Abstract
Soil erosion remains a major threat to sustainable agricultural production and environment. More recent studies have highlighted the role of soil erosion in soil, water and environmental degradation. Many authors, in their research efforts, identified fertilizers and other agricultural inputs as the major driving forces of water quality impairment. Although, this assertion is true when efforts are not enough to curtail the chief driving force “erosion” itself. The efforts to link soil erosion as the main driving force to water pollution rather than fertilizers overuse is still debatable. Although, models are less expensive and produce more rapid estimates, but they rely on measured data to provide confidence in predictions. This paper therefore synthesizes the most recent available knowledge and data on major players of non-point source pollution. This effort will spur a site-specific research in various scientific communities to address the sources, mechanisms and pathways of agricultural non-point source pollution and prioritize the knowledge gaps.

Keywords
Soil erosion; agricultural diffuse pollution; pollution sources; agricultural inputs

Cite this paper
Are K. S., Identifying the sources of non-point source pollution: Research progress and emerging challenges – A review , SCIREA Journal of Environment. Volume 3, Issue 4, August 2019 | PP. 94-110.

References

[ 1 ]	Are, K.S., Oshunsanya, S.O. & Oluwatosin, G.A., 2018. Changes 500 in soil physical health indicators of an eroded land as influenced by integrated use of narrow grass strips and mulch. Soil Till. Res. 184: 269-280
[ 2 ]	Aquilina, L., Vergnaud‐Ayraud, V., Labasque, T., Bour, O., Molénat, J., Ruiz, L., de Montety, V., De Ridder, J., Roques, C. & Longuevergne, L., 2012. Nitrate dynamics in agricultural catchments deduced from groundwater dating and long‐term nitrate monitoring in surface‐ and groundwaters. Sci. Total Environ. 435: 167–178.
[ 3 ]	Berhe A.A., Harden J.W., Torn M.S. & Harte J. 2008. Linking soil organic matter dynamics and erosion-induced terrestrial carbon sequestration at different landform positions. J. Geophys. Res. 113:G04039
[ 4 ]	Berhe, A.A., Barnes, R.T., Six, J. & Marin-Spiotta, E., 2018. Role of Soil Erosion in Biogeochemical Cycling of Essential Elements: Carbon, Nitrogen, and Phosphorus. Annu. Rev. Earth Planet. Sci. 46:521–48.
[ 5 ]	Bhattacharya, R., Praksh, V., Kundu, S. & Gupta, H. S., 2006. Effect of tillage and crop rotations on pore size distribution and soil hydraulic conductivity in sandy clay loam soil of the Indian Himalayas. Soil and Tillage Research 86: 129 – 140.
[ 6 ]	Borrelli, P., Robinson, D. A., Fleischer, L. R., Lugato, E., Ballabio, C., Alewell, C., Meusburger, K., Modugno, S., Schütt, B., Ferro, V., Bagarello, V., Van Oost, K., Montanarella, L. & Panagos, P., 2017. An assessment of the global impact of 21st century land use change on soil erosion. Nature Communications, 8, https://doi.org/10.1038 /s41467-017-02142-7
[ 7 ]	Chadwick, D., Wei, J., Yan’an, T., Guanghui, Y., Qirong, S. & Qing, C., 2015. Improving manure nutrient management towards sustainable agricultural intensification in China. Agric. Ecosyst. Environ. 209, 34–46.
[ 8 ]	Chen, W., He, B., Nover, D., Duan, W., Luo, C., Zhao, K., Chen, W. 2017. Spatiotemporal patterns and source attribution of nitrogen pollution in a typical headwater agricultural watershed in southeastern China. Environ Sci Pollut. Res. 25(3):2756–2773.
[ 9 ]	Cheng, X., Chen, L., Sun, R., Jing, Y. 2018. An improved export coefficient model to estimate non-point source phosphorus pollution risks under complex precipitation and terrain conditions. Environ Sci Pollut Res. 25: 20946–20955.
[ 10 ]	Cruzeiro C, Pardal MÂ, Rocha E, Rocha MJ (2015) Occurrence andseasonal loads of pesticides in surface water and suspended partic-ulate matter from a wetland of worldwide interest—the Ria FormosaLagoon, Portugal. Environ Monit Assess 187(11):669.
[ 11 ]	Erisman, J.W., Galloway, J.N., Seitzinger, S., Bleeker, A., Dise, N.B., Petrescu, A.M.R. 2013 Consequences of human modification of the global nitrogen cycle. Philos Trans R Soc Lond. Ser. B. Biol. Sci., 368:20130116
[ 12 ]	Fournier, M., Echeverría-Sáenz, S., Mena, F., Arias-Andrés, M., De la Cruz, E., Ruepert, C. 2017. Risk assessment of agriculture impact on the Frío River watershed and Caño Negro Ramsar wetland, Costa Rica. Environ Sci Pollut Res. 25:13347–13359.
[ 13 ]	Hillel, D. 2004. Introduction to Environmental Soil Physics. Elsevier Academic Press, Amsterdam, Netherlands.
[ 14 ]	Hou, Y., Wei, S., Ma, W., Roelcke, M., Nieder, R., Shi, S., Wu, J., Zhang, F. 2018. Changes in nitrogen and phosphorus flows and losses in agricultural systems of three megacities of China, 1990–2014. Resources, Conservation & Recycling 139: 64–75.
[ 15 ]	Jenny H, Gessel SP, Bingham FT. 1949. Comparative study of decomposition rates of organic matter in temperate and tropical regions. Soil Sci. 68:419–432
[ 16 ]	Kalcic, M., Crumpton, W., Liu, X., D’Ambrosio, J., Ward, A., Witter J. 2018. Assessment of beyond-the-field nutrient management practices for agricultural crop systems with subsurface drainage. Journal of Soil and Water Conservation 73(1): 62 – 74.
[ 17 ]	Kourakos, G., Klein, F., Cortis, A., Harter, T. (2012). A groundwater nonpoint source pollution modeling framework to evaluate long‐term dynamics of pollutant exceedance probabilities in wells and other discharge locations. Water Resources Research, 48, W00L13, doi:10.1029/2011WR010813.
[ 18 ]	Kumwimba, M.N., Meng, F., Iseyemi, O., Moore, M.T., Bo, Z., Tao, W., Liang, T.J., Ilunga, L. 2018. Removal of non-point source pollutants from domestic sewage and agricultural runoff by vegetated drainage ditches (VDDs): Design, mechanism, management strategies, and future directions. Sci. Total Environ. 639: 742–759.
[ 19 ]	Li, Y., Quine, T.A.A., Yu, H.Q.Q., Govers, G., Six, J., Gong, D.Z.Z., Wang, Z., Zhang, Y.Z.Z., Van Oost, K. 2015. Sustained high magnitude erosional forcing generates an organic carbon sink: test and implications in the Loess Plateau, China. Earth Planet. Sci. Lett., 411: 281–289.
[ 20 ]	Mularz, S., Drzewiecki, W., 2007. Risk assessment for soil water erosion within the Dobczyce Reservoir area based on numerical modeling results. Archiwum Fotogrametrii, Kartografii i Teledetekcji 17b, 535–548.
[ 21 ]	Niazi, M., Obropta, C., Miskewitz, R. 2015. Pathogen transport and fate modeling in the Upper Salem River Watershed using SWAT mode. J. Environ. Manage. 151: 167–177.
[ 22 ]	Ogbeide, O., Chukwuka, A., Tongo, I., Ezemonye, L. 2018. Relationship between geosorbent properties and field-based partition coefficients for pesticides in surface water and sediments of selected agrarian catchments: Implications for risk assessment. J. Environ. Manage. 217: 23–37
[ 23 ]	Oshunsanya, S.O., Li, Y., Yu, H. 2019. Vetiver grass hedgerows significantly reduce nitrogen and phosphorus losses from fertilized sloping lands. Sci. Total Environ. 661: 86–94.
[ 24 ]	Panagos, P., Standardi, G., Borrelli, P., Lugato, E., Montanarella, L., Bosello, F. 2018. Cost of agricultural productivity loss due to soil erosion in the European Union: From direct cost evaluation approaches to the use of macroeconomic models. Land Degrad. Dev. 8; 29:471–484.
[ 25 ]	Pavlis, M., Cummins, E., McDonnell, K. 2010. Groundwater vulnerability assessment of plant protection products: A review. Human and Ecological Risk Assessment. 16(3): 621–650.
[ 26 ]	Quinton, J.N., Govers, G., Van Oost, K., Bardgett, R.D. 2010. The impact of agricultural soil erosion on biogeochemical cycling. Nat. Geosci. 3:311–14.
[ 27 ]	Rattan, K.J., Blukacz-Richards, E.A., Yates, A.G., Culp, J.M., Chambers, P.A. 2019. Hydrological variability affects particulate nitrogen and phosphorus in streams of the Northern Great Plains. Journal of Hydrology: Regional Studies 21: 110–125
[ 28 ]	Rattan, K.J., Corriveau, J.C., Brua, R.B., Culp, J.M., Yates, A.G., Chambers, P.A. 2017. Quantifying seasonal variation in total phosphorus and nitrogen from prairie streams in the Red River Basin, Manitoba Canada. Sci. Total Environ. 575, 649–659.
[ 29 ]	Roberts, W.M., Gonzalez-Jimenez, J.L., Doody, D.G., Jordan, P., Daly, K. 2017. Assessing the risk of phosphorus transfer to high ecological status rivers: Integration of nutrient management with soil geochemical and hydrological conditions. Sci. Total Environ. 589:25–35.
[ 30 ]	Römkens, M. J. M. 1985. The soil erodibility factor: A perspective. Soil Erosion and Conservation. El-Swaify, S. A., Moldenhauer, W. C. and Lo, A. Eds. Soil and Water Conservation Society of America. Ankeny, Iowa. 445 – 461.
[ 31 ]	Rosendorf, P., Vyskoc, P., Prchalova, H., Fiala, D. 2016. Estimated contribution of selected non-point pollution sources to the phosphorus and nitrogen loads in water bodies of the Vltava River Basin. Soil and Water Res. 11:196–204.
[ 32 ]	Schilling, K., Zhang, Y. 2004. Baseflow contribution to nitrate‐nitrogen export from a large, agricultural watershed, USA. Journal of Hydrology. 295(1): 305–316.
[ 33 ]	Schilling, K.E., Streeter, M.T., Quade, D., Skopec, M. 2016. Groundwater loading of nitrate‐nitrogen and phosphorus from watershed source areas to an Iowa Great Lake. Journal of Great Lakes Research. 42(3): 588–598.
[ 34 ]	Schilling, K.E., Streeter, M.T., Arthur Bettis III, E., Wilson, C.G., Papanicolaou, A.N. 2018. Groundwater monitoring at the watershed scale: An evaluation of recharge and nonpoint source pollutant loading in the Clear Creek Watershed, Iowa. Hydrological Processes. 32: 562–575.
[ 35 ]	Shao, J., Huang Z., Deng H. 2018. Characteristics of nonpoint source pollution load from crop farming in the context of livelihood diversification. J. Geogr. Sci. 28(4): 459–476.
[ 36 ]	Smith, D.R., Wilson, R.S., King, K.W., Zwonitzer, M., McGrath, J.M., Harmel, R.D., Haney, R.L., Johnson, L.T. 2018. Lake Erie, phosphorus, and microcystin: Is it really the farmer’s fault? Journal of Soil and Water Conservation 73(1):48–57.
[ 37 ]	United States Environmental Protection Agency, 2019. Nonpoint Source Pollution: Agriculture. Washington, DC: U.S. Environmental Protection Agency (EPA). Retrieved on 2019-01-28.
[ 38 ]	Wang, F., Sun, Z., Zheng, S., Yu, J., Liang, X. 2018. An integrated approach to identify critical source areas of agricultural nonpoint-source pollution at the watershed scale. Journal of Environmental Quality. 47:922–929.
[ 39 ]	Wang, K., Lin, Z. 2018. Characterization of the nonpoint source pollution into river at different spatial scales. Water and Environment Journal. 32: 453–465.
[ 40 ]	Williams, M.R., Livingston, S.J., Penn, C.J., Smith, D.R., King, K.W., Huang, C. 2018. Controls of event-based nutrient transport within nested headwater agricultural watersheds of the western Lake Erie basin. J. Hydrol. 559: 749–761.
[ 41 ]	Wu, L., Qiao, S., Peng, M., Ma, X. 2018. Coupling loss characteristics of runoff-sediment-adsorbed and dissolved nitrogen and phosphorus on bare loess slope. Environ. Sci. Pollut. Res. 25:14018–14031.
[ 42 ]	Xu, W., Cai, Y., Rong, Q., Yang, Z., Li, C., Wang, X. 2018. Agricultural non-point source pollution management in a reservoir watershed based on ecological network analysis of soil nitrogen cycling. Environmental Science and Pollution Research. 25 (9):9071–9084
[ 43 ]	Yi, B., Zhang, Q.C., Gu, C., Li, J.Y., Abbas, T., Di, H.J., 2018. Effects of different fertilization regimes on nitrogen and phosphorus losses by surface runoff and bacterial community in a vegetable soil. J. Soils Sediments 11: 1–11.
[ 44 ]	Zhang, F., Cui, Z., Fan, M., Zhang, W., Chen, X., Jiang, R. 2011. Integrated soil–crop system management: reducing environmental risk while increasing crop productivity and improving nutrient use efficiency in China. J. Environ. Qual. 40, 1051.
[ 45 ]	Zhang, W., Huang, B. 2014. Soil erosion evaluation in a rapidly urbanizing city (Shenzhen, China) and implementation of spatial land-use optimization. Environ. Sci. Pollut. Res. 22(6):4475–4490.