Dynamics of dissolved and particulate phosphorus influenced by seasonal hypoxia in Green Bay, Lake Michigan

• Published in: The Science of the total environment Vol. 541; pp. 1070 - 1082
• Main Authors: Lin, Peng, Klump, J. Val, Guo, Laodong
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.01.2016
• Subjects: algal blooms; anaerobic conditions; Chemical speciation; Correlation; Dipping; Dissolution; dissolved organic carbon; dissolved oxygen; Dopants; Dynamics; ecosystems; eutrophication; Fox river; freshwater; Green bay; Hypoxia; inorganic phosphorus; Lake Michigan; Michigan, Lake; Nutrient; Nutrients; particulates; partition coefficients; Phosphates; Phosphorus; Rivers; sediment transport; summer; USA, Michigan L., Green Bay; North America, Great Lakes; Michigan, Lake; Lake Michigan; Green bay; Chemical speciation; Phosphorus; Nutrient; Hypoxia; Lake Michigan; Fox river
• DOI: 10.1016/j.scitotenv.2015.09.118
• ISSN: 0048-9697

Despite major investments in point source reductions, portions of the Great Lakes, like Green Bay, remain hypereutrophic and are subject to persistent seasonal hypoxia. Phosphorus (P) is generally a limiting nutrient in the Great Lakes ecosystem, but not all P species are equally bioavailable, and the dynamics of nutrients and their correlation to algal bloom remain poorly characterized, in part, due to a lack of adequate quantification of P chemical speciation. During summer 2014, water samples were collected from seasonally hypoxic Green Bay for measurements of dissolved and particulate inorganic and organic P to examine P cycling dynamics along a steep nutrient gradient ranging from Fox River inflow dominated eutrophic waters in the southern bay to mesotrophic northern waters near the bay's connection with open Lake Michigan. River-derived dissolved and particulate P was quickly removed from the water column in southern Green Bay through biological uptake and sedimentation. Concentrations of phosphate or dissolved inorganic P (DIP) dramatically decreased from 828±216nM in the Fox River, comprising 57±1% of the total dissolved P, to 24±9nM in northern Green Bay where dissolved organic P (DOP) became predominant (>80%). Generally low phosphate concentrations and extremely high dissolved organic C/P ratios (2090±1160 in August 2014) suggested high DOP turnover rates and active transformation between DOP and DIP through organic degradation during P-limited conditions in Green Bay. Elevated DIP levels were accompanied by low dissolved oxygen in deeper waters (10–15m) of central Green Bay where hypoxia-development occurred, suggesting the release of DIP through particle regeneration under hypoxic conditions enhanced by lateral transport and sediment resuspension. High partition coefficients (Kd) of both inorganic and organic P and their significant negative correlation with suspended particulate matter concentrations indicated the particle-reactive nature of P in freshwater environments and may imply that DOP could also be bioavailable under P-limitation. [Display omitted] •Dissolved and particulate P speciation was studied in Green Bay, Lake Michigan.•Steep gradients in P species exist from eutrophic river to mesotrophic bay waters.•Low DIP, high DOP and high DOC/DOP ratios were observed throughout Green Bay.•Hypoxia and sediment resuspension appeared to enhance DIP release from sediments.•High particle-reactivity of P may be a factor for P-limitation in lake waters.