Urea in Lake Erie: Organic nutrient sources as potentially important drivers of phytoplankton biomass

Abstract

Significant evidence shows that nitrogen (N) supply may influence microbial community structure and, in some cases, the rate of primary productivity in fresh waters. To date, however, most focus has been on dissolved inorganic N (i.e., ammonia and nitrate), or dinitrogen gas. Far less is known about the effects of dissolved organic N such as urea on plankton activity, although this compound is both produced by in-lake processes and is a significant component of external loading. We evaluated the urea distribution and the activity of the major enzyme responsible for its assimilation (urease) in Lake Erie, which has a significant history of eutrophication. During 2012 and 2013, lake-wide surveys estimated surface urea concentrations and urease activity, along with phytoplankton composition and biomass, cyanobacterial toxins (microcystin), major nutrients and other physico-chemical parameters. In parallel, in situ 48-hour microcosm experiments were executed to test whether different chemical forms of dissolved N could stimulate phytoplankton biomass. Results confirmed urea was a bioavailable form of N with in situ urea turnover times ranging from hours (for summer, i.e., Aug 2012 and July 2013) to days (May 2013). Furthermore, we observed a positive correlation between urease activity and both microcystin concentrations and cyanobacterial dominance. Results also indicated a potential seasonal shift in the nutrient limiting phytoplankton biomass from phosphorus (P) to N. Our results reinforce the importance of both N and P in promoting phytoplankton growth and highlighted the need to consider organic nutrient sources as potentially important drivers of cyanobacterial blooms and toxin production.

Urea Fluctuations in Stream Baseflow across Land Cover Gradients and Seasons in a Coastal Plain River System

“…levels in the Manokin watershed ranged from 0.015 to 0.221 mg N/L, which was consistent with published studies documenting urea-N concentrations of <0.001-1.441 mg N/L in freshwater and brackish environments (Table 3). Even though urea-N is widely recognized for its role in eutrophying freshwaters (Finlay et al 2010;Belisle et al 2016) and coastal zones , it is rarely included in most water quality analyses (Paerl et al 2016). Peak urea-N values that we observed in the Manokin Basin (0.221 mg N/L) were generally sevenfold lower than those reported by Glibert et al (2005) in nearby waters (1.441 mg N/L).…”

“…Nevertheless, 14% of baseflow urea-N concentrations exceeded the 0.06 mg N/L threshold that could potentially trigger harmful algal blooms (Glibert et al 2004). Even though urea-N is widely recognized for its role in eutrophying freshwaters (Finlay et al 2010;Belisle et al 2016) and coastal zones , it is rarely included in most water quality analyses (Paerl et al 2016). Results from the Manokin River watershed clearly demonstrate that urea-N is a ubiquitous form of DON in nontidal streams and tidal rivers, and therefore highlight the importance Notes: GW, groundwater.…”

Photosynthetic response to nitrogen source and different ratios of nitrogen and phosphorus in toxic cyanobacteria, Microcystis aeruginosa FACHB-905

“…In addition, Donald et al (2011) explored that the NH 4 -N and urea favored non-heterocystous cyanobacteria, and microcystin production was increased by up to 13-fold after N added. Belisle et al (2016) also evaluated the urea distribution and the urease activity in Lake Erie and confirmed that organic nitrogen source was an important driver of cyanobacterial blooms and toxin production.…”

Comparative effects of ammonium, nitrate and urea on growth and photosynthetic efficiency of three bloom‐forming cyanobacteria

“…Historically, N in fertilisers were based on nitrate () and ammonium (), but in recent years, there has been a shift towards urea (CO(NH 2 ) 2 )‐based fertilisers (Belisle et al., ; Glibert et al., ). Although /‐based fertilisers are still used today in some regions, urea‐based fertilisers are now the primary N source applied to agricultural landscapes (Glibert et al., ).…”

“…As organisms strategically select pathways that offer the greatest energetic return or least amount of manipulation, it is possible that urea could be a more energetically favourable N source compared to NH þ 4 . Historically, N in fertilisers were based on nitrate (NO À 3 ) and ammonium (NH þ 4 ), but in recent years, there has been a shift towards urea (CO(NH 2 ) 2 )-based fertilisers (Belisle et al, 2015;Glibert et al, 2006). Although NO À 3 /NH þ 4 -based fertilisers are still used today in some regions, urea-based fertilisers are now the primary N source applied to agricultural landscapes (Glibert et al, 2014).…”