Factors affecting the spatial and temporal distribution of E. coli in intertidal estuarine sediments

Funding: University of St Andrews, The James Hutton Institute. DMP received funding from the Marine Alliance for Science and Technology for Scotland (MASTS), funded by the Scottish Funding Council (grant reference HR09011).Microbiological water quality monitoring of bathing waters does not account for faecal indicator organisms in sediments. Intertidal deposits are a significant reservoir of FIOs and this indicates there is a substantial risk to bathers through direct contact with the sediment, or through the resuspension of bacteria to the water column. Recent modelling efforts include sediment as a secondary source of contamination, however, little is known about the driving factors behind spatial and temporal variation in FIO abundance. E. coli abundance, in conjunction with a wide range of measured variables, was used to construct models to explain E. coli abundance in intertidal sediments in two Scottish estuaries. E. coli concentrations up to 6 log10 CFU 100 g dry wt-1 were observed, with optimal models accounting for E. coli variation up to an adjusted R2 of 0.66. Introducing more complex models resulted in overfitting of models, detrimentally effected the transferability of models between datasets. Salinity was the most important single variable, with season, pH, colloidal carbohydrates, organic content, bulk density and maximum air temperature also featuring in optimal models. Transfer of models, using only lower cost variables, between systems explained an average deviance of 42 %. This study demonstrates the potential for cost-effective sediment characteristic monitoring to contribute to FIO fate and transport modelling and consequently the risk assessment of bathing water safety.PostprintPeer reviewe

Impacts of physical disturbance on the recovery of a macrofaunal community: A comparative analysis using traditional and novel approaches

The recovery of macrofaunal communities after marine aggregate dredging was assessed using both traditional indices (abundance, biomass and species diversity), and functional analysis techniques (Somatic Production, Taxonomic Distinctness, Infaunal Trophic Index, Biological Traits Analysis and Rao's Quadratic Entropy). A previously dredged area (Area 222), located off the southeast coast of England was selected for this investigation. Area 222 was split into sites that had been subjected to relatively high dredging intensity, relatively low dredging intensity, and undisturbed reference areas. Both traditional and functional analyses indicated that macrofauna at the low dredging intensity site had fully recovered at least 7 years after the dredging ceased. Recovery times at the high intensity site had a greater variability and most of the techniques recorded the recovery had yet to take place even 11 years after the dredging had ceased. Since Area 222 was dredged for a long period of time (approx. 25 years), it is suggested that a longer time series of study be carried out so that the definitive recovery period in this high intensity site can be determined. While a longer time series study is not always a realistic or cost effective, the present study could be useful to facilitate the selection of metrics to support in the assessment of macrofaunal recovery

Assessing the recovery of functional diversity after sustained sediment screening at an aggregate dredging site in the North Sea

The effects of dredging the seabed for aggregate on benthic functional diversity were assessed using a suite of suitable indices on a recovering macrofaunal assemblage. Recovery was assessed as the return of a dredged assemblage to a state found in neighbouring undisturbed (reference) sites. in situ sediment screening was permitted during dredging operations; a difference in the sedimentary profile of the seabed between dredged and undisturbed reference sites was also observed. At sites of relatively high and low dredging intensity the sediment appeared more homogenous than reference sites after the selective removal of the coarser component. Initial assessment of the macrofaunal assemblage using univariate analytical techniques suggested a recovery of functional diversity at the low dredging intensity site after two years (according to the Infaunal Trophic Index, Taxonomic Distinctness index and Rao's Quadratic Entropy coefficient). However, multivariate analyses of the same data and of all indices except Taxonomic Distinctness indicated that assemblages at both high and low dredging intensity sites remained statistically indistinguishable from each other yet markedly different to the assemblage present in the reference area during the four-year study. The study concluded that recovery of functional diversity to a level found in a neighbouring undredged habitat had not occurred at either dredged site five years after the cessation of dredging. It is thought that the damage by dredging to functional diversity and to the capacity of the macrofaunal assemblage to recover is immediate and not so dependent on dredging intensity. The cumulative and wider ranging effects of sediment screening cannot be ignored or dismissed as a contributing factor to the similarities observed. The wider significance of these findings on the regulation of dredging activities is discussed. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved