Sandusky Bay, Lake Erie, receives high nutrient loadings (nitrogen and phosphorus) from the Sandusky River, which drains an agricultural watershed. Eutrophication and cyanobacterial harmful algal blooms (cyanoHABs) persist throughout summer. Planktothrix agardhii is the dominant bloom-forming species and the main producer of microcystins in Sandusky Bay. Non-N₂ fixing cyanobacteria, such as Planktothrix and Microcystis, thrive on chemically reduced forms of nitrogen, such as ammonium (NH₄⁺) and urea. Ammonium regeneration and potential uptake rates and total microbial community demand for NH₄⁺ were quantified in Sandusky Bay. Potential NH₄⁺ uptake rates in the light increased from June to August at all stations. Dark uptake rates also increased seasonally and, by the end of August, were on par with light uptake rates. Regeneration rates followed a similar pattern and were significantly higher in August than June. Ammonium uptake kinetics during a Planktothrix-dominated bloom in Sandusky Bay and a Microcystis-dominated bloom in Maumee Bay were also compared. The highest half saturation constant (K_m) in Sandusky Bay was measured in June and decreased throughout the season. In contrast, K_m values in Maumee Bay were lowest at the beginning of summer and increased in October. A significant increase in V_max in Sandusky Bay was observed between July and the end of August, reflective of intense competition for depleted NH₄⁺. Metatranscriptome results from Sandusky Bay show a shift from cyanophycin synthetase (luxury NH₄⁺ uptake; cphA1) expression in early summer to cyanophycinase (intracellular N mobilization; cphB/cphA2) expression in August, supporting the interpretation that the microbial community is nitrogen-starved in late summer. Combined, our results show that, in late summer, when nitrogen concentrations are low, cyanoHABs in Sandusky Bay rely on regenerated NH₄⁺ to support growth and toxin production. Increased dark NH₄⁺ uptake late in summer suggests an important heterotrophic contribution to NH₄⁺ depletion in the phycosphere. Kinetic experiments in the two bays suggest a competitive advantage for Planktothrix over Microcystis in Sandusky Bay due to its higher affinity for NH₄⁺ at low concentrations.

伊利湖的桑达斯基海湾从桑达斯基河接收大量的营养物（氮和磷），桑达斯基河排泄了一个农业流域。整个夏天持续发生富营养化和蓝藻有害藻华（cyanoHAB）。浮游植物琼脂（Planktothrix agardhii）是桑达斯基湾（Sandusky Bay）的主要开花形成物种，也是微囊藻毒素的主要生产者。非固定氮_2的蓝细菌（例如Planktothrix和Microcystis）可通过化学还原形式的氮（例如铵（NH ₄ ⁺）和尿素）获得繁荣。在桑达斯基湾，对铵的再生，潜在的吸收率以及微生物群落对NH ₄ ^+的总需求进行了量化。潜在的NH ₄⁺从6月到8月，所有气象站的采光率都有所提高。暗吸收率也随季节增加，到8月底，与暗吸收率相当。再生率遵循类似的模式，八月份的再生率显着高于六月。铵摄取期间动力学Planktothrix桑达斯基湾-dominated开花和微囊-dominated莫米湾绽放进行了比较。六月，测量了桑达斯基湾的最高半饱和常数（K _m），并在整个季节内降低了饱和常数。相比之下，莫米湾的K _m值在夏季初最低，在10月增加。V _max显着增加在7月至8月底之间观察到桑达斯基湾的NH ₄ ⁺竞争激烈。桑达斯基湾的转录组结果显示，夏季初从氰霉素合成酶（豪华的NH ₄ ⁺摄取；cphA1）表达转变为八月份的氰霉素酶（胞内N迁移；cphB / cphA2）表达，这支持了微生物群落氮缺乏的解释。在夏末。综合起来，我们的结果表明，在夏末，当氮浓度较低时，桑达斯基湾的cyanoHAB依靠再生的NH ₄ ⁺来支持生长和毒素产生。暗NH ₄ ⁺增加夏末的吸收表明对营养层中NH ₄ ^+的消耗具有重要的异养作用。在两个托架动力学实验表明为竞争优势Planktothrix了微囊藻在桑达斯基湾由于对NH其较高的亲和力₄ ⁺在低浓度。