746 EIGHTH PACIFIC SCIENCE CONGRESS 



III. Secular Trends at the Port Stephens, Port Hacking and 

 Maria Island Coastal Stations 



In order to illustrate the latitudinal spread of the trends exhibited 

 by east Australian coastal waters, and also to provide as long a time 

 span as possible, only data from the three earliest established coastal 

 stations in New South Wales and Tasmania will be considered in this 

 section. 



Fig. 2 shows how the mean summer and winter surface and bottom 

 nutrient conditions at the Port Hacking station have varied over the 

 period 1943 to 1952. There is clear evidence of a gradual rise in in- 

 organic and total phosphorus for both surface and bottom layers, with 

 little difference between winter and summer conditions. Nitrate ni- 

 trogen values have also risen during the same period, but only in the 

 bottom layers. 



Fig. 3 demonstrates clearly the gradual decrease in Cl°/oo as- 

 sociated with an increase in the rainfall at the Port Hacking coastal 

 station during the same period. However, it is clear that the summer 

 bottom Cl°/oo was decreasing well in advance of the 1948 increase in 

 summer rainfall. At the Port Stephens coastal station (Fig. 4) there 

 is evidence of an increase in inorganic and total phosphorus from 1945 

 to 1950, but after that year the values have remained steady. It is to 

 be noted, however, that the magnitude of the increase is much less than 

 at the Port Hacking station. Moreover, nitrate values have decreased, 

 except for the rather inexplicable increase in the bottom winter waters. 

 At the same station the CP/oo of surface waters has been greatly af- 

 fected by land runoff (Fig. 5). However, it is important to note that 

 the Cl°/oo of the summer bottom waters has varied little during the 

 period. 



Off Maria Island (Fig. 6), the inorganic phosphates have increased 

 since 1946 to a maximum in 1950, but have remained at this level since 

 that year. The total phosphorus increase parallels that for inorganic 

 phosphate. There appears to have been little change in the nitrate 

 nitrogen of these waters during the same period. 



The CP/oo of these waters (Fig. 7) has increased at a steady rate 

 since 1947 and this is true of both summer and Avinter periods. The 

 decrease in rainfall particularly during the winter period is apparent. 



It IS clear then that at each of these three coastal stations at dif- 

 ferent latitudes along east Australia, there has been an increase in the 

 phosphate content, both in the inorganic and organic form, over the 

 past 7-10 years. The nitrate nitrogen has increased only at the Port 

 Hacking station and has decreased at the other two stations. 



