Abell, J. M., McBride, C. G., & Hamilton, D. P. (2013). Lake Tutira: historic water quality, monitoring recommendations and management options (ERI report). Hamilton, New Zealand: Environmental Research Institute, The University of Waikato.
Permanent Research Commons link: https://hdl.handle.net/10289/13000
Lake Tutira is located 30 km north of Napier and is an important recreational resource for the Hawke's Bay region. The lake has an area of 1.74 km², mean depth of 21 m and maximum depth of 42 m. It has a recent history of poor water quality, and over 2011 and 2012 there were severe blooms of blue-green algae (cyanobacteria), which detracted from the ecological and aesthetic value of the lake, and impacted on its suitability for recreational use. We analysed the recently-available (2009-2012) monitoring data for Lake Tutira, which included periods of regular (c. monthly) water quality monitoring measurements, as well as data from an automated high-frequency monitoring buoy. Poor water quality in Lake Tutira is not a recent problem and TLI values in the 1960s and 1970s were higher than those for the analysis period. High-frequency buoy data demonstrated that high-intensity rainfall events produced rapid increases in water level and increased turbidity. Increases in chlorophyll fluorescence a few days after major rainfall events indicate that rainfall events may also stimulate increases in phytoplankton biomass in the lake via increased nutrient inputs associated with stormflows. Grass carp were introduced into Lake Tutira in 2008 to control the invasive weed Hydrilla which had been present in the lake for some decades. There has been a rapid reduction in Hydrilla beds in the lake following the grass carp introduction. We recommend that the impact of grass carp on Lake Tutira be evaluated from an ecosystem perspective, given some marked changes in other components of the lake ecosystem since the introduction. We evaluated the suitability of Lake Tutira for application of an ecological model to assist with consideration of management options to improve lake water quality. Lake Tutira is a suitable candidate lake for both one-dimensional (1-D; vertically resolved) and three-dimensional (3-D) ecological model applications to represent the vertical variations and whole-lake water column variations, respectively. A comprehensive ecological model of Lake Tutira could be used to simulate the outcomes of various lake restoration strategies, thus acting as a decision support tool for proposed lake management actions. The likely performance of a model application and hence its value for informing management decisions could be improved considerably with substantial additional data collection (e.g. inflow water quality), as well as continuation of the current lake monitoring. A number of potential management options were considered for Lake Tutira and we recommend that these options be considered further with the 1-D and/or 3-D models in order to fully assess their feasibility, effectiveness and value for money.
Environmental Research Institute, The University of Waikato
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