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Estimate Of Dry Deposition Fluxes Of Nutrients And Their Impacts On The Succession Of Dominant Phytoplanktonic Species Over The East China Sea

Posted on:2014-08-01Degree:MasterType:Thesis
Country:ChinaCandidate:L ZhuFull Text:PDF
GTID:2180330434970605Subject:Environmental Science
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Atmospheric deposition is one of the important sources for nutrients to the surface ocean. The study on the atmospheric deposition of nutrient over the East China Sea (ECS) has an important significance on understanding the influence to the marine primary production. This study chooses Huaniao Island of the ECS as a sampling site which is a pristine island and over100km away from the shore. A total of57individual TSP,85individual PM2.5and23sets of size-segregated aerosols are collected concurrently using a high volume TSP sampler, a mid-flow PM2.5samplers and a cascade impactor at Huaniao Island (30.86°N,122.67°E) between April2010and March2011, Inorganic nitrogen components(NH4+-N, NO3-N) and Soluble P (SP) are determined using Ion Chromatography(IC) and ICP-OES. Air-mass backtrajectories are calculated from the National Oceanic and Atmospheric Administration (NOAA) GDAS data base using HYSPLIT program showing the synoptic situation and general sources of air masses sampled at Huaniao. Concentrations and size distribution of nutrient species (NH4+-N, NO3--N and SP) in aerosols over the ECS are discussed. A particle deposition model and cascade sample measurements are used to estimate dry deposition fluxes of nutrients to the ECS. Our estimates of dry deposition fluxes of NH4+and NO3-are about twice and1/6of those calculated by previous study using a single-mode particle model or conventional dry deposition velocity without considering size distribution of NH4+and NO3-.The present study mimics the ratios of NH4+-N to NO3--N in atmospheric dry deposition to the ECS and investigates the effects of increased portion of NH4+on the primary production and biomass of dominant phytoplanktonic species (mainly diatom and dinoflagellate) of this coastal area which may help understand the transformation of community structure and the mechanisms of algae bloom occurred tens of times every year. Concentrations of nutrient species and Chl-a are determined by nutrients Autoanalyzer and Fluorescence spectrometer respectively. Phytoplankton species and number are identified by an inverted microscope, The project will provide scientific basis for protection of the ecosystem health of the ECS and sustainable development of China’s economy, and will help to understand the coupling between atmospheric deposition and primary productivity of surface ocean and its role in the climate change. The major results of this study are as below:1. Soluble NH4+and NO3" are found to be two major components of dissolved inorganic nitrogen (DIN) in aerosols sampled at Huaniao ranged from3to359nmol m-3and16to467nmol m-3, respectively. SP ranges between0.02and0.85nmol m-3with the mean concentration of0.28nmol m-3. NH4+and NO3-demonstrate a significant seasonal pattern with the mean concentration decreasing in the order of early spring2011> late autumn2010> summer2010.2. High deposition rates of atmospheric nutrients are normally associated with the air masses with an inland origin carrying large quantities of dust and anthropogenic pollutants and leading to high levels of DIN and SP. The lowest concentrations of DIN, SP and TSP are recorded in summer as a result of prevailing southeasterly wind carrying relatively clean air masses from oceanic region as well as significant washing-out effect of summer monsoon.3. NH4+occurs mainly in fine mode (54%of the mass) with one peak at1.1-2.1μm, In contrast,59-69%of NO3-mass is associated with coarse-mode aerosols, Relatively small fraction of NO3-exists in fine mode as the possible form of NH4NO3, aerosol NH4+to non-sea-salt (nss-) SO42-ratio could be high and excess NH4+may drag34-54%of NO3-to fine mode aerosols, which may cause a large overestimation of dry flux of NO3-over the ocean by assuming its deposition velocity similar to that of coarse particle.4. The dry deposition fluxes of NO3-, NH4+, and SP are estimated to be6080,10006, and26μmol m-2yr-1respectively over the ECS using size-segregated samples. It is found that assuming a constant deposition velocity could overestimate the dry flux of NO3-by a factor of6while underestimate the flux of NH4+, which would alter the dry flux ratio of NH4+/NO3-from1.6to0.1with potential effects on the primary production and phytoplanktonic structure in the ECS.5. Significant augment of Chl-a is found in treatment with input of high proportion of NH4+suggesting that NH4-uptake is fast and preferred by phytoplankton over NO3-leading to the quick response. With the input of same amount DIN, different ratios of NH4+/NO3-may influence the growth rate of phytoplankton and determine the time that biomass reaches the maximum causing algal bloom.6. Our observations of nutrient enrichment experiment may verify that NO3-is a better source of protein-inducing nitrogen for diatom than NH4+while NH4+is preferred by dinoflagellate for uptaking and using. Our incubation experiment indicates that input of different forms of nitrogen may enhance the growth of different phytoplanktonic species causing alternation of dominant species, particularly NH4+ enrichment in the sampling area of ECS may lead to overwhelming growth of dinoflagellate and potentially algal bloom.
Keywords/Search Tags:dry deposition, nutrient, dry deposition flux, enrichment experiment, phytoplankton
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