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SPATIAL AND TEMPORAL VARIATIONS IN MICROBIAL ACTIVITY 203

Fig. 3 Distribution of Protease activity in Northern Adriatic during the three surveys.

During winter average protease activity (6.18 µg C h-1 dm-3 ) shows lower values
than in summer (9.69 µg C h-1 dm-3 ). As observed in the area of the Egadi Islands,
the break down of the thermocline affects the activity distribution; during this season,
the re-mixing condition determines a rapid sinking of organic matter in some stations
influenced by Po river runoff, and therefore a higher activity in the deeper rather than
surface layers. The variability in the area seems greater at depth (Variation
Coefficient = 136) than at the surface (V.C. = 93).

Greater temporal variations were observed in respiratory rates in the Northern
Adriatic (range 0.05- 11.51 µl O2 h-1 dm-3). These too, were related to the different
hydrological conditions governed by water circulation and river input. In particular,
high values were found in June 1996 and 1997 (mean values: 1.84 ± 1.55 and 3.31 ±
2.79 µl O2 h-1 dm-3, respectively), with increasing values over the two years. Lower
values were recorded in the winter (mean value: 0.34 ± 0.21µl O2 h-1 dm-3).

On seasonal scale, different correlations showed that during summer the
hydrolytic and respiratory processes are well coupled both each other and with other
parameters (Table 2). During winter the processes are uncoupled with each other and
showed different behaviour.