期刊
NEW ZEALAND JOURNAL OF MARINE AND FRESHWATER RESEARCH
卷 42, 期 2, 页码 207-217出版社
TAYLOR & FRANCIS LTD
DOI: 10.1080/00288330809509949
关键词
flocculation; alkalinity; Anabaena; Ceratium hirudinella; phosphorus
Aluminium sulfate (alum) was applied to Lake Okaro, a eutrophic New Zealand lake with recurrent cyanobacterial blooms, to evaluate its suitability for reducing trophic status and bloom frequency. The dose yielded 0.6 g aluminum m(-3) in the epilimnion. Before dosing, pH exceeded 8 in epilimnetic waters but was optimal for flocculation (6-8) below 4 m depth. After dosing, there was no significant change in water clarity, hypolimnetic pH decreased to 5.5, and soluble aluminium exceeded recommended guidelines for protection of freshwater organisms. Epilimnetic phosphate concentrations decreased from 40 to 5 mg m(-3) and total nitrogen (TN):total phosphorus (TP) mass ratios increased from 7:1 to 37:1. The dominant phytoplankton species changed from Anabaena spp. before dosing, to Ceratium hirudinella, then Staurastrum sp. after dosing. Detection of effectiveness of dosing may have been limited by sampling duration and design, as well as the low alum dose. The decrease in hypolimnetic pH and epilimnetic TP, and increase in Al3+ and chlorophyll a, are attributed to the low alkalinity lake water and coincidence of alum dosing with a cyanobacterial bloom and high pH.
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