Yang Bin, Lin Hui, Bartlett Sarah L, Houghton Erin M, Robertson Dale M, Guo Laodong
School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 East Greenfield Avenue, Milwaukee, WI 53204, USA; Guangxi Key Laboratory of Marine Disaster in the Beibu Gulf, Beibu Gulf University, Qinzhou 535011, China.
School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 East Greenfield Avenue, Milwaukee, WI 53204, USA.
Water Res. 2021 May 15;196:117025. doi: 10.1016/j.watres.2021.117025. Epub 2021 Mar 10.
Phosphorus (P) loadings to the Great Lakes have been regulated for decades, but re-eutrophication and seasonal hypoxia have recently been increasingly reported. It is of paramount importance to better understand the fate, transformation, and biogeochemical cycling processes of different P species across the river-lake interface. We report here results on chemical speciation of P in the seasonally hypoxic Fox River-Green Bay system and variations in sources and partitioning of P species along the aquatic continuum. During midsummer when productivity is generally high, phosphate and dissolved organic P (DOP) were the major species in river water while particulate-organic-P predominated in open bay waters, showing a dynamic change in the chemical speciation of P along the river-bay transect with active transformations between inorganic and organic P and between colloidal and particulate phases. Colloidal organic P (COP, >1 kDa) comprised 33‒65% of the bulk DOP, while colloidal inorganic P was generally insignificant and undetectable especially in open bay water. Sources of COP changed from mainly allochthonous in the Fox River, having mostly smaller sized colloids (1-3 kDa) and a lower organic carbon to phosphorus (C/P) ratio, to predominantly autochthonous in open bay waters with larger sized colloids (>10 kDa) and a higher organic C/P ratio. The observed high apparent distribution coefficients (K) of P between dissolved and particulate phases and high-abundant autochthonous colloidal and particulate organic P in the hypereutrophic environment suggest that, in addition to phosphate, colloidal/particulate organic P may play a critical role in the biogeochemical cycling of P and the development of seasonal hypoxia.
几十年来，流入五大湖的磷（P）负荷一直受到监管，但最近重新富营养化和季节性缺氧的情况却越来越多地被报道。更好地了解不同磷物种在河湖界面的归宿、转化和生物地球化学循环过程至关重要。我们在此报告了季节性缺氧的福克斯河 - 绿湾系统中磷的化学形态结果，以及沿水生连续体磷物种的来源和分配变化。在仲夏生产力普遍较高时，河水主要的磷物种是磷酸盐和溶解有机磷（DOP），而开阔海湾水域中颗粒有机磷占主导，这表明沿河 - 湾断面磷的化学形态存在动态变化，无机磷和有机磷之间以及胶体和颗粒相之间有活跃的转化。胶体有机磷（COP，>1 kDa）占总溶解有机磷的33% - 65%，而胶体无机磷通常含量极少且难以检测到，尤其是在开阔海湾水域。COP的来源从福克斯河中主要为外源的，胶体大多尺寸较小（1 - 3 kDa）且有机碳与磷（C/P）比值较低，转变为开阔海湾水域中主要为内源的，胶体尺寸较大（>10 kDa）且有机C/P比值较高。在富营养化环境中观察到的磷在溶解相和颗粒相之间较高的表观分配系数（K）以及大量丰富的内源胶体和颗粒有机磷表明，除了磷酸盐外，胶体/颗粒有机磷可能在磷的生物地球化学循环和季节性缺氧的发展中起关键作用。
