New Zealand Journal of Marine and Freshwater Research abstracts

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Submerged-vegetation changes in Lake Rotoroa (Hamilton, New Zealand) related to herbicide treatment and invasion by Egeria densa

CHRIS C. TANNER JOHN S. CLAYTON BRIAN T. COFFEY

Aquatic Plant Section Ruakura Agricultural Centre Ministry of Agriculture and Fisheries Private Bag, Hamilton, New Zealand

Abstract Lake Rotoroa is a small (54 ha), shallow (maximum depth 6 m), urban lake which has been subject to repeated chemical weed control since 1957. The distribution and abundance of aquatic macrophytes in the lake were studied in six SCUBA surveys between 1977 and 1986. During this period three applications of diquat herbicide resulted in periodic decreases in submerged vascular plant growths in the lake. Macrophy tes were present over c. 80% of the lake bed to a maximum depth of 5-5.5 m during the period of study. Emergent macrophytes, particularly Baumea articulata, Iris pseudacorus, Eleocharis sphacelata, and Typha orientalis, and floating-leaved Nymphaea, were recorded around c. 50% of the lakeshore. In 1977 the most abundant submerged vascularplants vitmLagarosiphonmajor and Elodea canadensis which were both recorded at all sampling sites. Egeria densa, which was first recorded in the lake in 1977, spread at the expense of these species to become the dominant vascular plant in the lake by 1986. In May 1986 it was present on all sampling profiles (35) and occupied an estimated 35% of the lake's vegetation whereas Lagarosiphon and Elodea occupied an estimated 6% and < 1 %, of the vegetation respectively. Extensive beds of charophytes (Chara corallina, Nitella hookeri, and N.pseudoflabellata) persisted in the lake during the period of study. In May 1986 charophytes occupied an estimated 52% of the vegetation, their abundance apparently enhanced by selective herbicidal control of vascular species.

Keywords Waikato lakes; aquatic vegetation; vegetation changes; macrophytes; charophytes; exotic plants; Egeria; Lagarosiphon; Elodea; aquatic weed control

New Zealand Journal of Marine and Freshwater Research, 1990, Vol. 24: 45-57 Crown copyright 1990
Received 13 October 1987; accepted 25 August 1989

PDF file of entire paper: medium quality (1012K); (scanned from paper original: notes about this process)

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