Assessment of Permissible Phosphorus Loads on Lake Basins

Aim. The purpose is to assess allowable phosphorus loads on lake basins.

Methodology. For 18 large lakes located in Russia, Sweden, Finland, Hungary, Italy, Norway, and Estonia, we estimate values of allowable phosphorus loads, allowing them to remain in an oligotrophic status. The considered lakes significantly differ in water surface areas (by 121.2 times), volume (by 1197.4 times) and average depth (by 63 times). For calculations, the method of P. A. Lozovik, the distinctive feature of which, compared with the traditionally used methods of Follenweider and Follenweider and Dillon, is that it comprehensively takes into account not only the morphometric (average depth, surface area) and hydrological (time of complete water exchange) characteristics of a water body, but also its assimilation (self-cleaning) ability in relation to phosphorus compounds. For the convenience of calculations, we used our program “Program for calculating the allowable phosphorus loads on freshwater lakes”¹.

Results. In a number of cases, the lack of initial hydrological data, especially on water runoff from lakes, does not allow the wide use of P. A. Lozovik’s method. Taking into account that the lake and its watershed are a single natural system, a hypothesis is formulated about the possible existence of a quantitative relationship between the values of permissible phosphorus loads on lakes and the areas of their watersheds. On the example of 18 large lakes, a statistically significant relationship was established between the natural logarithms of the allowable phosphorus loads on these lakes and their catchment areas. The revealed relationship is adequate, characterized by a high closeness of the relationship between the variables on the Chaddock scale and is suitable for predicting the allowable phosphorus loads on lakes and reservoirs. Approximate values of permissible phosphorus loads on three large lakes of the Vologda region and eight large lakes of the Murmansk region were calculated.

Research implications. The revealed quantitative ratios allow environmental authorities and specialists to improve the efficiency and reliability of decisions made on the required level of deeutrophication of the lakes under consideration by reducing the anthropogenic phosphorus load with runoff from point and diffuse sources.

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