The effect of vernalization and two growth regulators Fascination^TM and Pro-Gibb^R on the growth, inflorescence development and flowering of Omithogalurrt Chesapeake Snowflake＇ was studied. Regardless of growth regu...The effect of vernalization and two growth regulators Fascination^TM and Pro-Gibb^R on the growth, inflorescence development and flowering of Omithogalurrt Chesapeake Snowflake＇ was studied. Regardless of growth regulator treatment, chilling bulbs for 3 weeks at 10℃ before planting accelerated flowering of the first inflorescence by 5 to 6 days, elongated floral stem length by 1.5 to 2 cm and shortened leaf length by 4 to 5 cm as compared with non-chilled bulbs. When bulbs were chilled 3 weeks at 10℃ before planting, Fascination 2% and Pro-Gibb accelerated flowering of the first inflorescence by 2 to 6 days respectively as compared with the control. When bulbs were not chilled before planting, Fascination 2% and Pro-Gibb accelerated flowering of the first inflorescence by 6 to12 days respectively as compared with the control. The lengths of the leaves and the inflorescences were not affected by PGR treatment. Higher rates of Pro-Gibb （100 mg.L^-1 and 200 mg.L^-1） and more amount of Fascination 2%（100 μL and 200 μL） can cause abortion of inflorescence.展开更多
Recent observations support an emerging paradigm that climate variability dominates nutrient enrichment in costal eco-systems, which can explain seasonal and inter-annual variability of phytoplankton community composi...Recent observations support an emerging paradigm that climate variability dominates nutrient enrichment in costal eco-systems, which can explain seasonal and inter-annual variability of phytoplankton community composition, biomass (Chl-a), and primary production (PP). In this paper, we combined observation and modeling to investigate the regulation of phytoplankton dynamics in Chesapeake Bay. The year we chose is 1996 that has high river runoff and is usually called a 'wet year'. A 3-D physical-biogeochemical model based on ROMS was developed to simulate the seasonal cycle and the regional distributions of phytoplankton biomass and primary production in Chesapeake Bay. Based on the model results, NO3 presents a strong contrast to the river nitrate load during spring and the highest concentration in the bay reaches around 80 mmol Nm-3 . Compared with the normal year, phytoplankton bloom in spring of 1996 appears in lower latitudes with a higher concentration. Quantitative comparison between the modeled and observed seasonal averaged dissolved inorganic nitrogen concentrations shows that the model produces reliable results. The correlation coefficient r2 for all quantities exceeds 0.95, and the skill parameter for the four seasons is all above 0.95.展开更多
An assessment of stream health within the Chesapeake Bay Basin can be made using the Stream Health and Runoff Potential (SHARP) model, which is based solely on the relationship between land cover and stream constituen...An assessment of stream health within the Chesapeake Bay Basin can be made using the Stream Health and Runoff Potential (SHARP) model, which is based solely on the relationship between land cover and stream constituents: Total phosphorus (TP), total nitrogen (TN), and total suspended sediment (TSS). While not intended to compete with more complex models that utilize a range of specific input data, SHARP’s advantage is that it requires little input, is easily applied, and can show whether a stream or watershed is likely to be impacted (impaired). The model allows the user to define a watershed boundary on screen within which a stream health index (SHI), concentrations of TP, TN and TSS, percentages of five land cover types, a color-coded land cover snapshot, impervious surface area and fractional vegetation cover are output. The paper describes SHARP, its output and an overview of how it can be used.展开更多
The basic knowledge of tidal characteristics in Chesapeake Bay is a prerequisite to understand the tidal processes in Chesapeake Bay. The tidal characteristics in Chesapeake Bay were assessed in this paper using basic...The basic knowledge of tidal characteristics in Chesapeake Bay is a prerequisite to understand the tidal processes in Chesapeake Bay. The tidal characteristics in Chesapeake Bay were assessed in this paper using basic tidal hydraulic analysis. Tidal elevation, currents and salinity data of Chesapeake Bay from National Oceanic and Atmospheric Administration (NOAA) were retrieved, and analyzed to understand Chesapeake Bay tide. General knowledge of location, geometry, tides, freshwater inputs, wind, salinity, etc in Chesapeake Bay was described. Sediment distribution of Chesapeake Bay was briefly described and discussed. Amplitude and phase of the selected major constituent, form factor, phase difference between tide elevations and currents at a few tidal elevation stations within Chesapeake Bay were calculated. Tidal prism was figured out using cubature method. The analysis approach could also be used as a source of reference for basic tidal study in other tide-affected field.展开更多
Sea level rise due to climate change is a contentious issue with profound geographic and economic implications. One region in the USA identified as being particularly susceptible to seal level rise is the Chesapeake B...Sea level rise due to climate change is a contentious issue with profound geographic and economic implications. One region in the USA identified as being particularly susceptible to seal level rise is the Chesapeake Bay region, and it has been estimated that by the end of the century Norfolk, Virginia could experience sea level rise of 0.75 meters to more than 2.1 meters. Water intrusion is a serious problem in much of the Chesapeake Bay region. The question addressed here is whether this water intrusion is the result of climate-induced seal level rise or is being caused by other factors. Our findings indicate that the water intrusion problems in the region are due not to “sea level rise”, but primarily to land subsidence due to groundwater depletion and, to a lesser extent, subsidence from glacial isostatic adjustment. We conclude that water intrusion will thus continue even if sea levels decline. These findings are critical because the water intrusion problems in the Chesapeake Bay—and elsewhere—cannot be successfully solved unless their causes are correctly identified and appropriate remedies are devised. For the Chesapeake Bay region, the required remedy is the reversal of groundwater withdrawal rates, which has been used successfully elsewhere in the USA and other nations to solve water intrusion problems.展开更多
Tiny unicellular cyanobacteria or picocyanobacteria(0.5-3μm)are important due to their ecological significance.Chesa-peake Bay is a temperate estuary that contains abundant and diverse picocyanobacteria.Studies of Ch...Tiny unicellular cyanobacteria or picocyanobacteria(0.5-3μm)are important due to their ecological significance.Chesa-peake Bay is a temperate estuary that contains abundant and diverse picocyanobacteria.Studies of Chesapeake Bay picocy-anobacteria in the past 20 years led to the finding of new members of subcluster 5.2 Synechococcus.They laid the foundation for revealing the ecophysiology,biogeography,genomics,and molecular evolution of picocyanobacterial in the Chesapeake Bay and other coastal estuaries.The Bay picocyanobacteria are known to better tolerate the changes in temperature,salinity,and heavy metals compared to their coastal and open-ocean counterparts.Many picocyanobacteria isolated from the Bay contain rich toxin-antitoxin(TA)genes,suggesting that the TA system may provide them with a genetic advance to cope with variable estuarine environments.Distinct winter and summer picocyanobacteria are present in the Bay,suggesting a dynamic seasonal shift of the picocyanobacterial community in the temperate estuary.While the Bay contains subcluster 5.2 Synechococcus,it also contains freshwater Synechococcus,Cyanobium,and marine Synechococcus due to river influx and the ocean’s tidal influence.Some Chesapeake Bay picocyanobacterial clades were found in the Bering Sea and Chukchi Sea,showing a link between the Bay and polar picocyanobacteria.Genomic sequences of estuarine picocyanobacteria pro-vide new insight into the taxonomy and evolution of freshwater,estuarine,and marine unicellular cyanobacteria.Estuaries connect freshwater and marine ecosystems.This overview attempts to extend what we learned from Chesapeake Bay pico-cyanobacteria to picocyanobacteria in freshwater and marine waters.展开更多
The water exchange between the James River and the Elizabeth River, an estuary and sub-estuary system in the lower Chesapeake Bay, was investigated using a 3D numerical model. The conservative passive tracers were use...The water exchange between the James River and the Elizabeth River, an estuary and sub-estuary system in the lower Chesapeake Bay, was investigated using a 3D numerical model. The conservative passive tracers were used to represent the dissolved substances （DS） discharged from the Elizabeth River. The approach enabled us to diagnose the underlying physical processes that control the expansion of the DS, which is representative of potential transport of harmful algae blooms, pollutants from the Elizabeth River to the James River without explicitly simulating biological processes. Model simulations with realistic forcings in 2005, together with a series of processoriented numerical experiments, were conducted to explore the correlations of the transport process and external forcing. Model results show that the upriver transport depends highly on the freshwater discharge on a seasonal scale and maximum upriver transport occurs in summer with a mean transport time ranging from 15-30 days. The southerly/easterly wind, low river discharge, and neap tidal condition all act to strengthen the upriver transport. On the other hand, the northerly/westerly wind, river pulse, water level pulse, and spring tidal condition act to inhibit the upriver transport. Tidal flushing plays an important role in transporting the DS during spring tide, which shortens the travel time in the lower James River. The multivariable regression analysis of volume mean subtidal DS concentration in the mesohaline portion of the James River indicates that DS concentration in the upriver area can be explained and well predicted by the physical forcings （r = 0.858, p = 0.00001）.展开更多
Introduction:The Chesapeake Bay was once renowned for expansive meadows of submerged aquatic vegetation(SAV).However,only 10%of the original meadows survive.Future restoration effortswill be complicated by acceleratin...Introduction:The Chesapeake Bay was once renowned for expansive meadows of submerged aquatic vegetation(SAV).However,only 10%of the original meadows survive.Future restoration effortswill be complicated by accelerating climate change,including physiological stressors such as a predicted mean temperature increase of 2-6℃and a 50-160%increase in CO_(2)concentrations.Outcomes:As the Chesapeake Bay begins to exhibit characteristics of a subtropical estuary,summer heat waves will become more frequent and severe.Warming alone would eventually eliminate eelgrass(Zostera marina)from the region.It will favor native heat-tolerant species such as widgeon grass(Ruppia maritima)while facilitating colonization by non-native seagrasses(e.g.,Halodule spp.).Intensifying human activity will also fuel coastal zone acidification and the resulting high CO_(2)/low pH conditions may benefit SAV via a“CO_(2)fertilization effect.”Discussion:Acidification is known to offset the effects of thermal stress and may have similar effects in estuaries,assuming water clarity is sufficient to support CO_(2)-stimulated photosynthesis and plants are not overgrown by epiphytes.However,coastal zone acidification is variable,driven mostly by local biological processes that may or may not always counterbalance the effects of regional warming.This precarious equipoise between two forces-thermal stress and acidification-will be critically important because it may ultimately determine the fate of cool-water plants such as Zostera marina in the Chesapeake Bay.Conclusion:The combined impacts of warming,coastal zone acidification,water clarity,and overgrowth of competing algae will determine the fate of SAV communities in rapidly changing temperate estuaries.展开更多
A general spatial interpolation method for tidal properties has been developed by solving a partial differential equation with a combination of different orders of harmonic operators using a mixed finite element metho...A general spatial interpolation method for tidal properties has been developed by solving a partial differential equation with a combination of different orders of harmonic operators using a mixed finite element method. Numerically, the equation is solved implicitly without iteration on an unstructured triangular mesh grid. The paper demonstrates the performance of the method for tidal property fields with different characteristics, boundary complexity, number of input data points, and data point distribution. The method has been successfully applied under several different tidal environments, including an idealized distribution in a square basin, coamplitude and cophase lines in the Taylor semi-infiite rotating channel, and tide coamplitude and cophase lines in the Bohai Sea and Chesapeake Bay. Compared to Laplace’s equation that NOAA/NOS currently uses for interpolation in hydrographic and oceanographic applications, the multiple-order harmonic equation method eliminates the problem of singularities at data points, and produces interpolation results with better accuracy and precision.展开更多
The invasion of hydrilla in many waterways has caused significant problems resulting in high main- tenance costs for eradicating this invasive aquatic weed. Present identification methods employed for detecting hydril...The invasion of hydrilla in many waterways has caused significant problems resulting in high main- tenance costs for eradicating this invasive aquatic weed. Present identification methods employed for detecting hydrilla invasions such as aerial photography and videos are difficult, costly, and time consuming. Remote sensing has been used for assessing wetlands and other aquatic vegetation, but very little information is available for detecting hydrilla invasions in coastal estuaries and other water bodies. The objective of this study is to construct a library of spectral signatures for identifying and classifying hydrilla invasions. Spectral signatures of hydrilla were collected from an experimental tank and field locations in a coastal estuary in the upper Chesapeake Bay. These measurements collected from the experimental tank, resulted in spectral signatures with an average peak surface reflectance in the near-infrared （NIR） region of 16% at a wavelength of 818 nm. However, the spectral measure- ments, collected in the estuary, resulted in a very different spectral signature with two surface reflectance peaks of 6% at wavelengths of 725 nm and 818 nm. The difference in spectral signatures between sites are a result of the components in the water column in the estuary because of increased turbidity （e.g., nutrients, dissolved matter and suspended matter）, and canopy being lower （submerged） in the water column. Spectral signatures of hydrilla observed in the tank and the field had similar characteristics with low reflectance in visible region of the spectrum from 400 to 700 nm, but high in the NIR region from 700 to 900 nm.展开更多
Introduction:Marshes contribute to habitat and water quality in estuaries and coastal bays.Their importance to continued ecosystem functioning has led to concerns about their persistence.Outcomes:Concurrent with sea-l...Introduction:Marshes contribute to habitat and water quality in estuaries and coastal bays.Their importance to continued ecosystem functioning has led to concerns about their persistence.Outcomes:Concurrent with sea-level rise,marshes are eroding and appear to be disappearing through ponding in their interior;in addition,in many places,they are being replaced with shoreline stabilization structures.We examined the changes in marsh extent over the past 40 years within a subestuary of Chesapeake Bay,the largest estuary in the United States,to better understand the effects of sea-level rise and human pressure on marsh coverage.Discussion:Approximately 30 years ago,an inventory of York River estuary marshes documented the historic extent of marshes.Marshes were resurveyed in 2010 to examine shifts in tidal marsh extent and distribution.Marsh change varied spatially along the estuary,with watershed changes between a 32%loss and an 11%gain in marsh area.Loss of marsh was apparent in high energy sections of the estuary while there was marsh gain in the upper/riverine section of the estuary and where forested hummocks on marsh islands have become inundated.Marshes showed little change in the small tributary creeks,except in the creeks dominated by fringing marshes and high shoreline development.Conclusions:Differential resilience to sea-level rise and spatial variations in erosion,sediment supply,and human development have resulted in spatially variable changes in specific marsh extents and are predicted to lead to a redistribution of marshes along the estuarine gradient,with consequences for their unique communities.展开更多
文摘The effect of vernalization and two growth regulators Fascination^TM and Pro-Gibb^R on the growth, inflorescence development and flowering of Omithogalurrt Chesapeake Snowflake＇ was studied. Regardless of growth regulator treatment, chilling bulbs for 3 weeks at 10℃ before planting accelerated flowering of the first inflorescence by 5 to 6 days, elongated floral stem length by 1.5 to 2 cm and shortened leaf length by 4 to 5 cm as compared with non-chilled bulbs. When bulbs were chilled 3 weeks at 10℃ before planting, Fascination 2% and Pro-Gibb accelerated flowering of the first inflorescence by 2 to 6 days respectively as compared with the control. When bulbs were not chilled before planting, Fascination 2% and Pro-Gibb accelerated flowering of the first inflorescence by 6 to12 days respectively as compared with the control. The lengths of the leaves and the inflorescences were not affected by PGR treatment. Higher rates of Pro-Gibb （100 mg.L^-1 and 200 mg.L^-1） and more amount of Fascination 2%（100 μL and 200 μL） can cause abortion of inflorescence.
基金supported by the National Science Foundation project of M. Li (OCE-082543)
文摘Recent observations support an emerging paradigm that climate variability dominates nutrient enrichment in costal eco-systems, which can explain seasonal and inter-annual variability of phytoplankton community composition, biomass (Chl-a), and primary production (PP). In this paper, we combined observation and modeling to investigate the regulation of phytoplankton dynamics in Chesapeake Bay. The year we chose is 1996 that has high river runoff and is usually called a 'wet year'. A 3-D physical-biogeochemical model based on ROMS was developed to simulate the seasonal cycle and the regional distributions of phytoplankton biomass and primary production in Chesapeake Bay. Based on the model results, NO3 presents a strong contrast to the river nitrate load during spring and the highest concentration in the bay reaches around 80 mmol Nm-3 . Compared with the normal year, phytoplankton bloom in spring of 1996 appears in lower latitudes with a higher concentration. Quantitative comparison between the modeled and observed seasonal averaged dissolved inorganic nitrogen concentrations shows that the model produces reliable results. The correlation coefficient r2 for all quantities exceeds 0.95, and the skill parameter for the four seasons is all above 0.95.
文摘An assessment of stream health within the Chesapeake Bay Basin can be made using the Stream Health and Runoff Potential (SHARP) model, which is based solely on the relationship between land cover and stream constituents: Total phosphorus (TP), total nitrogen (TN), and total suspended sediment (TSS). While not intended to compete with more complex models that utilize a range of specific input data, SHARP’s advantage is that it requires little input, is easily applied, and can show whether a stream or watershed is likely to be impacted (impaired). The model allows the user to define a watershed boundary on screen within which a stream health index (SHI), concentrations of TP, TN and TSS, percentages of five land cover types, a color-coded land cover snapshot, impervious surface area and fractional vegetation cover are output. The paper describes SHARP, its output and an overview of how it can be used.
文摘The basic knowledge of tidal characteristics in Chesapeake Bay is a prerequisite to understand the tidal processes in Chesapeake Bay. The tidal characteristics in Chesapeake Bay were assessed in this paper using basic tidal hydraulic analysis. Tidal elevation, currents and salinity data of Chesapeake Bay from National Oceanic and Atmospheric Administration (NOAA) were retrieved, and analyzed to understand Chesapeake Bay tide. General knowledge of location, geometry, tides, freshwater inputs, wind, salinity, etc in Chesapeake Bay was described. Sediment distribution of Chesapeake Bay was briefly described and discussed. Amplitude and phase of the selected major constituent, form factor, phase difference between tide elevations and currents at a few tidal elevation stations within Chesapeake Bay were calculated. Tidal prism was figured out using cubature method. The analysis approach could also be used as a source of reference for basic tidal study in other tide-affected field.
文摘Sea level rise due to climate change is a contentious issue with profound geographic and economic implications. One region in the USA identified as being particularly susceptible to seal level rise is the Chesapeake Bay region, and it has been estimated that by the end of the century Norfolk, Virginia could experience sea level rise of 0.75 meters to more than 2.1 meters. Water intrusion is a serious problem in much of the Chesapeake Bay region. The question addressed here is whether this water intrusion is the result of climate-induced seal level rise or is being caused by other factors. Our findings indicate that the water intrusion problems in the region are due not to “sea level rise”, but primarily to land subsidence due to groundwater depletion and, to a lesser extent, subsidence from glacial isostatic adjustment. We conclude that water intrusion will thus continue even if sea levels decline. These findings are critical because the water intrusion problems in the Chesapeake Bay—and elsewhere—cannot be successfully solved unless their causes are correctly identified and appropriate remedies are devised. For the Chesapeake Bay region, the required remedy is the reversal of groundwater withdrawal rates, which has been used successfully elsewhere in the USA and other nations to solve water intrusion problems.
基金The research grant awards(OCE-9730602,OCE-0049098,MCB-0132070,MCB-0537041,and 1829888)the U.S.National Science Foundation have greatly advanced our knowledge of the ecology of picocyanobacteria in the estuarine environment.
文摘Tiny unicellular cyanobacteria or picocyanobacteria(0.5-3μm)are important due to their ecological significance.Chesa-peake Bay is a temperate estuary that contains abundant and diverse picocyanobacteria.Studies of Chesapeake Bay picocy-anobacteria in the past 20 years led to the finding of new members of subcluster 5.2 Synechococcus.They laid the foundation for revealing the ecophysiology,biogeography,genomics,and molecular evolution of picocyanobacterial in the Chesapeake Bay and other coastal estuaries.The Bay picocyanobacteria are known to better tolerate the changes in temperature,salinity,and heavy metals compared to their coastal and open-ocean counterparts.Many picocyanobacteria isolated from the Bay contain rich toxin-antitoxin(TA)genes,suggesting that the TA system may provide them with a genetic advance to cope with variable estuarine environments.Distinct winter and summer picocyanobacteria are present in the Bay,suggesting a dynamic seasonal shift of the picocyanobacterial community in the temperate estuary.While the Bay contains subcluster 5.2 Synechococcus,it also contains freshwater Synechococcus,Cyanobium,and marine Synechococcus due to river influx and the ocean’s tidal influence.Some Chesapeake Bay picocyanobacterial clades were found in the Bering Sea and Chukchi Sea,showing a link between the Bay and polar picocyanobacteria.Genomic sequences of estuarine picocyanobacteria pro-vide new insight into the taxonomy and evolution of freshwater,estuarine,and marine unicellular cyanobacteria.Estuaries connect freshwater and marine ecosystems.This overview attempts to extend what we learned from Chesapeake Bay pico-cyanobacteria to picocyanobacteria in freshwater and marine waters.
基金This research was funded by the National Natural Science Foundation of China （Grant Nos. 41406005 and 41666001）, Key Research Program of Frontier Sciences, CAS （No. QYZDJ-SSW-DQC022）, and the Fundamental Research Funds for the Central Universities of SCUT under Grant No. 2017ZD101. Parts of this study were supported by the Virginia Department of Environmental Quality （contracts # 15050 and 14835）. The development of the model was supported by USGS Project of Model Study of Change in Salinity under Different Sea-level Rise Scenarios in the York River and James River. We appreciate two anonymous reviewers＇ comments and constructive suggestions, which improve the manuscript. We thank Mac Sisson for his comments on the early version and help on editing the manuscript. This is the contribution number #3704 of Virginia Institute of Marine Science, College of William and Mary.
文摘The water exchange between the James River and the Elizabeth River, an estuary and sub-estuary system in the lower Chesapeake Bay, was investigated using a 3D numerical model. The conservative passive tracers were used to represent the dissolved substances （DS） discharged from the Elizabeth River. The approach enabled us to diagnose the underlying physical processes that control the expansion of the DS, which is representative of potential transport of harmful algae blooms, pollutants from the Elizabeth River to the James River without explicitly simulating biological processes. Model simulations with realistic forcings in 2005, together with a series of processoriented numerical experiments, were conducted to explore the correlations of the transport process and external forcing. Model results show that the upriver transport depends highly on the freshwater discharge on a seasonal scale and maximum upriver transport occurs in summer with a mean transport time ranging from 15-30 days. The southerly/easterly wind, low river discharge, and neap tidal condition all act to strengthen the upriver transport. On the other hand, the northerly/westerly wind, river pulse, water level pulse, and spring tidal condition act to inhibit the upriver transport. Tidal flushing plays an important role in transporting the DS during spring tide, which shortens the travel time in the lower James River. The multivariable regression analysis of volume mean subtidal DS concentration in the mesohaline portion of the James River indicates that DS concentration in the upriver area can be explained and well predicted by the physical forcings （r = 0.858, p = 0.00001）.
基金This review was adapted from the author’s contributions to the Chesapeake Bay Submerged Aquatic Vegetation(SAV)Habitat Requirements and Restoration Targets:A Third Technical Synthesis funded by the U.S.Environmental Protection Agency through a Chesapeake Bay Implementation Grant authorized by section 117 of the Clean Water Act.The authors acknowledge the assistance of Brooke Laundry(MDDNR)and numerous members of the technical synthesis workgroup(2014-2017).
文摘Introduction:The Chesapeake Bay was once renowned for expansive meadows of submerged aquatic vegetation(SAV).However,only 10%of the original meadows survive.Future restoration effortswill be complicated by accelerating climate change,including physiological stressors such as a predicted mean temperature increase of 2-6℃and a 50-160%increase in CO_(2)concentrations.Outcomes:As the Chesapeake Bay begins to exhibit characteristics of a subtropical estuary,summer heat waves will become more frequent and severe.Warming alone would eventually eliminate eelgrass(Zostera marina)from the region.It will favor native heat-tolerant species such as widgeon grass(Ruppia maritima)while facilitating colonization by non-native seagrasses(e.g.,Halodule spp.).Intensifying human activity will also fuel coastal zone acidification and the resulting high CO_(2)/low pH conditions may benefit SAV via a“CO_(2)fertilization effect.”Discussion:Acidification is known to offset the effects of thermal stress and may have similar effects in estuaries,assuming water clarity is sufficient to support CO_(2)-stimulated photosynthesis and plants are not overgrown by epiphytes.However,coastal zone acidification is variable,driven mostly by local biological processes that may or may not always counterbalance the effects of regional warming.This precarious equipoise between two forces-thermal stress and acidification-will be critically important because it may ultimately determine the fate of cool-water plants such as Zostera marina in the Chesapeake Bay.Conclusion:The combined impacts of warming,coastal zone acidification,water clarity,and overgrowth of competing algae will determine the fate of SAV communities in rapidly changing temperate estuaries.
文摘A general spatial interpolation method for tidal properties has been developed by solving a partial differential equation with a combination of different orders of harmonic operators using a mixed finite element method. Numerically, the equation is solved implicitly without iteration on an unstructured triangular mesh grid. The paper demonstrates the performance of the method for tidal property fields with different characteristics, boundary complexity, number of input data points, and data point distribution. The method has been successfully applied under several different tidal environments, including an idealized distribution in a square basin, coamplitude and cophase lines in the Taylor semi-infiite rotating channel, and tide coamplitude and cophase lines in the Bohai Sea and Chesapeake Bay. Compared to Laplace’s equation that NOAA/NOS currently uses for interpolation in hydrographic and oceanographic applications, the multiple-order harmonic equation method eliminates the problem of singularities at data points, and produces interpolation results with better accuracy and precision.
文摘The invasion of hydrilla in many waterways has caused significant problems resulting in high main- tenance costs for eradicating this invasive aquatic weed. Present identification methods employed for detecting hydrilla invasions such as aerial photography and videos are difficult, costly, and time consuming. Remote sensing has been used for assessing wetlands and other aquatic vegetation, but very little information is available for detecting hydrilla invasions in coastal estuaries and other water bodies. The objective of this study is to construct a library of spectral signatures for identifying and classifying hydrilla invasions. Spectral signatures of hydrilla were collected from an experimental tank and field locations in a coastal estuary in the upper Chesapeake Bay. These measurements collected from the experimental tank, resulted in spectral signatures with an average peak surface reflectance in the near-infrared （NIR） region of 16% at a wavelength of 818 nm. However, the spectral measure- ments, collected in the estuary, resulted in a very different spectral signature with two surface reflectance peaks of 6% at wavelengths of 725 nm and 818 nm. The difference in spectral signatures between sites are a result of the components in the water column in the estuary because of increased turbidity （e.g., nutrients, dissolved matter and suspended matter）, and canopy being lower （submerged） in the water column. Spectral signatures of hydrilla observed in the tank and the field had similar characteristics with low reflectance in visible region of the spectrum from 400 to 700 nm, but high in the NIR region from 700 to 900 nm.
基金This study was supported by Environmental Protection Agency Award:[Grant Numbers CD96329601-1 and CD-97386001-0].
文摘Introduction:Marshes contribute to habitat and water quality in estuaries and coastal bays.Their importance to continued ecosystem functioning has led to concerns about their persistence.Outcomes:Concurrent with sea-level rise,marshes are eroding and appear to be disappearing through ponding in their interior;in addition,in many places,they are being replaced with shoreline stabilization structures.We examined the changes in marsh extent over the past 40 years within a subestuary of Chesapeake Bay,the largest estuary in the United States,to better understand the effects of sea-level rise and human pressure on marsh coverage.Discussion:Approximately 30 years ago,an inventory of York River estuary marshes documented the historic extent of marshes.Marshes were resurveyed in 2010 to examine shifts in tidal marsh extent and distribution.Marsh change varied spatially along the estuary,with watershed changes between a 32%loss and an 11%gain in marsh area.Loss of marsh was apparent in high energy sections of the estuary while there was marsh gain in the upper/riverine section of the estuary and where forested hummocks on marsh islands have become inundated.Marshes showed little change in the small tributary creeks,except in the creeks dominated by fringing marshes and high shoreline development.Conclusions:Differential resilience to sea-level rise and spatial variations in erosion,sediment supply,and human development have resulted in spatially variable changes in specific marsh extents and are predicted to lead to a redistribution of marshes along the estuarine gradient,with consequences for their unique communities.
