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. 2017 Oct 23;7:13770. doi: 10.1038/s41598-017-13159-9

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© The Author(s) 2017

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Long-term trends (1977 to 2016) of mixing depth and orthophosphate concentrations. (a) Dotted line and triangles: mean water turnover depth (n = 40) with color code for years with mixing depth <100 m (red) and ≥100 m (blue), and regression line (f = y ₀ + a*x + b*x ² , r ² = 0.42, p = 0.08). Solid line: epilimnetic orthophosphate concentrations (n = 480) with highlighted periods of water turnover (January to April, light blue) and regression line (f = y ₀ + a*x + b*x ² + c*x ³ , r ² = 0.43, p < 0.05). The period 2009 to 2016 is enlarged to show that epilimnetic phosphorus enrichment stopped since the year 2013. (b) Relationship between mean mixing depth and epilimnetic orthophosphate for the years 1977 to 2016 (f = y ₀*e^b*x, r ² = 0.60, p < 0.001), and (c) 1995 to 2016 (f = b*x + a, r ² = 0.79, p < 0.001) with colors as in (a). (d) Hypolimnetic orthophosphate concentrations (solid line, n = 480) with highlighted periods of water turnover (January to April, light blue) and regression line (f = y ₀ + a*x + b*x ² + c*x ³, r ² = 0.53, p = < 0.01). Grey shaded areas in (a,c,d) show confidence intervals.