Alan D. Tappin

Characterisation and quantification of organic phosphorus and organic nitrogen components in aquatic systems: A Review

This review provides a critical assessment of knowledge regarding the determination of organic phosphorus (OP) and organic nitrogen (ON) in aquatic systems, with an emphasis on biogeochemical considerations and analytical challenges. A general background on organic phosphorus and organic nitrogen precedes a discussion of sample collection, extraction, treatment/conditioning and preconcentration of organic phosphorus/nitrogen from sediments, including suspended particulate matter, and waters, including sediment porewaters. This is followed by sections on the determination of organic phosphorus/nitrogen components. Key techniques covered for organic phosphorus components are molecular spectrometry, atomic spectrometry and enzymatic methods. For nitrogen the focus is on the measurement of total organic nitrogen concentrations by carbon hydrogen nitrogen analysis and high temperature combustion, and organic nitrogen components by gas chromatography, high-performance liquid chromatography, gel electrophoresis, mass spectrometry, nuclear magnetic resonance spectrometry, X-ray techniques and enzymatic methods. Finally future trends and needs are discussed and recommendations made.

Trace Metals in the Central and Southern North Sea

Measurements of both dissolved and particulate trace metals (Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn) were made on samples collected simultaneously in the central and southern North Sea (below 56°N), during four cruises covering the seasonal cycle. Analyses of trace metals in both phases were undertaken using similar analytical protocols, and the data subjected to rigorous quality controls. Clean techniques were used throughout sampling and analysis. Trace metal concentrations ranged from those characteristic of waters entering the shelf region from the North Atlantic Ocean to values which in some cases were two orders of magnitude higher. Marked increases in concentrations were often associated with waters directly influenced by riverwaters, but the results showed that the distributions could be influenced by processes other than fluvial inputs. The redox-sensitive metals, Fe and Mn, were influenced at some sites, including those overlying areas of fine-grained sediments, by benthic inputs associated with seasonal changes in oxidation-reduction conditions in the benthic interfacial zone. The behaviour of metals which are not redox-sensitive (Cd, Zn) in some cases paralleled those of Fe and Mn, suggesting an association with Mn-or Fe-rich solid phases, or with organic matter. However, seasonal variations in concentrations of Cd and Zn were not directly linked to the cycle of biological utilization and regeneration of nutrients, suggesting that their geochemistry is more influenced by boundary inputs. Resuspension of Pb-rich sediments, long-range transport of Pb-rich suspended particulate matter (SPM), and enhanced, though diffuse, atmospheric inputs of lead were considered to have contributed to the elevated concentrations of particulate Pb (mass metal/mass sediment) in the water column during winter. Estimates of partitioning (K D s) were derived from the dissolved and particulate data for each of the metals over the seasonal cycle. For the more particle-reactive metals (Co, Fe, Mn, Pb), transport in the suspended particulate phase is a significant, sometimes dominant factor. In contrast, for Cd, Cu and Zn, transport in solution will dominate under almost all conditions in the southern North Sea. Furthermore, the values of K D , for a particular metal, varied widely, partly in response to seasonal differences in the relative contributions of lithogenous and biogenous particles to the particles in suspension. Only for Cu and Zn during the winter could the partitioning be described by a narrow range of K D values covering the observed concentrations of SPM. The data from this study give unique information concerning the contemporaneous distribution of dissolved and particulate trace metals in the southers North Sea and they provide a baseline against which the effects of reductions of inputs into the North Sea may be more accurately assessed. Viewed in combination, the dissolved and particulate data have yielded new insights into mechanisms affecting trace metal cycling and transport, essential in the development of coupled hydrodynamic-geochemical models.

Comparison of sample storage protocols for the determination of nutrients in natural waters

There have been several reports on storage protocols for the determination of nutrients in natural waters but each one has been limited to a particular sample matrix and they have reached different, matrix specific conclusions. The aim of this study was therefore to systematically apply the various recommended storage protocols to a range of natural water matrices. Samples from four contrasting sites in the UK, collected in late winter (February, 1999), were filtered and stored under different conditions (-80 degrees C, -20 degrees C, 4 degrees C and at 4 degrees C and -20 degrees C with 0.1% (v/v) chloroform) for up to 247 days prior to analysis. The sites were the River Frome in Dorset (a chalk stream catchment) and three sites from the Tamar Estuary (draining a non-chalk catchment) with salinities of 0.5 per thousand, 10 per thousand and 34 per thousand, Samples and controls were analysed for total oxidised nitrogen (TON) and filterable reactive phosphorus (FRP) using a segmented flow analyser with spectrophotometric detection. To investigate possible seasonal effects (particularly changes in biological and chemical matrix composition). a second sampling campaign was undertaken in early autumn (October, 1999). The results showed that the optimum storage conditions for the determination of TON and FRP were highly matrix dependent. with significant differences in FRP stability between the Frome and Tamar catchments (due to different calcium concentrations) and between samples of different salinities (due to different bacterial populations and/or dissolved organic matter). General guidelines for sample handling and storage are listed and matrix specific recommendations presented for samples rich in calcium and dissolved organic matter.

Processes influencing the fate of trace metals in the North Sea

Measurements were made in the southern North Sea of trace metals (dissolved and particulate Mn, Fe, Ni, Co, Cu, Zn, Cd, Pb) with contrasting biogeochemical behaviours. The extent to which distributions of dissolved metals over the survey area were determined by the mixing of river waters with seawater varied among the metals, and also seasonally; even for nickel and copper, which behaved most conservatively, other processes were significant. Specific instances of the effects of scavenging by particles and of inputs from benthic recycling are evident from the data and these processes lead generally to modifications of fluxes of dissolved metals in estuarine plumes. While the effect of atmospheric inputs on dissolved concentrations of metals is, on the basis of other evidence, a factor contributing to spatial and temporal variability, specific features arising from them were not identified; they probably account, however, for increased concentrations of dissolved lead observed at high salinities in the Humber plume. Seasonal variations in concentrations of dissolved metals, paralleling those of micronutrients, were not identified but manganese showed a pronounced seasonal variability related to its reduction—oxidation chemistry. Wide differences occurred in the partition between dissolved and particulate fractions, although for copper and zinc the partition could be described by a narrow range of distribution coefficients under certain conditions.

European land-based pollutant loads to the North Sea: an analysis of the Paris Commission data and review of monitoring strategies

Abstract Paris Commission (PARCOM) data have been used to investigate regional patterns in land-based pollutant loads to the southern North Sea for the period 1990–1993. Despite measures to standardise the procedures for obtaining river load estimates, important methodological discrepancies remain. These discrepancies relate to: (i) the location of sampling with respect to tidal and saline limits along the river reach, (ii) frequency of sampling, (iii) whether sampling is periodic or aperiodic and biased to particular flow conditions, and (iv) the choice between two load estimation algorithms. The PARCOM data indicate that riverine and total land-based loads of metals, total-N and total-P to the southern North Sea are dominated by the Rhine/Meuse and Elbe, which have the largest catchment areas and drain major centres of population and industry in central and western Europe. UK rivers have both the highest riverine loads per unit area and the highest direct discharge loads for many determinands. The high loads per unit area may be a function of the relatively small catchment areas and the proximity of major sources of pollution to the downstream monitoring sites. Higher direct discharges for the UK rivers may occur because UK direct discharge estimates include effluent inputs to the freshwater tidal reaches. For the other major European river systems, effluent discharges to the tidal freshwater reaches are included in the riverine load estimate. More thorough evaluation of load estimation methodologies is required if these data are to be used for comparative purposes in an international policy-making and legislative context.

Distributions and seasonal variability of pH and alkalinity in the Tweed Estuary, UK.

Monthly axial profiles of the Tweed Estuary were carried out between July 1996 and August 1997 as part of the UK Natural Environment Research Council Land Ocean Interaction Study. During these surveys, master variables and a range of chemical constituents, including pH and total alkalinity, were measured between the mouth of the estuary, at Berwick-upon-Tweed, and the freshwater tidal reach, at Union Bridge, approximately 10 km up-estuary. Alkalinity and pH showed clear seasonal variations in values within the lower salinity region of the estuary, and these could be related largely to changes in river flows, and hence to variations in the ratios of the source waters. River waters at high flows were dominated by poorly buffered surficial runoff, and pH and alkalinity values were low; conversely at low flows, groundwaters rich in weathered bedrock ions dominated the river water, and pH and alkalinity values were significantly higher. Biological production and respiration also had an effect on this seasonal variability, although this was secondary. The behaviour of pH and alkalinity within the estuary appeared generally conservative, although apparent non-conservative distributions were observed in the freshwater tidal reach. In a number of cases this behaviour could be attributed to biological activity. Estimated values of the excess partial pressures of CO2 within the fresh-water tidal reach were low (< 4), reflecting the relatively pristine character of the Tweed. During the spring and summer, CO2 was significantly undersaturated with respect to the atmosphere; extensive production by bed-anchored macroalgae was probably the reason for this, although the effects of water column algae cannot be discounted. In winter, production was minimal and respiration more important. As a result, partial pressures within the water column increased to a maximum of approximately four times atmospheric. Only infrequently was the CO2 in equilibrium between the river and atmosphere, suggesting that the tidal reach of the Tweed is a dynamic environment with respect to carbon cycling processes.

Determination of dissolved organic nitrogen in natural waters using high-temperature catalytic oxidation

Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1% for C and 1.5% for N) and is applicable to a wide range of natural waters.

Dissolved silver in European estuarine and coastal waters

Silver is one of the most toxic elements for the marine microbial and invertebrate community. However, little is known about the distribution and behaviour of dissolved silver in marine systems. This paper reports data on dissolved and sediment-associated silver in European estuaries and coastal waters which have been impacted to different extents by past and present anthropogenic inputs. This is the first extended dataset for dissolved silver in European marine waters. Lowest dissolved silver concentrations were observed in the Gullmar Fjord, Sweden (8.9 +/- 2.9 pM; x +/- 1sigma), the Tamar Estuary, UK (9.7 +/- 6.2 pM), the Fal Estuary, UK (20.6 +/- 8.3 pM), and the Adriatic Sea (21.2 +/- 6.8 pM). Enhanced silver concentrations were observed in Atlantic coastal waters receiving untreated sewage effluent from the city of A Corũna, Spain (243 +/- 195 pM), and in the mine-impacted Restronguet Creek, UK (91 +/- 71 pM). Anthropogenic wastewater inputs were a source of dissolved silver in the regions studied, with the exception of the Gullmar Fjord. Remobilisation of dissolved silver from historically contaminated sediments, resulting from acid mine drainage or sewage inputs, provided an additional source of dissolved silver to the estuaries. The ranges in the log particle-water partition coefficient (K(d)) values of 5-6 were similar for the Tamar and Mero estuaries and agreed with reported values for other estuaries. These high K(d) values indicate the particle reactive nature of silver with oxic sediments. In contrast, low K(d) values (1.4-2.7) were observed in the Fal system, which may have been due to enhanced benthic inputs of dissolved silver coupled to limited scavenging of silver on to sediments rich in Fe oxide.

Flow Analysis Techniques for Spatial and Temporal Measurement of Nutrients in Aquatic Systems

Environmental Context.Eutrophication is a growing problem globally, and it has significant ecological and socio-economic consequences. Understanding the causes of eutrophication requires a knowledge of nutrient biogeochemistry in aquatic systems. Owing to the high spatial and temporal variability of nutrients in these systems, there is a need for autonomous in situ measurement techniques with rapid response and the ability to collect long-term data. Flow injection analysis is one technique that meets these demands. Abstract.Flow analysis offers a versatile and powerful approach to monitoring of the aquatic environment. The present review highlights the drivers for determining macro- and micro-nutrients in marine and fresh waters, and outlines the instrumental requirements for in situ instrumentation. The principles of flow analysis, specifically flow injection and derivative techniques, and the chemical bases for macro- and micro-nutrient detection are discussed, and key examples of suitable approaches are considered. The successful deployment of flow analysis nutrient monitoring systems for spatial and temporal measurements is illustrated by specific examples relating to surface transects, depth profiles and temporal deployments. Finally, the challenges and imperatives of research in this area are outlined.

Concentrations, distributions and seasonal variability of dissolved Cd, Co, Cu, Mn, Ni, Pb and Zn in the English Channel

Abstract Open ocean studies have shown that dissolved manganese, cobalt and lead exhibit vertical profiles that reflect external sources and short residence times due to scavenging on to particle surfaces. In contrast, dissolved cadmium, copper, nickel and zinc mirror, to different degrees, the profiles of the nutrients. The work reported here for three cruises (November–December 1985, May and July–August 1986) in a shallow shelf sea shows that seasonal variations are shown by metals of the scavenged group, whereas the metals whose cycling in the open ocean parallels those of the nutients, do not show these correlations and, in fact, show no measurable seasonal variability. Concentrations of manganese increased progressively from winter to summer [2.3 ± 0.7(mean± 1σ)to 5.0 ± 3.0 nmol l−1]. A surface enrichment in the upper mixed layer of the western Channel during summer was also observed. Concentrations of cobalt increased from winter to spring (from ≤0.02–0.50 to 0.08–0.71 nmol l−1), paralleling those of manganese, but then decreased into summer (to ≤0.08–0.56 nmol l−1). The regional distribution of lead changed during the spring, possibly reflecting removal by diatoms and decreased river inputs, although overall mean concentrations remained similar throughout the year (0.22 nmol l−1). Concentrations of cadmium (0.20 nmol l−1), copper (3.2 nmol l−1), nickel (3.8 nmol l−1) and zinc (7.6 nmol l−1), and their regional distributions, remained relatively uniform over the period of the observations.