Invertebrate drift in the regulated River Tees, and an unregulated tributary Maize Beck, below Cow Green dam

SUMMARY. The Cow Green dam was completed in the summer of 1970 and invertebrate drift was sampled below the dam and in an adjacent tributary, Maize Beck, on thirty-one occasions between July 1970 and September 1973. Drift was sampled by pumping river water through a filter. The intake was placed in Maize Beck for the first sample and in the Tees for the second, and so on alternately for the rest of the sampling period. Nets were used on ten occasions, nine of these in winter months and once when the pump broke down. A total of ninety-five taxa were recognized, of which eighty-six occurred in Maize Beck and seventy-one in the Tees. The Tees fauna was dominated numerically and in terms of biomass by a large population of micro-crustaceans originating in the reservoir. Hydra and Naididae also formed a large proportion of the Tees drift but contributed little to the biomass. Ephemeroptera were most abundant in Maize Beck samples. Diptera were abundant in drift catches in both streams with simuliid larvae most numerous in Maize Beck and chironomid larvae most numerous in the Tees. The greatest drift densities of the benthic fauna were observed between April and October; the mean number of organisms per 10 m³ were seventy-three in Maize Beck and 144 in the Tees. The mean densities in winter were very low, respectively two and seventeen per 10 m³ in the two rivers. There was no significant difference between the mean levels of the total bottom fauna (numbers and biomass) in the drift in the two rivers during the period April-October, but vrtnter biomass was significantly greater in the Tees. In July 1970 micro-crustaceans represented 29% (14 per 10 m³) of total drift numbers and 3% (0.7 mg wet-weight per 10 m³) of the biomass, whereas in 1973 they represented 99% of both the numbers (37 670 per 10 m³) and weight (2.2 g wet-weight per 10 m³). The relation between benthos and drift was examined. In the drift Plecoptera and Baetidae were more abundant in Maize Beck than in the Tees. Only Chironomidae and Nais spp. were more abundant in the Tees, In the benthos the density of Plecoptera and Baetidae was not significantly different in the two rivers, but all other groups with the exception of Simuliidae occurred at greater densities in the Tees. The proportion of baetids present in the drift was greatest in Maize Beck. No such difference was demonstrated for total fauna. Diel rhythms were observed in baetids and simuhids with densities greater in night catches. Nocturnal peaks of these organisms were less pronounced in the Tees. Chironomid larvae showed no diel changes in abundance. Significant diel changes in the mean weights of individual animals were not detected in baetid nymphs or chironomids. Micro-crustaceans showed no nocturnal peaks of abundance. Preliminary observations on the quality and quantity of seston caught in drift samples between April and October showed great differences between the rivers. In the Tees the bulk ofeach sample consisted of algal filaments derived from the river and micro-crustaceans from the reservoir. In Maize Beck algae were un-common and the sample was composed of peat and mineral particles. Data are presented on seston output at different discharges.     

A survey of stream invertebrates in the Cow Green basin (Upper Teesdale) before inundation

In 1967 a programme was initiated by the Freshwater Biological Association to study fish populations within the proposed Cow Green reservoir basin and in the Tees downstream of the dam, before and after impoundment. This paper describes the result of a supporting study on aquatic invertebrates covering the pre-impoundment period 1967–70. The benthic faunas of six streams in the reservoir basin, the Tees below Cauldron Snout and Maize Beck, a tributary ofthe Tees below the dam, were studied. Species list are presented for each habitat and changes in seasonal and annual abundance are discussed. All areas sampled lie at altitudes between 440 and 550 m O.D. and are situated amongst moorland and limestone grassland. Conditions in the streams ranged from slow-flowing peaty reaches to small streams with moss-covered bottoms and larger stony rivers and streams with relatively unstable bottoms. Samples were taken in riffles and pools using the ‘kick’ method wherever possible. An attempt was made to quantify kick-sample catches by comparing them with shovel-sample catches which cover a known area of stream bottom. It was found that 10 5 kicks gave a catch equivalent to the populations of 1 m², giving a population density of about 1200 animals/m for the reservoir-basin riffles. Over 120 taxa were recorded, 100 of which were at the species level. In the reservoir-basin streams, 116 taxa were found with seventy-one in Maize Beck and fifty-six in the Tees below Cauldron Snout. Ephemeroptera were the most abundant group in the reservoir basin and Maize Beck faunas with Rhithrogena semicohrata, Heptagenia lateralis and Baetidae being the most abundant forms, although Ecdyonurus spp. especially E. dispar were much more common in Maize Beck. In other groups Leuctra spp. and Gammarus pulex were very common. In the Tees below Cauldron Snout Limnaea peregra, Chironomidae and Baetidae formed the bulk of the fauna and Plecoptera were uncommon. Amongst the reservoir basin streams Weelhead Sike supported the largest number of species and species groups (eighty-one), and all the streams had forty-nine or more taxa represented. Information on seasonal changes in the numbers of those species or species groups composing 90% or more of the total fauna is presented. Faunal density was high in May with Ephemeroptera, particularly Ecdyonuridae, and the plecopteran Leuctra inermis being the most abundant forms. In August, the numbers of animals appeared t o fall and common members of the community were Baetidae, Diptera, Leuctra fusca and Ecdyonuridae. In October, Ecdyonuridae particularly R. semicolorata, were most abundant. A comparison ofthe bottom fauna of riffles and pools was made and more animals were found in riffles than in pools. The effect of gravel extraction on the bottom fauna of the Tees was examined. A severe drop in the numbers of animals was observed after extraction. Diptera were the first group to return to their pre-disturbance density. Elminthidae and Annelida were worst affected and slowest to recover. The fauna of the area is discussed and possible reasons for its relative species richness are put forward. Habitat diversity and chemical richness appear to be the most likely reasons for the relatively large number of species found.     

A quantitative study of the invertebrate fauna of the River Tees below Cow Green Reservoir

Monthly samples were taken in the River Tees below Cow Green dam from four sites differing in flow conditions, by means of trays containing stones from the river, which were immersed for a period of 1 month. Information on the distribution, abundance and biomass of the benthos of the River Tees is given with additional data on the life-histories of some of the more common species, during the period May 1971 to May 1972. Of the seventy-two taxa found, fourteen made up 95% of the total numbers. Hydra, Polycentropodidae, and the molluscs Limnaea peregra and Ancylus fluviatilis were the most abundant animals in the slower-flowing water (10–26 cm s^?1) and Simuliidae, Orthocladiinae, and Baetis rhodani dominate the riffle (50–75 cm s^?1) fauna numerically. Some organisms, Nais spp., Caenis rivulorum and Baetis scambus favoured intermediate flows of 20–60 cm s^?1. The slowest-flowing water contained the largest number of taxa and the site with the fastest flow supported the least. A mean monthly weight per square metre of 14·56 g (95% limits from 7 to 31) was calculated using data from all four sites. The frequency distribution of nymphal size-classes is given for B. scambus, C. rivulorum, Ephemerella ignita, and Brachycentrus subnubilus, and the association of certain nymphal size-classes with a particular site is analysed. The composition and distribution of the fauna is discussed. It is suggested that the relative richness of the fauna in terms of biomass is attributable to the organic enrichment of the river following the building of the Cow Green dam. The regulation of the flow has allowed the dense growth of algae and mosses, and the development of large molluscan populations, and the reservoir itself provides a rich source of food, particularly zooplankton and phytoplankton, for the river benthos.     

The numbers, biomass and transport downstream of micro-crustaceans and Hydra from Cow Green Reservoir (Upper Teesdale)

Fluctuations in numbers and biomass of Copepoda, Cladocera and Hydra drifting out of the Cow Green reservoir via the outflow were investigated during the period August 1972-November 1973. Cladocera, chiefly Daphnia hyalina var. lacustris Sars and Copepoda, were most abundant between July and September, occurring at mean densities of 1278 and 215 m^?3 respectively. Hydra was most abundant between August and October at a mean density of 19 m^?3. Winter densities of all groups were low and 98% of the total annual output occurred between July and October. An estimated 150 kg (136 kg of Cladocera, 13kg of Copepoda and 1 kg of Hydra) dry weight was released from the reservoir during the year November 1972-October 1973. During periods of peak abundance about 1–2% of the total fauna drifting out of the reservoir was found 6·5 km below the dam. The effect of reservoir discharge and flow in tributaries of the Tees on this transport downstream is discussed. It is suggested that the micro-crustaceans and Hydra, even if not fed upon directly, will have considerable influence on the Tees benthos when they settle out and decompose to produce a nutrient-rich detritus.     

Effects of impoundment on populations of bullhead Cottus gobio L. and minnow, Phoxinus phoxinus (L.), in the basin of Cow Green Reservoir

The distribution, growth and reproduction of bullhead, Cottus gobio , L., and minnow, Phoxinus phoxinus (L.), were studied at Cow Green Reservoir, Upper Teesdale, for 10 years following impoundment in 1970. Comparisons were made with pre-impoundment results. The length-for-age of bullheads increased after impoundment. The length-for-age of minnows decreased. In winter both species were confined mainly to deep water or to the stone facing of the earth dam. In summer they were found throughout the reservoir though bullheads were scarce in the littoral zone. Female bullheads became sexually mature at an earlier age (84% at age-group I) than before impoundment (33% at age-group I) but no change was apparent amongst males (67–62% in age-group I). The post-impoundment sex ratio did not differ from 1:1 and individual fecundity did not change after impoundment. There was a significant reduction in individual fecundity of the minnow. The mean instantaneous rate of mortality ( Z ) for bullhead of age-groups II to IV was 0.96 ± 0.34 year⁻¹, compared with 0.85 ± 0.29 year in the Tees before impoundment.     

Some physical and chemical effects of the Cow Green (Upper Teesdale) impoundment

SUMMARY. The paper describes observations on water temperature and dissolved oxygen in Cow Green reservoir and also changes caused by impoundment to temperature, chemistry, dissolved oxygen and the discharge regime of the River Tees immediately downstream of the dam.
Impoundment and river regulation have considerably smoothed-out fluctuations in discharge of the Tees and have ehminated the very low and very high discharges which were characteristic of the natural river.
Reservoir water levels show an annual pattern of draw-down during summer, refilling in autumn and overflow during winter and spring. Tliermal stratification of the reservoir occurs rarely and is generally of short duration. Water temperatures at mid-reservoir correspond closely to those of water discharged from the reservoir. The temperature regime in the river downstream is modified as follows:

• (1)

  reduction in amplitude of annual temperature fluctuations by 1–2°C,
• (2)

  marked reduction of diel fluctuations, (3) delay of the spring rise in water temperature by 20–50 days and of the autumn fall by 0–20 days. These temperature changes could reduce the annual maintenance ration of a 10 g brown trout ( Salmo trutta L.) by about 15% and delay the annual peak of metabolism by about 1 month. The effect upon growth rate of trout would be negligible.

Fluctuations in ionic content at the reservoir inflow are comparatively large and can be related approximately to river discharge. Fluctuations at the outflow are smaller and appear to be largely seasonal. Regulation has not appreciably altered the dissolved oxygen content of the River Tees.     

The macrophytic vegetation of the River Tees in 1975: observed and predicted changes

SUMMARY. An account is given of the distribution of macrophytes in the River Tees and its tributaries, north-east England, together with a critical discussion of the problems involved in recording data in a form which can be used for monitoring long-term changes of vegetation in rivers. Among the conventions and methods adopted in the present study are an attempt to define the vertical limits of the river sensu strictu as opposed to the bank, the extension of the term macrophyte to include as many visually obvious photosynthetic organisms as possible, the use of a check-list prepared in advance which contains a wider range of species than are actually expected for the river, and the collection of two different types of standard record for each 0.5 km length of river. The Tees has been the subject of intermittent observations on its vegetation for some 45 years. The most obvious change has taken place since 1965, with a substantial upstream spread of four submerged angiosperm species. Potamogeton crispus, Zannichellia palustris and Myriophyllum spicatum were previously present only in the lower reaches of the Tees, and have spread 25, 9.5 and 4.5 km respectively upstream from their previously known most upstream localities. Ranunculus penicillatus var. calcareus is an apparent invader to the river. It seems probable that these changes have taken place since 1971 as a result of regulation of the Tees by Cow Green Reservoir. Further changes are predicted with the advent of water transfer from the Tyne to Tees around 1980, because at least twenty-six macrophytes are known to be present in the former river that are either absent or confined to the lowest stretches of the latter.     

Phytobenthos of the River Tees and its tributaries

SUMMARY. A standard method is given for describing plant communities in fast-flowing streams and rivers. This involves the selection of a representative 10-m length of stream (termed a reach) which can be re-located exactly. Various estimates of the relative areas covered by different physiognomic forms and the relative proportions of species present are then combined to give a 'semi-quantitative' account, which can be compared with data collected at other sites or times. The method has been applied to six sites on the River Tees system. A site below Cow Green reservoir with markedly regulated flows, differs from the others in various ways. Bryophytes show a greater cover here than elsewhere throughout the year and a conspicuous cover of Phormidium occurs in autumn. Filamentous green algae of many different species are abundant at this site in late summer and early autumn. At the most downstream site where such seasonal growths also occur, a single species, Cladophora glomerata , is dominant. Conspicuous spring diatom 'bursts' occurred at the two upstream sites and a month later at the two downstream sites.     

The populations of fish in the River Tees system on the Moor House National Nature Reserve, Westmorland

The age, growth, population densities and annual production of an isolated population of brown trout ( Salmo trutta L.) and bullhead ( Coitus gobio L.) were investigated over a 5 year period in Trout Beck in the northern Pennines. Additional data were obtained from two other sites; Great Dodgen Pot Sike and the River Tees.
Trout growth rates were low, particularly in Dodgen Pot Sike, but ages up to VIII were recorded. Bullhead growth rates were similar to those in the Tees at Cow Green (Crisp et al. , 1974), though the Moor House bullheads had a higher survival rate. Population densities of trout ranged from 0.10–0.22/m², with a fry contribution of 0.80%. The bullhead population in Trout Beck was sparse, generally 0.1/m², though an 0 group value of 0.46/m^a was estimated in 1967. At Tees Bridge values ranged from 2.5–7/8/m². Most trout matured by age III, though in Great Dodgen Pot Sike only half of the females were mature at age IV.
Annual production was estimated from Allen graphs. Trout production ranged from 1.02–3.50 g/m²/year, the fry contributing up to 51.5% of the total. A value of 0.48 g/m²/year was obtained for bullheads in the Trout Beck system in a year of good recruitment, whilst bullhead production at Tees Bridge was 7.43 g/m²/year, with fry and I group contributing 48.7 and 37.5% respectively. The high survival rate, irregular recruitment, and poor growth of these high altitude populations is discussed. Growth and reproductive peculiarities of the Great Dodgen Pot Sike trout are also discussed.     

The effects of impoundment and regulation upon the stomach contents of fish at Cow Green, Upper Teesdale

The stomach contents of 1003 brown trout, 1551 bullheads and 800 minnows taken from the reservoir basin and below the dam, before and after impoundment of the river Tees, were examined. Their composition reflected observations by other workers on river and reservoir benthos, except for the increase in numbers of Hydra and Nais below the dam, and Mollusca, Hirudinea and oligochaetes in the reservoir.
Trout below the dam ate more Ephemeroptera nymphs and Chironomidae larvae but fewer terrestrial casualties after river regulation, whereas bullheads ate more Mollusca but fewer Plecoptera nymphs. In both species Baetidae nymphs increased in numerical importance relative to Ecdyonuridae. Trout, but not bullheads, took zooplankton discharged from the reservoir.
Before impoundment, trout within the reservoir basin ate chiefly benthic organisms and terrestrial casualties. Inundated terrestrial material, mainly earthworms, formed the bulk of their food for at least three years after impoundment, whilst from the second year onwards Chironomidae and, in some years, Gammarus became increasingly important. Zooplankton was taken by all sizes of reservoir trout.
Bullheads within the reservoir basin ate chiefly river benthos before impoundment, with Ephemeroptera and Plecoptera nymphs predominant in older fish, and aquatic Diptera and Coleoptera also important in the fry. After impoundment, Chironomidae and Gammarus were the main items taken by older bullheads, and Chironomidae and micro-crustacea by the fry. Among all sizes of minnow, Chironomidae, micro-crustacea and detritus increased in numerical importance after impoundment.     

Development of the macro-invertebrate fauna of Cow Green reservoir (Upper Teesdale) in the first five years of its existence

SUMMARY. The development of marginal (shore-line), sub-littoral (3–6 m) and profundal (15–18 m) fauna was followed using timed collections in shallow water and artificial substrata in deeper regions. The reservoir started filling in July 1970 and was close to top water level in the autumn of that year. Samples in the marginal zone contained drowned terrestrial organisms and some Cladocera (Chydoridae) in February 1971 but by October, Chironomidae and Oligochaeta became abundant and micro-crustaceans (copepods and cladocerans) formed about 98% of the total catch. Peak densities of micro-crustaceans in the marginal zone were reached in the summer of 1971, but chironomids and oligochaetes were most abundant in the second year after filling. The numbers of marginal zone animals were greatest at the most sheltered site, and lowest at a site on the windward shore. At a stream mouth the rheophilic fauna present in April 1971 was replaced with limnophilic organisms (Chironomidae and Tubificidae) by September 1971. In the sub-littoral, Hydra, Enchytraeidae, Orthocladiinae Tanytarsini and oribatoid mites were the most abundant taxa, whereas Naididae, Hirudinea, Ostracoda, Gammarus pulex, Chironomini and Pisidium spp. were numerous in the profundal zone. Total faunal numbers and biomass were greatest in the profundal zone in all years. The highest annual mean estimate of biomass in the sub-littoral was 3.07 g (wet wt)m^?2 in the second year after filling, thereafter both numbers and biomass fell. In the profundal the maximum biomass (about 29 gm^?2) was observed in the third and fourth years after filling. An estimate of total standing crop of benthic organisms below the drawdown limit, made in July 1974, gave a figure of about 43 tonnes, wet weight. Biomass estimates at Cow Green were compared with those in eighteen other reservoirs and were found to be high especially in relation to those from other upland areas.     

Long-term studies of the benthic biology of Tees bay and the Tees estuary

Tees bay on the north-east coast of England receives the waters from the highly industrialised Tees estuary. Since 1970 there have been considerable reductions in both the industrial and domestic sewage discharges to the estuary.The benthic populations of Tees bay have been routinely monitored since 1971, grabbing surveys have been completed at six areas in the spring, summer and autumn of each year. In 1979 the survey was extended to include stations within the Tees estuary itself.Tees bay appears to have a stable benthic fauna. Though the simple analysis of faunal statistics has demonstrated fluctuations within the benthos, neither this analysis nor classification analysis has indicated that there were any long-term changes in abundance or diversity.Classification analysis has also failed to differentiate between the fauna of the different areas within Tees bay. However, studies of biomass and T. fabula growth rate did indicate a difference between the areas close to the mouth of the Tees and those remote from it.The studies of the Tees estuary benthos indicated an improvement in both the abundance and the diversity of the fauna. However, the monitoring took place over a limited period and further work is necessary to ensure that this improvement does not simply represent natural fluctuations within the estuarine benthic population.     

The populations of fish in tributaries of the River Eden on the Moor House National Nature Reserve,northern England

The population dynamics of trout (Salmo trutta L.) were studied in two high-altitude streams flowing westwards into the River Eden in northern England. The results from one (Knock Ore Gill), which is accessible to spawners from downstream, were compared with published data from an isolated population in a nearby stream which flows eastward into the River Tees. The Knock Ore Gill trout had a population density of 0.4–0.9 fish m^–2, a biomass of 12.4 g m^–2, annual production of 12–14 g m^–2 year^–1 and an instantaneous mortality rate of 0.97 year^–1. Comparable values from the Tees tributary were 0.2, 3.3, 2.3 and 0.66 respectively. The Knock Ore Gill population also contrasted with that of the Tees tributary in having reliable recruitment from year to year. These differences were related to differences in the chemistry and spate characteristics of the two streams and to the fact that immigrants from downstream were responsible for over 30% of the annual oviposition in Knock Ore Gill.     

Reproductive investment of female brown trout, Salmo trutta L., in a stream and reservoir system in northern England

Within the basin of Cow Green reservoir, upper Teesdale, the brown trout, Salmo trutta L., spend their first two seasons in running water. After this some females remain resident and others migrate to Cow Green reservoir. A cohort of 1000 females at age 2 that remains resident in tributary streams will, during the lifetime of the cohort, lay, on average, 3·0 times as many eggs as a cohort which resides in the reservoir. This conclusion is apparently not consistent with the observation that most females take up reservoir residence.
Reservoir females have a higher growth rate (Walford constant k=0·61, c.f. 0·86 for stream residents) and shorter life expectancy ( M year⁻¹= 1·19, c.f. 0·56) than the stream residents. However, they are of larger average size than the stream residents, lay larger eggs (mean 0·074 g, c.f. 0·066 g) and bury them more deeply (mean depth 11·0 cm, c.f. 8·5 cm).     

A folding artificial substratum sampler for use in standing water

A new easily retrieved folding artificial substratum sampler is described and its performance compared with that of trays in Cow Green Reservoir at a depth of 15–18 m.     

Fish species composition before and after construction of a main stem reservoir on the White River,Colorado

Synopsis The completion in the fall of 1984 of Taylor Draw Dam on the White River, Colorado, formed Kenney Reservoir — thus impounding the last significant free-flowing tributary in the Upper Colorado River Basin. Fishes were sampled above and below the dam axis prior to closure of the dam and in the reservoir and river downstream following impoundment. While immediate effects of the dam to the ichthyofauna included blockage of upstream migration to 80 km of documented range for endangered Colorado squawfish, the reservoir also proved to have profound delayed effects on the river's species composition. Pre-impoundment investigations in 1983–1984 showed strong domination by native species above, within, and below the reservoir basin. By 1989–1990, non-native species comprised roughly 90% of the fishes collected in the reservoir and 80% of the fishes collected in the river below the dam. Initially, fathead minnow, whose numbers quickly increased in the new reservoir, dominated all post-impoundment collections, but red shiner became the most abundant fish collected in the river below the dam by 1989–1990. While agency stocking programs for the reservoir sought to emphasize a sport fishery for salmonids, primarily rainbow trout, local enthusiasm for warmwater sport fishes resulted in illicit transfers of these species from nearby impoundments. Several species, formerly rare or unreported in the White River in Colorado, including white sucker, northern pike, green sunfish, bluegill, largemouth bass and black crappie, were present in the river following impoundment. Our investigation indicates smaller-scale, main-stem impoundments that do not radically alter hydrologic or thermal regimes can still have a profound influence on native ichthyofauna by facilitating establishment and proliferation of nonnative species.Cooperators are the U.S. Fish and Wildlife, the Colorado Division of Wildlife, and Colorado State University     

Using movements and diet analyses to assess effects of introduced muskellunge (Esox masquinongy) on Atlantic salmon (Salmo salar) in the Saint John River, New Brunswick

The muskellunge was introduced in the Saint John River system from stockings in a headwater lake in the 1970s. They have migrated down the system as far as the river’s first dam, Mactaquac Hydroelectric Facility, at Fredericton and appear to have established several reproducing populations along the river. This exotic invader represents a potential threat to the severely depleted Atlantic salmon stocks in the river. We radio-tracked muskellunge over a 2-year period in the middle reaches. Home ranges extended to ∼100 km in both riverine and lacustrine areas, including 78% of individuals trans-located upstream of the dam making their way back through the dam successfully. Downstream of the dam, home ranges were <25 km. No spawning areas were detected. An isotope analyses of diet indicated that the large sub-adults and adults had established the greatest proportion of their biomass in a more ¹⁵N depleted environment typical of areas farther upstream. Isotope mixing models could not accurately determine the proportion of Atlantic salmon smolts that may have been consumed by muskellunge, but anadromous salmon had ≤7% probabilities of being in the diet. A bioenergetics model suggested ≤5% of the annual food intake by muskellunge occurs during the smolt out-migration period. For the Saint John River, the impacts of growing numbers of muskellunge are multi-faceted creating a complex management challenge. Muskellunge appear to minimally increase predation risk for Atlantic salmon smolts while their increasing numbers are creating a growing recreational fishery and potential threat to the native fish community and ecosystem.     

The influence of flow impoundment and river regulation on the distribution of riverine macroinvertebrates at Mammoth Cave National Park, Kentucky, U.S.A.

The effects of impoundment by a low-head dam and hypolimnetic release from a reservoir on benthic macroinvertebrate assemblages were studied in two lowland rivers. The first river (Green River) was initially divided into three zones (impounded, transitional, erosional) according to hydrological characteristics. The entire reach of the second river (Nolin River) was a regime unit. Only the Green River erosional zone was free-flowing with a linear sequence of riffle-run-pool reaches. A detrended correspondence analysis showed that the Green River impounded and transitional zones were taxonomically indistinguishable while the Green River erosional zone and the Nolin River were each distinct. A canonical correspondence analysis revealed that higher surface velocity, higher summer water temperatures and more turbid conditions, and lower water temperatures were contributing parameters to the separation of the Green River erosional zone, Green River transitional/impounded zones, and the Nolin River, respectively, in ordination space. A series of one-way ANOVA’s testing for differences of macroinvertebrates assemblages between the three Green River zones according to five metrics showed that the Green River erosional zone demonstrated significantly higher values and the transitional and impounded zones were ecologically similar.     

Distribution and abundance of the salmonid parasite Parvicapsula minibicornis (Myxozoa) in the Klamath River basin (Oregon-California, U.S.A.)

The distribution and abundance of the myxosporean parasite Parvicapsula minibicornis in the Klamath River mirrored that of Ceratomyxa shasta, with which it shares both its vertebrate and invertebrate host. Assay of fish held at sentinel sites and water samples collected from those sites showed that parasite prevalence was highest below Iron Gate dam, which is the barrier to anadromous salmon passage. Above this barrier parasite levels fluctuated, with the parasite detected in the free-flowing river reaches between reservoirs. This was consistent with infection prevalence in the polychaete host, Manayunkia speciosa, which was greater than 1% only in populations tested below Iron Gate dam. Although a low prevalence of infection was detected in juvenile out-migrant fish in the Trinity River, the tributaries tested did not appear to be a significant source of the parasite to the mainstem despite the presence of large numbers of infected adult salmon that migrate and spawn there. Rainbow trout became infected during sentinel exposure, which expands the host range for P. minibicornis and suggests that wild rainbow trout populations are a reservoir for infection, especially above Iron Gate dam. High parasite prevalence in the lower Klamath River is likely a combined effect of high spore input from heavily infected, spawned adult salmon and the proximity to dense populations of polychaetes.     

Biological Quality on the Basis of Macroinvertebrates in Dammed Habitats of Some Estonian Streams,Central – Baltic Europe

We assessed the impacts of damming on the biological quality of Estonian streams. A total of 24 dammed sites on 22 streams were sampled. Standard samples were taken during two consecutive springs, 2009 and 2010 in three habitat locations: above dam (reservoir), immediately below dam, and at an undisturbed (reference) site nearby. To estimate biological quality, the national multimetric index (based on five pollution‐sensitive and/or general quality metrics) was used. To estimate direct hydromorphological effects on macroinvertebrates, the locally adapted index, Macroinvertebrates in Estonia: Score of Hydromorphology (MESH) was employed. We found a significant decrease in the biological quality of the above‐dam sites compared to the undisturbed sites (probably due to accumulation of fine sediments and lower flow velocity). Of the five ordinary quality indicators tested, only one (ASPT index) was significantly different between the below‐dam sites and the undisturbed sites. However, the MESH indicated significant stress of macroinvertebrates both at the above‐dam and below‐dam sites, even when flow velocity and bottom type at the below‐dam sites was similar to that at the undisturbed sites. At the same time, hydrochemical parameters were constant among the three habitats. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)