Abstract
In order to understand the contribution of seaweed aquaculture to nutrients and carbon cycles in coastal environments, we measured the nutrients & carbon uptake rates of Porphyra yezoensis Ueda sampled at Nakdong-River Estuary using a chamber incubation method from November 2011 to April 2012. It was observed that the production rate of dissolved oxygen by P. yezoensis (n=30~40) was about $68.8{\pm}46.0{\mu}mol\;{g_{FW}}^{-1}h^{-1}$ and uptake rate of nitrate, phosphate and dissolved inorganic carbon (DIC) was found to be $2.5{\pm}1.8{\mu}mol\;{g_{FW}}^{-1}h^{-1}$, $0.18{\pm}0.11{\mu}mol\;{g_{FW}}^{-1}h^{-1}$ and $87.1{\pm}57.3{\mu}mol\;{g_{FW}}^{-1}h^{-1}$, respectively. There was a positive linear correlation existed between the production rate of dissolved oxygen and the consumption rates of nitrate, phosphate and DIC, respectively, suggesting that these factors may serve as good indicators of P. yezoensis photosynthesis. Further, there was a negative logarithmic relationship between fresh weight of thallus and uptake rates of nutrients and $CO_2$, which suggested that younger specimens (0.1~0.3 g) were much more efficient at nutrients and $CO_2$ uptake than old specimens. It means that the early culturing stage than harvesting season might have more possibilities to be developed chlorosis by high rates of nitrogen uptake. However, N & C demanding rates of Busan and Jeollabuk-do, calculated by monthly mass production and culturing area, were much higher than those of Jeollanam-do, the highest harvesting area in Korea. Chlorosis events at Jeollabuk-do recently might have developed by the reason that heavily culture in narrow area and insufficient nutrients in maximum yield season (Dec.~Jan.) due mostly to shortage of land discharge and weak water circulation. The annual DIC uptake by P. yezoensis in Nakdong-River Estuary was estimated about $5.6{\times}10^3\;CO_2$ ton, which was about 0.03% of annual carbon dioxide emission of Busan City. Taken together, we suggest more research would be helpful to gain deep insight to evaluate the roles of seaweed aquaculture to the coastal nutrients cycles and global carbon cycle.
부산시 강서구 낙동강 하구에서 채집한 방사무늬김(Porphyra yezoensis Ueda)의 용존산소 생산율은 $68.8{\pm}46.0{\mu}mol\;{g_{FW}}^{-1}h^{-1}$, 질산염과 인산염 흡수율은 각각 $2.5{\pm}1.8{\mu}mol\;{g_{FW}}^{-1}h^{-1}$, $0.18{\pm}0.11{\mu}mol\;{g_{FW}}^{-1}h^{-1}$ 그리고 용존무기탄소 흡수율은 $87.1{\pm}57.3{\mu}mol\;{g_{FW}}^{-1}h^{-1}$이었다. 용존산소 생산율과 질산염, 인산염, 용존무기탄소 흡수율은 각각 음의 선형관계를 보여, 광합성활동에 의한 결과물임을 파악할 수 있었다. 김의 생중량에 따른 이들 성분의 생산/흡수율은 로그함수적으로 감소하여, 성체(>~0.3 g)보다는 어린 엽체의 광합성효율이 매우 높은 것으로 나타났으며, 이는 질소부족으로 인한 황백화가 양식초기에도 발생할 수 있음을 제시하였다. 우리나라 시도 단위로 월별 생산되는 김 생산량과 양식면적을 바탕으로 질소요구량과 탄소흡수율을 산정한 결과, 생산량이 가장 높은 전라남도보다 부산(경상남도 포함)과 전라북도의 단위면적당 질소요구량이 높았다. 최근 김 황백화가 빈발하는 전라북도는 좁은 면적에서의 과밀 생산과 최대수확기가 육상과 저층으로부터 영양염 공급이 부족한 12~1월인 점 등이 황백화의 원인인 것으로 추정된다.
