Comparison of the performance of stochastic models in forecasting daily dissolved oxygen data in dam-Lake Thesaurus

This study presents the development and validation of three different stochastic models on the basis of (a) their efficiency to forecast and (b) their ability to utilize auxiliary environmental information. The three models are ARIMA models, transfer function (TF) models, and artificial neural networks. Four-year (2004–2007) daily measurements of dissolved oxygen at four different depths (1, 20, 40 and 70 m) of Thesaurus dam-lake in River Nestos, Eastern Macedonia, Greece, were used to obtain the best models for these time series. For the final selected models, four statistical criteria (mean square error (MSE), roοt-mean-square error (RMSE), MAPE, and NSC) were used to evaluate the accuracy of the forecast and to compare the forecasting ability for one step ahead of each approach. For 1- and 20-m depth, the best forecast is obtained by ARIMA models, while for the 40-m depth, TF models gives the best forecast. Finally for the 70-m depth, according to the MSE, RMSE, and NSC statistical criteria, ARIMA models are the best, while for the MAPE, TF models are the best. Further research could be carried out concerning on (a) the comparison of these models with other forecasting ones, (b) the application of forecasting for more than one step ahead (m = 2, 3, …), and (c) the implementation of such models in other deep lakes and the assessment of the comparison between them. © 2016 Balaban Desalination Publications. All rights reserved

Zooplankton population seasonal variations in relation to nutrients. Case study of Lake Kastoria, Western Macedonia, Greece

In order to evaluate the trophic status of Lake Kastoria, seasonal pattern of nutrients, chlorophyll-a and zooplankton have been examined from January to December 2011. Lake Kastoria is a polymictic lake, characterized by both urban and agricultural activities. It has an area of 27.9 Km2 and is located in the northwestern part of Greece. Forests and semi-natural areas are characterized as dominant land use type (52%) in the lake's watershed (281 km2) followed by agriculture areas (39%). Urban land covers 2% of the lake's watershed. The lake's water retention time varies due to hydraulic adjustments of its outflow to Gioli torrent. Water samples were collected monthly from 5 sampling sites. The average of the measured values in all sampling sites, was estimated and the seasonal variation is demonstrated. The sequence of dominant zooplankton species groups in Lake Kastoria was Rotifera > Copepoda > Cladocera. Correlation between zooplankton species and nutrient level was established. The chlorophyll-a, an indicator of phytoplankton biomass, reached its maximum during the summer period. The values of total P and total N were also in high values in early spring and early autumn. Concerning chlorophyll-a and TSI indexes values, the trophic status of Lake Kastoria varied from eutrophic to hypertrophic depending on the season. The present study was to investigate the composition and abundance of species of zooplankton in the coastal zone of Lake Kastoria. The diversity of zooplanktonic organisms in lake ecosystem worldwide is a "key" factor of the biological and ecological status of the lake, as links the functioning of the ecosystem, the complexity of the food web and ecosystem stability. © 2017 PSP