Abstract of the proposal

Coastal marine ecosystems are affected by dissolved nutrient inputs from circulating offshore water, river runoff, and groundwater seepage. Of these various sources, the input through submarine groundwater discharge (SGD) is least understood. SGD often contains chemicals with concentrations higher than those of river water and thus plays an important role in the health of coastal ecosystems. Although SGD has received increased attention in the last few years in relatively wealthy regions of the world, there are very few SGD studies in Asia, particularly in the Southeast China Sea. The China coast has been plagued repeated by harmful algal blooms (HAB), especially in recent years. Nutrients from river runoff and sewage are recognized as key factors responsible for HAB, but those from SGD into the coastal systems of the China Sea have been largely ignored. There has been little study on the possible impact of groundwater chemicals and their temporal variation on eutrophication.

We propose to investigate SGD and its environmental and ecological implications through a detailed study of Tolo Harbour, a semi-enclosed water zone with the most frequent red tides in Hong Kong waters. This site is unique because it has decades-long marine water, groundwater, and red tide monitoring data and because it has an independent groundwater recharge system of manageable size and well-defined boundaries where various SGD estimation methods can be explored and compared. We speculate that this area has relatively high SGD due to its special topographical and hydrogeological setting, and hypothesize that the SGD to the harbour may be a factor in formation of the red tides. The objectives of this project are to study: 1) the quality and quantity of SGD into the Harbour and 2) the effect of SGD on eutrophication and associated HAB. The work will be conducted by an interdisciplinary team using multiple approaches including field hydrogeological studies, radioisotope tracers, seepage meters, laboratory experiments, statistical analysis and numerical modelling. Successful completion of this study will provide a better understanding of the interaction between groundwater and seawater and the importance of SGD in coastal ecology. Thus, the findings from this project will have not only theoretical interest but will be of practical benefit for sustainable use and development of coastal ecosystems in Hong Kong and elsewhere.