Regulators of Ammonia Volatilization

Photosynthetic activity in the water column and pH Submerged aquatic vegetation and periphyton communities provide an ideal environment for pH alternation in the water column. 

FIGURE 8.32 Diel fluctuations in pH of the water column of reservoirs (a) dominated algae and (b) covered with floating mats of water hyacinths. 

Alkalinity and buffer capacity Dissociation of ammonium ions to ammonia results in the production of hydrogen ions. Unless the water column or soils are well buffered, the medium can be acidified and the rate of ammonia volatilization can decrease. Thus, a water column with high alkalinity and calcium carbonate content can buffer the system and maintain high-pH conditions. Alkalinity is affected by the balance between photosynthesis and respiration by algae and submersed macrophytes in the water column. Ammonia volatilization losses are directly proportional to the alkalinity of the system. 

FIGURE 8.33 Influence of various factors controlling ammonia volatilization in wetlands. 

Ammonia volatilization is recognized as the major process by which nitrogen fertilizers are lost from paddy fields, especially when urea or other ammonium-based fertilizers are surface applied to the water column. In tropical climates, high water temperatures associated with algal activity in the water column are conducive to enhance volatilization of added fertilizers. Urea, a common fertilizer for rice in Asia, is rapidly hydrolyzed within the week after application to submerged soils. Ammonia originating from the hydrolyzed urea accumulates in floodwater, and the peak concentration of ammonia in the floodwater of tropical rice fields typically occurs within 1-5 days after urea 

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