Photosynthesis and within limits a fixed ratio of nitrogen, phosphorous and carbon are required for microscopic algae to be produced in marine systems. The production therefore depends not only on the actual amount of nitrogen added but also on the phosphorus. In the open oceans the availability of phosphorous is generally regarded as the limiting factor and additional nitrogen will not have any effects on growth.  However in near-shore or harbour situations, where phosphorus is available (e.g. from river inputs, run-off from agriculture or direct input of domestic sewage), addition of nitrates may lead to enhanced biomass production [8].

To determine the influence of additionally added nitrogen from the wash water of an exhaust gas cleaning system, the nitrate levels were monitored over a ten-month period and a calculation made to determine the potential for biomass production. This showed that the potential for increase in production in a given year would be less than the actual production during one sunny day per square metre [4].