Spatial and Temporal Changes of Lake Wetlands in Jianghan Plain After the Implementing of ‘Thirty-Six-Word Policy’
Available online at www.sciencedirect.com
Procedia Environmental Sciences 10 ( 2011 ) 2574 – 2580
2011 3rd International Conference on Environmental Science and Information Application Technology (ESIAT 2011)
Spatial and temporal changes of lake wetlands in Jianghan Plain after the implementing of ‘thirty-six-word policy’
Wang Chengchenga, Wang Hongzhi and Xarapat Ablat
Faculty of Urban and Environmental Science, Huazhong Normal University, Wuhan, China a [email protected]
Abstract
After the cataclysm of the Yangtze River in 1998, the State Council put forward the “thirty-six-word policy” for harnessing large rivers and lakes. Jianghan Plain is one of the main areas to get harnessed according to the policy. Based on the CAS land use databases of 1995, 2000, 2005 and 2010, the spatial changes information of lakes in Jianghan Plain were captured and analyzed under the ARCGIS platform or by indexes of landscape ecology. The results show that: From 1995 to 2010, the area of lake wetlands has been grown constantly; Transitions from farmland and unused land to lake were dominant for the increase of lake area, while so were the transitions reversely; Lake wetlands were divided into two categories (lake and pond) to be analyzed according to the area of every lake wetland patch, lakes mainly increased in the area while ponds mainly increased in the number of patches. Ponds are not as curved as lakes in shape and more dispersed than lakes; Lakes became less curved and concentrated with the augment of the area of lake wetlands. The shape of pond wetlands changed little and its distribution became a little concentrated with the increasing number of pond wetlands. During the three five-year analyzed, the increase of wetlands of Jianghan Plain was notable during the period of from 2000 to 2005, though the area of wetlands increased during all the three periods. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Conference ESIAT2011 Organization© 2011 Published Committee. by Elsevier Ltd. Selection and/or peer-review under responsibility of [name organizer]
Keywords: Jianghan Plain; lake wetlands; spatial and temporal changes.
Introduction
Wetland is a special ecological system as an interaction of land ecological system and water ecosystems [1]. Wetland change research is a hot area as one of the important parts of the global change studies. At present, the researches on wetlands mainly concentrate on the dynamic change of landscape pattern of wetland and its driving forces. The study areas of wetland basically cover the important wetland distribution area, including the eastern coastal area, North-East Sanjiang plain, zoige plateau, the Yangtze river and the qinghai-tibet plateau area, etc, and mainly 3S technology and landscape ecology methods [2-13] were applied in those researches. Jianghan plain is located in the middle of the Yangtze River, which foumous for its mass of shallow lakes. Since nineteen fifties, large-scale reclamation lakes to farmland has been reduced the area of lake
1878-0296 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Conference ESIAT2011 Organization Committee. doi: 10.1016/j.proenv.2011.09.400 Wang Chengcheng et al. / Procedia Environmental Sciences 10 ( 2011 ) 2574 – 2580 2575 wetlands remarkably and the ecological environment condition of Jianghan plain lake wetlands has changed deeply [14]. Previous researchers studied wetland changes in Jianghan Plain mainly with a longer time scale. They drew a conclusion that the area of wetlands was decreasing, and the changes of spatial distribution and degradation of wetlands in Jianghan Plain were mainly attributed to the increase of polder land [14,15]. However, after the cataclysm of the Yangtze River in 1998, the State Council put forward the “thirty-six-word policy” for harnessing large rivers and lakes. Jianghan Plain is one of the main areas of national governance of large rivers and lakes. There is still no literature published on the recent studies of wetlands changes of Jianghan Plain after the implementing of the policy. In the study, the dynamic change of lake wetlands spatial pattern in Jianghan Plain after the implementing of the policy of “reclaimed farmland to lake” were analyzed based on the CAS land use databases of 1995, 2000, 2005 and 2010 to get the basic information of the effect of the implementing of the policy, which will be useful to support further government decisions.
Materials and methods
Study areas.Jianghan plain (29°26ƍ-31°10ƍN, 111°30ƍ-114°32ƍE) is located in the middle of the Yangtze river, with a total area of about 31034km2. It contains 15 county level administrative districts , they are Jingzhou (including Shashi and Jingling), Songzi, Gongan, Shishou, Jianli, Xiantao, Honghu, Qianjiang, Tianmen, Hanchuan, Yunmeng, Yingcheng, Dangyang, Zhijiang, Wuhan (excluding Jiangxia, Xinzhou and Huangpi) in Hubei province. Jianghan Plain is the part of the main body of the middle Yangtze river Plain and one of the major grain, cotton and edible oil production bases [16] in China. Here lakes cover densely, while rivers and canals interweave with one another. The wetlands in Jianghan Plain play an important role at many aspects such as climate regulation, flood storage, aquaculture, protection of biodiversity, water conservation and tourism. Data processing.The lake wetlands and its change data was extracted with overlaying analysis at ARCGIS platform based on the CAS land use databases of 1995, 2000, 2005 and 2010. According to land use database, landscape of the study area were classified into six types: farmland, water area (including river and lake), forestland, grassland, construction land, and unused land [17]. The land use transition data to or from wetland is focused. Analysis methodology.Land use change index and Landscape ecology index are mainly applied to analyze the wetland changes during three 5-year peroids, 1995-2000, 2000-2005, 2005-2010. Land use change index models include dynamic change degree index (K) and bilateral dynamic change degree index (Ki), which calculate based on land use transfer matrix and represent the lake wetland area change and transition direction and transition extent to related to wetland respectively. Dynamic change degree index (K): Ub - Ua 1 K u u 100 % Ua T ˄1˅
where K is the change rate of a certain land type during the study period; Ua and Ub represent the area of a land use type in the beginning and end of the study period, respectively. T is the study period (a). K indicates the annual change rate of the land type. Bilateral dynamic change degree index (Ki): Ki ^` ¦¦Uij Uji Ui u T u 100 % ˄2˅
where Ki is the bilateral land use dynamic degree of land type i during the study period; Uij is the area of type i transfer to type j. Uji is the transfering area to type i from land type j. Ua is the area of a land use type in the beginning year of the peroid we study. T is the study period (a) [18]. 2576 Wang Chengcheng et al. / Procedia Environmental Sciences 10 ( 2011 ) 2574 – 2580
Indexes of landscape pattern mainly reflect the structure makeup and space deploy of landscape quantitively. Patch area, patch number, fragmentation, separation, average patch-shaped index and average patch fractal dimension are used to present the dynamic changes of the lake wetlands in the Jianghan Plain [4,19].
Results and analyses
Transformation of lake wetlands
Table1 Transformation of lake wetlands in 1995-2000 [km2] Period 1995-2000 2000-2005 2005-2010 Lake to other types of land use 165.59 34.42 108.54 Other types of land use to lake 520.68 477.59 243.40 From 1995 to 2010, the area of lake wetlands has been grown constantly. Between 1995 and 2000, the area increased is 355.09 km2; between 2000 and 2005 , it is 443.17 km2, and 134.86 km2 between 2005 and 2010. Lake wetlands increased most rapidly during the peroid from 2000 to 2005. Transitions from farmland and unused land to lake were dominant for the increase of lake area, while so were the transitions reversely. During the period of 1995-2000 and 2005-2010, transition from farmland to lake was dominant for the net increase of lake area. Transitions from farmland and unused land to lake both contributed to the net increase of lake area between 2000 and 2005.These phenomena reflect the effect of “reclainled farmland to lake”. Figure 1 shows that the increase of lake wetlands was remarkable in Honghu, Xiantao and Jianli. In the process that lake transformed into other types of land, lake wetlands mainly transformed to unused land and farmland. The period with a minimum amount of transfer was 2000 to 2005. In the process that other land types of land transformed into lake wetlands, the transfer showed a decreasing of transition rate and farmland is the main source for the increase of lake area, followed by unused land.
Figure 1 Spatial and temporal dynamic change of lake wetlands in Jianghan Plain Wang Chengcheng et al. / Procedia Environmental Sciences 10 ( 2011 ) 2574 – 2580 2577
Characteristics of the lake wetlands landscape pattern changes from 1995 to 2010.Table 2 shows that, during the period from 1995 to 2010, the total area of lake wetlands increased from 2374.45 to 3307.57 km2. The percentage of wetlands area accounted for 8.41, 9.67, 11.24 and 11.71% of the whole land in 1995, 2000, 2005 and 2010, respectively. This trend indicated that the landscape dominance degree of lake wetlands increased gradually. Table 2 The changes of the ratio of lake wetlands to total area[%] Year 1995 2000 2005 2010 Area[km2] 2374.45 2729.54 3172.71 3307.57 Percentage[%] 8.41 9.67 11.24 11.71 According to the size of the patch, lake wetlands can be divided into two categories: lake and pond. Define a patch as lake if its area is greater than or equal to 0.08 km2 and define a patch as pond if its area is smaller than 0.08 km2. The landscape fragmentation is analyzed from the two aspects, amount and area. Table 3 Patch number, area and percentage of lake wetlands in 1995-2010 Year 1995 2000 2005 2010 Lake Patch number 2303 2341 2564 2571 Area[km2] 2281.34 2635.29 3067.46 3200.27 Percentage of 0.0808 0.0931 0.1086 0.1133 landscape[%] Pond Patch number 1968 2033 2430 2427 Area[km2] 93.11 94.25 105.25 107.30 Percentage of 0.0033 0.0033 0.0037 0.0038 landscape[%] As shown in Table 3, during the period from 1995 to 2010, the area of the lake wetlands increased from 2281.34 km2 to 3200.27 km2. Accordingly, the ratio of lake wetlands to total area increased from 8.08% to 11.33%. At the same time, the area of pond wetlands increased from 93.11 km2 to 107.30 km2 and the ratio of pond wetlands to total area increased from 0.33% to 0.38%. The number of the lake wetlands patches and pond wetlands both increased gradually. The issue of the increasing number of lake wetlands is analyzed in two parts. One part is the fragmentation of lakes and the other part is the growing of ponds. The number of the pond wetlands increased gradually but the area changed little. Table 4 The fragmentation and separation indexes of lake wetlands Year 1995 2000 2005 2010 Average patch area 0.9906 1.1257 1.1964 1.2448 Lake Fragmentation 1.01 0.89 0.84 0.80 Separation 1.77 1.54 1.39 1.33 Average patch area 0.0473 0.0464 0.0433 0.0442 Pond Fragmentation 21.14 21.57 23.09 22.62 Separation 40.03 40.19 39.35 38.57 Table 4 shows that the average patch area of lake wetlands in Jianghan plain increased, which shows there were not fragmentated of lakes. And the average patch area of ponds in Jianghan plain reduced gradually, which shows that pond tended to fragmentize during the past 15 years. The landscape separation reduced from 1.76 to 1.33. The diminution of fragmentation and landscape separation indicates that the distribution of lake wetlands became more concentrated with the augment of 2578 Wang Chengcheng et al. / Procedia Environmental Sciences 10 ( 2011 ) 2574 – 2580
the area of lake wetlands. The landscape separation of pond wetlands decreased from 40.03 to 38.57. Fragmentation increased while separation decreased, which shows that the distribution of pond wetlands became less dispersed with the increasing number of pond wetlands. Table 5 The shape indexes of lake wetlands in 1995-2010 Year 1995 2000 2005 2010 Perimeter[km] 13255.76 13330.22 15076.94 15014.36 Average patch fractal 1.0745 1.0710 1.0694 1.0682 Lake dimension Average patch-shaped 1.7169 1.6741 1.6620 1.6505 index Perimeter[km] 1997.04 2025.45 2305.28 2327.52 Average patch fractal 1.03 1.03 1.02 1.03 Pond dimension Average patch-shaped 1.1801 1.2215 1.1991 1.1907 index During the period from 1995 to 2010, the perimeter of lake wetlands increased from 13255.76km to 15014.36km. The average patch-shaped index decreased from 1.7169 to 1.6505, which indicates that the shape of lake wetlands became simpler. This downward trend also reflects lake wetlands influenced more and more greatly by human activities. At the same time, the perimeter of lake wetlands increased from 1997.04km to2327.52km. The average patch-shaped index of pond wetlands increased at the beginning and then followed by decrease, and changed little on the whole. As shown in Table 5, the average patch fractal dimension of lake wetlands and pond wetlands are both close to 1; which means both lake wetlands and pond are simple in shape and deeply influenced by the disturbance of human activities. The average patch-shaped index and average patch fractal dimension of lake wetlands are bigger than those of pond wetlands; which indicates that lake wetlands are more complex in shape and less influenced by the disturbance of human activities. The separation of pond wetlands is bigger than lake wetlands, which means the distribution of pond wetlands is more dispersed than lake wetlands’. Lake wetlands dynamic change.Between 1995 and 2000, Bilateral dynamic change degree of lake wetlands is almost twice of its dynamic change degree (Table 6), and it means a obvious bilateral trend. In the study, we found that the transformation area between lake wetlands and unused land took about the same amount. 80.76 km2 of lake transformed to unused land, and 79.59 km2 of unused land transformed to lake wetlands . The huge flood in 1998 maybe the reason. From 2000 to 2005, the calculations of the two indices are similar. It shows that the transformation trends to be unidirectional. The main transformation type is other types of land transformed into lake wetlands. From 2005 to 2010, the bilateral change dynamic degree is 2.6 times of the mount of Single change dynamic degree of lake wetlands, which shows a obvious bilateral trend. The area of lake transformed to other types of land use was 108.54 km2 while the area of other land use types transformed to lake wetlands was 243.40km2.The net transformation area was little. Table 6 Change dynamic degree of lake wetlands [%] Peroid Dynamic change degree Bilateral dynamic change degree 1995-2000 2.99 5.78 2000-2005 3.25 3.75 2005-2010 0.85 2.22
Conclusions and discussions Wang Chengcheng et al. / Procedia Environmental Sciences 10 ( 2011 ) 2574 – 2580 2579
After the State Council put forward the “thirty-six-word policy” for harnessing large rivers and lakes in 1998, the situation of reduction in lake wetlands area in Jianghan Plain has been reversed and the wetland area has been grown constantly. The ratios of lake wetlands to total area in Jianghan Plain in 1995, 2000, 2005 and 2010 are 8.41%, 9.67%, 11.24% and 11.71% respectively. Transitions from farmland and unused land to lake were dominant for the increase of lake area, while so were the transitions reversely; Farmland is the main lake wetlands sources, which reflects the effect of “reclaimed farmland to lake”. According to the area of the patch, lake wetlands can be divided into two categories: lake and pond. Lake wetlands mainly increased in the area while pond wetlands mainly increased in the number of patches. Pond wetlands are simper in shape and its distribution is more dispersed than lake wetlands’. Between 1995 and 2010, the shape of lake wetlands became simpler and its distribution became more concentrated with the augment of the area of lake wetlands. The shape of pond wetlands changed little and its distribution became less dispersed with the increasing number of pond wetlands. Both lake and pond wetlands were deeply influenced by the disturbance of human activities.
Acknowledgement
This work was supportted by Central Authorities Universities Fundamental Research Subsidy of Huazhong Normal University (CCNU10A02001) and NSFC (40771088).
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