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The loss of submerged plants with eutrophication III. Potential role of organochlorine pesticides: a palaeoecological study
Author(s) -
STANSFIELD JULIA,
MOSS BRIAN,
IRVINE KENNETH
Publication year - 1989
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1989.tb01087.x
Subject(s) - dominance (genetics) , bosmina , phytoplankton , ecology , eutrophication , dieldrin , cladocera , biology , zooplankton , algae , daphnia , pesticide , nutrient , biochemistry , gene
SUMMARY. 1 Mechanisms which might have caused a switch from submerged plant dominance to phytoplankton dominance in a series of shallow lakes, the Norfolk Broads, during the 1950s and 1960s, are reviewed. It is argued that a likely mechanism was a poisoning of the community of Cladocera which graze on algae and are associated with the plants. This allowed phytoplankton to take advantage of the increased nutrient loadings and to increase. The 1950s and 1960s were periods of liberal organochlorine pesticide use. Cladocera are particularly susceptible to organochlorine toxicity. 2. Sediment cores were taken from Hoveton Great Broad, in which the switch to phytoplankton has occurred, and from two Broads (Upton and Martham South Broads) in which submerged plants are still dominant. Analyses were made for cladoceran remains, diatoms and molluscs. Cross dating with previously taken dated cores allowed time‐scales to be applied. 3. In Hoveton Great Broad, a switch from clear‐water‐associated chydorids to turbid‐water forms was found to coincide with the loss of aquatic plants in the 1950s. No Daphnia remains were found. In the other two Broads, clear‐water chydorids, mostly plant‐associated, were found throughout the cores. 4. Residues of dieldrin (HEOD), DDD and TDE were found in the Hoveton Great Broad cores, with the DDT derivatives particularly associated with the end of the phase of submerged plant dominance and the beginning of that of phytoplankton dominance. Bosmina remains became more abundant after this point. Pesticide residues were scarce in the cores from the other two Broads and did not form any particular pattern. Residues of polychlorinated biphenyls were widespread in all cores. 5. Calculation of DDT concentration in the water at the time the sediments with greatest concentrations of residue were laid down suggests that concentrations above typical LC 50 values for Daphnia species could have been present.