Phosphorus cycle limiting nutrient

From a practical standpoint, stream fulvic acids which comprise over 90% of the stream humic substances are not an important food source for aquatic organisms, but all stream humic and fulvic acids are positive influences on biological growth in respect to phosphorus and nitrogen nutrient cycling, trace metal availability, and limiting potential metal toxicity. 

We have considered already that phosphate is a limiting nutrient in most freshwater and probably very often in marine water ecosystems as well. The P cycling is thus of great importance for understanding biogeochemical interactions inside aquatic ecosystems. Phosphorus always occurs as phosphate, in its many inorganic and or-... 

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 present model is based on mass balances for three main components representing phytoplankton (A), nutrients (E), and organic phosphorus (C), which can describe phosphorus cycle within a water body as follows. Phytoplankton biomass is produced by the photosynthesis reaction, consuming nutrients (in lakes and reservoirs, the limiting nutrient is phosphorus) and dissolved carbon dioxide, with solar radiation and adequate temperature. Upon death, phytoplankton biomass increases the pool of organic phosphorus, which is in turn converted to phosphate by mineralization bacteria. The model has several kinetic parameters that have to be estimated based on collected data from the specific reservoir under study. 

Arguably, phosphorus (P) and iron (Fe) are the two nutrients that most impact the global marine nitrogen (N) cycle. Over the past 15 years a proliferation of new work on Fe limitation has left no doubt that this micronutrient profoundly influences nitrogen biogeochemistry over perhaps the majority of the ocean s surface. Recent work has also brought a renaissance of renewed attention to P limitation, and to its reciprocal interactions with nitrogen. 

---