Anthropogenic changes in properties of the water and spatial structure of the vegetation of the lobelia lake Lake Modre in the Bytów Lakeland

Abstract

Lake Modre is a lobelia lake. Numerous typical plant species occur here, including Lobelia dortmanna, Littorella uniflora, Isoetes lacustris, and Sphagnum denticulatum. They develop the following associations: Lobelietum dortmannae (Oswald 1923) Tx. ap. Dierss. 1972, Isoetetum lacustris Szańkowski et Kłosowski 1996 n.n., and a community with Sphagnum denticulatum Brid.In 1991, the water of the lake was characterised by low concentrations of nutrients and calcium, acid reaction (pH<5), and Secchi depth visibility of 12 m. Following fry stocking in the lake in 1993 fish farming took place until approximately 1996. During this period the water quality in the lake changed radically in physiochemical terms. Water transparency decreased. Thermal and oxygen stratification developed, with oxygen deficits in the near-bottom layer. Concentrations of nutrient elements increased.Drastic long-term changes were observed in the spatial and quantitative features of the lake vegetation. These particularly related to the instability of Lobelia dortmanna, and the diminishment of the phytocoenosis of Lobelietum dortmannae.

Light requirements of water lobelia (Lobelia dortmanna L.)

“…Water lobelia, like other isoetid species (Littorella uniflora, Luronium natans, Isoëtes lacustris, Isoëtes echinospora), is a photophilic plant growing in shallow littoral. Most often it occurs at a depth of 0.5-2.0 m (Dąbska 1965;Sheldon and Boylen 1977;Moeller 1978;Szmeja 1992;Kraska and Piotrowicz 1994;Sand-Jensen et al 2005;Kraska et al 2013). The occurrence of lobelia only in shallow littoral is a consequence of its ecological requirements, including those resulting from a specific form of growth and developmental biology.…”

“…In the light of previous studies on the irradiance needs of various groups of submerged macrophytes, the obtained PAR irradiance limit values at the depth of z C depend on many additional factors affecting both the depth of macrophyte colonization as well as those shaping incident radiation due to external conditions. These factors include: the effect of latitude (Duarte and Kalff 1987;Middel-boe and Markager 1997), climate change (Uscka- Kowalkowska et al 2007), local topography (Schwarz et al 2000), physicochemical properties of water and bottom sediments ( Middelboe and Markager 1997;Schwarz et al 2000, Kraska et al 2013 as well as water level changes (Furey et al 2004;Vandel et al 2016). In addition, the final results are also influenced by the type of research methods used (laboratory/field) (Sand-Jensen and Madsen 1991) or even the conversion of the subjective results of Secchi disc measurements to the values of attenuation coefficients of downwelling irradiance in water (Chambers and Kalff 1985).…”

Deleterious interaction of light impairment and organic matter enrichment on Isoetes lacustris (Lycopodiophyta, Isoetales)

“…In addition, reduction in nutrient load has not been sufficient in many systems to restore eutrophic water bodies (Scheffer et al, 1993;Brock & Starrett, 2003) mainly due to the high organic matter accumulated in lake sediments. Actually, both factors co-occur when lakes are dammed, under cattle pressure or even with the operation of aquaculture facilities (see Kraska et al, 2013). Damming results in a prompt reduction of light because of water level increase and re-suspension of sediments and particles coming especially from the newly flooded area (Gacia & Ballesteros, 1998).…”

Surfactants: a real threat to the aquatic geoecosystems of lobelia lakes

“…Disappearance of indicator species that form assemblages in lobelia lakes and progressive eutrophication of these lakes is being observed. Due to their exceptional nature, the geoecosystems of these lakes generate increasing interest among researchers, who are concerned about the growing number of degraded lobelia lakes (Kraska 1994a, b;Kraska et al 2013). There are intensifying efforts to determine ways to save these unique elements of the Polish lake districts landscape.…”