Mark Miguil Castro(RPSEA) - Academia.edu (original) (raw)

Papers by Mark Miguil Castro(RPSEA)

The purpose of our study was to examine how environmental parameters influence the surface atmosp... more The purpose of our study was to examine how environmental parameters influence the surface atmosphere exchange of gaseous mercury in background soils of western Maryland. The parameters included soil temperature, redox potential, and volumetric water content. We also wanted to determine if soil pore air total gaseous mercury (TGM) concentrations were influencing atmospheric exchange. All parameters were measured at four depths below the soil surface, at the Oe - A soil horizon interface, A - E soil horizon interface, 5 cm into the E horizon, and 10 cm into the E horizon. Three plots were delineated in a forested area and three in a cleared area at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in western Maryland. TGM fluxes were measured with a dynamic flux chamber and soil pore air concentrations were measured with our newly developed soil pore TGM sampling method. Plots were sampled for soil pore air TGM concentrations and TGM flux every third week from July 2009 thr...

Case reports in ophthalmology, 2012

We present the case of an 18-year-old Caucasian male with a unilateral macular star and retinal v... more We present the case of an 18-year-old Caucasian male with a unilateral macular star and retinal vascular anomalies compatible with adult onset Coats' disease. Diagnosis was based on fundoscopic, fluorescein angiography and optical coherence tomography findings. The patient presented to our emergency department with complaints of low vision in his left eye (LE) detected 10 days before. The best-corrected visual acuity in the LE was 20/50. Fundoscopy of the LE evidenced a complete macular star. Optical coherence tomography showed increased retinal thickness, infiltration of the retinal wall, and detachment of the neuroepithelium. Angiography revealed no appreciable diffusion in the macula. Above the superior temporal (ST) arcade, anomalies in the retinal vasculature were found, with interruption of the peripheral vessels and vessels which were 'sausage'-like. After 1 month, the LE vision evolved to hand movements. Laser photocoagulation was performed in the ST quadrant. In...

Water, Air, & Soil Pollution, 2004

Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watershed... more Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeastern United States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha −1 yr −1 (mean = 6.4 kg N ha −1 yr −1 ; median = 7.0 kg N ha −1 yr −1). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg N ha −1 yr −1 (mean = 2.0 kg N ha −1 yr −1 ; median = 1.7 kg N ha −1 yr −1). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha −1 yr −1 (mean = 4.4 kg N ha −1 yr −1 ; median = 4.6 kg N ha −1 yr −1). Outputs of DIN in streamwater were predominantly NO 3-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.

Environmental science-Processes&Impacts, 2013

Water, Air, & Soil Pollution, 2010

The goal of this project was to develop a method to measure the total gaseous mercury (TGM) conce... more The goal of this project was to develop a method to measure the total gaseous mercury (TGM) concentrations in unsaturated soils. Existing methods did not allow for easy replication, were costly, and were more suited for other gases, such as CO 2 , that do not react with collection surfaces. To overcome these problems, we developed a method that simultaneously collects up to ten soil pore air samples. We used a single mass flow controller, one pump, and two banks of rotameters to draw soil air out of the ground at 25 smLmin −1 onto gold-coated quartz traps. Analysis of the gold traps was performed with a Tekran 2500 CVAFS mercury detector. The system was field tested at the Piney Reservoir Ambient Air Monitoring Station in western Maryland. Our system was relatively precise and accurate. For example, replicate TGM concentrations differed by less than 25% and recovery of known amounts of mercury were greater than 95%. Field measurements showed that the maximum soil pore air TGM concentrations, between 3 and 4 ngm −3 , occurred at the Oe-A soil horizon interface. At all other depths, the total mercury concentrations were lower than the ambient air concentrations of 1.8 ngm −3. We believe our new method can be used to precisely and accurately measure the TGM concentrations in unsaturated soils at multiple locations simultaneously.

Water, Air, and Soil Pollution, 1987

Water, Air, & Soil Pollution, 2011

The original Figure 4 did not include the units. The bottom axis of Figure 4 should read: TGM Con... more The original Figure 4 did not include the units. The bottom axis of Figure 4 should read: TGM Concentration (ng m-3)

Water, Air, & Soil Pollution, 2011

Water, Air, and Soil Pollution, 2008

The purpose of this study was to gather information on the spatial and temporal variation of stre... more The purpose of this study was to gather information on the spatial and temporal variation of stream water total mercury concentrations ([THg]) and to test the hypothesis that stream water [THg] increases as stream pH decreases in the Shenandoah National Park (SNP). We based our hypothesis on studies in lakes that found mercury methylation increases with decreasing pH, and studies

Science of The Total Environment, 2004

In this study we used the Watershed Assessment Tool for Evaluating Reduction Strategies for Nitro... more In this study we used the Watershed Assessment Tool for Evaluating Reduction Strategies for Nitrogen (WATERSN) model to evaluate a variety of management strategies for reducing nitrogen (N) loads to four US east coast estuaries: Casco Bay, Long Island Sound, Chesapeake Bay and Pamlico Sound. These management strategies encompass reductions in atmospheric emissions and deposition of N from sources including, fossil fuel burning utility emissions and mobile NO(x) emissions, N treatment in wastewater and controls on agricultural N inputs. We find that in primarily urban watersheds biological removal of N in wastewater treatment produces the greatest reduction in N loading (32-57% reductions), while in less urban watersheds, reductions in agricultural loading are more effective (5-56% reductions) in decreasing N loads to coastal ecosystems. Because anthropogenic N inputs are derived from a variety of sources, we also examined an integrated scenario targeting all major N sources; this resulted in 35-58% reductions in N loading. Nitrogen pollution originates from multiple sources and is transported through several media (air, soil, water); a major challenge of the development of N management strategies will be the control of multiple sources to effectively reduce N loads to estuaries.

Science of The Total Environment, 2012

The purpose of this study was to directly measure the dry deposition of gaseous oxidized mercury ... more The purpose of this study was to directly measure the dry deposition of gaseous oxidized mercury (GOM) in western Maryland. Annual estimates were made using passive ion-exchange surrogate surfaces and a resistance model. Surrogate surfaces were deployed for seventeen weekly sampling periods between September 2009 and October 2010. Dry deposition rates from surrogate surfaces ranged from 80 to 1512 pgm(-2)h(-1). GOM dry deposition rates were strongly correlated (r(2)=0.75) with the weekly average atmospheric GOM concentrations, which ranged from 2.3 to 34.1 pgm(-3). Dry deposition of GOM could be predicted from the ambient air concentrations of GOM using this equation: GOM dry deposition (pgm(-2)h(-1))=43.2 × GOM concentration-80.3. Dry deposition velocities computed using GOM concentrations and surrogate surface GOM dry deposition rates, ranged from 0.2 to 1.7 cms(-1). Modeled dry deposition rates were highly correlated (r(2)=0.80) with surrogate surface dry deposition rates. Using the overall weekly average surrogate surface dry deposition rate (369 ± 340 pg m(-2)h(-1)), we estimated an annual GOM dry deposition rate of 3.2 μg m(-2)year(-1). Using the resistance model, we estimated an annual GOM dry deposition rate of 3.5 μg m(-2)year(-1). Our annual GOM dry deposition rates were similar to the dry deposition (3.3 μg m(-2)h(-1)) of gaseous elemental mercury (GEM) at our site. In addition, annual GOM dry deposition was approximately 1/2 of the average annual wet deposition of total mercury (7.7 ± 1.9 μg m(-2)year(-1)) at our site. Total annual mercury deposition from dry deposition of GOM and GEM and wet deposition was approximately 14.4 μg m(-2)year(-1), which was similar to the average annual litterfall deposition (15 ± 2.1 μg m(-2)year(-1)) of mercury, which was also measured at our site.

Science of The Total Environment, 2012

The purpose of this study was to determine the effects of soil temperature, soil moisture, redox ... more The purpose of this study was to determine the effects of soil temperature, soil moisture, redox potential (Eh) and soil organic matter (SOM) on the total gaseous mercury (TGM) concentrations in background soils. Our measurements were made in a grass field and deciduous forest at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in Garrett County, Maryland. Three plots in each area were sampled every third week from July 2009 to June 2010 at the Oe-A soil horizon interface, the A-E soil horizon interface, and 5 and 10 cm into the E soil horizon. The mean soil TGM concentration for all depths in the forest (2.3 ± 2.2 ng m(-3)) was significantly higher than the mean soil TGM concentration in the grass field (1.5 ± 1.9 ng m(-3)). Soil TGM at all depths was most strongly and consistently correlated to soil temperature. The soil TGM concentrations were highest and most variable at the forest Oe-A soil horizon interface (4.1 ± 2.0 ng m(-3)), ranging from 1.5 to 8.4 ng m(-3). This soil horizon interface had 11 to 26% more SOM and the soil Eh was 100 to 400 mV lower than the other soil depths. Our results suggest that soil temperature, soil Eh and SOM are significant factors affecting TGM concentrations in forest soils. Future studies of TGM dynamics in background soils may benefit from closely monitoring the organic soil horizon.

Forest Ecology and Management, 2004

The production of nitric oxide (NO) in forest soils can indicate that the ecosystem is progressin... more The production of nitric oxide (NO) in forest soils can indicate that the ecosystem is progressing toward a state of nitrogen (N) saturation. Soil NO emissions may also have impacts on local tropospheric ozone (O 3) levels. During 2000-2001, we made firsttime measurements of NO emissions in two paired watershed studies. In each study, one watershed had been amended with aerial applications of 2.5-3.5 g N m À2 per year above background atmospheric deposition rates since 1989, and an adjacent watershed served as a reference. In plots at the Fernow Experimental Forest (FEF) in West Virginia and the Bear Brook Watershed in Maine (BBWM), NO emissions in N-amended watersheds (0.61-6.8 mg NO-N m À2 h À1) were higher than in the reference watersheds (0.21-1.4 mg NO-N m À2 h À1). In the N-amended watershed at BBWM, NO fluxes in plots dominated by hardwood species were higher than in plots dominated by softwood species, in contrast to previous studies in other forests. Field NO fluxes were correlated with mineral soil nitrate (NO 3 À) concentrations (r 2 ¼ 0:65, P ¼ 0:016) across all plots, suggesting that NO emissions may be a reliable indicator of NO 3 À leaching potential. Laboratory experiments indicated that nitrification was the dominant source of NO at both sites. At BBWM, increased NO emissions in N-amended soil appeared to result from more rapid nitrification. In contrast, reduced soil pH in N-amended soil at FEF may have caused increased protonation of nitrificationderived nitrite, and the subsequent abiotic formation of NO, even though nitrification rates were not significantly higher than in unamended soil. The results suggest that enhanced soil NO emissions are a characteristic response in forests subjected to elevated N inputs. One possible consequence of higher NO emissions is an increase in O 3-related phytotoxicity. This effect may mitigate the ability of forests to accumulate carbon in response to N inputs or increasing atmospheric CO 2 .

Estuaries, 2003

The purpose of this study was to quantify the nitrogen (N) inputs to 34 estuaries on the Atlantic... more The purpose of this study was to quantify the nitrogen (N) inputs to 34 estuaries on the Atlantic and Gulf Coasts of the United States. Total nitrogen (TN) inputs ranged from 1 kg N ha Ϫ1 yr Ϫ1 for Upper Laguna Madre, Texas, to 49 kg N ha Ϫ1 yr Ϫ1 for Massachusetts Bay, Massachusetts. TN inputs to 11 of the 34 estuaries were dominated by urban N sources (point sources and septic systems) and nonpoint source N runoff (5% of total); point sources accounted for 36-86% of the TN inputs to these 11 urban-dominated estuaries. TN inputs to 20 of the 34 estuaries were dominated by agricultural N sources; N fertilization was the dominant source (46% of the total), followed by manure (32% of the total) and N fixation by crops (16% of the total). Atmospheric deposition (runoff from watershed plus direct deposition to the surface of the estuary) was the dominant N source for three estuaries (

Environmental Science & Technology, 2002

ABSTRACT The purpose of this work was to determine the contribution made by atmospheric nitrogen ... more ABSTRACT The purpose of this work was to determine the contribution made by atmospheric nitrogen (N) deposition to the total N input to 10 estuaries on the east coast of the United States. We estimated the amount of N fixed by human activities in the watersheds (N fertilization, biotic N2fixation by legumes and pastures, atmospheric N deposition, and net food and feed import of N) of these 10 estuaries and used a land-use specific approach to estimate the N available for transport to the estuary from different watershed N sources (runoff from agriculture, urban areas and upland forests, point sources, and atmospheric deposition). Total atmospheric N inputs (watershed runoff plus direct deposition to the surface of estuary) accounted for 15-42% of the total N inputs to these 10 estuaries. Direct deposition to the surface of the estuary was an important atmospheric N source for four estuaries, accounting for 35-50% of the total atmospheric N inputs. Simulated reductions of atmospheric N deposition by 25% and 50% of current deposition rates reduced the contribution made by atmospheric N deposition to the total N loads by 1-6% and 2-11%, respectively. Largest reductions occurred in estuaries with direct atmospheric N deposition contributions >35% of the total atmospheric N input. Results from our simulated reductions suggest that considerable reductions (>25%) in atmospheric N deposition will be needed to significantly reduce the contribution made by atmospheric N deposition to the total N loads to our study estuaries. In addition, reductions in atmospheric N deposition will first be detected in estuaries with relatively high direct deposition inputs of atmospheric N deposition.

Environmental Pollution, 2006

The purpose of our study was to examine how environmental parameters influence the surface atmosp... more The purpose of our study was to examine how environmental parameters influence the surface atmosphere exchange of gaseous mercury in background soils of western Maryland. The parameters included soil temperature, redox potential, and volumetric water content. We also wanted to determine if soil pore air total gaseous mercury (TGM) concentrations were influencing atmospheric exchange. All parameters were measured at four depths below the soil surface, at the Oe - A soil horizon interface, A - E soil horizon interface, 5 cm into the E horizon, and 10 cm into the E horizon. Three plots were delineated in a forested area and three in a cleared area at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in western Maryland. TGM fluxes were measured with a dynamic flux chamber and soil pore air concentrations were measured with our newly developed soil pore TGM sampling method. Plots were sampled for soil pore air TGM concentrations and TGM flux every third week from July 2009 thr...

Case reports in ophthalmology, 2012

We present the case of an 18-year-old Caucasian male with a unilateral macular star and retinal v... more We present the case of an 18-year-old Caucasian male with a unilateral macular star and retinal vascular anomalies compatible with adult onset Coats' disease. Diagnosis was based on fundoscopic, fluorescein angiography and optical coherence tomography findings. The patient presented to our emergency department with complaints of low vision in his left eye (LE) detected 10 days before. The best-corrected visual acuity in the LE was 20/50. Fundoscopy of the LE evidenced a complete macular star. Optical coherence tomography showed increased retinal thickness, infiltration of the retinal wall, and detachment of the neuroepithelium. Angiography revealed no appreciable diffusion in the macula. Above the superior temporal (ST) arcade, anomalies in the retinal vasculature were found, with interruption of the peripheral vessels and vessels which were 'sausage'-like. After 1 month, the LE vision evolved to hand movements. Laser photocoagulation was performed in the ST quadrant. In...

Water, Air, & Soil Pollution, 2004

Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watershed... more Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeastern United States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha −1 yr −1 (mean = 6.4 kg N ha −1 yr −1 ; median = 7.0 kg N ha −1 yr −1). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg N ha −1 yr −1 (mean = 2.0 kg N ha −1 yr −1 ; median = 1.7 kg N ha −1 yr −1). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha −1 yr −1 (mean = 4.4 kg N ha −1 yr −1 ; median = 4.6 kg N ha −1 yr −1). Outputs of DIN in streamwater were predominantly NO 3-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.

Environmental science-Processes&Impacts, 2013

Water, Air, & Soil Pollution, 2010

The goal of this project was to develop a method to measure the total gaseous mercury (TGM) conce... more The goal of this project was to develop a method to measure the total gaseous mercury (TGM) concentrations in unsaturated soils. Existing methods did not allow for easy replication, were costly, and were more suited for other gases, such as CO 2 , that do not react with collection surfaces. To overcome these problems, we developed a method that simultaneously collects up to ten soil pore air samples. We used a single mass flow controller, one pump, and two banks of rotameters to draw soil air out of the ground at 25 smLmin −1 onto gold-coated quartz traps. Analysis of the gold traps was performed with a Tekran 2500 CVAFS mercury detector. The system was field tested at the Piney Reservoir Ambient Air Monitoring Station in western Maryland. Our system was relatively precise and accurate. For example, replicate TGM concentrations differed by less than 25% and recovery of known amounts of mercury were greater than 95%. Field measurements showed that the maximum soil pore air TGM concentrations, between 3 and 4 ngm −3 , occurred at the Oe-A soil horizon interface. At all other depths, the total mercury concentrations were lower than the ambient air concentrations of 1.8 ngm −3. We believe our new method can be used to precisely and accurately measure the TGM concentrations in unsaturated soils at multiple locations simultaneously.

Water, Air, and Soil Pollution, 1987

Water, Air, & Soil Pollution, 2011

The original Figure 4 did not include the units. The bottom axis of Figure 4 should read: TGM Con... more The original Figure 4 did not include the units. The bottom axis of Figure 4 should read: TGM Concentration (ng m-3)

Water, Air, & Soil Pollution, 2011

Water, Air, and Soil Pollution, 2008

The purpose of this study was to gather information on the spatial and temporal variation of stre... more The purpose of this study was to gather information on the spatial and temporal variation of stream water total mercury concentrations ([THg]) and to test the hypothesis that stream water [THg] increases as stream pH decreases in the Shenandoah National Park (SNP). We based our hypothesis on studies in lakes that found mercury methylation increases with decreasing pH, and studies

Science of The Total Environment, 2004

In this study we used the Watershed Assessment Tool for Evaluating Reduction Strategies for Nitro... more In this study we used the Watershed Assessment Tool for Evaluating Reduction Strategies for Nitrogen (WATERSN) model to evaluate a variety of management strategies for reducing nitrogen (N) loads to four US east coast estuaries: Casco Bay, Long Island Sound, Chesapeake Bay and Pamlico Sound. These management strategies encompass reductions in atmospheric emissions and deposition of N from sources including, fossil fuel burning utility emissions and mobile NO(x) emissions, N treatment in wastewater and controls on agricultural N inputs. We find that in primarily urban watersheds biological removal of N in wastewater treatment produces the greatest reduction in N loading (32-57% reductions), while in less urban watersheds, reductions in agricultural loading are more effective (5-56% reductions) in decreasing N loads to coastal ecosystems. Because anthropogenic N inputs are derived from a variety of sources, we also examined an integrated scenario targeting all major N sources; this resulted in 35-58% reductions in N loading. Nitrogen pollution originates from multiple sources and is transported through several media (air, soil, water); a major challenge of the development of N management strategies will be the control of multiple sources to effectively reduce N loads to estuaries.

Science of The Total Environment, 2012

The purpose of this study was to directly measure the dry deposition of gaseous oxidized mercury ... more The purpose of this study was to directly measure the dry deposition of gaseous oxidized mercury (GOM) in western Maryland. Annual estimates were made using passive ion-exchange surrogate surfaces and a resistance model. Surrogate surfaces were deployed for seventeen weekly sampling periods between September 2009 and October 2010. Dry deposition rates from surrogate surfaces ranged from 80 to 1512 pgm(-2)h(-1). GOM dry deposition rates were strongly correlated (r(2)=0.75) with the weekly average atmospheric GOM concentrations, which ranged from 2.3 to 34.1 pgm(-3). Dry deposition of GOM could be predicted from the ambient air concentrations of GOM using this equation: GOM dry deposition (pgm(-2)h(-1))=43.2 × GOM concentration-80.3. Dry deposition velocities computed using GOM concentrations and surrogate surface GOM dry deposition rates, ranged from 0.2 to 1.7 cms(-1). Modeled dry deposition rates were highly correlated (r(2)=0.80) with surrogate surface dry deposition rates. Using the overall weekly average surrogate surface dry deposition rate (369 ± 340 pg m(-2)h(-1)), we estimated an annual GOM dry deposition rate of 3.2 μg m(-2)year(-1). Using the resistance model, we estimated an annual GOM dry deposition rate of 3.5 μg m(-2)year(-1). Our annual GOM dry deposition rates were similar to the dry deposition (3.3 μg m(-2)h(-1)) of gaseous elemental mercury (GEM) at our site. In addition, annual GOM dry deposition was approximately 1/2 of the average annual wet deposition of total mercury (7.7 ± 1.9 μg m(-2)year(-1)) at our site. Total annual mercury deposition from dry deposition of GOM and GEM and wet deposition was approximately 14.4 μg m(-2)year(-1), which was similar to the average annual litterfall deposition (15 ± 2.1 μg m(-2)year(-1)) of mercury, which was also measured at our site.

Science of The Total Environment, 2012

The purpose of this study was to determine the effects of soil temperature, soil moisture, redox ... more The purpose of this study was to determine the effects of soil temperature, soil moisture, redox potential (Eh) and soil organic matter (SOM) on the total gaseous mercury (TGM) concentrations in background soils. Our measurements were made in a grass field and deciduous forest at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in Garrett County, Maryland. Three plots in each area were sampled every third week from July 2009 to June 2010 at the Oe-A soil horizon interface, the A-E soil horizon interface, and 5 and 10 cm into the E soil horizon. The mean soil TGM concentration for all depths in the forest (2.3 ± 2.2 ng m(-3)) was significantly higher than the mean soil TGM concentration in the grass field (1.5 ± 1.9 ng m(-3)). Soil TGM at all depths was most strongly and consistently correlated to soil temperature. The soil TGM concentrations were highest and most variable at the forest Oe-A soil horizon interface (4.1 ± 2.0 ng m(-3)), ranging from 1.5 to 8.4 ng m(-3). This soil horizon interface had 11 to 26% more SOM and the soil Eh was 100 to 400 mV lower than the other soil depths. Our results suggest that soil temperature, soil Eh and SOM are significant factors affecting TGM concentrations in forest soils. Future studies of TGM dynamics in background soils may benefit from closely monitoring the organic soil horizon.

Forest Ecology and Management, 2004

The production of nitric oxide (NO) in forest soils can indicate that the ecosystem is progressin... more The production of nitric oxide (NO) in forest soils can indicate that the ecosystem is progressing toward a state of nitrogen (N) saturation. Soil NO emissions may also have impacts on local tropospheric ozone (O 3) levels. During 2000-2001, we made firsttime measurements of NO emissions in two paired watershed studies. In each study, one watershed had been amended with aerial applications of 2.5-3.5 g N m À2 per year above background atmospheric deposition rates since 1989, and an adjacent watershed served as a reference. In plots at the Fernow Experimental Forest (FEF) in West Virginia and the Bear Brook Watershed in Maine (BBWM), NO emissions in N-amended watersheds (0.61-6.8 mg NO-N m À2 h À1) were higher than in the reference watersheds (0.21-1.4 mg NO-N m À2 h À1). In the N-amended watershed at BBWM, NO fluxes in plots dominated by hardwood species were higher than in plots dominated by softwood species, in contrast to previous studies in other forests. Field NO fluxes were correlated with mineral soil nitrate (NO 3 À) concentrations (r 2 ¼ 0:65, P ¼ 0:016) across all plots, suggesting that NO emissions may be a reliable indicator of NO 3 À leaching potential. Laboratory experiments indicated that nitrification was the dominant source of NO at both sites. At BBWM, increased NO emissions in N-amended soil appeared to result from more rapid nitrification. In contrast, reduced soil pH in N-amended soil at FEF may have caused increased protonation of nitrificationderived nitrite, and the subsequent abiotic formation of NO, even though nitrification rates were not significantly higher than in unamended soil. The results suggest that enhanced soil NO emissions are a characteristic response in forests subjected to elevated N inputs. One possible consequence of higher NO emissions is an increase in O 3-related phytotoxicity. This effect may mitigate the ability of forests to accumulate carbon in response to N inputs or increasing atmospheric CO 2 .

Estuaries, 2003

The purpose of this study was to quantify the nitrogen (N) inputs to 34 estuaries on the Atlantic... more The purpose of this study was to quantify the nitrogen (N) inputs to 34 estuaries on the Atlantic and Gulf Coasts of the United States. Total nitrogen (TN) inputs ranged from 1 kg N ha Ϫ1 yr Ϫ1 for Upper Laguna Madre, Texas, to 49 kg N ha Ϫ1 yr Ϫ1 for Massachusetts Bay, Massachusetts. TN inputs to 11 of the 34 estuaries were dominated by urban N sources (point sources and septic systems) and nonpoint source N runoff (5% of total); point sources accounted for 36-86% of the TN inputs to these 11 urban-dominated estuaries. TN inputs to 20 of the 34 estuaries were dominated by agricultural N sources; N fertilization was the dominant source (46% of the total), followed by manure (32% of the total) and N fixation by crops (16% of the total). Atmospheric deposition (runoff from watershed plus direct deposition to the surface of the estuary) was the dominant N source for three estuaries (

Environmental Science & Technology, 2002

ABSTRACT The purpose of this work was to determine the contribution made by atmospheric nitrogen ... more ABSTRACT The purpose of this work was to determine the contribution made by atmospheric nitrogen (N) deposition to the total N input to 10 estuaries on the east coast of the United States. We estimated the amount of N fixed by human activities in the watersheds (N fertilization, biotic N2fixation by legumes and pastures, atmospheric N deposition, and net food and feed import of N) of these 10 estuaries and used a land-use specific approach to estimate the N available for transport to the estuary from different watershed N sources (runoff from agriculture, urban areas and upland forests, point sources, and atmospheric deposition). Total atmospheric N inputs (watershed runoff plus direct deposition to the surface of estuary) accounted for 15-42% of the total N inputs to these 10 estuaries. Direct deposition to the surface of the estuary was an important atmospheric N source for four estuaries, accounting for 35-50% of the total atmospheric N inputs. Simulated reductions of atmospheric N deposition by 25% and 50% of current deposition rates reduced the contribution made by atmospheric N deposition to the total N loads by 1-6% and 2-11%, respectively. Largest reductions occurred in estuaries with direct atmospheric N deposition contributions >35% of the total atmospheric N input. Results from our simulated reductions suggest that considerable reductions (>25%) in atmospheric N deposition will be needed to significantly reduce the contribution made by atmospheric N deposition to the total N loads to our study estuaries. In addition, reductions in atmospheric N deposition will first be detected in estuaries with relatively high direct deposition inputs of atmospheric N deposition.

Environmental Pollution, 2006