Extension of a qualitative model on nutrient cycling and transformation to include microtidal estuaries on wave-dominated coasts: Southern hemisphere perspective

Abstract

Estuaries are dynamic transition zones acting as filters and transformers of nutrients passing from catchments to the sea. We propose an extension to an existing southern hemisphere model on nutrient dynamics in estuaries to include the relatively constricted, microtidal estuaries located along wave-dominated coasts in the region, specifically focusing on the limiting macronutrients nitrogen (N) and phosphorus (P) and on key processes, including physical (e.g. flushing, mixing and sedimentation), geochemical (e.g. flocculation), biochemical (e.g. remineralisation) and biological (e.g. primary production) processes. A simplified model of the physical states (primarily controlled by hydrological characteristics) is used as the basis for the qualitative model, where these are defined in terms of characteristic salinity-induced stratification of the water column, flushing time and the mouth condition.Four physical states are identified: a freshwater-dominated state, freshwater pulsed/recovery state, marine-dominated state and the closed mouth state. The states and their physical characteristics largely resemble that of the earlier model, except that the extended model reflects the dynamics of restricted inlets and introduces the closed mouth state. This model specifically explores the variation within southern African estuarine systems to better inform research and management programmes on the appropriate trophic, temporal and spatial scales at which uncertainties in ecosystem functioning need resolving. It can also be applied to other regions in the southern hemisphere, and even the northern hemisphere, with similar hydrological and estuarine geomorphological characteristics (e.g. the Mediterranean coast, the west coasts of North and South America, and the south-west and south-eastern coasts of Australia).

Impact of Berm Breaching on Hyperbenthic Macroinvertebrate Communities in Intermittently Closed Estuaries

“…Physical disturbance dominated the first period of breaching through flushing and habitat loss, while salinity changes occurred after flushing. Our results are consistent with reported changes in physicochemical parameters (Young and Potter 2002;Santangelo et al 2007;Taljaard et al 2009) and habitat (Gobler et al 2005;Becker and Laurenson 2008;Riddin and Adams 2008) due to berm breaching, as well as models developed by Stretch and Parkinson (2006) and Everett et al (2007).…”

The role of submerged macrophytes and macroalgae in nutrient cycling: A budget approach

“…In small shallow estuaries like the Great Brak, the closed mouth state eventually reverts to a well-mixed (due to wind turbulence) brackish system, with no distinct salinity gradient or stratification. Flushing times depend on the duration of mouth closure which can range from days to years (Taljaard et al, 2009a). This state therefore presents one of the most favourable environments for the growth of C. glomerata.…”

Geology, Morphology, and Sedimentology of Estuaries and Coasts

“…Their morphology and biology are geographically so variable (Jennings and Bird, 1967;Galloway, 1981;Dyer, 1990;Eisma, 1997;Allanson and Baird, 1999;Perillo et al, 1999) that classifications should restrict themselves to the identifica tion of a limited number of basic types that can easily be identified on the basis of a few characteristic parameters (accepting that, in reality, there will be numerous transitions between, and subdivisions within, any basic classification). Being mere conventions, there is nothing basically wrong with introducing a new (or modified) classification, and several classifications may well exist side by side, each reflecting the peculiarities of a particular region or set of parameters (e.g., Swaney et al, 2008;Taljaard et al, 2009). In a geotectonicmorphological context, one of the most widely used classifi cations that fulfills the criterion of simplicity is the one proposed by Fairbridge (1980; cf.…”