3. Results and Discussion
Significant eco-environment changes have taken in the upstream of Yellow River from 1987 to 1996. Changes under major eco-environment systems over time and space are discussed separately.

3.1 Sandy desertification
The sandy desertified land has been increased and kept a stable developing situation in all overall statues. The results reveal that the sandy desertified lands account for 17.5 per cent of total study area, among which the very severe, severe, on-going and potential sand decertified lands are 10.9, 1.3, 10.3 and 49 per cent respectively (table 1). The sandy desertification is getting severe from 1987 to 1996 (figure 3). In nearly one decade the nearly desertification process has kept on intensifying in overall study area, although there are some reversed situation in parts of the area. The very severs sandy desertification land has quickly spread at an average rate of 21 km2 per year from 1987 to 1996.

Table 1 Sandy desertification land and its changes from 1987 to 1996.

Types of sandy desertification	Area of sandy desertified land (km2) in 1987	Area of sandy desertified land (km2) in 1996	Changes of area (km2)
Very severe	1058.2976	1247.4120	189.1144
Severe	181.3191	152.2160	-29.1031
On-going	1268.1072	1182.5772	-85.5300
Potential	5729.0555	5634.1824	-94.8431

The results reveal that the major factors responsible for such changes are overgrazing natural pastures and overexploitation of land resources. Other factors are frequent droughts, windily weather, sparse vegetation cove and a plentiful supply of sand. The excessive human activities play an important role in the changes of sandy desertification.

3.1 Land use
The structure of land use is unitary and unreasonable. The results reveal that the land use patterns mainly consist of animal husbandry and rainfed agriculture, which are mainly dependent on the primary productivity. The areas under grassland, non-irrigated land and sand occupied respectively 80%, 4.8% and 10.9% of total study area (table 2). The grasslands with high and middle percentage of cover have degenerated. The areas of them have declined by 5 per cent and 3.1 per cent respectively, while sand and non-irrigated lands have increased by 17.8 per cent and 51.8 per cent during last nine years.

Table 2 Land use and its changes from 1987 to 1996

Types of land use	Area in 1987 (km2)	Area in 1996 (km2)	Area changes(km2)
Water	207.3641	227.8636	20.4995
Exposed rock	19.1310	19.1717	0.0407
Sand	1058.5100	1247.4436	188.9336
Marshland	12.6667	15.5149	2.8482
Non-irrigated	362.1053	549.6757	187.5704
Irrigated land	193.3551	245.8826	52.5275
Grassland with low Percentage of cover	181.3020	152.0878	-29.2142
Grassland with middlePercentage of cover	2673.4481	2590.1826	-83.2655
Grassland with high Percentage of cover	6787.7367	6447.7965	-339.9402

The results reveal that increased human population pressure has brought not only overexploitation of land resources but also overgrazing of pastures. Additionally, agriculture and animal husbandry have taken traditional extensive management. As a consequence the land productivity has decreased, which resulted the grassland degeneration and sandy decertified land expansion.

3.2 Water erosion
The results reveal that the water erosion is one of the most serious eco-environment in this area. Although the areas of very severe and severe water erosion are relatively less (table 3), they are mainly distributed in the area around Longyanxia reservoir and on the banks of yellow river and its branches (figure 5). The serious water erosion not only declined the land productivity, but also transformed plenty of sediments to the reservoir and downstream of the Yellow River. The water erosion affects the regional eco-environment, but also endangers the security of Longyanxia reservoir.

Table 3 Water erosion area and its changes in 1996

Types of water erosion	Gentle	Slight	Moderate	Severe	Very severe
Area Km2	7951.8778	1741.0950	825.0537	721.3906	27.2887

4. Conclusions
The excessive human activities play an important role in degradation of eco-environment in the upstream of the Yellow River. At present the acceleration of grassland degradation is attributed to the irrational human economical activities. The sandy desertification as well as water erosion has intensified extremely, which affected the regional economical sustainable development and endangered the security of Longyanxia reservoir. So it is necessary and urgent to combat desertification and protect eco-environment in the upstream of the Yellow River.

The results show that fully using the remotely sensed data with GIS for detecting and assessing the eco-environment is one of the effective measures of quantitative research.

Acknowledgements
The research project is supported by the National Science Foundation of China Grants (No. 49561006). The authors are highly grateful to Pro.Feng Xuezhi, department of urban and resource, Nanjing University for this direction and encouragement.

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