Predictive models in spatially and temporally variable freshwater systems

Abstract

This paper discusses the relationships between scaling and predictability in ecosystems. The logical basis of ecosystem modelling is explored using ideas first developed in complexity theory and analogies with the behaviour of complex adaptive systems. Any ecological model is a scale‐dependent entity and both empirical and dynamic models of freshwater systems have their strengths and weaknesses. The logical basis of modelling using functional groups is explored. I conclude that such an approach can be justified and that such models have predictive power. Any predictive model of freshwater systems must take the major scales of external (atmospheric and catchment) forcing into account as well as the scales of key processes in the ecosystem itself. The importance of so‐called ‘pink noise’ spectra, which arise both from external forcing and the internal dynamics of dynamic systems, is noted. The key scales of pattern and process in freshwater ecosystems are discussed in relation to the properties of the major functional groups. In order to have predictive power, I conclude that models of freshwater systems must include sediment exchanges and the properties of aquatic macrophytes as well as water column interactions and the pelagic components. When viewed at the scale of functional groups and the major biogeochemical processes, freshwater ecosystems may not be as complex as is often assumed.

Anthropogenic impacts on the ecosystems of coastal lagoons: modelling fundamental biogeochemical processes and management implications

“…Much of the conceptual development of this model was performed during the Port Phillip Bay study (Harris et al 1996;Murray and Parslow 1997, 1999a, 1999b. Further details of the conceptual development of the model used in the present paper may be found in Harris (1997Harris ( , 1998Harris ( , 1999. This model describes the ecosystems of the coastal embayments of south-east Australia.…”

“…Broadly, there is a set of pelagic interactions and a set of benthic interactions controlled by analogous sets of functional groups. This choice of model structure is outlined in Harris (1997Harris ( , 1998Harris ( , 1999. The model was run with all stocks (boxes) and flows (arrows) calculated as mass of nitrogen per unit area and mass of nitrogen per unit area per unit time, respectively.…”

This is not the end of limnology (or of science): the world may well be a lot simpler than we think

“…If we begin by accepting that evolution is fundamentally an algorithmic process (Dennett, 1995) then the complexity that we observe in the real world arises from simple causes and from the interaction of agents acting on local information driven by Darwinian processes (for an application of this argument to aquatic systems see Harris, 1994Harris, , 1998. If we begin by accepting that evolution is fundamentally an algorithmic process (Dennett, 1995) then the complexity that we observe in the real world arises from simple causes and from the interaction of agents acting on local information driven by Darwinian processes (for an application of this argument to aquatic systems see Harris, 1994Harris, , 1998.…”

“…Whilst Gasith & Hoyer (1998) define shallow lakes as those which are macrophyte-dominated (see Moss, 1995) many lakes exist in a turbid state dominated by phyto-and meroplankton, or the lake may switch between the two states over periods of many years (Blindow et al, 1993;Scheffer et al, 1993). There is competition between the littoral and the pelagic for light and nutrients and the two states of lakes and estuaries can be modelled by some simple relationships which rely on some simple physiological properties of the major groups (Harris, 1997(Harris, , 1998 One final point needs to be made. In all cases the overall cycling of major and minor elements within lakes and estuaries is controlled by microbial processes.…”

“…Harris (1997Harris ( , 1998 has argued that the answer is yes, and that we can aggregate the population dynamics of the phytoplankton into functional groups on the basis of form, function and fate. Do these populations of phytoplankton growing in the pelagic zone show emergence?, i.e.…”