The influence of sediment characteristics on pathogen transport from freshwater to coast
Intertidal sediments act as a reservoir for many bacteria, including human pathogens. Pathogens are bacteria that can induce disease in humans, and many can survive well in the environment outside of the host. An indication of the presence of human pathogens is the presence of coliforms and the organism Escherichia coli.
Occurrence of pathogens in the estuarine environment can be a direct result of pollution from point sources such as sewage treatment works and run-off from septic tanks, landfills and agricultural lands. Fecal contamination runs into waterways as it transported down-stream by surface run-off and groundwater into streams, rivers, eventually reaching estuaries and the sea. Throughout this process, pathogens are susceptible to sedimentation and resuspension, increasing residence time within waterways.
Preliminary experiments show Escherichia coli abundance is frequently over 2,000 colony forming units (cfu) per 100g wet sediment. The European Commission Bathing Water directive states that coastal and transitional water samples should not exceed more than 250 cfu per 100ml of water. When the sediment is resuspended in the water column through turbulent flows, high tides or high rainfall, the associated pathogens will be transported to potentially high risk areas such as bathing waters.
Aim 1: To identify the changing distribution of pathogens in intertidal sediments over a 1 year period.
Long- term monitoring of sediment properties and associated load of coliforms over a year period in the Ythan (Aberdeenshire) and the Eden (Fife) estuaries forms a major part of the project. A wide range of sediment characteristics are being analysed, along with environmental data obtained on land-use in the catchment, temperature, rainfall and tidal height. Samples will be taken monthly from 4 high resolution areas within the estuary, and then an estuary wide sampling campaign on the Ythan and the Eden will be completed quarterly.
Aim 2: To investigate native and non-native microbial biodiversity using molecular techniques.
Several molecular techniques will be used to analyse biodiversity within native microbial communities, and the biodiversity and genetic diversity within the pathogens present. The data obtained will provide information on the effect of the indigenous microbial life on the non- native pathogens that occupy the sediment. It will also tell us the proportions of different pathogens in the sediment in different environmental and sediment conditions, and the genetic variation inside the organism E. coli is. The genetic variation is being investigated as different strains and sub-types have different qualities, such as being more virulent, and being able to attach to sediment particles better through increased production of extra-cellular appendages.
Fourier-Transform Infrared (FTIR) spectroscopy is being investigated as a rapid and cost effective tool for analysing sediment characteristics. It works on the principal that molecular bonds in different components in the sediment absorb infrared radiation at different wavelengths from one another. The absorbance of these bonds is translated into spectra that can clearly shows peaks where the absorbance occurs (Figure. 2).
This method will be used as an alternative to time- consuming and labour intensive methods.
Ultimately, the method will used to try and make correlations between pathogen abundance, and acquired FTIR data.