Nutrient cycling analysis of anthropogenically influenced subtropical coastal ecosystems with a focus on pH-dependent phosphorus species compositions, distributions and transformations

• Applicant: Dr. Julian Oxmann
• Subject Area: Oceanography
• Term: from 2010 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 189711088

Due to the value of goods and services from coastal ecosystems and their increasing threat by anthropogenic perturbations, the development of sustainability recommendations is of immense importance. To achieve improvements, it is essential to understand processes of coastal nutrient cycling, especially of phosphorus (P) dynamics. For gaining insight into the P cycle, it is necessary to assess P speciations and transformations, their control by relevant factors and changes by human impacts. The project investigates nutrient cycling at New Zealand’s Firth of Thames. Coastal ecosystems of this large marine embayment are influenced by sediment and nutrient inputs due to an extensive agricultural catchment basin that caused obviously a rapid mangrove seaward expansion during the past decades. The aim is to determine the P speciation and transformation control of this P enriched region by relevant sediment properties. This can contribute to a better understanding of causes for detrimental effects of diffuse P pollution and the role of P enrichment and speciation in mangrove expansion. Due to the strong pH dependency of sedimentary P species, prevailing pH gradients along coastal transitions and current uncertainties of nutrient speciation changes by ocean acidification, this study will focus on the pH dependency of individual P species. For this approach, a previously developed method for P species quantification will be used and simultaneously improved. Specific objectives are to assess (i) pH and redox potential effects on nutrient limitations and on P speciation, transformation and availability; (ii) effects of temporal pH changes on P speciation and transformation; (iii) P speciation differences among different ecosystems; (iv) P speciation effects on P runoff, availability and uptake. Conclusions will be supported by modeling approaches and comparisons with P speciation assessments of earlier studies.

• DFG Programme: Research Fellowships
• International Connection: New Zealand
• Host: Dr. Luitgard Schwendenmann