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

由于沿海生态系统的商品和服务的价值及其受到人为干扰的日益严重的威胁，制定可持续性建议具有极其重要的意义。为了实现改进，必须了解沿海养分循环的过程，特别是磷(P)的动态变化。为了深入了解磷循环，有必要评估磷的形态和转化、相关因素对它们的控制以及人类影响的变化。该项目调查了新西兰泰晤士湾的营养循环。这个大型海洋海湾的沿海生态系统受到沉积物和养分输入的影响，这是因为一个广泛的农业集水区在过去几十年里明显地导致了红树林向海的快速扩张。目的是通过相关的沉积物性质来确定该富磷区的磷形态和转化控制。这有助于更好地了解扩散磷污染的有害影响的原因，以及磷的富集化和形态在红树林扩张中的作用。由于沉积物中磷物种的pH依赖性很强，海岸过渡带上普遍存在的pH梯度，以及海洋酸化对营养盐形态变化的不确定性，本研究将集中在单个磷物种的pH依赖性上。对于这一方法，将使用先前开发的P物种量化方法，并同时进行改进。具体目标是评估(I)pH和氧化还原潜力对营养限制以及对P形态、转化和有效性的影响；(Ii)时间pH变化对P形态和转化的影响；(Iii)不同生态系统之间的P形态差异；(Iv)P形态对P的径流、有效性和吸收的影响。结论将得到建模方法的支持，并与早期研究的P形态评估进行比较。

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.