Phosphorus enrichment limited

In contrast, an open ocean phosphorus enrichment experiment (CYCLOPS) conducted in the eastern Mediterranean did find evidence for P limitation of N2 fixation in bulk water (Rees et ah, 2006). 

FIGURE 8.55 Pore water ammonium profiles of select wetlands in Florida. WCA-2-F1 = water conservation area-phosphorus-enriched site WCA-2-217 = water conservation area-phosphorus-limited site Sunny Hill Farm = agricultural land converted to wetland ESA-TW = natrrral wetland used for wastewater treatment. 

Wetlands and aquatic systems are recipients of phosphorus loads from upland systems. Increased loading of phosphorus to a system can cause nitrogen limitations. The phosphorus enrichment of P-limited systems leads to eutrophication and ecosystem stress. The phosphorus cycle does not have a significant gaseous loss mechanism. Thus, most of the added P accumulates in the systems. 

Although phosphorus may no longer be limited to biota in the impacted zone, a high degree of phosphorus enrichment has induced nitrogen limitation. 

Inglett, P. W., K. R. Reddy, S. Newman, and B. Lorenzen. 2007. Increased soil stable nitrogen isotopic ratio following phosphorus enrichment historical patterns and tests of two hypotheses in a phosphorus-limited wetland. Oecologia. Online reference 10.1007/s00442-007-0711-5. 

Elwood, J. W., Newbold, J. D., Trimble, A. F. Stark, R. W. (1981). The limiting role of phosphorus in a woodland stream ecosystem effects of P enrichment on leaf decomposition and primary producers. Ecology, 62, 146-58. 

The Eastern Mediterranean is also unusual in being the largest body of water in the world in which the primary productivity is phosphorus limited. The annual phytoplankton bloom occurs in winter as soon as deep mixing occurs and ceases when the phosphate is depleted. The nitrate which remains is enriched in heavy 15N-N03. Nutrient enrichment experiments of bacteria show P limitation throughout the year. There is no evidence of Fe limitation in this system, and thus far no evidence of significant N-fixation by phytoplankton has been found. 

Substrate-induced phosphorus mineralization (SIPM) can indicate activity of microbes and associated enzymes involved in organic phosphorus mineralization. Hydrolysis of added substrates such as glucose-6-phosphate was not influenced by P enrichment in the litter layer (Chua, 2000). In the 0-10 cm soil layer, substrate hydrolysis decreased by approximately 67% at the impacted site. The mineralization coefficient (SIPM/MBP) also decreased by 54 and 74% in the litter and 0-10 cm soils, respectively, at the impacted site. These decreases suggest that phosphorus is not limiting to microbes. High substrate phosphorus hydrolysis at the reference site was attributed to limitation of labile inorganic phosphorus and high phosphatase activity. 

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