Interannual variations in atmospheric forcing determine trajectories of hypolimnetic soluble reactive phosphorus supply in a eutrophic lake

• Published in: Freshwater biology Vol. 59; no. 8; pp. 1646 - 1658
• Main Authors: Mackay, Eleanor B, Folkard, Andrew M, Jones, Ian D
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Science 01.08.2014; Blackwell Publishing Ltd; Blackwell; Wiley Subscription Services, Inc
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; climate change; Esthwaite Water; eutrophication; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; hypoxia; internal loading; lakes; mixing; mixing events; phosphorus; pollution load; prediction; solar radiation; soluble reactive phosphorus; summer; surface water; Synecology; temperate zones; thermal stability; wind speed; United Kingdom; British Isles, England, Cumbria, Lake District, Esthwaite Water; Freshwater environment; Esthwaite Water; Hydrobiology; Loading; Lakes; soluble reactive phosphorus; Phosphorus; mixing events; Eutrophication; Interannual variation; internal loading
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1111/fwb.12371

We tested the hypotheses that variability in soluble reactive phosphorus (SRP) loading from the hypolimnion to the epilimnion of a small, eutrophic, temperate zone lake is significant at both interannual and subannual scales, and that this variability is influenced by changes in lake thermal structure. We calculated weekly hypolimnetic fluxes of SRP, during the stratified periods of 2008 and 2009 in Esthwaite Water, U.K., and compared them with the SRP fluxes from external sources. As a result of variations in the supply of SRP from the hypolimnion, which differed by c. 80% between years, we found a 30% difference in overall SRP loading to the epilimnion between the 2 years. Despite similarities in mean summer meteorological conditions, relatively subtle differences in weather conditions during the midsummer of only 0.7 m s⁻¹ in wind speed and 8 W m⁻² in solar radiation between the 2 years resulted in two diverging trajectories of hypolimnetic SRP loading. In the first year, there was a high thermal lake stability of 102 J m⁻² on average, and a relatively shallow epilimnion until the late summer, giving rise to prolonged deep‐water anoxia and a large accumulation of SRP that was mixed into the surface waters at the end of the summer. In contrast, 30% lower thermal stability and 20% deeper epilimnetic mixing in the second year resulted in the arrest and early decline of deep‐water anoxia and SRP accumulation, leading to lower SRP fluxes to the epilimnion. Understanding this meteorologically driven variability in SRP supply is crucial for predicting nutrient loading in lakes. It is likely to become especially relevant to lakes around the globe for which the importance of internal loading is predicted to increase due to the effects of climate change.