A CONTRI'BUTION TO A BI.OLOGICAL RESOURCE RESIDENT; SUBIVERGED, MACROPHYTES AND PART 3: A SYL.T'IqiS OF' SUPJEYS DURII\G APRIL 1995 ANTD JAI.TUARY 1996 Pr:epared for: Prepared by: Carter Holt Harvey Private Bag. TOKOROA ij¡iañ Or:ffey Inquiries and ref'erence: please quote Bnan T. Coffey anci Associateq Limited BBRI / L. Maraetai I 03 C.FI.H.. January 1995 3?3.€t52 csp lcrest, Ha6ilron. New Zealand. Telephone lFax 64 [07] 856 1233. Mobile: (0?-5) 937 865 1.O SummarY reporl provides a baseline description of: . resident, submerged, macrophytes and invertebrates in water less than 30 m deep, across 12 cross sectÍons of Lake Maraetai., during April - May 1995 deep water benthos (30 - 60 m depth) at selected sites in Lake Maraetai during January 1996. Lake Maraetai is a man-made hydro-electric reservoÍr whÍch flooded a former steep-sided gorge formed by the V/aikato River. It is a highly turbid and enriched lake in which introduced plants and animals dominated littoral communities. Treated wastewater from the Kinleith Pulp and Paper MiIl is discharged into Lake Maraetai via the Kopakorahi Stream. The Kopakorahi Arm is on the right bank, in the middle section of the lake. ee differences in the structure of resident, bmerged, macrophyte and invertebrate communities ve been identified between the upstream and sections of lake Maraetai. The depth of the photic zorLe for submerged macrophytes and epipelic periphyton in the downstream section of Lake Maraetai is reduced relatjve to the upstream section of the lake. There is an increased frequency / abundance of "pollution indicators" in the downstream section of the Lake Maraetai including the Kopakorahi Arm of the lake. There is a reduced abundance of deep water benthos in t]:e downstream section of the lake, Brian T, Coffey and Associates Limited, Hamilron However it Ís noted that a viable benthic community s present throughout the deepest mainstream i of the lake during (.: : January 1996. \ ttoral beds of submerged macfophytes were dominated by two introduced lakewee ds, Ceratophgllum and Egería. d.ensa. e most restricted depth range of submerged rophytes \¡/as recorded in the Kopakora_hi Arm of the lake. Periphyton in the canopy of submerged weed beds was enerally dominated by the non-attached green alga Enteromorpha no:na. Macrobenthos such as the freshwate¡ musser HyrídeLLa menzíesí and the freshwater crayfish paranephrops Lanifrons were present on stable (well_consolidated) ubstrata in the main channel of the lake. low frequency of the freshwater spon ge Ephgdatía kakahuensis was present throughout the mainstream cha¡rnel of tl:e lake. enthic communities in depositional zones between rter depths of 12 to 25 m comprised a low diversity of bificid worms, chironomid larvae, ostracods and pea ssels. Below 30 m depth, lake bed sediments supported a low diversity of benthic organisms (almost exclusively larvae of the non-biting midge Chíronomus zelandícus and a single species of an unidentified tubificid worm). The dominant component of surficial, deep_water, sediments deposited in t].e old river channel at depths of 35 to 60 m was plankton debris, dominated by frustules of chain-forming species of the diatom MeLosíra.. generally most common in the upstream section of the lake or which were not recorded in the downstream tion of the lake included the macrophytes ELod_ea Brian T. Coffey and Associates Limited, Hamitton cc,nc,densis, MgriophgLLum triphgLLum, and Nitell.a hookerí: the mosses Drepanocladus adnuncus, urhgnchium austrinum, Fissidens rigiduLus, y pno dendr on mar g inatum a,nd Tr ido ntium tas manic a; cyanobacterium OsciLLatoria rubescens; a species of the filamentous alga Mtcrospora: the snails Potamopgrgus antipodarum, Lgmnaea tomento s a and GgrauLtts corinnai the bryozoan PLumateLl"a repens and the leech Glossþhonia. multístriata. Elsewhere in New d freshwaters, these species are generally associated with relatively high water quality. recorded as present only in the downstream section of the lake included species of the cyanobacteria genera Anabaena, Schízothnx and ToLgpothnx and the hed green filamentous alga Cladophora gLomerata. in New Zealand freshwaters, these taxa are neraliy associated with relatively low water quatity. eed bed fauna for which the highest replicate counts were recorded in the Kopakorahi Arm included amphipods, tubificid worrns and the snail Phgsa acuta. The mixing patterns of highly-coloured water entering Lake Maraetai from the Kopakorahi Arm were clearly complex, related to season (Zuur, 1989) and dependant on local weather conditions. Physical and chemical characters of the lake, together with a description of fish populations, were the subject of concurrent studies to describe receiving waters fo¡ treated wastewater from the Kinleith Pulp and Paper Mill (the Kopakorahi Arm of Lake Maraetai). e extent to which differences in submerged community structure can be associated with the Íscharge of bleached kraft mill effluent from the Kinleith Mill to the Kopakorahi Arm of Lake Maraetai 1 depend on the findings of these complementary dies. These collective data are to be collated and reported on by Kingett Mitchell a¡rd Associates Limited. Brian T. Coffey and Associates Limited, Hamilton 2,O Introduction This report provides a description of resident, submerged, macroscopic biological communities in water less than 30 m deep across 12 cross sections of Lake Maraetai during April 1995 (see Figures 1 to 4). ' a description of benthic community structure in water more tha¡ SO m deep at selected sites in Lake Maraetai during January 1gg6 (see Figures 2 and 3). Lake Ma¡aetai is the fifth of eight hydro-electric lakes downstream of Lake Taupo on the Waikato River. It formed behind an 86 m high dam between 1952 and 1953. The Maraetai I powerhouse was commissioned in I9b2 and its penstock intakes are close to the lake surface. A second powerhouse, (Maraetai II) was completed at the Maraetai Dam in l97l and its penstock intakes a¡e in deep water. The lake has an area of 4.2 kmz contained within a maximum length of 2.2 km and a maximum wÍdth of r.2 kilometres (viner tedJ, lggT). It has a maximum depth of 64.7 m (Irwin and van Kampen, f ggg) and an average depth of c 30 metres [Viner [ed], 1987). Lake level is at an altitude of g53 m (Viner [ed], 1987) or 188 metres above sea level relative to the Moturiki datum (Irwin and van Kampen, 1989). The centre of the lake is at a latitude of 4r's and a longitude of rr\' E (Irwin and van Kampen, Iggg). Treated wastewater from the Kinleith Pulp and Paper Mill is discharged into Lake Maraetai via the Kopakorahi Stream. Kingett Mitchel & Associates (1995) report that between september l9g4 and February lgg5, Bl%o of flow g4 in the Kopakorahi Stream (mean of 365 + Ml..day-t) was sourced from Ûre wastewater treatment system at the Kinleith Milt. The Mill Discharge constituted some O.920/o of the total discharge of Waikato River water to Lake Waipapa during this same period. Zuur (1989) reported that during 1988: ' the Kinleith discharge changed the colour of the Kopakorahi Arm of the lake and of the Waikato River to a measurable extent, and ' Kinleith effluent often did not disperse evenly as it mixed v/ith water in Lake Maraetai, but formed a plume that sank under lake water during summer and tended to flow over the top of lake water during the winter. Brian T. Coffey and Associates Limited, Hamilton 5 Figure 1. lnca-lity sketch for Lake Maraetai showing locality of Tra¡rsects I - L2 (also see Figures 2, 3 and 4 for lake bathymetry) NORTH ISLAND L. Whakamaru 50 51 52 53 54 Map references per.: NZMS 260,T16'Tokoroa and NZMS 260,T17'Whakamaru Meredith et al (1988) associated differences in the structure of animal communities in Lake Maraetai with the discharge of treated wastewater from the Kinleith Pulp and Paper Mill. Meredith et al (1988) also surveyed the Kopakorahi Stream upstream of Tlansect 8 (see Figure I). Brian T. Coffey and Associates Limited, Hamilton Figure 2. Part of Lake Maraetai showing bath¡rmetry (after Irwin and van Kampen, 1989) between Transects I0 to L2. Deep water stations sampled at rransect L2 on os January, lgg6 are shown in white on black. 52 Grid references per NZMS 260 T16 Tokoroa and NZMS 260 rrr, whakamanr Physical and chemical characters of the lake, together with a description of fish populations, were the subject of concurrent studies to descrÍbe receiving waters for treated wastewater from the Kinleith Pulp and paper Mill (the Kopakorahi Arm of Lake Maraetai). Brjan T, Coffey and Associates Limited, Hamilton Figure 3 Part of Lake Maraetai showing bathymetry (after Irwin and van Kampen, 1989) between Transects 4 to 9. Deep water stations sampled at Site A, Transect 6A and 9 on OS January, Igg6 a¡e shown in white on black þJ 54 55 Grid references per NZMS 260 T16 Tokoroa and NZMS 260rrr, whakamaru Brian T. Coffey and Associates Limited, Hamilton Figure 4 Part of Lake Maraetai showing bathymetry (after Irv¿in and va¡r Kampen, 1989) between Transects I to 4. 52 s3 Grid references per NZMS 260 T16 Tokoroa and NZMS 260 TI7 , Whaka.maru Brian T, Coffey and Associates Limited, Hamilton 10 The diver then inspected the lake bed in the vicinity of the lower depth limit of submerged macrophytes and swam direcuy to the shoreward marker recording the depth range, maximum height, average height, maximum cover class and average cover class of component macrophytes in each weed bed. The dÍver assigned an overall cover score to periphyton at each site and representative samples were returned to the laboratory for identification. 6_IOOo/o) The boat was then positioned in the surface or near-surface canopy of submerged weed beds and a 25O micron mesh hand net was used to take five replicate sweeps through a I.O m x 0.4 m surface area section of the weed canopy to a depth of O.4 metres.