Eutrophication control by lime addition: A preliminary approach in Sicilian reservoirs (original) (raw)
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Aquaculture International, 2000
Lime-induced changes of biogeochemical cycling bacteria were examined using doses of 25, 50, 100, 200, 500, 1000 and 2000 kg ha Ϫ1 in the first part, and post-lime inorganic and organic fertilization in the second part of the experiment. Heterotrophic, ammonifying, denitrifying, cellulose decomposing and phosphate solublizing bacteria were drastically reduced by 30-90% in 1000 kg ha Ϫ1 and 51-91% in 2000 kg ha Ϫ1. Density differences were minor in the remaining test doses for all groups of bacteria except for the dinitrifiers which were reduced in 500 kg ha Ϫ1 by 90% over the control. Similarly, reduced rates of ammonification, nitrification and denitrification were dose-dependent. Inorganic fertilization following lime application of 2000 kg ha Ϫ1 resulted in no marked increment of the counts of bacteria and activity processes, whereas organic manuring increased the density (50-200%) and the activities (212-292%) as well. Lime-induced changes of bacterial population and activities were explained as a result of high pH stress as well as a major shift in the CO 2-HCO 3-CO 3 equilibrium system. Increase of major nutrients in the post-lime organic treatment was significantly higher than that of inorganic fertilization resulting in favourable N/P ratio and water quality conducive to fish farming after 45 days of liming.
A northern Italian shallow lake as a case study for eutrophication control
Limnology, 2007
Lake Varese (northern Italy) has shown deterioration in water quality since the 1960s and, as a result of the long duration of direct discharge of untreated sewage into the lake, it was classifi ed as being hypertrophic. To recover the lake water quality, a series of externally and internally remedial actions were implemented in subsequent years. The applied sewage collecting system induced a reduction of the external P loads from 50 t P year −1 to 16 t P year −1 and the weighted mean annual TP concentration decreased from 352 µg P l −1 to 85 µg P l −1 , typical of eutrophic conditions. The hypolimnetic water withdrawals, adopted in the years 2000-2003, allowed a reduction of the internal P loads of about 3-5 t P. In the same years, 500 t O 2 were injected at depths of 4.5-8 m during the summer months. In spite of these internal remedial actions, no signifi cant reduction of the weighted mean annual concentration of the TP could be observed, and during the summer stratifi cation period no signifi cant reduction of the volumes of anoxic water and of the duration of the anoxia were detected. The anoxic conditions are still the prevailing force driving the lake P-budget, maintaining the lake in eutrophic status.
Estuaries and Coasts, 2018
The release of phosphorus (P) stored in the sediment may cause long-term delay in the recovery of lakes, ponds, and lagoons from eutrophication. In this paper, we tested on a laboratory scale the efficacy of the flocculant polyaluminium chloride (PAC) and a strong P-binding agent (lanthanum-modified bentonite, LMB) on their ability to flocculate a cyanobacterial bloom and hamper P release from a hypertrophic, brackish lagoon sediment. In addition, critical P loading was estimated through PCLake. We showed that cyanobacteria could be effectively settled using a PAC dose of 2 mg Al L −1 combined with 400-mg L −1 LMB; PAC 8 mg Al L −1 alone could also remove cyanobacteria, although its performance was improved adding low concentrations of LMB. The efficacy of LMB to bind P released from the sediment was tested based on potentially available sediment P. A dose of 400 g LMB m −2 significantly reduced the P release from sediment to over-standing water (either deionized water or water from the lagoon with and without cyanobacteria). In sediment cores, LMB + PAC reduced sediment P flux from 9.9 (± 3.3) to − 4.6 (± 0.3) mg P m −2 day −1 for the experimental period of 3 months. The internal P load was 14 times higher than the estimated P critical load (0.7 mg P m −2 day −1), thus even if all the external P sources would be ceased, the water quality will not improve promptly. Hence, the combined LMB + PAC treatment seems a promising in-lake intervention to diminish internal P load bellow the critical load. Such intervention is able to speed up recovery in the brackish lagoon once external loading has been tackled and at a cost of less than 5% of the estimated dredging costs.
Freshwater …, 2001
1. Whole-lake experiments were conducted in two hardwater lakes (Halfmoon and in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH) 2 and/or calcite: CaCO 3 ) treatments (5±78 mg L ±1 ) for up to 7 years. 2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments. 3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to < 1 mg m ±2 day ±1 compared with 3.6 mg m ±2 day ±1 during the winter after initial treatment. In the ®nal year of lime application, mean summer TPRR decreased to 4.5 mg m ±2 day ±1 compared with 7.6 mg m ±2 day ±1 in the pretreatment year. 4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Lake during lime application. Over the ®rst 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from¯oating to rooted plants. 5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.
Environmental Management, 2017
Increased nutrient enrichment in Mediterranean standing waters has enhanced the risk of being affected by cyanobacterial blooms. Because phosphorus abatement is shaped as a crucial strategy for controlling eutrophication, this study introduces a structural thinking, experiential learning laboratory with animation dynamic model elaborated for Cazalegas Reservoir (Spain) to assess the feasibility of implementing a set of internal and external control measures and hydromorphological adjustments to meet the goal of oligotrophication. This shallow reservoir is another case where recurrent eutrophication has led to reach annual mean total phosphorus concentrations (0.16 ± 0.08 mg total phosphorus/L) over the threshold of current water policies, triggering cyanobacterial growth up to undesirable levels in summer time (approximately 50,000 cells/mL). Modeling results showed that (i) after upgrading water treatment in the main tributary, (ii) applying a lanthanum-modified bentonite into the water column and sediment, and (iii) increasing reservoir water level, in-lake P concentrations and cyanobacterial abundance decreased in an 88% (below 0.01 mg total phosphorus/L) and 84% (below 6000 cells/mL), respectively in the most critical periods. However, the constraints of the proposed management strategies are associated with their costs of implementation and the time span for a stable trophic recovery of the reservoir. In that end, integrated management approaches are aimed to be adopted by water managers to reach adequate ecological status of freshwater bodies.
Environmental Science & Technology, 2013
An extraordinary bloom of Planktothrix rubescens, which can produce microcystins (MCs), was observed in early 2009 in the Occhito basin, used even as a source of drinking water in Southern Italy. Several activities, coordinated by a task force, were implemented to assess and manage the risk associated to drinking water contaminated by cyanobacteria. Main actions were: evaluation of analytical protocols for screening and confirmatory purpose, monitoring the drinking water supply chain, training of operators, a dedicated web site for risk communication. ELISA assay was considered suitable for health authorities as screening method for MCs and to optimize frequency of sampling according to alert levels, and as internal control for the water supplier. A liquid chromatography-tandem mass spectrometric method able to quantify 9 MCs was optimized with the aim of supporting health authorities in a comprehensive risk evaluation based on the relative toxicity of different congeners. Short, medium, and long-term corrective actions were implemented to mitigate the health risk. Preoxidation with chlorine dioxide followed by flocculation and settling have been shown to be effective in removing MCs in the water treatment plant. Over two years, despite the high levels of cyanobacteria (up to 160 × 10 6 cells/L) and MCs (28.4 μg/L) initially reached in surface waters, the drinking water distribution was never limited.
"The refinement of groundwater protection criteria is currently of major importance in Italy. The new D.L. 152/2006 and respective Addenda state that each Region should provide appropriate indications as to the setting up of protection zones, taking into consideration the hydrogeological features of different areas of the Italian territory. The present study has been focused on the refinement of protection measures for carbonate aquifers in central-southern Italy, taking into consideration their hydrogeological features and the results of several years of experimental researches in different test sites. In these aquifers a good protection can be obtained by integrating the D.L. 152/2006 with specific solutions. The integrative measures can be synthesized as follows: (a) introduction of new protection zones, (b) identification of criteria for delimiting zones IIa, (c) introduction of the concept of “developing protection zones”, and (d) use of “dynamic” protecting measures, when polluting human activities are already existent within the protection zones. The “map of land use restrictions” has been identified as the graphic core of a GIS-based sDSS which will aid decision-makers to protect the water resources against pollution. "
21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 29 March - 3 April 2008, Concepcion, Chile, 2008
Water pollution from point sources has been considerably reduced over the last few decades. Nevertheless, some water quality problems remain, which can be attributed to non-point pollution sources, and in particular to agriculture. In this paper the results of a study intended to assess the consequences, in terms of NO 3 water pollution, of growing a crop, whose impact in terms of P pollution is already well known, are presented. The potential consequences, in terms of water pollution from nitrates of a BMP expressly applied to reduce P pollution are also discussed. The study site is the Lake Vico basin, Central Italy, which has suffered a shift in trophic state since the mid 1990s, caused by P compounds used for intensive cultivation of hazelnut trees. The results of the monitoring campaign described in this paper allow to assert that hazelnut tree cropping has probably caused a considerable increase in nitrate concentration in the groundwater, although not in the lake water, because of the specific hydrogeological characteristics of the basin. The main conclusion is that monitoring is essential to single out en