The distribution of Plecoptera and Ephemeroptera in a Lowland Region of Britain (Lincolnshire)

Summary

o| li]1.|Biological Surveys of rivers and streams were carried out in Lincolnshire during 1961\2-67. li]2.|Lincolnshire is a lowland region, with calcareous rocks and soils intensively farmed. Pollution is mainly from small sewage disposal works and farms. li]3.|The rainfall is low, up to 27.5\rd (70 cm) annually. li]4.|Most river systems are less 50 km long and have sources from \s+ 33 m to 125 m above Mean Tide Level (ODN). There are two main types of watercourse

• a. Free flowing “streams” with sandy or stony substrata

• b. Canalised impounded “rivers” with clay banks and silt or mud substrata.

li]5.|The temperature of the streams is less variable throughout the year than that of rivers. li]6.|The two types of watercourse are chemically similar, but the rivers have higher B.O.D.'s and some reaches are affected by salt water during low freshwater flows. li]7.|The vegetation of streams differs from that of rivers. Plant species common in rivers are also found in pools and ponds. li]8.|Collections of invertebrates were made with a hand net in two standardised methods depending on the type of watercourse. li]9.|The distribution and habitat of each species is described and habitats are compared with those in other regions. Altitude ranges are higher in other regions but basic habitats are very similar. li]10.|Comparisons are drawn between the Plecoptera and Ephemeroptera faunas of

• a. Clean Lincolnshire streams and clean rivers

• b. Clean and polluted reaches

• c. Chalk and limestone river systems

• d. Stations with different substrata

• e. Lincolnshire and other regions of Britain

• 10a. Plecoptera are not usually found in rivers. Two groups of Ephemeroptera are defined — a “river” group and a “stream” group.

• b. Plecoptera are rare as pollution occurs. T. nebulosa, I. grammatica and A. standfussi are most tolerant. Ephemeroptera are also suppressed by pollution. B. rhodani, C. moesta and B. bioculatus are fairly tolerant.

• c. Plecoptera were more common in chalk streams. Of the mayflies, B. pumilus and H. fusca were only found in the chalk streams, B. bioculatus and C. macrura were only found in limestone streams.

• d. Few differences were found between the distribution of species in sandy and stony substrata, though only 3 species of Plecoptera and 3 of Ephemeroptera occurred in small, shingly headwaters.

• e. The Plecoptera fauna of Lincolnshire is sparse compared to the mountain regions. Of the Ephemeroptera, Ecdyonuridae were notable absentees, owing to the lack of suitable substrata. Distribution of species is in many cases inexplicably sporadic within the region as it is in other regions.