Oxygen profiles, actual oxygen uptake and electron transport system activity (ETSA) were studied in 4 intertidal sedirnents at Texel, NW Netherlands. Organic carbon content ranged from 0.02 to 0.4 O/ O dry weight. Profiles of oxygen were recorded with a needle minielectrode and showed that oxygen was present down to 18 mm in the sandy beach sediment with low carbon content, whereas oxygen only penetrated down to 1 to 3 mm in the organically richer sediments. Measured oxygen uptake ranged from 395 to 2315 pm01 O2 m-' h -' and exceeded oxygen uptake estimated on basis of molecular diffusion by 1.4 to 3.2 times. The difference between the 2 methods for measuring oxygen uptake indicates that bottom fauna activity significantly contributes to the sediment-water exchange of oxygen. The ETSA varied from 0.02 to 0.81 pm01 0, g-' h -' The ETSA at the sediment surface was positively correlated to sediment oxygen uptake. Nelther ETSA nor oxygen uptake showed correlation to organic carbon or nitrogen content in the sediment.
Oxygen concentration was measured in aerial roots (pneumatophores), horizontal cable roots and surrounding sediment of the tree Avicennia marina (Forsk.) Vierh. in a mangrove swamp at Ao Nam Bor, on the southeast coast of Phuket Island, Thailand. The O2 measurements were made in the field with a polarographlc oxygen minielectrode. The O2 concentration inside pneurnatophores was 63 to 88 % of air saturation, whereas the cable roots showed a lower concentration (62 to 73 %) indicating an O2 gradlent from the emerging parts to the subsurface roots. The O2 concentration in the roots was highest in the outer part of the aerenchyma. The oxic zone of the sediment around roots was thin (ca 0.5 mm) which may indicate that very litte O2 is released from the roots. Recording around a fiddler crab (Uca sp.) burrow revealed, for comparison, that the oxic layer of the burrow wall was ca 1 mm thick. The penetration depth for O2 at the surface of this tropical mangrove sediment (1.5 to 3 mm) was similar to that measured in temperate coastal sediments.Sediments in mangrove swamps are in general 0 2 -depleted, with only a thin oxic surface layer (Kristensen et aL unpubl.). Mangroves therefore possess special adaptations for supplying O2 to the respiring root system. Hence many mangroves have negatively geotropic roots that emerge above the sediment surface, and these contain well-developed aerenchyma tissue. Pneumatophores (aerial roots), which are found for example in Avicennia and Sonneratia, have long been considered as organs responsible for gaseous exchange between the atmosphere and the internal tissues of mangroves (Goebel 1886). Other genera as Bruguiera and Lumnitzera have emerging kneelike bends on their lateral roots. In Rhizophora spp. the prop roots are responsible for gaseous exchange (Chapman 1976).Chapman (1976) gives a review of the relatively few experimental studies that have been made on the function of the pneumatophores. These studies were made more than 30 yr ago, often with manometric techniques and on cut and isolated root parts. Scholander et al. (1955) found that the O2 concentration in Rhizophora O Inter-Research/Printed in F. R. Germany prop roots approached that of the atmosphere (14 to 19 %) whereas the CO2 concentration was higher (4 to 6 %). The same authors also studied mechanisms for gas transport in the root systems of Avicennia.The purpose of the present study was to measure O2 concentrations around and inside intact pneumatophores and cable roots of Avicennia marina in the field. If significant amounts of O2 are released from the gastransporting roots, an oxic zone outside the roots would be expected. For comparison we measured O2 profiles around an air-filled burrow of a fiddler crab (Uca sp.).Materials and methods. The investigation was cdrried oul in January i387 iri the Ao Narri Bor I I I~I Igrove on the southeast coast of Phuket Island, southwest Thailand (Frith et al. 1976, Christensen 1978. This mangrove forest is ca 200 m wide at the study site and is bordered by a ca 500 m...
Live Skeletonerna costatum (diatom) cells labeled with I4C were added to the sediment surface in 10 cores containing intertidal sediment from Saanich Inlet, Vancouver Island, Canada. The water overlying the sediment in 5 cores was sparged with atmospheric air, whereas the other 5 cores were sparged with NZ. Release of I4CO2 started immediately in the oxic cores, reaching a maximum at Days 3 to 4 , whereas release in the anoxic cores was slower with a maximum after 6 to 9 d. DO1'C (dissolved organic carbon) release also exhibited high rates initially, but w~t h the highest release in the anoxic cores. Degradation to ' T O 2 and D0I4C could be described by 2 successive exponential decays representing 2 decomposable fractions. After 80 d, 58 and 42 % of the added label had been released as I4CO2, and 2 and 13% were released as D0I4C in the oxic and anoxic cores, respectively. The porewater contained only small amounts of I4CO2 and DO1"C. However, oxic cores showed the lowest concentrations, indicating faunally enhanced solute fluxes in these cores. Between 31 and 37% of the added label remained as P0I4C (particulate organic carbon) in the sediment after 80 d. Similar amounts of dissolved carbon ( ' 4 C 0 2 + D 0 1 T ) were lost from the added algal POC under oxic and anoxic conditions, but the larger amounts of D0I4C released from the sediment in the anoxic cores ind~cated a slower anaerobic mineralization of D0I4C.
F l u e s of dissolved s h c a t e (&ss Si) across the sediment-water interface were measured by incubating cores from the Bay of Fundy, Canada and the Dutch Wadden Sea The influence of infauna on diss S1 transport was estimated by inactivation of infauna wlth formalin poisoning and asphyxiation Release of diss SI In the Bay of Fundy ranged from 2 2 to 6 9 mm01 S1 m-2 d-l (temp 18 to 22 "C) before, and from 0 7 to 2 5 mm01 m-' d-l after fauna-inactivation In the Dutch Wadden Sea these data were -1 2 to 21 3 and -0 05 to 9 7 rnmol diss S1 m-' d-l (temp 13 5 to 20 'C) respectively Effect of formalin-poisomng and asphyxiation compared well With only one exception fluxes of diss S1 after inact~vation of sediment fauna approached withln a factor of 2, fluxes calculated from pore-water gradients by assuming that molecular diffus~on is the only transport mechanism for &ss S1 exchange
The influence of Spartina alterniflora detritus on exchange of nitrate + nitrite, ammonia, and phosphate between sediment and water was studied after burial of plant litter in a muddy intertidal sediment in Cobequid Bay, Bay of Fundy. The enriched area in general showed higher flux rates than the control area. Dissolved inorganic nitrogen (DIN) flux was dominated by ammonium. Ammonium was normally only released from the sediment and maximum release rates were 300 and 180 pm01 NH:-N m-2 h-' in the enriched and control plot, respectively. In contrast, both uptake and release of nitrate + nitrite by the sediment was found; maximum uptake rates were 43 and 25 and release rates 98 and 51 pm01 NO;+NO;-N m-2 h-' in the enriched and control plot, respectively. Very low phosphate fluxes were observed in both plots. Initial C/N and C/P ratios of the Spartina material were 24 : 1 and 117 : 1, respectively. The C/N ratio showed a n initial decrease followed by a slow increase. The C/P ratio showed the opposite pattern. Only 8.8 % of the N and 2.7 % of the P initially added to the sediment remained after 4 mo decomposition as Spartina material (> 1 mm). The loss of N and P was larger than the cumulated release of DIN and DIP to the overlying water; thus 33 % of the N and 72 % of the P lost from the particulate detritus was retained in the sediment or lost in other ways. Flux rates of nitrate and ammonium in the enriched area were the only variables correlated. Exchange rates of nutrients were not correlated with in situ temperature. However, laboratory incubations at 7.5 and 17.5 "C showed Qlo-values of up to 10, indicating that short term changes of temperature in the field, e.g. die1 variation, may be significant. The nutrient concentration of the water was low during the summer period and increasing during the fall.
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