Nitrate contamination of groundwater in the alluvial fans of the Taihang Mts and Yanshan Mts

(Proc. 6th International Groundwater Quality Conference held in Fremantle, Western Australia, 2 7 December 2007). IAHS Publ. 324, 2008. 79 Nitrate contamination of groundwater in the alluvial fans of the Taihang Mts and Yanshan Mts F. D. LI 1,3, C. Y. TANG 2, Y. H. YANG 3, Q. Y. ZHANG 2, C. M. LIU 3 & W. J. ZHANG 3 1 Graduate School of Science and Technology, Chiba University, Chiba 263-8522, Japan lifadong@gmail.com 2 Faculty of Horticulture, Chiba University, Chiba 271-8510, Japan 3 Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, CAS, Shijiazhuang, 050021, China Abstract Nitrate contamination in groundwater is a source of rising concern in many countries. In alluvial fans characterized by shallow water tables, fast recharge processes and short-residence ages, groundwater is frequently contaminated by nitrate. The aim of this study is to determine nitrate contamination of shallow groundwater in an alluvial fan which is influenced by human activities. The study was carried out in the alluvial fans located on the piedmont of Taihang Mts and Yanshan Mts around the North China Plain. There are several metropolises along the alluvial fans, such as Beijing (with population 13.8 million), Tianjing (10.4 million), and Shijiazhuang (over 2.0 million). Nitrate concentrations in water samples from one rainfall event and 147 randomly-elected rural residential wells and urban water supply wells in the study area were analysed over an eight year period, 1998 2006. Data including water table elevation, well depth, EC and ph were collected in situ. Nitrate concentrations range from 0.1 to 449.2 mg/l. Twenty-nine percent of 148 samples have higher nitrate concentrations than 45 mg/l, the drinking water standard set by the WHO. Spatially, nitrate contamination is found in surface waters which flow relatively slowly, such as in small lakes, sewage rivers, and small streams. For spring waters, cattle and goat manure cause high nitrate concentration. Nitrate contamination of deep groundwaters was also found occasionally on the Yanshan Mts alluvial fan, where anthropogenic activities are stronger during the development of mega-cities Beijing and Tianjin than for other cities on the Taihang Mts alluvial fan. Key words nitrate contamination; groundwater; alluvial fan; Taihang Mts; Yanshan Mts INTRODUCTION Nitrate contamination of groundwater is a common occurrence in many areas of the world and has become a major problem in some shallow aquifers. Nitrate itself is relatively non-toxic to humans and animals. However, it can be reduced to toxic nitrite under favourable conditions or by denitrifying bacteria in the upper digestive tract of some infants (Johns & Lawrence, 1973). Therefore, WHO and national governments set the drinking water standard as 10 mg/l nitrate-n (45 mg/l as NO 3 ). The alluvial fan is a general geomorphological unit in the world (Bull, 1977). Alluvial fans have plentiful water resources and have been developed as farmland, new city centres, and so on. Nitrogen in the form of dissolved nitrate is the major nutrient for vegetation. In the past 30 years, a number of nitrogenous fertilizers have been Copyright 2008 IAHS Press

80 F. D. Li et al. applied for higher production. Alluvial fans are recharge zones for the adjacent plain. Nitrate contamination in alluvial fans will enter into more extensive adjacent aquifer systems by lateral recharge. Kreitler (1979) first introduced studies on nitrate contamination in alluvial fans. He found that the Taylor and Lockhart gravel fan aquifers (central Texas, USA) and the Seymour gravel aquifer (west Texas) contain average nitrate concentrations of 75 and 138 mg/l, respectively. Ammonium-type fertilizer and animal wastes from livestock and domestic waste were the main nitrate sources. Some authors have discussed nitrate concentrations in groundwater in northern China. Based on investigations in 14 cities and counties from October 1993 to June 1994, located mostly in the northern part of North China Plain (NCP), Zhang et al. (1996) showed that 38 out of 69 samples had nitrate concentrations >45 mg/l. As a case study in the NCP, Hu et al. (2005) presented the detailed spatial variability of nitrate in shallow groundwater in the Quzhou county covering 667 km 2. Six of 139 wells had higher nitrate concentrations than the Chinese Drinking Quality Standard recommended limit of 45 mg/l. Similar studies were carried out in a county in southern NCP, with an area of 509.5 km 2 (Liu et al., 2005). Zhao et al. (2007) surveyed nitrate concentrations of groundwater in the region around the Bohai Sea including Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan, and Liaoning Provinces. Thirty-four percent of all 1139 wells had higher nitrate concentrations than the WHO drinking water standard (10 mg/l N). Concentration decreased with increasing well depth. The mean value of nitrate concentrations in shallow wells (0 10 m in depth) was 21.7 mg/l. Furthermore, nitrate contamination caused by waste irrigation (Chen et al., 2003, 2005, 2006; Tang et al., 2003, 2004) and the effects of cropping system and leaching loss on groundwater systems also have been reported at local scales or points in NCP (Kou et al., 2005; Mack et al., 2005; Zhu et al., 2005; Fang et al., 2006; Guo et al., 2006; Ju et al., 2006; Yu et al., 2006). The objective of this study is to understand the spatial variation of nitrate concentrations along alluvial fans of the Taihang Mts and Yanshan Mts, and to identify the factors impacting on nitrate concentrations. SITE DESCRIPTION The Taihang Mts and Yanshan Mts are located in the northern part of China (Fig. 1). The Taihang Mts extend from the south, near the Yellow River to the north to connect with the Yanshan Mts. These two mountains surround the biggest plain the North China Plain in China. Many alluvial fans distribute along the Taihang Mts with a regional groundwater flow direction from west to east, and along the Yanshan Mts with a flow direction from north to south (Fig. 1). The area has a monsoon climate. The average yearly precipitation varies from 350 to >1000 mm in the high mountain areas, and the potential evaporation exceeds 1600 mm in most regions. As population and the development of economy and agriculture increase, groundwater level decreases significantly and surface water pollution is becoming more and more serious. Consequently, local residents and agriculture become more and more dependent on groundwater. Over 80% of drinking water in the big cities, such as Beijing, Tianjin, Shijiazhuang, Baoding, Hengshui and Xinxiang, are sourced from the upper reservoirs or are supported by exploitation from groundwater aquifers.

Nitrate contamination of groundwater in the alluvial fans of the Taihang Mts and Yanshan Mts 81 Fig. 1 Location of sample sites and the Taihang Mts and Yanshan Mts. J** designated samples of Jica 1998-2000, c** cbh2003, x** xx2006, n** swnt2006. METHODS The location of the 148 sampling sites, which were taken from precipitation, surface waters (rivers and reservoirs), spring waters, and groundwaters (shallow and deep) during several surveys in north China, from 1998 to 2006, are shown in Fig. 1. Well depth, EC and ph were measured in situ (except those taken in 2000), and 100 ml of

82 F. D. Li et al. water was sampled. Nitrate concentrations were analysed in Japan using LC-10AS (Shimadzu Liquid Chromatograph, Japan). The spatial distribution of sample locations is considered representative of the different well types, well depth and land uses for the two fans. RESULTS AND DISCUSSIONS Spatial distribution of nitrate concentrations The nitrate concentrations of all samples ranged from 0.1 to 449.2 mg/l with a mean value of 42.2 mg/l and median of 23.3 mg/l (Table 1). Twenty-nine percent of all samples have higher nitrate concentrations than the Chinese Drinking Quality Standard or WHO recommended limit of 45 mg/l. Nitrate concentration in precipitation is as low as 0.57 mg/l. The results in surface waters indicate that some of them are contaminated by nitrate, with a range between 3.7 and 73.9 mg/l. The contaminated surface waters are small lakes, rivers polluted by sewage, and small streams influenced by human activities in the headwater catchment. The mean and median values in spring waters and shallow groundwaters are similar. The most likely cause is the interaction between them. The spring waters are collected from the headwater catchments in the Taihang Mts, where cattle and goats are grazed freely. Their manure is responsible for the nitrate contamination (e.g. Aravena et al., 1993; Ju et al., 2006). Shallow groundwater, with 44% of wells having nitrate concentrations higher than 45 mg/l, are also like to be contaminated by nitrogen fertilizers. Major crops are winter wheat and maize in the study areas. To gain higher yields, application of nitrogen fertilizers greatly increased after the 1980s in China. Approximately 126 kg N was applied per hectare each year during the 1980s in farmland on the alluvial fan of the Yanshan Mts. (including Beijing, Tianjian, and Tangshan). From 1991 to 1995, mean values as high Table 1 Summary of nitrate, EC, and ph in precipitation (p), deep groundwater (gd), shallow groundwater (gs), surface water (s), and spring water (sp). Items Types Samples Mean Median Minimum Maximum Std. Deviation NO 3 (mg/l) EC (µs/cm) ph Well depth (m) p 1 0.6 s 32 25.8 19.4 3.7 73.9 19.1 sp 10 55.1 23.1 6.1 262.0 78.8 gs 69 55.5 38.8 0.1 449.2 66.5 gd 36 28.9 22.8 0.1 181.1 34.0 Total 148 42.2 23.3 0.1 449.2 54.7 gs 39 1035.5 985 335. 2400 440.8 gd 19 712.3 680 360 1440 279.2 Total 58 929.6 831 335 2400 421.4 gs 39 7.6 7.6 6.8 8.4 0.4 gd 19 7.8 7.7 7.3 8.3 0.3 Total 58 7.7 7.7 6.8 8.4 0.4 gs 39 40 37 6 80 20 gd 19 164 150 100 300 59 Total 58 81 50 6 300 69

Nitrate contamination of groundwater in the alluvial fans of the Taihang Mts and Yanshan Mts 83 as 293 kg N, i.e. 6.8 times higher than application rates in the USA, was used per hectare every year in Hebei Province, which covers most of the Taihang Mts alluvial fan in this study. Excess nitrogen will leach into the shallow groundwater with the recharge of precipitation and excess irrigation water. Nitrate concentrations in the deep groundwater are half that in the shallow groundwater. It is surprising that the highest value of 181.1 mg/l in the deep groundwaters was found in a 200-m deep well, which is located on the lower reach of the Haihe River, but very possibly caused by unclear aquifer information for the investigated well. In general, the mean nitrate concentrations in the Yanshan Mts alluvial fan were appreciably higher than those in the Taihang Mts alluvial fan (Table 2). Table 2 Summary of nitrate concentration, EC, and ph in the Taihang Mts (TMs) and Yanshan Mts (YMs) alluvial fans. Items Types N Mean Median Minimum Maximum Std. Deviation NO 3 (mg/l) EC (µs/cm) ph TMs 124 38.9 22.8 0.1 449.2 52.3 YMs 24 59.3 34.5 4.4 245.4 64.2 Total 148 42.2 23.3 0.1 449.2 54.7 TMs 34 1002.2 932.0 360.0 2400.0 456.0 YMs 24 826.8 742.5 335.0 1623.0 350.5 Total 58 929.6 831.0 335.0 2400.0 421.4 TMs 34 7.7 7.6 7.1 8.4 0.3 YMs 24 7.7 7.7 6.8 8.3 0.4 Total 58 7.7 7.7 6.8 8.4 0.4 Effects of well depth and EC on nitrate concentration Figure 2 shows how nitrate concentrations vary against well depth and EC. It shows that nitrate concentration decreases as well depth increases. Only four shallow wells were found to have nitrate contamination higher than the WHO standard in the headwater region of the Taihang Mts and Yanshan Mts. The deep and shallow groundwaters are divided according to Chen et al. (2005) who found groundwater in the NCP can be divided into two layers at 100 m depth. The nitrate concentrations in the study area scatter with a wide range between several metres and 100 m depth, whereas their variations become narrow below 100 m, except the values in four wells. In the shallow groundwater, nitrate concentrations tend to increase with EC increase. In the deep groundwater, however, this trend becomes unclear. High nitrate values are also found in lower EC conditions. Anthropogenic sources of nitrate contamination are clear. Three out of four wells are located at the Yanshan Mts alluvial fan. This region is very important for supplying vegetables to Beijing and Tianjin. Nitrogen excess is as high as 150 kg ha -1 in cropland, and a startling 1100 kg ha -1 in the vegetable growing areas (Liu et al., 2001). Nitrate is not appreciably attracted to soil particles. Hence, excess nitrogen will leach readily through the soil layer with percolating water, and recharges eventually into shallow and even deep groundwater, especially, during the flood season from June to September in the study area. In these sites, villages have no sewage treatment facilities and dispose waste either through septic tanks, cesspools, or through outhouses. Sewage and waste are the principal proved sources of nitrate contamination.

84 F. D. Li et al. Well depth (m) NO 3 (mg/l) 0 100 200 300 400 500 0 50 100 150 200 250 300 350 gd gs 2500 2000 EC (µs/cm) 1500 1000 500 gd gs 0 0 100 200 300 400 500 NO 3 (mg/l) Fig. 2 Nitrate concentrations vs well depths and EC values in the shallow and deep groundwaters. CONCLUSIONS The values of nitrate concentration, well depth, and EC from precipitation, spring water, surface water, and shallow and deep groundwater samples in the alluvial fans of the Taihang Mts and Yanshan Mts have been investigated during the past eight years. Low nitrate concentration in precipitation indicates that the contribution from rainfall is negligible. The spring waters in the headwaters are influenced by animal manures. Some surface waters have been contaminated by nitrate, in particular, the samples in small lakes, sewage channels and small streams. Nearly half of the shallow groundwater samples have higher nitrate concentrations than the WHO standard of 45 mg/l, whereas few deep wells exceed the limit. Excess nitrogen fertilizer application leads to higher nitrate concentrations in the shallow groundwater than those in the deep aquifer. The surveys found that several deep wells, i.e. over 100 m deep, were also contaminated by nitrate. If the EC values are over 1000 µs/cm, most of water samples have higher nitrate concentration than the WHO standard. Furthermore, more serious nitrate contamination in deep groundwaters was found in the Yanshan Mts alluvial fan where the anthropogenic activities are strong because of the development of the megacities Beijing and Tianjin than other cities in the Taihang Mts alluvial fan. More

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