Abstract
The study aims to analyse changes in the morphological conditions of the endorheic Lake Borówno (39.06 ha) that occurred in the 20th century and early 21st century. The analysis was based on bathymetric measurements carried out in 2018 and cartographic materials, and performed using QGIS 3.10 and SAGA GIS 6.4 software. Moreover, changes in physical (temperature, transparency), chemical (dissolved oxygen, phosphorus, and nitrogen content) and biological (chlorophyll a, phytoplankton) parameters were analysed based on the results of measurements conducted by the Voivodeship Inspectorate of Environment Protection (VIEP) in Bydgoszcz in the period 1984–2017. It was found that Lake Borówno is subject to a constant reduction in surface area and volume, the rate of which increased in the second decade of the 21st century. The lake’s progressive disappearance results from the co-occurrence of hydrological drought over the last several years and an increase in the use of groundwater resources. A decrease in the maximum depth of the lake entails a change in temperature distribution in the vertical profile, which contributes to the tendency toward the lake transforming into an unstratified reservoir. The increase in water temperature affects oxygen content in the bottom water, improves water transparency, and influences the maximum occurrence of chlorophyll a in spring.
Highlights
The processes affecting the hydrological and hydrochemical conditions in catchment areas depend on many factors such as climate, geological structure, soil conditions, and land use as well as anthropogenic activities including groundwater use [1,2,3]
Air temperatures recorded in Toruń indicate a significant increasing trend starting from the mid-20th century, which amounts to 0.31 ◦ C per 10 years
Air temperatures recorded in Toruń indicate a significant increasing trend starting from the mid20th century, which amounts to 0.31 °C per 10 years
Summary
The processes affecting the hydrological and hydrochemical conditions in catchment areas depend on many factors such as climate, geological structure, soil conditions, and land use as well as anthropogenic activities including groundwater use [1,2,3]. Endorheic lakes are susceptible to changes in these factors. Changes in land use in the catchment area affect the local water balance including surface run-off and underground drainage conditions, water retention in soil, and extent of evaporation [11,12,13,14,15,16,17]. Water used in agrotechnical processes is contaminated with fertilisers and organic substances As it returns via surface run-off to the lake, it may pose a threat to the lake’s chemical status [19,20]. Brda (a left-bank tributary of the Vistula River) [62]
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