My research interests are:

• Land sea fluxes of biogenic elements (C, N, P and Si)
• Man-made changes of N and P fluxes in watersheds
• Bioegochemistry of enclosed seas (Baltic Sea, Black Sea)
• Global warming induced changes in C fluxes in taiga and tundra biomes

Selected publications:

Ferreira, J.G.; Andersen, J.H.; Borja, A.; Bricker, S.B.; Camp, J.; Cardoso, M.; da Silva, M.; Garcés, E.; Heiskanen, A.-S.; Humborg, C.; Ignatiades, L.; Lancelot, C.; Menesguen, A.; Tett, P.; Hoepffner, N.; Claussen, U, 2011, Overview of eutrophication indicators to assess environmental status within the European Marine Strategy Framework Directive, Estuarine, Coastal and Shelf Science, Volume 93, Issue 2, 10 June 2011, Pages 117-131

In 2009, following approval of the European Marine Strategy Framework Directive (MSFD, 2008/56/EC), the European Commission (EC) created task groups to develop guidance for eleven quality descriptors that form the basis for evaluating ecosystem function. The objective was to provide European countries with practical guidelines for implementing the MSFD, and to produce a Commission Decision that encapsulated key points of the work in a legal framework. This paper presents a review of work carried out by the eutrophication task group, and reports our main findings to the scientific community. On the basis of an operational, management-oriented definition, we discuss the main methodologies that could be used for coastal and marine eutrophication assessment. Emphasis is placed on integrated approaches that account for physico–chemical and biological components, and combine both pelagic and benthic symptoms of eutrophication, in keeping with the holistic nature of the MSFD. We highlight general features that any marine eutrophication model should possess, rather than making specific recommendations. European seas range from highly eutrophic systems such as the Baltic to nutrient-poor environments such as the Aegean Sea. From a physical perspective, marine waters range from high energy environments of the north east Atlantic to the permanent vertical stratification of the Black Sea. This review aimed to encapsulate that variability, recognizing that meaningful guidance should be flexible enough to accommodate the widely differing characteristics of European seas, and that this information is potentially relevant in marine ecosystems worldwide. Given the spatial extent of the MSFD, innovative approaches are required to allow meaningful monitoring and assessment. Consequently, substantial logistic and financial challenges will drive research in areas such as remote sensing of harmful algal blooms, in situ sensor development, and mathematical models. Our review takes into account related legislation, and in particular the EU Water Framework Directive (WFD – 2000/60/EC), which deals with river basins, including estuaries and a narrow coastal strip, in order to examine these issues within the framework of integrated coastal zone management.

Humborg C., Mörth, C.-M., Sundom, M. & Wulff, F. (2007) Riverine Transport of biogenic elements to the Baltic Sea – Past and possible future perspectives. Hydrology and Earth System Science 11: 1593-1607

The paper reviews critical processes for the landsea fluxes of biogenic elements (C, N, P, Si) in the Baltic Sea catchment and discusses possible future scenarios as a consequence of improved sewage treatment, agricultural practices and increased hydropower demand (for N, P and Si) and of global warming, i.e., changes in hydrological patterns (for C). These most significant drivers will not only change the total amount of nutrient inputs and fluxes of organic and inorganic forms of carbon to the Baltic Sea, their ratio (C:N:P:Si) will alter as well with consequences for phytoplankton species composition in the Baltic Sea. In summary, we propose that N fluxes may increase due to higher livestock densities in those countries recently acceded to the EU, whereas P and Si fluxes may decrease due to an improved sewage treatment in these new EU member states and with further damming and still eutrophic states of many lakes in the entire Baltic Sea catchment. This might eventually decrease cyanobacteria blooms in the Baltic but increase the potential for other nuisance blooms. Dinoflagellates could eventually substitute diatoms that even today grow below their optimal growth conditions due to low Si concentrations in some regions of the Baltic Sea. C fluxes will probably increase from the boreal part of the Baltic Sea catchment due to the expected higher temperatures and heavier rainfall. However, it is not clear whether dissolved organic carbon and alkalinity, which have opposite feedbacks to global warming, will increase in similar amounts, because the spring flow peak will be smoothed out in time due to higher temperatures that cause less snow cover and deeper soil infiltration

Eriksson, H., M. Pastuszak, S. Löfgren, C.-M. Mörth & Humborg, C. (2007) Nitrogen budgets of the Polish agriculture 1960-2000 – Implications for riverine nitrogen loads to the Baltic Sea from transitional countries. Biogeochemistry 85: 153-168.

The Oder and the Vistula rivers are responsible for about 25% of the total riverine nitrogen input to the Baltic Sea and of this 60% have been estimated to originate from diffuse sources. In this study we have tested the hypothesis that changes in agricultural practices in Poland have changed the riverine nitrogen export from the rivers Oder and Vistula to the Baltic Sea. We calculated agricultural long-term nitrogen budgets (1960-2000) for the catchments of the Oder and the Vistula rivers. Poland went through severe economical changes in the early 1990s, which led to a drastic decrease in fertilizer consumption. The role of the calculated nitrogen surplus as an eutrophication capacitor and the potential to reduce this important capacitor to improve the environmental state of the Baltic Sea is discussed. N surplus for the entire country showed a maximum in 1980 (58 kg ha-1 sown area-1) and it dropped to 39 kg ha-1 sown area-1 in 2000. The surplus was, however, up to two times lower than that in other transitional countries, and much lower than in Western Europe with intensive agriculture. An observed decrease in nitrogen concentrations in both Polish rivers is not ascribed to drop in fertilizer use, but it results from nutrient removal in municipal wastewater treatment plants with tertiary treatment facilities. Comparison of trends in nitrogen concentrations in different transition countries indicates that factors other than reduced fertilizer application influenced the inertia of the water quality response. Hence, the potential to reduce diffuse nitrogen emissions from agriculture by reducing fertilization is constricted in areas with low-nitrogen surplus. In transitional countries like Poland the largest potential for nutrient reductions seem to be in improving the connectivity to waste water treatment plants with tertiary treatment.

Humborg C., Pastuszak, M., Aigars, J., Siegmund, H., Mörth, C.-M., & Ittekkot, V. (2006) Decreased silica land-sea fluxes through damming in the Baltic Sea catchment - significance of particle trapping and hydrological alterations, Biogeochemistry 75: 265-281

We tested the hypothesis that reservoirs with low water residence time and autochthonous production influence river biogeochemistry in eutrophied river systems draining cultivated watersheds. The effect of a single artificial water reservoir and consecutive reservoirs on silica (Si) river fluxes is exemplified by the moderately dammed Vistula River and the heavily regulated Daugava River that are compared with the practically undammed Oder River. The sum of the discharge weighted annual mean biogenic silica (BSi) and dissolved silicate (DSi) concentrations in the rivers Oder, Vistula and Daugava were about 160 μ M (40 + 120 μ M), 150 μ M (20 + 130 μ M) and 88 μ M (6 + 82 μ M), respectively. Assuming BSi and DSi concentrations as observed in the Oder River as typical for eutrophied but undammed rivers, complete trapping of this BSi could have lowered Si fluxes to the Baltic Sea from rivers with cultivated watersheds by 25%. The superimposed effect of hydrological alterations on reduced Si land–sea fluxes is demonstrated by studies in the boreal/subarctic and oligotrophic rivers Kalixälven and Lueälven. The DSi yield of the heavily dammed Luleälven (793 kg km-2 yr-1) constituted only 63% of that was found in the unregulated Kalixälven (1261 kg km-2 yr-1), despite the specific runoff of the Luleälven (672 mm m-2 yr-1) being 19% higher than that of theKalixälven (563 mm m-2 yr-1); runoff normalized DSi yield of the former, regulated watershed, was only half the DSi yield of the latter, unperturbed watershed. Based on these findings, it is hypothesized here that perturbed surface water–groundwater interactions are the major reasons for the reduced annual fluctuations in DSi concentrations as also seen in the heavily dammed and eutrophic river systems such as the Daugava and Danube.