Nitrogen Constrains the Growth of Late Summer Cyanobacterial Blooms in Lake Erie

Abstract

Phosphorus (P) is generally considered to be the main limiting nutrient to freshwater phytoplankton productivity. However, recent research is drawing attention to the importance of nitrogen (N) in freshwater eutrophication and N often constrains growth of cyanobacteria in small lakes. In this study we determined phytoplankton nutrient limitation in a large lake, Lake Erie during two growing seasons. During 2010 and 2011, nutrient enrichment bioassays (+P, +N and, +P and N) were conducted monthly from June through September with water collected in Maumee Bay (site MB18) and in the center of the western basin (site WB C). Nutrient concentrations were monitored every other week. At MB18, total P concentration was often >3 mol/L and nitrate concentration decreased from >250 mol/L in early summer to <1 mol/L in late summer. Nitrogen and P levels were about five-fold less at WB C. Bioassays indicated that phytoplankton nutrient limitation varied in summer, spatially, and even among phytoplankton groups. For site MB18, +P increased chlorophyll concentration in one of the eight bioassays, indicating that P did not typically limit production. For site WB C , +P increased chlorophyll concentration in six of the eight bioassays. As a result of very low ambient nitrate concentration (<5 mol/L) in late summer, +N (without P) increased chlorophyll concentration, suggesting symptoms of N-limitation. The N-fixing cyanobacterium Anabaena became dominant following N-limitation. This study highlights the need to reduce P loading to restore water quality. Furthermore, due to low nitrate concentration, the severity of the cyanobacterial blooms could be worse if not for N-limitation in western Lake Erie.

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

“…Calls to control eutrophication in Lake Erie have proposed targets for reduced P loading but have largely ignored N (Scavia et al, 2014). However, there is a growing dialogue surrounding the dual management of N and P in lacustrine systems (Gobler at al., 2016;Paerl et al, 2016), particularly as co-limitation of phytoplankton growth by both N and P has been demonstrated in the late summer in Lake Erie (Moon and Carrick, 2007;North et al, 2007;Chaffin et al, 2013;Steffen et al, 2014a). This seasonal N deficiency is consistent with reduced watershed loading of N into the lake's western basin over the past two decades (Stow et al, 2015) combined with active dissimilatory sinks for nitrate (Small et al, 2016).…”

Interactive Effects of Temperature, Nitrogen, and Zooplankton on Growth and Protein and Carbohydrate Content of Cyanobacteria from Western Lake Erie

“…Herbivores affected the response to N only in cyanobacteria (28 Sept.). Importantly, positive responses of algal growth to N generally were generally saturated by 50 -150 μM added N, which is below maximum N levels observed in western Lake Erie (typically in spring and early summer), but are above the low N levels typically observed in the late summer and fall, when cyanobacterial blooms usually occur [22]. Further, M. aeruginosa isolate growth responded positively to added N at all growth temperatures examined and A. flos-aquae did so only at 30˚C.…”

“…(primarily M. aeruginosa) during July and August, when lake dissolved inorganic N (mostly NO 3 ) concentrations are high (e.g., ≥200 μM), and then a second bloom of a N-fixing species (Anabaena spp.) under low N conditions (e.g., <10 μM or even zero) occurs in the late summer or early fall [22].…”

“…Although phosphorus may be the main driver of HABs in Lake Erie, nitrogen is important as a limiting nutrient in late summer when HABs reach their peak [22] [25]. Importantly, the interactive effects of increases in both temperature and inorganic N on cyanoHABs in the Great Lakes is not well understood, including effects on the dominant non-N-fixing vs. N-fixing cyanoHAB species in the system, and effects on algal food quality.…”

Dinâmica do fitoplâncton e assimilação de nitrato, amônio e ureia em reservatórios subtropicais com diferentes graus de trofia

“…WURTSBAUGH et al 1985;ELSER et al, 2007;CORNELISSENI et al, 2014), atuando como um co-limitante juntamente com o P (LEWIS & WURTSBAUGH, 2008;PEARL et al, 2011;CHAFFIN, et al, 2013).…”