Phthalates and Nonylphenols in Roskilde Fjord

The two diffusion curves and the two diffusion + sedimentation curvesare coincident, which implies that the numerical sediment model is consideredto be properly validated.In Figure 38 the validated numerical model is calibrated with the experimentalsediment concentration profile sampled 130 m from theWWTP discharge, cf. section 5.2.3.The model simulations uses the following parametersS = 2.5 mm ⋅ year -1k 1N = 2 ⋅ 10 -5 sec -1k 1D = 8 ⋅ 10 -6 sec -1 (below a depth of 5cm)K d = 10000 litre water ⋅ (kg dm) -1Total concentration in sediment[ng DEHP/g D.W.]350300250200150100500ExperimentalNumerical model(diff+sed+degr)Steady-State(diff+sed+degr)0 0,05 0,1 0,15 0,2 0,25Depth in sediment [m]Figure 38 Experimental sediment core concentrations at distance 130 from discharge,numerical sediment model (Equation 23) and steady-state solution(Equation 28).The curve in the upper 5 cm decreases according to the typical transportdegradationsituation with a constant degradation rate. The high degradationrate indicates aerobic conditions. This rate is the same order ofmagnitude as the aerobic rate found in the WWTP although the biomassand oxygen concentrations are considerably lower in the sediment.Deeper down in the sediment the profile flattens out and decreases withonly 10 % in 5 cm. The oxygen concentration is probably negligible. Adegradation rate of 8 ⋅ 10 -6 sec -1 points to either anoxic or anaerobic conditions.The periodic fluctuations from 12 to 20 cm are probably experimentalnoise but bioturbation by lugworm (Arenicola marina) could produce azone in depths around 10 to 20 cm corresponding to the experimentallyfound. As mentioned previously circumstances that disconfirm this suggestionare the hardness of the sediment core.The interpretation of the experimental data leads to two cases; The fluctuationsbelow approximately 12 cm are noise and the concentrations arezero. This gives a sedimentation rate of 2.5 mm ⋅ year -1 . Alternatively the75