EU workshop (2007) on climate change and eutrophication

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On January 29, 2007, the Centre for Environment, Fisheries and Aquaculture Science (CEFAS, UK) hosted a European workshop in London on “Future scenarios considering the impacts of climate change on the consequences of undesirable disturbance associated with eutrophication”. The event occurred due to the shared concern of European institutions and organizations about the need to integrate scientific knowledge on climate change and eutrophication for marine and coastal waters.

This workshop was preceded by an international conference on eutrophication, (Research and Management of Eutrophication in Coastal Ecosystems, Denmark, July 2006); and a preliminary COST proposal in the fall of 2006 to establish an European climate change and eutrophication cooperation network, all of which involved EUCC- The Coastal Union. There has been ongoing activity following the workshop, and discussion of regional implementation in the north Atlantic and Baltic region. These comments draw on this workshop and prior events, as well as scientific studies.

Although integration is highly complex, consideration is required of the degree to which existing eutrophication problems are likely to be influenced by climate change-induced variation of marine and coastal ecological, physical and chemical systems, and, in particular, the degree to which climate change will exacerbate future eutrophication problems and possibly increase the proliferation of harmful algal bloom.In marine and coastal waters, eutrophication occurs as a result of the additions of chemical nutrients (principally nitrogen and phosphates), which can promote excessive amounts of algal growth and may result in undesirable ecological balance and degraded water quality (Per.comm., Stephen Malcolm, CEFAS).

Warm early summers may favour spring spawning zooplanktivourous fish at the expense of autumn spawning species in oligotrophic lakes. This may lead to altered nutrient status and nutrient and phosphate rations. Changes in climate patterns and related runoff regimes can significantly influence nutrient losses from catchments. Future levels will be sensitive to: changes in the timing of seasonal and annual events (spring runoff, autumn low flow, ice and snow cover), and the frequency and severity of extreme events (floods, droughts, erosion).

Impacts of increased water temperatures may increase productivity, leading to higher phytoplankton biomass and the occurrence of phytoplankton blooms. Warm early summers may favour spring-spawning zooplanktivorous fish at the expense of autumn spawning species in oligotrophic lakes. This may lead to altered nutrient status and nutrient and phosphate ratios Warm and dry years are associated with reduced influxes of nutrients (particularly nitrate) in runoff, but may also lower minimum water levels, increasing re-suspension (particularly phosphate) from bottom sediments in shallow lakes. Changing nutrient and phosphate ratios which may lead to phytoplankton dominance shifts, with lower relative nutrient availability.

Climate scenarios point to moderate increases in mean annual river flow to the Black and Baltic by the late 21st century. Reduced influence of snow melt will increase the synchronisation between precipitation and stream discharge, reducing and extending summertime base flow but increasing wintertime runoff. Coastal areas may become more vulnerable to rainstorms and flood events, with severe effects on agricultural activities in former floodplain areas, as well as nutrient losses. Responses of nutrient losses to climate change will be faster and more direct in small agricultural catchments; internal material cycles will lead to more complicated dynamics in large catchments.

There are concerns as to whether land use changes will result in large eutrophication effects, such as the growth of bio-fuels and bio-energy crops. To what degree will hotter, dryer summers in regions that are already eutrophic, like the Baltic or Black Seas, result in changes to coastal water quality? What are the likely impacts of increased stratification on inshore waters? What options are available to mitigate increased eutrophication?

Some of these questions could be answered by examining historical time- series data. Others by using coupled climate-catchment-ecosystem models, or perhaps even using experimental mesocosms. It is essential that combinations of methods be used. It can also be difficult to separate the symptoms of eutrophication from climate change impacts. For example; while nutrient enrichment is a first-order cause of eutrophication; weather, wind, storminess, local physiographic conditions and cloud variation also determine the extent to which nutrient enrichment is likely to become problematic.

Current European marine environmental legislation does not identify climate change, but deals with environmental issues such as eutrophication and hazardous chemicals. Existing European directives, such as the Nitrate and Urban Waste Water Directive, have been somewhat successful in managing nutrients by controls on direct and diffuse sources of nutrient sources. Environmental legislation under the Water Framework Directive has moved beyond the assessment of nutrient concentrations, to the use of biological tools to assess the impact of nutrient enrichment. Current and future European agricultural and energy policy and legislation will affect this issue. For example, the promotion of bio-fuels may increase land under agricultural production and thus could result in more nutrient inputs into vulnerable ecosystems.

The Water Framework Directive does not directly refer to climatic change but does identify changing background conditions as part of the ongoing assessment of reference ecological conditions. The classification scheme is anchored on the definition of reference status. The definition of reference condition is type-specific, and therefore requires an analysis of natural variability, with reassessment of the natural variability every 6 years. Thus, it allows for a re-appraisal of reference conditions to include the impact of climate change on the biology.

The Water Framework Directive has also set out a number of ecological indicators which may be used to further assess the impacts of climate change and the interactions between climate and eutrophication driven changes. For example, the Water Framework Directive identifies the use of phytoplankton community and biomass as key indicators in the assessment of nutrient pressure on European water bodies. Changes in the timing of seasonal and annual events will influence spring and autumn runoff, with potential consequences for phytoplankton seasonal patterns. Phytoplankton tools could be used to assess the degree of change in phytoplankton bloom timing and community composition in comparison to reference sites for both climate and eutrophication pressures.

One can consider the impact of climate change and eutrophication within Europe by considering specific changes for temperature, precipitation, and river runoff in the already eutrophic Baltic Sea basin. There have been annual warming trends from 1871 to 2004 for the northern and southern Baltic catchment area, being 1.0 and 0.7 °C per 100 years. Over the latter part of the 20th century, northern Europe has on average become wetter, although the increase in precipitation is not uniform. Seasonally, the largest increases have occurred in winter and spring. In the northern part of the Baltic Sea basin, there have bee increases in the summer; there have been decreases in the southern parts of the basin. In winter, there are increases in the number of heavy precipitation events. During the latter half of the 20th century, a decrease in cloudiness and an increase in sunshine duration was observed in Poland in the south, while opposite trends were observed in Estonia in the north.

Positive trends in annual values of river runoff for 1920-2002 were detected for several rivers in Denmark, Southern Sweden and Lapland. In Russia for basins located south and southwest of the Gulf of Finland, annual runoff for 1978-2002 increased by about one third compared to long-term values. Significant positive trends were common in the entire north of the Baltic Sea basin in winter river runoff (Dec-Feb) during the period 1941-2002. Winter runoff from Finland in the Baltic Sea has increased at 785 m3 per second during the period 1912-2003. In the Russian part of the Baltic Sea basin, winter runoff has increased remarkably, with 40-140% increase in the basins south and southwest of the Gulf of Finland, and 6-44% in the Karelian isthmus. The increase of wintertime runoff has also been observed in Estonia, Latvia and in Belarus. A warming trend has been observed in the Finnish, Estonian and in the Byelorussian lakes (Baltic assessment of climate change).

The January 2007 workshop resulted in an overarching vision, as well as high level and more specific questions. The overall vision is increasing understanding of how climate change and eutrophication will impact on marine and coastal waters, and the degree to which climate change will exacerbate future eutrophication and harmful algal bloom problems? The questions raised below will require complex scientific and policy responses.

General questions:

Evidence that climate change is exacerbating existing coastal and marine eutrophication? To what degree will further climate driven environmental change result in eutrophication? What are the implications of eutrophication-related undesirable disturbance in terms of maintenance of ecosystem functions, and how much is too much, i.e. irreversible damage or irrecoverable loss of a species? What are the ‘common problems’ associated with eutrophication across regional seas, and how will different marine systems respond? What are the key factors to prioritise in bringing about recovery and reversal of eutrophication?

Specific questions:

How should we measure change in eutrophication? What are the appropriate assessment and measurement endpoints? How do we assess harm, and measure recovery? Can we limit and reverse damage or harm through reducing undesirable disturbance? Will increased temperature interact with continued high nutrient loading to increase the severity of eutrophication symptoms? How and why exactly is increased stratification increasing the scope, impact and effect of eutrophication? The potential of application of existing models to aid understanding and projection of areas likely to experience heightened problems of eutrophication as a result of climate change? Associated identification of future modelling requirements? Eutrophication in the coastal zone is a result of multiple 'pressures' including climatic forcing. How can we use available time-series from monitoring systems to allow the investigation of climate change as one of the pressures that can lead to eutrophication? What are the restoration and adaptation strategies? Are there eutrophication ‘hot spots’ in Europe? Can gaining better understanding of these areas help elsewhere? Potential transferability of developments and tools in the freshwater sector to the marine sector?