Influence of Spartina detritus enrichment on exchange of nutrients between sediment and water in an intertidal area of Bay of Fundy

Abstract

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.