Assessment of Water Buffer Capacity of Two Morphometrically Different, Degraded, Urban Lakes

Jolanta Grochowska

doi:10.3390/w12051512

Abstract

The research was conducted in Karczemne Lake (area, 40.4 ha; maximum (max.) depth, 3.2 m) and Klasztorne Małe Lake (area, 13.7 ha; max. depth, 20.0 m) located in the Kashubian Lake District (Northern Poland). From the beginning of the 1950s, these reservoirs have received municipal and storm wastewater. The long-term process of lake contamination has shaped the specific buffer capacity conditions and influenced the circulation of carbonate and bicarbonate in the water of these ecosystems. Extremely high concentrations of nutrients (Karczemne Lake: max. total phosphorous (TP) level, 7.5 mg P L−1; max. total nitrogen (TN) level, 5.6 mg N L−1; Klasztorne Małe Lake: max. TP level, 20.6 mg P L−1; max. TN level, 43.3 mg N L−1) have caused very intensive primary production processes (Karczemne Lake: max. chlorophyll-a level, 193.40 µg m−3; max. Secchi disc visibility, 0.85 m; Klasztorne Małe Lake: max. chlorophyll-a level, 160.01 µg m−3; max. Secchi disc visibility, 1.15 m). In the polymictic Karczemne Lake, the pH value of all water columns exceeded 10.0 (max. pH, 10.41), and in the meromictic Klasztorne Małe Lake, the pH of the surface water layers oscillated around 9.5. In the polymictic Karczemne Lake, despite intensive photosynthesis, the calcium content and alkalinity were similar throughout the whole water column due to constant circulation. In the meromictic Klasztorne Małe Lake, during the growing season, a decrease in calcium concentration and alkalinity of the surface water layers and an increase in calcium concentration at the bottom were noted.

Highlights

The contamination of freshwater with a wide range of pollutants has become a global problem over the past hundred years [1,2,3]
The statistical analysis of the obtained results showed that the long-term municipal sewage discharge to the lakes caused highly significant differences (α < 0.05) in pH values between the polymictic (Karczemne Lake) and meromictic (Klasztorne Małe Lake) lakes (Table 2)
In 1957, the pH of the surface water layers of Karczemne Lake ranged from 8.05 to 8.72, while that of the surface water layers of Klasztorne Małe Lake ranged from

Summary

Introduction

The contamination of freshwater with a wide range of pollutants has become a global problem over the past hundred years [1,2,3]. At the turn of the century, the development of industries has affected surface water pollution. Many pollutants have reached natural water through urbanization, industrialization, and agricultural use of areas near water reservoirs. The inflow of pollutants with a high content of nutrients and organic compounds has accelerated eutrophication or caused rapid degradation of water reservoirs. Urban lakes are endangered because they receive water from municipal, industrial, and precipitation waste treatments [7,8,9,10]. The untreated wastewater flowing into lakes is dangerous for these ecosystems because it transports a very high load of nutrients and organic matter [11,12]. Excessive nutrient loads contribute to the violation of the existing natural ecosystem balance and increase the intensity of primary production

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Discussion

Conclusion