Submerged macrophyte self-recovery potential behind restoration treatments: sources of failure.

When exploring the challenges of restoring degraded lakes, we often do not observe the expected results despite executing all planned activities. Our study elucidates the reasons that impede the recovery of submerged macrophytes despite ameliorated light conditions. When prolonged lake degradation occurs, subsequent efforts to increase light availability often prove insufficient, resulting in a persistent turbid water state. In this study, we attempted to determine the reasons for these failures through a germination test and propagule bank analysis conducted in bottom sediments from a severely degraded lake, which underwent restoration. Although the bottom sediments indicate relative potential in the number of oospores and seeds, their germination efficacy remained dismally low. Based on the germination test results and factors affecting the development of submerged macrophytes (physical and chemical parameters, lake morphology), we stated that improvement of light conditions in the lake could be insufficient to recover the vegetation, especially when the potential to renew diverse plant communities from sediments naturally is low. Our findings advocate for a paradigmatic shift in lake restoration strategies. A holistic approach that includes propagule bank assessments before embarking on restoration initiatives and enabling the identification of macrophyte resurgence potentials is recommended. We also advocate for a multifaceted restoration framework, emphasizing the indispensability of augmenting natural recovery mechanisms with targeted interventions. Consequently, in some cases, macrophyte reintroduction could be the only solution. By reintroducing autochthonic species to site-specific ecological dynamics, we anticipate an increased success rate in restituting submerged vegetation, thus catalyzing ecological regeneration within degraded lake ecosystems.

Iron-induced behavioural and biochemical responses of charophytes in consequence of phosphates coagulant addition: Threats to lake ecosystems restoration.

The study aimed to evaluate the impact of iron (Fe) on the physiological and behavioural reaction of Chara tomentosa L. Fe was introduced into the environment in the form of iron chloride, the most common coagulants used in the restoration of water bodies. The investigations concerned the oxidative stress comprising phenolic compounds content, antioxidant activity and photosynthetic pigments concentration. Research was conducted as a laboratory microcosm experiment with one-off application of Fe at the level of 26.8 mg dm-3. Coagulant application caused short-term acidification, increased salinity and deterioration of light conditions. The shading resulted initially from the increase of water colour and turbidity and was followed by covering of the charophytes with a precipitated suspension. C. tomentosa did not activate defensive mechanisms to prevent the shading effect such as intensive elongation and elevated concentration of chlorophylls. Neither oxidative stress nor production of stress-specific phenolic metabolites was found. It was a result of iron coagulant toxicity, which led to cell membrane damage and leakage of cell contents to the water environment. Charophyte growth was significantly impaired, and thalli suffered numerous chlorotic and necrotic spots which extended gradually during experiment and finally caused death of specimens.

In-situ behavioural response and ecological stoichiometry adjustment of macroalgae (Characeae, Charophyceae) to iron overload: Implications for lake restoration.

Eutrophication of water bodies markedly reduces their recreational and economic use, which in turn compels those interested to pursuing prompt and effective restoration. This also applies to waters with a moderate pool of biogenic resources which, following temporarily increased nutrient alimentation from the catchment area may become eutrophic. The in-situ experiment tested the impact of chemical restoration on benthic macroalgae (Chara hispida L.) found in meso-eutrophic waters. Commonly used doses of iron sulphate were applied, defined as Low - 10.8 g Fe m-2 and High - 21.6 g Fe m-2. It was presumed that the sudden shift of abiotic conditions of the environment will disturb growth and stoichiometry of the species. Analyses encompassed physicochemical water parameters (e.g. nutrient concentration, light availability), morphological features and elemental composition of the charophytes. Application of the coagulant caused shading of the plants and elimination of bioavailable phosphates from the water. This induced changes of behavioural ecology of the species, manifesting in elongation of the main axis and increase of the assimilation area (growth of branchlets and side-axes) as well as stoichiometric changes. It was found that shortage of phosphates in the water resulted in decreased phosphorus concentration in the thalli due to biological dilution. The increase of assimilation area and phosphorus dilution in the thalli have not been previously reported for charophytes. In this study, the qualitative transformation of the environment following application of iron as part of chemical lake restoration was evinced in significant ecological changes that adversely affected macrophytobenthos. The findings of the experiment can therefore be taken into account while planning restoration procedures, so as to preclude the risk of a negative trend of ecological changes.

Bioaccumulation and toxicity studies of macroalgae (Charophyceae) treated with aluminium: Experimental studies in the context of lake restoration.

The objective of this study was to examine the impact of aluminium on the perennial macroalgae Chara hispida L. and its bioaccumulation capacities. Aluminium (Al) was introduced into the environment in the form of polyaluminium chloride, an agent utilized in the restoration of waterbodies. Research was conducted in an experimental setting using mesocosms (volume 0.8m3) placed in the littoral zone of a lake with C. hispida. Three doses of the coagulant were applied, each with a different volume: low - 6.1g Al m-3, medium - 12.2gm-3 and high - 24.5g Al m-3. A significant acidification of environment was determined, which would imply the presence of toxic Al3+ ions. It has been demonstrated that aluminium penetrates and accumulates in the cells of the charophyte. This caused damage to the thalli, which manifested itself in chloroses, necroses, flaking of the cortex cells and softening of the thallus, whose severity was proportionate to the dose of the coagulant. The first negative signs were observed after 24h. The study shows that C. hispida is a poor accumulator of aluminium (bioconcentration factor < 200), while bioaccumulation capacity was inhibited at the concentration of approx. 2.0mg Al g-1 d.w. Accumulation in the thalli of the charophytes accounted for 58% of variation following removal of aluminium from the environment. The results of the experiment demonstrate a negative impact of aluminium on charophytes at concentrations used in aggressive restoration of lakes.