Freshwater Biology i\9S]) n, Growth and recession of aquatic niacrophytes on an unshaded section of the River Lamhourn, England, from 1971 to 1976 SUMMARY. The growth and recession of the macrophytes on an unshaded f section of the R. Lamboum was documented by a mapping procedure from March 1971 to December 1976. The seasonal patterns were determined mainly by the dominant macrophytes. RanututUiis penicillalns var. calcareus and Ranuncultis peltatiis. Ranunculus grew rapidly in spring and early summer, mainly colonizing areas of gravel and reached a summer maximum. TTie greatest loss of plants was in August and September but losses continued through the winter to give minimum cover in March. Berula and Callitriche did not show regular seasonal growth patterns but their 'growth was largely confined to times when there was little growth of Ranunculus. Increase in area of Ranunculus in the spring was positively correlated with the mean discharge at that time. The growth of Ranunculus appeared to be restricted when shading was caused by turbid water due to dredging or by accumulation of epiphytic algae on the surface of the plants in years when discharge was low. Discharge also influenced the substrata underlying Ranunculus and the area of silt under Ranunculus beds was negatively correlated with discharge. The factors thought to influence growth of Ranunculus were used to develop a conceptual model of growth.

Freshwater Biology (1982) 12, 1-15. Growth and recession of aquatic macrophytes on a shaded section of the River Lamhourn, England, from 1971England, from to 1980 SUMMARY. The growth and recession of macrophytes on a shaded section of the R. Lambourn were documented by a mapping procedure. With the exception of Ranunculus spp.. the changes in total cover did not indicate directly the pattern of growth and recession of the macrophyles. Analysis of gross changes, expressed as gains and losses tn cover, indicated that colonization of gravel and silt by the dominant macrophyte, Bertda erecta, did not vary seasonally. Colonization was at a constant rate of about 8% of the site each month throughout the year and this accounted for 50% of the total number of gains by Berula. Gains of Berula from Ranunculus showed an annual cycle with a maximum during the summer when Ranunculus was in recession. Gains of Berula from Callitriche spp. also varied annually but the maximum was during the autumn. Total losses of Berula were at a constant rate throughout the year but were to gravel and silt during the winter, to Ranunculus in spring and early summer and to Callitriche in late summer and autumn. Analysis of loss of Berula with time indicated that the position of the Berula carpet was constantly changing. The growth and recession of Berula could not be linked in a meaningful way to environmental variables. Callitriche and Rammculus both showed an annual pattern of growth and recession. TTiere was temporal separation of the two macrophytes with Ranunculus growing mainly in spring and early summer and Callitriche showing maximum growth in late summer and autumn, and some evidence of spatial separation. The observed differences between years in the growth of Callitriche could not be attributed to any of the environmental variables measured.Discharge was thought to be an important variable controlling the growth of Ranunculus since increase of Ranunculus in the spring was positively correlated with the mean discharge at that time. In years when discharge was low, the growth of Runtoicultis appeared to be restricted by shading from epiphytic algae which accumulated on the plant surfaces under these conditions. Correspondence; A. D. Berrit. Freshwaier Biological Association, River Laboratory, East Stoke. Wareham. Dorset BH206BB, England. (X)46-5070/S2/()2()()-()(X)l $02.00© 1982 Blackwel! Scientihc Publications .V. F. Ham eta].

Three methods of mapping macrophytes on short sections of river are described and compared. All methods involve setting up a l-m grid system over the site using permanent stakes to locate a series of temporary strings. The first method (detailed mapping), which generates a map. uses the grid system to locate accurately the position of macrophytes and substrata on the river bed. It is very time consuming and objectivity in mapping is difficult to achieve. The second method (points method) involves recording the macrophytes and substratum below each Intersection of the I-m grid system covering the study site. This method is fast, capable of giving estimates of percentage cover for the different substrata and macrophytes but does not produce a map. The third method (rectangles method) is regarded as both the most efficient and also the most objective of the three mapping procedures. The substratum or macrophyte dominating each 50 X 100 cm rectangle of river bed is recorded together with additional substrata and macrophytes present. The procedure is rapid to use in the field, provides a simplified map of the study site and is more amenable to detailed analysis than the two previous methods. All three mapping methods are best suited to rivers less than 20 m wide where safe wading and good visibility can be guaranteed.