Combining Historical Records and Palaeolimnology to Reconstruct Changes in Aquatic Macrophyte Communities in Shallow, Brackish Lakes: A Norfolk Broads Case Study

ABSTRACT The majority of studies investigating ecological change in aquatic plant communities focus on the presence, absence and abundance of fossilised plant remains (macrofossils) in lake sediment cores, historical records of plants and/or, very occasionally, a combination of the two. This study compiles low‐resolution macrofossil analyses alongside datasets of macrophyte presence for Hickling Broad and Martham Broad, two shallow, brackish lakes in the River Thurne valley of the Norfolk Broads, United Kingdom. We demonstrate that a combined approach can provide robust analyses through findings indicating that reliance solely on palaeoecological data is likely to underrepresent the full macrophyte community in sediment cores. Macrofossil analyses, however, revealed the presence of a nationally rare species ( Ruppia maritima ), identifying unknown highly saline past conditions. Ellenberg indicator values (EIVs) of species salinity tolerance recorded in historical accounts increase over time from 0 to 2 in each lake, likely attributable to anthropogenic drainage modifications that have increased ambient salinity levels. The combined approach highlights the unique environment and high conservation value of the River Thurne valley not possible to identify through historical records alone and acts as a test bed for the combination of records to inform management in similar environments. The addition of low‐resolution macrofossil analyses with open‐access historical records is, therefore, a cost‐effective tool for conservation organisations to identify historical conditions.