| Mariculture has provided remarkable profits in recent decades and decreases the pressures on excessive exploition on wild living resources in China. However, Many coast regions are at risk from eutrophication which is a process resulting from an increase in anthropogenic nutrient inputs and other biogenic elements from estuarine waters, intensive animal mariculture activities and other sources. The marine environmental ecosystem in semi-enclosed or enclosed bay was impacted by both poor hydrological exchange and anthropogenic origin. Intensive mariculture is the occupied activity in coastal bays which leads to serious deterioration of water column.Sansha Bay is located in southeast of Fujian province, China, belonging to the enclosed deepwater bay. In 2015, the number of fish cages has increased to 1.15×104 ones, mainly for Pseudosciaena crocea. Meanwhile, Crassostrea gigas and Sea Cucumber are also cultivated in a large scale for recent decades. The excess nutrients which entered the environment as dissolved ammonia, faces and uneaten feed stimulated phytoplankton growing rapidly. Yantian bay, one part of this enclosed bay, has been influenced greatly by industrial and domestic wastewater pollution as located in an area with dense industries and population, in addition, the waters exchange rate is slow. Previous studies have showed great beneficial influences of the culture of large of seaweed. Macroalgea is one of the most important primary productivities and can absorb overmuch dissolved nutrients in aquatic ecosystem as a kind of bioremediation technique. Commercially, macroalgea is a valuable resource of food, oil raw materials and fodder.So in this paper, we evaluated intensive mariculture quality of Yantian bay during the cruises from November 2012 to August 2013. The spatial and seasonal variations of dissolved inorganic carbon system parameters and aqueous p CO2 were investigated in a large-scale mari-aquaculture area in Yantian bay, Sansha Bay. And the sea-air CO2 flux was also evaluated. The environmental quality of sediment and Spatial-temporal variability of phytoplankton assemblages were investigated at the same time. Then, we did some researches on bioremediation capabilities of macroalgea, including Gracilaria lemaneiformis and Laminaria japonica. Above on all of these, macroalgea was used to balance the nutrient produced by marine aquatic animal farming in an Integrated Multi-trophic Aquaculture(IMTA) system. 1. The survey and assessment of environmental quality in the mariculture area in the enclosed Yantian bay.Ten sampling sites were designed and evenly distributed in different mariculture functional areas. The annual concentration of DIC, HCO3-, CO32- and CO2 was in the range of 955-1957.08μmol/L,905.08-1848.13μmol/L, 10.14-124.78μmol/L and 11.48-39.78μmol/L, respectively. There were significant differences between seasons in concentrations of DIC, HCO3-, CO32- and CO2(P<0.01). The annual value of aqueous p CO2 was in the range of 391.27-1200.49μatm, and sea-air CO2 flux was in the range of 0.252~6.925μmol/m2·d. These demonstrated that the Yantian Harbor was the weak source of atmospheric CO2. The concentration of TN and TP in sediment ranged from 0.15 to1.39 g/kg and 0.11 to 1.08 g/kg, respectively. The concentration of OC was in the range of 1.00 to 14.71 g/kg with an average value of(8.26±3.78) g/kg, which was highest in the oyster aquaculture area than other three functional areas. The OC concentration in the macroalgae aquaculture area was lower than in the fish cage area, but higher than that in the control area. The Pi of TN was 1.23, 1.84, 1.56 and 1.67 in spring, summer, autumn and winter, respectively. The phytoplankton of Yantian bay exhibited extensive variability in respect to the number of taxa. Over the twelve months study period, a total of 6 taxonomic groups, 147 species(genera) of phytoplankton were identified. Phytoplankton abundance ranged from 0.18×104 cell/L to 18.75×104 cell/L with an average of 2.88×104 cell/L among the stations throughout the study period which presented dual-peak in February and July. The lowest abundance occurred in number. The Shanon-Wiener index(H’) of phytoplankton varied from 0.309 to 4.240 with an average of 2.370 among stations during the study period. Pielou evenness index(J) was ranged from 0.251 to 0.754, with an average of 0.541. The lowest and the highest values were recorded in July and March, respectively.2. Studies on bioremediation functions of Gracilaria lemaneiformis cultivation in Yantian bay.In macroalgea-cages ecosystem, Gracilaria lemaneiformis cultivation can improve dissolved oxygen(DO) in water(P<0.05). DO of the surface layer varied from(5.92±0.36) mg/L to(7.85±0.08) mg/L with an averageof(7.12±0.23) mg/L during the measurement period. The cut rates of Si O3-Si in two bioremediation areas were 6.60% and 9.51% and cut rates of COD were 6.2% and 11.8%, respectively. The average of dissolved inorganic nitrogen(DIN) values in fishing area and two bioremediation areas were(0.675±0.047) mg/L,(0.595±0.094) mg/L and(0.549±0.128) mg/L. No.2 macroalgea area’s cut rate was as high as 18.7%. The average of PO4-P concentration(DIP) values in these three areas were(0.131±0.007) mg/L,(0.118±0.014) mg/L and 0.117±0.012) mg/L, whose cut rates were 10.4% and 10.8%, respectively.Meanwhile, in Gracilaria lemaneiformis-Crassostrea gigas ecosystem, the SGR of macroalgea were 4.52%/d and 4.11%/d in two bioremediation areas with the comparision of control area of 3.66%/d. The average Si O3-Si concentration values over the sampling period were(1.59±0.09) mg/L,(1.62±0.12) mg/L and(1.59±0.12) mg/L. Results showed that COD concentration in the G. lemaneiformis cultivation areas were significantly lower than those in the shellfish area(P<0.05). The cut rates of COD in two bioremediation areas were 37% and 16%. The average TN concentration values were(0.710±0.064) mg/L and(0.681±0.054) mg/L in two bioremediation areas and concentration in the shellfish area was(0.774±0.074)mg/L. The range of TP was(0.134±0.015) mg/L to(0.141±0.015) mg/L. DIN values in these three areas(0.639±0.076) mg/L,(0.600±0.082)mg/L and(0.719±0.040)mg/L. The cut rates of DIP in two bioremediation areas were 11.1% and 16.3%.3. Studies on bioremediation functions of Laminaria japonica cultivation in Yantian bay.We used L. japonica to ameliorate cages ecosystem and kept monitoring every four days in April, 2015. The DO in two bioremediation areas was clearly higher than cages area. The average concentration of COD was(0.81±0.06) mg/L, while the others were(0.64±0.04) mg/L and(0.69±0.07) mg/L with the cut rate of 21.5% and 14.6%. Compared with cages water quality, the TN value was similar concentration of(0.782±0.084) mg/L and(0.780±0.077) mg/L. During the L japonica cultivation period, the concentration of TP declined distinctly. The concentration in the first bioremediation area was(0.149±0.014) mg/L and the other was(0.116±0.009) mg/L. And the DIN concentration declined from(0.996±0.069)mg/L to(0.550±0.058)mg/L with the average cut rate of 36.7%. The average DIP concentration values were(0.065±0.007) mg/L and(0.063±0.007) mg/L in two bioremediation areas and concentration in the shellfish area was(0.078±0.008) mg/L. The cut rates of DIP in two bioremediation areas were 28.6% and 41.1%. The SGR of macroalgea were 3.6%%/d and 3.8%/d in two bioremediation areas with the comparision of control area of 3.2%/d.In macroalgea-shellfish ecosystem, we designed four fouctional areas, namely shellfish areas, two bioremediation areas and mixed-culture area. During the monitoring period, the DO in two bioremediation areas was clearly higher than shellfish area and mixed-culture area.The concentration of Chl a declined clearly owing to cultivation of L. japonica. Results also showed that nutrients concentration in the L. japonica cultivation area were significantly lower than those in the shellfish area, especially in macroalgea cultivation alone(P<0.05). The concentration of DIN in bioremediation areas was(0.637±0.121) mg/L with cut rate of 27.5% and the average cut rate of DIP in bioremediation areas was 24.9% and 19.1%. 4. Bioremediation strategy of macroalgae cultivation in the intensive mariculture bay.According to the present mariculture situation, we analyzed bioremediation capabilities of macroalgea and suggested a removal model of nutrients concentration by macroalgae, including Gracilaria lemaneiformis and Laminaria japonica cultivation in turn. DIN was selected as the best indicator to balance between macroalgea absorption and animal production. In conclusion, there were 210 thousand cages in Sansha bay. The two kinds of maximum removing efficiency of these macroalgeas were 2.65% and 2.06%. The optimal proportion of Gracilaria lemaneiformis was suggedted to cultivate 1.24 times and Laminaria japonica was suggedted to cultivate 2.38 times than present farming output. |
PDF Full Text Request