H. B. N. Hynes

The recolonization mechanisms of stream benthos

The animals recolonizing an area of denuded stream substrate are thought to come from four main sources. These are drift, upstream migration within the water, migration from within the substrate, and aerial sources, e.g., oviposition. An experiment in a Canadian stream showed drift to be the most important source of recolonizing animals, contributing 41.4% of the total number that settled on an area of 1800 cm2. This compares with 28.2% from aerial sources while upstream migration and movement up from within the substrate contributed about equally (18.20% and 19.1 00, respectively). Clearly then, all four directions are important in repopulating bare areas. Further, many groups of organisms were found to have preferred directions from which they recolonize and this, it is argued, may lead to the establishment of separate and distinct faunal assemblages if the other directions are excluded.

Groundwater and stream ecology

In the light of findings in recent years about the extent and nature of the hyporheal zone, the rate of uptake of organic matter by stream beds, and the fact that groundwater contains dissolved organic matter, it is suggested that stream ecologists should learn much more than they now know about groundwater. It seems probable that it is an important source of organic matter to the stream ecosystem which has escaped consideration to date.

The importance of groundwater in the transportation of allochthonous dissolved organic matter to the streams draining a small mountain basin

The importance of groundwater in the dissolved organic matter (DOM) budget of small upland streams is not well understood. This paper is concerned with the amount of streamflow which can be attributed to groundwater, the organic chemistry of rainwater, streamwater, and groundwater, and the rate of transfer of DOM in groundwater to the streams of a small mountain catchment basin in Alberta. Using naturally occurring isotopes (18O and tritium) groundwater is concluded to be the largest contributor to stream discharge throughout the year. This means that most of the water which reaches the stream must pass through the soil column and be exposed to microbial attack. Groundwater in the Marmot Basin spends an average of about ten years in the ground before being discharged into streams. In this area it appears that the majority of DOM from forest productivity is consumed in the soil and only small amounts of refractory by-products reach the stream. This is in keeping with the finding of Fisher & Likens (1973) that 99% of forest productivity is consumed terrestrially. It is probable that bacteria in stream sediments are capable of taking up refractory compounds which deep soil bacteria can not. Increases in DOM concentration in streams are not usually observed during storm runoff because of the ability of bacteria to take up groundwater DOM and because most of stream discharge is groundwater low in DOM being flushed into the channel even during snowmelt and rainfall events.

Wave-Zone Macrobenthos of the Exposed Canadian Shores of the St. Lawrence Great Lakes

Abstract Two series of qualitative collections of the benthic macroinvertebrates inhabiting the wave-zone (0-2m) along the exposed Canadian shores of the St. Lawrence Great Lakes were made in the summer of 1974. This fauna consisted largely of typically lotic water forms, including Heptageniidae (Ephemeroptera) and Hydropsychidae (Trichoptera). The variety and relative abundance of invertebrates was directly related to substrate stability. Insects other than chironomids were rare in Lake Ontario and hypotheses to explain this different fauna are presented.

Dissolved organic carbon in streams and groundwater

Minipiezometers installed at different vertical levels within the streambed (20–140 cm) were used to study temporal and spatial variation in the dissolved organic carbon (DOC) content of streamwater and groundwater in three southern Ontario streams. Groundwater, as represented by our streambed samples, contained considerable quantities of DOC but variation between replicate samples was high. Diel fluctuations in DOC content of streamwater were consistent with daytime autochthonous production and night-time uptake by heterotrophs. Water from the streambed neither consistently diluted nor enhanced streamwater levels of DOC. At some stations, DOC variation with depth, including streamwater, seemed to be largely random. At other stations, DOC concentrations from the deepest piezometers were consistently higher than concentrations at intermediate depths, suggesting a loss of DOC from deeper waters to overlying sediments. However, at these stations DOC concentrations were highest at 20 cm and at the surface. Interflow delivery of DOC to the shallow layers of the streambed may be a significant source of carbon for a stream ecosystem, especially in agricultural areas. Late summer diel fluctuations at one station may be related to changing patterns of intermixing of stream and groundwater in the upper layers of the streambed as governed by velocity heads, convective currents and evapotranspiration.

Distribution of the benthos within the substratum of a Welsh mountain stream

Samples collected with a standpipe corer at depths of 10-15 and 15-25 cm below the gravel surface of the Afon Hirnant show that benthic invertebrates occur in considerable numbers down to at least 25 cm, which is only 5 cm above the bedrock. The numbers in these samples, together with estimates of the numbers in the top 5 cm as revealed by kick samples, indicate a faunal density of around a quarter of a million per square metre. This is a far greater number than is usually reported from stream beds, but it is shown to be in line with estimates made in very different streams by methods that collect specimens from deep in the substratum. Clearly the usual types of quantitative sample are quite inadequate.

Movement of immature aquatic insects in a lotic habitat

The movement of immature insects up down and across Salem Creek, Ontario, was measured with traps and nets at two week intervals from January to December 1977. Drift of most taxa was more strongly correlated with water velocity from August to December than it was over the whole year. That of Baetis, however, was not correlated with water velocity and it was significantly greater at the side of the stream than at the centre from May to July. Upstream movement, as measured in three different ways, was small compared with drift, being only 2.1, 7.3 and 15.2 percent respectively.Upstream and across stream movements were not consistently different from one another, changes in their intensity apparently merely representing changes in numbers and behaviour of the animals. It is concluded therefore that upstream movement is only random movement.Colonization of empty sediment in trays on and above the substratum confirmed that most reoccupation of denuded areas is by drift. This supports the finding that drift is far geater than random wandering of the insects.

The effect of road deicing salt on the drift of stream benthos

A study was made to determine whether the levels of salt resulting from road runoff affect the drift of benthic invertebrates of urban streams in southern Ontario. The three major ions in common road salts (Cl−, Na+, Ca++) were monitored in Laurel Creek from December 1973 to February 1975. Maximum concentrations occurred during the winter, the highest levels being 1770 mg/litre Cl−, 9550 mg/litre Na+ and 4890 mg/litre Ca++. Since most of the salt was entering the creek as NaCl, this chemical was used in the laboratory to test the drift response of three organisms, Hydropsyche betteni, Cheumatopsyche analis and Gammarus pseudolimnaeus. Pulses of salt up to concentrations of 800 mg/litre Cl− had no effect on their drift patterns. These results were then tested in the field. Several experiments were run in a section of Lutteral Creek which had been longitudinally divided by a metal barrier on each side of which drifts nets were stationed. Levels as high as 750 mg/litre Cl− produced no differences in the drift between the salted and unsalted channels. However, during the last experiment, a pulse of 2165 mg/litre Cl− increased the drift of all organisms in the salted channel. This became apparent only when the concentration had exceeded about 1000 mg/litre.

Zonation of the invertebrate fauna in a West Indian stream

Samples of the invertebrate fauna collected at ten points on a mountain stream in Trinidad reveal that the fauna is altitudinally zoned and that the apparent boundary between rhithron and potamon is below 30 m. This is very much lower than has previously been reported in the tropics.SummaryGeneral collections of the benthos and water striders were made at 10 points from 550-17 m altitude on the Arima River, Trinidad, a swift mountain stream. It was possible to conclude that 38 of the taxa that occurred commonly in some of the samples were probably single species. These displayed marked vertical zonation of the fauna and a change in the community that can be interpreted as the rhithron-potamon boundary at less than 30 m. This markedly lower than has previously been reported from the tropics.

Movements of adult aquatic insects near streams in Southern Ontario

Sticky traps placed across a stream in southern Ontario in June and September showed that only females of the mayfly Baetis intercalaris and the caddisfly Lype diversa were flying upstream and so conforming to the concept of the colonization cycle. Other species, B. vagans, Cheumatopsyche oxa, C. campyla, Hydroptila consimilis, Chimarra aterrima and Polycentropus centralis seemed to be flying at random along the stream. There was a distinct downstream movement of Baetis subimagos near the water surface. It is shown that a series of 4 traps across the stream gives a better indication of directional movement than a single one.In March the winter stonefly Allocapnia vivipara was shown to walk away at approximately right angles to the stream and to ascend trees at the edge of the woods 16 m away.