Nutrient exchange across sediment-water interface in wetlands

In order to reducing benthic nutrients release,we investigate the effectiveness of three physical amelioration measures (fine sand covered,sediment loosened,and reed planting)on the diffusive flux from sediment-overlying water.An in-situ sampling technique (Peeper)was employed to obtain the vertical distribution of nutrient elements and diffusive fluxes on the Nansi Lake in China.The results show that in the case of all three amelioration measures,the sediment water content and porosity have increased by 91% and 54% compared to the Control Treatment,respectively.The nutrient profiles NH₄⁺ and PO₄^3- in pore water on the sediment-water interface exhibit a nearly exponential increase with depth with a concentration maximum being at the 8 cm depth.The contents of NH₄⁺, PO₄^3- and NO₃^- decrease significantly in pore water after reed planting.With all three amelioration measures,the proportion of NH₄Cl-extractable PO₄^3- to the total content of PO₄^3- in sediments is found to be decreased in upmost sediments,whereas those of bicarbonate dithionite (BD)BD-extractable PO₄^3- are increased as the result of amelioration measures.Such result is enhanced by reed planting.The diffusive flux across the sediment-water interface could be calculated using the Fick's First Law of diffusion.It is found that the diffusive fluxes of NH₄⁺and PO₄^3- have been reduced from 57.47～72.19 μg/(m²·d)and 2.55～3.21μg/(m²·d)to -95.54～-130.94 μg/(m²·d)and 1.50～2.05 μg/(m²·d)after sediment loosened.The measure of surface sediment loosening can decrease the diffusive fluxes of NH₄⁺,PO₄^3- from surface sediments.The measure is thus recommended as one of the effective controls towards the internal nutrient load reduction in lakes.