Water Quality Trends in a Coastal Lagoon Impacted by Non-point Source Pollution after Implementation of Protective Measures

Abstract

Water quality data from two different monitoring periods are used to evaluate the trophic state and effectiveness of various protective measures on the restoration of a eutrophic, coastal Mediterranean lagoon. Main protective measures included elimination of municipal/industrial raw wastewater discharges in the rivers outflowing to the lagoon, sediment/erosion control practices in the lagoon's drainage basin (i.e., construction of sediment/debris dams and grade control structures, reforestation and ban on livestock grazing), and reduction of fertilizer application quantities as a result of changes in crops. Water quality data include, among others, chlorophyll a, dissolved oxygen and nutrient concentrations, various physicochemical parameters, and transparency, measured during two monitoring periods, i.e., before and after (1998-99) implementation of protective measures. Rainfall depth for the two time periods was also available. Empirical equations were developed, from statistical analyses of the data, relating the water quality parameters during the two monitoring periods. These models help identify water quality trends. Based on the analyses, it seems that measures were effective in reducing sediments transported into the lagoon. However, the lagoon remains eutrophic to hypereutrophic, mostly due to phosphorus released in the water column from bottom sediments. Therefore, future restoration efforts should be directed towards the management of bottom sediments.

Seasonal and Spatial Variations in Water Physicochemical Quality of Coastal Potou Lagoon (Côte d’Ivoire, Western Africa)

“…pH had positive correlations ( Table 4) with water temperature (R = 0.342, p < 0.01), DO (R = 0.462, p < 0.05), and Chl-a (R = 0.280, p < 0.05 ), what may be explained by the fact that higher primary production rates consume CO 2 , which leads to higher pH values, and increase DO in the water. Coastal lagoons usually present higher pH values especially because of the sea water influence [7] [28]- [31]. The presence of humic materials, on the other hand, can acidify the waters [23].…”

“…Higher temperatures increase primary production, which leads to higher Chl-a values, CO 2 consumption and consequently higher pH. High Chl-a is usually associated to eutrophication problems but even coastal lagoons subjected to pollution show lower concentrations than Peri lagoon [7] [12] [33] [34]. Coastal lagoons from the near state of Rio Grande do Sul (similar weather conditions and freshwaters) also showed lower Chl-a values in spite of higher nutrients concentrations [35].…”

Water Quality of Drainage Canals and Assessment of Nutrient Loads Using QUAL2Kw

“…In algal cells the N/P ratio (expressed as mass) is 7.2:1 (Redfield ratio) and is calculated based on dissolved inorganic nitrogen and orthophosphate (Gikas et al 2006b;Gikas et al 2009b). The N/P ratio at T1, T2, T3 and T4 canals during the monitoring period are presented in Fig.…”

The Decline and Restoration of a Coastal Lagoon (Lake Veere) in the Dutch Delta

“…The observed delay in macrozoobenthic communities responding to improved water quality conditions after the restoration measure can also be the effect of less improvement of quality in the sediment. Moreover improved mixing and an increase of bottom currents can result in resuspension or uncovering of sediments, nutrients, and pollutants (e.g., Lardicci et al 2001;Gikas et al 2006;Flower et al 2009). Such processes might have worsened the situation, particularly in the eastern part of Lake Veere.…”