Nitrification and ammonium dynamics in Taihu Lake, China: seasonal competition for ammonium between nitrifiers and cyanobacteria

Abstract

Abstract. Taihu Lake is hypereutrophic and experiences seasonal, cyanobacterial harmful algal blooms. These Microcystis blooms produce microcystin, a potent liver toxin, and are linked to anthropogenic nitrogen (N) and phosphorus (P) loads to lakes. Microcystis spp. cannot fix atmospheric N and must compete with ammonia-oxidizing and other organisms for ammonium (NH + 4 ). We measured NH + 4 regeneration and potential uptake rates and total nitrification using stable-isotope techniques. Nitrification studies included abundance of the functional gene for NH + 4 oxidation, amoA, for ammonia-oxidizing archaea (AOA) and bacteria (AOB). Potential NH + 4 uptake rates ranged from 0.02 to 6.80 µmol L −1 h −1 in the light and from 0.05 to 3.33 µmol L −1 h −1 in the dark, and NH + 4 regeneration rates ranged from 0.03 to 2.37 µmol L −1 h −1 . Nitrification rates exceeded previously reported rates in most freshwater systems. Total nitrification often exceeded 200 nmol L −1 d −1 and was > 1000 nmol L −1 d −1 at one station near a river discharge. AOA amoA gene copies were more abundant than AOB gene copies (p < 0.005) at all times; however, only abundance of AOB amoA (not AOA) was correlated with nitrification rates for all stations and all seasons (p < 0.005). Nitrification rates in Taihu Lake varied seasonally; at most stations, rates were highest in March, lower in June, and lowest in July, corresponding with cyanobacterial bloom progression, suggesting that nitrifiers were poor competitors for NH + 4 during the bloom.Regeneration results suggested that cyanobacteria relied extensively on regenerated NH + 4 to sustain the bloom. Internal NH + 4 regeneration exceeded external N loading to the lake by a factor of 2 but was ultimately fueled by external N loads. Our results thus support the growing literature calling for watershed N loading reductions in concert with existing management of P loads.

A streamlined method to quantify the fates of 15N in seawater samples amended with 15N‐labeled organic nitrogen

“…A calibration curve is established for each batch run using standard solutions with the same salinity as the samples. The overall precision of 15 NH 4 + measurement with AIRST‐HPLC is generally within ±3%, and accuracy is close to 100%, based on previous studies (e.g., McCarthy et al ; Hampel et al ).…”

Nitrogen cycling in Sandusky Bay, Lake Erie: oscillations between strong and weak export and implications for harmful algal blooms

“…In comparable systems, remineralization rates are on the same order as uptake rates, and this recycling represents a crucial N supply for cHABs (Hampel et al, 2018). The observation of higher TKN concentrations in Sandusky Bay than in the Sandusky River (Fig.…”

Resistant ammonia‐oxidizing archaea endure, but adapting ammonia‐oxidizing bacteria thrive in boreal lake sediments receiving nutrient‐rich effluents

“…However, even AOB could not grow under extreme wastewater influence in Saarijärvi and Lievestuore. As AOB abundance and nitrification rates are commonly tightly linked in ammonium-rich environments (e.g., Di et al, 2009;Hampel et al, 2018), the high abundance of AOB suggests also high nitrification activity at wastewaterinfluenced sediments.…”