Edinburgh Napier University

  Semi-enclosed coastal systems are of great importance both environmentally and economically. ln recent years, increased
anthropogenic activities in these areas brought the need for integrated, ecosystem-scale management. This study proposes to estimate the assimilative capacity of a small fjord.
This study had three main aims. The first one was to compare the pelagic properties observed in the 2000s to those observed at the same site in the 1970s, the second one was to design an accurate but simple, two dimensional dynamic model of a fjordic system for the prediction of chlorophyll and nutrient concentrations, and the third one was to propose a method for the estimation of the assimilative capacity of the fjord. This study was carried out on Loch Creran, a shallow fjord in the Scottish Highlands, in which a large sh farm was established in the 1980s.
A sampling campaign was carried out 2003-2004 in order to collect time series of chlorophyll, dissolved inorganic nutrients and particulate organic matter concentrations; temperature, salinity, density and turbidity proles and microplankton and mesozooplankton diversity, abundance and biomass. Similar time series from the 1970s were gathered from the literature. The data from both decades were compared and showed significant changes in some physical, chemical and biological properties.
The cessation of activity of an alginate production plant, changes in weather patterns and the introduction of aquaculture were identified as possible causes.
A simple two-dimensional, three-box dynamic model of Loch Creran was designed. It has only three state variables (chlorophyll, nitrogen and phosphorus concentrations) and two crucial parameters (the exchange rate and the yield of chlorophyll from nutrients) as well as an optical-photosynthetic sub-model. The model was tested against observations for the years 1975 and 2003 and showed an overall good t. The model was then run under different scenarios in order to estimate the assimilative capacity of Loch Creran for nitrogen and phosphorus and its carrying capacity for farmed salmon.