Nitrification and inorganic nitrogen distribution in a large perturbed river/estuarine system: the Pearl River Estuary, China

Abstract

Abstract. We investigated the spatial distribution and seasonal variation of dissolved inorganic nitrogen in a large perturbed estuary, the Pearl River Estuary, based on three cruises conducted in winter (January 2005), summer (August 2005) and spring (March 2006). On-site incubation was also carried out for determining ammonium and nitrite oxidation rates (nitrification rates). We observed a year-round pattern of dramatic decrease in NH , accompanied by extremely high concentrations of ammonia (up to >800 µmol L −1 ) and nitrate (up to >300 µmol L −1 ). In summer, the upper estuary showed higher nitrification rates (ammonia oxidation rate ∼1.5-33.1 µmol N L −1 d −1 , nitrite oxidation rate ∼0.6-32.0 µmol N L −1 d −1 ) with lower concentrations of ammonia (<350 µmol L −1 ) and nitrate (<120 µmol L −1 ). The Most Probable Number test showed relatively lower nitrifier abundance in summer at most sampling stations, indicating a greater specific nitrification rate per cell in the warm season. Temperature appeared to control nitrification rates to a large degree in different seasons. Spatial variability of nitrification rates appeared to be controlled by a combination of many other factors such as nutrient concentrations, nitrifier abundance and dissolved oxygen (DO) concentrations. In addition to aerobic respiration, nitrification contributed significantly to the consumption of DO and production of free CO 2 at upper estuary. Nitrification-induced consumption accounted for up to approximately one third of the total waCorrespondence to: M. Dai (mdai@xmu.edu.cn) ter column community DO consumption in the upper estuary during the surveyed periods, boosting environmental stress on this large estuarine ecosystem.

Distribution, fluxes and decadal changes of nutrients in the Jiulong River Estuary, Southwest Taiwan Strait

“…This phenomenon is similar to the Yangtze [41], but it is different from the upper reach of the Pearl River Estuary of China. The latter is significantly impacted by municipal sewage from Guangzhou, where NH 4 -N is the dominant chemical species of DIN [35]. Figure 4(a), (e) and (f) also summarizes the historical datasets of NO 3 -N, SRP and DSi collected during 1982-1997.…”

“…SRP, DSi and NH 4 -N were measured based on the standard phospho-molybdenum blue, silicon molybdenum blue and indophenol blue [36] spectrophotometric procedures, respectively. NO 3 -N, NO 2 -N, and SRP were determined using an AA3 Auto-Analyzer (Bran+Luebbe Co., Germany) [35], while NH 4 -N and DSi were measured using a Tri-223 continuous Auto-Analyzer [35]. Detection limits of the AA3 Auto-Analyzer were 0.1, 0.04 and 0.08 mol L 1 for NO 3 -N, NO 2 -N and SRP/DSi, respectively.…”

“…NO 3 -N and NO 2 -N were measured by reducing NO 3 − to NO 2 − with a Cd column, and then determining NO 2 − using the standard pink azo dye spectrophotometric method [35]. SRP, DSi and NH 4 -N were measured based on the standard phospho-molybdenum blue, silicon molybdenum blue and indophenol blue [36] spectrophotometric procedures, respectively.…”

Nitrate sources and dynamics in a salinized river and estuary – a δ&lt;sup&gt;15&lt;/sup&gt;N–NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; and δ&lt;sup&gt;18&lt;/sup&gt;O–NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; isotope approach

“…DO concentrations were relatively enriched in this study (higher than 7.2 mg L −1 ), excluding the DO depleted area upstream of the HH River (lower than 5.0 mg L −1 ). (Dai et al, 2008) in South China Sea, but higher than those in the Elbe Estuary (Dähnke et al, 2008) in Europe and the San Francisco Bay estuary (Wankel et al, 2006) in the United States. The specific reasons causing such variations could potentially be linked to internal/external N source contributions and different N dynamics in the rivers and the estuaries.…”

“…Many estuarine studies have focused on tracing N sources and assessing N dynamics in large estuarine systems, such as the Elbe Estuary (Dähnke et al, 2008) and the Atlantic coast (Middelburg and Herman, 2007) in Europe, the San Francisco Bay estuary (Wankel et al, 2006), the Mississippi River estuary (Rabalais et al,1996), and the mid-Atlantic coast (Dafner et al, 2007) in the United States, and the Yangtze River estuary (Chai et al, 2009) and Pearl River estuary (Dai et al, 2008) in China. Compared to these large estuarine systems with high discharge of freshwater, the levels of freshwater discharge are relatively low in the small estuaries, which are characterized by salinization from seawater intrusion for rather long distances upstream (Graas and Savenije, 2008).…”