OPET's measurements of the summer of 1998 were also taken at the traditional 4 Pondwatchers locations (OPHead, OP1, 0P2, OP3) at depth intervals of 2m. Salinity was a uniform 1.4-1.5 ppt to a depth of 4 m at all locations except at the freshwater inflow site OPHead, where it was 0. Even at 6 m at 0P3, salinity was only 2-3ppt (see graph). On 4-11-99, the pond was 1.5 ppt to 6m, and 1.6 ppt at 6.25m. This represents a further freshening of the pond from last year's level. The formerly large high-salt pools in the deep parts of the pond have shrunk and have become diluted.
Dissolved oxygen.
Dissolved oxygen is the most important index of health of a pond. The most critical periods are the warm summer months that generally lack winds strong enough to cause significant wave action that brings oxygen to the deeper layers. In past years, dissolved oxygen dropped off sharply below 2 m and was consistently nil at or deeper than 4 m during the summer months. During 1998, the south basin's (OP3) dissolved oxygen at 4m ranged 4 - 7.4 mg/L, compared to surface oxygen of 9.5-11.5 mg/L -a marked improvement in oxygenation of the deeper water layer. In the northern deep basin (OPI) there was no oxygen at 4 m except for the 8-23-98 sample which showed a level of 4.7 mg/L. The pond is getting healthier!
Secchi Depth
Secchi depth also had improved last summer. Between 1988 and 1995, mean Sechi depth ranged from 0.6 to 1.8 m. In the summer of 1998, it ranged from 1.5 to 2.5m.
PO4
Phosphate ranged from 0 to 0.3 µM throughout the pond except at 6 m depth where it ranged between 10 and 37, and at Oyster Pond Head (OPHEAD), the point of surface water inflow into the pond, where it ranged 0.7 to 1.1 µM.
Total Nitrogen
Total nitrogen ranged 8-11 µM in the surface layers and 40-90 µM at or deeper than 4 m, with the north end of the pond higher than the south end and OPHEAD showing 13 - 75 µM. Dissolved inorganic nitrogen in the freshwater inflow into the pond (at OPHEAD) was 65-82 µM. The nitrate and P04 values are not significantly different from those of the previous years, including at higher salinities.