Temporal variations in microbenthic metabolism and inorganic nitrogen fluxes in sandy and muddy sediments of a tidally dominated bay in the northern Wadden Sea

Abstract

Factors controlling seasonal variations in benthic metabolism (O,, flux) and dissolved inorganic nitrogen (DIN) fluxes were examined during a 12-14 month period at three intertidal Wadden Sea stations. Since the flux measurements were made as small-scale laboratory core incubations, the results are primarily related to the microbenthic community (microalgae, bacteria, micro-, meio-and small macrofauna) and cannot be considered representative of the total benthic community in the Wadden Sea. Furthermore, it has to be emphasized that light intensity during daytime simulations were constant and saturating at all times. Benthic primary production and oxygen uptake appeared to be temperature dependent with a 'seasonal Q10' of 1.7-1.8 and 2.7-4.3, respectively. Inundation had no effect on oxygen fluxes as evidenced by similar sediment respiration with and without water cover. A stronger temperature dependence of primary production in muddy than in sandy sediment indicated that the overall control in the latter may be complex due to factors like macrofaunal grazing and nutrient availability. Benthic respiration may not be controlled by temperature alone, as sedimentary organic matter content correlated significantly with both temperature and benthic respiration. Annual gross primary production in high intertidal sandy sediment was 10 and 50 % higher than in low intertidal sandy and muddy sediments, respectively. Since annual benthic community respiration was 2 times higher in muddy than sandy sediments, the annual net primary production was about 0 in the former and 17-19 mol C m -2 yr -1 in the latter. However, heterotrophic contribution by larger faunal components as well as removal of organic carbon by waves and tidal currents, which are not included here, may balance the budget at the sandy stations. There was no or only weak relationships between (light and dark) DIN exchange and factors like temperature, sedimentary organic content, and oxygen fluxes. Factors related to nutrient fluxes, such as denitrification and nutrient concentration in the overlying water, may have hampered any such relationships. In fact, DIN fluxes at all three stations appeared to be strongly controlled by DIN concentrations in the overlying water. On an annual basis, the sediment appeared to be a net sink for DIN. I N T R O D U C T I O NI n t e r t i d a l areas, like t h e W a d d e n Sea, are c h a r a c t e r i z e d by a h i g h l y f l u c t u a t i n g p h y sical a n d c h e m i c a l e n v i r o n m e n t . B e n t h i c c o m m u n i t i e s ( m i c r o a l g a e , b a c t e r i a a n d a n i m a l s ) in s u c h a r e a s m u s t e n d u r e l a r g e v a r i a t i o n s in factors like t e m p e r a t u r e , salinity, w a v e s a n d c u r r e n t s on t i m e s c a l e s of h o u r s (e.g. d i u r n a l a n d tidal cycles) to m o n t h s (e.g. s e a s o n s ) . In a d d i t i o n , t h e activity of b e n t h i c p r i m a r y p r o d u c e r s a n d d e c o m p o s e r s are h i g h l y d e p e n de n t u p o n t ...

Organic matter and benthic metabolism in euphotic sediments along shallow sub-tropical estuaries, northern New South Wales, Australia

“…The relative contributions of algal material to sediment OM during the current study were estimated assuming a carbon-to-chlorophyll ratio of 40. Contributions averaged 0.7% (±1.3%) in the upper estuaries, 1.9% (± 2.5%) in the middle estuaries, to around 8.6% (± 5.6%) in the highly productive lower estuary sands, which is in agreement with estimations from other shallow estuarine systems (Cadee & Hegeman 1977, Kristensen et al 1997. Using total sediment chloropigments raises the percent contributions in the upper estuaries (where pheophytin concentrations are generally highest) by up to an order of magnitude.…”

“…The relative contributions of living BMA biomass to the sediment carbon pool may be estimated by applying a chlorophyll-to-carbon (biomass) conversion factor. The reported range for the ratio of biomass to chl a in pelagic phytoplankton varies between 22 and 154 (Valiela 1995) and may be as high as 200 (Parsons et al 1977), while that of BMA averages about 42 within a range of 18 to 79 (Cadee & Hegeman 1977, Gould & Gallagher 1990, Valiela 1995, Kristensen et al 1997). During the current study, chl c yielded the tightest relationship with productivity, with maximum productivity and un-degraded biomass (chlorophyll:pheophytin = 1.7) occurring at a chl a:c of 5, which suggests that diatoms are the predominant BMA taxa (Mackey et al 1996).…”

“…Labile material in these sediments may also be due to the release of dissolved organics from living cells, which are thought to yield higher energy for heterotrophs than particulate detritus (Newell et al 1981). The increase in the lability of the OM pool would stimulate higher heterotrophic microbial and meiofaunal activity per unit carbon (Lancelot & Billen 1985, Kristensen et al 1997.…”

Spatial and temporal patterns of mineralization rates and oxygen distribution in a permeable intertidal sand flat (Sylt, Germany)

“…Seasonal pattern of mineralization rates and oxygen distribution-As reported in numerous studies, benthic mineralization rates vary in the sediments of the Wadden Sea over the year because of the dependency of chemical and biological processes on temperature and because of the variation of the organic matter supply by the water column and benthic primary production (Kristensen et al 1997). …”

“…For OCRs, differences between sites were less pronounced than for SRRs, which could be explained by a variety of factors. The organic material at the upper station might be more refractory and, thus, more susceptible to aerobic than anaerobic mineralization (Hulthe et al 1998;Kristensen and Holmer 2001) and thereby maintain higher aerobic mineralization rates. A contribution by meiofauna to the utilization of oxygen might increase toward the upper flat stations, where highest abundances were found (Armonies and Hellwig-Armonies 1987).…”