Ecohydraulics model development and quantification of intertidal wetland
Date Issued
2005
Date
2005
Author(s)
Shih, Shang-Shu
DOI
zh-TW
Abstract
This study is to establish conceptual ecohydraulics model of intertidal wetland and quantify the characteristics of ecology and hydraulics. The Guandu Nature Reserve was taken as an example in this study. Besides, the fictitious case studies were also investigated and discussed which include density of invertebrate benthos, flooding impact, depositions of wetland and landscape index variations of waterbirds.
Six chapters were constructed and introduction of each chapter was described as follows:
Chp1: The 5-W hypothesis plot was represented to construct the main idea of this chapter. The operating matrix of nature, near-nature and manmade habitat was also brought up to concentrate on the topic and objective of this study. Meanwhile, some literature reviews were cited to support the point of issue and distinguish from the complicated problems in wetland.
Chp2: The theories of ecohydraulics model, including several modules, were constructed and discussed in this chapter. The flow chart and process of this study were also elaborated. The case study in chapter 5 could therefore persist as this chapter well-done.
Chp3: The investigations and collections of hydraulic characteristics, i.e. water surface elevation variations, flow velocity variations and water quality variations, were evaluated and discussed in this chapter. The results of this chapter were basis and foundation of case study in chapter 5.
Chp4: The investigations and collections of ecological characteristics, including landscape variations, benthos density variations, waterbird species variations, different flood surface elevation and sediment deposition variations, were calculated and discussed in this chapter. The results of this chapter were basis and foundation of case study in chapter 5.
Chp5: Several case studies were built up in this chapter to quantify some adverse effects after mangrove spread. Meanwhile, ecohydraulics model were calibrated and verified from different modules validation, i.e. hydraulic module, GIS module, multivariate statistical module, habitat module and assessment module. Moreover, mangrove removal effects were also evaluated in this chapter.
Chp6: Conclusions of above 5 chapters and some useful suggestions were also represented in further study.
Among above introductions of each chapter, several aerial photographs of 1986, 1997, 1998, 2001 and 2002 were differentiated and calculated in GIS module. The results reveal that the coverage area of Kandelia candel (L.) Druce mangrove increased from 7.2 hectare in 1986 to 23.8 hectare in 2002; coverage area of mudflat declined from 18.1 hectare in 1986 to 1.1 hectare in 2002 and coverage area of tidal creek declined from 6.9 hectare in 1986 to 4.2 hectare in 2002. It was thus concluded that the marsh habitats, dominated by Cyperus malaccensis Lam. and Phragmites communis (L.) Trin., have changed into a swamp habitat, dominated by Kandelia candel (L.) Druce.
The relationship between dimensionless density of invertebrate benthos (D’) and environmental factors affected the richness of benthos were analyzed and regressed in multivariate statistical module. Additionally, the environmental factors were investigated and found out as dissolved oxygen (DO), soil salinity (S), concentration of organic matter (TO), substrate size (D) and sieve coefficient (SC). The results show that different species of benthos was fond of different habitat types.
According to the habitat module analysis, the Shannon’s diversity index decreased from 0.98 in 1986 to 0.77 in 2002; the Shannon’s evenness index decreased from 0.77 in 1986 to 0.56 in 2002, and the dominant index increased from 0.41 in 1986 to 0.62 in 2002. It was therefore concluded that the landscape type became monotonous year by year. Furthermore, the preference habitat area of Family Charadriidae and Family Scolopacidae which were original dominant species in this wetland declined from 18.1 hectare in 1986 to 1.1 hectare.
Four cases with different removal ratios were investigated in hydraulic module and was found that the water surface elevation decreases as the removal ratio increases. When the removal ratio of Kandelia candel (L.) Druce reaches 20%, the variations of the water surface elevation in the wetland became insignificant. Significant sediment deposition occurs due to the extensive root network of Kandelia candel (L.) Druce. The average deposition is about 33 mm during a 200 years return period flood event. Removal of Kandelia candel (L.) Druce is able to reduce the sediment deposition rate. When the removal ratio reaches 20%, the reduction in sediment deposition is about 5 mm. Considering the factors of flood protection and sediment deposition, the optimal removal ratio is between 10% and 20%. It is also found that mangrove remove will improve the ecological restoration of Uca (Thalassuca) Formosensis Rathbun which is an endemic species of the fiddler crab in Taiwan.
Subjects
潮間帶濕地
生態水利模式
水筆仔紅樹林
底棲無脊椎動物
景觀類型指數
紅樹林疏伐
生態復育
Intertidal wetland
ecohydraulics model
Kandelia candel (L.) Druce mangrove
benthos
Geographic Information System (GIS)
landscape type index
mangrove removal
ecological restoration
SDGs
Type
thesis
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