Urban land-use effects on groundwater phosphate distribution in a shallow aquifer, Nanfei River basin, China Jiazhong Qian & Lulu Wang & Hongbin Zhan & Zhou Chen Abstract Groundwater, surface water, soil and river sediment samples, and information on land use in the Nanfei River basin (NRB) of China have been analyzed to study the geochemistry, distribution, and mobilization of phosphorus. The distribution of phosphate (PO43–) and the relationships between PO43– and several constituents in groundwater were studied. Partial correlation analysis relating PO43– to types of land use was conducted using the data analyzing tool SPSS 15.0. The processes controlling the transport of PO43– are discussed. The conclusions from this study are: (1) urban land use has obvious impact on PO43– in groundwater, the average concentration of PO43– being 4.37mg/L, greater than that resulting from farmland and mixed land use, which have average PO43– concentrations of 0.10 and 0.18mg/L, respectively; (2) the partial correlation between PO43– and types of land use is significant with a coefficient of 0.760; (3) the PO43– concentrations in surface water are generally higher than those in groundwater, and the total phosphorus (TP) concentrations in river sediments are generally higher than those in soil samples; (4) groundwater is a carrier of PO43– and is likely responsible for the redistribution of PO43– in different regions of NRB.
Received: 6 May 2010 / Accepted: 16 July 2011 Published online: 6 August 2011 * Springer-Verlag 2011 J. Qian : L. Wang : Z. Chen School of Resources and Environmental Engineering, Hefei University of Technology, Hefei, Anhui Province 230009, People’s Republic of China e-mail:
[email protected] H. Zhan ()) Department of Geology & Geophysics, Texas A&M University, College Station, TX 77843-3115, USA e-mail:
[email protected] Tel.: +1-979-8627961 Fax: +1-979-8456162 H. Zhan Faculty of Engineering and School of Environmental Studies, China University of Geosciences, Wuhan, Hubei Province 430074, China Hydrogeology Journal (2011) 19: 1431–1442
Keywords Urban groundwater . Groundwater monitoring . Partial correlation analysis . Phosphate . China
Introduction Groundwater flow has played an important role in carrying nutrients to surface water. Excess input of nitrogen (N) and phosphorus (P) to surface water can lead to eutrophication which is a serious environmental concern (Belanger and Mikutel 1985; Kim et al. 2008; Lee et al. 2009). Some studies have shown that growth of algae in most of the eutrophic lakes is limited by the concentration of P rather than N (Schindler 1977; Kamaya et al. 2004). It is important to understand the pathways in which P may be delivered to such ecosystems by hydrological processes. Point-source P inputs are relatively easy to quantify and can be managed via legislation on P use in domestic products and/or by enhanced waste-water-treatment technology. Understanding non-point source or diffusive P inputs has proved to be more difficult. Very little attention has been paid to evaluating transport of P via groundwater due to the long-held belief that adsorption and metal-complex formation retain the majority of potentially mobile P (Sims et al. 1998; Holman et al. 2008). To date, the studies related to P in groundwater mainly fall into two categories. The first category is related to non-point source P from agricultural activity, with a focus on transfer of P from agricultural land to surface water via surface runoff and sub-surface discharge (Sawhney 1978; McDowell et al. 2001; Heathwaite et al. 2005; Oenema et al. 2005; Withers and Haygarth 2007). For instance, Jalali (2009) conducted a survey on P concentration, solubility and species in groundwater in a semi-arid basin, southern Malayer, western Iran. Jalali (2009) showed that large amounts of P fertilizer, inadequate management of P fertilizer use, and low irrigation efficiency, coupled with sandy soils in some parts of the study area, could be mainly responsible for the elevated P concentration in groundwater. The second category involves studying the transport mechanism of non-point source P based on hydrochemical analysis. For example, Kulabako et al. (2008) studied P attenuation and adsorption capacities of DOI 10.1007/s10040-011-0770-x
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soils in the laboratory and the field, and suggested that P dynamics was related to calcium (Ca), Iron (Fe) and organic carbon content of the soils. Carlyle and Hill (2001) studied groundwater P dynamics in a river riparian zone and showed that the sources of P associated with buried channel sediments could also influence subsurface reactive transport and release of P to streams. Holman et al. (2010) proposed that groundwater P contributions should not automatically be viewed as a source of dilution, but rather as having the potential to trigger and/ or maintain eutrophication, based on field studies in the UK and Ireland. To date, much less attention has been paid to investigating the urban land-use effects on groundwater P distribution and transport, which has been the primary focus of this study. The selected field site, Nanfei River basin (NRB), is located between Hefei City and Chaohu Lake (see Fig. 1) in China. Chaohu Lake is the fourth largest freshwater lake in China. Since the middle of 1980s, algae blooms have occurred each year in this lake (Zhu et al. 2006). It has been reported that Chaohu Lake has significant eutrophication as a result of the development of agriculture and industry near the lake (Jin et al. 2005). To reduce the eutrophication in Chaohu Lake, national and local governments have paid great attention to the control of point-source P inputs through regulating P use in domestic products and by enhancing waste-watertreatment technology. However, such efforts have not alleviated the problem of eutrophication in Chaohu Lake (Jin et al. 2005; Zhu et al. 2006). This has lead to the authors hypothesizing that non-point source P from groundwater discharged to Chaohu Lake, which has not been taken into account previously, could be considerably large and may be responsible for persistent eutrophication in the lake. This issue has, so far, not been studied at this site with the exception of a preliminary hydrochemical survey on groundwater and surface water in NRB by Qian et al. (2007). The objective of this study is to study the spatial distribution of PO43– in groundwater affected by land use and urbanization in NRB and the geochemical factors affecting the P mobilization and transport.
Description of the study area Geology and hydrogeology of the site Nanfei River basin is located in the Jianghuai hilly country, near Hefei City, the capital of Anhui Province of China, as shown in Fig.1. Nanfei River, as one of the largest rivers discharging into Chaohu Lake in this basin, originates from south of the Dabieshan Mountain at the center of Anhui Province of China. Nanfei River is 70 km long with a catchment area of 1,446 km2. The climate of the area is sub-tropic and humid. Nanfei River basin is an important industrial and agricultural base in Anhui Province. Groundwater in NRB is mainly recharged by rainfall and surface runoff. According to data collected at North Gate Hydrological Station of Hefei, the average depth to the water table at NRB is 11.56 m, compared to Hydrogeology Journal (2011) 19: 1431–1442
the water-table depth of 12.4~29.5 m at Hefei City. Fluctuations of the water table in NRB are closely related to rainfall events, and are partially related to groundwater withdrawals. Surface runoff is greatest during May to August annually, which is also the growth period of rice paddy in this region. Hilly monadnock and flood plains are the main landforms of this area. The hilly monadnock plain stretches across the northern and eastern parts of the study area with elevation about 15.0–28.0 m above sea level (a.s.l.) with geographic gradients about 3–5°. It is formed by long-term cutting of intermittent running water. The flood plain is along Nanfei River, and in the southern part of the study area near Chaohu Lake, with elevation about 6.5–9.5 masl. It is mainly formed by periodic flooding of Nanfei River and Chaohu Lake, and is mostly used for agriculture. A Quaternary stratum nearly covers the entire study area, as shown in Fig. 1. Late Archeozoic–early Proterozoic stratum is the basement at the study area. Various geological layers, including Cretaceous (K), Tertiary (E), Quaternary (Q) and Igneous rock (γ) can be found at the study site. There are two hydro-stratigraphic groups, namely the loose rock group and the clastic rock group. For the loose rock group, four types of hydro-stratigraphic units can be identified. One is the Quaternary pore water (Qhw) with a single-well yield of 10~100 m3/day, and a thickness of 4–30 m. The second is the fracture-pore water (Qp3x) with a single-well yield less than 10 m3/day, and a thickness of 10–25 m. The third is the carbonate fracturekarst water (Qp 1–2 g) with a single-well yield of 10~500 m3/day, and a thickness of 2–18 m. The fourth is the fracture water (E1–2dn) with a single-well yield of 10~100 m3/day, and a thickness of greater than 20 m. For the clastic rock group, the single-well yield is less than 100 m3/day. This stratigraphic group is divided into several units including mild sandy soil, muddy silty sand rock, mild clay, clay, muddy clay and sand (see Fig. 1). Decline of the water table at the study site is caused by pumping for irrigation and municipal usage. There is also close interaction between groundwater and surface water in the study area. Equipotential lines of water-table elevation are shown (as dashed lines) in Fig. 1 and groundwater generally flows from northwest to southeast before discharging to Nanfei River and Chaohu Lake (Qian et al. 2007).
Sampling and analysis To understand the chemical characteristics of groundwater and the fate and transport of P, groundwater samples were collected from 39 wells between Hefei City and Chaohu Lake in NRB. The geographical locations of the wells were determined with a GARMIN handheld global positioning system (GPS) and are shown in Fig. 1. The collection of groundwater samples was carried out from 5–10 December 2006. DOI 10.1007/s10040-011-0770-x
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N S1 S2 S3
Rive
8
11
S4
r
Qhw
S5
Qp3x
S6
Nan
14
17
A
fei
S7 Qhw
14
Qhw
11
Qp3x
8
S8
A’
(a) Elevation (masl)
A 40 30 20 10 0 -10 -20 -30 -40 -50
129 Qp3x Qp3x
Qhw
Qp3x
Qp1-2g
E1-2dn
E1-2dn
A’ 40 30 20 10 0 -10 -20 -30 -40 -50
(b)
Legend 1. Single-well water yield (m 3/d)
