SECULAR TRENDS AT £. AUSTRALIAN COASTAL STATIONS : 1942-52 747 



For the New South Wales stations, the decrease in chlorinity of the 

 surface waters particularly has been associated with increases in rain- 

 fall, but on the other hand, at the Maria Island station there has been 

 an increase in CP/oo accompanied by a decrease in rainfall. 



IV. Factors of Possible Importance in the Genesis 

 OF these Trends 



(a) Riverine dilution and nutrient enrichment of coastal waters. 



The parallelism between surface Cl°/oo and rainfall trends at the 

 three stations considered in the previous section, suggests that land 

 drainage can greatly affect the Cl°/oo of these coastal waters. 



The considerable scatter evident in the plotting of the relationship 

 between rainfall and coastal surface Cl°/oo in east Australian waters 

 (Fig. 8), is not unexpected, because of the varying time lag between 

 rainfall and its effect as riverine discharge on coastal Cl°/oo and also 

 because of the varying depth to which such discharges are mixed into 

 the coastal water structure. However, it is clear that surface waters are 

 diluted by riverine discharge with increasing effectiveness as the rain- 

 fall increases. Moreover, there is clear evidence of the existence of two 

 principal surface water masses, a New South Wales above 37 °S and an 

 eastern Tasmanian below 37 °S. Is it possible that these riverine dis- 

 charges could vary the phosphate levels of these coastal waters to the 

 extent that has been experienced at the three stations discussed in 

 Section III? 



In Fig. 9, the relationship between inorganic phosphates and 

 CP/oo at the Port Hacking station is shown. It is clear that surface 

 and bottom waters exhibit a different Cl°/oo-phosphate relationship. 



In the surface layer a decrease in Cl^'/oo from 19.70 to 19.40"/oo 

 is accompanied by a rise in inorganic phosphates of Gfxg P/L. Assuming 

 that the decrease in CP/oo is due to land drainage and that the rise 

 in inorganic phosphates has been wholly an effect of such riverine dis- 

 charges, then the phosphate concentration in the discharge would have 

 to be about 400yng P/L. This figure is about 10 times greater than the 

 maximum phosphate level in coastal rivers of the phosphate rich north- 

 ern New South Wales region and about 40 times greater than the rivers 

 immediately adjoining Port Hacking. 



In tJie bottom waters the decrease in CP/oo from 19.70 to 19.53 is 

 paralleled by a rise in inorganic phosphates of 9/xg P/L. This would 

 imply a phosphate concentration of 1200/..,g P/L in the diluting water, 

 which phosphate concentration is quite impossible. 



