Development of an integrative water quality monitoring programme for Te Waihora/Lake Ellesmere

Abstract

Fresh water lakes are highly valued in today’s world. The use and management of this freshwater resource is critical to all four well-beings (social, economic, environmental, and cultural) worldwide and specifically (for this thesis), in Canterbury, New Zealand. Lake Ellesmere/Te Waihora is a coastal ICOLL (Intermittently Closed and Open Lake or Lagoon) where the effects of the local climate patterns, the use and management of the large catchment associated with this lowland lake, its numerous stakeholders and changing legislation, have created a situation where robust relevant data is essential to ensure best and most cost-effective management of this resource. New Zealand legislation acknowledges the importance of this ICOLL within the whole system of New Zealand lakes, and views it as an indicator of New Zealand ICOLL behaviour. Water quality is an important facet of freshwater management and is one aspect of an overarching monitoring strategy for Te Waihora developed in 2015. Water quality monitoring in the lake is carried out by the regulatory body as well as many other stakeholders. This has led to an abundance of data addressing very specific objectives but also a number of gaps in the data required to assess the overall state of Te Waihora itself. The purpose of this research is to design a water quality monitoring programme integrating and augmenting existing programmes which will cost-effectively add to the information required for stakeholders and support current and future management. This research initially compiled information pertaining to lake character, the effects of land use within the large catchment and the local climatic conditions relevant to the lake, as well as existing monitoring programmes. An ‘ideal’ water quality monitoring programme with the main objective being “to assess the state and trends of water quality in Te Waihora and its immediate catchment” was then designed using specific predetermined criteria to select tributaries, monitoring sites, parameters and monitoring frequency. Current legislation and the importance of the local conditions for targeted monitoring to be achieved were incorporated and further information needs identified. The proposed monitoring programme requires monthly monitoring of six lake and eight tributary sites. The NPS-FM 2014 (amended 2017) and CLWRP water quality parameters, as well as parameters specific to Te Waihora are taken account of. These include monthly lake attributes (parameters) of lake level, pH, temperature, electrical conductivity, DO, turbidity, TSS, VSS, Secchi Disc, NO2-N, NO3-N, NH4-N, TN, DRP, TP, chl a and E. Coli and monthly tributary attributes (parameters) of discharge, pH, temperature, conductivity, DO, clarity, turbidity, TSS, NO2-N, NO3-N, NH4-N, TN, DRP, TP and E. Coli, with yearly monitoring for Cu, Pb, Zn, Cd, selected emerging contaminants and polyaromatic hydrocarbons (PAH). Additional monitoring is proposed for further specific parameters (e.g., flood and flow loads) at predetermined events (e.g., when tributary flow reaches a predetermined level). Tributary flow, lake level, climatic conditions and ICOLL status (open or closed) should also be recorded. This designed water quality monitoring programme has been compared with existing stakeholder monitoring programmes, to identify gaps and omissions and recommend methods for these to be addressed. Additional recommendations for methods to achieve the overarching integrative water quality monitoring objectives for foreseeable future requirements for management and modelling are also made. The ‘robustness’ and quality control of all aspects of the monitoring (practical and financial) is acknowledged as essential for longevity. Additional research into key areas, such as the sediment load related to flooding events, the combination of more extreme intermittent climatic conditions with increased intensification of catchment use, the effect of the Central Plains Water Ltd (CPWL) irrigation scheme and the effect of openings and closings on Te Waihora, are recommended to aid management decisions, aimed at not only sustaining the environment of the lake, but regenerating and improving it.