| Mariculture provides economic profits and decreases the intensity ofexploitation on descending wild living resources. However, accelerateddevelopment of mariculture has had some negative impacts on theenvironment. In some mariculture waters, high N/P concentrations havecaused serious environmental problems, such as eutrophication andecological imbalance. Intensive mariculture of fish, shrimp, shellfish or theother economic aquatic animals not only results in an increase of nutrientconcentrations in coastal waters, but also leads to changes of the dissolvedinorganic nutrient structures and sedimentary environments. There havebeen extensive studies on how to make water quality better and reduce thenutrients loading from mariculture environment. A series of studies havedemonstrated the potential beneficial influences of the culture of seaweedson wastewater treatment and bioremediation. Macroalgae are important incycling and transforming nutrients in aquatic ecosystems, owing to theircapacity to absorb and store nitrogen and phosphorous in their tissues. It isvery important and commercially valuable resource for food, fodder, soil conditioners and pharmaceuticals. Therefore, macroalgae not only can offeran ecologically friendly alternative for the system, but also as an additionalincome source for producers.So in this study, the quality of the water environment, quality ofsediments and types and quantities of phytoplankton in Yantian Harbor,Sansha Bay was monitored and investigated from2012to2013. Themainly term is basic physical and chemical indexes and nutrients such asNH4-N, NO2-N, NO3-N, PO4-P, TN and TP. Analysis the water quality,organic pollution index and eutrophication of Yantian Harbor base on theresult of investigation. Then cultivated G. lemaneiformis in disparatetrophic structure in experiment according to Yantian Harbor, compare thegrowth, pH in the water, DIC and nutrition removal capacity, to assessmentthe potential of G. lemaneiformis as a biological filter. After these,cultivating G. lemaneiformis in farming area and large-scale cultivationarea, measure the SD, DO, Chl-a, SS, the maximum quantum yield andweight of seaweed, and calculate the SGR of G. lemaneiformis. Here is themain results:1. The effect of N concentration on the SGR of algae is significant (P<0.05). The increase of N concentrations has a stimulative effect on thegrowth of G. lemaneiformis. G. lemaneiformis can significantly improve thepH of the water under a wide range of concentrations. The high concentration of N and P has no harmful effect on DIC removal rate of G.lemaneiformis. As a whole, the change of P concentration had smallinfluence on N removal rate of seaweed. When N concentration waselevatory, N removal rate was promoted to some extent. Higher Pconcentration was beneficial to P removal rate. By the above findings, wesuggested that in the N and P concentration range of our experimentalsetting, Gracilaria lemaneiformis is suitable to be the culture species thatcontribute to bioremediation in eutrophic water.2. The SS of Yantian Harbor was in line with III types of water qualitystandards, the pH was in the line with III/IV types, the DIN and DIP werein line with III/IV types of water quality standards or even worse. Theresults of organic pollution index and eutrophication showed that themariculture sea area in Yantian Harbor have been in a serious state ofeutrophication, the organic pollution was also very serious. The range ofTN of surface sediments was0.04~1.39g/kg, and the annual average ofTN was0.74g/kg. The range of TP was0.11~1.58g/kg, the annualaverage was0.62g/kg. The range of TC was0.01~1.47%, the annualaverage was0.71%. Spatial distribution of nutrients in this area wassimilar, the area of cultivation and the export of this bay owned morenutrients, the concentration of nutrients the upstream region was lower.There were138kinds of phytoplankton detected, the major was Bacillariophyta, which was dominant species all round year,Dinoflagellates was following. The cell density of phytoplankton was0.16~18.76×104cells/L. The range of H’ was0.31~4.24, the range of J′was0.07~0.86, the range of dMawas0.80~3.25, the differences of thesethree indexes were highly significant (P<0.01) in different month.3. The N/P of Yantian Harbor was much higher than the fixed ratio(16:1), this showed that this area is a system with surplus nitrogen or limitphosphorus. And the range of phosphate is0.0268~0.103mg/L, mostlyhigher than the thresholds of eutrophication,0.045mg/L. So, according tothe result, Yantian Harbor was a system with surplus nitrogen. The seawaterhas become eutrophication because of the higher nitrogen output ofaquaculture. In order to absorb more nitrogen, the cultivation area ofseaweed needed expand, the best cultivation area of seaweed is14660tonsof Laminaria japonica, and36640tons of Gracilaria lemaneiformis.4. Among the experiment of fishing boats, the SGR of Gracilarialemaneiformis was steady, the SGR of low-density group was higher thanhigh-density group, which archived4.51%/d. The DO of mixed culturearea was clearly higher than independent culture area of Pseudosciaenacrocea, the concentration of NO3-N、NH4-N and PO4-P of mixed culturearea was notable lower than independent culture area. The oxygenicphotosynthesis rate (RDO) and Photosynthetic carbon fixation rates (RDIC) of Gracilaria lemaneiformis could achieve17.29and6.69mg/g DW·h, theabsorption rate of nitrogen could achieve10.91~38.68μg/(g·h), theabsorption rate of Phosphorus could achieve10.21μg/(g·h).5. Among the experiment of large-scale cultivation, the SGR ofGracilaria lemaneiformis archived12.68%/d. The DO of seaweed culturearea was clearly higher than aquaculture area,the concentration of NO3-N、NH4-N and PO4-P of seaweed culture area was notable lower thanaquaculture area. The oxygenic photosynthesis rate (RDO) andPhotosynthetic carbon fixation rates (RDIC) of Gracilaria lemaneiformiscould achieve21.13and9.25mg/g DW·h, the absorption rate of NO3-N、NO2-N、NH4-N and PO4-P was23.82、7.63、56.98and14.54μg/(g·h). |
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