Impact of land use changes on water quality in headwaters of the Three Gorges Reservoir

Abstract

The assessment of spatial and temporal variation of water quality influenced by land use is necessary to manage the environment sustainably in basin scales. Understanding the correlations between land use and different formats of nonpoint source nutrients pollutants is a priority in order to assess pollutants loading and predicting the impact on surface water quality. Forest, upland, paddy field, and pasture are the dominant land use in the study area, and their land use pattern status has direct connection with nonpoint source (NPS) pollutant loading. In this study, two land use scenarios (1995 and 2010) were used to evaluate the impact of land use changes on NPS pollutants loading in basins upstream of Three Gorges Reservoir (TGR), using a calibrated and validated version of the soil and water assessment tool (SWAT) model. The Pengxi River is one of the largest tributaries of the Yangtze River upstream of the TGR, and the study area included the basins of the Dong and Puli Rivers, two major tributaries of the Pengxi River. The results indicated that the calibrated SWAT model could successfully reproduce the loading of NPS pollutants in the basins of the Dong and Puli Rivers. During the 16-year study period, the land use changed markedly with obvious increase of water body and construction. Average distance was used to measure relative distribution patterns of land use types to basin outlets. Forest was mainly distributed in upstream areas whereas other land use types, in particular, water bodies and construction areas were mainly distributed in downstream areas. The precipitation showed a non-significant influence on NPS pollutants loading; to the contrary, interaction between precipitation and land use were significant sources of variation. The different types of land use change were sensitive to NPS pollutants as well as land use pattern. The influence of background value of soil nutrient on NPS pollutants loading was evaluated in upland and paddy field. It was found that total nitrogen (TN) and total phosphorous (TP) in upland were more sensitive to NPS pollutants loading than in paddy fields. The results of this study have implications for management of the TGR to reduce the loading of NPS pollutants into downstream water bodies.

Water quality issues and management of large rivers

“…The results show an influence on fish species. Yang et al (2016) focus on the water quality changes correlated to changes in land use patterns of the Three Gorges Reservoir in China. A priority was connecting nonpoint source nutrient pollutants to the main land use categories forest, upland, paddy field, and pasture over a study period of 16 years.…”

Forest cover and water quality in tropical agricultural watersheds

“…Low-order streams, often located on steeper slopes, are more sensitive to nonpoint source pollutants loading than flat areas in the watershed (Yang et al, 2016;Yu et al, 2016). Then, the environmental planning of these areas is crucial to ensure water with high quality downstream.…”

“…For example, the riparian forest can reduce nitrates, phosphorus, and sediment loading into the river (Krutz et al, 2005; and it can also influence the energy balance . Replacing riparian forest by other land-cover types leads to a decrease in water quality due to the bank erosion, consequently increasing nutrient and sediment loads into the river Yang et al, 2016).…”

“…Although the riparian forest can contribute to the water quality protection, it is one of the most degraded ecosystems in the world (Nilsson and Berggren, 2000;Kuglerova et al, 2014). Replacing riparian forest by other land uses decreases water quality due to bank erosion, increasing nutrient and sediment loads into the river Yang et al, 2016a). Therefore, land use change in riparian zones is one of the most significant threats to water quality in stream ecosystems, bringing the importance of understanding the benefits from their restoration Yang et al, 2016b).…”

“…The vegetation provides protection against erosion, retention of pollutants, excessive nutrients runoff and increased water temperature (Sopper, 1975;Sweeney et al, 2004;Lima and Zakia, 2006; and benefits both the quality of human life and survival of aquatic species Yang et al, 2016a;. Especially in the currently context in that agriculture and urban growth have been appointed as the primary cause of water quality degradation Lin et al, 2015;.…”