Quantification of long-term changes in the German Bight using an ecological development index

Radach, Günther

doi:10.1006/jmsc.1998.0403

Cited by 26 publications

(9 citation statements)

References 23 publications

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“…Even with the inherent limitations of the Helgoland Roads data due to hydrodynamic conditions as described by Hickel (1998) and Radach (1998) and others it was possible to characterise potential long-term trends in occurrence of the three diatoms and to determine the variables associated with those trends. The SOGP is not a qualitative estimate like the date of the first exponential growth rate (see Wiltshire et al, 2008), but a quantitative one which captures the mean features of the seasonality of the three diatoms and could be compared to ecosystem models which do not resolve the growth phase explicitly.…”

Section: Discussionmentioning

confidence: 99%

“…These copepods are considered to play a key role in the transfer of phytoplankton carbon to higher trophic levels (Gowen et al, 1999). Beside the limitations due to the hydrographic environment as described by Hickel (1998) and Radach (1998) the extreme regularity, length and satisfactory data quality of the Helgoland Roads time series allow the detection of even weak long-term overall trends (Wirtz and Wiltshire, 2005).…”

Section: Data Setsmentioning

confidence: 99%

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Long-term changes in the seasonality of selected diatoms related to grazers and environmental conditions

Schlüter¹,

Kraberg²,

Wiltshire³

2012

Journal of Sea Research

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The decoupling of trophic interactions could be one of the severe consequences of climate warming in aquatic systems. The timing of phytoplankton blooms, in particular, can affect competition within the plankton community as well as food-web interactions with zooplankton and fish. Using long-term data from Helgoland Roads in the southern North Sea, we examine diatom seasonality, using three representative diatom species combined with environmental and copepod time series over the last four decades. The long-term annual abundances of Guinardia delicatula, Thalassionema nitzschioides and Odontella aurita exhibited interannual variations and dissimilar cyclic patterns during the time period under study . Of the three diatoms, G. delicatula showed a significant trend towards earlier bloom timings for 1962-2008 and a later decline of its abundance over time was found. Grazing and water transparency explained most of the bloom timing fluctuations of the diatoms considered. The annual timing of occurrences of each diatom species was correlated with their preceding concentrations. Earlier bloom timings occurred when autumn/winter concentrations were higher than average and later bloom timings occurred when autumn/winter concentrations were lower than average. Different environmental and predation variables related to the diatom bloom timings were found suggesting that climate warming might not affect the onset of the blooms of the three diatom species in the same manner. The results of the multiple linear regression analyses showed that the timings of decline of the three diatoms were mainly correlated with decreasing nutrient concentrations. Sunshine duration could prolong the duration of the blooms of T. nitzschioides and O. aurita provided that enough nutrients were available. In the case of G. delicatula, however, sunshine duration was negatively correlated with its end of the growth period. G. delicatula and T. nitzschioides showed later decreases in abundances under warmer spring and summer temperatures. Such species specific differences in the sensitivity to the forcing variables could lead to shifts in community structure and could ultimately have wider implications to the overall ecosystem health of the North Sea.

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Section: Discussionmentioning

confidence: 99%

Section: Data Setsmentioning

confidence: 99%

Long-term changes in the seasonality of selected diatoms related to grazers and environmental conditions

Schlüter¹,

Kraberg²,

Wiltshire³

2012

Journal of Sea Research

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“…The ratio of N and P inputs is important for the way the coastal ecosystem reacts to the inputs, for example with respect to changes in species composition and increasing primary production (Hickel 1998;Radach 1998). The N:P ratios are given here as tN/tP, to correspond with the previous calculations; e.g., the value 7.23 (tN/tP) is equivalent to the molar Redfield ratio of 16 (mol N/mol P).…”

Section: N:p Ratiomentioning

confidence: 99%

Variability of continental riverine freshwater and nutrient inputs into the North Sea for the years 1977–2000 and its consequences for the assessment of eutrophication

Radach¹,

Pätsch²

2007

Estuaries and Coasts

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We determined the monthly and annual riverine freshwater, nitrogen (N) and phosphorus (P) loading into the North Sea from Belgium, The Netherlands, and Germany for the years 1977-2000. An average of 133 km 3 yr 21 of the 309 km 3 yr 21 precipitation into the watershed is carried by the rivers into the sea. Total freshwater discharge fluctuates with a strong 6-7 yr periodicity, is strongly correlated with precipitation, and exhibits a slight long-term decrease. The temporal changes of regional patterns of precipitation lead to changing ratios of annual discharge of the western rivers compared to the eastern rivers, varying between 2.2 and 3.5. The long-term oscillations in discharge were more pronounced as discharge increased. The annual means of total and dissolved inorganic N and P loads were estimated to be 722 and 582 kt N yr 21 and 48 and 26 kt P yr 21 , respectively. The monthly N loads were much more strongly correlated with discharge, compared to the monthly P loads. Total N and P as well as dissolved inorganic N also demonstrated a 6-7 yr periodicity. The annual N loads decreased by about 17 kt N yr 21 from 1977 to 2000. The total phosphorus and phosphate loads decreased from about 80 and 50 kt P yr 21 in the 1980s to 25 and 12 kt P yr 21 , respectively, in the 1990s. The western rivers contributed the major part of the nutrient loads. The long-term oscillations in their nutrient loads were much more pronounced, compared to the eastern rivers. The area-specific loading rates estimated for all rivers are comparable to earlier estimates using shorter data records, smaller sample sizes, and a less complete watershed monitoring program. The monthly and annual average N:P ratios and their variability increased considerably for individual rivers during the study interval. These results confirm that the water quality of European continental rivers is strongly influenced by intense land use. They demonstrate the necessity for using long time series monitoring results to assess change and evaluate the effects of climate change on the North Sea coastal ecosystems, using ecosystem models on decadal time scales.

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“…This is unfortunate, because the phytoplankton, in its important position at the base of aquatic food chains, determines the primary energy flow through the system. We do know from the literature that the trigger mechanisms governing phytoplankton events and seasonality probably have changed substantially in response to climate change in the shallow North Sea (Radach 1998).…”

mentioning

confidence: 99%

Resilience of North Sea phytoplankton spring bloom dynamics: An analysis of long‐term data at Helgoland Roads

Wiltshire

Malzahn

Wirtz³

et al. 2008

Limnology & Oceanography

265

235

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Analyzing one of the most extensive long-term data series in the North Sea, the Helgoland Roads time series, we investigated the changes in the factors that potentially drive phytoplankton bloom dynamics in the German Bight. We compared the changes in these factors with the changes in the spring bloom phenology. We combined zooplankton, nutrient, weather, and phytoplankton data to analyze whether there has been a shift in trophic interactions in the North Sea affecting the spring bloom timing. The potential influence of temperature, with a mean increase of 1.5uC, was investigated. We showed that the German Bight around Helgoland is a highly dynamic system and has undergone considerable change in the last 30 yr. Nutrient levels, temperature, underwater light climate and wind speed have all changed. However, the spring bloom dynamics have hardly changed at all. We showed that the spring bloom tends to come later in warmer years but that this is not directly correlated with the overall warming trend. The known regime shift of the late 1980s is clearly visible in our data in terms of average phytoplankton winter densities and average cell size, but even so the start of the spring bloom has not changed.

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Quantification of long-term changes in the German Bight using an ecological development index

Cited by 26 publications

References 23 publications

Long-term changes in the seasonality of selected diatoms related to grazers and environmental conditions

Long-term changes in the seasonality of selected diatoms related to grazers and environmental conditions

Variability of continental riverine freshwater and nutrient inputs into the North Sea for the years 1977–2000 and its consequences for the assessment of eutrophication

Resilience of North Sea phytoplankton spring bloom dynamics: An analysis of long‐term data at Helgoland Roads

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