Seasonal budgets of the nutrient elements N and P at the surface of the German Bight during winter 1996, spring 1995, and summer 1994
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Summary
Between 1994 and 1996, within the interdisciplinary projects TRANSWATT and KUSTOS, horizontal gradients of nutrients, dissolved and particulate organic matter were analysed during summer, spring and winter at the surface of the German Bight and at the same time in the adjacent German Wadden Sea in order to estimate the seasonal state of conversion of nutrient elements and discharges during different seasons. During winter inorganic nutrients were dominant, accounting for 50 to 80 % of total nitrogen and phosphorus. This was also the case for nitrate and ammonium during spring, whereas during summer dissolved organic nitrogen and dissolved organic phosphorus dominated in the central bight. Contributions of particulate matter to total nitrogen and phosphorus were especially high in and off the tidal flats, partly by local production, even during winter, and partly by frequent resuspension. Here, the opposite was the case with dissolved organic compounds: contributions of dissolved organic nitrogen and phosphorus were low. N/P ratios of inorganic nutrients were especially high (> 200) in the open waters during spring, indicating a seasonal phosphorus deficiency. N/P ratios for particulate material were generally lower towards the coasts; ratios of dissolved organic matter increased. Silicate concentrations reflected the seasonal development as well: (i) low production and gradients dominated by discharges during winter, (ii) fixation of nutrients at high discharges during spring, and (iii) low discharges, fixation of nitrogen and significant remobilisation of silicate and phosphorus, especially in the tidal flats during summer.
Keywords
Total Nitrogen Tidal Flat Dissolve Organic Nitrogen German Bight River PlumeSaisonaler Stoffhaushalt der NÄhrsalzelemente N und P an der WasseroberflÄche der Deutschen Bucht im Winter 1996, Frühjahr 1995 und Sommer 1994
Zusammenfassung
Zwischen 1994 und 1996 wurden in den interdisziplinÄren Projekten TRANSWATT und KUSTOS horizontale Gradienten von NÄhrsalzen, gelösten und partikulÄren organischen Substanzen an der WasseroberflÄche in der Deutschen Bucht und im angrenzenden Wattenmeer untersucht, um den saisonalen Status von Umsatz- und Transportprozessen zu bestimmen. Im Winter (1996) dominierten die anorganischen NÄhrsalze mit 50-80 % die Gesamtstickstoff- und Gesamtphosphorkonzentrationen. Dies war auch der Fall für Nitrat zusammen mit Ammonium im Frühjahr (1995), wÄhrend im Sommer (1994) die gelösten organischen Stickstoff- und Phosphorverbindungen in der zentralen Bucht vorherrschten. PartikulÄre Stickstoff- und Phosphorverbindungen erreichten die höchsten Anteile im Wattenmeer und an seinem Rand, verursacht durch Resuspension und lokale Produktion, die selbst wÄhrend des Winters (1996) stattfand. Im Gegensatz dazu waren die Anteile der gelösten organischen Stickstoff- und Phosphorverbindungen im Wattenmeer niedrig. Die N/P-VerhÄltnisse waren für die NÄhrsalze besonders im offenen Wasser im Frühjahr hoch (> 200), ein Hinweis auf eine mögliche Phosphorlimitierung. N/P-VerhÄltnisse der partikulÄren Fraktion nahmen zur Küste hin ab, die der gelösten organischen Fraktion stiegen an. Auch die Silikatkonzentrationen spiegelten die saisonale Entwicklung wider: (i) geringe Produktion und durch EintrÄge dominierte Gradienten im Winter, (ii) Festlegung von NÄhrsalzen bei hohen EintrÄgen im Frühjahr und (iii) niedrige Flu\eintrÄge und weitgehende Festlegung von Stickstoff bei einer fortgeschrittenen Remobilisierung von Silikat und Phosphat, besonders im Wattenmeer im Sommer.
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