. The highest P levels at TO and SO were observed during the rising limb of the hydrograph. Surface intakes accounted for 15.2% of the total discharge at SO and 23.6% of the total discharge at TO. It was also estimated that 28.2% of the TP load at SO originated from surface intakes. Due to surface intake contribution to subsurface tile-drains, similar P concentrations were observed in TO and SO. This study improves understanding of the P dynamics and transport pathways in tile drained agricultural watersheds. Therefore, contaminant source identification and quantification during TMDL development must acknowledge the underappreciated transport pathway of P (surface intake) in tile drained watersheds. The Hickory Grove Lake beach was listed on Iowa\u27s 303d list of impaired waters due to elevated E. coli concentrations, and therefore, a novel approach was proposed to develop a bacteria TMDL. Fecal bacteria monitoring data at the Hickory Grove Lake Inlet, Lake Outlet, and Lake Beach was used to develop linear regression relationships and understand the influence of fecal bacteria sources in the watershed on the Lake Beach E. coli levels. It was determined that fecal bacteria from the HGLW had very little effect on E. coli levels at the Lake Beach, instead fecal bacteria from waterfowl were regulating the E. coli levels at the beach. Spatial monitoring of the lake suggested that E. coli levels were elevated at the Lake Beach and at other locations where geese reside year-round. A TMDL developed using a Near-Shore Beach Volume model was set at 1.8 x 1011 cfu/day for the single sample mean (SSM) target and 1.01 x 1011 cfu/day for the geometric mean target. The daily fecal bacteria load from as few as 5 resident geese were sufficient to cause E. coli levels at the Lake Beach to exceed the SSM standard. Therefore, efforts to achieve the bacteria TMDL must focus on deterring the resident geese at the lake. Conservation practice recommendation and placement to mitigate contaminant transport is the next step after TMDL development. Spatial monitoring of the Hickory Grove Lake in November 2012 indicated that the east basin of the lake is now filled with sediment. The Light Detection and Ranging (LiDAR) data and precision conservation technologies were used in this study to identify potential locations for grassed waterway (GWW) placement in the HGLW to reduce sediment transport. The compound topographic index (CTI) model supplemented with 3 m LiDAR data was used to identify GWW locations. The CTI model identified all existing GWWs and recommended new locations for GWW placement at a CTI threshold of 30. The CTI model overestimated the lengths of existing GWWs suggesting a need to further extend the GWWs. The design recommendations of the predicted GWWs suggested that the total surface area required for predicted GWWs was 29.3 ha. The results of this study imply that LiDAR derived terrain attributes can be effectively used in identifying potential locations for GWWs. The overall results of the complete study suggest that conventional TMDL development may not be appropriate for all impaired waterbodies; a novel and holistic approach is required depending on the contaminant source and its transport pathways, watershed characteristics, and hydrology of the watershed