Natural background concentrations of nutrients in the German Bight area (North Sea)

Abstract

Natural background concentrations of nutrients are needed for the assessments of eutrophication processes and their status. Natural background concentrations of total nitrogen (TN) and total phosphorus (TP) were modelled for the rivers discharging into the German Bight and the Rhine considering individual catchment sizes, freshwater flows and soil types. These data were validated by comparison with data from unpolluted rivers. The consistency of modelled and some compiled nutrient concentrations was confirmed by their area-specific load dependency on freshwater discharges. Pristine inorganic nutrient concentrations were deduced from modelled relations to TN and TP in unpolluted rivers. Pristine nutrient gradients between rivers and offshore waters were estimated by linear mixing until a salinity of 32, continued by hyperbolic fits towards recent mean offshore values (salinity 34.5-35). Based on these gradients and recent mean salinities, maps of pristine surface gradients were plotted for the whole German Bight. Variability was transferred from recent conditions as percentage of standard deviation. Reported historical nutrient data and concentrations from unpolluted rivers, coastal and offshore North Sea waters are discussed concerning their relations to natural background conditions.

A model-based projection of historical state of a coastal ecosystem: Relevance of phytoplankton stoichiometry

“…For an evaluation of the ecological status of the system, the reference conditions, representing the minimally perturbed state of the system needs to be known. For the German Bight and the surrounding coastal Wadden Sea, there has been earlier work on the construction of reference states based on statistical methods and budget considerations (van Beusekom, 2005;Brockmann et al, 2007;Topcu et al, 2011). Although these studies have been successful in gaining insight 280 and assisting the management of the system (Claussen et al, 2009), a process-based modelling approach has been lacking so far, which is needed to develop understanding of the specific mechanisms driving the differences between the reference and recent states.…”

Multivariate Analysis of Extreme Physical, Biological and Chemical Patterns in the Dynamics of Aquatic Ecosystem

“…Plankton trophic structure in a downwelling-upwelling cycle at the SE Brazilian coast related to particulate organic carbon production is mainly due to phytoplankton (98%) and did not differ between periods [10]. However, elevated nutrient concentrations are the main origin of coastal eutrophication processes and their monitoring allows direct estimates of the degree of contamination, and obviously making possible their management [16] [17]. A flow cytometer in-situ was used by [18] at Anjos Bay, Arraial do Cabo city, to quantify the abundances of phytoplankton and cyanobacteria, which were identified by chlorophyll a and phycoerythrin autofluorescence, respectively.…”

Assessment of Uncertainties in Scenario Simulations of Biogeochemical Cycles in the Baltic Sea

“…According to several earlier estimates, the water masses at the entrance to the Kattegat consist of about 80% of Atlantic waters from the central North Sea, while German Bight and Baltic waters contribute only about 10% each (e.g., Aarup et al, 1996;Kristiansen and Aas, 2015). Despite a marked decrease of nutrient concentrations in the Dutch coastal areas, almost returning to the pre-industrial levels with slightly higher N:P ratio (e.g., Troost et al, 2014;Burson et al, 2016), the concentrations in the offshore areas of the German Bight, where the Jutland Coastal Current originates, have not changed much since the known regime shift in the late 1980s (e.g., Lenhart et al, 2010;Topcu et al, 2011).…”