Algal biomass and biogeochemistry in catchments and aquatic ecosystems: scaling of processes, models and empirical tests

This paper sets Out a conceptual framework for modelling events in aquatic ecosystems as coupled processes in catchments, water columns and sediments. This theoretical framework is developed using ideas from the behaviour of complex adaptive systems. I show that it is possible to use similar models for each subsystem and that there are analogous processes in each, differing only in scale. In this framework the phytoplankton appear as 'system canaries'. Nuisance algal blooms appear as a result of perturbations to the system biogeochemistry at a range of scales. Macrophytes are identified as important components of the coupled catchment, water, sediment system. Thinking of models of algal blooms as coupled sets of catchment, water column and sediment models focuses attention on the flows of materials between the subsystems. Such flows of dissolved and particulate organic and inorganic nutrients (carbon, nitrogen and phosphorus) are rarely fully quantified. The balance of particulate and dissolved organic nutrient loads (including detritus) is an important parameter which determines events in aquatic ecosystems. This balance is affected by a number of anthropogenic changes including land use, trophic state and flow regulation. Scaling of temporal and spatial patterns and processes in catchments, water columns and sediments will need to be further studied if this model framework is to be developed.