Variations in source apportionments of nutrient load among seasons and hydrological years in a semi-arid watershed: GWLF model results

Abstract

Quantifying source apportionments of nutrient load and their variations among seasons and hydrological years can provide useful information for watershed nutrient load reduction programs. There are large seasonal and inter-annual variations in nutrient loads and their sources in semi-arid watersheds that have a monsoon climate. The Generalized Watershed Loading Function model was used to simulate monthly nutrient loads from 2004 to 2011 in the Liu River watershed, Northern China. Model results were used to investigate nutrient load contributions from different sources, temporal variations of source apportionments and the differences in the behavior of total nitrogen (TN) and total phosphorus (TP). Examination of source apportionments for different seasons showed that point sources were the main source of TN and TP in the non-flood season, whereas contributions from diffuse sources, such as rural runoff, soil erosion, and urban areas, were much higher in the flood season. Furthermore, results for three typical hydrological years showed that the contribution ratios of nutrient loads from point sources increased as streamflow decreased, while contribution ratios from rural runoff and urban area increased as streamflow increased. Further, there were significant differences between TN and TP sources on different time scales. Our findings suggest that priority actions and management measures should be changed for different time periods and hydrological conditions, and that different strategies should be used to reduce loads of nitrogen and phosphorus effectively.

A lagged variable model for characterizing temporally dynamic export of legacy anthropogenic nitrogen from watersheds to rivers

“…The agreement for annual TN fluxes between those estimated by LOADEST and those modeled by Eq. (6) was evaluated using correlation (R 2 ) and Nash-Sutcliffe coefficient metrics (Moriasi et al 2007;Du et al 2014). …”

“…Anthropogenic activities have substantially increased nitrogen (N) availability in many terrestrial ecosystems to an extent that exceeds the ability to assimilate N, often resulting in large increases in riverine N fluxes to coastal waters (Bouraoui and Grizzetti 2014;Du et al 2014). Various management efforts have been implemented to control excessive N in riverine ecosystems, as it degrades aquatic ecosystem health, decreases water quality for several beneficial uses, and causes eutrophication and hypoxia in downstream freshwater and coastal waters (Sun et al 2013;Li et al 2014).…”

“…Various lumped watershed models (e.g., export coefficient models, SPARROW, and PolFlow) and mechanistic models (e.g., AGNPS, HSPF, and SWAT) (De Wit et al 2003;Moriasi et al 2007;Li et al 2014;Du et al 2014), as well as N budgeting approaches such as net anthropogenic nitrogen inputs (NANI) (Han et al 2011;Hong et al 2012;Howarth et al 2012), are available for quantifying the impact of anthropogenic N inputs on riverine N fluxes. However, the calibration procedures for these models contain considerable uncertainty since measured riverine N fluxes are a mixture of N and water sources with different ages and the lag time is often larger than the temporal extent of available calibration data (Meals et al 2010;Bouraoui and Grizzetti 2014).…”

Estimating internal P loading in a deep water reservoir of northern China using three different methods

“…The areas in Northern China are faced with serious water shortage (Du et al 2014). Hence, it is extremely important to keep water quality clean and safe in Northern China.…”

The potential impact of an inter-basin water transfer project on nutrients (nitrogen and phosphorous) and chlorophyll a of the receiving water system

“…In 2002, China launched the SNWTP to alleviate water shortage problems in northern China (Du et al, 2014;Liu and Zheng, 2002). The primary channel of the middle route of the SNWTP has a total length of 1267 km, and the average amount of water transferred per year can reach 14.14 billion cubic meters.…”