Lake Rotomanuka North and South

GENERAL INFORMATION

Lake Rotomanuka North and South are connected by approximately 10 ha of wetland area. They are two remnants of a historically larger lake. This has resulted from diverted inflows, increased Drainage from surrounding farmland and peat shrinkage.

Sediment cores taken from the northern side of Rotomanuka by Thompson and Champion (1993) revealed that close to the lake there is a shallow peat deposit arising from marginal vegetation, which is overtopped by mineral soil. Further from the lake there is 1.5m of oligotrophic (acid) peat overtopped the underlying mineral layer. These observations confirm that Lake Rotomanuka is associated with the edge of the Moanatuatua bog and deep peat deposits.

Stratification and anoxia of the hypolimnion in Rotomanuka North has been recorded during summer (Boswell et al., 1985). These conditions are likely to reduce binding of phosphorus to the sediments, resulting in phosphorus releases to the overlying water (Søndergaard et al., 2003).

Lake Rotomanuka Statistics

Area	17.1 ha, combined
Maximum depth	8.7 m
Trophic state	eutrophic (Rotomanuka N), hyper-eutrophic (Rotomanuka S)
Catchment	Pastoral, dairy farming
Recreation	Game bird hunting, bird watching
Restoration progress	The perimeter of Lake Rotomanuka North and South and the wetland that adjoins the two lakes has been fenced to exclude stock. Some native planting on the north side of Rotomanuka.
Peat influence	Moderate
Reserve status	Wildlife management reserve, administered by the Department of Conservation. The Waipa District Council have a number of local purpose (esplanade) reserves flanking the lake margins that provide buffer planting for restoration. There is a joint effort by the DoC and a motivated community group for restoration initiatives.
Submerged vegetation	In 1977 Potamogeton ochreatus, Utricularia australis and Elodea sp. were found. Since then Egeria densa has dominated the lake when submerged vegetation has been present. No vegetation has been found in Rotomanuka South.
Harmful algae
Invasive fish	Catfish, goldfish

Images

Boswell et al. (1985). Waikato small lakes: resource statement. Waikato Valley Authority.

Champion et al. (1993). The Vegetation of the Lower Waikato Lakes. Volume 2: Vegetation of thirty-eight lakes in the lower Waikato. NIWA Ecosystems Publication No.8 August 1993.

Faithfull et al. (2006). Waikato peat lakes sediment nutrient removal scoping exercise. Environment Waikato Technical Report TR06/15.

Thompson K. & Champion P.(1993). Esplanade Reserve Recommendations for Lakes Serpentine, Mangahia, Rotomanuka, Ruatuna and Cameron. Prepared for Waipa District Council & Waikato Conservancy, Department of Conservation.