Nutrient budget and water balance for Lake Ngaroto CBER Report 54 Report prepared for Waipa District Council By Rowena Beaton, David Hamilton, Marcel Brokbartold, Christoph Brakel and Deniz Özkundakci Centre for Biodiversity and Ecology Research Department of Biological Sciences The University of Waikato Private Bag 3105 Hamilton 3240 June 2007 Table of contents List of figures ........................................................................................... II List of tables ............................................................................................ III Acknowledgements ................................................................................ IV Executive summary ................................................................................... 1 1 Introduction ........................................................................................ 3 2 Methods ............................................................................................... 6 2.1 Study sites ..................................................................................................... 6 2.2 Sampling ....................................................................................................... 7 2.2.1 Lake ........................................................................................................ 8 2.2.2 Inflows and outflow ................................................................................ 9 2.3 Analytical techniques ................................................................................. 10 2.3.1 Light attenuation coefficient ................................................................ 10 2.3.2 Nutrient analysis .................................................................................. 10 2.3.3 Chlorophyll a analysis ......................................................................... 11 2.3.4 Suspended solids .................................................................................. 11 2.3.5 Phytoplankton ...................................................................................... 12 3 Results ............................................................................................... 13 3.1 Inflows and outflow.................................................................................... 13 3.2 Lake results................................................................................................. 20 4 Discussion .......................................................................................... 31 References ................................................................................................ 35 Appendix A .............................................................................................. 36 Appendix B .............................................................................................. 37 I List of figures List of figures Figure 1: Aerial picture of Lake Ngaroto showing in-lake sample sites, inflow sites and the outflow. ............................................................................................................. 7 Figure 2: Discharge [m3 d-1] in inflows and the outflow for the period 18 December 2006 to 27 January 2007.. ............................................................................................ 13 Figure 3: Concentrations of TP [mg L-1] in inflows and the outflow of Lake Ngaroto. ...................................................................................................................................... 14 Figure 4: Concentrations of TN [mg L-1] in inflows and the outflow of Lake Ngaroto.. ...................................................................................................................... 15 Figure 5: Concentrations of chl a [µg L-1] in inflows and the outflow of Lake Ngaroto. ....................................................................................................................... 15 Figure 6: Concentrations of SS [mg L-1] in inflows and the outflow of Lake Ngaroto. ...................................................................................................................................... 16 -1 Figure 7: Concentrations of NH4-N [mg L ] in inflows and the outflow of Lake Ngaroto. ....................................................................................................................... 16 -1 Figure 8: Concentrations of NO3-N [mg L ] in inflows and the outflow of Lake Ngaroto. ....................................................................................................................... 17 -1 Figure 9: Concentrations of PO4-P [mg L ] in the inflows and outflow of Lake Ngaroto. ....................................................................................................................... 17 Figure 10: Concentrations for TP [mg L-1] for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. .................................................. 20 Figure 11: Concentrations for TN [mg L-1] for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. .................................... 21 Figure 12: Concentrations for chl a [µg L-1]for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. .................................... 21 Figure 13: Concentrations SS [mg L-1] concentrations for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. ........................... 22 -1 Figure 14: Concentrations NH4-N [mg L ] for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. .................................... 22 -1 Figure 15: Concentrations NO3 [mg L ] for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. .................................................. 24 -1 Figure 16: Concentrations PO4 [mg L ] for the five sampling sites in Lake Ngaroto for the period 9 December 2006 to 30 January 2007. .................................................. 24 Figure 17: Temperature in the middle of the lake at three depths, surface (0 m), 1.5 m and 3.5 m, for the period 19 December 2006 to 29 January 2007. .............................. 25 Figure 18: Vertical profiles of (A): Temperature [°C], (B): dissolved oxygen concentration [mg L-1], (C): conductivity [µS cm-1], and (D): fluorescence [mV] for all sampling days.......................................................................................................... 27 Figure 19: Algal cell counts separated into blue-green and other species. Samples collected on the 9 and 19 of December 2006 and the 9 and 16 of January 2007. ........ 30 II List of tables List of tables Table 1: Abbreviations for in-lake samples sites and inflow and outflow sampling sites. ............................................................................................................................... 6 Table 2: Values for flow [m3 d-1], TN [mg L-1], TP [mg L-1], Chl a [µg L-1] and SS [mg L-1] for the inflows and outflow of Lake Ngaroto. See Figure 1 and Table 1 for the locations of the inflows and the outflow. ............................................................... 18 -1 -1 -1 Table 3: Concentrations of NH4-N [mg L ], NO3-N [mg L ] and PO4-P [mg L ] for the inflows and the outflow of Lake Ngaroto. .. ......................................................... 19 Table 4: In lake concentrations for TN [mg L-1], TP [mg L-1], Chl a [µg L-1] and SS [mg L-1] at the three stations (north, middle and south), and the three depths in the middle station; at the surface and 1.5 and 3.5 m.. ........................................................ 23 -1 -1 Table 5: Concentrations in Lake Ngaroto of NH4-N [mg L ], NO3-N [mg L ], PO4-P [mg L-1] at the three stations (north, middle and south), and the three depths in the middle station, at the surface and 1.5 and 3.5 m. ......................................................... 26 -1 Table 6: kd [m ] for Lake Ngaroto during the investigation period 09 January to 30 January 2007. ............................................................................................................... 28 Table 7: In-lake concentrations of phytoplankton species [cells mL-1], recorded at the centre of the lake on the first four sampling days ........................................................ 29 III Acknowledgements Acknowledgements We are grateful for funding support for this project from the Waipa District Council and the University of Waikato. The funding from Waipa District Council supported our field work and provided for assistance by a University of Waikato technician, Alex Ring, to whom we are grateful to for his assistance with all of the field work. This funding also supported our laboratory analyses. We thank Tony Roxburgh (Waipa District Council) for initiating this project and supporting our data requirements. The University of Waikato is acknowledged for support of a Summer Scholarship to the first author, Rowena Beaton, which enabled her to be resident at the University for the duration of the project. The Lippe and Höxter University of Applied Sciences in Germany is acknowledged for support of Marcel Brokbartold and Christoph Brakel, as part of their study internships at the University of Waikato. We thank Robin Walker from Opus Consultants for assisting us with provision of data for Lake Ngaroto. This project would not have been possible without support through the Foundation of Research,