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Sylaios G.K.,Laboratory of Ecological Engineering and Technology | Sylaios G.K.,Greek National Agricultural Research Foundation | Kamidis N.,Laboratory of Ecological Engineering and Technology | Kamidis N.,Greek National Agricultural Research Foundation | Tsihrintzis V.A.,Laboratory of Ecological Engineering and Technology

In this paper, the question of freshwater induced stratification at the mouth of two dam-controlled Greek rivers is addressed. Results from a monitoring program are presented along Strymon River estuary and Nestos River coastal zone, two of the most important freshwater suppliers in the North Aegean Sea. Strymon River flow is man-controlled through Kerkini Dam, while Nestos River discharge patterns depict significant alterations, due to the operation of two hydropower dams. Moreover, a stratification-mixing model was developed based on the water column potential energy φ{symbol}TOTAL, which accounted separately for the local contributions to stratification (solar heating and freshwater buoyancy) and mixing (wind and bottom shear stresses). The model was run under two different scenarios: a) the influence and the absence of Kerkini Dam for the case of Strymon River, and b) the presence and absence of the hydropower dams for the case of Nestos River. Results show that Kerkini Dam affects the stratification conditions in Strymon River mouth during spring and early summer (April to June), by reducing φ{symbol}TOTAL by approximately 13%. In Nestos River mouth, the water column dynamics are highly affected by river damming, as φ{symbol}TOTAL appeared reduced during November to July, by approximately 50.2%. © 2009 Elsevier B.V. All rights reserved. Source

Papaevangelou V.A.,Laboratory of Ecological Engineering and Technology | Tsihrintzis V.A.,Laboratory of Ecological Engineering and Technology | Gikas G.D.,Laboratory of Ecological Engineering and Technology
Fresenius Environmental Bulletin

The role and importance of évapotranspiration (ET) on constructed wetland (CW) operation is examined through controlled experiments. For this, ten pilot-scale, cylindrical, thermally insulated metal tanks, of diameter 1.5 m and height 1.0 m, operated as lysimeters to evaluate CW ET. Four different substrate materials were used, i.e., river sand, medium gravel, cobbles and clay soil, with a total thickness of 0.5 m. The plant types used were Phragmites australis (reeds) in two CW units, Arundo Donax (giant reeds) in two units and Typha latifolia (cattails) in four units, while two units were unplanted. Six units simulated horizontal subsurface flow (HSF) CWs and four units freewater surface (FWS) systems. Under this configuration, interesting conclusions were drawn about the effect of substrate material, plant and CW type on ET rates. All units operated for nine months (April to December 2009), during which daily measurements of ET were made based on the water budget method. Results show a seasonal variation of ET values (higher values in summer, lower in winter) for all planted units, while the unplanted units had significantly lower variations. Overall, higher ET values were observed for the units planted with reeds, while cattails were more active during the summer months. Pearson correlation coefficients were computed to identify meteorological and other parameters affecting CW ET. The measured data were also used to produce simple empirical relations to predict daily ET rates based on meteorological and other parameters. Source

Gikas G.D.,Laboratory of Ecological Engineering and Technology | Dimou D.,Laboratory of Ecological Engineering and Technology | Tsihrintzis V.A.,Laboratory of Ecological Engineering and Technology
Fresenius Environmental Bulletin

The monitoring effort of Lissos River, located in Rhodope County, Thrace, North Greece, is presented. The river springs from Rhodope mountains and discharges into the Thracean Sea in the North Aegean, in an area protected by the Ramsar Convention. There are point and non-point pollutant sources in Lissos watershed resulting from human activities. Monitoring of Lissos River is essential for two reasons: first its water is used for irrigation of cultivated fields, and second it is included into the EU "Natura 2000" network. For the purposes of this study, a data collection program was established, aiming to collect data useful for the evaluation of the water quality of the river and its trophic state. The data include the following: (a) hydrologie (i.e., precipitation, air temperature, etc.) in a total of 2 stations over the watershed; (b) streamflow and sediment transport (i.e., cross-sectioning, velocity, suspended sediment, etc.) in a total of 7 stations in various torrents and in the main river course, at a frequency of ten days; (c) Electrical Conductivity (EC), pH, Dissolved Oxygen (DO) and Temperature (T) measured in situ simultaneously with discharge measurements; and (d) water samples collected and analyzed for the determination of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), nitrates, nitrites, ammonium, total phosphorus (TP), ortho-phosphates (OP), alkalinity and various anions (i.e., SO4 1 , Cl-) and cations (i.e., Na +, K+, Mg+2, Ca+2). Monitoring results showed influence on the EC values and nitrogen and phosphorus concentrations in the tributary of Lissos where a wastewater treatment plant discharges its effluent. The one-way between groups ANOVA showed that there were statistically significant differences of mean values of measured parameters (i.e., BOD, COD, TP, Cl-, SO4-2 etc.) between various stations of the river, indicating pollutant sources. The trophic state of Lissos was found eutrophic due to increased concentrations of nutrients, indicating the need for management measures in order to improve river water quality. The water quality of Lissos River, for irrigation use, was found satisfactory and suitable for almost all crops. Source

Kotti I.P.,Laboratory of Ecological Engineering and Technology | Gikas G.D.,Laboratory of Ecological Engineering and Technology | Tsihrintzis V.A.,Laboratory of Ecological Engineering and Technology
Ecological Engineering

In order to investigate the effect of temperature, hydraulic residence time (HRT), vegetation type, substrate material and wetland shape on the performance of free-water surface (FWS) constructed wetlands treating wastewater, 5 pilot-scale units were constructed and operated continuously from December 2004 until March 2007 in parallel experiments. Four of the units (A, B, C, D) were rectangular in plan view with dimensions 3.40 m in length and 0.85 m in width, and contained substrate material at a thickness of 0.45 m. The fifth unit (E) had a trapezoidal plan view shape, with a width at the inlet of 1.15 m and at the outlet of 0.55 m, while the length and the thickness of the substrate were the same as in the other four. All units operated at a water depth of 0.10 m. Units B-E contained clay substrate and unit A contained sand. The four units with clay were planted as follows: two with cattails (B and E), one with common reeds (C), and one with giant reeds (D). Unit A, containing sand, was planted with cattails. Planting and substrate material combinations were appropriate for comparison of the effect of vegetation and material type on the function of the system. Synthetic wastewater was introduced in the units. During the operation period four HRTs (i.e., 6 days, 8 days, 14 days and 20 days) were used, while wastewater temperatures varied from about 0.0 °C to 29.1 °C. The removal performance of the five constructed wetland units was good, since it reached on the average 77.5%, 67.9%, 60.4%, 53.9%, 56.0% and 51.7% for BOD, COD, TKN, ammonia (NH4-N), ortho-phosphate (PO4-P) and total phosphorus (TP), respectively. BOD and phosphorus removal efficiencies showed dependence on temperature in most units. The 14-day HRT was found adequate for acceptable removal of organic matter, nitrogen and phosphorus for most temperatures. A 20-day HRT is recommended for acceptable removal of BOD and PO4-P in the cold season. The unit with the trapezoidal plan view shape showed the best performance, with mean removals of 80.1%, 73.5%, 70.4%, 68.6%, 64.7% and 63.5% for BOD, COD, TKN, NH4-N, PO4-P and TP, respectively. The cattail was found statistically more efficient than the other two plants in COD and PO4-P removal. The unit that contained the clay substrate was found statistically more efficient in phosphorus removal than the unit containing sand. HSF CW units were found more efficient than FWS units in removal of most pollutant. © 2010 Elsevier B.V. All rights reserved. Source

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