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

Abstract

This paper sets out a conceptual framework formodelling events in aquatic ecosystems as coupledprocesses in catchments, water columns and sediments.This theoretical framework is developed using ideasfrom the behaviour of complex adaptive systems. I showthat it is possible to use similar models for eachsubsystem and that there are analogous processes ineach, differing only in scale. In this framework thephytoplankton appear as ’system canaries‘. Nuisancealgal blooms appear as a result of perturbations tothe system biogeochemistry at a range of scales.Macrophytes are identified as important components ofthe coupled catchment, water, sediment system.Thinking of models of algal blooms as coupled sets ofcatchment, water column and sediment models focusesattention on the flows of materials between thesubsystems. Such flows of dissolved and particulateorganic and inorganic nutrients (carbon, nitrogen andphosphorus) are rarely fully quantified. The balanceof particulate and dissolved organic nutrient loads(including detritus) is an important parameter whichdetermines events in aquatic ecosystems. This balanceis affected by a number of anthropogenic changesincluding land use, trophic state and flow regulation.Scaling of temporal and spatial patterns and processesin catchments, water columns and sediments will needto be further studied if this model framework is to bedeveloped.