The River Shannon Callows, Ireland: An examination of how flooding patterns and farming practices affect plant communities and dipteran assemblages on unregulated floodplain meadows
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Floodplains provide numerous essential ecosystem services, including flood attenuation and biodiversity protection. The lowland floodplains along the River Shannon are largely unregulated, support rare and endangered bird and plant life, and are of ecological importance on a European scale. Hydrological fluctuations exert the strongest influence on wetland biodiversity. Thus, a thorough understanding of the hydrology is necessary to assess its impacts on biodiversity. The hydrological regime of this low-nutrient floodplain is characterised and these findings related to plant communities and dipteran assemblages. Recognising that different taxonomic groups may respond in different ways, the response of plant species richness, sciomyzid (Diptera: Sciomyzidae) species richness and abundance and syrphid (Diptera: Syrphidae) abundance were analysed for comparison. The catchment topography, including a wide flat river basin and low longitudinal gradient of the river, is an important determining factor in maintaining the hydrological functioning of the floodplains. Detailed digitised flood models were constructed to allow visualisation of the inundation dynamics of the flood meadows with respect to flood duration. Plant community composition and diversity vary along hydrological gradients with plant species diversity being negatively correlated with increased hydroperiod. Sciomyzid species richness and total abundance were both positively correlated with increased hydroperiod and flood depth while syrphids responded negatively to increases in hydrological variables. After hydrological fluctuations, agricultural practices are the second most influential variable affecting biodiversity in agricultural floodplains. Thus, details of farming practices were attained using questionnaires and management variables quantified and categorised. Agricultural practices on the callows are generally of low intensity, but there are variations in nutrient inputs and grazing practices, both current and historical. While the maintenance of the hydrological heterogeneity and the diversity of mowing regimes are important in maintaining biodiversity, variation in nutrient inputs and previous management, within the range investigated here, is of lesser importance for Syrphidae and Sciomyzidae. The spatial and temporal variability of the hydrological regime, in conjunction with microtopography, is responsible for maintaining biodiversity. Second to these variables a range of low intensity agricultural practices add the overall diversity of the flood meadows.