The Assessment of External and Internal Nutrient Loading as a Basis for Lake Management

Abstract

Successful management of lake ecosystems used for recreation requires firstly an identification of nutrient sources. It is necessary to identify the factors causing the deterioration of water quality and to plan measures for their mitigation. Analyses of the external and internal nutrient loading were carried out for the hypereutrophic Raczyńskie Lake. The study included flows from lake tributaries, stormwater runoff from impermeable areas and direct catchment impact as external sources of nitrogen and phosphorus, as well as bottom sediments as an internal source of phosphorus. In the case of external sources, the largest load (about 80% of N and 67% of P) is supplied from croplands via the shoreline. Both external and internal loading was characterized by distinct seasonal variability. The loads from watercourses supplying the lake played the most significant role in spring, whereas the release of phosphorus from bottom sediments (accounting for 81.4% of the total P load) was responsible for cyanobacterial blooms in summer. In order to improve Raczyńskie Lake water quality it is crucial to implement both in-catchment and in-lake measures by means of diversion of stormwater runoff, reduction of nutrient content in some of tributaries at their inflow to the lake (gabions filled with dolomite surrounded by macrophytes) and restoration treatments aiming at the inactivation of phosphorus in the water column and reduction of its release from sediments.

Decision Support for Lake Restoration: A Case Study in Swedish Freshwater Bodies

“…Many efforts have been done for lake management, such as assessment of external and internal nutrient loading [10], identifying and analyzing existing lake management strategies [11], and lake restoration approaches [12].…”

Sequential Application of Different Types of Coagulants as an Innovative Method of Phosphorus Inactivation, on the Example of Lake Mielenko, Poland

“…Also, the provisions of the Water Framework Directive [14] oblige all Member States to take measures to protect and sustain the use of inland surface waters. To improve the quality of lake waters, various protective measures are taken, consisting of limiting the inflow of biogenic substances from external sources, i.e., cutting off point sources (municipal and industrial sewage), improving water and sewage management in communes, introducing rational agricultural management, and using phosphorus-absorbing aggregates in the beds of watercourses feeding lakes [15][16][17][18][19][20]. However, these actions can bring good results only in the case of poorly or moderately eutrophicated lakes.…”