Comparative seasonal estimates of primary productivity in the Waikato River lakes during summer, autumn, and winter

Primary productivity measurements were made at 1 m and 10 m depths in six of the eight impoundments on the Waikato River. At 1 m depth during the summer, carbon productivity varied from 17.68 mg.m^‐3.h^‐1 in oligotrophic Lake Aratiatia to 509.4 mg.m‐³.h^‐1 in eutrophic Lake Karapiro; intervening lakes had intermediate values. The highest values were found in the autumn at 1 m depth (22.3 mg.m^‐3.h^‐1 to 970.9 mg.m^‐3.h^‐1). The winter 1 m values were lower than the summer and autumn values by an order of magnitude. At 10 m depth, productivity appeared to be light limited and was comparable in all the lakes in the summer and autumn assays, decreasing by an order of magnitude in the winter. Nitrogen may have limited productivity during the relatively dry summer. Regression analysis indicated that nitrogen and light penetration were the principal factors affecting productivity. Dark‐bottle counts indicated dark carbon fixation processes which could have been biochemically different in the eutrophic and oligotrophic waters.

Keywords:

• Primary productivity
• Freshwater lakes
• Waikato
• Light
• Temperature
• Nitrogen
• Phosphorus
• Dark‐fixation
• Eutrophication

Notes

Present address: Department of Zoology, University of Rhodesia, P.O. Box MP 167, Mount Pleasant, Salisbury, Zimbabwe