## 3 Results  
The concentrations of the OP in the lake water showed different dynamics depending on the treatment applied. In the control mesocosom the OP concentration showed a rising tendency throughout the experiment duration and increased from 0.52 to 0.61 mg PO4\({}^{3-}\) L\({}^{-1}\) (Figure 5a). Consequently, the OP mass balance for this mesocosom was positive (Figure 5b). This indicates release processes due to the decomposition of the organic material without the reuse of the free phosphate (limited light access). Compared to control, in the chambers with laminates and modules, a different pattern in the OP dynamics was clearly visible. The OP concentration decreased starting from the very initial stage of the experiment. This effect was seen already after 3 days--the OP concentration continued to decrease while an opposite change took place in the control mesocosom (Figure 5a). Initially, both, laminates and modules, showed similar levels of OP elimination, lowering the OP availability by about 17-18% within 7 days compared to the initial level and 24-26% compared to the control chamber (Figure 5a). At this point, the OP mass balance was thus clearly negative in both treatments (Figure 5b). At longer exposure, the laminates were not able to force a further decline, and the OP concentration started to rise, almost reaching the initial OP level (Figure 5a). However, the OP concentration remained at least 15% lower compared to the control mesocosom for the next 35 days (Figure 5a). Modules, in contrast, showed continuous OP elimination lasting throughout the experiment duration (~40 days) and did not show any signs of approaching their sorption capacity (Figure 5a). Compared to the initial conditions, at the end of the experiment, the modules reduced the OP concentration by 45% (from 0.51 to 0.28 mg PO4\({}^{3-}\) L\({}^{-1}\)) while an increase of ca. 18% took place in the control mesocosom (0.52 to 0.61 mg PO4\({}^{3-}\) L\({}^{-1}\)). Thus, the OP balance in the treatment with modules was negative and accounted for ~42.3 mg PO4\({}^{3-}\) L\({}^{-1}\) (which was 16 times more compared to laminates (~2.6 mg PO4\({}^{3-}\) L\({}^{-1}\)) (Figure 5b)). With respect to the control, in the lake water treated with modules, the OP concentration was 54% lower at the end of the experiment (0.28 vs. 0.61 mg PO4\({}^{3-}\) L\({}^{-1}\)) (Figure 5a). We left the incubation chamber with modules for the next two weeks and observed slight but continuous OP sorption onto modules (with the OP concentration reaching ca 0.24 mg PO4\({}^{3-}\) L\({}^{-1}\) after 2 months). To further compare the performance of laminates and modules, we calculated the total mass of the OP removed by laminates and modules (Table 1). The modules removed 2.7 times more OP compared to laminates. At the total areas of calcite layer of 740 cm\({}^{2}\) and 1500 cm\({}^{2}\) for modules and laminates, respectively, this produced a ca. 6-fold difference in the P removed per unit of surface area with a clear advantage for the modules. However, at the total mass of calcite applied (300 vs. 3.6 g, accordingly), this yielded almost 30 times more P removed by laminates when expressing the OP uptake per gram of the calcite material (Table 1). The pH of the lake water tended to increase during the experiment and changed from 7.8-7.9 to 8.1-8.3 (Figure 6a). The treatment applied had a clear effect on the lake water pH. In the presence of laminates and modules, depending on the treatment duration, the pH was 0.05-0.22 lower compared to the control chamber, and this difference could be seen throughout the experiment duration, with the pH being slightly lower under the