Suspended solids induce increasing microbial ammonium recycling along the river‐estuary continuum of the Yangtze River

Abstract

Many large rivers worldwide are enriched with high levels of suspended solids (SS), which are known to be hotspots of many nitrogen (N) transformation processes (e.g., denitrification, nitrification). However, the influence of SS on microbial ammonium (NH 4 + ) recycling remains unclear. Water column NH 4 + regeneration rates (REGs) and potential uptake rates (U pot s) as well as community biological NH 4 + demand (CBAD) was measured in the river-estuary continuum of the third longest river in the world-Yangtze River, which has dramatic SS gradients. We found that REGs, U pot s, and CBAD all increased downriver, with higher REGs, U pot s, and CBAD in the estuary than in the river sections. The regeneration and uptake of NH 4 + were nearly balanced in the river sections, while the positive CBAD in the estuary indicated obvious NH 4 + demand of microbes. Concentrations of SS, which also control the content of chemical oxygen demand and particulate N, were the main factor influencing NH 4 + recycling rates and CBAD. SS-induced regenerated NH 4 + in the river-estuary continuum of Yangtze River was estimated to be 11.02 Â 10 8 kg N yr À1 and accounted for about 14% of total

High ammonium recycling in an anthropogenically altered Yeongsan River Estuary, South Korea

“…Our results in the dark treatment were also 22 times higher than those in the Peruvian upwelling system (Fernandez et al, 2009). The maximum value in this study (dark regeneration rate of 1.19 mmole N L −1 h −1 in July 2012) was comparable to the rates obtained from a coastal mangrove swamp in India (Dham et al, 2002), Lake Okeechobee (Hampel et al, 2019), Yangtze River (Xue et al, 2021a), and lower than those of the subtropical eutrophic Lake Taihu in China (McCarthy et al, 2007;Hampel et al, 2018;Jiang et al, 2019;Xue et al, 2021b). YRE ammonium uptake rates were higher than those observed in other estuaries, including the nitrate-rich Thames Estuary (Middelburg and Nieuwenhuize, 2000b), turbid European tidal estuaries (the Ems, Douro, and Rhine; Middelburg and Nieuwenhuize, 2000a), the West Florida Shelf (Bronk et al, 2014), Copano Bay (Bruesewitz et al, 2015), and Cochin Estuary (Bhavya et al, 2016).…”

“…YRE ammonium uptake rates were higher than those observed in other estuaries, including the nitrate-rich Thames Estuary (Middelburg and Nieuwenhuize, 2000b), turbid European tidal estuaries (the Ems, Douro, and Rhine; Middelburg and Nieuwenhuize, 2000a), the West Florida Shelf (Bronk et al, 2014), Copano Bay (Bruesewitz et al, 2015), and Cochin Estuary (Bhavya et al, 2016). However, ammonium uptake rates were similar to those observed for the Mississippi River plume (Gardner et al, 1997), a coastal mangrove swamp in India (Dham et al, 2002), St. Lucie Estuary (Hampel et al, 2019), Yangtze River (Xue et al, 2021a), a Lake Erie wetland (Lavrentyev et al, 2004;Hoffman et al, 2022), and the mesohaline region of the Loire and Scheldt estuary (Middelburg and Nieuwenhuize, 2000a). The ammonium uptake rates were also lower than the values of the Lake Okeechobee (Hampel et al, 2019) and Lake Taihu (Hampel et al, 2018;Jiang et al, 2019).…”

“…The regeneration of ammonium through active ammonium recycling is likely to supports high phytoplankton production during the springsummer season in the YRE. Previous studies have suggested that water column N recycling contributes significantly to phytoplankton N demand in aquatic environments (Bronk et al, 2014;Hampel et al, 2018;Jiang et al, 2019;Xue et al, 2021a;Xue et al, 2021b;Xu et al, 2021;Hoffman et al, 2022). In the West Florida Shelf, regenerated ammonium was sufficient to supply the ammonium demand, and supported 85% of the ammonium uptake even during blooms of Karenia brevis (Bronk et al, 2014).…”

C/N Ratio of Resuspended Sediment Regulates Phytoplankton Growth in Shallow Eutrophic Lakes

“…The total dissolved nitrogen (TDN), total dissolved phosphorus, as well as ammonium (NH 4 + –N) and nitrate (NO 3 – –N) concentrations in the water were determined using standard methods . The dissolved organic nitrogen (DON) concentration was calculated as the difference between TDN and inorganic nitrogen concentration (NH 4 + –N + NO 3 – –N), and the standard deviations for DON were determined via a propagation of error analysis.…”