Maximum growing depth of submerged macrophytes in European lakes

Submerged macrophytes are important elements for the structure and functioning of lake ecosystems. In this study, we used chemical and maximum colonisation depth (C_max) data from 12 European countries in order to investigate how suitable C_max may describe the impact by eutrophication. The analyses include data from 757 lakes and 919 lake years covering oligotrophic to eutrophic lakes. Overall, C_max was closely related to Secchi depth (R ² = 0.58) and less closely to chlorophyll a (R ² = 0.31), TP (R ² = 0.31) and total nitrogen, TN (R ² = 0.24). The low coefficients of determination between C_max and nutrient concentrations suggest that other response factors than nutrient-phytoplankton-light conditions are important for C_max and that it will be difficult to establish strong relationships between external nutrient loading and C_max. Yearly monitoring for 13–16 years in eight Danish lakes showed considerable year-to-year variability in C_max, which for the individual lakes only related weakly to changes in Secchi depth. The use of C_max as an eutrophication indicator is especially relevant in not very shallow lakes (maximum depth >4–5 m), not too turbid lakes (C_max >1 m) and not very humic lakes (colour <60 mg Pt/l).