River Pollution 21

from flow-through curves of "tracer" under varying hydraulic conditions in a number of streams are included.

Calculations are given embodying mixing corrections to the mathematical model outlined above, to see if the predicted distributions of dissolved oxygen so obtained differ markedly from those obtained without this refinement.

Some consideration is also given to the effects of changes in temperature, light intensity, and biomass of plant present on the distribution of oxygen in rivers; hypothetical examples are used in illustration. Potential applications of the model in river management are also discussed.

Studies on natural factors affecting phosphate absorption and its utilization by algae. JOSEPH SHAPIRO, M i n n e a p o l i s , M i n n e s o t a , U . S . A .

It is generally believed that alleviation of eutrophication of surface waters would result from lowering the concentration in, or supply to, these waters of nutrient elements, particularly nitrogen and phos- phorus. However, difficulties arise in setting limits of concentration of these nutrients at which "water blooms" or otherwise undesirable growth would be restricted. Therefore, as part of a program directed at determining the factors affecting algal production, we have pursued the question of whether all waters can be treated alike, in the sense of their being merely the diluting medium, or whether there are factors to be considered in addition to those of presence or absence of essential ions, or concentration of nutrients. In particular we have investigated the possibility that there are factors in natural waters which are capable of inhibiting or facilitating the use of phosphate by algae, and whether these factors are present in different waters to the same extent.

Previous work by two investigators has suggested that these factors exist. In 1948 RODHE demon- strated that the diatom Asterionellaformosa would grow luxuriantly in lake water with nitrogen and phosphate added if the phosphate-phosphorus were at a concentration as low as 0.002 mg/l. This contrasted strongly with the phosphate concentration of 0.200 mg/1 required for the same growth in medium made by adding inorganic salts to distilled water. The difference in the two media was ascribed to an accessory factor in the lake water, possibly organic, and subsequently called the "phosphate sparing factor". Its importance is that, if it exists, and exists to a different extent in different waters, these waters will produce markedly different responses to phosphorus enrichment. Therefore, we are now assaying different waters for this factor. The basic procedure has been to add a wide range of nutrients, including trace elements, to a filtered sample, following which the sample is divided into

90

I10.

70.

60,

50.

,~ 4o.

E

z zo.

Io,

o

i , . . . . . . . . . . ' " "'"

? ~s~3.~ ......... / . . . . . . . . . . .

~ i .el / . . - "

~o ~oo ,5~o zdo* z;*o Oiss. P y / !

FIG. 1. Growth of cultures of Mierocystis aeruginosa in media made up with distilled water, lake water, and deionized lake water. The single encircled point is for a 1 : 1 mixture of lake water-

deionized lake water.

22 River Pollution

aliquots, to each of which is added a different amount of phosphate. Growth of a standard algal inoculum in these media is compared with growth in media based on distilled water. A typical result is shown in FIG. 1 in which Microeystis aeruginosa was used as the test organism. Apparently this water sample contains some factor facifitating the use of phosphate by Microcystis. Experiments using ion exchange resins suggest that the factor is ionic. Similar assay experiments are being performed with a wide variety of waters and with different algae. Later work will concentrate on the nature of the factor.

Work by MACKE~TH in 1953 suggested the presence in lake water of another similar factor. By comparing the rate of absorption of phosphate by Asterionellaformosa suspended in lake water with the rate in distilled water, he found the rate in lake water to be much higher. He was unable to add any nutrient or combination of nutrients or set of conditions to the distilled water to make it as effective as lake water; and he concluded after experiments, that lake water contains a factor, capable of stimulating phosphate absorption, which can be eliminated by boiling the water or charring the dried residue. We have performed numerous similar experiments and have been able to corroborate Mackereth's finding that "something" is present in lake water which is not in distilled water, and which stimulates phosphate absorption. But our work has not led in the direction of some organic factor. Rather, the results using Microcystis aeruginosa as the test organism, show that the concentra- tion of inorganic anions is probably the important parameter. F I o u ~ 2 shows results of a typical experiment. Several interesting features have emerged from this study.

0.12 [

O,h

o.oe 8 .c_

O.OE

i

0.04

b.o2

~2 :3 O {2

istilled Water

o Big Lake + Salts

I I I I I I 20 40 60 80 I00 120 Time (minutes)

FIG. 2. Absorption of phosphate by Microcystis cells suspended in different media. The "salts" referred to are those normally used in the culture medium in which the algae were grown.

1. Certain lakes (such as that shown in FIo. 2) have been found which are dilute enough so that addition of salts increases the rate of phosphate uptake by the algae. Significantly, even some samples from Lake Superior show this behaviour.

2. Of the ions tested, nitrate seems to be the most potent. This is especially interesting in view of an apparent threshold-concentration effect and the fact that when lakes are fertilized over many years their nitrate concentration increases proportionately more rapidly than that of phosphate until suddenly the lake begins to throw algal blooms, i.e. perhaps eutrophication speeds up suddenly when a certain concentration of nitrate is attained.

River Pollution 23

3. Although we have found anions to be of prime importance a recent study, by SmGEtcrI-~LER et aL (1967) on a marine fungus, shows sodium to be the key substance in phosphate uptake, Therefore we are investigating different algae to see whether they all respond to the same substance or whether the rate of phosphate absorption is conditioned differently in different groups of algae.

Our hope is that the studies described will help in interpreting data already gathered on such phenomena as sewage-induced eutrophication, and will contribute to an analytical approach to the creation of realistic water quality standards. The work is being supported by the Federal Water Pollution Control Administration under Research Grant WP-177.

R E F E R E N C E S

MACr~RETH F. J. H. (1953) Phosphorus utilization by Asterionella formosa Hass. J. exp. Bot. 4, 296-313.

Roorm W, (1948) Environmental requirements of fresh-water plankton algae. Symb. Bot. Upsall 10, 1-149.

SmOErcrnALER P, A., BELSKY M. M. and GOLDSTErN S. (1967) Phosphate uptake in an obligately marine fungus: A specific requirement for sodium. Science N. Y. 155, 93-94.

Avoidance reactions of salmonid fish to representative pollutants. JOHN B. SPRAGUE, C a n a d a

Avoidance by fish of polluted waters is often named as one of four or five probable sublethal effects of pollution on aquatic life. However, there have been relatively few investigations to demonstrate whether avoidance reactions are in fact of great importance.

Five common pollutants were tested in the laboratory against small rainbow trout or Atlantic salmon. Results indicated that strong avoidance reactions to sublethal concentrations would occur for only one of the five pollutants. For the others, avoidance responses would not necessarily save fish from lethal concentrations.

Tests were conducted by presenting fish with a choice between clean water and successively higher concentrations of a pollutant, one concentration at a time. Complete records of movements of individual fish were made and analysed. Statistical significance of response was tested by non-para- metric means.

Tested against zinc sulphate in soft water, rainbow trout showed a threshold avoidance level of only 0.005 mg/l Zn, which is about 0.01 of the lethal threshold. Furthermore the avoidance response was sharply defined; a range of two orders of magnitude of concentration of zinc sulphate covered the change from no avoidance response to nearly complete avoidance. This avoidance threshold for zinc sulphate is about ten times lower than the one previously reported for small Atlantic salmon, although both are in low sublethal ranges.

By contrast, rainbow trout were not able to avoid phenol at any concentration, from 0-001 mg/l to 10 rag/l, although the latter concentration is almost lethal. At the higher concentrations, fish were obviously disturbed, swam frantically, but apparently could not discriminate between "clean" and "polluted" water.

Tested against an ABS detergent, trout showed mild avoidance of all concentrations from 0.001 to 0-1 rag/l, and moderately strong avoidance of 1.0 mg/1. At 10 mg/1, although fish were obviously disturbed, they were confused and were not able to avoid the water containing detergent. It seems likely that a lag in rinsing of detergent from sensory receptors prevented fish from discriminating between "clean" and "polluted" water. Destruction of olfactory receptors by detergent, reported by others, could also be important.

The pattern of response to chlorine was peculiar. Rainbow trout showed significant avoidance as low as 0.01 mg/1 of chlorine, which would be lethal in ten days. They also avoided 1'0 rag/1 which would be rapidly lethal. However, at an intermediate concentration of 0'1 mg/l, lethal in about four days, fish showed a net preference for water containing chlorine, as against clean water. Eleven out of fourteen fish showed this preference although individual responses were generally not statistically significant. Details of fish behaviour indicated an unusual physiological "trap" involving the sensory