2. Materials and Methods
2.1. Study Area
2.2. Data Description
- MODIS NDVI time-series products: the monthly composite MODIS 250 m normalized difference vegetation index (NDVI) dataset spanning five growing seasons (January 2003 to December 2007) were created for the research area.
- Field monitoring data: field data were obtained from Changzhou Conservancy Bureau, listing parameters describing monthly water conditions such as total phosphorous (TP), total nitrogen (TN) and chemical oxygen demand (COD) concentrations (January, 2007 to August, 2009).
- Land use map: land use data for 2005 were obtained from the land use survey database, at the scale of 1:10000.
- Hydrological network map: the distribution map of primary and secondary river channels was obtained from the hydrological network map of the whole of Changzhou city.
- DEM data: elevation data and slope data were provided by ISDSP (International Scientific Data Service Platform) with the spatial resolution of 30 m (2009).
- Statistical data: Statistical Yearbooks of Wujin District from 2000 to 2008 were obtained in which population and economic data were included.
- Auxiliary data: other data collected included the local Water Conservancy Construction Report in the National Eleventh Five-Year Plan (2005 to 2020), the local Social and Development Planning Report (2005–2020), agricultural and aquatic development planning reports and so on.
2.3. Selection of Indicators
2.4. Normalized Difference Vegetation Index Extraction
2.5. Integrated Assessment
3. Results and Discussions
3.1. NDVI Extraction and Analysis
3.2. Integrated Assessment of Aquatic Ecological Carrying Capacity
- Social, economic and ecological context was explicitly investigated in our case, formulating the background for the identification of indicators and the establishment of indicator hierarchy.
- The spatial and temporal variation of NDVI was carried out and the extension of vegetation cover into Ge Lake was observed, which should be paid more attention by local authorities.
- Ecological resilience assessment was made with the integrated consideration of aquatic and terrestrial ecosystems, in which RS and GIS technologies were of great assistance in obtaining the final result.
- Vegetation cover has increased in central and eastern parts of Wujin District in the past few years, which could be observed in NDVI products. However, the phenomena of cyanobacteria bloom and the decreasing of water area make it imperative to reduce agricultural activities around Ge Lake, since it will impair the aquatic ecological balance and aggravate water eutrophication.
- Concentrations of COD, TN and TP were considerably higher than the national standards for pollutant emission; thus water eutrophication was still diagnosed as the main problem in Wujin District. As a result, it is suggested that pollutant emission reduction should be strengthened, especially for industrial waste water discharge and agricultural activities.
- In the long run, aquatic ecological carrying capacity has increased slightly, which reveals that government planning on land use, economic growth, population growth and technological levels was able to improve water management and could be reasonably conducted.
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|GDP per capita||104 yuan per capita||<2||2–2.5||2.5–3.75||3.75–5||>5|
|Agricultural water use per cultivated land||106 m3/ha||<30 or >142||30–60 or 112–142||60–69 or 103–112||69–73 or 99–103||73–99|
|Industrial water use per industrial added value||m3/104 yuan||>100||56–100||45–56||31–45||<31|
|Fertilizer application per cultivated land||kg/ha||>1200||600–1200||525–600||300–525||<300|
|Industrial waste water per GDP||m3/104 yuan||>25||13–25||10–13||7–10||<7|
|Concentration of TP||mg/L||0.9–1.3||0.2–0.9||0.05–0.2||0.01–0.05||0.001–0.01|
|Concentration of TN||mg/L||9–16||2–9||0.5–2||0.1–0.5||0.02–0.1|
|Concentration of COD||mg/L||40–60||10–40||4–10||1–4||0.15–1|
|Aquatic biological Shannon diversity||/||<1||1–1.8||1.8–2.5||2.5–3.5||>3.5|
|Shannon diversity of landscape||/||<0.5||0.5–1.25||1.25–1.75||1.75–2.25||>2.25|
|(AECC) Aquatic ecological carrying capacity||The threshold of aquatic ecological carrying capacity assessment was 0.6 and scores above it mean the ecosystem is capable of bearing the human activities.|
|Industrial added value||104 yuan||1,260,405||2,477,723||5,556,690|
|Cultivated land area||ha||78,457||48,629||39,975|
|Irrigation water use||106 m3||632.16||359.52||280.42|
|Industrial water use||106 m3||127||136.79||150.52|
|Fertilizer application||106 kg||112.84||67.48||45.56|
|Industrial wastewater discharge||106 t||39.75||87.87||88.5|
|January 2007||April 2007||July 2007||January 2008||May 2008||July 2008||May 2009||August 2009|
|Water eutrophication (pollutants concentration)||TP||0.35 mg/L||Water eutrophication condition is assessed by the sum of the evenly weighted three pollutants evaluated values|
|Drainage density (DD)||2.37 km/km2||DD = Length/catchment area|
|NDVI||1.55||Mean value of the research area|
|Elevation||5.59 m||Mean value of the research area|
|Slope||1.102 degree||Mean value of the research area|
|Aquatic biological diversity (Shannon diversity index of plankton community)||Algae||2.93||Aquatic biological diversity is assessed by the sum of the three evenly weighted evaluated Shannon index of planktons|
|Shannon diversity of landscape (SHDI)||2.18||It is calculated according to Land Use Classification System (2001 version) in China|
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