대기 오염이 연근해 지역의 탄소와 영양염의 생지화적 순환에 미치는 영향에 대한 연구

Abstract

This dissertation work investigated the impact of increasing atmospheric CO2 and pollutant nitrogen species on the ocean environment with a particular focus on coastal and marginal seas located downstream of highly industrialized and populated areas. Atmospheric CO2 and pollutant nitrogen have caused ocean acidification, shifts in seawater nutrient limitation, and probably a change in phytoplankton productivity, thereby altering the aquatic ecosystems. The adverse effects of these environmental problems are likely to be more severe in the coastal and marginal seas because the sources of the pollution are largely concentrated on the coast. Prominent examples are coastal waters of East Asia and eastern North America. However, we still lack knowledge about how these pollutants have altered the waters in these two areas. Therefore, more investigation of the response of these seas to increased atmospheric CO2 and deposition of pollutant nitrogen is needed. Knowing the current consequences of the effects of these two pollutants will help to provide useful insights in dealing with these environmental problems and in preparing for expected threats in the future. This dissertation is composed of the following three parts: the study of i) ocean acidification in the East Sea, ii) increasing nitrate concentration in the East Asian marginal seas, and iii) the fertilization effect of wet nitrogen deposition on the US east coast. The first study investigated how the East Sea was affected by ocean acidification over time using a multiparameter linear regression (MLR) model together with the estimated uptake of anthropogenic CO2. The MLR model of aragonite saturation state (ΩARG, a proxy for ocean acidification) as a function of temperature, pressure and O2 concentration in the upper 1,000 m of the East Sea was derived with an uncertainty of 0.020 (1). The ΩARG data used to derive the ΩARG prediction model were collected during a field survey in 1999 and were corrected for anthropogenic CO2. Evaluation of the model with datasets obtained in 1992 and 2007 yielded correlation coefficients of 0.995  0.013 for 1992 (n = 64, p << 0.001) and 0.995  0.009 for 2007 (n = 137, p << 0.001), and root mean square errors of 0.064 for 1992 and 0.050 for 2007. The strong correlation between measurements and predictions suggests that the model can be used to estimate the distribution of ΩARG on varying time scales when basic hydrographic data are available. Application of the model to past measurements for the East Sea indicated that interdecadal variability (2 from the mean) in ΩARG corrected for anthropogenic CO2 was generally high (0.10.7) in the upper water layer (<200 m depth), and decreased (0.050.2) with depth for waters deeper than 500 m. The interdecadal variability is largely controlled by variations in the degree of water column ventilation. Superimposed on this natural variability, the input of CO2 derived from fossil fuels has markedly acidified the upper water layers during the anthropocene, and thereby moved the aragonite saturation horizon upward by 50–250 m. The second study showed nitrogen availability over phosphorus (N* = N – RN:P  P, where N, P and RN:P are nitrate concentration, phosphorus concentration and mean N:P ratio, respectively) has increased over the East Asian marginal seas over the past three decades. The observed N* increase, which was mainly led by the increase in nitrate concentration, was attributed to the riverine and atmospheric input of anthropogenic nitrogen. The N* values in two major rivers (Changjiang and Han River) discharging to the East China Sea and Yellow Sea is higher than ~100 μM. The riverine N* values were compared to N* in the corresponding marine areas where the riverine influence is probably greatest. As a result, we found significant correlations in the Changjiang Rivers (but not in the Han River). However, the influence of nitrogen flux from the Changjiang River appears to be confined to estuary based on the analysis of plume extent and nutrient distribution in summer 1998 when the Changjiang River discharge was the greatest observed since the 1950s. The atmospheric nitrogen deposition estimated in the three air monitoring stations in Korea and one in Japan had a high temporal correlation with seawater N* in the study area, except in the areas wherein riverine N load showed significant positive correlations. This suggests atmospheric nitrogen deposition as a major cause of the N* increase. In particular, total N deposition since 1980s agreed well with the change in N* inventory for the same period in the East Sea where no major river flows. Finally, the increase in N availability caused by atmospheric deposition and riverine input has switched the extensive parts of the study area from being N-limited to P-limited. The third study evaluated the impact of precipitation (including wet nitrogen deposition) on ocean productivity in coastal waters of the eastern United States using satellite data products (i.e. precipitation, wind speed, and chlorophyll-a) and found that precipitation discernably increased chlorophyll-a levels up to ~20% in the low nutrient areas (nitrate < 1µM), but contrarily decreased them in the high nutrient areas (nitrate > 1 µM). The two contrasting responses of ocean productivity to precipitation were probably attributed to different limitations of phytoplankton to nutrient and light during photosynthesis. An increase in wind speed typically accompanied by precipitation events, which deepened the mixed layer

the net effect is the addition of extra nutrient to the mixed layer but the reduction of light availability. The added nutrient increased phytoplankton productivity in the nutrient-depleted area while the reduced light availability lowered production in the nutrient-replete area where light limits the growth of phytoplankton. The contribution of wet deposition of pollutant nitrogen was estimated to be less than 7% of new production (using direct measurements of wet deposition) and less than 5% of chlorophyll concentration (using a satellite-based precipitation product). These results show the significant roles of atmospheric anthropogenic CO2 and nitrogen on ocean acidification (by reduced ventilation), relative nutrient limitation and ocean fertilization, which were yet to be fully appreciated. Therefore, this dissertation would enhance our understanding of the changing ocean environment under human footprint.