Algal blooms in lakes have become a common global environmental problem. Nowadays, remote sensing is widely used to monitor algal blooms in lakes due to the macroscopic, fast, real-time characteristics. However, it is...Algal blooms in lakes have become a common global environmental problem. Nowadays, remote sensing is widely used to monitor algal blooms in lakes due to the macroscopic, fast, real-time characteristics. However, it is often difficult to distinguish between algal blooms and aquatic vegetation due to their similar spectral characteristics. In this paper, we used modified vegetation presence frequency index(VPF) based on Moderate-resolution Imaging Spectroradiometer(MODIS) imagery to distinguish algal blooms from aquatic vegetation, and analyzed the spatial and temporal variations of algal blooms and aquatic vegetation from a phenological perspective for five large natural lakes with frequent algal bloom outbreaks in China from 2019 to 2020. We simplified the VPF method to make it with a higher spatial transferability so that it could be applied to other lakes in different climatic zones. Through accuracy validation, we found that the modified VPF method can effectively distinguish between algal blooms and aquatic vegetation, and the results vary from lake to lake. The highest accuracy of 97% was achieved in Hulun Lake, where the frequency of algal outbreaks is low and the extent of aquatic vegetation is stable, while the lowest accuracy of 76% was achieved in Dianchi Lake, which is rainy in summer and the lake is small. Analyses suggests that the time period when algal blooms occur most frequently might not coincide with that when they have the largest area. However, in most cases these two are close in terms of time period. The modified VPF method has a broad scope of application, is easy to implement, and has a high practical value. Furthermore, the method could be established using only a small amount of measured data, which is useful for water quality monitoring on large spatial scales.展开更多
Maintaining beneficial, native plant structure and diversity while reducing invasive, nuisance species dominance is an important management domain for natural resource managers. One such vegetation component in North ...Maintaining beneficial, native plant structure and diversity while reducing invasive, nuisance species dominance is an important management domain for natural resource managers. One such vegetation component in North American lakes and reservoirs is submerged aquatic vegetation—a valuable aquatic resource which serves as productive habitat for fish, aquatic macroinvertebrates, and other wildlife. Reservoirs in the southern parts of the United States have experienced varying aquatic plant dominance dynamics due to historical water resource management actions, including drawdowns and introduction of herbivorous fish for the purpose of controlling invasive aquatic vegetation. Some of these management options have also been detrimental to native submerged aquatic vegetation. This paper explores an adaptive management research effort by installing herbivore-protected, fenced-pen submerged aquatic vegetation sites in a high-herbivore reservoir to determine effectiveness of protecting habitat and serving as founder colony sources for propagule spread. Four experimental sites with three management treatments each were planted with American eelgrass. Each site utilized one un-fenced treatment and two treatments with varying mesh sizes for protective fencing-pens. Site integrity, species survival and spread, and grazing were documented. One additional site was installed and planted with other native submerged aquatic vegetation species for nominal species performance descriptions. No plants survived unprotected in the high-herbivore system and plants, in general, performed consistently better within the smaller mesh size. These test planting results were ultimately used to inform adaptive management decision making for plant installation and expansion designs for managing reservoirs invested with Hydrilla, considered one of the most serious invasive aquatic plants in the United States.展开更多
In order to study the flow characteristics in water bodies with rigid aquatic vegetation,series of laboratory experiments are carried out in an open channel,in which glass rods are used as plants with diameters of 6mm...In order to study the flow characteristics in water bodies with rigid aquatic vegetation,series of laboratory experiments are carried out in an open channel,in which glass rods are used as plants with diameters of 6mm,8mm and 10mm,respectively.For each diameter of glass rods,four typical cases are considered with various densities and arrangements of glass rods.The flow velocities in the four cases are measured by the 3-D laser Doppler velocimeter(LDV).The water surface slope,the flow velocity,the water head loss,the vegetation drag force and the hydraulic slope are calculated,analyzed and discussed.The horizontal,vertical and total vegetation densities in the vegetation area are defined and the relationship between these physical parameters and the water surface slope are studied.The head loss and the hydraulic slope in the vegetation area are also calculated,compared and analyzed.It is indicated that the water surface slope and velocity,the head loss and the hydraulic slope in the vegetation area have a close relationship with the arrangement,the density,and the plant diameter of the vegetation.展开更多
Introduction:Submerged aquatic vegetation(SAV)has multiple functions in Lake Okeechobee.It provides critical habitat for fish and wildlife,stabilizes sediments,reduces phosphorus(P)concentration in the water column by...Introduction:Submerged aquatic vegetation(SAV)has multiple functions in Lake Okeechobee.It provides critical habitat for fish and wildlife,stabilizes sediments,reduces phosphorus(P)concentration in the water column by preventing re-suspension of P-rich sediments,and provides a substrate for attached algae,which also helps to remove P from the water column.Ten year water quality and SAV growth simulations are presented and compared with observed SAV and water quality data collected in the nearshore zone in Lake Okeechobee.Methods:The SAV theory and approach used in the LOEM are modified from the Chesapeake Bay model and incorporate three state variables:shoots(above the bed sediment),roots(in the bed sediment),and epiphytes(attached to the shoots).The SAV model has direct linkages with the water quality model,including(1)a link between the growth and decay of SAV and the nutrient pool of the water quality model;(2)a link between the photosynthesis and respiration of SAV and dissolved oxygen dynamics,and(3)the ways in which settling of particulate organic matter and nutrient uptake affect nutrient levels in the water column and in the sediment bed.Results:Total suspended solids affect light attenuation and are another major driving factor for SAV growth in the nearshore and littoral zone area.The model performs reasonably well in reproducing the spatial distribution of SAV.Conclusions:The theoretical analysis and model sensitivity tests indicate that SAV growth is primarily controlled by light and nutrients.The light available for SAV growth depends on the water depth and the turbidity.In this full scale simulation,the water depth comes from the LOEM hydrodynamic model,and the turbidity depends on the suspended sediment concentration and algal concentration.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
The aquatic vegetation can significantly affect the flow structure,the sediment transport,the bed scour and the water quality in rivers,lakes,reservoirs and open channels.In this study,the lattice Boltzmann method(LBM...The aquatic vegetation can significantly affect the flow structure,the sediment transport,the bed scour and the water quality in rivers,lakes,reservoirs and open channels.In this study,the lattice Boltzmann method(LBM)is applied in the two-dimensional numerical simulation of the flow structure in a flume with rigid vegetation.A multi-relaxation time model is applied to improve the stability of the numerical scheme for flows with a high Reynolds number.The vegetation induced drag force is added in the lattice Boltzmann equation model in order to improve the simulation accuracy and an algorithm of the multi-relaxation time is developed.Numerical simulations are performed for a wide range of flow and vegetation conditions and are validated by comparing with the laboratory experiments.Analysis of the simulated and experimentally measured flow Helds shows that the numerical simulation can satisfactorily reproduce the laboratory experiments,indicating that the proposed lattice Boltzmann model enjoys a high accuracy for simulating the flow-vegetation interaction in open channels.展开更多
基金Under the auspices of National Key Research and Development Project of China (No. 2021YFB3901101)National Natural Science Foundation of China (No. 41971322, 42071336, 42001311, 41730104)+2 种基金Jilin Provincial Science and Technology Development Project (No. 20180519021JH)Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2020234)China Postdoctoral Science Foundation (No. 2020M681057)。
文摘Algal blooms in lakes have become a common global environmental problem. Nowadays, remote sensing is widely used to monitor algal blooms in lakes due to the macroscopic, fast, real-time characteristics. However, it is often difficult to distinguish between algal blooms and aquatic vegetation due to their similar spectral characteristics. In this paper, we used modified vegetation presence frequency index(VPF) based on Moderate-resolution Imaging Spectroradiometer(MODIS) imagery to distinguish algal blooms from aquatic vegetation, and analyzed the spatial and temporal variations of algal blooms and aquatic vegetation from a phenological perspective for five large natural lakes with frequent algal bloom outbreaks in China from 2019 to 2020. We simplified the VPF method to make it with a higher spatial transferability so that it could be applied to other lakes in different climatic zones. Through accuracy validation, we found that the modified VPF method can effectively distinguish between algal blooms and aquatic vegetation, and the results vary from lake to lake. The highest accuracy of 97% was achieved in Hulun Lake, where the frequency of algal outbreaks is low and the extent of aquatic vegetation is stable, while the lowest accuracy of 76% was achieved in Dianchi Lake, which is rainy in summer and the lake is small. Analyses suggests that the time period when algal blooms occur most frequently might not coincide with that when they have the largest area. However, in most cases these two are close in terms of time period. The modified VPF method has a broad scope of application, is easy to implement, and has a high practical value. Furthermore, the method could be established using only a small amount of measured data, which is useful for water quality monitoring on large spatial scales.
文摘Maintaining beneficial, native plant structure and diversity while reducing invasive, nuisance species dominance is an important management domain for natural resource managers. One such vegetation component in North American lakes and reservoirs is submerged aquatic vegetation—a valuable aquatic resource which serves as productive habitat for fish, aquatic macroinvertebrates, and other wildlife. Reservoirs in the southern parts of the United States have experienced varying aquatic plant dominance dynamics due to historical water resource management actions, including drawdowns and introduction of herbivorous fish for the purpose of controlling invasive aquatic vegetation. Some of these management options have also been detrimental to native submerged aquatic vegetation. This paper explores an adaptive management research effort by installing herbivore-protected, fenced-pen submerged aquatic vegetation sites in a high-herbivore reservoir to determine effectiveness of protecting habitat and serving as founder colony sources for propagule spread. Four experimental sites with three management treatments each were planted with American eelgrass. Each site utilized one un-fenced treatment and two treatments with varying mesh sizes for protective fencing-pens. Site integrity, species survival and spread, and grazing were documented. One additional site was installed and planted with other native submerged aquatic vegetation species for nominal species performance descriptions. No plants survived unprotected in the high-herbivore system and plants, in general, performed consistently better within the smaller mesh size. These test planting results were ultimately used to inform adaptive management decision making for plant installation and expansion designs for managing reservoirs invested with Hydrilla, considered one of the most serious invasive aquatic plants in the United States.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11861003,11761005).
文摘In order to study the flow characteristics in water bodies with rigid aquatic vegetation,series of laboratory experiments are carried out in an open channel,in which glass rods are used as plants with diameters of 6mm,8mm and 10mm,respectively.For each diameter of glass rods,four typical cases are considered with various densities and arrangements of glass rods.The flow velocities in the four cases are measured by the 3-D laser Doppler velocimeter(LDV).The water surface slope,the flow velocity,the water head loss,the vegetation drag force and the hydraulic slope are calculated,analyzed and discussed.The horizontal,vertical and total vegetation densities in the vegetation area are defined and the relationship between these physical parameters and the water surface slope are studied.The head loss and the hydraulic slope in the vegetation area are also calculated,compared and analyzed.It is indicated that the water surface slope and velocity,the head loss and the hydraulic slope in the vegetation area have a close relationship with the arrangement,the density,and the plant diameter of the vegetation.
基金thank the Okeechobee Data Collection Team for SAV data collection.The authors also wish to thank Amy Peters for preparing Figures 2 and 3.
文摘Introduction:Submerged aquatic vegetation(SAV)has multiple functions in Lake Okeechobee.It provides critical habitat for fish and wildlife,stabilizes sediments,reduces phosphorus(P)concentration in the water column by preventing re-suspension of P-rich sediments,and provides a substrate for attached algae,which also helps to remove P from the water column.Ten year water quality and SAV growth simulations are presented and compared with observed SAV and water quality data collected in the nearshore zone in Lake Okeechobee.Methods:The SAV theory and approach used in the LOEM are modified from the Chesapeake Bay model and incorporate three state variables:shoots(above the bed sediment),roots(in the bed sediment),and epiphytes(attached to the shoots).The SAV model has direct linkages with the water quality model,including(1)a link between the growth and decay of SAV and the nutrient pool of the water quality model;(2)a link between the photosynthesis and respiration of SAV and dissolved oxygen dynamics,and(3)the ways in which settling of particulate organic matter and nutrient uptake affect nutrient levels in the water column and in the sediment bed.Results:Total suspended solids affect light attenuation and are another major driving factor for SAV growth in the nearshore and littoral zone area.The model performs reasonably well in reproducing the spatial distribution of SAV.Conclusions:The theoretical analysis and model sensitivity tests indicate that SAV growth is primarily controlled by light and nutrients.The light available for SAV growth depends on the water depth and the turbidity.In this full scale simulation,the water depth comes from the LOEM hydrodynamic model,and the turbidity depends on the suspended sediment concentration and algal concentration.
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.
基金Supported by the National Natural Science Foundation of China(Grant No.11861003,11761005).
文摘The aquatic vegetation can significantly affect the flow structure,the sediment transport,the bed scour and the water quality in rivers,lakes,reservoirs and open channels.In this study,the lattice Boltzmann method(LBM)is applied in the two-dimensional numerical simulation of the flow structure in a flume with rigid vegetation.A multi-relaxation time model is applied to improve the stability of the numerical scheme for flows with a high Reynolds number.The vegetation induced drag force is added in the lattice Boltzmann equation model in order to improve the simulation accuracy and an algorithm of the multi-relaxation time is developed.Numerical simulations are performed for a wide range of flow and vegetation conditions and are validated by comparing with the laboratory experiments.Analysis of the simulated and experimentally measured flow Helds shows that the numerical simulation can satisfactorily reproduce the laboratory experiments,indicating that the proposed lattice Boltzmann model enjoys a high accuracy for simulating the flow-vegetation interaction in open channels.
