Nitrate, ammonium, and phosphorus drive seasonal nutrient limitation of chlorophytes, cyanobacteria, and diatoms in a hyper‐eutrophic reservoir

Abstract

Nitrogen (N) and phosphorus (P) inputs influence algal community structure and function. The rates and ratios of N and P supply, and different N forms (e.g., NO 3 and NH 4 ), from external loading and internal cycling can be highly seasonal. However, the interaction between seasonality in nutrient supply and algal nutrient limitation remains poorly understood. We examined seasonal variation in nutrient limitation and response to N form in a hypereutrophic reservoir that experiences elevated, but seasonal, nutrient inputs and ratios. External N and P loading is high in spring and declines in summer, when internal loading because more important, reducing loading N:P ratios. Watershed NO 3 dominates spring N supply, but internal NH 4 supply becomes important during summer. We quantified how phytoplankton groups (diatoms, chlorophytes, and cyanobacteria) are limited by N or P, and their N form preference (NH 4 vs. NO 3 ), with weekly experiments (May-October). Phytoplankton were P-limited in spring, transitioned to N limitation or colimitation (primary N) in summer, and returned to P limitation following fall turnover. Under N limitation (or colimitation), chlorophytes and cyanobacteria were more strongly stimulated by NH 4 whereas diatoms were often equally, or more strongly, stimulated by NO 3 addition. Cyanobacteria heterocyte development followed the onset of N-limiting conditions, with a several week lag time, but heterocyte production did not fully alleviate N-limitation. We show that phytoplankton groups vary seasonally in limiting nutrient and N form preference, suggesting that dual nutrient management strategies incorporating both N and P, and N form are needed to manage eutrophication.

Seasonal variation in effects of urea and phosphorus on phytoplankton abundance and community composition in a hypereutrophic hardwater lake

“…Enrichment of freshwater and marine habitats with nitrogen (N) and phosphorus (P) fuels proliferation of harmful algal blooms (Elser et al., 2007; Glibert, Maranger, Sobota, & Bouwman, 2014; Schindler, 1977). Although nutrient management strategies for freshwater ecosystems have traditionally focused on the effects of P (Bormans, Maršálek, & Jančula, 2016; Dillon & Rigler, 1974; Litke, 1999; Schindler, Carpenter, Chapra, Hecky, & Orihel, 2016), research shows that addition of N to P‐rich lakes can additionally degrade water quality, stimulate phytoplankton abundance, and promote growth of toxic cyanobacteria at the expense of other phytoplankton taxa (Andersen, Williamson, Gonzalez, & Vanni, 2019; Bunting, Leavitt, Gibson, McGee, & Hall, 2007; Conley et al., 2009; Glibert, Maranger, et al, 2014; Harris, Wilhelm, Graham, & Loftkin, 2014; Van de Waal, Smith, Declerk, Stam, & Elser, 2014). Recent studies also suggest that hypereutrophic lakes may exhibit seasonal variation in nutrient limitation, with P regulation of phytoplankton production during winter and spring, while N limitation is paramount during summer and autumn (Andersen et al., 2019; Chaffin, Bridgeman, & Bade, 2013; Hayes, Vanni, Horgan, & Renwick, 2015; Paerl et al., 2011, 2015).…”

“…Although nutrient management strategies for freshwater ecosystems have traditionally focused on the effects of P (Bormans, Maršálek, & Jančula, 2016; Dillon & Rigler, 1974; Litke, 1999; Schindler, Carpenter, Chapra, Hecky, & Orihel, 2016), research shows that addition of N to P‐rich lakes can additionally degrade water quality, stimulate phytoplankton abundance, and promote growth of toxic cyanobacteria at the expense of other phytoplankton taxa (Andersen, Williamson, Gonzalez, & Vanni, 2019; Bunting, Leavitt, Gibson, McGee, & Hall, 2007; Conley et al., 2009; Glibert, Maranger, et al, 2014; Harris, Wilhelm, Graham, & Loftkin, 2014; Van de Waal, Smith, Declerk, Stam, & Elser, 2014). Recent studies also suggest that hypereutrophic lakes may exhibit seasonal variation in nutrient limitation, with P regulation of phytoplankton production during winter and spring, while N limitation is paramount during summer and autumn (Andersen et al., 2019; Chaffin, Bridgeman, & Bade, 2013; Hayes, Vanni, Horgan, & Renwick, 2015; Paerl et al., 2011, 2015). However, predictions of the seasonality of N effects are complicated by temporal variation in the predominant chemical form of N added to surface waters (Cade‐Menum et al, 2013; Lomas, Trice, Glibert, Bronk, & McCarthy, 2002; Newell et al., 2019; Stepanauskas, Laudon, & Jørgensen, 2000), as well as inherent differences in the unique effects (i.e.…”

Comment on bg-2021-36

“…How the methods were used 30 in this study is summarized in Table 1. We used auxiliary meteorological and limnological measurements from stream gauging stations, a weather station, and thermistor string maintained by the Miami University (Renwick et al 2018;Andersen et al 2020), the locations of which are also shown in Fig. 1a.…”

What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control

“…Some of this debate is general (see, e.g. Conley et al, 2009, the mini-review by Paerl & Otten, 2016;Paerl et al, 2019;Scott et al, 2019;Andersen et al, 2020) and some specific to the waterbody studied (e.g. Müller & Mitrovic, 2015).…”

“…It is increasingly recognised that in many waterbodies summer phytoplankton is co-limited by P and N (e.g. Elser et al, 2007;Kolzau et al, 2014;Shatwell & Köhler, 2019;Andersen et al, 2020;Maberly et al, 2020), and N:P ratios are also quoted to argue for the need to reduce N loads.…”