INTRODUCTION
Previous field studies the significant decline in the areas of croplands,woodlands and grasslands, and a significant increase in the area of built-up lands and water bodies. It is estimated that most of the changes occurred right after the construction of the dam in 1999 occurred and the clearing of individuals began. Studies demonstrate that 400 to 7000 vascular plant species will be flooded once the water in the dam reaches its maximum levels. This poses a great threat to native species composition because they are being wiped out allowing invasive species to take over the landscape. Studies demonstrate how the vegetation cover in the woodland, crop and forested area have decline at similar rates to those of sediment build up. There is a strong correlation between sedimentation and soil erosion and vegetation production.
The Three Gorges Dam was meant to alleviate the environmental problems and restore forested areas but as it has been made evident the areas surrounding the dam have deteriorated. Provinces like Sandoupingzhen and Taipingxizhen have been greatly affected after the construction of the Three Gorges Dam began. The farmers are struggling to make a living in what seems to be unfruitful growing seasons. The limited growing season which is from January to October, the poor soil quality and the limited rainfall are problems which farmers in these areas are constantly dealing with. This study plans to monitor the changes in vegetation patterns due to the construction of the Three Gorges Dam in hopes that there are restoration projects which restore the study areas natural ecology prior to the construction of the dam.
METHODOLOGY
Infrared:
Density Slice:
Has a breakdown of the classification of the vegetation based on pixel size for the years 1987, 1999 and 2011. Below are the legend and the slideshow for the images for the pertaining years.
Change Detection:
Demonstrate the changes in vegetation for the years 1987, 1999 and 2011. The blue indicate a decrease in vegetation and the red indicate an increase in vegetation.
DISCUSSION
While looking for satellite images of my location it was quite difficult to find an image that was not affected by cloud cover or that was available for download. The images that were of better quality were not available and so I had to do my analysis without them. There were only 3 images from the 3 different time frames were used in order to perform the analysis and were the basis of this study. There are very few studies done on the riparian zone near the Three Gorges Dam, there are mostly predictions on the effects that this large dam would cause because of its immense structure. There predictions proved to be correct with my results. There has been an increase in vegetative areas near the Three Gorges Dam.
Furthermore, if I were to improve on this project I would do some sort of statistical analysis to determine the rate at which the vegetation is increasing and determine whether or not it is significant. I not only would test the vegetation but would classify the vegetation into classes (forest, woodland, crops and barren land) and determine the differences within each class. My future study will include not only vegetation surrounding the dam but also include both upstream and downstream. The future study is to include a wider range of study points or images.
REFERENCES
Floods deplete the soil from nutrients and affect the amount of vegetation produced in the riparian zone. The construction of the Three Gorges Dam has been very damaging on the soil because it has stripped valuable soil nutrients which are essential for any sort of crop growth. The construction of the Three Gorges Dam affected not only the land through the flooding which has caused an increase in sediment build-up in surrounding areas which have a direct effect on the landscape and its transformation. The transformation arises in the changes in the shoreline vegetation through the impoverished nutrient soil composition. The lack of nutrient rich soil leads to a decline in vegetation production which in turn leads to a decline in animal biodiversity.
The images below demonstrate some of the vegetation losses which were attributed to the construction of the dam.
The images below demonstrate some of the vegetation losses which were attributed to the construction of the dam.
Previous field studies the significant decline in the areas of croplands,woodlands and grasslands, and a significant increase in the area of built-up lands and water bodies. It is estimated that most of the changes occurred right after the construction of the dam in 1999 occurred and the clearing of individuals began. Studies demonstrate that 400 to 7000 vascular plant species will be flooded once the water in the dam reaches its maximum levels. This poses a great threat to native species composition because they are being wiped out allowing invasive species to take over the landscape. Studies demonstrate how the vegetation cover in the woodland, crop and forested area have decline at similar rates to those of sediment build up. There is a strong correlation between sedimentation and soil erosion and vegetation production.
The Three Gorges Dam was meant to alleviate the environmental problems and restore forested areas but as it has been made evident the areas surrounding the dam have deteriorated. Provinces like Sandoupingzhen and Taipingxizhen have been greatly affected after the construction of the Three Gorges Dam began. The farmers are struggling to make a living in what seems to be unfruitful growing seasons. The limited growing season which is from January to October, the poor soil quality and the limited rainfall are problems which farmers in these areas are constantly dealing with. This study plans to monitor the changes in vegetation patterns due to the construction of the Three Gorges Dam in hopes that there are restoration projects which restore the study areas natural ecology prior to the construction of the dam.
METHODOLOGY
The focus of this study is the area surrounding the Three Gorges Dam mainly the region pertaining to the Yangtze River in China, focused on the riparian zone right off the river. After the construction of the dam this area has been greatly affected not only putting strain on the terrain but affecting the soil composition and in essence the land productivity. Damming such a large area leads to significant changes in the shoreline vegetation not only affecting the diversity of crops but abundance as well. The Sandoupingzhen and Taipingxizhen provinces have the most vegetation damage due to their proximity to the dam. A time series comparison on vegetation was done from 1987 running through 2011. Images pertaining to the growing season which ran from January through October were downloaded and used. A total of three images were to be downloaded one for 1987 prior to construction of the TGD, one in 1999 after initial construction and one in 2011 after the dam has been completed and has been running for a few years.
Global Land Cover Facility, USGS and Echo Reverb were used to collect Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) images. A search on ESDI was used to locate the dam. The most visible images were downloaded for the study.
After the images were downloaded, the analysis of the location began after they were entered into the ENVI software program. The images were subset to focus the study on the Three Gorges Dam and the surrounding provinces. For the images that were ETM+ a separate adjusting had to take place in attempts to get rid of the lines cutting across through the image. To do this we have save the image and load the image. After the image is loaded we go to the Topographic function on the tool bar and Replace All the Bad Values with 0’s. The end result will give us a useable image.
The images were first converted into infrared using the bands 3 and 4. Converting the images into infrared was meant to show the healthy vegetation as pink hue and everything else that is not vegetation as a green hue. After that a Normalized Difference Vegetation Index (NDVI) was performed on the image. This makes the image into a grey scale which shows vegetation as the white. Since the NDVI doesn’t give a clear image on the vegetation changes a Density Slice was applied to the image. The density slice was then modified to only include vegetation index which was from 0-1 divided into four classes. The highest class pertains to forested areas.
Change Detection was performed on the images to determine the changes in the vegetation. A comparison of the images was done in the following manner: 1987-1999, 1999-2011 and 1987-2011. The images are a blue and red in color. To determine if there is a significant change the bluer the image is refers to a decrease in vegetation and the red demonstrates an increase in vegetation.
RESULTS
Study Area:
The following images are from 1987, 1999 and 2011 demonstrating the topography of the subset.
Infrared:
Demonstrate the healthy vegetation can be determined by the pinkish hue for the years 1987, 1999 and 2011.
Normalized Detection Vegetation Index (NDVI):
The white determine forested areas, greys determine the vegetation and black refers to no vegetation for the years 1987, 1999 and 2011.
The white determine forested areas, greys determine the vegetation and black refers to no vegetation for the years 1987, 1999 and 2011.
Density Slice:
Has a breakdown of the classification of the vegetation based on pixel size for the years 1987, 1999 and 2011. Below are the legend and the slideshow for the images for the pertaining years.
Demonstrate the changes in vegetation for the years 1987, 1999 and 2011. The blue indicate a decrease in vegetation and the red indicate an increase in vegetation.
 |
| 1987-2011 Change Detection |
 |
| 1987-1999 Change Detection |
 |
| 1999-2011 Change Detection |
DISCUSSION
Soil nutrient composition is one of the main factors for vegetation growth. The soil is affected by the sediment accumulation because of the Three Gorges Dam as well as the water fluctuations which have caused elevation changes in the dam and nearby lakes causing flooding and stripping the soil of its nutrients. The change detection of the years 1987-2011 shows a strong decline in vegetation in the areas to the north of the dam, while an increase in vegetation the areas south of the dam. The changes between 1987-1999 and 1999-2011 are stronger for 1987-1999 rather than 1999-2011 and it may have to do with the remodeling of the area in order to construct the dam. The density slice in 1987 shows very little forest canopy surrounding the dam but as the years progress the 1999 and 2011 density slice show an increase in forest area to the south of the dam. The reason for the increase can be attributed to the hydropower electric use rather than having to use the wood for power. This could have boosted the forest growth in the north.
While looking for satellite images of my location it was quite difficult to find an image that was not affected by cloud cover or that was available for download. The images that were of better quality were not available and so I had to do my analysis without them. There were only 3 images from the 3 different time frames were used in order to perform the analysis and were the basis of this study. There are very few studies done on the riparian zone near the Three Gorges Dam, there are mostly predictions on the effects that this large dam would cause because of its immense structure. There predictions proved to be correct with my results. There has been an increase in vegetative areas near the Three Gorges Dam.
Furthermore, if I were to improve on this project I would do some sort of statistical analysis to determine the rate at which the vegetation is increasing and determine whether or not it is significant. I not only would test the vegetation but would classify the vegetation into classes (forest, woodland, crops and barren land) and determine the differences within each class. My future study will include not only vegetation surrounding the dam but also include both upstream and downstream. The future study is to include a wider range of study points or images.
REFERENCES
· "GLCF: Earth Science Data Interface." Global Land Cover Facility.
·
· Fearnside, P.M. 1988. China's Three Gorges Dam: "Fatal" project or step toward modernization? World Development 16(5): 615-630. http://philip.inpa.gov.br/publ_livres/Preprints/19881/3GORGWD1.pdf
· Li et al,Yue-Sheng. "Large Water Management Projects and Schistosomiasis Control, Dongting Lake Region, China."Emerging Infectious Diseases13.7 (2007): 973-979. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2878251
· New et al, Thomas. "Impacts of large dams on riparian vegetation: applying global experience to the case of China's Three Gorges Dam." Biodiversity Conservation 17 (2008): 3149-3163. http://www.springerlink.com/content/c061gn40703hj227/fulltext.pdf.
· "USGS Global Visualization Viewer." USGS Global Visualization Viewer
