Environmental Science & Technology About 30% of China’s wheat and 20% of its corn are produced in the agricultural area between Beijing and Tianjin.15 The consequences are grave deterioration of water bodies and shifts in marine algal communities due to the altered Si:N:P ratio.16,17 Some areas of the Chinese coastal waters are listed among the largest dead zones of the world,18 and harmful algal blooms are becoming increasingly more serious.19,20 Nine new wastewater treatment plants (WWTPs) were installed before the 2008 Olympic Games with the aim of treating 90% of the Beijing wastewater, but their eﬀectiveness has so far not been evaluated. The goal of our research was to establish an overarching budget of nutrient ﬂuxes in the main waterways of the Beijing- Tianjin region−a task that has seldom been carried out to date in any of the rapidly developing centers of Asia and Africa. We assessed the spatial and temporal patterns and loads of nitrogen and phosphorus species from the Shahe reservoir upstream of Beijing to the Bohai Bay at Tianjin, with the aim of providing a basis for appropriate mitigation strategies in these semiarid regions. ■ MATERIALS AND METHODS Hydrology. The Shahe reservoir upstream of Beijing is a shallow 1.8 km2 lake from where the Wenyu River (called North Canal further downstream) runs for 240 km to the Bohai Bay (Figure 1). On its way, this river grows from a trickle of ∼1 Figure 1. Haihe river system, land use, and population in the Beijing− Tianjin region, China. The numbers depict our sites of investigation [corresponding geo-positions are provided in Table SI-1 of the Supporting Information (SI)]. Letters A−D denote tributaries draining the wastewater eﬄuents of Beijing, i.e.: A: Qing River; B: Beixiao River; C: Tonghui River; and D: Liangshui River. Note that Beijing had a total population of some 20 million in 2010, from which wastewater of 14 million was discharged into the studied river system. m3/s at site 1 to a 150-m-wide canal at site 13. It receives a large fraction of the Beijing WWTP eﬄuents by way of four tributaries: the Qing River (between sites 3 and 4, Figure 1), the Beixiao River (between sites 4 and 5), the Tonghui River (between sites 5 and 6), and the Liangshui River (between sites 6 and 7). In the upper reaches (between sites 2 and 4), untreated wastewater is discharged into the river from numerous small open sewers. Two major canals divert water from the North Canal for irrigation to the agricultural area between Beijing and Tianjin, i.e., to the Chaobaixin River (between 5 and 6) and the Qinglongwan River (between 8 and Article 9). Gauge readings for daily river water discharge at sites 1, 5, 9, and 13 were acquired from the central hydrology station of Beijing and the Bureau of Hydrology and Water Resources Survey of Langfang, Hebei Province. Data of daily loads of treated wastewater discharged by the nine Beijing WWTPs were obtained from the facility managers. Wastewater from Tianjin is discharged chieﬂy to the Yongdingxin River, between sites 13−16, i.e., downstream from the last dam in the catchment (Figure 1). This ﬁnal river section is brackish and tidal, which prevents quantiﬁcation of riverine water discharge. Sampling Sites, Water Analyses, and Budgets. To gain a ﬁrst overview on the occurrence and abundance of nutrient species, river water was collected along the 240-km river section at 16 selected study sites (Figure 1) in the dry season in April 2009 as well as in the wet season in July 2009. On the basis of this initial assessment, key sites 1, 5, 9, 12, and 13 were then monitored monthly from July 2009 to June 2010. Weekly and diurnal variations were investigated with daily samples (collected at the same hour from July 20−27, 2009) and hourly samples (July 23−24, 2009), respectively, at sites 1, 5, 9, 12, and 13. The four tributaries Qing, Beixiao, Tonghui, and Liangshui, which drain the wastewaters from Beijing, were also investigated. Eﬄuents from the ﬁve largest Beijing WWTPs (Qinghe, Jiuxianqiao, Beixiaohe, Gaobeidian, and Xiaohong- men) were sampled in May 2009, December 2010, and March 2011 (24 h-composite samples) to assess per-capita nutrient loads from Beijing. Water was collected by scooping river water with a bucket from a bridge or a dam. Temperature, pH, and dissolved oxygen (DO) were measured in the ﬁeld, whereas DO measurements were veriﬁed with spectrophotometric Winkler titrations.21 Details of sample preparation and chemical analyses are described in the Supporting Information (SI) for alkalinity, total suspended solids, water isotopes, as well as for N and P speciation, that is total phosphorus (TP),23 particulate phosphorus (PP), total dissolved phosphorus (TDP), dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), total nitrogen (TN), total dissolved nitrogen (TDN), particulate nitrogen (PN), NO2−, NO3−, and NH4+ (sum of NH3 and NH4+), and dissolved organic nitrogen (DON). Calculations of loads and budgets of water and nutrients are also detailed in the SI, together with estimated errors. ■ RESULTS AND DISCUSSION River Discharge and Water Budget. No periodicity (daily, weekly or seasonally) in river water discharge was observed. The occasional operation of river dams caused intermittent ﬂuctuations in ﬂow, but no systematic time patterns were noted. The water ﬂow diagram established in this study (Figure 2) shows that Beijing discharges an annual average of 29.5 m3 s−1 raw or treated wastewater into the Haihe river system. At a daily average consumption of 200 L inh−1,22 this corresponds to about 14 million people, or 70% of Beijing’s current population. The large contribution of wastewater to the river discharge was well reﬂected in the isotopic composition of river water (δ2H and δ18O), which mirrored the signatures of raw and treated wastewater as well as of groundwater used as supply water in Beijing (see Figure SI-1 of the SI). About 480 mm yr−1 of rain fell in this semiarid landscape in 2009−2010, which is representative of the average of 450 mm yr−1 for the years 1999−2004.23 Around 80% of the precipitation occurred between June and September, the warmest season with an average annual evaporation of ∼1100 5295 dx.doi.org/10.1021/es3004415 | Environ. Sci. Technol. 2012, 46, 5294−5301