Phosphorus-limited growth systems

Bothwell ML (1985) Phosphorus limitation oflotic periphyton growth rates an intersite comparison using continuous-flow trough (Thompson River system, British Columbia). Limnol Oceanogr 30 527-542. 

A proper balance of nutrients is required for plant growth. In marine systems, the stoichiometry of primary production is determined by the ratio of elements in the cytoplasm (Redfield ratio) that supports optimal metabolism of phytoplankton (Redfield, 1958). The C N P ratio is fairly constant in marine phytoplankton, and this ratio in primary producers constrains the cycling of aU elements (Elser et al., 2000). The amount and proportions of nitrogen and phosphorus available determine the amount of carbon fixed by phytoplankton. Limitation by either of these... 

Two immediate consequences of the inhibition of an ectoenzyme, such as alkaline phosphatase, are the cessation of algal growth by nutrient limitation and (he disruption of phosphorus cycling. As emphasized later, ectoenzymes promote an interdependence among the cycles of major and minor elements in aquatic systems. 

The possibility that limited root development is attributable to insufficient available major and minor nutrients has received considerable attention. Sometimes the addition of available nitrogen and phosphorus has increased the depth and extension of root systems, but in most cases the increase has not been marked, and there was no certainty as to how much of the increases obtained was due to the nutrients per se, and how much to the mechanical operations involved in the addition of the nutrients. Where the A-horizon is present, most of the nutrients needed for growth in the subsoil are readily obtained from the topsoil, but in exposed subsoils added available nitrogen and phosphorus may be very essential for extensive root proliferation. If the physical conditions are satisfactory, plants produce a surprisingly large amount of roots on a minimum of nutrients they appear to send out roots in search of nutrients, particularly nitrogen. 

The performance model reflects and is limited by the current state-of-the-art in algae growth. Several important, basic relationships have yet to be quantitied. As a result, several parameters must be introduced as input data. For example, the level of wastewater treatment is only partially predictable by the process options selected. Nutrient removal efficiencies must be input for each different level of treatment. Similarly, the solar conversion efficiency cannot be predicted by the model and must be input. Finally, algae digestion is essentially a "black box" operation at this point. This fact prevents a quantitative assessment of nitrogen and phosphorus mass balances in the system. Within these limitations, equations were developed to predict (1) the flows and (2) the required equipment sizes for the various process operations. 

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