## 4 Discussion
### Effect on Phosphorus
This means their effect on the OP availability would be achieved gradually. [PERSON] et al. [35], when testing their tea-bag design (the sorbent placed in bags), observed altered sorption kinetics compared to the sorbent applied as powder and explained it with a physical influence of the bag material, limiting the water exchange between the bag interior and the surrounding solution. Such an effect was rather not possible in the case of our study as we did not observe any kinetic difference between the OP removal when using loose calcite and calcite layer in modules (both with and without mesh coverage) in the prototype tests [39]. Still, in field applications, the kinetics of OP uptake by modules can be strongly affected by specific in-lake conditions. In particular, OP delivery to the calcite layer can be limited under field conditions compared to laboratory tests. Mixing was applied in our experiment to assure a contact between the lake water and calcite layer in both carriers (laminates and modules), while in a water body, the transport will be determined by diffusion and advection, possibly representing a less dynamic exchange compared to our experimental conditions. Assuming a sort of a delay in the substantial OP uptake by the calcite layer in modules (Figure 5a), the phytoplankton will be able to assimilate OP for some time following the modules' installation in a water body if the modules are applied in the euphotic zone (light access). In this context, to more effectively prevent intense phytoplankton growth by reducing the OP availability, the modules should be applied in advance before the start of the vegetation season (if they are to be used in the surficial layers of a water body). Anothersolution is their application at higher depths, below the euphotic zone, as simulated in our experiment. The possibility of adjusting the depth of application is an important advantage of the non-invasive P removal approach [41]. In such a case (treatment of deeper layers below the euphotic zone), the P inactivation will mainly address the P released by the decomposition of detritus settling from the euphotic zone and/or liberated from the sediments iby internal loading. By this, the P binding onto the modules can limit the OP transport between deeper layers and the productive zone and consequently contribute to lower OP concentrations in the upper water layers. A similar approach is sometimes used in traditional P immobilization in lakes by applying the P biding agent into hypolimnion [63]. Regarding the kinetics and efficiency of the OP uptake by modules and laminates, few modifications to the technical design are possible. The problem of relatively low mass of calcite present in laminates could be, in theory, overcome by adjusting the size of the laminates' area and their number. However, if one would like to add the same amount of calcite as applied in modules, 12.5 m\({}^{2}\) of the laminates' area would be needed for 180 L of the lake water (the lake volume used in the experiment in each chamber), which is unrealistic in field applications. Another option to increase the laminate's performance in OP removal is the two-side coverage of the carrier material with the calcite material. Although this will double the calcite mass possible to be applied per unit surface area of the laminate, it is still in an order of magnitude less compared to modules. Finally, in the case of modules, a further adjustment option is a change in their design by enlarging the number of trays and reducing the thickness of the P binding agent layer added to a single tray. This will enhance the surface area of the agent interacting with the solution, most likely causing a faster sorption (compared to using few trays with thicker layers of the reactive material, as in the design we employed in this study). Another improvement option, applicable for both laminates and modules, is enhancing the sorption ability of the P binding agent applied. The efficiency of the calcite material can be modified in a number of ways.