Spatiotemporal patterns and source attribution of nitrogen pollution in a typical headwater agricultural watershed in Southeastern China

Abstract

Excessive nitrogen (N) discharge from agriculture causes widespread problems in aquatic ecosystems. Knowledge of spatiotemporal patterns and source attribution of N pollution is critical for nutrient management programs but is poorly studied in headwaters with various small water bodies and mini-point pollution sources. Taking a typical small watershed in the low mountains of Southeastern China as an example, N pollution and source attribution were studied for a multipond system around a village using the Hydrological Simulation Program-Fortran (HSPF) model. The results exhibited distinctive spatio-seasonal variations with an overall seriousness rank for the three indicators: total nitrogen (TN) > nitrate/nitrite nitrogen (NO-N) > ammonia nitrogen (NH-N), according to the Chinese Surface Water Quality Standard. TN pollution was severe for the entire watershed, while NO-N pollution was significant for ponds and ditches far from the village, and the NH-N concentrations were acceptable except for the ponds near the village in summer. Although food and cash crop production accounted for the largest source of N loads, we discovered that mini-point pollution sources, including animal feeding operations, rural residential sewage, and waste, together contributed as high as 47% of the TN and NH-N loads in ponds and ditches. So, apart from eco-fertilizer programs and concentrated animal feeding operations, the importance of environmental awareness building for resource management is highlighted for small farmers in headwater agricultural watersheds. As a first attempt to incorporate multipond systems into the process-based modeling of nonpoint source (NPS) pollution, this work can inform other hydro-environmental studies on scattered and small water bodies. The results are also useful to water quality improvement for entire river basins.

Net Ecosystem Production of a River Relying on Hydrology, Hydrodynamics and Water Quality Monitoring Stations

“…It also proposes an integration of hydrologic and hydrodynamic models with water quality data which can also be implemented as an automated procedure to estimate NEP. Development, calibration and validation of a hydrologic model to represent a drainage area along a river within the spatiotemporal domain must consider phenomena such as infiltration, evaporation and streamflow [13][14][15]. The hydrologic model took account of information about land use and topography specifications to handle hydro-climatic conditions in order to determine streamflow [16].…”

Impacts of Landscapes on Water Quality in A Typical Headwater Catchment, Southeastern China

“…Therefore, keeping water resources clean and purifying the water for supply are the practicable ways [6,7]. Generally, among different kinds of water resources, headwater is widely used for drinking water supply and cropland irrigation [8][9][10]. As a result, the contaminated water sources are risks to public health [11,12].…”

“…As a result, the contaminated water sources are risks to public health [11,12]. Several factors can cause the degrading of water quality, both anthropogenic and natural [8,9]. The former one includes industrial activities (energy production, manufacturing, and transportation) [7], agricultural activities (fertilization, irrigation, and livestock and poultry farming) [8,9], medical pollution sources (microbial pathogen, virus, and poisonous substance) [13,14], and water conservancy projects (hydropower construction and water project operation) [15,16].…”

“…Several factors can cause the degrading of water quality, both anthropogenic and natural [8,9]. The former one includes industrial activities (energy production, manufacturing, and transportation) [7], agricultural activities (fertilization, irrigation, and livestock and poultry farming) [8,9], medical pollution sources (microbial pathogen, virus, and poisonous substance) [13,14], and water conservancy projects (hydropower construction and water project operation) [15,16]. The latter one includes meteorological factors (precipitation and temperature) [5,17,18], weather events (storm and arid) [19,20], and hydrogeological processes (soil erosion, hydrogeological hazard, and flooding) [21][22][23].…”

“…The perspective choosing remains to be the nonnegligible problem because landscape is a complex concept in a catchment [34,35]. Many researches tried to find out the relationship between landscape and water quality by calculating the impacting sensitivities of different land-use types [27,36,37], while some others focused on the effect of water bodies and the connections [9,38]. Both aspects have their shortcomings: from the aspects of land-use types only, the direct outlet of nonpoint pollutant cannot be found [28,30]; and from the water body configurations only, the main driving factors and activities have barely been studied [33].…”