Hydrology and the Variation of Dissolved Organic Carbon in Soil and Stream Waters of Two Headwater Catchments PDF Download
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Author: Elizabeth Weeks Boyer
Publisher:
ISBN:
Category :
Languages : en
Pages : 204
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Author: Elizabeth Weeks Boyer
Publisher:
ISBN:
Category :
Languages : en
Pages : 204
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Author: Thomas Adler
Publisher:
ISBN:
Category : Acid pollution of rivers, lakes, etc
Languages : en
Pages : 98
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Variability in export of dissolved organic carbon (DOC) from forested headwater catchments has been attributed to an array of hydrologic, biotic and geochemical drivers. In the Northeast United States specifically, one of the most commonly cited drivers is recovery from acid rain. A major challenge in understanding DOC dynamics has been relating long-term regional trends and patterns to catchment-scale processes and we address this challenge by integrating data driven and experimental methods to analyze trends and processes across spatial scales. On the regional scale, we quantify long-term trends of stream DOC concentrations in USGS headwater catchments with flow adjusted Seasonal Kendall tests. We then compared trend results to catchment attributes compiled in a comprehensive and publicly available dataset (i.e. Catchment Attributes and MEteorology for Large-sample Studies (CAMELS)). Our trend analyses showed notable spatial and temporal variability in export patterns across the Northeast United States. Only for data prior to 2004 increasing stream DOC correlated with decreasing atmospheric sulfate deposition, confirming a transient effect of recovery from acidification. Investigation of climatic, topographic and hydrologic catchment attributes vs. directionality of DOC indicated that soil depth and catchment connectivity as additional driver of DOC exports. At the catchment scale, we tested specific process hypotheses on the role of changes in rain composition (ionic strength (IS) and pH variations) on soils in highly connected riparian vs. disconnected hillslope soils. We performed leaching experiments in replicate on top-soil cores from two forested headwater catchments in the Northeast, the SSHCZO in Pennsylvania and the SRRW in Vermont. These catchments were subjected to sulfate deposition and are now recovering. Compared to SSHCZO, SRRW soils released more DOC under neutral pH and low IS conditions (i.e. recovering conditions); scanning electron microscope imaging indicates a significant DOC contribution from destabilizing soil aggregates. Furthermore, soils from less hydrologically connected landscape positions released significantly more DOC in most cases, confirming the important role landscape position in DOC generation. Overall, our results at regional and local scales are consistent and link local process explanations to regional patterns.
Author: George M. Hornberger
Publisher: JHU Press
ISBN: 9780801858574
Category : Science
Languages : en
Pages : 320
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"An outstanding text that can greatly facilitate improved education in hydrology... Personally, starting next year, I plan to use this book as one of the assigned texts for the three-quarter-long Environmental Earth Science series at Stanford." -- Keith Loague, "Ground Water"
Author: Catherine Louise Wearing
Publisher:
ISBN:
Category : Acid deposition
Languages : en
Pages :
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Concentrations of dissolved organic carbon (DOC) measured within water bodies have been increasing on a global scale over the last two decades. Changes in temperature and rainfall have been shown to increase the production and export of DOC from catchments with peat soils in the UK (Freeman et al., 2001). However it is not clear whether increases in DOC concentrations are caused by production increases induced by temperature changes or by a greater incidence of high flows induced by rainfall changes. Increases in both temperature and rainfall have been predicted in Scotland over the next few decades (Kerr et al., 1999) which may further increase current DOC concentrations and exports. The implications of this include both a decrease in water quality and an increase in mobility of metals in upland water bodies. The overall aim of the thesis is to determine if the relationship between dissolved organic carbon (DOC) concentrations and discharge has changed over a 20 year period in small stream catchments in Scotland, in order to better understand the role of hydrology, in driving changes in DOC concentration. To achieve this streams draining two coniferous forest sites and one moorland site were monitored intensively between June 2004 and February 2006. Analysis of the relationship between DOC and discharge, within the catchments, identified the importance of the amount of precipitation falling on the catchment, antecedent precipitation and season, on the concentration of DOC that was measured within the stream. Models were then developed using variables to represent these drivers in terms of both the production (seasonal sine values and 14 day average temperatures) and movement (log of discharge (log Q), days since previous storm event and rising or falling stage) of DOC. In the Ochil Hills catchment, the best predictive model, used 4 hour average discharge and 1 day average 30cm soil temperatures (R2= 0.88). In the Duchray and Elrig catchments, the best predictive models produced used discharge and seasonal sine values; the strength of the model was greater in the Elrig (R2= 0.80) than the Duchray (R2= 0.48) catchment. The strength of the regression models produced highlighted the importance of precipitation in the movement of DOC to the stream and temperature variables representing production in the surrounding catchment. To determine if dissolved organic carbon (DOC) concentrations had changed within the three study catchments, since previous research was conducted at the same sites in the early 1980s and 1990s (Grieve, 1984a; Grieve, 1994), then regression analysis conducted in the previous research was repeated, so changes in the DOC and discharge relationship could be identified. Analysis of the Ochil Hills regression equations identified higher log of discharge and lower temperature and seasonal sine values in the present study (2004-06), when compared to the previous study (1982-83). This suggests that more DOC is now available for movement from the soil, and that the difference between winter and summer DOC production has decreased, potentially because of increasing temperatures. This would explain the limited increase in DOC concentration within the Ochil Hills stream. In the Duchray and Elrig streams, a large increase in DOC was identified at all discharges when all the models produced were compared between the two sampling periods (1989-90 and 2004-06). The increasing trend in DOC concentrations is too large to have been produced by change in temperature alone and it is suggested that the measured reduction in acidic deposition has resulted in the increased DOC concentrations measured in the Duchray and Elrig. The results from this research have identified that concentrations of DOC have increased in Scottish streams over the last 20 years and that the increases in DOC have been induced, potentially by temperature changes in climate. However, changes in temperature are not the only driver of this change as the reduction in acidic deposition is potentially more important, specifically in areas with base poor geology such as the Duchray and Elrig catchments.
Author: Catherine Grace Winters
Publisher:
ISBN: 9781369354133
Category :
Languages : en
Pages : 204
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Biotic and abiotic factors both play critical roles in the cycling of organic matter and nutrients in aquatic ecosystems. Understanding the relative control of these factors on solute fate and transport in fluvial systems is important for understanding how climatic changes can affect water quality. Many processes that control solute cycling in streams occur at sub-daily scales, making high-frequency, in situ, sub-hourly measurements important for capturing the response of dissolved organic matter and nutrients to changes in the strength of controlling processes. The tightly coupled aquatic and terrestrial environments present in headwater streams make them particularly useful systems for studying high-frequency changes in water chemistry. In this study, we examined the patterns of dissolved organic carbon, nitrate, dissolved oxygen, temperature, dissolved organic matter fluorescence, and stream discharge using in-stream measurements at sub-hourly to monthly time scales to understand the daily and seasonal controls of aquatic organic matter and nutrient processing. We also conducted a laboratory incubation to measure the effects of dissolved organic carbon and nutrient treatments on consumption of carbon and nitrogen in our system. Our main objectives were to identify: 1) the relative controls of diel biotic and abiotic processes on stream dissolved organic carbon and nitrate-N; and 2) the mechanisms controlling rapid autumnal changes in dissolved organic carbon and nitrate-N in stream runoff. We found that hydrology plays a key role in transporting solutes to a forested headwater stream in the Piedmont Region, Maryland; however, once solutes reach the stream biotic controls dominate the stream solute patterns. Biology is an important regulator of diel patterns of streamwater dissolved organic carbon and nitrate concentrations during springtime and autumn leaf fall. Diel cycling is most apparent during the spring prior to leaf out when the water temperature is increasing. Where patterns were evident, nitrate (annual average in second order stream: 17:00) and discharge (17:28) reached their minimums during the afternoon within a few hours of the peaks in dissolved oxygen (13:16), temperature (15:17), dissolved organic carbon (16:06), and dissolved organic matter fluorescence (17:23). Larger amplitudes of dissolved oxygen, nitrate, dissolved organic carbon, and dissolved organic matter fluorescence correspond with larger daily temperature changes. Laboratory incubations showed increased consumption of nitrogen in the presence of labile carbon, but not in the presence of labile carbon plus nutrients, which indicates our system is carbon limited. Autumn dissolved organic carbon and nitrate dynamics also indicate our system is carbon limited. Increased rates of leaf litter fall corresponded with increased consumption of stream nitrate leading to a late October depression, or annual minimum, in nitrate concentration. Storm events accelerated the recovery of stream nitrate to early autumn concentrations as nitrate was mobilized and transported from soils to the stream. Hydrology is important for solute transport to and export from the stream. Autotrophic activity dominates on the daily scale, while heterotrophic activity controls seasonal responses in organic matter and nutrient cycling in this forested watershed. Carbon and nitrogen dynamics have been studied in other forested systems, as well, but the controlling processes vary among these watershed. Our results highlight the importance of understanding controlling processes within specific watersheds when making large scale predictions of the potential export of carbon and nitrogen from forested systems.
Author: Alba Guarch Ribot
Publisher:
ISBN:
Category :
Languages : en
Pages : 177
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"Dissolved organic matter (DOM) is an important source of carbon for aquatic microorganisms and it regulates many biogeochemical processes. Therefore, changes in river DOM concentration and properties could notably affect the functioning of fluvial and coastal ecosystems and alter the global carbon cycle. The DOM in headwater streams is strongly influenced by hydrology, as a consequence of the modification of catchment flow paths with high discharges. During storm events, the catchment hillsides are washed and terrigenous DOM is transported to rivers. In the Mediterranean region, the precipitation regime and evapotranspiration strongly modulate fluvial hydrology, which shows low discharges in summer and even flow disappearance. These dry–wet cycles of conditions affect many ecological and biogeochemical processes. In this thesis, I analyse a long time series of discharge and DOM data from Fuirosos, an intermittent headwater stream in NE Spain. My aim is to examine the relationship between DOM and hydrology at different temporal scales. First, I characterise the hydrological regime of this Mediterranean stream. A decrease in discharge was revealed, although trends in temperature and precipitation were not significant. In contrast, I did not find a clear temporal trend in dry period duration. However, rewetting has been significantly delayed, moving from September to October. The frequency of storm events decreased over the interval 1998–2015, showing a significant positive relationship with solar activity with a 2-year lag. Dissolved organic carbon (DOC) concentration saw a slight decrease during the study period, which was opposed to that observed in boreal systems. This pattern might respond to a reduction of terrigenous DOC input from forest hillsides as a consequence of the decrease in flushing episodes. The DOC temporal dynamics during the rewetting was regulated by dry period duration. Discharge oscillations explained up to 50% of total DOC variability during the wet period. Notably, this weight of discharge increased significantly over the years. DOM quality was also explored, and described in terms of absorbance and fluorescence properties. Most of the DOM properties were strongly related to discharge, revealing the input of allochthonous, degraded, aromatic, humic and large-molecular DOM under high flow conditions. However, these relationships were altered during drying and rewetting periods. The DOM responses at the individual storm event scale were highly heterogeneous. Multiple linear regression and commonality analyses showed that, in addition to the magnitude of storm episodes, antecedent hydrological conditions, namely pre-event basal flow and the magnitude of the previous storm event, played a significant role in regulating the trends and shapes of DOM–discharge hysteresis. Finally, I identified the differences and similarities in the DOM–discharge relationships between the intermittent Mediterranean stream analysed herein and a perennial Alpine stream with higher mean discharge (Oberer Seebach). The DOM in Fuirosos was significantly more concentrated, more terrigenous, more degraded, more aromatic and more humified. The sign of the global DOM–discharge response was the same in both streams. However, discharge was a more robust predictor of DOM variability in Oberer Seebach. In fact, low flow and rewetting periods in Fuirosos introduced considerable dispersion into the relationship. During snowmelt in Oberer Seebach the sensitivity to discharge also decreased or disappeared. The flushing/dilution patterns were essentially associated with the magnitude of storm events in Fuirosos. In contrast, the DOM quality change was more coupled to basal flow conditions in Oberer Seebach, while the storms were behind the DOC oscillations. This study attests to the importance of generating and analysing long-term and high-frequency biogeochemical series, which allow relationships between DOM and hydrology to be explored in intermittent headwater streams that are subjected to extreme hydrological regimes." -- TDX.
Author:
Publisher:
ISBN:
Category : Water
Languages : en
Pages : 1196
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Author: Caitlin Bristol
Publisher:
ISBN:
Category : Hubbard Brook Experimental Forest (N.H.)
Languages : en
Pages : 122
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Over the past few decades, dissolved organic carbon (DOC) concentrations in headwater streams in the northern hemisphere changed. Because these changes in DOC coincided with decreased acid deposition, a potential link was proposed early on. More recent research indicated that catchment attributes, especially soil characteristics and the presence of Ca-bearing minerals, play an important role in modulating DOC release from watersheds, but further research is necessary. To investigate the role of catchment characteristics on DOC dynamics, I use several watersheds in the Northeastern United States with similar attributes and well-constrained differences. Sleepers River Research Watershed (SRRW) has naturally occurring Calcium (Ca) bearing minerals versus Hubbard Brook Experimental Forest (HBEF) which has experimentally added Ca minerals in one watershed. To assess differences in long-term stream DOC trends in response to shifts in acid deposition, I use stream pH and flow-adjusted DOC stream water concentrations and performed Seasonal Kendall tests. I complement these analyses with experiments on soil cores across watersheds at SRRW and HBEF, seasons (SRRW only), and landscape positions. Despite similar increasing pH trends, SRRW and HBEF have contrasting long-term DOC responses. My results show that all watersheds show a significant increase in DOC, but the timing and magnitude of this increase vary. My soil experiments with simulated acidification and recovery treatments indicate SRRW varies significantly by season, and generally, recovery solutions extract more DOC. In contrast HBEF soils, landscape positions largely influenced DOC export (and aggregate sizes). I also investigate these findings with a conceptual lens of resistance and resilience as these are widely used concepts to evaluate response to disturbances. In this context, I discuss the long-term data for all watersheds and provide ideas for integrating experimental data in the timeline of changes in atmospheric deposition.
Author: Dipankar Dwivedi
Publisher: Frontiers Media SA
ISBN: 2889710742
Category : Science
Languages : en
Pages : 285
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Author: Yi Mei
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 135
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