08 Nov Researchers from the SECOS Millennium Institute demonstrate the need to know the different land uses in the watersheds of Chiloé and their impacts on the coastal zone and aquaculture.

The study contrasted the effects of the discharge of two rivers that flow into the inland sea of Chiloé. One in the north of the island, subjected to intense anthropogenic activity, and the other in the extreme south of the island, which stands out for its unintensified soil and significant native forest cover. The results demonstrate the importance of generating more knowledge about the influence of rivers on the sea, especially for aquaculture planning. The study of the influence of rivers on the sea is an area of great relevance for coastal zones. Human activities have generated multiple changes in the soils that drain into the watersheds, with consequences on the physical-chemical properties of the coastal zone where these waters reach, and which are just beginning to be known in detail, especially their impact on activities such as aquaculture and artisanal fishing. In this context, a study by the Millennium Institute in Coastal Socio-Ecology (SECOS) showed that nutrient flows to the coastal zone are greater in watersheds where agricultural use dominates, while those watersheds where the degree of human intervention is lower, and where native forests dominate, discharge large quantities of colored dissolved organic matter (CDOM). This organic matter, upon reaching the sea, can generate conditions of high levels of carbon dioxide (pCO2) and lower carbonate concentrations, which are necessary for mollusks to build their calcareous structures, or “shells”. The research also emphasizes the importance of planning aquaculture activities, especially miticulture. The study led by Elizabeth Curra-Sánchez, a student of the Doctoral Program in Environmental Sciences at the University of Concepción, compared two watersheds that reach the sea in Chiloé: the Colu River, to the north near Quemchi, and the estuary of the Yaldad River, which originates in Tantauco Park, at the southern tip of the island. The former stands out for the anthropic activities that take place in its surroundings, such as agriculture, which dominates 38% of the watershed, while the latter is located in a watershed with 82% native forest and in an area little intervened by human activities. “Watersheds are large catchment areas for rainwater that washes soils and carries sediments, nutrients and organic matter to the coastal zone,” says Curra-Sánchez. “In recent years, land use change in watersheds represents a global environmental problem, not only because of deforestation and loss of biodiversity, but also because of all the other changes, processes and activities that take place in the watershed, such as agriculture or urbanization,” she adds. “In areas where the flow of terrestrial material is very large, as is the case of the Yaldad River, although they provide a lot of detritus and organic matter that can be used as nutrients by filtering organisms such as plovers, these can generate water conditions that are corrosive for this type of organisms, which build calcium carbonate shells, which can cause them to dissolve or make it much more difficult for them to build these structures,” explains Elizabeth Curra-Sánchez, lead author of the publication. In this way, the study looked at the chemical characteristics of the rivers and the implications of certain variables, such as nutrients, in the sea. This research was conducted under the guidance of Dr. Cristian A. Vargas of the Laboratory of Coastal Ecosystems and Global Environmental Change (ECCALab) of the Faculty of Environmental Sciences of the University of Concepción, and researcher of the SECOS Millennium Institute and the Millennium Institute of Oceanography (IMO). “This type of results is very useful for the spatial planning of aquaculture and its governance, since it provides information that can be used to think in advance about which sectors are more suitable than others for planting seeds”, explains Dr. Vargas.   Thus, the results of this exploratory study generate the need to know more details about how changes in land use on the Isla Grande de Chiloé could affect the chemistry of seawater in the coastal zone, through runoff and freshwater discharges from rivers. In addition, it is especially important to understand how these changes could have uncertain consequences for marine organisms and ecosystem services in the coastal zone, where aquaculture and artisanal fisheries are developed, even more so in the context of climate change and ocean acidification. “Currently, apart from measuring what the health authority asks you to measure, we know little about other chemical parameters of seawater and of relevance for ecosystem services, such as aquaculture and fishing. This is one of the first studies to be carried out in Chile, however, the rivers are all very different from each other, so it is necessary to better understand the physical-chemical characteristics of freshwater discharges that reach the sea, before making more concrete recommendations on marine spatial planning,” explains Bernardo Broitman, researcher at SECOS, UPWELL Millennium Nucleus and academic at the Universidad Adolfo Ibáñez.   “The research gives us an answer to how the type of land use upstream has an impact on water quality in the coastal zone, particularly in certain elements that negatively impact shellfish aquaculture. This, despite the fact that current regulations do not ask you to measure these types of parameters, such as pH, CO2, or carbonate content in seawater,” adds the ecologist. Researchers from the Pontificia Universidad Católica de Valparaíso, Universidad Austral de Chile, Universidad Católica de la Santísima Concepción, Universidad del Biobío, Universidad Adolfo Ibáñez, and the EULA Center of Universidad de Concepción also collaborated in the study. .