Aquatic & marginal vegetation of Lake Serpentine North

Report: TR 2001/03

Author: Grant Barnes

The Northern Waikato Region has an abundance of freshwater ecosystems ranging from large peatbogs, minerotrophic wetlands, peat lakes associated with developed peatlands, and small shallow riverine lakes. There are more than 40 lakes ranging in size from less than 0.01 km² (Lake Posa, near Koromatua) to 34.4 km² (Lake Waikare).

The peat lakes of the Waikato region are concentrated around the Waikato, Hamilton and Waipa fistricts, where their association with peat formations has had a marked effect on their physical, chemical and biological nature. There are 15 lakes located in the Waipa District, 12 in the Waikato District and one within Hamilton city.

The Waikato peat lakes form the largest group of peat lake habitats in New Zealand and are valuable conservation refuges for many unique plant and animal species. They also represent some of the few remaining areas of wetland in the formally extensive Komakorau, Rukuhia and Moanatuatua peat bogs, as well as being important recreational areas for hunting, boating and picnicking.

Aquatic macrophytes play an important role in regulating lake ecology. These plants enhance habitat complexity and heterogeneity, which in turn provides substrate for fish spawning, sessile invertebrates and periphyton communities, and refugia for zooplankton. Macrophytes can also improve water clarity by bank stabilisation, wave moderation and by promoting the settling out of suspended sediments from the water column.

The presence and composition of submerged vegetation within a lake is influenced by a number of interacting factors including water clarity, introduction of exotic species, competition by marginal vegetation, exposure and season. Exotic species influence aquatic vegetation composition by displacement by invasive oxygen weeds (Hydrocharitaceae and Ceratophyllaceae) and predation and/or disturbance by exotic herbivorous fish (rudd – Scardinius erythrophthalmus) and omnivorous fish (catfish – Ameiurus nebulosus).

A survey of the marginal and aquatic vegetation of the Waipa peat lakes was undertaken in the early 1990s where the presence of native submerged vegetation was noted in several lakes (Champion et al., 1993). Recent re-surveys of some of these lakes have found that the aquatic vegetation has completely collapsed, leaving Lake Serpentine North as the last remaining lake requiring survey. This report describes the results of a botanical survey of the marginal and submerged vegetation of Lake Serpentine North, undertaken during February 2001.