Investigation of submarine groundwater discharge and associated nutrient inputs into Laizhou Bay (China) using radium quartet.

Radium is widely used to estimate flushing time, submarine groundwater discharge (SGD), and submarine fresh groundwater discharge (SFGD), however there are important sources of uncertainty in current methods. Here an improved method is proposed, incorporating all radium quartet information to estimate flushing time, SFGD, SGD, and associated nutrient fluxes during wet and dry seasons in Laizhou Bay, China. Both SGD and SFGD in dry season are comparable to that in wet season, likely due to higher groundwater hydraulic gradients resulting from higher groundwater table and lower mean sea level in dry season. Estimated dry and wet season SFGD are of the same order of magnitude as the annually-averaged Yellow River discharge, highlighting SFGD's importance to the bay environment. Nutrient inputs into Laizhou Bay were estimated for the wet season, suggesting that SGD-derived nutrients are indeed important and significant for coastal environments compared to local river discharge estimates.