Long-term phosphorus reduction and phytoplankton responses in an urban lake (USA)

Eutrophication is one of the primary factors causing harmful cyanobacteria blooms in freshwater lakes. This study investigated long-term changes water quality and summer phytoplankton assemblages Oswego Lake, OR, USA, relation to phosphorus reduction through hypolimnetic aeration alum applications. Both were sampled biweekly during summers from 2001 2013. The concentrations total phosphorus, soluble reactive nitrogen decreased 66%, 93% 31%, respectively, response treatments since 2005. Summer showed a 62% biovolume shift dominance (2001–2005) diatom chlorophyte (2006–2013). Cluster analysis identified four statistically different groups (denoted Groups 1–4). Nonmetric multidimensional scaling indicated that associated with conditions. Group 1 occurred prior was primarily comprised cyanobacteria, conditions high nutrients production. 2, dominated by chlorophytes, between surface application. 3 diatoms after 4 included R-strategist quickly respond environmental years following injection, drawdown, inflow treatment. reduced lake. We conclude these lake management practices had strong effects on both production community compositions phytoplankton, advocate for future studies large-scale climate impacts ecosystems identify corresponding best practices.