The most direct method to control harmful phytoplankton blooms is to reduce inputs of nutrients such as phosphorus that drive their growth.
There is increasing evidence that the inputs of nutrients to the Bohai Sea are closely related to submarine groundwater discharge (SGD).
In the last few decades, increased inputs of nutrients (mostly nitrogen and phosphorus) to agricultural land have led to runoff transporting an ever growing portion of these nutrients from non-point (diffuse) pollution sources into rivers and lakes, thus threatening freshwater quality.
Although inputs of nutrient-rich continental waters can be observed, the intensified aforementioned current velocities may also resuspend inorganic sediments.
This is shown to be mainly caused by an increase of algae production in the surface waters due to eutrophication following increased inputs of nutrients from human activities.
Atmospheric inputs have increased in recent years, whereas the inputs of nutrients from point sources have remained relatively unchanged, indicating no significant reduction in nutrient loads in recent times (Figure 4).
Nutrient scarcity is especially prevalent in the surface mixed layers of highly stratified systems, with inputs of nutrients often restricted to new production (e.g. nitrogen fixation) or atmospheric (dust) deposition [1].
Despite a substantial reduction in riverine and direct point source inputs of nutrients since the 1990s (Figure 4), the overall status of eutrophication does not indicate a corresponding improvement.
Geographically localized sources of variation in resources arise from several sources including episodic inputs of nutrients from rivers, mixing due to storms and eddies, and vertical mixing at the Brunt-Väisälä frequency [48], [49].
Human impacts on coastal marine ecosystems are ever-increasing, and threats include inputs of nutrients, organic contaminants, and metals, as well as changes in temperature, decreasing ocean pH, and deoxygenation [5].
Eutrophication, caused by excess inputs of nutrients including N, is a leading problem facing US coastal waterways which is likely to worsen as human use of inorganic fertilizers and fossil fuels continues to increase [4].
