The benthic algae of the River Itchen : with particular reference to epilithic algae and epiphytic algae on selected macrophytes
The benthic algae of the River Itchen : with particular reference to epilithic algae and epiphytic algae on selected macrophytes
Benthic algae in the River Itchen were studied for 2 years at Otterbourne where the river is about 16 m wide and 21 cm deep, with a mean flow rate of 0.33 m/s and a discharge ranging through the year from 0.34 to 2.46 m3/s. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO-3/1. Epilithic algae removed from the small stones that form the stream bed showed a seasonal change in abundance and species composition. The chlorophyll a content of these algae ranged from 115 to 415 mg/12 of stream floor, with maximum values in April and a minor peak in autumn. Estimates of organic biomass based on chlorophyll values gave a mean of 7.6 mg C/m2, and reflect an estimated production of epilithic algae of 230 g C/m2 of stream floor, derived from an average generation time of nearly 2 days. Numbers of algal cells ranged from 5 x 102 to 7 x 103 cells mm2 stream floor, with highest densities in spring. Diatom dominate the epilithic flora, comprising 85-95% of all algae, but highest numbers of chlorophytes occurred in summer and cyanophytes increased in autumn. The principal plants providing substrates for epiphytic algae in this part of the river were Ranunculus penicillatus var calcareus and Cladophora glomerata. Ranunculus tended to be washed out by winter spates, but grew rapidly in spring, decreased in summer and grew again in autumn. Numbers of epiphytes removed from Ranunculus varied through the year from 52 x 103 to 271 x 103 cells/mm2 stream floor, with maximum values in April. Diatoms represented 65-98% of these cells, with chlorophytes and cyanophytes increasing through summer and autumn. Estimates of biomass were more difficult for these epiphytic forms, but measurement of chlorophyll c values suggests an approximate mean biomass of 38.5 g/m2, and a cautious estimate of about 1185g C/m2 stream floor for the annual production of epiphytes on Ranunculus. Cladophora showed an annual cycle in which it almost disappeared in summer, but grew vigorously in autumn, was partly washed away in winter and grew again in spring. Numbers of epiphytes ranged from 3 to 22 x 103 cells/mm2 stream floor, with a spring maximum, representing a estimated annual production of about 276 g C/m2 stream floor. Diatoms were again the principal epiphytic algae; these and the other algae were mostly of the same species on both host plants, with many of the species also being epilithic. Levels of nitrate (ca 4 mg/1), phosphate (ca 80 μg/1) and silicate (ca 4 mg/1) remained high throughout the year in the River Itchen, and are not thought to have limited algal growth. It is likely that grazing insects exert an important influence on algal numbers, especially on the stones. Numbers of chironomids, ephemeropterans and plecopterans range from 2 to 21 x 10^4/m^2 stream floor. Large numbers of algae occur in the guts of these insects, and it is calculated that they consume up to half of the epilithic algal production in June, when they are at their peak, rather lower amounts in other seasons; insects probably have a lesser impact on epiphytic algae. The benthic algae of a nutrient poor, acidic stream in the New Forest, the Ober Water, was studied as a comparison. The numbers and biomass of epilithic algae were much lower than the River Itchen, and different species were present, although several species were common at both sites. (D73655/87)
University of Southampton
1986
Shamsudin, Lokman Bin
(1986)
The benthic algae of the River Itchen : with particular reference to epilithic algae and epiphytic algae on selected macrophytes.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Benthic algae in the River Itchen were studied for 2 years at Otterbourne where the river is about 16 m wide and 21 cm deep, with a mean flow rate of 0.33 m/s and a discharge ranging through the year from 0.34 to 2.46 m3/s. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO-3/1. Epilithic algae removed from the small stones that form the stream bed showed a seasonal change in abundance and species composition. The chlorophyll a content of these algae ranged from 115 to 415 mg/12 of stream floor, with maximum values in April and a minor peak in autumn. Estimates of organic biomass based on chlorophyll values gave a mean of 7.6 mg C/m2, and reflect an estimated production of epilithic algae of 230 g C/m2 of stream floor, derived from an average generation time of nearly 2 days. Numbers of algal cells ranged from 5 x 102 to 7 x 103 cells mm2 stream floor, with highest densities in spring. Diatom dominate the epilithic flora, comprising 85-95% of all algae, but highest numbers of chlorophytes occurred in summer and cyanophytes increased in autumn. The principal plants providing substrates for epiphytic algae in this part of the river were Ranunculus penicillatus var calcareus and Cladophora glomerata. Ranunculus tended to be washed out by winter spates, but grew rapidly in spring, decreased in summer and grew again in autumn. Numbers of epiphytes removed from Ranunculus varied through the year from 52 x 103 to 271 x 103 cells/mm2 stream floor, with maximum values in April. Diatoms represented 65-98% of these cells, with chlorophytes and cyanophytes increasing through summer and autumn. Estimates of biomass were more difficult for these epiphytic forms, but measurement of chlorophyll c values suggests an approximate mean biomass of 38.5 g/m2, and a cautious estimate of about 1185g C/m2 stream floor for the annual production of epiphytes on Ranunculus. Cladophora showed an annual cycle in which it almost disappeared in summer, but grew vigorously in autumn, was partly washed away in winter and grew again in spring. Numbers of epiphytes ranged from 3 to 22 x 103 cells/mm2 stream floor, with a spring maximum, representing a estimated annual production of about 276 g C/m2 stream floor. Diatoms were again the principal epiphytic algae; these and the other algae were mostly of the same species on both host plants, with many of the species also being epilithic. Levels of nitrate (ca 4 mg/1), phosphate (ca 80 μg/1) and silicate (ca 4 mg/1) remained high throughout the year in the River Itchen, and are not thought to have limited algal growth. It is likely that grazing insects exert an important influence on algal numbers, especially on the stones. Numbers of chironomids, ephemeropterans and plecopterans range from 2 to 21 x 10^4/m^2 stream floor. Large numbers of algae occur in the guts of these insects, and it is calculated that they consume up to half of the epilithic algal production in June, when they are at their peak, rather lower amounts in other seasons; insects probably have a lesser impact on epiphytic algae. The benthic algae of a nutrient poor, acidic stream in the New Forest, the Ober Water, was studied as a comparison. The numbers and biomass of epilithic algae were much lower than the River Itchen, and different species were present, although several species were common at both sites. (D73655/87)
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Published date: 1986
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Local EPrints ID: 461023
URI: http://eprints.soton.ac.uk/id/eprint/461023
PURE UUID: 850795c2-8ff9-4581-b5cc-7f431a4bb6ad
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Date deposited: 04 Jul 2022 18:34
Last modified: 04 Jul 2022 18:34
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Author:
Lokman Bin Shamsudin
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