Dynamics of dissolved oxygen during algal bloom in Lake Kasumigaura, Japan

Huter R,'~earch Vol. I4, pp 179 to 183 © Pcrgltmon Press Lid Igxo Printed in Great Britain

(Xl43-1354 ~0 0201-(1179S02.(K10

DYNAMICS OF DISSOLVED OXYGEN D U R I N G ALGAL BLOOM IN LAKE KASUMIGAURA, JAPAN H. SEKi, M. TAKAHASHI,Y. HARA and S. ICHIMURA Institute of Biological Sciences, University of Tsukuba, Sakuramura, Ibaraki, Japan 300-31

(Receired 8 March 1979) Abstract--Dynamics of dissolved oxygen during an algal bloom were studied in Lake Kasumigaura. Great amounts of oxygen arose from photosynthesis, and the concentration of dissolved oxygen reached 190°,, of saturation at 12 h. The majority of the dissolved oxygen produced was liberated into the atmosphere or consumed by microorganisms. Only minor fractions were transported into the dysphotic zone due to the low eddy diffusion coefficient in deeper waters of the euphoric zone.

INTRODUCTION

Approximately 1.9 x 109 g of nitrogen and 9.4 x 107g of phosphorus are annually introduced into Lake Kasumigaura (surface area 178 km 2; maximum depth 7 m ; mean depth 4 m ; volume 8 × 10 s m3; watershed 1950 kin2; water renewal time 7 months) as agricultural and domestic wastes (Seki, 1974; lbaraki University, 1977). Nuisance blooms of blue-green algae, predominantly Microcystis spp. and Anabaena spp. have been serious during summer and autumn since 1963 in the lake. Most serious cases of the algal growth were observed in 1964 and 1965 at the northern part of the lake: a large amount of Microcystis spp. and Anahaena spp. accumulated on the water surface as heavy neustonic mats of decimeters thickness, which were then washed ashore to give obnoxious odors during putrefaction. Oxygen is mainly supplied into the lake water by means of oxygen generation, by photosynthesis and agitation by wave action in the upper water, being subsequently incorporated into the deeper waters by diffusion and water movements. Generally, thermal stratification is interrupted and reestablished at any region of the lake even during summer because of mixing due to strong winds occurring almost every afternoon, as the detailed studies of physicochemical investigations (The National Institute for Environ-. mental Studies, 1976). This is one of the reasons why this shallow lake is usually free from hypolimnetic oxygen deficiency. This vertical mixing throughout the lake in any season mixes algae throughout the water column, approximately 4 m depth on the average, whereas the compensation depth for algal photosynthesis is often only 0.2m in blue-green algal blooms even without heavy neustonic mats since 1963 (Freshwater Fisheries Experiment Station, lbaraki Prefecture, 1976). However, summer fishkill has sometimes been caused by local oxygen depletion, for instance, in fish cultivation enclosures. Thus, dynamics of dissolved oxygen during bluegreen algal blooms in Lake Kasumigaura must be 179

thoroughly understood to prevent catastrophic destruction of the lake ecosystem. The dynamics during a maximum of the algal bloom at the beginning of August 1977 are shown as a typical example of a series of investigations being conducted to study diel variation of dissolved oxygen with special reference to oxygen supply within the euphotic zone in Lake Kasumigaura. MATERIALS AND METHODS Water samples were collected during an algal bloom at 4 h intervals from 4:00 on 1 August to 4:00 on 2 August, 1977. The sampling station 136 06' N, 140 24' E) was at the end of a pier at lbaraki Freshwater Fisheries Experiment Station (Fig. 1), approximately 50 m offshore with a depth of 190cm. The increase of oxygen arising from photosynthesis for 4-h incubation was measured in situ in a 100ml BOD bottle. At the same time, the decrease of oxygen in a darkened bottle was used to measure any respiration occurring simultaneously with photosynthesis (Strickland and Parsons, 1968). Inorganic nutrients (nitrate. nitrite, ammonium and reactive phosphorus), adenosine triphosphate (ATP) measured using Aminco Chem-Glow-Photometer and chlorophyll a extracted by freezing were determined by the procedures in Strickland and Parsons (1968). The in situ dissolved oxygen and temperature were measured by YSI model 57 oxygen meter (Ohio). Solar radiation and underwater light intensity were measured by an actinograph (Ohta Keiki. Tokyo) and an underwater light meter (Maruyama DenkL Tokyo), respectively. The pH and redox potential of lake water were measured by a pH meter model HM-IF (Toa Electronics Ltd, Tokyo) and a redox meter model RM-IF (Toa Electronics Ltd, Tokyo), respectively. Total number of bacteria was counted directly under a Nikon phase contrast microscope with a bacteria counting chamber (Erma, Tokyo). RESULTS Phytoplankters in the euphotic zone were composed predominantly of the following algal species;

Microcystis aeruginosa, Anabaena spiroides, Cryptomonas erosa, Coscinodi~'us i'othii. Coscinodiscus lacustris, Carteria cordiformis, Scenedesmus quadricauda, Scenedesmus actiformis, Pandorina morum, Eudorina

180

H. SEKL M. TAKAHASHI,Y. HARA and S. ICHIMURA

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River Tonegawo Tokyo TokyoBayI ~(~ Fig. 1. Location of sampling station in Lake Kasumigaura. unicocca and Coelastrum microporium. Each of these predominant phytoplankters exhibited no change of their vertical distribution in the water column during the study period (Hara et al., 1978}. Major groups of the biological agents (indicated by ATP) responsible for the production and consumption are phytoplankton (indicated by chlorophyll a) and bacteria, respectively. The statistical analyses (Table 1) show that these agents exhibited no significant vertical stratification with the average and standard deviation as follows: ATP (/lg ATP/1)= 6.2 _+ 3.2, Chlorophyll , (/.~g/l)= 150_+ 41, and Total bacteria (per m l ) = 1.2 × l0 T_+0.8 × 107 . In situ dissolved oxygen started to increase in the shallower water (above 60cm) immediately after dawn (at 4:00, and for solar radiation, see Fig. 2) on

August 1, whereas it was decreasing in the deeper waters (below 60cm) in the early morning (Fig. 3). Dissolved oxygen reached the maximum concentration at 12:00 when the concentration at each depth throughout the water column (except for the bottom) was almost doubled compared to the one at dawn. The maximum concentration in the upper water was 190°o of saturation, when pH and Eh were 8.90 and 294 mV at 32.0°C, respectively. Thereafter dissolved oxygen decreased almost continuously until the next dawn. However, dissolved oxygen below the compensation depth still showed high concentration at 20:00 due to some increase after 16:00 on August 1. Contribution of photosynthesis and respiration to the concentration of dissolved oxygen within the euphotic zone is shown in Fig. 4. Theoretical concen-

Tablc 1. Analyses of variance in the distribution of biological paramctcrs in lakc water Source of variation

Degree of freedom

ATP

Variance ratio Chlorophyll a

Total bacteria

Fo.o~

Between sampling depth Between sampling time Residual Total

6 5 30 41

0.31 2.78

0,06 0.61

(I.91 0.31

3.47 3.70

Table 2. Analyses of variance in the distribution of inorganic nitrogen compounds (NH4 + NO2 + NO 3) and phosphate in lake water Source of variation

Degree of freedom

Between sampling depth Between sampling time Residual Total

6 5 30 41

Variance ratio Nitrogen Phosphorus /~.oJ (I.27 0.64

1.08 1,53

3A7 3,7(I

181

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tration in the figure is defined here as the concentration of dissolved oxygen starting from 4:00 on August 1 as influenced by the changes of dissolved oxygen due to biological activities without vertical transportation of oxygen by diffusion, physical movements of water or loss to the atmosphere. The increase of dissolved oxygen by photosynthesis was greater than the decrease of dissolved oxygen by respiration at any depth within the euphoric zone. Two layers could be distinguished in the euphotic zone, hyperoxygenative and hypooxygenative. The hyperoxygenative layer could be observed in topmost water of the lake, where major proportions of oxygen arising from photosynthesis are always transported to other layers or liberated from the water surface into the atmosphere. The hypooxygenative layer occurred in deeper water next to the hyperoxygenative layer, from which is received oxygen, although daily oxygenation in the deeper layer is positive. The statistical analyses show that inorganic nutrients in lake water exhibited no stratification dur-

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Fig. 4. Comparison of m situ and theoretical dissolved oxygen at each depth within the euphotic zone. ing the study period (Table 2) and inorganic nitrogen compounds [NH4(~ug atm/l} = 0,98 + 1.30; NO2(/,tg atm/I} = 0.13 _+ 0.04; NO3(~g atm/I) = 0.18 _ 0.20] had been taken up by phytoplankton down to the nutrient level that is conventionally classified as that of oligotrophic lakes, and the reactive phosphorus concentration [PO4(pg atm/I) = 0.33 + 0,38] was characteristic of eutrophic lakes. The nitrogen then became the controlling factor. DISCUSSION

Much work has been done on the oxygen distribution in different types of lakes (as reviewed in Hutchinson, 1957: Kusnezow, 1959; Golterman, 1975). The results of this work shows detailed static features of oxygen in lakes and suggests that oxygen

in eutrophic lakes, or hypereutrophic lakes as their extreme, could be highly dynamic due to violent biological activities of photosynthesis and respiration. As communities of the lake ecosystem are composed ot mostly obligate aerobes, organisms actively modifying aerobic condition in such an aquatic environment of oxygen unstability threaten even the existence ol themselves. The unfavourable oxygen conditions, oversaturated and microaerobic, are modified partly by oxygen transportation through physicochemical processes in lake water Absorption of atmospheric oxygen or liberation ol dissolved oxygen through water surface is directly proportional to the difference between saturation concentration, O~, and in situ concentration, O, in the water (Lewis and Whatman, 1924). That is. ?O/?t = K (0~ - 0), where K is the absorption coefficient at saturation deficit in water or liberation coefficient at saturation surplus in water. Adeney (1926) has used the same approach to determine the absorption of oxygen (ml/cm2/min) ?O/?t = 9.61t + 361 (O~ - O) x 10 -~. where t is temperature. The absorption (plus) of atmospheric oxygen and liberation (minus) of dissolved oxygen were calculated (Table 3) and daily oxygen budget at the water surface was determined as 2.1 mg O2/cm 2 liberated per day. Sverdrup's formula (1938) has been successfully applied to the dynamic explanation of dissolved oxygen in the sea. The formula could be applied also for the freshwater environments because each component of the formula has the same behaviour both in the freshwater and marine environments (Hutchinson, 1957: Sverdrup et al., 1961). In the case of the environment here (Tables 1 and 2: as well as reported in Freshwater Fisheries Experiment Station, Ibaraki Prefecture, 19761, since horizontal inhomogeneity ol dissolved oxygen at the region of the sampling station in the lake is negligible, the formula of Sverdrup can be rearranged as t~O/Ct = D~t320/p2 2 --.]', where D: is eddy diffusion coefficient and f is oxygen consumption. The oxygen consumed by microorganisms (rag O2/l/day) was measured in situ as respiration in darkened bottles as 6.2, 4.7, 3.L 3.2 and 3.9 at each zone of 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100cm, respectively. On the other hand, D: tcm2/s) is calculated as 6.7, 17.4, 14.9, l.l and 2.3 at each zone of 0-20 cm, 2 0 4 0 cm, 40-60 cm, 60--80 cm and 80 100 cm, respectively, assuming dai b ? O / ? t = 0 at each zone because of almost the same

Table 3. Analysis of variance in the distribution of phosphates in lake water Source of variation

Sum of squares

Degree of freedom

Mean square

Variance ratio

Fo.o~

Between sampling depth Between sampling time Residual Total

0.91 1.07 4.12 6. l 0

6 5 30 4I

0.15 0.21 0.14

1.08 1.53

3.47 3,70

Average and standard deviation for 42 samples. /~llg atm/l-~1 = 0.33 ___0.38.

Dissolved oxygen during algal bloom

183

Table 4. The rate of vertical transportation of dissolved oxygen by liberation from the water surface and by downward transportation due to eddy diffusion Depth (cm)

4:00

8:00

Liberation from water surface (mg/cm2/h) 0 1.9 + 10 -2 -3.1 × 10 -2 Eddy diffusion D:. ;20/?:" (mg/I/h) 0-20 -0.53 -0.11 2(L40 0.19 -0.31 40-60 -0.06 -0.28 60-80 - 0.04 - 0.02 80-100 0.01 - 0.05

1 August 12:00

16:00

20:00

0:00

4:00

-2.6 × 10 -7

-2.3 x 10 - t

-9.5 × 10 -2

-9.7 x 10 2

1.7 x 10 2

-0.65 -0.97 -0.13 0.01 0.02

-0.54 -0.59 -0.28 - 0.02 -- 0.04

-0.56 -0.35 -0.10 - 0.01 -- 0.02

-0.08 0.03 -0.25 - 0.01 - 0.03

-0.08 0.16 -0.13 - 0.04 - 0.01

vertical profile of dissolved oxygen at 4:00 on August l and 2. These D: values are similar to those commonly measured directly by physical oceanographers in the surface layers of the neritic region of Japan (e.g. Watanabe, 1977). Vertical transportation of dissolved oxygen, O:'?20/t'~z 2, is then calculated as shown in Table 4. The daily transportation (mg O2/1/day) to the lower waters was 10, 7.4, 4.9, 0.52 and 0.48 at each zone of 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100 cm, respectively. In conclusion, major parts of the dissolved oxygen produced during the algal bloom were liberated from the water surface or respired by microorganisms, as low eddy diffusion coefficient value at deeper layers within the euphotic zone prevent the efficient supply of dissolved oxygen to the dysphotic zone. This mechanism seems to be favourable for minimizing the direct influence of high unstability of oxygen conditions in the euphotic zone into the dysphotic zone.

Acknowledoements--The authors are indebted to Drs C. D. McAllister and R. A. Vollenweider, the Environment Canada, who gave useful comments on the first draft of this manuscript. They are grateful to the staff of Freshwater Fisheries Experiment Station of lbaraki Prefecture, K. Kuroiwa and Y. Takahaxa for their assistance. This work was supported by special projects "Eutrophication of water systems in Tsukuba district" of University of Tsukuba and "The impact of human activities on ecosystem dynamics of Lake Kasumigaura and its basin area" of the Miffistry of Education of Japan. REFERENCES

a,deney W. E. (1926) On the rate and mechanism of the aeration of water under open-air conditions. Sei. Proc.

2 August

R. Dublin Sot.. n.s. 18, 211 217 {cited in Hutchinson, 1957). Freshwater Fisheries Experiment Station, lbaraki Prefecture 11976) Report of Freshwater Fisheries Experiment Station, lbaraki Prefecture 13, 1-101. (In Japanese.) Golterman H. L. (1975) Physiological Limnolog.v. Elsevier Sci., Amsterdam, Oxford and New York, 489 pp. Hara Y., Saitow M. and Chihara M. (1978) Diel distribution of phytoplankters in Lake Kasumigaura. Era'ironmental Studies in Tsukuha District, Vol. 3. University of Tsukuba, 116-124. (In Japanese.) Hutchinson G. E. (1957) ,4 Treatise on Limnology, Vol. 1. Geography, Physics and Chemistry. Wiley, New York. 589 pp. lbaraki University (1977) Kasumigaura. Sankyo Kagaku Sensho. Tokyo, 203 pp. (In Japanese). Kusnezow S. I. 0959) Die Rolle der Mikroorganismen im Stoffkreislauf der Seen. Veb Deutscher Verlag der Wissenschaften. Berlin. 301 pp. Lewis W. K. and Whitman W. G. (1924) Principle of gas absorption. Ind. Engng Chem. 16, 1215-1220. Seki H. (1974) Lake Kasumigaura. Survey of lake rehabilitation techniques and experiences. Tech. Bull. Department of Natural Resources, Madison, Wisconsin 75. 56. Strickland J. D. H. and Parsons T. R. (1968) A Practical Handbook of Seawater Analysis. 2nd edition, Bull. Fish. Res. Bd. Can. 167, 420. Sverdrup H. U. 11938) On the explanation of the oxygen minima and maxima in the oceans. J. Cons. int. Explor. Met. 13, 163 172. Sverdrup H. U., Johnson M. W. and Fleming R. H. (1961) The Oceans. Their Physics, Chemistry, and General Biology. Prentice-HaU, Englewood Cliffs, 1087 pp. The National Institute for Environmental Studies (1976) Eutrophication of Lake Kasumigaura. Occasional Publication R-l, 1-145. (ln Japanese.) Watanabe T. (1977) Problems on the interchange of seawater in conjunction with the improvement of fishing ground. Bull. coast. Oceano.qr. 14, 65 78. (In Japanese.)