Nitrogen mineralization and immobilization in sediments of the East China Sea: Spatiotemporal variations and environmental implications

Abstract

Nitrogen (N) mineralization and immobilization are important processes of N biogeochemical cycle in marine sediments. This study investigated gross N mineralization (GNM) and NH4+ immobilization (GAI) in the sediments from the East China Sea (ESC), using 15N stable isotope dilution technique. Results show that measured rates of GNM and GAI ranged from 0.04 to 6.1 µg N g−1 d−1 and from undetectable to 9.82 µg N g−1 d−1, respectively. In general, both GNM and GAI rates were significantly greater in summer as compared to winter, and the high rates occurred mainly in the muddy area and increased gradually from the Yangtze Estuary to Zhe‐Min Coastal muddy areas. The GNM and GAI processes were related closely to sediment temperature, pH, ammonium (NH4+), nitrate (NO3−), total organic carbon (TOC), and total nitrogen (TN) contents in the muddy area, while they were associated tightly with sediment temperature, pH, NH4+, TOC, TN, sulfide, and Fe(III) concentrations in the sandy area. In addition, the total mineralized and immobilized N in the East China Sea (ECS) were estimated to be approximately 2.1 × 106 t N yr−1 and 2.7 × 106 t N yr−1, respectively. Overall, these results highlight the importance of N mineralization and immobilization in controlling the N budget in the ECS and improve the understanding of both processes and associated controlling mechanisms in the coastal marine ecosystem.

Nitrogen Fixation in the Intertidal Sediments of the Yangtze Estuary: Occurrence and Environmental Implications

“…The measured rates (0.39 to 7.74 nmol N g −1 dry sediment hr −1 ) of nitrogen fixation in this study are comparable to the values reported from other estuarine and coastal sediments (Table ), and the rates are much lower than the denitrification rates (12.04 to 67.13 nmol N g −1 dry sediment hr −1 ) while approximately equivalent to the anammox rates (0.94 to 6.61 nmol N g −1 dry sediment hr −1 ) in the study area (Hou et al, ). If the annual mean rate (1.65 nmol N g −1 dry sediment hr −1 ) of sediment nitrogen fixation obtained in this study is extrapolated to the entire Yangtze Estuary, it is roughly estimated that approximately 1.02 × 10 5 t of nitrogen was fixed annually into the estuarine and coastal environment, given that the bulk density of dry sediment is about 1.19 g cm −3 (Lin et al, ). This calculated amount accounts for about 9.3% of the terrigenous inorganic nitrogen (1.1 × 10 6 t) transported annually into the Yangtze Estuary (Hou et al, ).…”

Ammonium Production and Removal in the Sediments of Shanghai River Networks: Spatiotemporal Variations, Controlling Factors, and Environmental Implications

“…Temperature is an important factor regulating nitrogen transformations, because it affects microbial metabolism directly (Grenon et al, ). The warm season favors the activities of these nitrogen transforming microbes (Jäntti et al, ; Lan et al, ; Lin, Hou, Liu, Li, Zheng, et al, ; Teal et al, ). Interestingly, previous studies reported that temperature is not an important factor controlling the DNRA activity in marine and estuarine sediments (Deng et al, ; Jäntti et al, ; Lisa et al, ; McTigue et al, ), but other studies suggest that higher temperatures enhance DNRA rates in coastal and lacustrine sediments (Brin et al, ; Gardner et al, ; Giblin et al, ).…”

“…Gross nitrogen mineralization and NH 4 + immobilization rates were related positively to Eh of overlying water (Table ), mainly because nitrogen mineralization and NH 4 + immobilization processes often occur under aerobic conditions (Updegraff et al, ; Zhou et al, ). NO 3 − is a significant factor regulating the gross nitrogen mineralization because it is an electron acceptor that can oxidate the organic material in aerobic conditions (Lin, Hou, Liu, Li, Zheng, et al, ; Pena et al, ).…”

“…Subsequently, one half of the vials were sacrificed immediately by addition of 100 μL saturated HgCl 2 , and the remaining vials were incubated in the dark at in situ temperature for 12 h on a shaker table (150 rpm/min) and then stopped by HgCl 2 , and the vials were incubated 12 h. The generated 15 NH 4 + of 0 and 12 h incubations were determined by OX/MIMS (Yin et al, ). The potential rates of nitrogen fixation were calculated by the following equation: where F (μg N g −1 d −1 ) is the potential rates of nitrogen fixation, H i and H f (μg N g −1 ) are the respective concentrations of 15 NH 4 + in initial and final sediment slurries, and t (d) is the time of incubation.The gross nitrogen mineralization and NH 4 + immobilization rates were determined using the nitrogen isotope dilution technique, as described by Lin, Hou, Liu, Li, Zheng, et al (). Slurries were made and preincubated as described above.…”

“…NH 4 + was then extracted with 2 M KCl from the initial and final sediment slurries (Lin, Hou, Liu, Li, Yin, et al, ). After extraction, the total NH 4 + ( 14 NH 4 + plus 15 NH 4 + ) in extractants were analyzed by a continuous‐flow nutrient autoanalyzer, and the 15 NH 4 + determined by OX/MIMS (Lin, Hou, Liu, Li, Yin, et al, and Lin, Hou, Liu, Li, Zheng, et al, ; Yin et al, ). Gross nitrogen mineralization and NH 4 + immobilization rates were quantified as described previously (Lin, Hou, Liu, Li, Yin, et al, and Lin, Hou, Liu, Li, Zheng, et al, ).…”