Identifying nearshore groundwater and river hydrochemical variables influencing water quality of Kaoping River Estuary using dynamic factor analysis

The Kaoping River Estuary receives a large amount of nonpoint source pollution and sedimentary discharge from the Kaoping and Tungkang Rivers each year. The Kaoping River Estuary is an integral part of the Kaoping River, shelf, and submarine canyon, which makes prediction of water quality variation difficult. This study attempts to determine the main factors regulating temporal and spatial variations in the water quality in the Kaoping River Estuary over a 9-year period (2003–2011), using dynamic factor analysis (DFA) and min/max autocorrelation factor analysis (MAFA). The result from the MAFA shows that Chlorophyll-a (Chl-a) has the highest canonical correlation coefficient with the min/max autocorrelation factor (MAF) axis of water quality. Therefore, Chl-a can be used as an indicator of water quality in the Kaoping River Estuary. The water quality and environmental variables measured downstream of the Kaoping and Tungkang Rivers, as well as submarine groundwater, influence temporal variations of Chl-a in the estuary. The optimal DFA model successfully described Chl-a variations (coefficient of efficiency = 0.969) in the Kaoping River Estuary. DFA results indicate that dissolved oxygen (DO), total suspended sediment (TSS), dissolved inorganic nitrogen (DIN), chemical oxygen demand (COD), as well as the biological oxygen demand (BOD) of river discharge, and the ammonium–nitrogen (NH4–N) concentration of groundwater discharge significantly influenced Chl-a dynamics. Submarine groundwater discharge, which is a significant source of nutrients for the coastal ocean, appears to impact the level of Chl-a concentration substantially. Understanding the relationship between environmental variables and the variability of Chl-a concentration provides a useful approach for setting water quality criteria and pollution prevention plans for the Kaoping River Estuary.