The isolation and characterisation of dissolved organic matter from freshwater and marine enviroments

Freshwater and marine dissolved organic matter (DOM) is a complex mixture of chemical components that are central to many environmental processes, including carbon and nitrogen cycling. Due to its wide range of chemical-physical properties, the sampling and separation of its components is challenging, mainly due to coelution and irreversible sorption issues on traditional chromatographic columns. For this reason, questions remain as to its chemical characteristics, sources and transformation mechanisms. Here, we employ novel passive sampling techniques for isolation coupled with advanced analytical techniques for the characterisation of DOM from marine and freshwater environments. The spatial and temporal variation of DOM composition was investigated in a number of freshwater bodies along with the development and application of novel passive samplers within marine environments. In Chapter 2 we employ 1- and 2-D nuclear magnetic resonance (NMR) spectroscopy to investigate the structural components of lacustrine DOM from Ireland, and how it varies within a lake system, as well as to assess potential sources. Major components found, such as carboxyl-rich alicyclic molecules (CRAM) are consistent with those recently identified in marine and freshwater DOM. Lignin-type markers and protein/peptides were identified and vary spatially. Phenylalanine was detected in lake areas influenced by agriculture, whereas it is not detectable where zebra mussels are prominent. The presence of peptidoglycan, lipoproteins, large polymeric carbohydrates and proteinaceous material supports the substantial contribution of material derived from microorganisms. A major challenge in environmental chemistry at the moment is finding materials that can isolate all components of DOM from both fresh and marine water. In the freshwater studies of chapter 2 a cellulose sorbent was used to isolate the DOM from water. However, cellulose use is not possible in marine water studies as the Cl- ions compete for binding sites affecting the sorption of DOM. Therefore activated carbon was investigated as a possible sorbent of DOM within marine environments in chapter 3. Activated carbon passive samplers showed an steady uptake of organic carbon over time, however NMR results were inconclusive as major DOM signals CRAM and MDLT were absent from 1H spectra. Consequently, cation exchanged monmorillonite clays were investigated as sorbents and showed very good potential, at least in the sorption of the aliphatic component of DOM. After a 28 deployment within marine and freshwater environments GCMS analysis identified a large aliphatic component sorbed to the clay. In addition sterols and sugars were also identified in the DOM matrix. To further investigate clay as an isolation medium for DOM it was included in a more in-depth study of water chemistry in the Shannon Pot, Co Cavan, Ireland (Chapter 4). The DOM composition and hydrochemistry within this karst aquifer was investigated using: 1. clay passive samplers followed by GCMS TMAH chemolysis, 2. NMR and 3. water quality indicators over a fifteen month period. This data was correlated with rainfall records. Phosphate and dissolved oxygen levels exceeded recommended concentrations at times of high precipitation indicating that fertiliser use is influencing the water chemistry at this important site. These events were also evident in DOM chemistry as an increase in biopolymers such as lignin was observed during the same periods of increased precipitation. Furthermore, evidence for anthropogenic influence in the surrounding landscape was found in the DOM including herbicides that may be more stable in the environment than previously thought. The results indicate than the DOM composition and its hydrochemistry is strongly influenced by the hydrological events such as rainfall

Microfluidic platforms with bioinspired functionalities: new concepts for future devices

Through developments in fabrication technologies in recent years, it is now possible to build and characterize much more sophisticated 3D platforms than was formerly the case. Regions of differing polarity, binding behaviour, flexibility/rigidity can now be incorporated into these fluidic systems. Furthermore, materials that can switch these characteristics can be incorporated, enabling the creation of microfluidic building blocks that exhibit switchable characteristics such as programmed microvehicle movement (chemotaxis), switchable binding and release, switchable soft polymer actuation (e.g. valving), and selective uptake and release of molecular targets. These building blocks can be in turn integrated into microfluidic systems with hitherto unsurpassed functionalities that can contribute to bridging the gap between what is required and what science can currently deliver for many challenging applications. Recent developments now enable complex 3D arrangements of soft, switchable polymer gel structures to be created with sub-micron feature size resolution, opening completely new possibilities for control of the chemistry of liquid-solid system. This emerging transition from existing engineering-inspired 2D to bioinspired 3D fluidic concepts appears to represent a major turning point in the evolution of microfluidics. For example, implementation of these disruptive concepts may open the way to realising biochemical sensing systems with performance characteristics far beyond those of current devices

Development of an autonomous sensing platform for detection of nutrients in natural waters

Nutrients such as Phosphate, Ammonia, Nitrite and Nitrate are central in any environmental processes, including several microbial, plant and animal metabolic processes. The nutrient platform is based on a combination of microfluidic analytical systems, colorimetric reagent chemistries, low cost LED based optical detection and wireless communications. Each component was developed, assessed and optimised to evaluate the suitability before being integrated to form a working pre-competitive prototyp

Development of cost effective sensors for the in-situ monitoring of eutrophication

This work is carried out as part of the COMMON SENSE European FP7 project. The COMMON SENSE project aims to provide a reliable sensing platform for in-situ measurements on key marine water quality parameters relating to eutrophication, heavy metal contaminants, marine litter and underwater noise. The COMMON SENSE nutrient sensor is based on a combination of microfluidic analytical systems, colorimetric reagent chemistry, low-cost LED-based optical detection, and wireless communications. The reliable quantification of nutrients in marine environments is challenging due to the low concentration of these solutes in the ocean and the nature of the matrix in which they are held. Initial studies are focussed on validating a method for the sequential determination of nitrite and nitrate in marine environments. Coupled with the traditional well established Griess–Ilosvay reaction for the determination of nitrite, a vanadium chloride (VCl3) solution is used as the reducing agent. The method shows potential as an alternative to the toxic cadmium column for the reduction of NO3- to NO2- in marine water as results indicate that there are no apparent interferences from variances in salinity. The method was tested on a series of samples with varying salinities and sample matrices (costal, estuarine and freshwater), the method is low cost, reproducible and requires low volumes of sample and reagents

Sensors for in-situ monitoring of eutrophication in marine environments

Accelerated eutrophication of marine ecosystems as a result of nutrient enrichment is a widespread problem within European marine margins. Eutrophication has several adverse effects on the marine ecosystem such as the formation of harmful algae blooms reduced water clarity and reduced oxygen levels. The reliable quantification of the causative nutrients is challenging due to the matrix within which they are held. Here we propose methods for the identification and optimisation of appropriate detection chemistries for phosphate, ammonia, nitrate and nitrite in marine matrices. The work presented is carried out as part of the COMMON SENSE FP7 European project. COMMON SENSE aims to provide a reliable sensing platform for in-situ measurements on key parameters relating to eutrophication. The nutrient sensor is based on a combination of microfluidic analytical systems, colorimetric reagent chemistry, low-cost LED-based optical detection, and wireless communications

Understanding and mitigating global change with aquatic sensors: current challenges and future prospects

Human activities are causing global change around the world including habitat destruction, invasive species in non-native ecosystems, overexploitation, pollution, and global climate change. While traditional monitoring has long been used to quantify and aid mitigation of global change, in-situ autonomous sensors are being increasingly used for environmental monitoring. Sensors and sensor platforms that can be deployed in developed and remote areas and allow high-frequency data collection, which is critical for parameters that exhibit important short-term dynamics on the scale of days, hours, or minutes. In this article, we discuss the benefits of in-situ autonomous sensors in aquatic ecosystems as well as the many challenges that we have experienced over many years of working with these technologies. These challenges include decisions on sensor locations, sensor types, analytical specification, sensor calibration, sensor drift, the role of environmental conditions, sensor fouling, service intervals, cost of ownership, and data QA/QC. These challenges result in important tradeoffs when making decisions regarding which sensors to deploy, particularly when a network of sensors is desired to cover a large area. We also review recent advances in designing and building chemical-sensor platforms that are allowing researchers to develop the next-generation of autonomous sensors and the power of integrating multiple sensors into a network that provides increased insight into the dynamics of water quality over space and time. In the coming years, there will be an exponential growth in data related to aquatic sensing, which will be an essential part of global efforts to monitor and mitigate global change and its adverse impacts on society