Multi-scale relationship between land use/land cover types and water quality in different pollution source areas in Fuxian Lake Basin.

Shihua Li,Shuangyun Peng,Yingxin Li,Junsong Zhou,Baoxuan Jin

doi:10.7717/peerj.7283

Abstract

The spatial-temporal evolution of land use and land cover (LULC) and its multi-scale impact on the water environment is becoming highly significant in the LULC research field. The current research results show that the more significant scale impact on LULC and water quality in the whole basin and the riparian buffer scale is unclear. A consensus has not been reached about the optimal spatial scale problem in the relationship between the LULC and water quality. The typical lake basin of the Fuxian Lake watershed was used as the research area and the scale relationship between the LULC and water quality was taken as the research object. High resolution remote sensing images, archival resources of surveying, mapping and geographic information, and the monitoring data of water quality were utilized as the main data sources. Remote sensing and Geometric Information Technology were applied. A multi-scale object random forest algorithm (MSORF) was used to raise the classification accuracy of the high resolution remote sensing images from 2005 to 2017 in the basin and the multi-scale relationship between the two was discussed using the Pearson correlation analysis method. From 2005 to 2017, the water quality indicators (Chemical Oxygen Demand (COD), Total Phosphorous (TP), Total Nitrogen (TN)) of nine rivers in the lake’s basin and the Fuxian Lake center were used as response variables and the LULC type in the basin was interpreted as the explanation variable. The stepwise selection method was used to establish a relationship model for the water quality of the water entering the lake and the significance of the LULC type was established at p < 0.05.The results show that in the seven spatial scales, including the whole watershed, sub-basin, and the riparian buffer zone (100 m, 300 m, 500 m, 700 m, and 1,000 m): (1) whether it is in the whole basin or buffer zone of different pollution source areas, impervious surface area (ISA), or other land and is positively correlated with the water quality and promotes it; (2) forestry and grass cover is another important factor and is negatively correlated with water quality; (3) cropping land is not a major factor explaining the decline in water quality; (4) the 300 m buffer zone of the river is the strongest spatial scale for the LULC type to affect the Chemical Oxygen Demand (COD). Reasonable planning for the proportion of land types in the riparian zone and control over the development of urban land in the river basin is necessary for the improvement of the urban river water quality. Some studies have found that the relationship between LULC and water quality in the 100 m buffer zone is more significant than the whole basin scale. While our study is consistent with the results of research conducted by relevant scholars in Aibi Lake in Xinjiang, and Erhai and Fuxian Lakes in Yunnan. Thus, it may be inferred that for the plateau lake basin, the 300 m riparian buffer is the strongest spatial scale for the LULC type to affect COD.

Highlights

With the rapid development of the global society and economy, greater attention has been paid by the international academic community to research the effects that land use and land cover (LULC) has on the water environment by Johnson et al (1997), Meneses et al (2015), Sajikumar & Remya (2015), Zhou et al (2016)
The research on LULC type and water quality focuses on the response of water quality indicators such as TN (Total Nitrogen), Total Phosphorus (TP) (Total Phosphorous), pH, CODMn (Chemical Oxygen Demand-Mn), TSS (Total Soluble Solid), BOD5 (Biochemical Oxygen Demand, BOD), DO (Dissolved Oxygen), etc. to LULC changes from land use, land use structures, and land use patterns and has reached a consensus
The present study addresses the following research questions: (1) What land use category has the strongest effect on water quality? (2) How do spatial and temporal variations in LULC within and across watersheds influence water quality metrics in the Lake Fuxian watershed? (3) At what spatial scale does the LULC type act to influence water quality? (4) How the multi-scale relationship between land use types and water quality indicators can be used to balance relationship between land use and water protection?

Summary

Introduction

With the rapid development of the global society and economy, greater attention has been paid by the international academic community to research the effects that LULC has on the water environment by Johnson et al (1997), Meneses et al (2015), Sajikumar & Remya (2015), Zhou et al (2016). Due to the multi-scale and distribution pattern of land use (Tu, 2011; Zhou et al, 2012), there is a significant scale correlation between LULC changes and water quality indicators, which leads to uncertainty about the relationship between land use patterns and river water quality. The optimal or strongest spatial scale problem of the relationship between land use and water quality has not reached a unanimous conclusion (Johnson et al, 1997; Sliva & Williams, 2001; Shen et al, 2015; Ding et al, 2016)

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Results

Discussion

Conclusion