Life in Lakes and Rivers. T. Macan T.
The Duddon is one of the few valleys in which there is no lake. Its highest tributary, Gait-scale Gill, rises at an altitude of 735 m. (2400 ft.) in a flat area covered with bog and small pools of open water. Beyond this it tumbles steeply down the fellside, dropping 300 m. in 900 m. (33%). At the foot of this slope there is a delta of large stones under which the water disappears in dry periods. Exceptional rainfall towards the end of the year during which Kuehne and Minshall were at work enlarged this delta, and incidentally carried away every one of about twelve maximum and minimum thermometers which they had buried in various parts of the system. The analyses made by these two workers showed that the calcium ranged from 0.57 to 1.10 parts per million in Gaitscale Gill, a low value, even for the Lake District, but after the flood the concentration below the delta rose to 3.0 p.p.m. This illustrates the point, stressed earlier, that freshly exposed faces yield more nutrients than those which have been leached for some time. The highest temperature recorded in the gill was 17.2° C., 5.6° C. lower than the highest temperature recorded elsewhere in the system.
Several streams run down the fellside parallel with Gaitscale Gill and feed the main river which here runs roughly westwards. Beside it runs a road, originally made by the Romans, probably as a line of communication through the area to facilitate the subjection of the natives (Rollinson, 1967). It is now used mainly by tourists, for there are no dwellings beside it between Langdale at one end and Eskdale at the other. The river swings round to take a southerly direction in an upper valley with a comparatively slight incline. There were four farms in this valley, but only two are used for farming today. In autumn a few green fields around them stand out among the predominant greyish-yellow of the poorer pastures, probably as a result of liming. Sheep, which range far and wide over the surrounding fells, particularly in summer, are the chief product. A few conifers, planted recently, are the only trees.
The slope steepens to separate the lower from the upper valley. The slope in the lower valley is 1 %, the river is floored with round stones of all sizes, and it flows torrentially down to the estuary. There is no plain region, and only the first two of Carpenter’s four zones and the first of Butcher’s five can be recognized. There are two small villages in the lower valley, residences scattered outside them, and some twelve farms on which cattle as well as sheep are reared. Deciduous woods cover extensive areas of the valley sides. The upper valley comes to an end about 175 m. above sea level, the lower at sea level. The difference in climate between the two is obviously great but no figures are available. The temperature of the swift river gives no indication of it. The valley walls rise steeply on both sides but to the west there is a plateau over which flows the longest tributary.
The River Duddon is about 11 miles (18 km.) long. We pass from it to the River Tees (Butcher, Longwell, and Pentelow, 1937) which is about 100 miles (160 km.) long. It rises in the Pennines and flows to the North Sea. The gathering ground drained by the headstreams is fairly large. It is high above sea level, it receives a relatively heavy rainfall of about 60 inches (1520 mm.) a year, and the rock is impermeable. The result of these four factors is a severe scour in time of flood, and this has carved out a deep bed. Consequently the energy of a flood is not dissipated in inundating the surrounding country and the effect is concentrated on the river-bed. On one occasion some carts were being filled with gravel at the water’s edge when the river rose so suddenly that the carts had to be abandoned and were swept away. This illustrates a most important condition affecting the plants and animals of the river.
The small town of Croft is about 45 miles (70 km.) from the mouth and about 65 miles (100 km.) from the source, travelling by river, and is a convenient dividing point. Above Croft all the river is rapid with little rooted vegetation and few fish except trout, grayling, and minnows. The river downstream is still moderately swift but there is much more rooted vegetation and various coarse fish are plentiful. After flowing for 20 miles (32 km.) from Croft the river reaches the head of the estuary, which is some 25 miles (40 km.) long.
The Tees rises on Cross Fell at a point about 2,500 feet (760 m.) above sea level. Many small tributaries also rise just on the eastern side of the Pennine watershed, and some of them originate in thick peat beds. One, for example, drains the peat pools which were mentioned in Chapter 4. These little streams run down the hillside with a fairly though not extremely rapid flow, because the eastern slopes of the Pennines are not steep. About six miles from the source three main tributaries have coalesced and the river is some 12 metres wide with a fair flow over a bottom of stones and boulders. Then it enters a quiet stretch and for three miles the current is sufficiently slow to allow the deposition of some fine sediment, which provides a foothold for a few higher plants, Potamogeton alpinus, the alpine pond-weed, Callitriche intermedia, the water starwort, and Sparganium simplex, the simple bur-reed. The only other attached plants are the mosses, Fontinalis antipyretica, and Eurhynchium rusciforme, and, at certain seasons, the algae Lemanea fluviatilis and Cladophora glomerata.
This slow stretch provides a pretty example of the sort of exception to the general plan which is to be found in almost any river. It is caused by a stratum of hard rock, and at the end of it there is a fine waterfall. A little farther on, some 16 miles (20 km.) from the source and 1,000 feet (305 m.) above sea level, the river strikes a road and some human habitations, and comes to the end of what may conveniently be taken as the first part of its course. A chemical station was set up just here and the results obtained are shown in Table 4.
Table 4. Some dissolved substances in the Tees near the end of the first part, that is above any pollution
The average amount of calcium is about 12 parts per million, and so the water is soft although the river has been flowing over limestone. But there are big fluctuations in the concentration of all the substances except oxygen, which is plentiful at all seasons and at all times of day and night.
Trout occur in this part of the river and may be taken almost up to the source. They are plentiful but of small size, the average length being but six inches (15 cm.).
The next part of the course extends all the way down to Croft, which is at the point where the river changes in character. The river crosses several geological formations, which affect its nature, but it remains rapid throughout with a bottom of bare rock or stones. There is hardly any rooted vegetation.
The main difference between this and the preceding part of the river is that it receives sewage effluents from towns along its route. The first place of any size is Middleton-in-Teesdale, some twenty-two miles from the source, and the biggest is Barnard Castle, about eight miles farther on. The population connected with the sewage systems of the two places was 1,700 and 5,000 respectively when the survey was made. Below the outfalls there were changes in the flora, and there can be no doubt that these changes were directly attributable to sewage and the products of sewage decomposition. Below some of the larger works the dominant organism on the river bed was the sewage fungus. Father downstream there was a characteristic association of algae, but this finally gave place to the same association as was found in the upper waters, where there was no pollution. Below the smaller sewage outfalls there was no sewage fungus, but there was the characteristic change in the algal community encrusting the stones and boulders. In all this part of the river the amount of sewage was small compared with the volume of water into which it was discharged and pollution was not great. Oxygen concentration in the summer was lower than in the first part of the river (Table 4) but it never reached a seriously low level. Chloride rose, probably as a result of the sewage. The amount of calcium also increased and an average figure just above Croft was 24 parts per million; this rise was probably mainly due to the limestone over which the water had flowed.
Trout occurred throughout this part of the river and reached a greater size than in the first part, 1/4 to 3/4 lb. (120–360 g.) in weight with a few specimens of 3–4 lb. (1.4–1.8 kg.). It contained minnows almost throughout, and grayling in the lower half; thus, although there are no marked physical changes, the river enters the third of Carpenter’s zones in this part of its course.
At Croft, 100 feet (30 m.) above sea level, there are several important changes in the river. It enters