184
R. Ula´ nczyk et al.
that the curtain can be an effective measure only if it is adjusted in a real-time to the
quality of two main inflows and the wind speed and gust.
8.2.4 Ł˛ ekuk Wielki Lake
The lake Ł˛ ekuk Wielki has an area of 21.3 ha and mean and maximum depths of 5.2
and 12.5 m, respectively [31]. Its catchment (13.2 km
2 ) has been monitored since
1994 as a station called “Puszcza Borecka” and included in the Integrated Monitoring of Natural Environment—IMNE (part of the state environmental monitoring
system in Poland). Since 2018, analyses reported by the IMNE, are not based on
the monitoring data only but are supplemented by mathematical modelling aimed
at the calculation of the water and nutrients balance in monitored catchments. The
primary tool used for this purpose is the Soil And Water Assessment Tool (SWAT),
a mathematical model developed for the assessment of impacts of water and land
management or other factors on the water balance and water quality in river basins
[32]. SWAT, however, does not allow for in-depth analyses of processes occurring in
lakes and reservoirs, and therefore, the modelling system developed for the “Puszcza
Borecka” station was extended by the AEM3D. The aim of the AEM3D application was to identify factors affecting the water quality in the lake Ł˛ ekuk Wielki and
to enable predictions based on trends in the long-term monitoring data including
meteorological conditions, deposition, and changes in the land cover. The model of
the lake was composed of 33,622 cells of 10 m horizontal resolution and thickness
ranging from 0.25 m in the top layer to 1 m in the bottom. The model was used
to simulate water hydrodynamics and water temperature considered as key factors
affecting the water quality and aquatic ecosystems. Taking into account the scope of
simulated parameters, the model calibration was aimed at matching the observed and
simulated water balance and water temperature. The only component of the water
balance calculated by the AEM3D was the evaporation. Therefore, the model was
calibrated using the observed (monthly) values resulting in the R
2
= 0.83 and the
NSE = 0.88. Regarding the water temperature, the model was calibrated based on
temperature profiles (including 8 intervals) resulting in the R
2
= 0.72 and the NSE =
0.28. Simulations indicated that the average, yearly difference between bottom and
surface water layers ranged from 11.8 to 18.2°C in the period of May–November. In
remaining months the difference decreased to less than 1 °C. The calculated average
water retention time was 280 days in the entire lake except for the areas close to
surface inflows. During the warm season, the retention time was different at different
depths. The difference between top and bottom reached 70 days (Fig. 8.7).
R. Ula´ nczyk et al.
that the curtain can be an effective measure only if it is adjusted in a real-time to the
quality of two main inflows and the wind speed and gust.
8.2.4 Ł˛ ekuk Wielki Lake
The lake Ł˛ ekuk Wielki has an area of 21.3 ha and mean and maximum depths of 5.2
and 12.5 m, respectively [31]. Its catchment (13.2 km
2 ) has been monitored since
1994 as a station called “Puszcza Borecka” and included in the Integrated Monitoring of Natural Environment—IMNE (part of the state environmental monitoring
system in Poland). Since 2018, analyses reported by the IMNE, are not based on
the monitoring data only but are supplemented by mathematical modelling aimed
at the calculation of the water and nutrients balance in monitored catchments. The
primary tool used for this purpose is the Soil And Water Assessment Tool (SWAT),
a mathematical model developed for the assessment of impacts of water and land
management or other factors on the water balance and water quality in river basins
[32]. SWAT, however, does not allow for in-depth analyses of processes occurring in
lakes and reservoirs, and therefore, the modelling system developed for the “Puszcza
Borecka” station was extended by the AEM3D. The aim of the AEM3D application was to identify factors affecting the water quality in the lake Ł˛ ekuk Wielki and
to enable predictions based on trends in the long-term monitoring data including
meteorological conditions, deposition, and changes in the land cover. The model of
the lake was composed of 33,622 cells of 10 m horizontal resolution and thickness
ranging from 0.25 m in the top layer to 1 m in the bottom. The model was used
to simulate water hydrodynamics and water temperature considered as key factors
affecting the water quality and aquatic ecosystems. Taking into account the scope of
simulated parameters, the model calibration was aimed at matching the observed and
simulated water balance and water temperature. The only component of the water
balance calculated by the AEM3D was the evaporation. Therefore, the model was
calibrated using the observed (monthly) values resulting in the R
2
= 0.83 and the
NSE = 0.88. Regarding the water temperature, the model was calibrated based on
temperature profiles (including 8 intervals) resulting in the R
2
= 0.72 and the NSE =
0.28. Simulations indicated that the average, yearly difference between bottom and
surface water layers ranged from 11.8 to 18.2°C in the period of May–November. In
remaining months the difference decreased to less than 1 °C. The calculated average
water retention time was 280 days in the entire lake except for the areas close to
surface inflows. During the warm season, the retention time was different at different
depths. The difference between top and bottom reached 70 days (Fig. 8.7).