Examining the Relationships between Watershed Urban Land Use and Stream Water Quality Using Linear and Generalized Additive Models

Abstract

Abstract:Although close relationships between the water quality of streams and the types of land use within their watersheds have been well-documented in previous studies, many aspects of these relationships remain unclear. We examined the relationships between urban land use and water quality using data collected from 527 sample points in five major rivers in Korea-the Han, Geum, Nakdong, Younsan, and Seomjin Rivers. Water quality data were derived from samples collected and analyzed under the guidelines of the Korean National Aquatic Ecological Monitoring Program, and land use was quantified using products provided by the Korean Ministry of the Environment, which were used to create a Geographic Information System. Linear models (LMs) and generalized additive models were developed to describe the relationships between urban land use and stream water quality, including biological oxygen demand (BOD), total nitrogen (TN), and total phosphorous (TP). A comparison between LMs and non-linear models (in terms of R 2 and Akaike's information criterion values) indicated that the general additive models had a better fit and suggested a non-linear relationship between urban land use and water quality. Non-linear models for BOD, TN, and TP showed that each parameter had a similar relationship with urban land use, which had two breakpoints. The non-linear models suggested that the relationships between urban land use and water quality could be categorized into three regions, based on the proportion of urban land use. In moderate urban land use conditions, negative impacts of urban land use on water quality were observed, which confirmed the findings of previous studies. However, the relationships were different in very low urbanization or very high urbanization conditions. Our results could be used to develop strategies for more efficient stream restoration and management, which would enhance water quality based on the degree of urbanization in watersheds. In particular, land use management for enhancing stream water quality might be more effective when urban land use is in the range of 1.1%-31.5% of a watershed. If urban land use exceeds 31.5% in a watershed, a more comprehensive approach would be required because water quality would not respond as rapidly as expected.

Complex Relationships of the Effects of Topographic Characteristics and Susceptible Tree Cover on Burn Severity

“…An interesting feature of GAM is that it allows determination of the shape of the response curves from the data instead of fitting an a priori parametric model, making it data-driven instead of model driven [57]. GAMs have been widely applied to investigate nonlinear relationships between dependent and non-explanatory variables in various fields of study such as plant and aquatic ecology (e.g., [58]) and water quality (e.g., [59]), as well as for nonlinear relationships among biotic and bon-biotic variables in environmental settings due to complex interactions between environmental factors. Many studies have identified nonlinear relationships among components of forest ecosystems (e.g., [3,50,[60][61][62][63][64][65]).…”

“…In general, models with higher R 2 values explain the variance of the explanatory variables better than models with lower R 2 values. Similarly, the AIC represents the relative likelihood of delineating the true nature of the relationships among variables and smaller AIC values represent a higher likelihood of explaining the nature of the data than other models with higher AIC values; therefore, larger AIC values for models are associated with a lower probability [59]. Despite its usefulness and widespread use, AIC has been criticized for its tendency to select overly complex models [68].…”

Water Quality Index for Determining the Development Threshold of Urbanized Catchment Area in Indonesia

“…Although the results are still debatable, due to limited data, the relational equation between IC and WQI for an individual pond is tested to estimate the threshold of development on the catchment area, considering the findings of Hwang et al (2016). Based on their investigation at 527 sampling sites on five major river systems in Korea, Hwang states that the linear relationships only confirmed the findings of previous studies in moderate land use conditions with 1.131.5% urban land use.…”

Ecological Monitoring, Assessment, and Management in Freshwater Systems

“…Hwang et al [21] examined the relationships between urban land use and water quality in Korea. They analysed the data derived from NAEMP by using linear and generalised additive models.…”