Effects of hypolimnetic aeration on the quantity and quality of settling material in a eutrophied dimictic lake

Effects of hypolimnetic aeration (pumping of epilimnetic water into the hypolimnion) on the quantity of settling material in eutrophied Lake Vesijarvi, Finland were studied by comparing spatially comprehensive gross sedimentation rates as dry and organic matter prior to aeration activity and during two aerated years. Possible changes in the organic matter (as loss on ignition, LOI), carbon (C) and nitrogen (N) contents and changes in the C/N ratio of the settling material and surface sediment were quantified. Thermal stratification broke up earlier due to aeration and was followed by sedimentation peaks. The absolute amount of dry and organic matter as well as C and N settling to the lake bottom were significantly higher in the aerated years. Increased sedimentation rates were especially pronounced in the deep zones indicating enhanced sediment focusing. Increased sedimentation of C and N reflected higher primary production during the aerated years, which most likely was associated with increased temperature and turbulence and the subsequent regeneration and recycling of nutrients in the water body. Aeration seemed to slightly enhance degradation, but contrary to its ultimate aim, it failed to decrease the phosphorus content of the water column and deposits of organic material in the deep zones of the lake.Peer reviewe

Effects of water colour on the pigment content of a floating-leaved macrophyte - Implications of lake brownification

Brownification of lakes is a widely spread environmental problem. Brownification is a severe phenomenon, because water colour strongly shapes lake ecosystems through effects on the physical-chemical environment and biological communities. The effects of brownification on aquatic macrophytes are poorly known. Therefore, the aim of this study was to find out the effects of increasing water colour on the photosynthetic pigment content of the floating-leaved macrophyte Nuphar lutea. Field data on water quality and pigment content of N. lutea were collected from 27 lakes in southern and central Finland. The concentration of chlorophyll a+b in the floating laminae or in the petioles was not dependent on water colour, but the depth where the maximum chlorophyll a+b concentration was observed in the petioles, decreased with increasing water colour. Chlorophyll a:b ratio in the petioles and in the floating laminae decreased with increasing water colour. The response of the laminae was explained by decreased upward irradiance of light in high-colour lakes. However, the decreasing light intensity along increasing water colour could not alone explain the variations in chlorophyll a:b. The effects of water colour on the spectral composition of light probably also had a regulatory role. The results showed that the effects of lake brownification on pigments of macrophytes may not be limited to submerged species, but floatingleaved species can also be affected, with consequences for their photosynthesis.Peer reviewe

Should I stay or should I go? The diurnal behaviour of plant-attached zooplankton in lakes with different water transparency

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Redox-related release of phosphorus from sediments in large and shallow Lake Peipsi: evidence from sediment studies and long-term water monitoring data.

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3D-modelling of the thermal circumstances of a lake under artificial aeration

A 3D-model was developed to study the effects of hypolimnetic aeration on the temperature profile of a thermally stratified Lake Vesijärvi (southern Finland). Aeration was conducted by pumping epilimnetic water through the thermocline to the hypolimnion without breaking the thermal stratification. The model used time transient equation based on Navier–Stokes equation. The model was fitted to the vertical temperature distribution and environmental parameters (wind, air temperature, and solar radiation) before the onset of aeration, and the model was used to predict the vertical temperature distribution 3 and 15 days after the onset of aeration (1 August and 22 August). The difference between the modelled and observed temperature was on average 0.6 °C. The average percentage model error was 4.0% on 1 August and 3.7% on 22 August. In the epilimnion, model accuracy depended on the difference between the observed temperature and boundary conditions. In the hypolimnion, the model residual decreased with increasing depth. On 1 August, the model predicted a homogenous temperature profile in the hypolimnion, while the observed temperature decreased moderately from the thermocline to the bottom. This was because the effect of sediment was not included in the model. On 22 August, the modelled and observed temperatures near the bottom were identical demonstrating that the heat transfer by the aerator masked the effect of sediment and that exclusion of sediment heat from the model does not cause considerable error unless very short-term effects of aeration are studied. In all, the model successfully described the effects of the aerator on the lake’s temperature profile. The results confirmed the validity of the applied computational fluid dynamic in artificial aeration; based on the simulated results, the effect of aeration can be predicted.Peer reviewe

Water quality of a small headwater lake reflects long-term variations in deposition, climate and in-lake processes

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Troubled by the humics — effects of water colour and interspecific competition on the feeding efficiency of planktivorous perch

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