[Response of Inflow Water Quality to Land Use Pattern in Northern Watershed of Lake Erhai].

The inherent relationship between land use pattern and inflow water quality is essential for nonpoint source pollution study. Response of inflow river quality to land use pattern in Northern part of Lake Erhai Watershed was analyzed in aspects of land use composition and configuration using spatial analysis and statistical analysis methods. The results indicated that as land use composition indexes, average slope and vegetation area percentage had significant relationship with TN and TP of inflow rivers. As land use configuration indexes, patch density, patch density of agriculture land and landscape shape index of water had significant relationship with TP and NH4+-N of inflow rivers. Response of inflow river quality to land use pattern was better at class level than at landscape level. Water quality response indicators were TP in rainy season and NH4+-N in dry season, of which regression adjustment coefficient R2 was 0.761 and 0.978, respectively. Response of inflow river quality to land use pattern was better in dry season than in rainy season, and the water quality response indicators were TN, TP and NH4+-N. Improving vegetation coverage and agriculture land intensive degree and avoiding human disturb to natural water area especially in dry season were suggested in nonpoint source pollution control of northern watershed of Lake Erhai Watershed. Later research on relationship between land use configuration and inflow river quality should better be at class level.

[Relationship Between Agricultural Land and Water Quality of Inflow River in Erhai Lake Basin].

We studied the relationship between agricultural land and water quality of inflow river in Erhai Lake Basin, by means of spatial and statistical analysis, from the perspective of comprehensive agricultural land and the area percentage of different types of agricultural land. The obtained results indicated that inflow water quality showed a significant spatial difference, the inflow TP pollution in the western inflow rivers of Erhai Basin was serious. The major pollution indicators in the northern and southern inflow rivers (except for D3) were organic matter and nitrogen. The area percentage of agricultural land had a significantly indicative effect on the water quality of inflow river. The area percentage of comprehensive agricultural land negatively correlated with permanganate index, NH4(+) -N, TN and TP contents in wet season, the correlation coefficients were - 0.859, - 0.565, - 0.693, - 0.181. It negatively correlated with permanganate index and NH4(+) -N content in dry season, the correlation coefficients were - 0.384, - 0.328. It had positive relationships with and TN, TP content in dry season, the correlation coefficients were 0.221 and 0.146. The area percentage of different types of agricultural land had an obviously indicative effect on the inflow water quality. Farmland positively correlated with TN and TP contents both in wet and dry seasons. The correlation coefficients between farmland and TN, TP were 0.252, 0.581 in rainy season and were 0.149, 0.511 in dry season. It had positive and negative relationships with permanganate index, NH4(+) -N content in wet season and dry season, respectively. The correlation coefficients between farmland and permanganate index, NH4(+) -N were 0.388, 0.053 in rainy season and were -0.137, -0.147 in dry season. Forest land exhibited an opposite performance to that of farmland. The correlation coefficients between forest land and TN, TP, permanganate index, NH4(+) -N were - 0.526, - 0.275, - 0.469, -0.155 in rainy season and were -0.012, -0.100, 0.282, 0.151 in dry season. Fishpond had a weakly indicative effect on TN and TP contents. Meadowland and orchard had a similar performance with that of farmland in wet season, but were opposite to that of farmland in dry season. Therefore, management for farmland, meadowland and orchard in the north and south during wet season should be emphasized during the agricultural nonpoint source control in Erhai Lake Basin.