Eutrophication patterns in an eastern Mediterranean coastal lagoon: Vassova, Delta Nestos, Macedonia, Greece

Abstract

The results of an intensive monitoring study of main eutrophication parameters in relation to fish farming management, climate and hydrography in the Vassova coastal lagoon (Nestos Delta) are presented. The overall aim is to produce basic knowledge in order to contribute to the management of eutrophication of coastal lagoons at local and national levels. Due to extensive spatiotemporal variability of the measured parameters correlation and regression polynomial analysis was used to identify patterns (p<0.05). Freshwater was the main source of nitrate and phosphate in the lagoon. This finding has justified the reduction of freshwater inflow in the past, which, however, has increased mean salinity to 30 PSU and reduced spatial salinity gradients. Maximum nitrate values in winter coincided with adverse climatic and hydrographic conditions (high precipitation, strong NE to E winds and low tide) and fish farming management that hinder water circulation. Dissolved phosphorus variability indicated the combination of the external (freshwaters) and internal (sediment) P-sources. N/P water values indicated nitrogen being the most important nutrient for primary producers throughout the year, except in winter, when phosphorus was the most important nutrient. Practical measures for improving fish farming practices to decrease “eutrophication risk” during winter are suggested. Existing nutrient data from the Vassova and from other Greek lagoons in comparison were also presented and discussed.

Variation of structural and functional metrics in macrophyte communities within two habitats of eastern Mediterranean coastal lagoons: natural versus human effects

“…Indeed mean nitrogen concentrations, one of the main factors influencing macrophyte communities shifts in coastal lagoons (Howarth . Although high variability of coastal lagoon abiotic factors due to climatic and hydrological influence was noticed elsewhere (Petihakis et al, 1999;Basset et al, 2001;Orfanidis et al, 2005) the nutrient values measured in this study should be regarded as representative. Moreover, since sampling in MA-Agiasma was undertaken during the period of restricted sea water exchange with the sea because of fish aquaculture practices the measured values should rather over-estimate lagoon trophic conditions.…”

“…are capable of rapid uptake and accumulation of nutrients (Pedersen and Borum, 1997) during the outflow periods that can be utilized later when nutrient-poor, clearer sea water flows into the lagoon from the sea (Schramm, 1999). Changes in the phosphorus to nitrogen ratio after Ulva decay combined with wind-driven resuspension phenomena or seasonal changes in rainfall (Orfanidis et al, 2005) may favour the growth of Cyanobacteria during autumn and winter months in MM habitat of Agiasma (Viaroli et al, 2008). The intensity of such changes will be related to the dimensions of the lagoon (Holling, 1992).…”

Nutritional importance of minor dietary sources for leaping grey mullet Liza saliens (Mugilidae) during settlement: insights from fatty acid δ13C analysis

“…width = 30 m) and shallow (mean depth = 0.8 m) channel, classifying the lagoon as choked (Kjerfve 1994). Freshwater and nutrient input occurs through precipitation and a number of small inlets connecting the northern part of the lagoon to adjacent drainage channels (Orfanidis et al 2005). During the study period, temperature and salinity in the central basin ranged from 25 to 29°C and 15 to 25 psu, respectively.…”

“…Opportunistic macroalgae (Gracilaria sp., Ulva sp.) totally cover the central basin and annual chlorophyll a (chl a) means are very low (1.41 µg l -1 ) (Orfanidis et al 2005). Sampling.…”

Salinity as the main factor structuring small-bodied fish assemblages in hydrologically altered Mediterranean coastal lagoons

“…This fact might explain the negative correlation between nutrient loading and salinity that is common in coastal systems affected by agriculture activities (Chapelle et al 2000, Lucena et al 2002, Pérez-Ruzafa et al 2005a. Moreover, this freshwater input could promote turbulence, favouring the internal recycling process in the lagoons, as has been suggested for phosphate and ammonium (Chapelle et al 2000, Orfanidis et al 2005, Badosa et al 2007). …”