On the role of morphometry in coastal ecosystem modelling and management

Sammanfattning: Many signs show that the Baltic Sea is increasingly eutrophicated. Primary production hasincreased significantly resulting in gradually decreasing deep water oxygen concentrationsduring the twentieth century. In the coastal zone, problems are often manifested as oxygendepletion resulting in extinction of macrobenthic fauna. Therefore, there has been an increased need for methods and predictive models for environmental impact assessments. Themain hypothesis in this thesis is that the coastal morphometry to a large extent regulatescoast-ecological key parameters, like surface and deep water turnover and bottom dynamicconditions. All these factors influence the dispersal, sedimentation and recirculation of different substances (e.g., nutrients) in the coastal zone. This thesis focuses on simple andpractically applicable models to predict such key parameters, using information from nautical charts, Defined archipelago areas in the size range 1-100 km2 are of primary interest in this thesis.A computerised method to calculate topographic characteristics of coastal areas was developed. The method includes a help to define a relevant, coastal ecosystem, a necessary prerequisite when calculating morphometric characteristics.Predictive models were derived from statistical relationships between empirical data on surface and deep water turnover, proportion of accumulation areas and coastal morphometry data. All models yielded r2-values > 0,7 (n=14-23). A dynamic (i.e., time dependent) model predicting seasonal variability in oxygen concentration and oxygen consumption was also developed. The model can be used to identify areas where low oxygen concentrationsare likely to appear and to predict the lowest oxygen concentration during the year.A sediment survey in the St. Anna archipelago resulted in a new approach to estimatethe historical development of laminated sediments. It is suggested that this approach may beused as an effective tool for establishing effect-related water quality criteria.The overall conclusion from this thesis is that the coastal morphometry can provide veryuseful information for coastal management models, e.g., to assess the sensitivity of differentareas to an increased load of nutrients.