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: A distributed directory service for Greenstone

authors: Buchanan, George

subjects: computer science

abstract: Greenstone is a software for creating and maintaining distributed digital library collections. It provides a sophisticated federation mechanism for the collections.
In order to support alerting notification about changes in the distributed collections, we propose a distributed directory service for the management of the distributed Greenstone installations. The Greenstone directory service (GDS) acts on top of the distributed Greenstone structure for the management of collections. This paper describes both, the initial distributed Greenstone structure and the distributed directory service.

text: A distributed directory service for Greenstone Greenstone is a software for creating and maintaining distributed digital library collections. It provides a sophisticated federation mechanism for the collections.
In order to support alerting notification about changes in the distributed collections, we propose a distributed directory service for the management of the distributed Greenstone installations. The Greenstone directory service (GDS) acts on top of the distributed Greenstone structure for the management of collections. This paper describes both, the initial distributed Greenstone structure and the distributed directory service.

year: 2005-01-01

title: Monitoring and hydrodynamic modelling of groundwater inflows into Lake Rotokakahi, New Zealand

authors: Noakes, Katie

subjects: Groundwater

abstract: Lake Rotokakahi is located 10 km south of Rotorua and is of immense cultural importance to the local iwi. The lake also has significant historical and recreational values, which prompted iwi to make the lake private in 1996. Lake Rotokakahi is one of several Rotorua/ Te Arawa lakes. Several of these lakes have become eutrophic and some have declining water quality. This study was prompted by declining water quality of Lake Rotokakahi and the need to identify potential sources of nutrients to the lake, particularly groundwater inflows.

The interaction between groundwater and surface water has a major influence on the trophic status of lakes, particularly those that are predominantly or solely groundwater fed systems. Lake Rotokakahi has one small spring-fed surface water inflow and one outflow, the Te Wairoa stream. Thus the lake is predominantly groundwater fed. The main objective of this thesis was to quantify the contribution of groundwater and surface water to Lake Rotokakahi and to examine interactions of the groundwater system with the lake, in order to provide a basis to improve lake management practices. Multiple monitoring sites were established around the perimeter of the lake to determine the spatial and temporal variation of groundwater inputs, as well as the groundwater nutrient dynamics. A three-dimensional hydrodynamic lake model was set up and simulations were used to examine how groundwater and surface water inflows were dispersed within the lake upon entry.

Monitoring of the shallow groundwater system took place from 1 January to 1 July 2016. Three separate storm events were monitored at high frequency within this monitoring period. The monitoring results showed the groundwater system varied significantly both spatially and temporally and also contributed a high proportion of the total nutrient load to the lake. Groundwater discharge and nutrient concentrations generally increased in association with or immediately following high rainfall events.
 
The three-dimensional model ELCOM was set up using hydrological data for the catchment, meteorological data from a nearby station and bathymetry of the lake. Simulations were based upon different methods of calculating groundwater inflows. Simulation 1 was based upon the common water balance equation method. Simulation 2 used constant groundwater inflow and outflow volumes as determined by a groundwater flow model, MODFLOW, which had been applied to the catchment by White et al., (2015). Simulation 3 combined MODLFOW values and measured groundwater levels to create a varying inflow volume based on water level. The three simulations accurately captured surface and bottom temperatures and had varying lake water levels. Only simulation 3 accurately captured the presence of the groundwater spring near the lake shore and was concluded the more accurate method of groundwater inflow calculation.

text: Monitoring and hydrodynamic modelling of groundwater inflows into Lake Rotokakahi, New Zealand Lake Rotokakahi is located 10 km south of Rotorua and is of immense cultural importance to the local iwi. The lake also has significant historical and recreational values, which prompted iwi to make the lake private in 1996. Lake Rotokakahi is one of several Rotorua/ Te Arawa lakes. Several of these lakes have become eutrophic and some have declining water quality. This study was prompted by declining water quality of Lake Rotokakahi and the need to identify potential sources of nutrients to the lake, particularly groundwater inflows.

The interaction between groundwater and surface water has a major influence on the trophic status of lakes, particularly those that are predominantly or solely groundwater fed systems. Lake Rotokakahi has one small spring-fed surface water inflow and one outflow, the Te Wairoa stream. Thus the lake is predominantly groundwater fed. The main objective of this thesis was to quantify the contribution of groundwater and surface water to Lake Rotokakahi and to examine interactions of the groundwater system with the lake, in order to provide a basis to improve lake management practices. Multiple monitoring sites were established around the perimeter of the lake to determine the spatial and temporal variation of groundwater inputs, as well as the groundwater nutrient dynamics. A three-dimensional hydrodynamic lake model was set up and simulations were used to examine how groundwater and surface water inflows were dispersed within the lake upon entry.

Monitoring of the shallow groundwater system took place from 1 January to 1 July 2016. Three separate storm events were monitored at high frequency within this monitoring period. The monitoring results showed the groundwater system varied significantly both spatially and temporally and also contributed a high proportion of the total nutrient load to the lake. Groundwater discharge and nutrient concentrations generally increased in association with or immediately following high rainfall events.
 
The three-dimensional model ELCOM was set up using hydrological data for the catchment, meteorological data from a nearby station and bathymetry of the lake. Simulations were based upon different methods of calculating groundwater inflows. Simulation 1 was based upon the common water balance equation method. Simulation 2 used constant groundwater inflow and outflow volumes as determined by a groundwater flow model, MODFLOW, which had been applied to the catchment by White et al., (2015). Simulation 3 combined MODLFOW values and measured groundwater levels to create a varying inflow volume based on water level. The three simulations accurately captured surface and bottom temperatures and had varying lake water levels. Only simulation 3 accurately captured the presence of the groundwater spring near the lake shore and was concluded the more accurate method of groundwater inflow calculation.

year: 2016