Graham P. Harris

Biogeochemistry of nitrogen and phosphorus in Australian catchments, rivers and estuaries: effects of land use and flow regulation and comparisons with global patterns

This paper reviews the factors influencing the nitrogen (N) and phosphorus (P) exports from Australian catchments. Pristine, forested catchments export little N and P and the predominant form of N is dissolved organic nitrogen (DON). As catchments are cleared, exports increase and the predominant form of N changes from DON to dissolved inorganic N (DIN). Soluble reactive P (SRP) represents a roughly constant fraction of total P in these systems. As catchments are cleared, DIN:SRP export ratios increase sharply and DIN comes to represent a larger and larger fraction of the total N. The ratios of total N:P and DIN:SRP in rivers reflect land use and the residence times of the water. In Australian lakes and reservoirs, DON and total Kjeldahl N (TKN)are consumed and DIN is exported downstream. Australian freshwater systems with long residence times show stoichiometric evidence of N limitation, and the frequent occurrence of N-fixing cyanobacterial blooms. Despite TN:TP loading ratios equalling or exceeding Redfield stoichiometry, many Australian estuaries and coastal lagoons also show extensive evidence of rapid denitrification and N limitation. Coastal lagoons also have long water residence times (up to 1 year) and a high proportion of the N load is denitrified.

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

This paper presents a biogeochemical model of a coastal lagoon intended to be representative of lagoons occurring along the south-east and south-west coasts of Australia. Many of these lagoons are threatened by increased nutrient loads because of land use change, by alterations to their freshwater inflows and by modification to their tidal flushing regimens. The model simulates the biogeochemical response of the lagoon to nutrient (nitrogen) loading and includes nutrient transformation processes in the sediments, as well as in the water column. The paper focuses on the response of primary producers to increasing and decreasing nutrient loads and how the response is altered by changes in the flushing rate of the lagoon with the sea. In common with lakes, the modelled lagoon exhibits alternative stable states representing macrophyte or phytoplankton dominance depending on nutrient loading and history. A third state representing severe degradation occurs when denitrification shuts down. A characteristic of Australian coastal lagoon systems is that, due to highly sporadic rainfall patterns, nutrient inflows are dominated by intermittent extreme events. The modelling demonstrates that such a loading regimen may be expected to generally increase the vulnerability of the lagoon to increasing nutrient loads. The results of the analysis presented are pertinent to several questions raised by coastal managers, such as what are the expected benefits of improving flushing by dredging and what are the consequences of altering the timing and magnitudes of the loads reaching the lagoons?

Remote Sensing of Marine Photosynthesis

The oceans occupy 70% of the earth’s surface, and estimates of their contribution to global photosynthesis range from 10% to 50% (Perry, 1986) or 20 to 50 × 1015 g C y−1 (McCarthy, 1984; Martin et al., 1987). Photosynthesis in the oceans is of interest as the basis of marine food chains (Ryther, 1969) and for its role in global biogeochemical cycles (e.g., Sundquist, 1985). The nature and dynamics of marine producers differ markedly from those of their terrestrial counterparts. The pool of living plant carbon in the oceans is small (about 0.5 to 5.0 gC m−2) and consists principally of microscopic unicellular organisms that turn over rapidly, on time scales of the order of days (Harris, 1980a). These turnover rates are thought to be controlled primarily by light and nutrient limitation. Because of the low biomass concentrations, estimates of photosynthetic rates have been based primarily on the measurement of rates of incorporation of 14C-labeled isotopes in incubations (Harris, 1984). While there has been a long-standing discussion of the interpretation of these data (Peterson 1980; Harris, 1984), debate has recently intensified with the development of alternative methodologies (e.g., Shulenberger and Reid, 1981; Jenkins and Goldman, 1985). Evidence of the importance of extremely small cells (picoplankton) (Johnson and Sieburth, 1979, 1982; Platt and Li, 1986) and of incubation artifacts such as metal contamination (Fitzwater et al., 1982) has cast further doubt on the large historical set of marine primary production estimates.

Global remote sensing programmes, global science, global change: An Australian perspective

Abstract The so-called ‘post-modern’ era lacks the political will and vision of the early days of the space programme, and economic depression has caused budgets of all kinds to be cut back. ‘Big science’ is no longer popular and space, as the biggest science of all, has changed accordingly. The emphasis is now on ‘capturing benefit’ and recovering costs. This article reflects on the changing nature of space programmes and global science programmes in the 1990s and tries to understand why it has been so difficult to convince successive Australian governments that a realistic space programme is desirable. It concludes by suggesting that Australia needs to espouse a new kind of space programme for the 1990s, not a copy of the ‘modern’ programmes developed 30 or more years ago.

The chemical environment

The chemistry of natural waters has been reviewed in a number of major texts (Hutchinson, 1957b; Davis and DeWiest, 1966; American Chemical Society, 1971; Allen and Kramer, 1972; Broecker, 1974; Holland, 1978; Stumm and Morgan, 1981; Drever, 1982) and the reader is referred to such texts for the complete treatment of the topics to be outlined here. There has been much emphasis of late on the global biogeochemical cycles of nutrients and other elements and the influence of human interference on such cycles (Woodwell and Pecan, 1973; Stumm, 1977; Trudinger and Swaine, 1979). Events in natural waters must be seen as part of a much larger, global picture. The ionic composition of natural waters is as much a function of the solution chemistry of the lithosphere as it is a function of chemical equilibria in situ. The ionic composition of the oceans may be thought of as resulting from a massive titration, with the acids provided by gases from volcanic activity and the bases provided by the rocks (Stumm and Morgan, 1981). Similarly the ionic composition of lakes results from the dissolution of rocks and other materials in the basin. In this case the dominant mechanism of chemical weathering is carbon dioxide dissolved in the groundwater. The quality of water in a lake is therefore heavily influenced by events in the drainage basin and must be seen in the light of soil type, land use and agricultural practice in that basin. In all that follows I will concentrate on events in surface waters where the phytoplankton grow. The distribution of nutrients in surface waters is, however, very much influenced by regeneration in deep water and events at the sediment interface and, where pertinent, such events will be discussed here. The reader is referred to the texts listed above for details of the full cycles of elements within lake and ocean basins.