Contamination with As, Cd and Hg, their spatial and temporal distribution are reported from the coastal wetland sediments of the northern Beibu Gulf, South China Sea. The content of As, Cd, Hg and TOC in surface sediments is 8.1±5.8μgg−1, 0.08±0.14μgg−1, 0.034±0.028μgg−1 and 0.45±0.39%, respectively. The mean sedimentation rates are 0.93–1.37cmyear−1 during 1920s to 2008 determined by 210Pb and 137Cs dating in three cores. The vertical profiles of As, Cd and Hg content in the cores retrieved from Qin and Nanliu River estuaries show increasing trends during 1985–2008 due to anthropogenic impact caused by local economic development. Locally the surface sediments have potential ecological risk of As to benthos according to the NOAA sediment quality guidelines.

Average and 75 % biochemical oxygen demand (BOD) in the Yamato-gawa River, Japan, in 1963 were smaller than the criteria determined in 1970 (5 mg l⁻¹); however, they were deteriorated up to 22–32 mg l⁻¹ in 1970. The deterioration was caused by the population increase and economic and urban development. The national-level regulations on ambient water quality and pollutant discharge have been established in 1970. Municipal wastewater is the major contributor in pollutant discharges in the river basin. Estimated BOD discharge (PD(BOD)) in the river basin reduced to the level of 1963 in 2000; however, average and 75 % BOD were more than the criteria. Analysis on the relationship between BOD and PD(BOD) resulted in the five phases in 1963–2009. The equilibrium conditions changed from phase I to II because of the perturbation caused by the excess BOD discharge, self-correcting mechanisms were found in phase III, and equilibrium conditions changed from phase III to IV and V. The comparison of estimated BOD based on pollutant generation (PG) without measures and monitored BOD represented the following situations in 47 years: (1) It took several years before the effects of centralised WWTPs were observed, (2) PD(BOD) was less than 35 t-BOD day⁻¹ for the linear relationship of PD(BOD) and BOD, and (3) combined effects of wastewater treatment, river water purification facilities and soft measures were estimated to be about 10 mg-BOD l⁻¹ in 2010.

Provincial-level data for population, livestock, land use, economic growth, development of sewage systems, and wastewater treatment rates were used to construct a river nitrogen (N) export model in this paper. Despite uncertainties, our results indicated that river N export to coastal waters increased from 531 to 1,244 kg N km(-2) year(-1) in the Changjiang River basin, 107 to 223 kg N km(-2) year(-1) in the Huanghe River basin, and 412 to 1,219 kg N km(-2) year(-1) in the Zhujiang River basin from 1980 to 2010 as a result of rapid population and economic growth. Significant temporal changes in water N sources showed that as the percentage of runoff from croplands increased, contributions of natural system runoff and rural human and livestock excreta decreased in the three basins from 1980 to 2010. Moreover, the nonpoint source N decreased from 72 to 58 % in the Changjiang River basin, 80 to 67 % in the Huanghe River basin, and 69 to 51 % in the Zhujiang River basin, while the contributions of point sources increased greatly during the same period. Estimated results indicated that the N concentrations in the Changjiang, Huanghe, and Zhujiang rivers during 1980-2004 were higher than those in the St. Lawrence River in Canada and lower than those in the Thames, Donau, Rhine, Seine, and Han rivers during the same period. River N export will reduce by 58, 54, and 57 % for the Changjiang River, Huanghe River, and Zhujiang River in the control scenario in 2050 compared with the basic scenario.