Anthropogenic oligotrophication via liming: Long-term phosphorus trends in acidified, limed, and neutral reference lakes in Sweden

Abstract

Restoration of acidified lakes by liming does not, in many cases, improve productivity to a pre-acidified state. We hypothesize that the poor recovery detected in many of these lakes is due to constrained in-lake phosphorous (P) cycling caused by enhanced precipitation of metals in higher pH, limed waters. Long-term (1990-2012) data for 65 limed, circum-neutral (pH 6-8), and acidified lakes in Sweden were analyzed to determine trends for P and potential drivers of these trends. Limed lakes not only had lower mean values and stronger decreasing trends for total P than non-limed lakes, but they also had the highest percentage of decreasing trends (85 %). A P release factor (Hypolimnetic P/Epilimnetic P) was developed to elucidate differences in internal P cycling between lake groups. Consistently, lower P release factors in limed lakes show limitation of internal P cycling during summer months that may be a factor limiting P bioavailability and thus productivity of these systems.

Fig. 1

Geographical location of lakes included in the study

Fig. 2

Box-plot of epilimnetic TP by lake group (1990–2012). In each box, the central line is the median value, the upper and lower limits of each box are the lower and upper quartiles (25 and 75 %), and the whiskers extend 1.5 times the interquartile range

Fig. 3

Box-plot of standardized Theil slope values (delta ug TP L⁻¹ yr⁻¹/mean epilimnetic TP) by lake group. In each box, the central line is the median value, the upper and lower limits of each box are the lower and upper quartiles (25 and 75 %), and the whiskers extend 1.5 times the interquartile range

Fig. 4

Changes in annual PRF-value index, by lake group, calculated from PRF-values from 1990 to 2011. PRF is the P release factor (i.e., hypolimnetic TP/epilimnetic TP)

Fig. 5

Frequency of PRF (hypolimnetic TP/epilimnetic TP)-values by lake group from 1990 to 2011. Summer is defined as the period from June to the first half of September. Only one PRF-value was used for each summer according to monthly data priority (Table 10.1007/s13280-014-0573-0), thus the prioritized months (June and July) carry more weight