Comparing and Linking Organic Carbon and Iron in Soil and Headwater Stream in a Pasture and a Forest Catchment in a Central Appalachian Region, West Virginia

Continued global warming and surface water brownification are two main environmental issues which have attracted attention and are related to soil organic carbon (SOC) cycling. Iron oxides differ in reducibility and thus have essential roles in regulating SOC preservation and remineralization in soil and transport of dissolved organic carbon (DOC) from soil to surface water. In the central Appalachian region, anthropogenic disturbances are increasing, which leads to major issues of soil degradation and depletion of SOC concentrations. Cropland and pasture soils are subject to intense disturbances compared to the forest soil, which may lead to differences in SOC fractions and Fe oxides, their interactions, and the export of DOC to surface water. Variable geology and climate have confounding effects on SOC fractions and dynamics. Thus, the use of pseudo-replicated studies may be informative. Thus, a single fine-scale watershed was chosen in this study, which was derived from the same parent materials and had similar climate conditions. These perspectives will provide a theoretical basis for a better understanding of SOC cycling in watersheds of differing scales. They will also aid the development of agricultural best management practices to increase soil ecological functions in mitigating global warming and surface water brownification. SOC fractions have various stabilization mechanisms and turnover times, which change with depth and are highly influenced by land use. In this study, we used total organic carbon (TOC), particulate organic carbon (POC), mineral-associated organic carbon (MOC), and carbon management index (CMI) as indicators to compare cropland with manure application (CM) and continuous pasture (CP) to a hardwood forest (HF) at soil depths of 0-10 and 10-25cm. Land use, depth, and the interactions between them all had significant influences on TOC, POC, MOC, MOC/TOC ratio, and CMI except for the main effect of land use on TOC. CM showed significantly larger POC (12.4 g kg-1) and smaller MOC (8.36 g kg-1) at 10-25cm compared to HF and CP soils. CM soil at 10-25cm had improved soil quality and SOC lability as indicated by a significantly larger CMI value (419.2) while CP soil had decreased soil quality and SOC lability at both 0-10cm (83.7) and 10-25cm (73.6) compared to HF soil. This study implied high sensitivity of the SOC in cropland and pasture surface soils to degrade under disturbance, which implies that better management strategies are still needed to improve soil carbon quality for these agricultural systems. The essential roles of Fe oxides in stabilizing long-term soil SOC, especially aromatic dissolved organic carbon (DOCaro), are well-established in forest soils and sediments. We chose to focus on these processes in agricultural soils in which the input and translocation of native DOC to deeper soils is impacted by management practices. We quantified SOC, Fe oxide bound SOC (Fe-bound OC), and the DOCaro sorption in a forest, a cropland, and a pasture soil at 0-10 and 10-25 cm. Significantly larger amounts of Fe oxides in the cropland soil was observed compared to the forest and pasture soils at both depths (p \u3c 0.05). Land management practices and depth both significantly influenced proportion of the Fe-bound OC (p \u3c 0.05). Larger maximum sorption of DOC in the cropland (315.0 mg kg-1) and pasture (395.0 mg kg-1) soils than the forest soil (96.6 mg kg-1) at 10-25 cm was found. DOCaro sorption decreased in the three soils at 0-10 cm (slope of -0.002 to -0.014 L2 mg-2 m-1) as well as the forest soil at 10-25 cm (-0.016 L2 mg-2 m-1) with increasing equilibrium DOC concentration. Conversely, the cropland and pasture soils at 10-25 cm increased (0.012 to 0.014 L2 mg-2 m-1). These results indicate that the forest, cropland, and pasture managed soils may have more complex sorption behaviors in stabilizing DOCaro and non- DOCaro than previously known. DOC and iron (Fe) have been observed to be important contributors to surface water brownification. Additionally, the DOC quality influences water color by forming Fe-DOC complexes that provide additive effects and is influenced by dominant land use type within watersheds. However, the influence of quantity and quality of DOC on Fe and water color is poorly understood in headwater streams. The aim of this study was to investigate the effects of DOC and Fe on water color in forest (FC) and pasture (GFC) fine-scale watersheds to remove the confounding effects of climate and soil parent materials. Significant differences of DOC, Fe, and water absorbance at 420 nm (a420) between FC and GFC were found (p \u3c 0.05). A dominant contribution to water color was from DOC (95.5 - 63.7%) with a decreasing trend when Fe increased from 0.011 to 0.258 mg L-1. There were no significant interactions between FC and GFC and Fe on either a420/DOC (p = 0.06) or specific ultraviolet absorbance at 254 nm (SUVA254) (p = 0.30). Increasing a420/DOC and SUVA254 were significantly associated with increasing Fe concentration (p \u3c 0.01). Significant interactions were found between FC and GFC and Fe on spectral slope ratio (S ratio) (p \u3c 0.01). The response rate of S ratio with increasing Fe per unit was 0.235 for GFC while it was -11.043 for FC. These differences indicate that land use may change the quality of DOC, influence Fe-DOC interactions, and thus affect water color. DOC and Fe concentrations cause surface water brownification. Land-use effects on the quantity and quality of DOC are well-established in large-scale watersheds. However, there is more to understand about how soil Fe oxides are involved in DOC and Fe processes in soil and stream, especially in fine-scale catchments. We investigated DOC, SUVA254, exchangeable Fe (Feex), and amorphous Fe concentrations (Feamor) in soils as well as DOC, SUVA254, and dissolved Fe in stream water within a fine-scale forest and pasture catchment. Forest soil had a significantly larger average DOC concentration (71.7 ± 33.8 mg kg-1) and lower average SUVA254 (2.8 ± 1.0 L m-1 mg-1) than the pasture soil at 0-10 cm (DOC: 71.7 ± 33.8 mg kg-1; SUVA254: 4.2 ± 1.4 L m-1 mg-1). The pasture soil at 0-10cm had significantly larger average Feex (132.8 ± 57.6 mg kg-1) and Feamor (813.9 ± 461.2 mg kg-1) concentrations than the forest soil (Feex:120.3 ± 55.4 mg kg-1; Feamor: 303.2 ± 213.5 mg kg-1). Negative correlations between Feex and DOC in the forest soil and positive correlations between Feex, Feamor and SUVA254 in both forest and pasture soils were found (p \u3c 0.05). The pasture headwater stream had significantly larger DOC, SUVA254, and Fe than the forest headwater stream (p Collectively, the results indicated land use and season were important factors altering the SOC and Fe dynamics in agricultural and forest catchments. Additionally, this study indicated Fe oxides may interact with DOC differently in watersheds differing in scale, which leads to differences in the quantity and quality of DOC and dissolved Fe in these watersheds. Therefore, studies combining the effects of Fe-reducing processes are helpful in explaining the changes of DOC and Fe and thus surface water brownification at local scale. To better understand Fe-oxyhydroxides and DOC interactive processes at fine-scale local environments, the next step should be to establish the effects of hydrologic processes and DOC sources. This may help explain DOC stabilization and destabilization as well as surface water brownification

Ecology and extent of freshwater browning-What we know and what should be studied next in the context of global change

Water browning or brownification refers to increasing water color, often related to increasing dissolved organic matter (DOM) and carbon (DOC) content in freshwaters. Browning has been recognized as a significant physicochemical phe-nomenon altering boreal lakes, but our understanding of its ecological consequences in different freshwater habitats and regions is limited. Here, we review the consequences of browning on different freshwater habitats, food webs and aquatic-terrestrial habitat coupling. We examine global trends of browning and DOM/DOC, and the use of remote sensing as a tool to investigate browning from local to global scales. Studies have focused on lakes and rivers while sel-dom addressing effects at the catchment scale. Other freshwater habitats such as small and temporary waterbodies have been overlooked, making the study of the entire network of the catchment incomplete. While past research inves-tigated the response of primary producers, aquatic invertebrates and fishes, the effects of browning on macrophytes, invasive species, and food webs have been understudied. Research has focused on freshwater habitats without consid-ering the fluxes between aquatic and terrestrial habitats. We highlight the importance of understanding how the changes in one habitat may cascade to another. Browning is a broader phenomenon than the heretofore concentration on the boreal region. Overall, we propose that future studies improve the ecological understanding of browning through the following research actions: 1) increasing our knowledge of ecological processes of browning in other wetland types than lakes and rivers, 2) assessing the impact of browning on aquatic food webs at multiple scales, 3) examining the effects of browning on aquatic-terrestrial habitat coupling, 4) expanding our knowledge of browning from the local to global scale, and 5) using remote sensing to examine browning and its ecological consequences.Peer reviewe

Integrated Water Resources Research

Anthropogenic and natural disturbances to freshwater quantity and quality are a greater issue for society than ever before. To successfully restore water resources requires understanding the interactions between hydrology, climate, land use, water quality, ecology, and social and economic pressures. This Special Issue of Water includes cutting edge research broadly addressing investigative areas related to experimental study designs and modeling, freshwater pollutants of concern, and human dimensions of water use and management. Results demonstrate the immense, globally transferable value of the experimental watershed approach, the relevance and critical importance of current integrated studies of pollutants of concern, and the imperative to include human sociological and economic processes in water resources investigations. In spite of the latest progress, as demonstrated in this Special Issue, managers remain insufficiently informed to make the best water resource decisions amidst combined influences of land use change, rapid ongoing human population growth, and changing environmental conditions. There is, thus, a persistent need for further advancements in integrated and interdisciplinary research to improve the scientific understanding, management, and future sustainability of water resources

Ecology and extent of freshwater browning - What we know and what should be studied next in the context of global change

Water browning or brownification refers to increasing water color, often related to increasing dissolved organic matter (DOM) and carbon (DOC) content in freshwaters. Browning has been recognized as a significant physicochemical phenomenon altering boreal lakes, but our understanding of its ecological consequences in different freshwater habitats and regions is limited. Here, we review the consequences of browning on different freshwater habitats, food webs and aquatic-terrestrial habitat coupling. We examine global trends of browning and DOM/DOC, and the use of remote sensing as a tool to investigate browning from local to global scales. Studies have focused on lakes and rivers while seldom addressing effects at the catchment scale. Other freshwater habitats such as small and temporary waterbodies have been overlooked, making the study of the entire network of the catchment incomplete. While past research investigated the response of primary producers, aquatic invertebrates and fishes, the effects of browning on macrophytes, invasive species, and food webs have been understudied. Research has focused on freshwater habitats without considering the fluxes between aquatic and terrestrial habitats. We highlight the importance of understanding how the changes in one habitat may cascade to another. Browning is a broader phenomenon than the heretofore concentration on the boreal region. Overall, we propose that future studies improve the ecological understanding of browning through the following research actions: 1) increasing our knowledge of ecological processes of browning in other wetland types than lakes and rivers, 2) assessing the impact of browning on aquatic food webs at multiple scales, 3) examining the effects of browning on aquatic-terrestrial habitat coupling, 4) expanding our knowledge of browning from the local to global scale, and 5) using remote sensing to examine browning and its ecological consequences.</p

Shining light on the storm: Using high-frequency optical water quality sensors to characterize and interpret storm nutrient and carbon dynamics among contrasting land uses

Elevated nutrient concentrations present significant challenges to surface water quality management globally, and dissolved organic matter mediates several key biogeochemical processes. Storm events often dominate riverine loads of nitrate, phosphorus, and dissolved organic matter, and are expected to increase in frequency and intensity in many regions due to climate change. The recent development of in situ optical sensors has revolutionized water quality monitoring and has highlighted the important role storms play in water quality. This dissertation focuses on improving the application of in situ optical water quality sensors and interpreting the high-frequency data they produce to better understand biogeochemical and watershed processes that are critical for resource management. We deployed in situ sensors to monitor water quality in three watersheds with contrasting land use / land cover, including agricultural, urban, and forested landscapes. The sensors measured absorbance of ultraviolet-visible light through the water column at 2.5 nanometer wavelength increments at 15-minute intervals for three years. These deployments provided a testbed to evaluate the sensors and improve models to predict concentrations of nitrate, three phosphorus fractions, and dissolved organic carbon using absorbance spectra and laboratory analyses through multivariate statistical techniques. In addition, an improved hysteresis calculation method was used to determine short-timescale storm dynamics for several parameters during 220 storm events. Goals of each dissertation chapter were to: (1) examine the influences of seasonality, storm size, and dominant land use / land cover on storm dissolved organic carbon and nitrate hysteresis and loads; (2) evaluate the utility of the sensors to determine total, dissolved, and soluble reactive phosphorus concentrations in streams draining different land use / land covers, and perform the first statistically robust validation technique applied to optical water quality sensor calibration models; and (3) analyze storm event dissolved organic matter quantity and character dynamics by calculating hysteresis indices for DOC concentration and spectral slope ratio, and develop a novel analytical framework that leverages these high frequency measurements to infer biogeochemical and watershed processes. Each chapter includes key lessons and future recommendations for using in situ optical sensors to monitor water quality

Forest and Rangeland Soils of the United States Under Changing Conditions

This open access book synthesizes leading-edge science and management information about forest and rangeland soils of the United States. It offers ways to better understand changing conditions and their impacts on soils, and explores directions that positively affect the future of forest and rangeland soil health. This book outlines soil processes and identifies the research needed to manage forest and rangeland soils in the United States. Chapters give an overview of the state of forest and rangeland soils research in the Nation, including multi-decadal programs (chapter 1), then summarizes various human-caused and natural impacts and their effects on soil carbon, hydrology, biogeochemistry, and biological diversity (chapters 2–5). Other chapters look at the effects of changing conditions on forest soils in wetland and urban settings (chapters 6–7). Impacts include: climate change, severe wildfires, invasive species, pests and diseases, pollution, and land use change. Chapter 8 considers approaches to maintaining or regaining forest and rangeland soil health in the face of these varied impacts. Mapping, monitoring, and data sharing are discussed in chapter 9 as ways to leverage scientific and human resources to address soil health at scales from the landscape to the individual parcel (monitoring networks, data sharing Web sites, and educational soils-centered programs are tabulated in appendix B). Chapter 10 highlights opportunities for deepening our understanding of soils and for sustaining long-term ecosystem health and appendix C summarizes research needs. Nine regional summaries (appendix A) offer a more detailed look at forest and rangeland soils in the United States and its Affiliates

Surface Water Chemistry in White Oak Creek, North-East Texas: Effect of Land Use

Over the last few decades increasing attention has been paid to the effects of land use activities and land management on stream water quality. Recent research has largely focused on dominant land uses such as urban development and agricultural cropland. The relative effect of land use activities and management on stream chemistry in sub-tropical rangeland ecosystems, where much of the land use is converted to pasture and agriculture is largely unknown. This study examined stream water quality and land use in a sub-tropical watershed in Northeast Texas largely dominated by rangeland. The study site, White Oak Creek Watershed located in the Sulphur River Basin, has been identified as an impaired stream due to low dissolved oxygen concentrations and subsequently listed on the Texas Commission for Environmental Quality's 303d list (TCEQ). In an attempt to determine potential sources of the low dissolved oxygen concentrations, twenty different chemical constituents were analyzed at 18 different sample sites in the tributaries of White Oak Creek and also along the main stem from April 2010 to March 2011. Dissolved oxygen concentrations over the study period were consistently above the minimum standard required by TCEQ and showed no indication of impairment. Correlation analysis did not show any clear correlation between dissolved oxygen and any specific land use, or any chemical constituent. Some nutrients and suspended sediment concentrations were significantly different among the sub-catchments of White Oak Creek. Urban land uses were significantly and positively correlated to electrical conductivity, ammonium-N, magnesium, calcium, and dissolved organic carbon. Agricultural land use was significantly and positively correlated to orthophosphate-P, dissolved organic nitrogen, total suspended solids, and turbidity. Forests were inversely and significantly related to nitrate-N, orthophosphate-P, sulfate, dissolved organic carbon, total suspended solids, and turbidity. The study suggested that by maintaining a relatively high proportion of forested land in a watershed that water quality can be improved