Abstract of the proposal

The high nitrogen loading of rivers in the Pearl River Delta (PRD) has been a major concern because of an adverse effect on human health and on various environmental processes such as eutrophication. About 80% of the nitrogen in Hong Kong waters is from the PRD. This enrichment of nitrogen has been commonly attributed to anthropogenic activities such as sewage discharge and agricultural and industrial wastes, but there have been no studies on possible natural sources of nitrogen in the PRD aquifers. However, naturally-occurring groundwater with abnormally high ammonium concentrations up to 560 mg/L and total area of over 130 km2 was discovered in the PRD in the 1970's. Unfortunately, the existence of this ammonium-rich groundwater is not widely known and the mechanisms of the generation and maintenance have not been well studied. Consequently, the contribution of the ammonium groundwater to nitrogen budgets and cycles and its ecological influences on the river and coastal waters have been ignored. We speculate that this groundwater may be a large and hitherto unappreciated source of nitrate to surface waters in the PRD, and that this unrecognized natural non-point source of nitrogen contamination may have a profound influence on water quality. We propose to investigate the source(s) of this ammonium water and its environmental and ecological implications. We speculate that the water may be an important source of nitrogen loading, especially when its environment is disturbed by large-scale sand dredging in river channels. The objectives of this project are to determine: 1) the hydrogeochemistry of the source and reservoir formations of the ammonium water; 2) the mechanisms of its generation and preservation, and 3) its contribution to nitrogen loading in rivers in natural and human environments.