Ecological Importance of Alkaline Phosphatase Activity and Acid Phosphatase Activity in Lakes with Different Catchment Use Structures  
[PERSON]  
1 Department of Land Improvement, Environmental Development and Spatial Management, Poznan University of Life Sciences, Piatkowska 94, 60-649 Poznan, Poland; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Land Improvement, Environmental Development and Spatial Management, Poznan University of Life Sciences, Piatkowska 94, 60-649 Poznan, Poland; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Construction and Geogen  
The European Commission's Standard Measurements and Testing (SMT) Program introduced a P fractionation method, classifying phosphorus in various forms, including total phosphorus (P), organic phosphorus (org-P), inorganic phosphorus (IP), reactive P sorbed on metal oxides (NaOH-P), and calcium-bound phosphorus (HCl-P). In lake ecosystems, org-P plays a pivotal role in the phosphorus balance, serving as a significant source of phosphorus released from sediments in eutrophic lakes. The fundamental processes governing org-P release in lakes are closely tied to mineralization and the breakdown of phosphatase enzymes, specifically acid phosphatase (ACP) and alkaline phosphatase (ALP). Acid phosphatase primarily originates from microorganisms and plant root secretions, while ALP is predominantly produced by microorganisms [9]. The form, like ALP, plays a role in dephosphorylating organic phosphorus compounds by disrupting the phosphodieser linkage, leading to the removal of phosphate groups and the formation of orthophosphates. Earlier studies have demonstrated that environmental factors, including land use type, climate, pH, and agricultural practices, play a substantial role in influencing the activities of phosphatase enzymes and the diversity of microorganisms that harbor these enzymes [4; 10; 11; 12]. Notably, the pH in both soil and sediments stands out as a decisive factor, particularly for phosphatase, as it governs both the extent and nature of phosphatase activities [13]. The sediment-water interface in lakes is a specific connection important for the biogeochemical nutrient cycle [14]. Various physical, chemical, and biological reactions occur at the junction of two surfaces (water and sediment), which makes this place the basis for regulating and controlling the circulation of elements between sediments and overlying water [14; 15]. The sorption and desorption of P and organic matter at the water-sediment interface may affect the bioavailability of P, such as organic carbon [16; 17] and P [18; 19; 20], and may also increase the activity of phosphatase enzymes [21; 22]. Phosphatase, a key enzyme for the internal circulation of phosphorus in lakes, is common in both water and sediments [23; 24; 25]. Its action can be attributed to phosphatases found on the surface of algae and bacteria cells and dissolved enzymes originating from autolysis or the excretion by algae, bacteria, or zooplankton [23]. Serving as an essential catalyst, phosphatase hydrolyzes organic P in soil and sediment, releasing available org-P for use by plants and microbes [26]. In lakes, both ALP and ACP are capable of hydrolyzing monoester P, except for phytate [23; 25]. ACP is frequently found inside algal cells and is likely produced to modulate the internal metabolism of P [23]. The aim of the study is, therefore, to evaluate the activity of phosphatase enzymes in the two lakes characterized by different land use patterns in their immediate catchment areas. Additionally, the aim is to examine whether there is a reaction between org-P in overlying water and ALP and ACP in bottom sediments. We hypothesize that: (1) Different land uses determine the levels of both ACP and ALP. (2) In the case of the lake situated within a forested catchment, the values of ALP will be higher compared to the lake within an agroforestry catchment. (3) The primary factor influencing the levels of phosphatase enzymes is org-P content.