Nutrient dynamics in the macro-tidal Yalujiang Estuary

Field observations of the macro-tidal Yalujiang Estuary were undertaken in 1992-1996, including during both drought and high flow wet seasons, to investigate the nutrient biogeochemistry. In the river the dissolved inorganic nitrogen is up to 400-500 μM, and phosphate concentration is ∼0.05-0.1 μM. Dissolved silica in the Yalujiang is within the range typical for Chinese rivers. In the estuary, dissolved silica is dominated by the dilution of nutrient poor marine waters from the Yellow Sea. Nitrate illustrates different distributions between the dry and flood seasons. Considerable phosphate and ammonia concentrations are regenerated in the estuary, presumably from desorption and degradation of organic detritus. The DIN/P ratio of 500-1000 induces a phosphate-limited situation for photosynthesis in adjacent coastal waters. In the Yalujiang Estuary, nutrient dynamics are strongly affected by the natural (e.g. typhoon) and anthropogenic (e.g. waste drainage) disturbances, changing the seaward flux of chemical species in this region. Based on field observation and laboratory analysis, nutrient budgets are established for the Yalujiang Estuary. The flux of phosphate and dissolved silica in the flood (wet) season can be 2-4 times that for the dry season, while DIN is up to one order of magnitude higher, corresponding to elevated chemical yields from the drainage basin.