MEAD: An interdisciplinary study of the marine effects of atmospheric deposition in the Kattegat

doi:10.1016/j.envpol.2005.08.010

Environmental Pollution

Volume 140, Issue 3, April 2006, Pages 453-462

https://doi.org/10.1016/j.envpol.2005.08.010 Get rights and content

Abstract

This paper summarises the results of the EU funded MEAD project, an interdisciplinary study of the effects of atmospheric nitrogen deposition on the Kattegat Sea between Denmark and Sweden. The study considers emissions of reactive nitrogen gases, their transport, transformations, deposition and effects on algal growth together with management options to reduce these effects. We conclude that atmospheric deposition is an important source of fixed nitrogen to the region particularly in summer, when nitrogen is the limiting nutrient for phytoplankton growth, and contributes to the overall eutrophication pressures in this region. However, we also conclude that it is unlikely that atmospheric deposition can, on its own, induce algal blooms in this region. A reduction of atmospheric nitrogen loads to this region will require strategies to reduce emissions of ammonia from local agriculture and Europe wide reductions in nitrous oxide emissions.

Introduction

The coastal seas are amongst the most valuable resources on the planet but they are threatened by human activity. We rely on the coastal area for mineral resources, waste disposal, fisheries and recreation and the effective management of these conflicting uses requires collaborations between diverse groups of users, scientists and coastal managers (e.g. v. Bodungen and Turner, 2001). In Europe, high population densities and high levels of industrial activity mean that the pressures on coastal seas are particularly acute. One of the main problems concerning coastal seas is the rapid increase in the amounts of nitrogen-based contaminants entering the water (henceforth referred to as nitrogen, recognising it does not include unreactive N₂ gas). These nitrogen inputs, which come from many sources, particularly vehicles, industry and agriculture, can be used by phytoplankton as nutrients promoting an increase in primary production leading to a range of deleterious effects usually collectively described as eutrophication (Nixon, 1995, Jickells, 1998). Human activity has probably doubled the input of nitrogen to the environment globally (Galloway et al., 1995). In Europe the increases in nitrogen have been greater than this, leading to real concern over the health of coastal waters. Rivers have, until recently, been thought to be the most important source of nitrogen to the coastal seas, but we now know that nitrogen inputs from the atmosphere are large and can equal, or exceed, those from the rivers (e.g. Paerl, 1995, Valigura et al., 2000), while atmospheric phosphorus inputs are relatively small (Jickells, 1998). Atmospheric nitrogen inputs are dominated by nitric acid/nitrate and ammonia/ammonium inputs by wet and dry deposition. These have very different sources, reduced nitrogen primarily from animal farming and nitrate from combustion sources emitted as NO and NO₂. They also have different patterns of deposition with ammonia rapidly deposited and oxidised nitrogen only deposited after oxidation to nitric acid, a process that can take many hours or longer (see Spokes and Jickells, in press).

The Kattegat (Fig. 1), the transitional area between the Baltic Sea and the North Sea, has received considerable attention, because intense ammonia and nitrogen oxide emissions in this region (see http://www.emep.int and http://www.ier.uni-stuttgart.de/public/de/organisation/abt/tfu/projekte/genemis) result in high rates of atmospheric deposition (Hertel et al., 2003). Symptoms of eutrophication are evident in this region (Møhlenberg, 1999, Meyer-Reil and Köster, 2000). A Chrysochromulina sp. bloom in 1988, which first developed in the northern Kattegat, devastated fish farms along the western Scandinavian coast with significant economic losses (Moestrup, 1994). In the summer of 2002, levels of oxygen in the Great Belt region were the lowest ever measured for that time of year (Ærtebjerg, 2002), and there appears to be a long term trend of decreasing deep water oxygen in this area (Ærtebjerg et al., 2003).

The MEAD Project (Marine Effects of Atmospheric Deposition) investigated how inputs of nitrogen from the atmosphere affect the chemistry and biology of the Kattegat and how this information can be used to help manage this coastal area. MEAD represents a unique collaboration between atmospheric and marine modellers and field scientists including ecologists, biogeochemists and physical oceanographers. The particular challenge in considering the effects of atmospheric inputs to marine systems is the wide range of space and time scales involved and the differences between these in the atmosphere and marine systems (Fig. 2). For example, atmospheric deposition events characteristically last a period of hours to a day or so, while the development of phytoplankton blooms can take many days to weeks. Such differences in time and space scales must be considered in developing programmes to investigate the effects of atmospheric deposition.

In the MEAD approach described here we assess the likelihood of bloom development assuming that the biggest N inputs are most likely to trigger blooms. This is generally true but a relatively small N input under suitable physical conditions can trigger a bloom (Kononen, 2001). Nutrient starved algae can rapidly assimilate nutrient inputs, although any blooms will take time to develop.

MEAD field work involved atmospheric and water column chemical and physical measurements using ships, automated buoys and coastal stations. Field work was concentrated in the summer when phytoplankton growth conditions are optimal, but nutrient availability is restricted, although other factors beside nutrient supply, such as water column stability and light availability, are of course important and incorporated in our models. Under summer conditions, atmospheric deposition events are most likely to have a significant impact. The results obtained in MEAD were incorporated in computer models that allowed us to determine how atmospheric pollutants are transported in the atmosphere, deposited to the ocean and how this affects the growth of phytoplankton. These models have then been used to predict whether changing the amounts and types of nitrogenous contaminants entering the atmosphere could affect phytoplankton growth in coastal waters. We have also used existing monitoring data on phytoplankton abundance in the Kattegat in a retrospective analysis to identify bloom events and test for any relation between these and atmospheric deposition. Here we summarise the results of this programme and consider management options for nitrogen inputs into this region. While the work of MEAD is clearly site specific, the approach used and some of the conclusions drawn are of broader applicability to coastal seas.

Section snippets

Materials and methods

Most of the methods for the individual components of the MEAD work have been published elsewhere. In these cases we summarise the methods briefly and provide appropriate references. Methods for the statistical treatment of long term data sets are described within Section 3.1. Here we focus on MEAD experimental and modelling methods.

MEAD undertook water column studies of physical, chemical and biological parameters to describe the cycling of nutrients and the biogeochemical controls on

Long term monitoring evidence for phytoplankton blooms in the Kattegat and the mechanisms which regulate them

MEAD initially investigated the available data for bloom occurrence based on historic monitoring in Swedish and Danish coastal waters (see http://www.dmu.dk/AtmosphericEnvironment/MEAD/). Using this database, statistical analyses were carried out to investigate the potential cause–effect relationships between atmospheric deposition and phytoplankton abundance based on water column chlorophyll a measurements. The overall aim was to describe potential underlying mechanisms generating blooms. An

Conclusions

Our statistical analysis shows that summer phytoplankton blooms within the Kattegat are rare. Results from the MEAD project suggest that the main factor regulating nitrogen supply and bloom occurrence in the Kattegat is entrainment of nitrogen from deep waters. Other than those results available from the continuous plankton recorder surveys (e.g. Reid et al., 1998), the MEAD retrospective analysis is one of the few systematic studies of bloom frequencies carried out (Hasager et al., 2003).

These

Acknowledgements

MEAD was funded by the EU under contract number EVK3-CT-1999-00014. We thank all who helped with fieldwork, particularly the crew of the Skagerrak.

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MEAD: An interdisciplinary study of the marine effects of atmospheric deposition in the Kattegat

Abstract

Introduction

Section snippets

Materials and methods

Long term monitoring evidence for phytoplankton blooms in the Kattegat and the mechanisms which regulate them

Conclusions

Acknowledgements

Estuarine, Coastal and Shelf Science

Atmospheric Environment

Marine Pollution Bulletin

Marine Pollution Bulletin

Coastal and Shelf Science

Nutrients and eutrophication in Danish marine waters. A challenge for science and management

National Environmental Research Institute

Science and Integrated Coastal Management

Frequency, composition and causes of summer phytoplankton blooms in a shallow coastal ecosystem, the Kattegat

Limnology and Oceanography

Nitrogen fixation: anthropogenic enhancement-environmental response

Global Biogeochemical Cycles

Time-dependent modeling of the Baltic entrance area. 1. Quantification of circulation and residence times in the Kattegat and the straits of the Baltic Sill

Estuaries

On extreme atmospheric and marine nitrogen fluxes and chlorophyll-a levels in the Kattegat Strait

Atmospheric Chemistry and Physics

Operational mapping of atmospheric nitrogen deposition to the Baltic Sea

Atmospheric Chemistry and Physics

Nutrient biogeochemistry of the coastal zone

Science