Degradation capability of the coastal environment adjacent to the Itata River in central Chile (36.5° S)

Abstract. The response of the coastal ocean influenced by both river discharges and inputs of photosynthetically derived organic carbon product of upwelling, was evaluated by estimating rates of microbial hydrolysis of macromolecules with the goal of estimating the potential degradation capability of the coastal ecosystem off central Chile. Extracellular enzymatic activity (EEA) in seawater was dominated by aminopeptidase activity on substrate L-leucine-4-methyl-7-coumarinylamide (MCA-leu) (1.2 to 182 nmol l⁻¹ h⁻¹) followed by 4-methylumbelliferyl-ß-D-glucoside (MUF-glu) (0.08–61 nmol l⁻¹ h⁻¹) and 4-methylumbelliferyl-ß-D-cellobiose (MUF-cel) (0.15–7 nmol l⁻¹ h⁻¹), with the highest rates measured during spring-summer. In riverine waters, extracellular enzymatic hydrolysis remained within the range of 45 to 131 nmol l⁻¹ h⁻¹ for MCA-leu and ca. 20 nmol l⁻¹ h⁻¹ for glucosidic substrates, year-round. Contrary to the EEA observed for the marine water column, surface sediment extracellular enzymatic hydrolysis of MCA-leu (0.04 to 6.13 nmol g⁻¹ dw h⁻¹) was in the same order of magnitude as the rates observed for MUF-cel (0.004 to 5.1 nmol g⁻¹ dw h⁻¹) and MUF-glu (0.007 to 10.5 nmol g⁻¹ dw h⁻¹). Moreover, hydrolysis in sediments was characterized by higher rates during winter compared with spring-summer in the coastal and estuarine zone. The five years of data allowed us to evaluate the potential capability of microbial processing of organic carbon in the coastal area adjacent to the Itata river discharge where the increase in primary production in the productive seasons is accompanied by the increase in hydrolysis of macromolecules.