Responses of lake phytoplankton to micronutrient enrichment: a study in two New Zealand lakes and an analysis of published data

Abstract

Natural and anthropogenic changes in nutrient concentrations can affect phytoplankton in marine and freshwater environments. However, potential micronutrient limitation of phytoplankton productivity in fresh waters is often overlooked. To investigate the responses of lake phytoplankton to micronutrient enrichment, we conducted a study in two contrasting New Zealand lakes, and analysed data from the published international literature. We undertook nutrient enrichment bioassays of phytoplankton communities sampled from a mesotrophic reservoir and an eutrophic coastal lake to determine the relative occurrence of micronutrient (iron, boron, cobalt, copper, molybdenum) and macronutrient (nitrogen, phosphorus) limitation. In the mesotrophic reservoir, phytoplankton productivity was phosphorus limited. No evidence of micronutrient limitation was found in six bioassays in summer. In the eutrophic lake, tenfold enrichment of ambient micronutrient concentrations increased the primary productivity in four of 11 bioassays. During a cyanobacterial bloom in the eutrophic lake, experimental enrichment with boron, cobalt, copper or molybdenum increased primary productivity by 40 %. These four micronutrients are commonly applied as agricultural fertiliser in the lakes catchment. Nitrogen or phosphorus enrichment had no effect on phytoplankton productivity at this time. Micronutrient limitation has been reported in more than 40 lakes internationally, and our analysis of published data suggests that the prevalence of micronutrient limitation is unrelated to lake size or trophic state. As micronutrient enrichment can significantly increase phytoplankton productivity in a range of lakes types, the potential contribution of micronutrient enrichment to eutrophication should not be overlooked.

Assessment of Microcystis growth rate potential and nutrient status across a trophic gradient in western Lake Erie

“…Recent studies of Lake Erie phytoplankton (Moon and Carrick, 2007;North et al, 2007) have demonstrated limitation by nutrients other than P and N. Additionally, trace metal limitation has been documented in surface cyanobacterial blooms (Downs et al, 2008). Therefore, it is important to assess Microcystis micronutrient status in western Lake Erie.…”

Experimental iron amendment suppresses toxic cyanobacteria in a hypereutrophic lake

“…Experimental Fe additions can trigger blooms of equatorial marine phytoplankton (Martin et al 1994, Coale et al 1996, but there is no evidence that Fe controls primary productivity at the ecosystem-level in freshwater. Instead, bottle-scale experiments have shown that Fe can be a proximate limiting nutrient of algal growth (Wurtsbaugh and Horne 1983, Twiss et al 2000, Downs et al 2008. In vitro and in vivo experiments have also shown that changes in Fe availability affect the outcome of competition among phytoplankton species (Pollingher et al 1995, Vuorio et al 2005, Molot et al 2010.…”

Significance of groundwater discharge along the coast of Poland as a source of dissolved metals to the southern Baltic Sea

“…Calculated fluxes of Co via groundwater discharge into West Neck Bay (Long Island, New York, USA) ranged from 3.4x10 2 μmol day −1 to 8.2x10 3 μmol day −1 , depending on sampling location and season. Other research has suggested that micronutrients, including B, Co, Cu, Fe, and Mo, can increase algal or cyanobacterial growth when concentrations of macronutrients (i.e., nitrogen and phosphorus) are already high and the system is already characterized as eutrophic (Zhang, 2000;Downs et al, 2008). As eutrophic conditions in coastal waters are expected to become more prevalent in the future (Rabalais et al, 2009), the role of metal micronutrients, including those associated with groundwater discharge, may become more important.…”