Effects of Nutrient Pollution of Marine Waters

The biological production in marine waters mainly depends on (besides other factors, e.g. light intensity, temperature) the amounts of available nitrogen (N) and phosphorus (P) (213, 372). Moderate increases in nutrient supply may have beneficial effects, e.g. on fish stocks. Any oversupply (overnutrition, hyperfeeding) or an unbalanced supply originating from agriculture, aquaculture, urbanization, traffic or industries which stimulates the primary production of toxic algae forming bloom will, however, have a negative effect on the aquatic ecosystem (27, 28, 225, 375), known as eutrophication (13, 17, 24, 27, 33, 87, 139, 142, 161, 185, 194, 248, 320, 322, 360, 366, 378).
It will also negatively affect the water quality (3, 6, 8, 31, 40, 49, 54, 181, 235, 256, 259, 270, 284, 336, 338, 365).

The oversupply of both the nutrients nitrogen (N) or phosphorus (P) will lead to an increase in the production of algae biomass (39, 72, 77, 195, 227, 330). It will also alter number and proportion of species (25, 288, 289), and it will change the natural phytoplankton composition. This may lead to algae bloom or yellowing (171, 252, 253, 323, 344, 346, 351, 356); though not every algae bloom is the result of nutrient oversupply (83, 96, 102, 141, 376). However, together with the frequency of algae bloom, the probability of toxic algae bloom also increases (105, 111).
For the decomposition / mineralization of a larger amount of biomass thus produced, a greater supply of oxygen (O) is needed. When the available oxygen can no longer meet the greater requirement, the oxygen concentration decreases and will become too low for sustaining animal life (28, 37, 128, 207, 294).

When the algae sink to the bottom, in severe cases anaerobic conditions may occur, leading to hypoxia (50, 58, 65, 130, 216, 224). In particular in cases where there is a lack of mixing of bottom water with oxygen containing surface water, this happens.
Especially wet deposition (104, 105) of nitrogen in the form of ammonium (NH4) will particularly cause an acidification/acidulation of waters (45, 278). In oceans or seas with coral growth (345) phosphorus pollution may contribute to coral death (333, 353).