Assessment of the Spatiotemporal Effects of Land Use Changes on Runoff and Nitrate Loads in the Talar River

Abstract

This research surveyed the effects of land use changes on flow nitrate pollution in the Talar River (northern Iran), using Landsat images of 1991 and 2013 and the Soil and Water Assessment Tool (SWAT). The results indicated that forest areas decreased by 14.9% and irrigated crops, dry land farming areas, range lands and residential areas increased by 46.8%, 31.1%, 4.7% and 17.5%, respectively. To calibrate and validate the studied period, the Nash Sutcliffe model efficiency (NSE) and coefficient of determination (R 2 ) were applied, ranging from 0.57 to 0.75 and from 0.62 to 0.76 for flow simulation and 0.84 and 0.63 and 0.75 and 0.83 for nitrate simulation, respectively. The results of land use scenarios indicated that respective water flow and nitrate loads increased by 34. 4% and 42.2% in 1991-2013 and may even increase by 42.3% and 55.9% in the simulated period of 2013-2050 in all sub-basins. It is likely that the main reason for these results was due to the increase in agricultural activities and the decrease in forestry areas. Our findings showed the useful combination of modelling techniques (land cover changes and SWAT) to develop valuable maps able to design correct land management plans and nature-based solutions for water quality of runoff water harvesting systems in the future.

Climate Change Impact on Flood Frequency and Source Area in Northern Iran under CMIP5 Scenarios

“…Talar River Basin is located in the mountainous region of the Mazandaran Province in northern Iran close to the Caspian Sea and covering an area of 1727 km 2 [27,28]. The basin constitutes one of the subbasins of Haraz and Gharasou watersheds located between 52 • 35 to 53 • 25 East and 35 • 45 to 36 • 20 North [29] (Figure 1).…”

“…where SW t and SW 0 are the final and initial soil water content for day i, respectively, R day is rainfall that reaches soil surface, Q surf is surface runoff, E a is evapotranspiration, w seep is interflow, and Q gw is base flow [47]. It is noted that the ability of this model to generate discharge at a monthly time step for the studied basin has been tested by Kavian et al [27].…”

“…A Digital Elevation Model (DEM) of the Talar River Basin with 30 m resolution was used to generate slope data ( Figure 2). The soil map was obtained from the Forest, Rangeland, and Watershed Management Organization (FRWO) of Iran [27]. To generate the land use map, Landsat 8 images (Operational Land Imager; OLI) covering the study area were used.…”

“…Finally, eight types of land use were detected ( Figure 2) and fed into the land use look-up table in the SWAT model. In addition, 58 types of soils with different physical and chemical properties were used [27]. Daily rainfall data from 14 stations and maximum and minimum temperature data from 7 stations for the studied basin were collected from the Iranian Meteorological Organization (IMO) and the Iran Water Resources Management Company (IWRMC).…”

Long-Term Water Quality Patterns of a Flow Regulated Tropical Lowland River

“…Such data sets also indicate long-term changes in catchment responses and may contain evidence of rare events (e.g., severe droughts or floods) or rapid shifts in the system's behaviour [43][44][45]. Globally, studies have made use of long-term data in order to assess changes in river water quality including nitrate fluxes [46], hydrology [38], the effects of agriculture [47], the impact of reservoir construction on downstream flow regime [9] and the effects of land use changes [48]. In addition, the use of multivariate approaches and water quality indices, such as the Physicochemical Driver Assessment Index (PAI), allows for the interpretation of complex data sets in order to better understand the quality and ecological status of a studied ecosystem [3].…”