The ecology of a land drainage channel—II

[-t,:aWr R~'~ Voi i8. No. 7. pp. Si?-S25, t9,:4 Printed :n Great Britain, All ,"i,.-_zLntsreset'cod

THE

ECOLOGY

0~M-3-135,..t:54 53.00 +0.00 Copyright ~ l'a~4 Pergam,~n Press Ltd

OF A LAND

DRAINAGE

CHANNEL--II

BIOLOGY. CHEMISTRY AND SUBMERGED WEED CONTROL E. J. P. MARSHALL* Department of ,Applied Biology, University of Wales Institute of Science and Technology. King Ed~ard VII A',enue. Cardiff" CF1 3NU, Wales t Receiced October 198"1

Abstract--Shallow land drainage channels lying behind a seawall were found to contain slightly brackish eutrophic water, and certain species of the flora and fauna were characteristic of such conditions, l-ivc study lengths were dominated bv the angiosperms Myrioph.vlhmz spicatum L. and Potamogeton pectinatus g. The herbicide diquat was applied to three sites in mid and late summer to control submerged plants. Certain plant species were eliminated, though slow phmt decomposition was noted after midsummer applications. There were no coincident effects amongst the fauna. Key wor&--drainage channel, ecology, macrophytes, invertebrates, herbicide, diquat

INTRODUCTION Land drainage channels are of econotnic i m p o r t a n c e to the agriculture of large areas of Britain and form an extensive aquatic h a b i t a t in England anti Wales with a channel length of 1.3 × 10 ' k m d r a i n i n g an area of 1.3 x l0 b ha (Marshall et al., 1978). Regular m a n a g e m e n t of such channels is required to m a i n t a i n drainage efficiency: approx. 3.0 x l0 + km of arterial channel receive m a n u a l , mechanical or chemical m a i n t e n a n c e operations each year. Despite the extensive distribution of drainage channels and their potential as a refuge for aquatic flora a n d fauna, there have been few studies of their biology a n d chemistry. In order to assess the i m p o r t a n c e of c h a n n e l s a n d to u n d e r s t a n d their ecology, several studies o f ditches on the G w e n t Levels, South Wales, have been conducted. The general drainage system has been described by Scotter et al. (1977) and studies o f dredging effects (Wade, 1977) and m a c r o i n v e r t e b r a t e distribution (Clare, 1978) have been completed. This p a p e r is the second o f two describing the ecology of short channel lengths and the effects of submerged weed control using the herbicide diquat. In the first paper, m a r k e d vertical gradients of dissolved oxygen and t e m p e r a t u r e were reported ( M a r shall, 1981 ). T h e results o f the study could be relevant to the estimated 2000 km of arterial channel in England and Wales which receive chemical control of submerged weeds each year (Marshall et al., 1978). SITE DESCRIPTION Studies of biology and chemistry were m a d e in a *Present address: Agricultural Research Council, Weed Research Organisation, Begbroke Hill. Yarnton. Oxford OX5 IPF, England.

c h a n n e l near the village o f Goldcliff (U.K. N a t i o n a l G r i d Reference: ST 378823). The ditch, or "'teen", runs for 1400 m behind a seawall which was built in 1967 to protect the area from tidal inundation. T h e reen is divided by culverts into four sections o f different dimensions and is connected to the local d r a i n a g e network by a single channel. Investigations were made in four 50 m study lengths, noted as A, B, C a n d D on Fig. I a n d some additional data were collected from length E. Physical dimensions of the five sites are s u m m a r i s e d in Fig. 1. During the summer, water in the channels was static for long periods a n d flow was only observed after high raint:all. METHODS Physical measurements Water temperatures were recorded by maximumminimum thermometers which were read and reset each fortnight. Meteorological data were provided by Cleppa Park Research Station (ll km distant), Chemistry Water samples were taken near the water surface in iodised plastic bottles (Heron, 1962) every fortnight, three samples being taken from each site on a stratified random basis. Major cations (K-, N a ' , Ca-'-, Mg TM)were analysed every month, while some other components of water chemistry were analysed each fortnight, using standard methods (Golterman, 1969: DOE, 1972). Mean concentrations were examined for seasonal trends, and non-parametric Spearman Rank Correlations calculated as a means of identifying possible relationships between variables. Flora Plant cover within each site was estimated monthly from sketches made on scale maps. Macrophyte standing crop (gin-:), excluding root material, was estimated from 0.25 m-" quadrats in 1974, and from three 50 cm wide strips taken across each site each month in 1975. Plant material cut from the channels was sorted into species for wet and dry (I05:C) weight determination. Total standing crop for

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each species was calculated from cover within each sample strip, sample weight and total co~er within each site. Cover o[ Lemna spp was taken from distribution sketche~, and data were augmented in 1975 by examining cover ~Gthin I m: quadrats at three fixed points in each site. The presence of tilamentous algal species was noted each month and an estimate of amounts of micro-algae tn the channel:, ',~as made every formight by measuring chlorophyll a concentration after extraction (Strickhmd and Parsons. 1965).

Fauna Macroinvertebrates associated with the angiosperms were sampled at approximately monthly intervals by he(sweeping a 5 m distance, using a 250 ,urn mesh pond net: Occasional samples were also taken by enclosing plant material in 250 l~m mesh bags. Animals were preserved in 5"0 I'ormalm. sorted into species and species groups using identification texts and counted (Marshal!, t978). The microerustaceans of the Cladocera, Copepoda and Ostracoda were not identified. Seasonal trends of invertebrate diversity were investigated using the Shannon-Weaver information index (Pietou, 1966).

Herbicide applications Applications of diquat were made during the summer of 1975. The whole of the channel containing site B (Fig. 1) was sprayed on II June 1975. Site E and the western part of channel C was sprayed on I0 July. The remaining part of channel C, including site C. was treated on 19 August 1975. The herbicide Reglone, provided by ICI Plant Protection Ltd and containing 140 g I - ~diquat cation. was diluted with tapwater and applied by knapsack sprayer producing an initial maximum concentration of 1.0 m g l in the channel water. Water samples were collected in acid-cleaned glass bottles for diquat residue analysis by column extraction and direct reading tPope and Benner. 1974). RESULTS

Water chemisto' Water temperature in the sites exhibited a clear seasonal pattern, with maximum values t 2 9 C . site D) found in summer when water was static for long periods. Components of water chemistry were vari-

able: results of water san(pie analyses are sumrnaris~*d in Table l, The data indicated the channels were brackish eutrophic en,+ironments. Soluble orthophosphate concentrations werc low in ~inter. but showed rapid increases in ear[,',' summer. Some soluble phosphate was probably derived from anoxic sedirnents, a condition found in the channels during summer (Marshall, 198l). Nitrate concentrations showed irregular peaks throughout the year. Weak: positive correlation (P < 0.05) between mean daily rainfall and nitrate concentration indicated that some nitrate was introduced in runoff" from adjoining fields. Concentrations of ammoniacal-nitrogen declined in spring and increased in autumn, coincident to macroph,,te growth and sensecence. High ~alues ,~1 water colour (200 Hazen units) were recorded, though no consistent pattern was found in all the sites. Subsurface pH values showed an annual pattern With summer maxima of 9.8 and Ibllowed seasonal temperature and solar energy effects on photosynthesis. Photosynthesis affects the carbonate-bicarbonate

Table 1. Mean. minimum and maximum ~'alues of chemica[ variables in Gotdcliff channel v.aters Variable PO~--P NO~-N SiO. NH]-N COi Ca:" Mg:" K" Na CI " SO.~ Conductivity Water colour pH

Mean 0.34 0.13 36g 0.23 2255 49.5 42.7 25.0 22(1.l) 355 ) 547

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The ccoiog', of a land drainage channel--ll

819

Table 2. Vascular plant species found in the Golddiff channels Site Spe,.'~es

A

B

C

D

E

Ranuncutus baudotit Godr. R sceleratus L Polvffonum amphtbium L. ).[yriophyl!um ~'picatum L. Cuilitriche sp. Epilobium hirsumm L. Oenanthe fistulosa L. Elodea canadena~s Michx. . llisma plantago-aquatica L Pot~trnogeton crL~pus L. P. pectinatus L. Lerrtnu minor L. L. trisuica L. J:incus" a(utifloru; Ehrh. ex Hofl'm. Eleochuris palu.~tris (L) Scirpus maritimus L S. hlbertlaetrlOtl&lglt' C. C. Omel Phraernites australis (Car.) Trin ex Steudet Glv ceria fluitanx ( L ) ,4:ol!a .[ihculoides Lain.

equilibrium and pH, by removing free CO, and bicarbonate ions (Golterman, 1969). Nevertheless seasonal patterns of bicarbonate concentration were not consistent. Conductivity showed major increases during August 1975, caused by incursions of saline water from adjacent watercourses. Essentially similar patterns were found for major cation and chloride concentrations. Whilst cation analyses of water samples from the local drainage network revealed saline incursions into the experimental channels in 1975, concentrations in the adjacent ditches were predominantly lower than those in the sites. Cation concentrations in rainwater samples collected between January and April 1975 were always below 5 mg 1-t. High cation concentrations, which were a feature of the channels, were therefore probably partly maintained by irregular seawater incursions through blocked tidal flaps and the local drainage network and in part by seepage of seawater through the adjacent seawall. Physical stability of the water column, found during summer days, promoted vertical gradients of dissolved oxygen (Marshall, 1981). Similarly, water samples taken at different depths during 24 h periods showed pH gradients were present during daytime, with a progression towards homogeneity at night following mixing.

cover between 1974 and 1975 in site B (5-11~,~: -o/. P < 0.05). P < 0.0l) and site D ( 1-,~,'o, 300 r Site ^ 200

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Flora Twenty macrophyte species were found in the five sites (Table 2) including Ranunculus baudotii Godr. and Scirpus marit#nus L. which are associated with brackish conditions. Sites A and B were dominated by P. pectinatus, L. minor and L. trisulca, while M. spicat:#n dominated sites C and D, In site E, M. spicatum and P. pectinatus were co-dominant. Extensive lengths of channel margin were covered with the common reed, Phragmites austratis (Cav.) ex Steudel. This species showed significant increases in

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A total of 137 macroinvertebrate species were recorded from the Goldcliff channels iAppendixi. The insects were the most diverse group pro! iding 8; species groups including 17 species of Hemiptera. 19 species of Coleoptera and 20 species groups oi" (Thironomidae. A total o{" 19 species of Hydracarina were round, and the Mollusca, which provided the greatest number or individuals [PotamopyrA, u.; /unkmw (Smith): 60,000 m-'~], were represented by 12 ~pecic-; Changes in the numbers of the Mollusca, tnsecta and other invertebrate fauna, illustrated for site B in Fig, 5, were not regular. The Moltusca were dominated by P..Nnkinsi and kvnmaea perexra ~Mull:). snails which are widely distributed in Britain (Macan, 1969). The most abundant members or the Ephcm-

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Seasonal patterns of macrophyte standing crops, estimated from cover and crop samples, are shown in Fig. 2. P. pecdnams and £emna spp exhibited annual development from their perennating organs which represented a small initial biomass. In contrast, M. spicamm maintained a considerable standing crop over winter. Potamogeton crispus L., present in small amounts in sites B and C, grew during winter and spring and died back in summer. Maximum cover of floating g. n, inor and free-floating g. trisulca was achieved in mid-summer in site A, while cover in site B, which was sprayed with diquat, reached maximum values later in the year (Fig. 3). M. spicatum and P. pectinatus provided the greatest cover and standing crop, and estimates of maximum standing crops of these species were similar to those reported by Brooker and Edwards (1973). Cladophora sp. was the commonest filamentous alga in the sites; other species included Anabaena sp.. Oscillatoria sp., Enteromorpha intestinalis L. and Spirogyra sp. The maximum biomass of filamentous algae was recorded for Cladophora sp. at 29 g dry wt m-:, in site D during June 1974. Chlorophyll a concentrations showed considerable variation during the study (Fig. 4), and sLmaificant differences between I974 and 1975 mean concentrations were

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eroptera and Odonata were Cloeon dipterum (L.) and lshneura elegans (van der Linden) respectively. The hemipteran Plea leachi McGreg & Kirk reached high densities amongst the macrophytes (300 m-Z: April 1974, site C) and smaller numbers of llyocoris cimicoides (L.) and Sigara spp were found irregularly. A peak of Trichoptera numbers during May 1975 in site B was mainly made up of Leptocerus teneiformis Curtis with smaller numbers of Hydroptilidae. L. teneiformis was particularly abundant in sites C and D associated with the angiosperm Myriophyllum spicatum, and reached densities of 7000 m-2 during September 1975 in site C. Members of the Haliplidae, Haliplus ruficollis (Degeer) and H. lineatocollis (Marsham), were the dominant Coleoptera. In site B, larval Ceratopogonidae were the most numerous Diptera early in 1974, with Eucricotopus spp becoming more abundant after June 1974. Peak numbers of Diptera in early April 1975 was mostly made up of Eucricotopus spp, and included tow densities of Trichocladius spp and Corvnoneura spp. Eucricotopus spp remained the most abundant dipterans during August 1975, and increases in the numbers of Glyptotendipes spp and Psectrocladius spp were recorded in October. Numbers of individuals showed large variation during the study, probably reflecting the inaccuracies of the netsweep sampling method. Seasonal trends were therefore difficult to establish (Fig. 5). The Shannon-Weaver information index did not show well-defined patterns (Fig. 6), though declines early in the year may have resulted from increases in numbers of a few species, particularly the snail L. peregra. The information index was calculated at both generic and species/species group level, but differences between the levels were not significant. Fifty invertebrate species were common to sites A, B, C and D, and the most abundant are listed in Table 3. Several species were exclusive to individual sites, the greatest number

(9) being found in site B, which also supported the greatest total number of different species in a site during the study (109). This high number of species may have resulted l¥om immigrations into site B from local ditches along the connecting channel. The majority of invertebrate species found at Goldcliff are

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822

E.J.P..'~,I~RSH.aI.i. "[able 3 Channc! fauna Abundan~ 5pecie_-, m the Goldch i=. .:h:tnneb,

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typical of weedy lentic environments and 21 species have previously been found in brackish habitats, occasionally in ditches near the sea {Wakon, 1943: BailOut-Browne, 1958: Butler and Popham, lt,~58: Verhoeven, t975). Six species have distributions limited to euryhaline conditions (Table 3).

Herbicide efl_ects Diquat concentration in water samples taken from sprayed sites showed rapid reduction over a 3 week period following application. The herbicide had dissipated to 20~o of its initial concentration between 4 and I0 days, and was undetectable (<0.001 mg I -z) between t7 and 21 da~,s aRer spraying. BipyridyIium herbicides are rapidly adsorbed onto organic surfaces in water (Yeo, I967). Midsummer applications of diquat to site B on 11 June 1975 produced differing effects on the macrophyte species. Elodea cunudensis Michx. was killed by the herbicide and no regrowth was lbund during the remainder of the season. M. apicumm was also killed. but small amounts of the specms were found growing in late October. P. pectinatus appeared chlorotic following spraying but decline in standing crop was considerably slower than previous reports I Brooker and Edwards, 1973) (Fig. 2). Cover ofLemna spp was reduced by diquat (Fig. 3L but while chlorotic plants were present in the week lbltowing application. healthy plants were abundant bv the end of June. The alga Cladophora sp. appeared chlorotic after spraying and Ulothrix sp. became the major component of algal mats. However Cladophora sp. recovered in August 1975. Whilst peaks of chlorophyll a concentration were recorded in both sires B and C following

applications (Fig. 4L coincident peaks m unspra~ed sites rendered the results equivocal. Slow rates of decomposition of P. pccimatus and 3-1. spicutum v,ere noted in site K, following diquat spraying on !0 July t975. Lea~es of P,dvgonum amphibium L. were scorched by diquat, but plants were regrowing after 13 days. Floating A:olla filiculoides Lain. and the rush Juntas acutf/torus Ehrh. Ex Hoffm. were susceptible to diquat at [,0 m g l L Site C ~vas sprayed on 19 August t'075 after maximum macrophyte standing crop had been achieved. Both M..Tficatum and P. pectilu~tu.r were killed by the herbicide at this time and standing crop declined rapidly. L. trisulca was also susceptible and disappeared from the site. The reduction in photosynthesis, i%und over a period betv,een 10 and 15 days in sprayed ~:hannets (Marshall, 1981), increased bicarbonate alkalinity and reduced carbonate concentrations, as reported by Brooker and Edwards (1973). Changes in available nitrogen and phosphorus might be expected following plant decay. However. the only significant change was an increase in soluble ortho-phosphate in site C. Increases in variation and not mean concentration of phosphate were tbund in site B, where slow decomposition of P. pectinatus was recorded. Data collected from netsweep sampling indicated that diquat may not have affected macroinvertebrate populations. The intbrmation index of diversity did not reveal changes associated with spraying (Fig. 6/ and no species were eliminated. Population changes coincident to spraying were onl? noted for the hemipteran Plea h'achL though extreme fluctuauons in the numbers of this water bug before spraying indicated that changes were probably unrelated ~ me herbi-

The ecolog? of a land drainage channel--II cide. The fauna was adapted to a rapidly changing dissoived oxygen environment and conditions follov.ing herbicide application were within the range of variation found without spraying. DISCUSSION Studies on the effects of aquatic herbicides have principally been made in closed systems such as ponds and lakes, not drainage channels. Brooker ( 1976a, b) reported that chemical control of emergent macrophytes in a channel habitat caused minimal direct and indirect effects on the aquatic environment. In the present study, the herbicide diquat killed the plants M. spicatum and P. pectinatus, though slow rates of decomposition were noted in two sites. Other plant species killed by the herbicide were L, minor, L, trisulca, E. canaden.vis, J. acut(]torus and A. filiculoides. P. amphibium, found in one site. was resistant to diquat and M. spicatum was found regrowing in one site. L. minor and the alga (Tadophora sp. were only controlled for a short time. Temporary control of duckweeds using diquat has been reported by Robson (1967). The short period ofdiquat activity will not give lasting control of moderately susceptible algae, such as Cladophora sp. Significant decrease in pH and carbonate concentration and increases in bicarbonate concentration were recorded following diquat applications. Such changes, caused by a suppression of photosynthesis and respiration, were temporary and rates of oxygen production returned to values comparable to unsprayed sites after approx. 15 days (Marshall, 1981). Slow rates of plant decomposition and therefore oxygen utilisation and the temporary nature of chemical changes, probably account in part for the lack of recorded effects on the fauna, which must have been adapted to the rigorous oxygen regime. No macroinvertebrate species were eliminated following spraying, and coincident changes in animal numbers, as found for P. leachi, were probably unrelated to herbicide applications. Water chemistry analyses, summarised in Table I, indicated the channels could be classified as moderately hard oligohaline eutrophic waters. Channel water had a mean chloride concentration of 355mgl -~ and according to the Venice System of brackish water classification (de Jonge, 1974) was oligohaline. High concentrations of calcium, magnesium and alkalinity and high pH values indicated that the water was moderately hard. According to nitrogen concentration and the change in alkalinity from winter to summer channel water was mesoeutrophic, or hyper-eutrophic according to phosphorus concentration (Vollenweider, 1968). Concentrations of dissolved nutrients were such that none were likely to limit plant growth, Seawater appeared to be a major influence on the composition of the flora and fauna at Goldcliff. Saline influences are found in many channels close to

823

the sea. In East Anglia such effects are i\mnd further inland, where peat outcrops in the sea and brackish water is drawn underground into inland channels, Many drainage channels only carry flowing water during and after periods of rainfall and act as long ponds under static conditions in summer. The Goldcliff channels are representative of such ditches and the patterns of physical and chemical variation reported here, arc probably typical of many land drainage channels. Nevertheless. the experimental site was a simplification of many field situations, as there was only a single connection to the drainage network. Under conditions of water exchange between numerous channels, physical, chemical and biological patterns might be expected to be obscured. From a conservation viewpoint, results confirmed that such channels are capable of supporting a large number of plant and animal species and at Goldcliff the httter were adapted to widely fluctuating dissolved oxygen concentrations in summer. Clare (1978), using classification and ordimttion techniques to describe channel fauna from 50 sites over the Gwent Levels, concluded that the Goldcliff channels maintained a specialised l:auna adapted to an enviromnent of fluctuating salinity. Submerged plant control operations using diquat did not appear to affect adversely the ecology of the channels, though applications were made rather later than current recommendations, which are l\)r late spring and early summer. This would suggest that diquat will cause only minor effects to the invertebrates of such habitats, though more successful plant control might be expected to cause more changes in the ecosystem and thus affect invertebrates. From the drainage engineer's point of view, diquat gave moderately successful submerged weed control. The herbicide was active for a limited period and may have been adversely affected by the brackish conditions. Acknowledgements--The author would like to thank Prolessor R. W. Edwards for help throughout the study and T. O. Robson, P. J. Terry and P. R. F. Barrett for comments on the text. Useful discussions were held with P. M. Wade and P. Clare: the latter also identified the Coleoptera. The work was supported by a grant from the Science Research Council and IC1 Plant Protection Ltd. REFERENCES

Balfour-Browne F. (1958) British Water Beetles, Vol. III. The Ray Society, London. Brooker M. P. (1976a) The ecological effects of the use of dalapon and 2.4-D for drainage channel management. I. Flora and chemistry. ,4rch. Hydrohial. 78, 396--412. Brooker M. P. (1976b) The ecological effects of the use of dalapon and 2,4-D for drainage channel management. II. Fauna. Arch. Hydrobiol. 78, 507-525. Brooker M. P. and Edwards R. W. (1973) Effects of the herbicide paraquat on the ecology of a reser~'oir. I. Botanical and chemical aspects. Freshwat. Biol. 3, 157-175. Butler P. M. and Popham E. J. (1958) The effects of the floods of 1953 on the aquatic insect fauna of Spurn (Yorkshire). Proc. R. ent. Soc. Lond. (A) 33, 149-158.

~2a,

E. J P, MMtSHALL

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APPENDIX List of macroinvertebrates found in the Gotdcliff channels, with their occurrence in individual sites

Species Hydrozoa H.wlra oligactis (Pallas) Platyhelminthes Polycelis nigra (O.F.M) P. tenuis (ljima) Polyzoa Phonatetla sp. Mollusca Vah'ata piscinalis (Mull.) Potamopyrgusjenkinsi {Smith) Bithynia tentaculata (L.) Lymnaeaperegra (Mull.) Aplexa hypnorum (L.)

Sites A B C D A B B

D C

B A B B A B

C C D C C D C

Species

Phyla Jbn;mak~ {L.) Planorbis F!anorbis !L.} P. ,.'ortex ( L. ) P. ieueosr¢~ma Millet P. crrsta (L.) Acroloxus [acuatris (L,) Sphaenidae Oligochaeta Vais eariabilis tL.j Stylaria Iacustr,s I L.} Dero d~gitata (O.F.M.) Tub{rex tubi_l'e.v (Muller) Limnodrilus elaparedeanus Ratzd L. hq,qmeixteri Claparede Lumbriculux rariegatus (0. F'. M.t Hirudinea Theramyzon tessutat,lm (O.F.M.I Glossiphonia heteraclita (L.) G. complanata {L.) Helobdella stagnatis (L.) Erpobdetla octocu&ta (L.) Hydracarina Hydrachna cruenta (Muller) H. con)ecru Koenike H. globo~a (de Geer) Evlais extendens {Muller) Hydrvphantes dispar (Schat, b) ttwlrodroma despiciens (Muller) Limnesia eonnata Koenikc L,./ulgida Koch L. mueulata iMuller) L. undutatu (Muller) Hygrobates longt]oalpis (t-[ermann) Neumania deltoides (Piers{g) Piona alp{cola (Neuman) P. earnea (Koch) P. coccinea (Koch) P. conglobata (Koch) Arren,~rus cusp{direr Piersig A. buccinator (Muller) A. globator (Muller) Cladocera Daphnia pulex de Geer Simocephah~s e.winosus Koch S. ,~etulus (O.F.M.) Ostracoda Copepoda Branchiura Argulus foliaceus L, Malacostraca ,4sellus aquaticus L, A. meridianus Rac. Gammarus tigrinus Sexton Palaemonetes varians (Leach) Ephemeroptera Cloeon dipterum (L.) Caenis robusta Eaton C. horaria (L.) Odonata Ischnura elegans (van der Linden) Sympetrurn striolatum Charpentier Hemiptera l]yocoris cimicoides (L.) Notonecta viridis Delc. Plea leachi McGreg. & Kirk. Cymatia eoleoptrata (Fab.) Callieorixa praeusta (Fieb.) Corixapanzeri (Fieb.) Hesperoeorixa linnei(Fieb.) H. sahlbergi (Fieb.)

Sites

B A B C C B C A B C D C ~ .a B ~ B C B C B C A B C B C A

D D D D D

A B C D A B C D B D B B C A B C A B C B C A B C ,\ B C C A B C B C :x, B C B A B A 13 A C A B C A B ~\ B C A B (' A B C A A A A A

B B B B

A

C C C C

t) D D D D D D D D D 17)

D D

D D D D

C D

A B C D A D 13 D A C D A B C D A B C D B C D A B (7 D A C D A A A A

B B B B

C O C D C D C D C A B C D A B C D C continued overleqf

The ~ o i o ~ , of a land drainage channei--II

.4?pendzx continued

Species

Species

Sites

Sieara dorsulis (Leach) S. diatincta (Fieb.) S. lalieni (Fieb.) S. jbssarum (Leach) S. rcorti IFieb.) S. !ateralis (Leach) S. n~erotmeata (Fieb.) S. concmna (Fieb.) S. stagnalis (Leach)

A B C D A B A B C D B C D D C D A B C A B C

Coleoptera

Haliplus lineatocollis (Marsham) H. ru/icollis (Degeer) Noterua c!uvicornis (Degeer) Laccophih~s minutus (L.) Hyphydrus ocatus (L.) H.vgrotus maequalis I Fab.t H. versicoh)r (Schaller) Hydroporus palustris (L.) Graptodytes pictus (Fab.) Ochthehius nanus Stephens Helophorus brecipalpis Bedci H. mmutus Fab. Laccobius biguttatus Gerhardt L. bipunctatus (Fab.) Helochares liuidus (Forster) Enochrus courctatus (GredIer) E. quadripunctutus (Herbst) Ben~sus qffinis Brulle Curculionidae Trichoptera

Holocentropus picicornis (Stepheus) Eenomus tenellus (Rambur) Hydroptitidac

Phryganea grandis L.

B B B B B A B

C C C C C C C

D D D D

B A B C A B A B C B A B C C B A A C A B C

D D D D

D D

B

D D B C D

D

Limnephilidae

Atllripsodesaterrimus

A A A A

(Stephens)

A B C D A B C D

Mysmcides longieornis (L.) Triaenodes bicolor tCurtis) Leptocerus tinei_ibrmis Curtis

825

Sites C D A B C D A B C D

Lepidoptera

Cataetysta lemnam (L.) Diptera Tipulidae Chaoboridae Culicidae Ceratopogonidae Procladius sp. Tanypodinae sp. Pentaneura sp. Eucricotopus sp. A Eucricotopus sp. B Trichocladius sp. Psectrocladius sp. A Psectrocladius sp. B Corynoneura sp. Chironomus plumosus Chironomus sp. A Cryptochironomus "del'ectus" group C. "pararostratus" group Glyptotendipes sp. Microtendipes sp. Parachironomus "rarus" group Phaenopseetra 'tenzia" group Po(vpedilum "laetum" group P. "nubeeulosum" group Paratanytarsus sp. Odontomyia ornata (Meigen) O. uiridula (Fab.) Stratiomys longicornis (Scop.) Empididae Tabanidae Ephydridae

C D A B D B B C D A B C D C A C D A B C D A B C D C D A B C D A B C D B C D A B C D

B B B A B D A B C D D A B C B D C D A C D A B D C A B C D B B C D A B C D A B C D