The influence of restoration measures on phosphorus internal loading from the sediments of a hypereutrophic lake

Abstract

Uzarzewskie Lake was a hypereutrophic, dimictic lake characterized by low water transparency, high chlorophyll-a concentration and intense phytoplankton blooms; thus, restoration treatment was started. A chemical treatment, based on phosphorus inactivation with small doses of iron sulphate, was undertaken in 2006–2007. Nitrate-rich groundwater flowing from seepage springs was directed into the lake hypolimnion to increase redox potential since 2008. Phosphorus internal loading was reduced by more than 80% as a result of restoration treatment. In the profundal zone, where P release from the bottom sediments prevailed throughout the year, it decreased from 13.02 mg P m−2 day−1 in 2010 to 2.81 mg P m−2 day−1 in 2015. Meanwhile, in the littoral zone, P accumulation in bottom sediments predominated; hence, the mean value of internal loading was increasing from 2.61 mg P m−2 day−1 in 2011 to 10.24 mg P m−2 day−1 in 2015. The annual P load from the bottom sediments in the profundal zone was much higher than from the littoral zone as a result of (i) a higher P release in most years and (ii) the greater area of this zone (82% of the lake’s area). The fraction of residual phosphorus (Res-P) has the largest share, and in recent years, this has shown a tendency to decrease. The sum of bioavailable fractions was low (average 5.7%) showing a downward trend in recent years. Sustainable restoration of the lake resulted in a slow but steady decreasing trend in internal phosphorus loading.

Functional Groups of Phytoplankton and Their Relationship with Environmental Factors in the Restored Uzarzewskie Lake

“…In the beginning, during the period 2008-2012, a higher biomass of phytoplankton could be observed. This trend was similar to the average values of both soluble reactive and total phosphorus in the water column [11] and was connected with quite high concentrations of phosphorus above the bottom sediments and its internal loading [60]. This increased internal loading was most likely associated with faster mineralization of organic matter as a result of oxygen supply to the bottom area.…”

Internal Loading of Phosphorus from Bottom Sediments of Two Meso-eutrophic Lakes

“…Significant P release from sediments in autumn was also noted in other lakes situated in the course of the River Cybina, namely, Swarzędzkie Lake and Uzarzewskie Lake, which are also 7 m deep (Kowalczewska-Madura and Kowalczewska-Madura et al 2015. High release was also observed in autumn in Rusałka Lake (9 m deep) (Kowalczewska-Madura et al 2008.…”

“…This was probably the main reason for differences between these lakes in P release in summer from profundal sediments. The role of nitrates in limiting the internal P loading was demonstrated during the restoration of Uzarzewskie Lake, where as a result of an innovative method of supplying nitrates to the bottom of the lake, the internal P loading was reduced by over 80% (Kowalczewska-Madura et al 2017). The lower concentration of nitrates and higher organic matter content found in Prawe Lake was a result of the use of the adjacent catchment, which was dominated by forest.…”

A shallow lake in an agricultural landscape – water quality, nutrient loads, future management

“…Rapid, short-term thermal stratification, mixing caused by water turbulence and increased water flow velocity are crucial in shallow lakes (Søndergaard et al 2001) as they may result in an orthophosphate concentration gradient in the water-sediment interphase, thus increasing P release. The occurrence of this process has been noted in many lakes in aerobic conditions (Kowalczewska-Madura et al 2008, 2011Kowalczewska-Madura and Gołdyn 2009;Gržetić and Čamprag 2010). In shallow lakes flux of P from the sediments into the water column is further increased by benthic macroinvertebrates (Ji et al 2011).…”