Seepages and flushes
A flush in Burgoo Stream, West Nelson, with Gentianella grisebachii (Peter Williams)
Seepages and flushes form where groundwater emerges on hillsides to form soils that are mostly permanently saturated with relatively nutrient and oxygen rich water. Seepages tend to be wetter for longer periods than flushes, which are often formed by a periodic pulse of water following rain (Johnson & Gerbeaux 2004).The high water table excludes most woody plants from these habitats and herbaceous species dominate. They are particularly rich in species where they form on limestone rock. They may be extensive in some circumstances, but they are often relatively small, covering no more than a few dozen square metres.
Synonyms
Filtration spring
Where do they occur?
Seepages and flushes occur throughout New Zealand from sea level to the upper alpine zone and are most common in the montane zone of wetter districts.
Notable flora and fauna
Threatened plants include nationally critical Acaena rorida, Deyeuxia lacustris, hairy willowherb (Epilobium hirtigerum), Hypericum minutiflorum, New Zealand mousetail (Myosurus minimus subsp. novae-zelandiae), stalked adder’s tongue fern (Ophioglossum petiolatum), creeping foxglove (Ourisia modesta), Oeder’s Apple-moss (Plagiopus oederiana) and marsh arrow grass (Triglochin palustris); nationally endangered Carex uncifolia, Gunnera densiflora, whipcord hebe (Hebe salicornioides), Lobelia carens, Matthew’s forget-me-not (Myosotis matthewsii) and Lagenifera montana; nationally vulnerable Gratiola nana, Iphigenia novae-zelandiae and Ladys tresses (Spiranthes novae-zelandiae); declining willowherb (Epilobium insulare) and Ranunculus brevis; naturally uncommon Abrotanella patearoa, Aciphylla cartilaginea, feeble bent (Agrostis imbecilla), mountain bent (Agrostis oresbia), Brachyglottis turneri, Talbot’s onion (Bulbinella talbotii), sedges (Carex berggrenii, C. druceana, C. edgariae, C. lachenalii subsp. parkeri, C. trachycarpa), Tin Range mountain daisy (Celmisia polyvena), snow tussocks (Chionochloa lanea, C. crassiuscula subsp. directa), Helms crassula (Crassula helmsii), cudweeds (Euchiton ensifer, E. paludosus, E. polylepis), Euphrasia integrifolia, little gentian (Gentiana lilliputiana), Gentiana lineata, Juncus scheuchzerioides, wind grasses (Lachnagrostis pilosa subsp. nubifera, L. uda), Myosotis tenericaulis, Poa incrassata, buttercups (Ranunculus kirkii, R. maculatus, R. pinguis, R. simulans, R. ternatifolius), and Schizeilema pallidum. The spider orchid (Nematoceras rivulare) is data deficient.
Threatened and rare indeterminate flora include nationally critical Limosella (b) (CHR 515038; Manutahi), Ranunculus (b) (CHR 324466; Burgoo Stream), and Ranunculus (a) (AKU 19876; Hope); the naturally uncommon Myosotis aff. pygmaea (CHR 244566; Volcanic Plateau) and Myosotis aff. tenericaulis (AK 7570; Garvie Mountains).
Several invertebrates can be found in seepages, Trichoptera and Diptera dominate the habitat. There also have been found some undescribed species of the amphipod Paraleptamphopus, the stratiomyid Odontomyia, the chironomid ?Apsectrotanypus, the caddis Orthopsyche thomasi and Alloecentrella magnicornis, and several species of scirtid, elmid and hydrophilid beetles. In addition, some species new to science were discovered, including species of cased chironomid belonging to the genus Stempellina (Tanytarsini), the first record of this genus in New Zealand, and two new species of hydrobiid snails (Collier & Smith 2006).
Threat status
Endangered (Holdaway et al. 2012)Threats
Increased nutrients and aeration associated with seepages/flushes may favour establishment of weeds, e.g. pasture grasses and herbs. Because they may be small, they are often not recognised and suffer insidious deterioration in and near agricultural settings. Unfenced seepage/flush wetlands in agricultural and natural settings are susceptible to grazing, trampling, and nutrient enrichment by domestic and feral animals. Seepages/flushes are usually easily drained and converted to agriculture.
Further reading
Brownsey PJ 1985. Ophioglossum petiolatum at Hokio Beach. Wellington Botanical Society Journal 42: 33-34.
Clarkson BD, Clarkson BR 2015. A new record of Brachyglottis turneri from North Taranaki. New Zealand Botanical Society Newsletter 121: 8-10.
Collier KJ, Smith BJ 2006. Distinctive invertebrate assemblages in rockface seepages enhance lotic biodiversity in northern New Zealand. Biodiversity and Conservation 15: 3591-3616.
Johnson P, Gerbeaux P 2004. Wetland types in New Zealand. Wellington, Department of Conservation.
Wardle P 1991. Vegetation of New Zealand. Cambridge University Press. 672 p.