Here, coincident sediment-water measurements of Excitation emission matrix (EEM), dissolved inorganic nitrogen, urea, free amino acid (DFAA) and combined amino acid (DCAA), and sediment enzyme activities acquired in St. Lucie Watershed were used to evaluate aquatic quality.
Results/Conclusions
Either in sediment or water, concentrations of DCAA were much higher than DFAA. Water dissolved organic nitrogen (DON) was the dominant dissolved N form. Sum of urea and amino acids accounted for ~20% of water DON, suggesting high bioavailability of water DON. Four fluorescence compounds were identified, three in humic acid and one in protein form. Humic acid form constitute ~96% of total fluorescence, indicating the terrestrial origin of aquatic dissolved organic matter and aquatic low biodegradation activates. Composition of total hydrolyzed amino acid (THAA) was dissimilar between water and sediment. Sediment NH4-N concentration associated closely with 14 water DFAA. Relative lower degradation index of water suggesting that sediment is the source of water amino acids through denitrification process. Composition of amino acids, and urea concentrations in water and sediment varied with land use. A five factor model, consisting of sediment DON, NH4-N, acid phosphatase (AP), leucine aminopeptidase (LAP), C1 and C2, can effectively represent the variations of water NH4-N (55%), NO3-N (77%), DOC (83%), DON (64%), DFAA ( > 88%), DCAA (62-96%), fluorescence compounds (35-55%) and indexes (98%). It becomes reliable that including urea and amino acids in monitoring routine and more accurate to evaluate water quality. We suggest future studies should be conducted in situ across larger environmental gradients to incorporate real world complexity and increase generality of the model.