Hydrologic Dynamics Control Dissolved Organic Matter Export from Watersheds

Hydrologic Dynamics Control Dissolved Organic Matter Export from Watersheds
Author: Rebecca Anne Bellmore
Publisher:
Total Pages:
Release: 2014
Genre:
ISBN:
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Dissolved organic matter (DOM) is an important component of nutrient cycling and energy transfer within and between ecosystems. Understanding controls over the magnitude and quality of DOM that is transferred from soils to surface water is needed to better characterize the terrestrial-aquatic carbon flux and effects of terrestrial DOM on downstream ecosystems. A meta-analysis of the response of in-stream dissolved organic nitrogen concentration (DON) to high flow events indicates that DON typically increases with flow across a wide range of ecosystem types, likely as novel DOM sources in the landscape are mobilized and transported to streams and rivers. Mechanisms controlling DOM export, including dissolved organic carbon (DOC) and DON concentrations and the quality of DOM, were examined in a small agricultural catchment in eastern Washington State. In the soil column, DOC concentration declined and source of DOM shifted from humic-like and plant-derived to microbially-derived with depth through the profile. Across seasons and years, DOM exported via drain discharge during low flows resembled that found deep in the soil profile, and DOM exported during high flows suggests topsoil and litter sources contribute to export. A simple mixing model suggests that litter leachate can contribute over 50% of DOM during peak flow. Based on modeled contributions of litter, topsoil and subsoil DOM during storm events, DOC concentration is over-predicted, except for peak flows, suggesting removal via sorption and/or microbial decomposition in the soil column control DOC export on the timescale of events. Although the character of exported DOM shifts with flow conditions, laboratory incubations suggest bioavailability to the stream sediment microbial community is consistently low, with a maximum of 7% loss over 6 days, indicating exported DOM is likely transported beyond the immediate stream reach. An analysis of anticipated effects of climate change on the flow regime in the catchment projects the wettest years to become more variable, with non-linear effects on the magnitude of DOC export. Finally I explore how climate change assessments can be incorporated into nonpoint source nutrient management plans, despite current uncertainty about the magnitude and timeframe of climate effects on nutrient loading.

Hydrology and Landscape Structure Control Subalpine Catchment Carbon Export

Hydrology and Landscape Structure Control Subalpine Catchment Carbon Export
Author: Vincent Jerald Pacific
Publisher:
Total Pages: 298
Release: 2009
Genre: Carbon
ISBN:
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Carbon export from high elevation ecosystems is a critical component of the global carbon cycle. Ecosystems in northern latitudes have become the focus of much research due to their potential as large sinks of carbon in the atmosphere. However, there exists limited understanding of the controls of carbon export from complex mountain catchments due to strong spatial and temporal hydrologic variability, and large heterogeneity in landscape structure. The research presented in this dissertation investigates the control of hydrology and landscape structure and position on two major avenues of carbon loss from mountain watersheds: soil respiration and stream dissolved organic carbon (DOC) export. Measurements of soil respiration and its biophysical controls (soil water content, soil temperature, vegetation, soil organic matter, and soil physical properties) and stream and groundwater DOC dynamics are presented across three years and multiple riparian-hillslope transitions within a complex subalpine catchment in the northern Rocky Mountains, Montana. Variability in soil respiration was related to hydrologic dynamics through space and time and was strongly influenced by topography and landscape structure. Cumulative soil CO 2 efflux was significantly higher from wet riparian landscape positions compared to drier hillslope locations. Changes in hydrologic regimes (e.g. snowmelt and precipitation timing and magnitude) also impacted soil respiration. From a wet to a dry growing season, there were contrasting and disproportionate changes in cumulative growing season surface CO 2 efflux at wet and dry landscape positions. Stream DOC export was also influenced by landscape structure and hydrologic variability. The mobilization and delivery mechanisms of DOC from the soil to the stream were dependent upon the size of DOC source areas and the degree of hydrologic connectivity between the stream and the riparian and hillslope zones, which varied strongly across the landscape. This dissertation provides fundamental insight into the controls of hydrology and landscape structure on carbon export from complex mountain watersheds. The results of this research have large implications for the carbon source/sink status of high elevation mountain ecosystems, the influence of changing hydrologic regimes on soil respiration, and the use of landscape analysis to determine the locations of large source areas for carbon export.

Dissolved Organic Matter Sources and Dynamics in an Agricultural Watershed

Dissolved Organic Matter Sources and Dynamics in an Agricultural Watershed
Author: Sandrine Journet Matiasek
Publisher:
Total Pages:
Release: 2014
Genre:
ISBN: 9781321019490
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Agriculture is a dominant land use on Earth, but its impacts on dissolved organic matter (DOM) sources, processing, and fate remain relatively unclear. The goal of this research was to study DOM sources and dynamics in an irrigated agricultural watershed of Central Valley, California by 1) assessing the quantitative and qualitative impacts of organic matter (OM) desorption from sediments and soils, and by 2) generating an amino acids time series to link seasonal processes (natural and anthropogenic) to changes in stream DOM chemistry and reactivity. Abiotic desorption experiments revealed that mineral-bound organic carbon (OC) desorption is a predictable and finite process in agricultural surface waters, contributing 5 - 7% of the annual dissolved OC (DOC) export, with local maxima up to 50% of typical field runoff concentrations and 20% of winter storm DOC concentrations. The relevance of OM desorption was even more evident at the molecular level. Relative to mineral-bound OM, desorbed DOM was nitrogen-poor and depleted in amino acids and lignin. Distinct fractionation patterns of amino acids and lignin phenols led to a more acidic DOM pool that appeared substantially more degraded than particulate OM, with decreased mole fractions of basic amino acids, increased molar contributions of non-protein amino acids, decreased degradation index values, and increased proportions of acidic lignin phenols. If unaccounted for, the profound alteration of DOM composition incurred by desorption could lead to misinterpretations of indicators commonly used to assess the diagenetic state of OM. At the watershed scale, the role of land use and hydrologic controls on labile DOM dynamics was evidenced by elevated total hydrolyzable amino acid (THAA) concentrations throughout the low-discharge irrigation season and by seasonal compositional differences. DOM during winter baseflow was the most degraded, with the lowest THAA content and the lowest degradation index (DI), while winter storms and summer irrigation were two critical hydrologic regimes for DOM cycling with the largest amino acid contents, the largest proportions of basic amino acids, and the largest DI values, indicative of a relatively fresh DOM pool. The biogeochemical relevance of irrigation practices was therefore demonstrated by the mobilization of DOM similar in concentration and reactivity to DOM during winter storms.

Field Measurements for Forest Carbon Monitoring

Field Measurements for Forest Carbon Monitoring
Author: Coeli M Hoover
Publisher: Springer Science & Business Media
Total Pages: 242
Release: 2008-10-20
Genre: Science
ISBN: 1402085060
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In the summer of 2003, a workshop was held in Portsmouth, NH, to discuss land measurement techniques for the North American Carbon Program. Over 40 sci- tists representing government agencies, academia and nonprofit research organi- tions located in Canada, the US and Mexico participated. During the course of the workshop a number of topics were discussed, with an emphasis on the following: • The need for an intermediate tier of carbon measurements. This level of study would be more extensive than state-level inventories of the US Forest Service Forest Inventory and Analysis Program, but less detailed than intensive ecos- tem studies sites such as those in Long Term Ecological Research network. This tier would ideally provide a basis to link and scale remote sensing measurements and inventory data, and supply data required to parameterize existing models (see Wofsy and Harriss 2002, Denning et al. 2005). • The design criteria that such a network of sites should meet. The network and s- pling design should be standardized, but flexible enough to be applied across North America. The design also needs to be efficient enough to be implemented without the need for large field crews, yet robust enough to provide useful information. Finally, the spatial scale must permit easy linkage to remotely sensed data. • The key variables that should be measured at each site, and the frequency of measurement.

Watershed Export of Dissolved Organic Matter in Response to Anthropogenic and Hydroclimatic Drivers in Subtropical Streams and Rivers

Watershed Export of Dissolved Organic Matter in Response to Anthropogenic and Hydroclimatic Drivers in Subtropical Streams and Rivers
Author: Shuo Chen
Publisher:
Total Pages:
Release: 2021
Genre: Electronic dissertations
ISBN:
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Dissolved organic matter (DOM) is an assemblage of heterogeneous organic compounds that play important roles in terrestrial and aquatic ecosystems. In this dissertation, I investigated changes in the amount, source, composition, lability, and ecological functions of stream water DOM in response to agricultural land use, hydrological events, and downstream transport and transformation in the southeastern United States. The dissertation includes three stand-alone studies presented in Chapters 2, 3 and 4, respectively. In Chapter 2, I evaluated the effects of hurricane-induced storm events on the quantity and quality of DOM exported from ten watersheds of various physical and land-use characteristics within five Gulf and South Atlantic states. We found that large storms can significantly enhance the concentrations and yields of terrestrially-derived dissolved organic carbon (DOC) and nutrients in streams and rivers but decrease the percentage bioreactive DOC. This study demonstrates that extreme weather and climate events can lead to rapid, ecosystem-level disturbances that significantly shift energy and nutrient availability within drainage networks. The objective of Chapter 3 was to quantify the relative importance of agricultural land use and natural hydroclimatic drivers in affecting the quality and quantity of DOM in a group of 15 streams draining watersheds of a gradient of agricultural land use. The partial least square path modeling (PLS-PM) identified that agricultural land use increased stream water DOM quantity primarily through increasing allochthonous carbon sources. This study demonstrates that structural equation modeling is a powerful tool that should be more widely adopted to distinguish among multiple drivers and mechanisms regulating freshwater biogeochemistry. Chapter 4 investigated the longitudinal transformations of DOM in relation to ecosystem metabolism along a fluvial section including 3rd order, 7th and 8th order streams. From upstream to downstream, DOC concentrations and the relative contributions of freshly-produced DOM increased. The gross primary productivity was positively correlated with the contributions of autochthonous DOM, yet the ecosystem respiration did not vary with the quantity or quality of DOM. This study highlights the complexity of DOM transformations in relation to stream metabolism along the river continuum. Collectively, the three independent but connected studies reveal the complexity and sensitivity of inland water DOM in response to hydroclimatic and anthropogenic drivers. The findings provide new insights into potential shifts in energy and substrates exported across the terrestrial-aquatic boundary due to human activities and climate change and how these shifts can alter water quality and fluvial biogeochemical functions.

Scale Issues in Hydrological Modelling

Scale Issues in Hydrological Modelling
Author: J. D. Kalma
Publisher: John Wiley & Sons
Total Pages: 518
Release: 1995-09-11
Genre: Science
ISBN:
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There is a growing need for appropriate models which address the management of land and water resources and ecosystems at large space and time scales. Theories of non-linear hydrological processes must be extrapolated to large-scale, three-dimensional natural systems such as drainage basins, flood plains and wetlands. This book reports on recent progress in research on scale issues in hydrological modelling. It brings together 27 papers from two special issues of the journal Hydrological Processes. The book makes a significant contribution towards developing research strategies for linking model parameterisations across a range of temporal and spatial scales. The papers selected for this book reflect the tremendous advances which have been made in research into scale issues in hydrological modelling during the last ten years.

The Effect of In-line Lakes on Dissolved Organic Matter Dynamics in Mountain Streams

The Effect of In-line Lakes on Dissolved Organic Matter Dynamics in Mountain Streams
Author: Keli J. Goodman
Publisher:
Total Pages: 183
Release: 2010
Genre:
ISBN:
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This research combines observation, experimentation, and modeling to evaluate the influence of lakes on dissolved organic matter (DOM) quantity, quality and export in subalpine watersheds of the Sawtooth Mountain Lake District, central Idaho. First, I conducted an empirical study of the hydrologic and biogeochemical controls on DOM dynamics in stream-lake fluvial networks. I hypothesized that lakes would decrease temporal variability (i.e., buffer) and alter the characteristics of DOM from inflow to outflow. I tested these hypotheses by evaluating DOM temporal patterns and measuring annual export in seven-paired lake inflows and outflows. I then evaluated how ultraviolet (UV) exposure affected DOM characteristics during snowmelt and baseflow, and how UV alters baseflow DOM bioavailability and nutrient limitation. Given that increased water residence time increases UV exposure, I hypothesized that lake outflow DOM would be more photorecalcitrant than DOM from lake inflows. I further hypothesized that UV exposure would increase DOM quality, heterotrophic processing, and nutrient demand. Results indicate that lakes can buffer stream temporal variability by acting as a DOM sink during snowmelt and a DOM source during baseflow. Lake outflow DOM photodegradation was similar to lake inflows during snowmelt (p=0.66). Conversely, outflow DOM was 2X more photorecalcitrant than inflow DOM during baseflow (ANOVA, p=0.03) and was strongly related to water residence time (WRT). During baseflow, light exposure increased inflow and outflow DOM bioavailability (p=0.059 and 0.024, respectively) and nutrient limitation (p=0.03 and 0.09, respectively). Combined, these results indicate that WRT in subalpine lakes strongly influences DOM temporal variability and DOM degradation and processing. Thus, lakes can provide temporal stability of DOM and potentially increase both carbon and nutrient uptake by heterotrophs in lake outflows. I then evaluated how global changes could alter hydrologic and nutrient dynamics in a subalpine lake. Model results indicate that the magnitude and timing of snowmelt runoff can have a substantial effect on water and nutrient exports. In phosphorus (P)- limited lakes, increases in inorganic N concentrations within and exported from lakes are likely to occur with increased temperatures and lake WRT. Increases in atmospheric N deposition will further enhance inorganic N exports in P-limited subalpine lakes.

Seasonal Dynamics of Organic Matter and Inorganic Nitrogen in Surface Waters of Alaskan Arctic Streams and Rivers

Seasonal Dynamics of Organic Matter and Inorganic Nitrogen in Surface Waters of Alaskan Arctic Streams and Rivers
Author: Matthew Solomon Khosh
Publisher:
Total Pages: 316
Release: 2015
Genre:
ISBN:
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Climate-linked changes in hydrology and biogeochemical processes within Arctic watersheds are likely already affecting fluvial export of waterborne materials, including organic matter (OM) and dissolved inorganic nitrogen (DIN). Our understanding of Arctic watershed OM and DIN export response to climate change is hampered by a lack of contemporary baselines, as well as a dearth of seasonally comprehensive studies. This work focuses on characterizing OM and DIN concentrations and sources in six streams/rivers on the North Slope of Alaska during the entirety of the hydrologic year (May through October) in 2009 and 2010. The highest OM concentrations occurred during spring snowmelt, with results indicating that terrestrial vegetation leachates are the major source of dissolved OM, while particulate OM originates from a degraded soil source. Over the hydrologic year, soils became a progressively increasing source of dissolved OM, while autochthonous production made up a sizeable proportion of particulate OM during base flow conditions. DIN concentrations were low throughout the spring and summer and increased markedly during the late summer and fall. Our findings suggest that penetration of water into thawed mineral soils, and a reduction in nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. Although recent studies of Arctic rivers have emphasized the importance of the spring thaw period on OM export, our understanding of the mechanisms that control water chemistry observations during this time are still lacking. Experimental leaching results, from experiments conducted in 2014, suggest that aboveground plant biomass is a major source of dissolved OM in Arctic catchments during the spring, and that the timing of freezing and drying conditions during the fall may impact dissolved OM leaching dynamics on that same material the following snowmelt. Improved knowledge of OM and DIN temporal trends and the mechanisms that control seasonal concentrations is essential for understanding export dynamics of these water constituents in Arctic river systems. Perhaps more importantly, increased understanding of the seasonal controls on OM and DIN export in Arctic rivers is critical for predicting how these systems will respond under future climate change scenarios.