Nutrients And Organic Matter Dynamics In Constructed Wetland Of Shanghai And Aquaculture System Of Sanggou Bay

Elevated concentration of nutrients and organic matter are considered to be one of the main concerns of pollution for the coastal ecosystem. Human activities such as industrial, domestic, aquaculture, agriculture waste and city construction etc are the major sources of the pollutants and responsible for degradation of coastal water quality. Rapid expansion of these industries have promoted the need for the development of techniques for effective environmental management. In present work, one of such technique of constructed wetland was applied to treat the pond aquaculture wastewater and second was the study of integrated multi-trophic aquaculture (IMTA) in the coastal waters. In order to understand the role of these techniques in the reduction of nutrients, constructed wetland experiment was carried out in the suburban area of Shanghai. Whereas seasonal surveys were conducted in the Sanggou Bay. Shandong province in Northern China to study the influence of aquaculture activities, river discharge and water mixing with Yellow Sea on the nutrient and organic matter concentrations of the bay.A free water surface constructed wetland was integrated into two commercial and one control ponds of giant freshwater prawn (Macrobrachium rosenbergii). Results showed significant (p<0.05) decrease in total suspended solids (TSS,73.2±15.4%) and total nitrogen (TN.39.6±44.2%) between wetland inflow and wetland outflow. The performance of constructed wetland was highly impacted by low concentration of dissolved nutrients at the inflow of constructed wetland and heavy rainfall events. Results showed about 43.8±24.6% NO3-,25.7±23.0% NH4-,14.3±1.0% NO2-. 28.4±18.8% DIN and 13.1±10.0% PO43-were removed.The present study was designed to study the fate of dissolved nutrient and organic matter in three culture area of shellfish, combined shellfish and seaweed (polyculture) and seaweed in the integrated multi-trophic aquaculture system of Sanggou Bay. For this purpose four seasonal cruises were carried out in spring (April),summer (August; dry season), autumn (October) and winter (January; wet season) in 2011-12. Dissolved nutrients (NO3-, NO2-, NH4-,PO43-,SiO32-) were measured at 19 stations, covering culture areas of the bay. The summer was highly impacted by excess water discharge and aquaculture activities than benthic sediments source; however other seasons were mostly influenced by the Yellow Sea. Results showed that nutrients were vertically mixed and integrated multi-trophic aquaculture helped in reducing the elevated nutrient concentration generated by water discharge and the mixing process. The N/P ratio indicated phosphate as a limiting nutrient. A simple mass-balance model was employed to determine the nutrient budget which showed that nutrients were mostly from the river input. This implies an increase in the anthropogenic activities and assimilation of PO43- in the Sanggou Bay.Source, sink, flow of carbon and nitrogen and trophic relationship among the cultured species in the Sanggou Bay were determined during summer and winter seasons using stable isotopes (δ13C and δ15N). Results showed that higher terrestrial input of organic matter occurs during the summer compared to the winter in the Sanggou Bay. Organic matter in suspended particulates (POM) showed marine- and terrestrial-derived signatures during summer, as revealed from their ranges in δ13C (-27.4 to-20.7‰) and δ15N (4.7 to 9.4‰). Sedimentary organic matter (SOM) showed signatures of marine-derived organic matter during both seasons, with ranges in δ13C and δ15N of-22.4 to-21.4‰ and 1.7 to 6.4‰, respectively. Shellfish and polyculture cultures in Sanggou Bay had potential to reduce organic matter received from the fish cages as well as from the seasonal inputs from rivers. Mixing with Yellow Sea water, combined with prevailing circulation, favours the dispersal, dilution and transformation of organic matter and maintains and improves water quality.The mixing of organic matter as well as water circulation supported in dispersal of organic matter and contributed in maintaining water quality. Salinity, chlorophyll-α and dissolved organic carbon showed large spatial and seasonal variations during sampling period. Dissolved organic carbon increased with increasing chlorophyll-α in spring, summer and autumn while dissolved organic carbon decreased with increasing salinity in summer season as compared to other seasons. Maximum surface concentration of dissolved organic carbon (108.0 μM to 875.2 μM) and minimum (134.4 μM to 184.7 μM) were found in summer and spring seasons, respectively. Terrestrial input, phytoplankton and seaweed were the main sources of dissolved organic carbon in Sanggou Bay. Shellfish culture area was enriched in organic matter as well as served to reduce dissolved organic carbon levels in the bay. As indicated by annual dissolved organic carbon removal mainly occurred in the shellfish (avg.42%) and lowest (avg. 32%) in poly-culture areas. Additionally, preliminary controlled experiment results showed that seaweed produced approximately 64.81±40.86 μM d-1 and shellfish generated approximately 13.36±6.07 μM d-1 and assimilated 17.07±13.12 μM d-1 dissolved organic carbon in Sanggou Bay. Accumulation of dissolved organic carbon at bottom was due to long term aquaculture activities in bay. Integration of sea-cucumber into integrated multi-trophic aquaculture can be useful to reduce the stocking of organic matter at the bottom. Based on our results and comparison with previous literature, water quality of the Sanggou Bay is still in the acceptable range due to integrated multi-trophic aquaculture activities and mixing with Yellow Sea.Finally status and history of shrimp farming is also highlighted in this study to make an attempt to recommend for the future prospects of shrimp farming in Pakistan. Advanced aquaculture technology and previous experience of China and other countries could be helpful in developing environmentally friendly system of aquaculture in Pakistan.