Artificial lakes (reservoirs) are regulated water bodies with large stage fluctuations and different interactions with groundwater compared with natural lakes. A novel modelling study characterizing the dynamics of these interactions is presented for artificial Lake Turawa, Poland. The integrated surface-water/groundwater MODFLOW-NWT transient model, applying SFR7, UZF1 and LAK7 packages to account for variably-saturated flow and temporally variable lake area extent and volume, was calibrated throughout 5 years (1-year warm-up, 4-year simulation), applying daily lake stages, heads and discharges as control variables. The water budget results showed that, in contrast to natural lakes, the reservoir interactions with groundwater were primarily dependent on the balance between lake inflow and regulated outflow, while influences of precipitation and evapotranspiration played secondary roles. Also, the spatio-temporal lakebed-seepage pattern was different compared with natural lakes. The large and fast-changing stages had large influence on lakebed-seepage and water table depth and also influenced groundwater evapotranspiration and groundwater exfiltration, as their maxima coincided not with rainfall peaks but with highest stages. The mean lakebed-seepage ranged from ~0.6 mm day⁻¹ during lowest stages (lake-water gain) to ~1.0 mm day⁻¹ during highest stages (lake-water loss) with largest losses up to 4.6 mm day⁻¹ in the peripheral zone. The lakebed-seepage of this study was generally low because of low lakebed leakance (0.0007–0.0015 day⁻¹) and prevailing upward regional groundwater flow moderating it. This study discloses the complexity of artificial lake interactions with groundwater, while the proposed front-line modelling methodology can be applied to any reservoir, and also to natural lake interactions with groundwater.

Jacek Gurwin. Episodes 2014;37:172-81. https://doi.org/10.18814/epiiugs/2014/v37i3/002

The present study deals with the assessment of the quality of natural waters by the use of chemometric interpretation of monitoring data from physicochemical parameters and toxicity tests. The data set consists from data originating from the Turawa reservoir (surface water, sediment core water and groundwater). All 154 samples were analysed for 33 physicochemical parameters as well as for acute and chronic toxicity by respective biotests. The monitoring results were considered both separately (chemical and toxicity data) and simultaneous in order to identify pollution sources in the region and to detect correlation between chemical and toxicity tests. The chemometric methods applied were cluster and principal components analysis. The identified latent factors responsible for the data structure resemble the impact of sources like marine influence, water hardness, turbidity, nutrition etc. It is quite interesting to detect that there is no direct high correlation between chemical and toxicity data, which is an important indication that the water quality has to be assessed by both groups of parameters. Still, some indications for the formation of acute and chronic toxicity by some chemical parameters are found and discussed.