Organic phosphorus (nonreactive E NRP) is a major component of P in sediments, but information about its chemical forms and dynamic transformation is limited. The chemical forms and dynamic behaviors of NRP in a sed...Organic phosphorus (nonreactive E NRP) is a major component of P in sediments, but information about its chemical forms and dynamic transformation is limited. The chemical forms and dynamic behaviors of NRP in a sediment profile from Lake Talhu, a freshwater and eutrophic lake in China, were investigated. Five forms of NRP in the sediments were extracted based on a chemical fractionation technique, including easily labile NRP (NaHCO3-NRP), reactive metal oxide-bound NRP (HCl-NRP), humic acid-associated NRP (NaOH-NRPnA), fulvic acid-associated NRP (NaOH-NRPFA) and residual NRP (Res-TP). There were notable transformations with increasing sediment depth from the labile NaHCOa-NRP and NaOH-NRP pools to the recalcitrant HCl-NRP and Res-TP pools, which caused the NRP to become increasingly recalcitrant as the early diagenetic processes proceeded. Further analyses showed that the relative changes in contents of organic matter and reactive Fe oxides in the sediment profile triggered a competition for binding NRP fractions and led to the transformation of NRP. The results highlighted the importance of abiotic processes in regulating the diagenesis of organic P and its stability in sediments.展开更多
The understanding of organic phosphorus(P) dynamics in sediments requires information on their species at the molecular level,but such information in sediment profiles is scarce.A sediment profile was selected from ...The understanding of organic phosphorus(P) dynamics in sediments requires information on their species at the molecular level,but such information in sediment profiles is scarce.A sediment profile was selected from a large eutrophic lake,Lake Taihu(China),and organic P species in the sediments were detected using solution phosphorus-31 nuclear magnetic resonance spectroscopy(31 P NMR) following extraction of the sediments with a mixture of 0.25 mol/L NaOH and 50 mmol/L EDTA(NaOH-EDTA) solution.The results showed that P in the NaOH-EDTA extracts was mainly composed of orthophosphate,orthophosphate monoesters,phospholipids,DNA,and pyrophosphate.Concentrations of the major organic P compound groups and pyrophosphate showed a decreasing trend with the increase of depth.Their half-life times varied from 3 to 27 years,following the order of orthophosphate monoesters 〉 phospholipids DNA 〉 pyrophosphate.Principal component analysis revealed that the detected organic P species had binding phases similar to those of humic acid-associated organic P(NaOH-NRP HA),a labile organic P pool that tends to transform to recalcitrant organic P pools as the early diagenetic processes proceed.This demonstrated that the depth attenuation of the organic P species could be partly attributed to their increasing immobilization by the sediment solids,while their degradation rates should be significantly lower than what were suggested in previous studies.展开更多
The aim of this study is to estimate and compare soil erosion,in the Mount Elgon region,eastern Uganda,during the last decade.Possible trends and changes in erosion are linked to precipitation/climate change as well a...The aim of this study is to estimate and compare soil erosion,in the Mount Elgon region,eastern Uganda,during the last decade.Possible trends and changes in erosion are linked to precipitation/climate change as well as changes in land cover.Two different versions of the Revised Universal Soil loss Equation(RUSLE)are implemented and compared,one using slope length and the other using flow accumulation to estimate the slope length and steepness factor(LS).Comparisons of the modeled soil erosion vs.field data indicate that RUSLE based on flow accumulation is preferable.The modeling is carried out for the years 2000,2006,and 2012,and is based on ASTER remotely sensed data,digital elevation models,precipitation data from the study area,as well as existing soil maps.No significant trends in estimated soil erosion are found to be present during the last decade.Over exploitation of land is probably compensated by improved agricultural management and no significant increase in precipitation.Even if there are reports of more intense and increasing amounts of rainfall in the area,this could not be verified,neither through the analysis of climate data,nor by trends in the estimated soil loss.展开更多
Airborne laser scanning (ALS) is a technique used to obtain Digital Surface Models (DSM) and Digital Terrain Models (DTM) efficiently, and filtering is the key procedure used to derive DTM from point clouds. Gen...Airborne laser scanning (ALS) is a technique used to obtain Digital Surface Models (DSM) and Digital Terrain Models (DTM) efficiently, and filtering is the key procedure used to derive DTM from point clouds. Generating seed points is an initial step for most filtering algorithms, whereas existing algorithms usually define a regular window size to generate seed points. This may lead to an inadequate density of seed points, and further introduce error type I, especially in steep terrain and forested areas. In this study, we propose the use of object- based analysis to derive surface complexity information from ALS datasets, which can then be used to improve seed point generation. We assume that an area is complex if it is composed of many small objects, with no buildings within the area. Using these assumptions, we propose and implement a new segmentation algorithm based on a grid index, which we call the Edge and Slope Restricted Region Growing (ESRGG) algorithm. Surface complexity information is obtained by statistical analysis of the number of objects derived by segmentation in each area. Then, for complex areas, a smaller window size is defined to generate seed points. Experimental results show that the proposed algorithm could greatly improve the filtering results in complex areas, especially in steep terrain and forested areas.展开更多
基金supported by the National Natural Scientific Foundation of China (No. 40871220,40730528)the Natural Scientific Foundation of Jiangsu Province,China (No. BK2010606)the Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences(No. NIGLAS2010KXJ01)
文摘Organic phosphorus (nonreactive E NRP) is a major component of P in sediments, but information about its chemical forms and dynamic transformation is limited. The chemical forms and dynamic behaviors of NRP in a sediment profile from Lake Talhu, a freshwater and eutrophic lake in China, were investigated. Five forms of NRP in the sediments were extracted based on a chemical fractionation technique, including easily labile NRP (NaHCO3-NRP), reactive metal oxide-bound NRP (HCl-NRP), humic acid-associated NRP (NaOH-NRPnA), fulvic acid-associated NRP (NaOH-NRPFA) and residual NRP (Res-TP). There were notable transformations with increasing sediment depth from the labile NaHCOa-NRP and NaOH-NRP pools to the recalcitrant HCl-NRP and Res-TP pools, which caused the NRP to become increasingly recalcitrant as the early diagenetic processes proceeded. Further analyses showed that the relative changes in contents of organic matter and reactive Fe oxides in the sediment profile triggered a competition for binding NRP fractions and led to the transformation of NRP. The results highlighted the importance of abiotic processes in regulating the diagenesis of organic P and its stability in sediments.
基金supported by the National Scientific Foundation of China (No. 40871220,40730528)the Natural Scientific Foundation of Jiangsu Province,China (No.BK2010606)the Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences (No. NIGLAS2010KXJ01)
文摘The understanding of organic phosphorus(P) dynamics in sediments requires information on their species at the molecular level,but such information in sediment profiles is scarce.A sediment profile was selected from a large eutrophic lake,Lake Taihu(China),and organic P species in the sediments were detected using solution phosphorus-31 nuclear magnetic resonance spectroscopy(31 P NMR) following extraction of the sediments with a mixture of 0.25 mol/L NaOH and 50 mmol/L EDTA(NaOH-EDTA) solution.The results showed that P in the NaOH-EDTA extracts was mainly composed of orthophosphate,orthophosphate monoesters,phospholipids,DNA,and pyrophosphate.Concentrations of the major organic P compound groups and pyrophosphate showed a decreasing trend with the increase of depth.Their half-life times varied from 3 to 27 years,following the order of orthophosphate monoesters 〉 phospholipids DNA 〉 pyrophosphate.Principal component analysis revealed that the detected organic P species had binding phases similar to those of humic acid-associated organic P(NaOH-NRP HA),a labile organic P pool that tends to transform to recalcitrant organic P pools as the early diagenetic processes proceed.This demonstrated that the depth attenuation of the organic P species could be partly attributed to their increasing immobilization by the sediment solids,while their degradation rates should be significantly lower than what were suggested in previous studies.
文摘The aim of this study is to estimate and compare soil erosion,in the Mount Elgon region,eastern Uganda,during the last decade.Possible trends and changes in erosion are linked to precipitation/climate change as well as changes in land cover.Two different versions of the Revised Universal Soil loss Equation(RUSLE)are implemented and compared,one using slope length and the other using flow accumulation to estimate the slope length and steepness factor(LS).Comparisons of the modeled soil erosion vs.field data indicate that RUSLE based on flow accumulation is preferable.The modeling is carried out for the years 2000,2006,and 2012,and is based on ASTER remotely sensed data,digital elevation models,precipitation data from the study area,as well as existing soil maps.No significant trends in estimated soil erosion are found to be present during the last decade.Over exploitation of land is probably compensated by improved agricultural management and no significant increase in precipitation.Even if there are reports of more intense and increasing amounts of rainfall in the area,this could not be verified,neither through the analysis of climate data,nor by trends in the estimated soil loss.
基金Acknowledgements The authors would like m thank the anonymous reviewers for providing comments to improve the quality of this paper, and iSPACE of Research Studios Austria FG (RSA) (http://ispace.researchstudio. at/) for providing the ALS datasets. The study described in this paper is funded by the National Natural Science Foundation of China (Grant No. 41301493), the High Resolution Earth Observation Science Foundation of China (GFZX04060103-5-17), and Special Fund for Surveying and Mapping Scientific Research in the Public Interest (201412007).
文摘Airborne laser scanning (ALS) is a technique used to obtain Digital Surface Models (DSM) and Digital Terrain Models (DTM) efficiently, and filtering is the key procedure used to derive DTM from point clouds. Generating seed points is an initial step for most filtering algorithms, whereas existing algorithms usually define a regular window size to generate seed points. This may lead to an inadequate density of seed points, and further introduce error type I, especially in steep terrain and forested areas. In this study, we propose the use of object- based analysis to derive surface complexity information from ALS datasets, which can then be used to improve seed point generation. We assume that an area is complex if it is composed of many small objects, with no buildings within the area. Using these assumptions, we propose and implement a new segmentation algorithm based on a grid index, which we call the Edge and Slope Restricted Region Growing (ESRGG) algorithm. Surface complexity information is obtained by statistical analysis of the number of objects derived by segmentation in each area. Then, for complex areas, a smaller window size is defined to generate seed points. Experimental results show that the proposed algorithm could greatly improve the filtering results in complex areas, especially in steep terrain and forested areas.