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 aqu atic ecosystems as coupled processes in catchments, water columns and sediments. This theoretical framework is developed using ideas from th e behaviour of complex adaptive systems. I show that it is possible to use similar models for each subsystem and that there are analogous pr ocesses in each, differing only in scale. In this framework the phytop lankton appear as 'system canaries'. Nuisance algal blooms appear as a result of perturbations to the system biogeochemistry at a range of s cales. Macrophytes are identified as important components of the coupl ed catchment, water, sediment system. Thinking of models of algal bloo ms as coupled sets of catchment, water column and sediment models focu ses attention on the flows of materials between the subsystems. Such f lows of dissolved and particulate organic and inorganic nutrients (car bon, nitrogen and phosphorus) are rarely fully quantified. The balance of particulate and dissolved organic nutrient loads (including detrit us) is an important parameter which determines events in aquatic ecosy stems. This balance is affected by a number of anthropogenic changes i ncluding land use, trophic state and flow regulation. Scaling of tempo ral and spatial patterns and processes in catchments, water columns an d sediments will need to be further studied if this model framework is to be developed.