Features of the Modern Formation of Nutrient Load from the Urban and Rural Population on the Catchment Area of Water Bodies within the Borders of the Republic of Tatarstan

A comparative analysis of the formation of the nutrient load caused by the formation of communal discharges from the urban population and the dispersed load from the rural population for the period 2002-2015 yrs was carried out on the catchment of the Kuibyshev reservoir within the boundaries of the Republic of Tatarstan. It was revealed that the average value of the mass of nitrogen and phosphorus compounds formed in the catchment from municipal wastewaters of the urban population over the period is Ntot 5343 tons, Ptot 1790 tons; from the dispersed load of the rural population Ntot. 515 tons and Ptot 207 tons. It is shown that the contribution of the nutrient load from municipal wastewaters of the urban and rural population is Ntot. 96,3% and 3,7%, and according to Ptot. 96,9% and 3,1%, respectively.


Introduction
At present, the excess intake of nutrients, which triggers the process of eutrophication of water bodies and watercourses, is a serious problem for most countries. Eutrophication is an increase in the biological productivity of water bodies as a result of the accumulation of nutrients in water [1]. Anthropogenic eutrophication is caused, in particular, by the discharge of nutrients with wastewater and surface runoff and differs from natural by the high rate of the process.
In recent decades, both national and international agreements on the reduction of nutrient discharges have been developed and standards for the discharge of nutrient pollutants have been developed [2]. The adopted Directive (Directive 91/271) is essentially binding on the countries of the European Community, but the choice of methods of environmental protection and ways of ensuring them is not regulated. Directive 91/271 establishes quality requirements for treated wastewater discharged into water bodies subject to eutrophication, depending on the number of conventional inhabitants of a settlement. In the Russian Federation, for the regulation of the content of nutrients, maximum permissible concentrations of pollutants (MPC) [3] are established, which regulate the quality of water in the design section of the river, located downstream of the stream at a distance of 500 m from the place In connection with the deteriorating condition of water bodies, the assessment of the impact of urban wastewater as part of communal discharges, as well as the impact of a dispersed load from the rural population on water resources is a very urgent task necessary to develop management decisions to minimize the impact of nutrients on eutrophication of surface waters.
In this work, in continuation of a series of works on the assessment of biogenic pollution of the lowland reservoir in the European part of Russia [5 -14], an assessment of the impact of the urban and rural population and isolation of their contribution to external biogenic pollution of the catchment area of the Kuibyshev reservoir within the Republic of Tatarstan was carried out.

Materials and methods
The calculation of the load on the private catchment area of the Kuibyshev reservoir, due to the input of nutrients from the urban and rural population, was carried out taking into account the recommendations given in [15].
Total nutrient load (Lpop) of total nitrogen (Ntot) and total phosphorus (Ptot). for the private catchment area of the Kuibyshev reservoir, formed by the urban and rural population, was calculated by the formula: (1) where Lu -is the load generated by the urban population, tons per year; Lr -is the load generated by the rural population, tons per year.
When calculating the load on the private catchment area of the Kuibyshev Reservoir, due to the input of nutrients from the urban population according to formula (1), according to [16], it is assumed that one person releases Ptot -2,5 gram per day from 1 person and Ntot. -13 gram per day from 1 person.
When calculating the load on the private catchment area of the Kuibyshev reservoir, due to the input of nutrients from the rural population according to formula (1), according to [17], it is assumed that Ptot is released by one person-0,60 gram per day from 1 person and Ntot -1,49 gram per day from 1 person.
When calculating the load of inputs of phosphorus and nitrogen compounds from the urban population into the Kuibyshev reservoir, taking into account the functioning of existing biological treatment facilities, the purification efficiency was taken according to [18,19] for phosphorus 30% and for nitrogen compounds -60%.

Results and discussion
We have estimated the dynamics and trend of the load formed in the private catchment area of the Kuibyshev reservoir, due to the emission of Ptot. and Ntot. from the urban population, taking into account the efficiency of the treatment facilities ( Fig. 1 -2) and the dispersed load from the rural population ( Fig. 3 -4) for the period 2002-2015 yrs. In addition, we obtained regression equations describing the relationship between the load of nutrients Ptot and Ntot depending on the size of the urban and rural population.   In general, the contribution of wastewater from the urban population in the composition of municipal discharges prevails over the impact of the dispersed load from the rural population and amounts to 96,9% for Ptot and 96,3% for Ntot, respectively (Fig. 5). 4. The contribution of the nutrient load from wastewater of the urban population in the composition of communal discharges and the dispersed load from the rural population to the formation of the nutrient load of the Kuibyshev reservoir within the borders of the Republic of Tatarstan has been isolated. The contribution of the nutrient load from the wastewater of the urban population in the composition of communal discharges and the dispersed load from the rural population amounted to Ptot amounted to 96,9% and 3,1%, respectively. The contribution of the nutrient load from wastewater of the urban population in the composition of communal discharges and the dispersed load from the rural population amounted to Ntot amounted to 96,3% and 3,7%, respectively.