Resuspension of Sediment as a Possible environmental Management Method for Coastal Lagoons and Aquaculture Ponds

Abstract

Although efforts have been made to reduce nutrient loads from civil wastewater treatment and industry (including land-based fishfarms), many lagoons still have serious environmental problems. The solutions usually used for remediation or to counteract the effects of eutrophication are often expensive and have a heavy impact on the lagoon and surrounding environments. They include earth-moving operations, excavation of channels and openings to the sea, deviation of rivers and drainage channels in farmland [5-15]. Not only do they denature lagoon characteristics and alter the coastal belt, but their cost/benefit ratio may be high and their effects short-lasting. For example, underwater channels excavated to improve internal water circulation in lagoons may silt up in a few years and require frequent costly maintenance. In the case of algal blooms, harvesting and disposal are often tried [16-22], but these operations are costly and frequently conducted with inappropriate methods and timing. Contrary to theory, the disposal of harvested algae is difficult and industrial uses of this material are rarely found. As an alternative solution for the management of lagoon eutrophication, recent field experiments have been conducted to The surface layer of sediment accumulates bioavailable organic matter and with the intervention of microbes, provides nutrients for the development of opportunistic vegetation. Superficial sediment subject to frequent disturbance may undergo an increase in the oxidative mineralization rate of organic matter [25]. Oxidation accelerates nitrification and leads to predominance of nitrates over reduced forms, increasing denitrification (which occurs in anoxic microhabitats in an oxidative milieu), with the result that part of the nitrogen is lost as gases [26]. Resuspension may lead to oxidation of sediment iron to ferric oxides, which adsorb orthophosphates, removing them from interstitial water and the water column [27]. By virtue of the geo-chemico-physical effects it produces, resuspension leads to selection of microbial, plant and animal populations, in the opposite direction to the selection produced by eutrophication and dystrophy. Opportunistic macroalgae suffer phosphorus limitation and seagrasses that take up nutrients directly through their roots can recolonize the substrate [28]. Frequent disturbance of sediment does not have significant negative effects on the water column, such as increase in pH and nutrients or decrease in