Science of the Total Environment 657 (2019) 1419–1431 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Organic matter distribution, composition and its possible fate in the Chilean North-Patagonian estuarine system Humberto E. González a,b,⁎, Jorge Nimptsch a, Ricardo Giesecke a,b,NelsonSilvac a Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile b Centro FONDAP de Investigación de Ecosistemas Marinos de Altas Latitudes (IDEAL), Universidad Austral de Chile, Valdivia, Chile c Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile HIGHLIGHTS GRAPHICAL ABSTRACT • The distribution, composition and transport of both DOC and POC, were studied across a terrestrial-marine transition system. • A fDOM land-ocean gradient from humic-C1 terrigenous-derived to tyrosine-like C3 autochthonous fDOM was observed. • The UVC to UVA humic ratio was correlated with salinity, highlighting the high variability in fDOM chemical characteristics. • Climate warming and anthropogenic practices boost the mobilization of terrestrial carbon pools. article info abstract Article history: The distribution, composition, and transport of both dissolved and particulate organic carbon (DOC and POC) Received 25 June 2018 were studied across a terrestrial - marine transition system in the Chilean North-Patagonia (41°S). Received in revised form 26 November 2018 At the land-fjord boundary we reported: (i) high concentrations of both silicic acid (up to 100 μM) and integrated Accepted 29 November 2018 − chlorophyll a (62 mg m 2), (ii) dominance of nanophytoplankton (63%), humic-, terrigenous-derived, and Available online 04 December 2018 protein-like DOC (19 and 36%, respectively), and (iii) a shallow photic zone (12 m depth). In contrast, the μ Editor: Daniel Wunderlin estuarine-ocean boundary was characterized by (i) high concentrations of nitrate and phosphate (20 and 2 M respectively) and low chlorophyll a concentration (11 mg m−2), (ii) dominance of microphytoplankton (59%) Keywords: and tyrosine-like C3 autochthonous DOC (34%), and (iii) a deep photic zone (29 m depth). North-Patagonia Fjord Allochthonous DOC input at the fjord head and the ocean accounted for 60% and 10% of total DOC, respectively. DOC The input of humic-like substances was enhanced by intense forestry and agriculture activity around the Puelo POC River watershed, contributing from 50% to 14% of total DOC along the fjord - ocean transect. In contrast, autoch- Fluorescent DOM thonous tyrosine-like substances increased from 25% to 41% of total DOC, highlighting the role of bacterial metab- Organic matter olism in regulating DOM composition. The high correlation (R2 = 0.7) between the UVC-humic:UVA-humic ratio and salinity suggest that processes associated to freshwater input impinged on the DOC chemical characteristics and origins. Overall, our observations support the view that climate warming (freshwater input) and ⁎ Corresponding author at: Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile. E-mail address: [email protected] (H.E. González). https://doi.org/10.1016/j.scitotenv.2018.11.445 0048-9697/© 2018 Elsevier B.V. All rights reserved. 1420 H.E. González et al. / Science of the Total Environment 657 (2019) 1419–1431 anthropogenic practices (aquaculture) boost the mobilization of terrestrial carbon pools and their intrusion into coastal ocean areas, a process that should be given more attention in climate prediction models. © 2018 Elsevier B.V. All rights reserved. 1. Introduction S) POC flux is slightly lower (234 mgC m−2 d−1), albeit representing 65% of net primary production (González et al., 2013). Estuarine systems are extremely complex, with high spatial and The study area includes a strong gradient in both freshwater input temporal variability. The physical and chemical characteristics of total and its TOM load from the terrestrial forest watershed to oceanic wa- organic matter (TOM), either dissolved (DOM) or particulate (POM), ters, starting from RF into which two major rivers (Petrohué and depend on the interplay among multi-factorial processes of production, Puelo) discharge freshwater at a combined rate of 500 to 1000 m3 s−1, utilization, reactivity, and export of organic matter along a continuous with a minimum in February and a maximum in July. However, a de- land-ocean gradient. For example, in aquatic systems DOM affects creasing trend in the terrestrial signal associated with reduced precipi- light attenuation, metal speciation and bioavailability (possible nutrient tation and river discharge has been reported over the last 400 years in sources) for the microbial community (Cory and McKnight, 2005). Estu- northern Patagonia (Lara et al., 2008; Rebolledo et al., 2015). arine productivity is supported by total allochthonous organic matter When and where rivers behave as active reactors versus passive (OMal) from various sources but is most likely mainly composed of pipes for DOM stands as a major knowledge gap in land-ocean contin- plant litter, given that the northern Patagonian systems are surrounded uum biogeochemistry (Casas-Ruiz et al., 2017). In a previous study by forests and agricultural land which most likely contribute a signifi- (González et al., 2010) we demonstrated that freshwater discharge, nu- cant amount of refractory TOM (Raymond and Bauer, 2001). In estua- trient availability, and solar radiation strongly affect the structure and rine systems, the upper freshwater plume seems to be mainly loaded functioning of the pelagic community of the RF and Inner Sea of Chiloé with POMal (Vargas et al., 2011), while the underlying saline layer con- (ISCh). Said analysis lacked the DOC components (concentration, com- tains autochthonous organic matter (POMau) which most likely origi- position, and either autochthonous or allochthonous origin), and this nates from microbial degradation and phytoplankton exudates contribution aimed to fill that knowledge gap regarding the carbon (Canuel et al., 1995). Thus, in a terrestrial to marine gradient OMal and pools in the northern Chilean Patagonia fjords. OMau might predominate at the heads (Silva and Prego, 2002)and We aimed to evaluate the spatial input of autochthonous and alloch- mouths (Singh et al., 2010; Martineau et al., 2004) of the fjords, respec- thonous OM and their biochemical composition, accounting for the con- tively. It is possible that the relative availability and utilization of OMal nectivity across ecosystems (terrestrial-estuarine-marine) and the versus OMau by bacterioplankton would follow the same spatial gradi- interactions within compartments (pelagic-benthic). The main objec- ent, enabling microbial communities to exploit energy that escapes tives were to establish, in a transect from the land to the ocean, (i) the from upstream ecosystems. Furthermore, a fraction of the OMal utilized physical and chemical characteristics of the water (temperature, salin- by microorganisms can be mobilized to invertebrates and vertebrates ity, dissolved oxygen, and macronutrients), as well as UV and PAR through the pelagic and benthic food webs (Lusseau and Wing, 2006; light penetration into the water column, (ii) chlorophyll-a size- McLeod and Wing, 2007; McLeod and Wing, 2009; Vargas et al., fractions, bacterioplankton abundance, and microplankton distribution 2011). This organic matter flow from lower to higher trophic levels in- and composition, and (iii) concentrations of DOM - POM and the origin creases the overall energy utilization at the ecosystem level (Battin of the OM (OMal versus OMau). The analysis was complemented by et al., 2008) and accounts for up to one-fifth of estuarine metabolism identifying a specific fluorescent dissolved components and a stable iso- (Smith and Hollibaugh, 1993). topic signal, both measured along a transect from the Puelo and Estuarine systems are usually in a heterotrophic state i.e. net pri- Petrohué river mouths in RF to the coastal marine system of the ISCh. mary production is lower than community respiration (PPn b CR) (Dale and Prego, 2005; Karlsson et al., 2007; Gupta et al., 2009), suggest- 1.1. Materials and methods ing that they might also rely on OMal. The traditional view of the self- sustainability of aquatic systems has therefore been challenged and 1.1.1. Study area and physico-chemical conditions the input coupled to the important contribution of OMal to benthic Sampling took place from July 1 to 20, 2011, aboard the Chilean Navy and pelagic trophic webs has now been generally recognized (Pantoja oceanographic vessel AGS 61 “Cabo de Hornos”. The study area included et al., 2010), including implications for the metabolic balance of plank- RF (41°38′S), an east-west orientation with a total length and width of ton communities. This terrestrial input of OMal may include a mixture 55 and 2.8 km, respectively, and the ISCh (from 42 to 44°S). A transect of labile, semi-labile, and refractory matter, where components of the with 19 sampling stations traversed from the head of RF (Stn 7) to the watershed, such as freshwater discharge, tidal currents, vegetation, coastal oceanic area of the Guafo Entrance (Stn 50) (Fig. 1). Water sam- river morphology, water residence time, and the chemical and physical ples were collected at these stations with a bottle-rosette system with characteristics of TOM itself play a major role in making DOM available the purpose of determining DOC