Modelling of restoration scenarios for Lake Ngaroto CBER Report 81 Report prepared for Waipa District Council By Wendy Paul, Deniz Özkundakci and David Hamilton Photo: Warrick Powrie Centre for Biodiversity and Ecology Research Department of Biological Sciences The University of Waikato Private Bag 3105 Hamilton 3240 August 2008 I 65BTable of contents 0HList of figures .............................................................................................. 113 HIV 1HList of tables ................................................................................................ 114 HVI 2HList of Appendices ..................................................................................... 115 HVII 3HAcknowledgements ...................................................................................116 HVIII 4HExecutive summary ....................................................................................... 117 H9 5H1 Introduction ............................................................................................... 118 H10 6H2 Methods ...................................................................................................... 119 H12 7H2.1 Sampling sites .................................................................................................... 120 H12 8H2.2 Sampling ............................................................................................................. 121 H14 9H2.2.1 Lake ................................................................................................................. 122 H14 10H2.2.2 Inflow and outflow ........................................................................................... 123 H14 11H2.3 Analytical techniques ........................................................................................ 124 H15 12H2.3.1 Light attenuation coefficient ............................................................................ 125H15 13H2.3.2 Nutrient analysis ............................................................................................. 126 H15 14H2.3.3 Chlorophyll a analysis .................................................................................... 127 H15 15H2.3.4 Suspended solids ............................................................................................. 128 H16 16H2.3.5 Phytoplankton .................................................................................................. 129 H16 17H2.4 Model DYRESM-CAEDYM ............................................................................ 130 H16 18H2.4.1 Meteorological data ........................................................................................ 131 H17 19H2.4.2 Water balance ................................................................................................. 132 H18 20H2.4.3 Inflow and outflow data ................................................................................... 133 H21 21H2.4.4 Morphometry of the Lake ................................................................................ 134 H22 22H2.4.5 Initial profile ................................................................................................... 135 H22 23H2.4.6 Phytoplankton .................................................................................................. 136 H22 24H2.4.7 Suspended solids ............................................................................................. 137 H22 I 25H2.5 Model simulation of restoration scenarios ...................................................... 138 H23 26H2.5.1 Scenario I ........................................................................................................ 139 H23 27H2.5.2 Scenario II ....................................................................................................... 140 H23 28H2.5.3 Scenario III ...................................................................................................... 141 H24 29H2.5.4 Scenario IV ...................................................................................................... 142 H24 30H2.5.5 Scenario V ....................................................................................................... 143 H24 31H2.5.6 Scenario VI ...................................................................................................... 144 H25 32H2.5.7 Scenario VII ..................................................................................................... 145 H25 33H3 Results ......................................................................................................... 146 H26 34H3.1 Flow results ........................................................................................................ 147 H26 35H3.1.1 Temperature, dissolved oxygen, pH and conductivity ..................................... 148 H26 36H3.1.2 Nutrients .......................................................................................................... 149 H26 37H3.1.3 Chlorophyll a ................................................................................................... 150 H27 38H3.1.4 Suspended solids ............................................................................................. 151 H27 39H3.2 Lake Results ....................................................................................................... 152 H27 40H3.2.1 Temperature, dissolved oxygen, pH and conductivity ..................................... 153 H27 41H3.2.2 Nutrients .......................................................................................................... 154 H28 42H3.2.3 Chlorophyll a ................................................................................................... 155 H28 43H3.2.4 Suspended solids ............................................................................................. 156 H29 44H3.2.5 Light attenuation coefficient (Kd) and secchi depth ....................................... 157 H29 45H3.2.6 Phytoplankton .................................................................................................. 158 H29 46H3.3 Model results ...................................................................................................... 159 H30 47H3.3.1 Temperature .................................................................................................... 160 H30 48H3.3.2 Dissolved oxygen ............................................................................................. 161 H31 49H3.3.3 Nutrients .......................................................................................................... 162 H32 50H3.3.4 Chlorophyll a ................................................................................................... 163 H34 51H3.3.5 Suspended solids ............................................................................................. 164 H34 52H3.4 Restoration scenario results ............................................................................. 165 H36 53H3.4.1 Scenario I ........................................................................................................ 166 H36 54H3.4.2 Scenario II ....................................................................................................... 167 H36 55H3.4.3 Scenario III ...................................................................................................... 168 H36 56H3.4.4 Scenario IV ...................................................................................................... 169 H42 II 57H3.4.5 Scenario V-1 .................................................................................................... 170 H42 58H3.4.6 Scenario V-2 .................................................................................................... 171 H42 59H3.4.7 Scenario VI ...................................................................................................... 172 H48 60H3.4.8 Scenario VII ..................................................................................................... 173 H48 61H4 Discussion .................................................................................................... 55 62H5 References ................................................................................................... 57 63HAppendices .................................................................................................. 59 III 66BList of figures 64H Figure 1: Aerial photograph of Lake Ngaroto showing in-lake, inflow and outflow sampling sites. .................................................................................................................................. 13 65H Figure 2:Meteorological data used as input to the DYRESM model, including (A) air temperature Tair (°C), (B) short wave radiation (SW), (C) surface wind speed (u0), (D) vapour pressure (es) and (E) cloud cover (CC). ............................................................... 17 66H Figure 3:Lake evaporation vs wind speed. .............................................................................. 18 67H Figure 4: Inflows measured and modelled ............................................................................... 19 68H Figure 5:Outflow measured and outflow modelled ................................................................. 19 69H Figure 6: Temperature measured, estimated and DO estimated .............................................. 22 70H Figure 7: Daily averages of the temperature in the middle of the lake at three depths, surface (0 m),