Monitoring and Analysis of Water,Salt and Nutrient Fluxes at the Mouth of a Lagoon

An intensive sampling program of physical and chemical parameters has been undertaken at Vassova lagoon, northeast Greece, in order to examine water circulation and estimate the instantaneous and residual fluxes of water, salt, nutrients and chlorophyll-a through the entrance canal of this lagoon. Field data of hydrographic and water quality parameters were collected under neap and spring tidal cycles, and under winter and summer conditions, to account for the fortnight and seasonal effects in the lagoon. The analysis showed that the Eulerian residual transport is positive in direction during both tidal cycles, thus pushing water, salt, nitrate-nitrogen, phosphate-phosphorus and chlorophyll-a inward Vassova lagoon. Tidal pumping was mostly positive during the neap tide and negative during the spring tidal cycle, thus pushing water, salt, phosphorus and chlorophyll-a outwards of Vassova lagoon.     

Quantification of Water, Salt and Nutrient Exchange Processes at the Mouth of A mediterranean Coastal Lagoon

Vassova lagoon is a typical Mediterranean (small, shallow, micro-tidal, well-mixed) coastal lagoon, receiving limited seasonal freshwater inflows from direct precipitation and underground seepage. An intensive study was carried out in order to quantify the mechanisms responsible for the intra-tidal and residual transport of water, salt, nutrients and chlorophyll at the mouth of this lagoon and to assess the lagoon's flushing behavior. Results indicated that although the system is micro-tidal, tidal effects appeared to be the dominant factor for the longitudinal distribution of physical and chemical parameters, while the associated residual flow is also important and serves as a baseline measure of overall circulation. However, analysis of the net longitudinal currents and fluxes of water, salt and nutrients revealed the importance of non-tidal effects (wind effect and precipitation incidents) in the mean tidal transport. It is shown that the Eulerian residual currents transported water and its properties inwards under southern winds, while a seaward transport was induced during precipitation incidents and northern winds. The Stokes drift effect was found an order of magnitude lower than the Eulerian current, directed towards the lagoon, proving the partially-progressive nature of the tide. Nutrients and chlorophyll-α loads are exported from the lagoon to the open sea during the ebb phase of the autumn and winter tidal cycles, associated with the inflow of nutrient-rich freshwater, seeped through the surrounding drainage canal. The reverse transport occurs in spring and early summer, when nutrients enter the lagoon during the flood tidal phase, from the nutrient-rich upper layer of the stratified adjacent sea. Application of a tidal prism model shows that Vassova lagoon has a mean flushing time of 7.5 days, ranging between 4 to 18 days, affected inversely by the tidal oscillation.     

Water quality trends in Polyphytos reservoir, Aliakmon River, Greece

A water quality monitoring program was undertaken from June 2004 to May 2005, on a monthly basis, in Polyphytos Reservoir of Aliakmon River. Depth, water temperature, dissolved oxygen, conductivity, pH and transparency (Secchi disk) were measured in situ, while collected water samples were analyzed in the laboratory for the determination of BOD, COD, total phosphorus (TP), ortho-phosphate (OP), chlorophyll-a (Chl-a), ammonium, nitrite and nitrate, total Kappajeldahl nitrogen (TKN) and heavy metals (Fe, Mn, Cu, Cr, Pb, Ni and Cd). Measured concentrations were compared to those from two previous studies conducted in July 1987 to June 1988 and January 1991 to February 1993. The following conclusions are drawn: the effect of the watershed on the lake environment, mostly through Aliakmon River, is significant, and it accelerates the eutrophication of the lake. The anoxic zones, which were defined in the lake, reinforce this conclusion. Nitrate, nitrite and ammonia were measured at lower concentrations compared to previous studies, while total phosphorus and chlorophyll-a were found at increased concentrations. The current trophic state of Polyphytos reservoir is eutrophic, based on the OECD method and Carlson's Trophic State Indices (TSI). The concentration of BOD and COD ranged at low levels. Furthermore, the mean concentrations of metals Fe, Mn, Cu, Cr, Pb, and Cd were below the potable water standards set by WHO and EU. During most part of the study period the ratio N/P for Polyphytos reservoir was higher than 7.2:1, and therefore, phosphorus is the limiting nutrient for algal growth.     

Characterization of Rain and Roof Drainage Water Quality in Xanthi, Greece

Thirteen field campaigns were undertaken in the period from December 2, 2002 until September 1, 2004 to collect water samples in order to characterize the quality of rainfall and roof drainage in the city of Xanthi, a typical provincial city in Greece. In each campaign, water samples were collected from 10 representative sites in the city (in total 130 samples), representing areas of distinct land use and human activities (i.e., traffic volume, residence density and industrial activity). The water samples were analyzed according to drinking water criteria for total coliform (not detected), temperature (range: 0.9–20°C), pH (range: 3.6–11.4), alkalinity (range: 0–21.5 mg CaCO₃/L), nitrate (range: 0–2456 μg/L), ammonium (range: 0–2628 μg/L), sulfate (range: 0–0.5 mg/L), calcium (range: 259.1–3064 μeq/L), magnesium (range: 0.8–488.8 μeq/L), potassium (range: 0.0–110.6 μeq/L) and dissolved heavy metals (Fe, range: 0.01–0.18 mg/L; Mn, range: 0.01–0.09 mg/L; Zn, range: 0.01–0.54 mg/L; Cu, Cr and Ni, not detected). Pollutant concentrations were generally higher in roof drainage than in rainwater, but both were lower than drinking water standards. Dissolved heavy metal concentrations were generally higher in the areas of intensive human activities, such as roads with high traffic volume and densely populated residential areas. The satisfactory quality of rainwater, which results from this analysis, makes its use as grey water possible.