Water quality and plankton ecology— The Christina river, Delaware

Abstract

The Christina river, with headwaters in the rolling hills of Chester County, Pennsylvania, crosses into Maryland and then into Delaware through rapidly growing New Castle County before its confluence with the Delaware river some 53 km away. Analyses performed during the summer of 1970 at 11 sampling stations covering 51·5 km of this partially tidally affected river (lower 25·7 km) show that, although organic loadings were low (biochemical oxygen demand less than 10 mg/l), increasing dissolved oxygen deficits ( 0·5 mg/l at the headwaters vs. 5·0 mg/l near the river mouth), increasing chloride levels (up to 70 mg/l in the downstream reaches), and ammonia-, nitrite-, and nitrate-nitrogen data for the lower two-thirds of the river were typical of a degraded water course unable to cope with the pollutional loading. Plankton counts, although low at all stations, increased with distance downstream (from 396/l at station 1 to 228,000/l at station 11). Free CO 2 concentrations increased steadily from an average 1·4 mg/l in the upper 4 stations to 8–9·5 mg/l at station 11. The luxurious growth of Plectonema boryanum, using CO 2-saturated, filtered media from each station, demonstrated the possibility that the limiting plankton growth factor in the Christina river may be the low carbon concentrations.