MAURI ORA, 1976, 4: 121-131 121

AN ELEMENT SURVEY OF TH E AQUATIC MACROPHYT E S,

WATER AND PLANKTON FROM THE RIVER,

NORTH ISLAND, NEW' ZEALAND

DAVID J. RAWLENCE

Department of Extension Studies, University of Canterbury, Christchurch,

and

J.S. WHITTON

Soil Bureau, D.S.I.R., Private Bag, Lower Hutt, New Zealand

ABSTRACT

Element levels were determined in aquatic macrophytes, water, and plankton from six hydro-electric storage lakes on the , North Island, Ne\~ Zealand. Lakes Ohakuri, Atiamuri, Whakamaru, Maraetai, Arapuni and Karapiro, sampled on 14·and 15 March 1973, yielded the following species: Cerat:ophy11um demersum L., Elodea canadensis Michx., Dagarosiphon major (Ridley) Moss, Egeria densa Planch., pot:amoget:on crispus L., Pot:amoget:on cheesemanii A. Bennett, and Nymphaea alba L. The plankton and macrophytes were analysed for Si, K, P, Na, Mg, Ca, S, Al, Cl, Fe, Zn, Cu, Mn, Co, Mo, Ni, V, Cr, Sr, Ba, Pb, Ti, Ga, and Zr. Water samples were analysed for the same elements, except for P. Ceratophy11um from Lake Atiamuri contained the highest levels of 4 of the 5 macronutrients determined: K, 54 000 ~9/gi P, 5 100 ~g/g; Mg 5 000 ~g/gi S, 6 500 ~g/g. The Lagarosiphon sample from contained the highest Ca level: 14 800 ~g/g. The highest levels of the six micro­ nutrient elements determined were: Cl, 21 000 ~g/g, Mn, 4 700 ~g/g (both-in Ceratophyllum); Fe, 1 130 )Jg/g, Co, 10.4 ~g/g, and lY",o, 5.6 ~g/g (in Potamoget:on crispus) i and Cu, 5 ~g/g (in Egeria densa).

These maxima were more distributed th~oughout the 6 lakes than the maximum values for the macronutrient elements. Two adventive species, Cerat:ophy11um demersum and Potamoget:on crispus, were clearly able to absorb large quantities of several essential elements. The influence of these plants on the nutrient balance of the lake system is considered, and the possible relationship between competitive success and enhanced capacity for nutrient absorption is also considered.

INTRODUCTION

Aquatic macrophytes have, with rare exception, rated scientific interest in New Zealand only as weeds to be controlled or eradicated. Various species which have thrived under local conditions include Elodea canadensis Michx. in Lake Rotorua, Dagarosiphon major (Ridley) Moss in Lake Rotorua and the upper lakes of the Waikato River hydro-electric storage system, Egeria densa ?lanch. in Dakes Karapiro and Maraetai, and Ceratophy11um demersum L. in most lakes of the Waikato River. Macrophytes 122 MAURI ORA, 1976, Vol. 4 make a significant contribution to annual production in fresh­ wate.r and, therefore, play an important role in the nutrient budget of many lakes and rivers. Much of the scanty literature dealing with the chemical composition of macrophytes has been reviewed by Caines (1965). More recently, the effects of nutrient enrichment on macrophyte chemical composition have received more attention (Boyd 1969, Boyd and Vickers 1971, Gossett and Norris 1971, Ryan et a1. 1972). An extensive body of literature on the protein, fibre, dry matter, ash content and carotenoid values of macrophytes was reviewed by Little (1968). Other studies have dealt with the relationship between water chemistry and weed distribution (Moyle 1945), the nutritive value of weed (Nelson et a1. 1939), the role of macrophytes as limnological indicators (Seddon 1972), and the relationship between macrophyte morphology and nutrient levels (Adams et a1. 1971). The formulation of a nutrient budget for any body of water requires a comprehensive set of hydrological data, as well as chemical analyses of the water, plankton, and macrophytes. Although some values have been published for a few elements in macrophytes collected in New.Zealand (Fish and Will 1966, Lancaster et a1. 1971, Reay 1972) there is no comprehensive data even for the species from a single site. '1'0 provide information toward a nutrient budget for the Waikato River hydro-electric storage lakes, element levels were determined in macrophyte samples from Lakes Ohakuri to Karapiro. Because of the restricted shallow or other areas suitable for macrophyte growth in many of these lakes, phytoplankton probably account for a considerable amount of the total lake production. Element levels were therefore determined in a plankton sample from each lake, and in a representative water sample.

DESCRIPTION OF THE AREA

The Waikato River and its sources, Lakes Taupo and Rotoaira, are shown in Fig. 1. Between LaRes Aratiatia and Ohakuri the Waikato River receives geothermal waters from the Broadlands, waiotapu, andOrakeikorako thermal areas. Lake Ohakuri is also subject to runoff from the extensively farmed Whirinaki and Waikite Valleys. Vegetation on land surrounding Lakes Atiamuri, Whakamaru, and Maraetai is predominantly exotic forest, while the catchments of Lakes Arapuni and Karapiro are dominated by pastoral farming. The catchments of all the Waikato River lakes are rhyolitic in nature, and include lahar deposits, pumice breccia and tuffs, massive ignimbrite sheets, and current-bedded alluvial sands and gravels derived from pumice and ignimbrite. Consequently, the river is subject to similar geochemical influence from Lakes Aratiatia to Karapiro, maximum geothermal influence at Lake Ohakuri, and the influ-ence of pastoral farming from the catch­ ments of Lakes Ohakuri, Arapuni and Karapiro. RriiVLENCE & fYHITTON - WAIKATO RIVER ELEMENT LEVELS 123

-- dam

Lake Karapiro

Lake Arapuni I I

Whirinaki Arm I Waiotapul Lake ~ o I Lake I Lake I I o I

Wairakei 0 " I Broadlands \ Lake Aratiatia

Lake Taupo

Lake Rotoaira

o :> km

Fig. 1. The Waikato River hydroelectric storage lake syste~ and Lakes Rotoaira and Taupo. 124 MAURI ORA, 1976, Vol. 4

METHODS

Lakes Ohakuri I Atiamuri I Whakamaru, Ma.raetai, Arapuni and Karapiro (Fig. 1) were sampled on 14 and 15 March 1973. The physical features of each are summarised in Table 1. Because of its dominance by , Lake Aratiatia was included with the former in a separate survey (in preparation) .

TABLE 1. PHYSICAL FEATURES OF THE SIX WAIKATO RIVER HYDRO-ELECTRIC STORAGE LAKES SAMPLED IN THE STUDY.

Maximum height above Lake Year filled (ha) Area sea level (rn) Ohakuri 1961 1295 287 Atiarnuri 1958 220 252 Whakarnaru 1951 712 226 Maraetai 1952 505 188 Arapuni 1929 932 111 Karapiro 1947 777 54

All sampling was carried out from a boat. Ten to twelve complete plants of each macrophyte species were recovered by grapple, washed, and processed as a single sample. Two hundred grams wet weight of weed was collected wherever possible. A 10 1 water sample, and a tow with a 30 lIm mesh net were taken near the centre of each lake. Plant samples were oven dried at 110°C, finely ground in a Krups coffee mill, and bottled. Plankton and water samples were evaporated to near dryness in platinum basins on a hot­ plate under infra-red lamps, dried in an oven at 110°C, finely ground in a mortar, and bottled. The following elements were analysed by emission spectro­ scopy: Na, Mg, Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Ga, Sr, Zr, Mo, Ba and Pb. S, P, Cl, K, Ca and Zn were analysed by x-ray fluorescence spectroscopy. Because of the high levels encountered in these samples, Mn was determined by atomic absorption. As the amounts of several macrophyte samples were insufficient for Kjeldahl analysis, the incomplete data for N is omitted from this contribution. For emission spectroscopic analysis, all samples were ignited in platinum basins at 500°C for 2 h. A 10 mg sample of the ash was mixed with carbon powder containing an Ag internal s·tandard, in a 1:3 ratio of ash to carbon powder. Sample electrodes were burnt in a d.c. arc as cathode at 10 amps, using a Hilger Large Quartz Spectrograph, until the sample was consumed. Exposures were made on Ilford G.30 chromatic plates, which were marked for the elements of interest, using a Hilger projection comparitor. Element line densities were measured with a zeiss Microdensitometer, and concentration was assessed from graphs of line density against element concentration. For x-ray fluorescence analysis, 2 g of sample in a mylar based holder was irradiated, using a Philips PW 1540 spectro­ graph. A Cr target tube and PE analysing crystal were used for S, Cl, K and Ca, and a W target tube and LiF analysing crystal were used for Zn. A counting procedure was used for the estimation of all elements' except Zn, where a graphic procedure was followed. RAWLENCE & WHITTON - WAIKATO RIVER ELEMENT LEVELS 125

Standard mixtures of trace elements were prepared following the procedures of Mitchel (1964), and calibration graphs were prepared for each element. These were checked for accuracy against various standard reference materials (Flanagan 1969, 1973, Roubalt et al. 1966, Bowen 1967). Throughout this paper plankton and macrophyte element values are expressed as ~g/g of the element in oven dry material. and values for water are expressed as mg/l or ~g/l. RESULTS

WATER The level of dissolved solids, represented by the ash values (Table 3), decreased steadily between Lakes Ohakuri and Arapuni and increased slightly in Lake Karapiro. The range of dissolved solids values (116 to 148 mg/l) for the Wakato lakes is significantly higher than the values for Lake Taupo (58 to 64 mg/l, in preparation). The variation downstream in amounts of K, Mg, S, Na, Mo, Cr, Sr, Ba and Ti showed a trend similar to that for dissolved solids. The levels of Si, Al and Fe decreased only as far as Lake Maraetai, and then increased through Lake Arapuni to Lake Karapiro. Cobalt and B decreased steadily downstream from Lake Ohakuri to Lake Karapiro. The high levels of K, S, Na, Cl, Si and B in Lake Ohakuri largely relate to the various geothermal inflows to the lake. The erosion of soil, which includes residues of serpentine superphosphate, probably contributed significantly to the high levels of Ca, Mg, S, Al, Fe, Ti, Cr, Co, Ni, and Ga in Lake Ohakuri. Farming in the catchments of Lakes Arapuni and Karapiro may well have contributed to the increased levels of K, Mg, S, AI, Si, Fe, Cu, Ni, and Ga in the two lowest lakes, while the influence of recreational boating is apparent in the Pb levels for Lake Karapiro. MACROPHYTES The following species were collected during this survey: Ceratophyllum demersum L., Elodea canadensis Michx., Lagarosiphon major (Ridley) Moss, Egeria densa Planch., Potamogeton crispus L., Potamogeton cheesemanii A. Bennett, and Nymphaea alba L. The highest values in this study for 4 of the 5 macro­ nutrients analysed (K, P, Mg, S) were recorded for Ceratophyllum demersum from Lake Atiamuri. The highest single Ca value occurred in Lagarosiphon from Lake Karapiro. The sample of Potamogeton crispus from Lake Ohakuri contained the highest levels of all three non-essential elements present in large amounts throughout the system (Si, Na, AI). Seven micronutrient elements analysed in this study were: Cl, Fe, Cu, Mn, Co, Zn, and Mo. Overall, there was no distinct pattern to the distribution of maximum values. The single highest Cl value (21 000 ~g/g) occurred in Ceratophyllum from Lake s Atiamur i, 1,'1hakamaru and Arapuni I and the Mn maximum of 4 700 ~g/g in the same species from Lake Karapiro. The highest Fe value (1 130 ~g/g) was found in Potamogeton crispus from Lake Ohakuri, and the Co (10.4 ~g/g) and Mo (5.6 ~g/g) maxima in the same species from Lake Atiamuri. The highest Cu value (5 ~g/g) occurred in Egeria from Lake Maraetai. I-' IV 0"\ TABLE 2. ELEMENT LEVELS IN AQUATIC MACROPHYTES FROM T"llE WAlKATO RIVER HYDRO-ELECTRIC STORAGE LAKES. All values are expressed as ~g/g of dry weight. not detected

Macronutrients Micronutricnts

xl04

Area and K P Mg Ca S Na Fe Mo CU Mn Co Zn Ni V Cr Sr Sa Pb Ti Ga Zr B species Al Si C1 1 a 5.1. 0.36 0.46 0.34 0.48 0.04 0.55 0.46 1.5 460 0.6 1.1 110 0.5 35 1.6 0.5 1.5 49 31 4 15 b 2.7 0.28 0.24 1.07 0.38 0.06 4.4 0.59 0.49 700 2.4 0.7 140 1.5 28 1.8 1.6 8.0 94 110 24 26 c 0.97 0.23 0.39 0.80 0.30 0.05 4.4 0.55 0.69 600 1.1 0.9 140 1.1 17 2.8 0.7 12 115 135 20 19 44 ~ d 2.0 0.13 0.30 0.81 0.32 0.13 8.2 0.72 0.79 1130 3.4 1.3 200 1.8 31 6.8 2.8 22 127 147 5 14 0.9 50 36 ~ e 2.5 0.27 0.20 0.53 0.39 0.03 3.4 0.47 1.2 550 1.7 2.8 100 '0.5 39 2.3 1.0 7.4 66 57 20 24 I-! 2 a 5.4 0.51 0.50 0.34 0.65 0.03 0.48 0.59 2.1 480 1.1 1.6 460 0.4 53 0.4 0.6 1.3 43 39 4 n b 3.2 0.50 0.28 1.36 0.44 0.02 1.2 0.47 0.4 340 1.6 0.6 84 0.4 31 0.5 0.7 1.3 74 130 3 * 25 ~ c 2.4 0.46 0.30 0.86 0.46 0.03 5.2 0.60 1.0 750 5.6 4.1 190 10.4 39 1.9 1.9 5.8 112 240 2.6 14 0.4 28 '-' 3 a 5.2 0.48 0.34 0.52 0.03 0.45 0.46 2.1 350 0.7 1.3 140 0.8 30 0.8 0.7 1.0 63 45 5 13 \Q 0.33 'J b 3.4 0.41 0.31 1.2 0.34 0.03 2.4 0.47 0.53 490 1.6 0.9 86 0.6 28 0.7 0.8 0.9 94 160 1.9 9 26 ,0) c 2.9 0.44 0.26 0.98 0.43 0.03 4.8 0.60 1.2 430 2'.2 1.1 66 0.2 24 0.9 0.9 0 .. 5 72 94 9 26 4 a 4.7 0.18 0.38 0.36 0.51 0.027 0.96 0.40 1.7 480 0.4 2.4 240 0.3 48 1.4 0.5 1.2 36 27 2 20 ~ b 2.8 0.23 0.27 1.25 0.40 0.016 1.2 0.37 0.41 320 0.4 5.0 390 0.5 67 0.7 0.4 3.9 150 180 4 80 .... c 2.1 0.24 0.26 0.68 0.17 0.025 0.11 0.50 1.83 100 0.4 1.4 36 1.3 46 0.3 0.3 0.4 39 4.0 0.3 2 36 5 a 5.2 0.29 0.43 0.35 0.53 0.03 0.33 0.49 2.1 230 0.5 2.9 180 1.6 33 2.3 0.4 0.7 43 71 5 16 "" b 2.8 0.23 0.23 1.34 0.53 0.02 1.8 0.44 0.51 360 1.0 1.8 120 0.8 33 0.7 0.5 4.4 57 190 12 47

6 a 3.7 0.25 0.50 0.49 0.53 0.06 3.7 0.52 1.65 760 0.6 3.5 4700 3.0 56 4.3 1.3 1.7 65 145 16 37 b 3.0 0.31 0.29 1.14 0.42 0.026 1.9 0.41 0.47 370 O.S 3.0 1300 1.5 56 2.1 0.7 6.5 130 210 2.1 11 • 74 c J..7 0.39 0.32 1.48 0.41 0.03 2.1 0.49 1.07 390 0.8 1.1 400 3.5 51 0.8 1.1 4.6 73 170 2.7 12 27

Area and species are as follows: I, Lake Ohakuri: a, Ccratophyllum; b , Elodea; c, Lagarosiphon; d, Potamogeton crispus; c, Potamogeton cheesemanii. 2, Lake Atiamuri: a, Ceratophyllum: h, Elodea; c, Potamogoton crispus. 3, Lake Whakamaru: a, Cera tophyll um; b , Elodea: c, Potamogeton crispus. 4, Lake Maraetai: a, Ceratophyllum; b, Egeria dcnsa; c, Nymphaca alba~ 5, Lake Arapuni: a, Ceratophyl1um; b, Elodea. 6, Lake Karapiro: a, Ceratophyllum; b, Egcria; c, Lagarosiphon~ TABLE 3. ELEMENT LEVELS IN PLANKTON AND WATER SAMPLES FROM THE WAIKATO RIVER HYDRO-ELECTRIC STORAGE LAKES. N.D. Not Detected.

PLANKTON

Macronutrients Micronutrients ~ ~g/g x 104 I'g/g Ash K P Mg Ca S Al Si Na Cl Fe Mo Cu Mn Co Zn Ni v Cr Sr Ba Pb Ti Ga Zr B I Lake Ohakuri 50 0.54 0.15 0.60 0.50 0.22 0.165 17 1.8 1.15 2100 1. 5 42 140 15 23 130 5.5 2.6 120 65 11 70 2.6 N.D. 40 '" Lake Atiamuri 62 0.42 0.10 0.47 0.41 0.15 0.260 24 1.9 0.97 3100 1. 3 16 340 12 21 93 6.8 3.2 130 110 11 230 3.5 100 105 ~ Lake Whakamaru 51 0.28 0.09 0.34 0.31 0.16 0.165 21 1.4 0.89 2000 0.6 3.6 160 2.2 28 23 3.4 1.8 75 50 10 48 2.5 N.D. 91 I--j Lake Maraetai 52 0.34 0.17 0.62 0.44 0.25 0.155 21 1.6 1.22 2200 0.67 14 130 2.8 37 29 3.9 2.9 110 72 11 62 1.7 N.D. 85 Lake Arapuni 63 0.19 0.05 0.33 0.20 0.11 0.170 29 1.1 0.35 2400 0.13 4.2 400 N.D. 19 8.3 2.5 1.9 95 70 9 76 2.5 N.D. 35 ~ Lake Karapiro 67 0.24 0.08 0.37 0.24 0.11 0.360 28 1.3 0.32 4000 1.1 15 2600 0.9 37 44 8.0 5.0 114 175 10 32 4.0 120 29 ~ WATER ~ mg/l I'g/1 (5 ~ Lake Ohakuri 148 6.5 4.0 7.4 6.4 133 38 25 29 162 0.7 1.0 13 0.49 2.7 16 1.8 0.8 47 13 2 6 0.45 N.D. 810 ~ Lake Atiamuri 131 5.6 3.0 5.2 1.5 118 30 24 27 146 0.6 3.4 19 0.37 2.4 8 1.6 0.2 47 8 2 2 N.D. N.D. 740 ~ Lake Whakamaru 124 4.8 2.6 4.2 1.1 88 31 22 26 113 0.6 4.9 16 0.16 1.8 5 0.9 0.1 30 9 3 2 N.D. N.D. 480 Lake ~hlraetai 118 4.6 2.4 5.0 1.0 86 22 20 27 64 0.4 1.5 3 0.15 2.6 7 1.1 0.1 27 7 2 2 N.D. N.D. 410 Lake Arapuni 116 3.9 2.1 4.4 0.95 116 23 19 23 89 0.4 5.0 15 N.D. 1.6 110.70.120 6 1 2 N.D. N.D. 190 Lake Karapiro 128 4.0 2.8 4.5 1.2 12.8 36 21 26 165 0.5 8.6 5 N.D. 1.8 14 0.6 0.2 41 15 5 4 0.59 N.D. 360 I'"3 &; ~ t:-< tt,

I-' ....,'" I-' coN TABLE 4. SUMMARY OF THE DISTRIBUTION OF AAXIMUM ELEMENT VALUES FOR AACROPHYTES IN THE WAIKATO RIVER HYDRO-ELECTRIC STORAGE LAKES.

Lake Si K P Na Mg Ca S Al Cl Fe Zn Cu Mn Co Mo Ni V Cr Sr Ba Pb Ti Ga Zr B Macrophyte

Elodea Ohakuri c.· Potamogeton crispus • • • ": •• • Ceratophyllum Atiamuri ~•• • !~ ~ Potamogeton crispus §i .~ ..... Whakamaru Ceratophyllum 0 .-: :>:l : :.,. .... 0-': Maraetai Egeria densa E ;:::'.: .1 N \0 • '-l Arapuni ':.: Ceratophyllum !!' <:: 0 Ceratophyllum f.., Karapiro .-: .::.::...... :: ...... ; .. :::.:.: .: ...... :.:/j Lagarosiphon ""

Macronutrients F9 Micronutrients • = Maximum Value C] ~ RAWLENCE & WHITTON - WAIKATO RIVER ELEMENT LEVELS 129

The highest individual values for the non-essential elements in the system occurred in Potamogeton crispus (Ni 6.8, V 2.8, Cr 22, Pb 5 ~g/g) and Elodea (Ti 24 ~g/g), both from Lake Ohakuri. The highest Ba value was recorded for Potamogeton crispus from Lake Atiamuri (240 ~g/g) and the highest Sr value (150 ~g/g) for Egeria from Lake Maraetai. The distribution throughout the system of the maxima for each of the elements analysed is summarised in Table 4.'

PLANKTON All samples were dominated by phytoplankton. In the case of only a small group of elements; K, Ca, Fe, Mo, Co, Ni, and Ba, was there any correspondence between the maximum values for those elements in water and plankton (Table 3).

DISCUSSION MACROPHYTES As in other plants, element levels in macrophytes vary seasonally. However, as all samples were collected at the same time, the relative differences between the species are not likely to be qreatly altered. The autumn (March) element levels recorded (Table 2) probably represent values close to the seasonal peak. With few exceptions, present macronutrient element values for Ceratophyllum, Elodea, and Lagarosiphon compare with published values for these species (Lancaster et al. 1971, Fish and Will 1966). In the present studv, the P values for Laqarosiphon in Lakes Ohakuri (2300 ~g/g) and Karapiro (3 900 ~g/g) were lower than the levels recorded for autumn samples from Lake Rotorua (average 6 800 ~g/g) by Fish and Will (1966), and the Ohau Channel (linking Lake Rotorua with Lake Rotoiti) (74 000 ~g/g) by Lancaster et al. (1971). Fish (1971) noted that P levels in Lake Ohakuri were "rather higher" than those found in Lake Rotorua (0.005-0.01 ~g/g). The lower P values in Lake Ohakuri may reflect the high sediment load and lower water clarity in the Waikato River. The same explanation may also account for the difference in K level between Lagarosiphon from the Ohau Channel (34 600 ~g/g; Lancaster et al. 1971) and that from Lakes Ohakuri and Karapiro (13 350 ~g/g average). Without a collection of similar species from each lake, determination of any trends in nutrient element uptake throughout the system is difficult. However, a number of general features are evident. 1. Ceratophyllum was collected from all b lakes. Within each lake, this species had the highest levels of more than half the macronutrients analysed. 2. Considering the lakes overall, the highest levels of 4 of the 5 macronutrient elements occurred in Ceratophyllum from Lake Atiamuri. 3. The distribution of macronutrient maxima does not reflect the distribution of maximum values for the same elements in water (Table 3). The levels of K, P, Mg, and S were all highest in Ceratophyllum from Lake Atiamnri, but the highest levels of the same elements occurred in water from Lake Ohakuri (Table 3). The surface arp-a of Lake Atiamuri is only 17%that of Lake Ohakuri, but the greater water 130 MAURI ORA, 1976, Vol. 4

movement in the smaller lake may have aided nutrient replace­ ment in the weed stands and thereby accentuated the rate of nutrient uptake, particularly in the dense stands of Ceratophyllum. 4. No clear pattern emerged in the distribution of micronutrient and non-essential element maxima. While Potamogeton crlspua clearly abscrbed greater quantities of more micronutrient elements than other species in both Lakes Ohakuri and Atiamurf (Table 2), this species did not dominate nutrient absorption ~n the other 4 lakes (Table 2).

It is possible to argue bhat the ecological success of plants such as Ceratophyllum and Potamogeton crispus is related to their ability to accumulate considerable quantities of nutrients. In common with many species of macrophytes, Ceratophyllum and Potamogeton crispus have a highly developed capacity for vegetative reproduction. Fragments of rhizomes, upright shoots, tubers, and turions can all serve as centres for new growth in Potamogeton, and. a similar purpose is served by fragments of the brittle vegetative system of C~ratophyllum. Such reliance on vegetative reproduction reflects the vagaries of the aquatic environment, and could hardly be so successful without considerable supplies of readily available nutrients - supplies which can be translocated rather than absorbed .to facilitate new growth. The characteristic ecological success of species such as Ceratophyllum and Potamogeton crispus may well be a concomitant to their highly developed capacity for vege­ tative reproduction and nutrient accumulation.

PLANKTON With the exception of Mn, the present element values fall within the range of world values given by Healey (1973). Lake Karapiro was slightly discoloured when sampled, and the high No value may well be due to the presence of fragments of decayed macrophytes which contain particularly high levels of Mn (personal research, in prep.).

ACKNOWLEDGMENT

The authors would like to thonk Dr C.K. Beltz, Department of Botany, University of Canterbury for her helpful review of the manuscript.

LITERATURE CITED

ADA11S, F.S., MacKENZIE, D.R., COLE, H. and ~RlCE, M.W. 1971 The influeno~ of nutrient pollution levels upon element constitution and morPhology of Elodeq canadensis RiCh. in Hichx, 8pvLronmentqJ Pollution 1: 285-298. BOWEN, H.J .M. 1967. Comparative elelllent <\nalysis of il st'mdard :plant material. Analyst 92; 124-131.

BOYD, C.E. 1%9. The m~i:+it:i.ve Val~e of t.ln:efl spac:i.ef! of water We~qs. Economic Botqng 23: 123-127. BOYp, C.B. and V+CIq;;RS, P.H, 1971. Vq+~qt:i.~n ~n th~ ~l~m~nta+ PQnt~nt of Ei9~prniq c~qssipes. ffyar9bla~p~iq 3a; 409-4l4. RAWLENCE & WHITTON - WAIKATO RIVER ELEMENT LEVELS 131

CAINES, L.A. 1965. The phosphorus content of some aquatic macrophytes with special reference to seasonal fluctuations and applications of phosphate fertilizers. Hydrobio1ogia 25: 289-301. FISH, G.R. 1971. Nutrient incomes and water quality of Lake Rotorua. In: Duncan, C. (Ed.), The Waters of the waikato: 195-201. University of Waikato, Hamilton, New Zealand. 229 pp. FISH, G.R. and WILL, G.M. 1966. Fluctuations in the chemical composition of two lakeweeds from New Zealand. Weed Research 6: 346-349. FLANAGAN, F.J. 1969. U.S. Geological Survey Standards 2. - First compilation of data for U.S.G.S. rocks. Geochimica Cosmochimica Acta 33: 81-120. 1973. 1972 values for international reference samples. Geochimica Cosmochimica Acta 37: 1189-1200. GOSSETT, D.R. and NORRIS, W.E. 1971. Relationships between nutrient availability and content of nitrogen and phosphorus in tissues of the aquatic macrophyte, Eichhornia crassipes (Mart.) Solms. Hydrobio1ogia 38: 15-28. HEALEY, F.P. 1973. Inorganic nutrient uptake and deficiency in algae. CRC Critical Reviews in Microbiology 3: 69-113. LANCASTER, R.J., COUP, M.R. and HUGHES, J.W. 1971. Toxicity of arsenic present in lakeweed. New Zealand Veterinary Journal 19: 141-145. LITTLE, E.C.S. 1968. The control of water weeds. Weed Research 8: 79-105. MITCHELL, R.L. 1964. The spectrochemical analysis of soils, plants and related materials. Commonwealth Bureau of Soils Technical Communication No. 44A. 225 pp. MOYLE, J.B. 1945. Some chemical factors influencing the distribution of aquatic plants in Minnesota. American Midland Natur.a1ist 34: 402- 420. NELSON, J.W., PALMER, L.S., WICH, A.N., SANDSTROM, W.M. and LINDSTROM, H.V. 1939. Nutritive value and chemical composition of certain freshwate~ plants of Minnesota. University of Minnesota, Agricultural Experimental Station, Technical Bulletin No. 136. 47 pp. REAY, P.F. 1972. The accumUlation of arsenic from-arsenic-rich natural waters by aquatic plants. Journal of Applied Ecology 9: 557-565. ROUBALT, M., ROCHE, H. and GOVINCLARAJU, K. 1966. Report on four rock standards granites GR, GA, GH and basalt BR. Science de 1a Terre 11: 105-121. RYAN, J.B., RIEMER, D.N. and TOTH, S.J. 1972. Effects of fertilization on aquatic plants, water and bottom sediments. Weed Science 20: 482-486. SEDDON, B. 1972. Aquatic macrophytes as 1imnologica1 indicators. Freshwater Biology 2: 107-130.