Phosphorus gradients

Following are the examples of wetlands, where long-term phosphorus loading has resulted in soil phosphorus gradients ... 

FIGURE 9.3 Soil and water column phosphorus gradients resulting from point sources of external loading to a wetland. 

FIGURE 9.25 Influence of soil phosphorus gradients (distance from point source loading) on soil EPCq (equilibrium phosphorus concentration at which point adsorption equals desorption) (Clark, 2002). 

FIGURE 17.9 An experimental transect established along soil phosphorus gradient has been used by a number of investigators to study biogeochemical processes in soil and water column. 

FIGURE 17.20 Ratio of microbial biomass phosphorus to total phosphorus in soils along soil phosphorus gradient in WCA-2A. (From Chua, 2000.)... 

FIGURE 17.31 Relationship between extractable ammonium nitrogen and nitrification rates in surface soils along phosphorus gradient in the WCA-2A. (From White and Reddy, 2003.)... 

Doran, R. R, T. V. Armentano, L. D. Whiteaker, and R. D. Jones. 1997. Marsh vegetation patterns and soil phosphorus gradients in the Everglades ecosystem. Aquat. Bot. 30 1-19. 

McKee, K. L., Feller, I. C., Popp, M. and Wanek, W. (2002) Mangrove isotopic (81SN and 813C) fractionation across a nitrogen vs. phosphorus limitation gradient. Ecology 83, 1065 1075. 

Physico-chemical characteristics of the soils were summarized in Table 1. The values were comparable to that described in the previous reports about the SERS (Doi and Sakurai 2003 Doi et al. 2004 Sakurai et al. 1998). The one-way ANOVA indicated that most of the soil variables significantly reflected the land degradation with high values of bulk density, sand content and exchangeable acidity, and low values of moisture content, pH, OM, base (K, Ca, Mg) contents, EC, CEC, base saturation rate, TN and TC contents, available phosphorus and MPN on the glucose medium with no antibiotics. These results also told that the human activities induced several soil environmental gradients. 

Thus, the characteristic topographic function increases continuously from the surface (z = z0) to the lake bottom (z = 0) where it becomes infinitely large. In fact, at the lake bottom a tiny lake volume stays in contact with a finite sediment area. This explains the great spatial and temporal gradients often found close to the bottom of lakes for compounds which are exchanged at the sediment-water interface (oxygen, phosphorus, methane, etc.). 

The gradient is larger for Equation 2 than for Equations 3 and 4 because the trans influence of PPh3 is lower than that of PEt3. These relationships are sufficiently accurate to make a useful calculation of an unknown coupling constant when the result for an analogous complex with a different phosphorus donor is available. 

Figure 2.2 Separation of PolyPs of low molecular weight by ion-exchange chromatography on Dowex 1 XIO in a KC1 gradient. The numbers 1-12 represent the number of phosphorus atoms in the PolyP molecules constituting the various fractions (Matsuhashi, 1963).

---