Nitrogen dynamics in a eutrophic lake sediment

Abstract

Nitrogen flux from sediment of a shallow lake and subsequent utilization by water hyacinth (Eichhornia crassipes [Mart] Solms) present in the water column were evaluated using an outdoor microcosm sediment-water column. Sediment N was enriched with 15N to quantitatively determine the movement of NH4-N from the sediment to the overlying water column. During the first 30 days. 48% of the total N uptake by water hyacinth was derived from sediment 15NH4-N. This had decreased to 14% after 183 days. Mass balance of N indicates that about 25% sediment NH4-N was released into the overlying water, but only 17% was assimilated by water hyacinth. NH4-N levels in the water column were very low, with very little or no concentration gradients. NH4-N levels in the interstitial water of the sediment were in the range of 30–35 mg L−1 for the lower depths (> 35 cm), while in the surface 5 cm of depth NH4-N levels decreased to 3.2 mg L−1. Simulated results also showed similar trends for the interstitial NH4-N concentration of the sediment. The overall estimated NH4-N flux from the sediment to the overlying water was 4.8 µg cm−2 day−1, and the soluble organic N flux was 5.8 µg N cm−2 day−1. Total N flux was 10.6 µg N cm−2 day−1.