Artificial ponds as hotspots of nitrogen removal in agricultural watershed

Abstract

Small waters, like ponds, are the most abundant freshwater environments, and are increasingly recognized for their function in ecosystem service delivery. In agricultural watershed, artificial ponds play an essential role in reducing nitrogen pollution. However, until now artificial ponds remain the least investigated part of water environments. The importance of microbial activities has seldom been discussed, which makes the microbial pathways and processes rates in nitrogen removal poorly understood. To illustrate the role of artificial ponds in microbial nitrogen removal in agricultural watersheds, 21 pond sediments and 11 soils are collected in an agricultural watershed of China. Results show that surface sediments in ponds carry significantly higher dissolved inorganic nitrogen (9.1-21.9 mg/kg) and total organic matter (64.8-113.0 g/kg) compared to the surrounding agricultural soils. High rates of microbial nitrogen removal in ponds (12.4-25.5 nmol N g -1 h -1 ) are observed, which are 2-9 times higher than those in dryland soils. In pond sediments, denitrification dominates (> 90% N-loss) the microbial nitrogen removal process with only a minor contribution of anaerobic ammonium oxidation. A high potential of N 2 O production (up to 9.4 nmol N g -1 h -1 ) occurs in ponds along with the rapid nitrogen removal. For denitrifier genes, nir gene are always more abundant than nosZ gene.Additionally, the nirS gene is more abundant under flooded conditions, while nirK gene prefers higher dissolved oxygen and NO 3 -in drylands. These findings present essential information on the mechanisms of microbial nitrogen removal in ponds, and highlight the ecosystem function of ponds in agricultural watersheds.

Effect of Aquaculture Reclamation on Sediment Nitrates Reduction Processes in Mangrove Wetland

“…The nirS (3.80 ± 0.47 × 10 8 copies g −1 and 8.01 ± 2.27 × 10 8 copies g −1 in mangrove and aquaculture, respectively) and nrfA (4.58 ± 0.19 × 10 8 copies g −1 and 3.11 ± 0.43 × 10 8 copies g −1 in mangrove and aquaculture, respectively) genes were detected with high copy numbers in aquaculture and mangrove surface sediments, being higher than those reported for marine, estuarine, and coastal sediments [4,9,12,13,52]. The ANAMMOX 16S gene abundances (2.57 ± 0.32 × 10 6 copies g −1 and 10.3 ± 0.48 × 10 6 copies g −1 in mangrove and aquaculture, respectively) in this study are of considerable value when compared with other aquaculture [51,53] and mangrove ecosystems [27].…”

“…This is mainly due to the fact that we only collected the winter samples, and incubation occurred at a low temperature (~16 • C). Similarly, the denitrification (10.96 ± 1.22 nmol g −1 h −1 ), anammox (0.37 ± 0.02 nmol g −1 h −1 ), and DNRA rates (1.39 ± 0.10 nmol g −1 h −1 ) in aquaculture surface sediments (0-5 cm) were also much lower than those reported in other aquaculture ecosystems [51]. Previous studies have shown that N loss in pond surface sediments was higher than in other natural habitats (including tidal rivers, marines, and reservoirs) due to human nutrients and organic matter inputs [51].…”

“…Similarly, the denitrification (10.96 ± 1.22 nmol g −1 h −1 ), anammox (0.37 ± 0.02 nmol g −1 h −1 ), and DNRA rates (1.39 ± 0.10 nmol g −1 h −1 ) in aquaculture surface sediments (0-5 cm) were also much lower than those reported in other aquaculture ecosystems [51]. Previous studies have shown that N loss in pond surface sediments was higher than in other natural habitats (including tidal rivers, marines, and reservoirs) due to human nutrients and organic matter inputs [51]. The nirS (3.80 ± 0.47 × 10 8 copies g −1 and 8.01 ± 2.27 × 10 8 copies g −1 in mangrove and aquaculture, respectively) and nrfA (4.58 ± 0.19 × 10 8 copies g −1 and 3.11 ± 0.43 × 10 8 copies g −1 in mangrove and aquaculture, respectively) genes were detected with high copy numbers in aquaculture and mangrove surface sediments, being higher than those reported for marine, estuarine, and coastal sediments [4,9,12,13,52].…”

Nitrate Addition Increases the Activity of Microbial Nitrogen Removal in Freshwater Sediment

“…29 N 2 and 30 N 2 signals in the tubes were detected with a membrane inlet mass spectrometry (MIMS, HPR40, Hiden, Warrington, UK). Detailed methods are described in Cai, et al [ 35 ].…”

“…The concentration of N 2 O in the headspace gas was detected by means of gas chromatography (GC-2014C, Shimadzu, Kyoto, Japan). Detailed methods are described in Cai, et al [ 35 ].…”