If ammonia was accumulating in the sediment
NH4 certainly does accumulate in sediments. This:Inorganic N is not stored as NH3/NH4, NO2, NO3 in the sediment.
The mean levels of ammonium concentration in the water column were 0.60 ± 0.18 at Bawe and 0.60 ± 0.16 µM at Chapwani........... Pore water ammonium concentration differed significantly between the sites with 342 ± 68.4 µM of ammonium measured at Chapwani and 690 ± 81.2 µM at Bawe
Measurements of nutrient fluxes revealed that there were movements of ammonium and soluble reactive phosphate from the sediment into the water column