title: Purpose of weed harvesting

authors: Matheson, Fleur E.

abstract: Harvesting is one potential option to control nuisance growths of lake weeds. Mechanical harvester units can typically remove lake weed to 2-3m below the water surface. Yet common weed species in NZ lakes often grow to deeper depths, so typically only the upper canopy of large weed beds can be removed with this technique. Nevertheless, harvesting can be a useful tool to reduce weed abundance in sensitive areas (e.g. boat ramps, beaches), or from areas where it is likely to detach and form drifting rafts that interfere with various recreational or commercial interests. It is not a suitable option for weed control in areas where weed fragments generated by the harvesting activity pose a biosecurity risk. For example, in areas where an infestation of a new weed has been found or the weed has a limited distribution within the lake. Most New Zealand lake weed species can grow vegetatively from fragments broken off the main weed bed. Even small fragments (<1-2cm length) can remain viable for long periods of time if kept wet.
In areas where harvesting units can operate efficiently (e.g. sheltered sites without underwater obstacles), large quantities of weed can conceivably be removed which may benefit lake water quality or offset nutrient inputs from the catchment through removal of nutrients that have been assimilated into the plants as they grow. However, potential downsides of harvesting, particularly where it is done on a large scale, include the kill of fish and other biota trapped in the weed bed at the time of harvest, removal of habitat and
flipping of the lake ecosystem to an algal dominated state. Disposal of harvested weed can also be problematic. Lake weeds often bioaccumulate contaminants (e.g. arsenic) that render them unsuitable for use as a compost or stock feed. In lake disposal via pulverizing and/or deep water discharge of negatively buoyant material is a much cheaper option than ferrying harvested weed to shore for transport to an onshore disposal site but is not a suitable option for situations where removal of lake nutrients assimilated into weed is desired. A final consideration is the movement of harvester units between lakes or other waterbodies and any potential biosecurity risks that this raises. A number of New Zealand’s worst lake weeds (e.g. hornwort) currently have a limited distribution so ensuring that fragments of such weeds are not inadvertently introduced into a new location by a harvesting unit is paramount. Units must be thoroughly decontaminated before being moved.

text: Purpose of weed harvesting Harvesting is one potential option to control nuisance growths of lake weeds. Mechanical harvester units can typically remove lake weed to 2-3m below the water surface. Yet common weed species in NZ lakes often grow to deeper depths, so typically only the upper canopy of large weed beds can be removed with this technique. Nevertheless, harvesting can be a useful tool to reduce weed abundance in sensitive areas (e.g. boat ramps, beaches), or from areas where it is likely to detach and form drifting rafts that interfere with various recreational or commercial interests. It is not a suitable option for weed control in areas where weed fragments generated by the harvesting activity pose a biosecurity risk. For example, in areas where an infestation of a new weed has been found or the weed has a limited distribution within the lake. Most New Zealand lake weed species can grow vegetatively from fragments broken off the main weed bed. Even small fragments (<1-2cm length) can remain viable for long periods of time if kept wet.
In areas where harvesting units can operate efficiently (e.g. sheltered sites without underwater obstacles), large quantities of weed can conceivably be removed which may benefit lake water quality or offset nutrient inputs from the catchment through removal of nutrients that have been assimilated into the plants as they grow. However, potential downsides of harvesting, particularly where it is done on a large scale, include the kill of fish and other biota trapped in the weed bed at the time of harvest, removal of habitat and
flipping of the lake ecosystem to an algal dominated state. Disposal of harvested weed can also be problematic. Lake weeds often bioaccumulate contaminants (e.g. arsenic) that render them unsuitable for use as a compost or stock feed. In lake disposal via pulverizing and/or deep water discharge of negatively buoyant material is a much cheaper option than ferrying harvested weed to shore for transport to an onshore disposal site but is not a suitable option for situations where removal of lake nutrients assimilated into weed is desired. A final consideration is the movement of harvester units between lakes or other waterbodies and any potential biosecurity risks that this raises. A number of New Zealand’s worst lake weeds (e.g. hornwort) currently have a limited distribution so ensuring that fragments of such weeds are not inadvertently introduced into a new location by a harvesting unit is paramount. Units must be thoroughly decontaminated before being moved.

year: 2015

title: Species composition and cyanotoxin production in periphyton mats from three lakes of varying trophic status

authors: Wood, Susanna A.

subjects: cyanobacteria

abstract: In lakes, benthic micro-algae and cyanobacteria (periphyton) can contribute significantly to total primary productivity and provide important food sources for benthic invertebrates. Despite recognition of their importance, few studies have explored the diversity of the algal and cyanobacterial composition of periphyton mats in temperate lakes. In this study, we sampled periphyton from three New Zealand lakes: Tikitapu (oligotrophic), Ōkāreka (mesotrophic) and Rotoiti (eutrophic). Statistical analysis of morphological data showed a clear delineation in community structure among lakes and highlighted the importance of cyanobacteria. Automated rRNA intergenic spacer analysis (ARISA) and 16S rRNA gene clone libraries were used to investigate cyanobacterial diversity. Despite the close geographic proximity of the lakes, cyanobacterial species differed markedly. The 16S rRNA gene sequence analysis identified eight cyanobacterial OTUs. A comparison with other known cyanobacterial sequences in GenBank showed relatively low similarities (91–97%). Cyanotoxin analysis identified nodularin in all mats from Lake Tikitapu. ndaF gene sequences from these samples had very low (≤ 89%) homology to sequences in other known nodularin producers. To our knowledge, this is the first detection of nodularin in a freshwater environment in the absence of Nodularia. Six cyanobacteria species were isolated from Lake Tikitapu mats. None were found to produce nodularin. Five of the species shared low (< 97%) 16S rRNA gene sequence similarities with other cultured cyanobacteria.

text: Species composition and cyanotoxin production in periphyton mats from three lakes of varying trophic status In lakes, benthic micro-algae and cyanobacteria (periphyton) can contribute significantly to total primary productivity and provide important food sources for benthic invertebrates. Despite recognition of their importance, few studies have explored the diversity of the algal and cyanobacterial composition of periphyton mats in temperate lakes. In this study, we sampled periphyton from three New Zealand lakes: Tikitapu (oligotrophic), Ōkāreka (mesotrophic) and Rotoiti (eutrophic). Statistical analysis of morphological data showed a clear delineation in community structure among lakes and highlighted the importance of cyanobacteria. Automated rRNA intergenic spacer analysis (ARISA) and 16S rRNA gene clone libraries were used to investigate cyanobacterial diversity. Despite the close geographic proximity of the lakes, cyanobacterial species differed markedly. The 16S rRNA gene sequence analysis identified eight cyanobacterial OTUs. A comparison with other known cyanobacterial sequences in GenBank showed relatively low similarities (91–97%). Cyanotoxin analysis identified nodularin in all mats from Lake Tikitapu. ndaF gene sequences from these samples had very low (≤ 89%) homology to sequences in other known nodularin producers. To our knowledge, this is the first detection of nodularin in a freshwater environment in the absence of Nodularia. Six cyanobacteria species were isolated from Lake Tikitapu mats. None were found to produce nodularin. Five of the species shared low (< 97%) 16S rRNA gene sequence similarities with other cultured cyanobacteria.

year: 2012-02

title: The source, composition and typology of ‘Limestone’ Adzes from Eastern North Island, New Zealand

authors: Nelson, Campbell S.

subjects: adzes

abstract: Collections of stone adzes (toki) from the eastern North Island of New Zealand include a number of typologically early (Archaic) forms made from what has been previously described as ‘siliceous or silicified limestone’. Seventy five finished adzes and preforms of this material were recorded in the present study. Their geographic distribution is primarily restricted to southern Hawkes Bay – Wairarapa, and they apparently originated from a single manufacturing centre at Owahanga, on the northern Wairarapa coast. Chemical and mineralogical analyses (by X-ray fluorescence, portable XRF, vacuum gasometry and X-ray diffraction) of two artefacts from Owahanga show they contain about 20–30 per cent CaCO3 (as calcite), while samples of the presumed local source rock have a slightly higher carbonate content but comparable silica (quartz) and Rb concentrations. The rock type used in the manufacture of adzes was therefore not a true limestone but calcareous mudstone, compositionally distinct from siliceous limestones in southern Wairarapa and probably derived from the Whangai Formation. Possible reasons for the use of this stone material are discussed.

text: The source, composition and typology of ‘Limestone’ Adzes from Eastern North Island, New Zealand Collections of stone adzes (toki) from the eastern North Island of New Zealand include a number of typologically early (Archaic) forms made from what has been previously described as ‘siliceous or silicified limestone’. Seventy five finished adzes and preforms of this material were recorded in the present study. Their geographic distribution is primarily restricted to southern Hawkes Bay – Wairarapa, and they apparently originated from a single manufacturing centre at Owahanga, on the northern Wairarapa coast. Chemical and mineralogical analyses (by X-ray fluorescence, portable XRF, vacuum gasometry and X-ray diffraction) of two artefacts from Owahanga show they contain about 20–30 per cent CaCO3 (as calcite), while samples of the presumed local source rock have a slightly higher carbonate content but comparable silica (quartz) and Rb concentrations. The rock type used in the manufacture of adzes was therefore not a true limestone but calcareous mudstone, compositionally distinct from siliceous limestones in southern Wairarapa and probably derived from the Whangai Formation. Possible reasons for the use of this stone material are discussed.

year: 2016