Influencia de la descarga de nutrientes y gases de efecto invernadero (óxido nitroso y metano) de la desembocadura del río Itata a la zona costera.
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Date
2025
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Universidad de Concepción
Abstract
Las cuencas hidrográficas son rutas clave para la transferencia de nutrientes, gases de efecto invernadero (GEI) y material particulado hacia las zonas costeras. Estos flujos están modulados por factores geomorfológicos, climáticos, hidrográficos y biogeoquímicos, que se ven alterados por procesos antropogénicos, afectando la composición química y la calidad del agua. La cuenca del río Itata, de régimen pluvionival, presenta máximas descargas invernales con variaciones interanuales influenciadas por el Niño Oscilación del Sur (ENSO); sin embargo, ha sido impactada por una sequía prolongada desde 2010 y por cambios en el uso de suelo hacia monocultivos desde los años 2000.
El estudio analiza las variaciones estacionales y decadales de la descarga de nutrientes (NO₃⁻, NO₂⁻, PO₄³⁻, Si (OH)₄), sólidos disueltos totales (SDT) y GEI (N₂O y CH₄), evaluando el papel de factores climáticos y antrópicos. Bajo la hipótesis de que estas descargas están predominantemente controladas por factores climáticos estacionales y decadales, por encima de los impactos antrópicos como el cambio de uso de suelo, se propone que las exportaciones de GEI y SDT son mayores en invierno debido a incrementos en el caudal y la escorrentía, pero disminuyen a largo plazo debido a la sequía y la creciente demanda hídrica.
El objetivo general fue analizar la variación estacional y decadal en la descarga de nutrientes, GEI y otras variables ambientales (temperatura, salinidad, SDT), identificando los factores responsables de los patrones observados. Para ello, se realizó un muestreo estacional en el estuario interno del río Itata (desembocadura), complementado con datos históricos de acceso libre recopilados durante las últimas dos décadas.
Los ciclos estacionales de nutrientes y GEI en la desembocadura del río Itata mostraron variaciones significativas influenciadas por la precipitación y el caudal. El NO₃⁻ y Si (OH)₄ alcanzaron máximos en invierno, con descargas de 600 g/s y 3000 g/s, respectivamente, mientras que el PO₄³⁻ presentó un incremento en primavera (0,45 mg/L). El N₂O exhibió una marcada estacionalidad con máximos invernales (14,722 nM), mientras que el CH₄ mostró menor variabilidad, con máximos en invierno (106,2 nM). Estas tendencias reflejan la interacción entre procesos hidrológicos y biogeoquímicos, junto con cambios antropogénicos como el uso de fertilizantes fosfatados.
Las series de tiempo indican una disminución en las descargas de nutrientes en el tiempo, excepto para el PO₄³⁻ y el SDT. Las correlaciones entre el caudal, nutrientes y GEI destacan la influencia del régimen hidrológico en la dinámica biogeoquímica. El caudal mostró relaciones positivas con el SDT y Si (OH)₄, pero negativas con NO₃⁻ y PO₄³⁻, indicando un desfasaje entre su exportación y las concentraciones e indicando diferentes procesos de mineralización, intemperización y escorrentía. El N₂O presentó correlaciones positivas con NO₃⁻ y NO₂⁻, reflejando su dependencia de procesos de ciclo del nitrógeno, mientras que el CH₄ no mostró correlaciones con otras variables, excepto el SDT.
El análisis de uso de suelo revela un aumento de las plantaciones forestales (+10%) a costa de la disminución de terrenos agrícolas y vegetación natural en zonas bajas y medias de la cuenca, áreas críticas para el aporte de nutrientes a cuerpos de agua. Aunque los cambios de uso de suelo entre 2001 y 2021 no fueron estadísticamente significativos y se requiere de un análisis de décadas anteriores, se relacionan con cambios decadales significativos en nutrientes y GEI, caudal y precipitación, subrayando el impacto potencial de las actividades humanas en los ciclos biogeoquímicos. Estos hallazgos subrayan la interacción entre procesos climáticos y antrópicos en la dinámica biogeoquímica del río Itata, destacando la importancia de estrategias integradas de manejo de cuencas para mitigar los impactos en la calidad de los ecosistemas costeros.
Watersheds are key routes for the transfer of nutrients, greenhouse gases (GHG) and particulate matter to coastal areas. These flows are modulated by geomorphological, climatic, hydrographic and biogeochemical factors, which are altered by anthropogenic processes, affecting the chemical composition and water quality. The Itata river basin, with a pluvial-nival regime, presents maximum winter discharges and interannual discharges influenced by El Niño-Southern Oscillation (ENSO); However, it has been impacted by a prolonged drought since 2010 and by changes in land use towards monocultures since the 2000s. The study analyses the seasonal and decadal variations in the discharge of nutrients (NO₃⁻, NO₂⁻, PO₄³⁻, Si (OH)₄), total dissolved solids (TDS) and GHG (N₂O and CH₄), evaluating the role of climatic and anthropogenic factors. Under the hypothesis that these discharges are predominantly controlled by seasonal and decadal climatic factors, above anthropogenic impacts, such as land use change, it is proposed that exports are higher in winter due to increases in flow and runoff but decrease in the long term due to drought and increasing water demand. The general objective was to analyse the seasonal and decadal variation in the discharge of nutrients, GHG and other environmental variables (temperature, salinity, TDS), identifying the factors responsible for the observed patterns. To this end, seasonal sampling was carried out in the internal estuary of the Itata River, complemented by open-access historical data collected during the last two decades. The seasonal cycles of nutrients and GHG at the mouth of the Itata River showed significant variations influenced by precipitation and flow. NO₃⁻ and Si(OH)₄ reached maximums in winter, with discharges of 600 g/s and 3000 g/s, respectively, while PO₄³⁻ showed an increase in spring (0.45 mg/L). N₂O exhibited a marked seasonality with winter maximums (0.08 mg/L), while CH₄ showed less variability, except for an increase in winter. These trends reflect the interaction between hydrological and biogeochemical processes, together with anthropogenic changes such as the use of phosphatic fertilizers. Time series indicate a decrease in the discharges of these compounds over time, except for PO₄³⁻ and TDS. Correlations between flow, nutrients and GHG highlight the influence of the hydrological regime on biogeochemical dynamics. Flow showed positive relationships with TDS and Si(OH)₄, but negative relationships with NO₃⁻ and PO₄³⁻, indicating a lag between their export and concentrations and indicating different mineralization, weathering and runoff processes. N₂O showed positive correlations with NO₃⁻ and NO₂⁻, reflecting its dependence on nitrogen cycle processes, while CH₄ had less interaction, except for a significant negative compensation with the flow rate and TDS. The land use analysis reveals an increase in forest plantations (+10%) at the expense of a decrease in agricultural land and natural vegetation in low and middle areas of the basin, critical areas for the contribution of nutrients to water bodies. Although land use changes between 2001 and 2021 were not statistically significant and an analysis of previous decades is required, they are related to significant decadal changes in nutrients and GHG, flow and precipitation, highlighting the potential impact of human activities on biogeochemical cycles. These findings underline the interaction between climatic and anthropogenic processes in the biogeochemical dynamics of the Itata River, highlighting the importance of integrated watershed management strategies to mitigate impacts on the quality of coastal ecosystems.
Watersheds are key routes for the transfer of nutrients, greenhouse gases (GHG) and particulate matter to coastal areas. These flows are modulated by geomorphological, climatic, hydrographic and biogeochemical factors, which are altered by anthropogenic processes, affecting the chemical composition and water quality. The Itata river basin, with a pluvial-nival regime, presents maximum winter discharges and interannual discharges influenced by El Niño-Southern Oscillation (ENSO); However, it has been impacted by a prolonged drought since 2010 and by changes in land use towards monocultures since the 2000s. The study analyses the seasonal and decadal variations in the discharge of nutrients (NO₃⁻, NO₂⁻, PO₄³⁻, Si (OH)₄), total dissolved solids (TDS) and GHG (N₂O and CH₄), evaluating the role of climatic and anthropogenic factors. Under the hypothesis that these discharges are predominantly controlled by seasonal and decadal climatic factors, above anthropogenic impacts, such as land use change, it is proposed that exports are higher in winter due to increases in flow and runoff but decrease in the long term due to drought and increasing water demand. The general objective was to analyse the seasonal and decadal variation in the discharge of nutrients, GHG and other environmental variables (temperature, salinity, TDS), identifying the factors responsible for the observed patterns. To this end, seasonal sampling was carried out in the internal estuary of the Itata River, complemented by open-access historical data collected during the last two decades. The seasonal cycles of nutrients and GHG at the mouth of the Itata River showed significant variations influenced by precipitation and flow. NO₃⁻ and Si(OH)₄ reached maximums in winter, with discharges of 600 g/s and 3000 g/s, respectively, while PO₄³⁻ showed an increase in spring (0.45 mg/L). N₂O exhibited a marked seasonality with winter maximums (0.08 mg/L), while CH₄ showed less variability, except for an increase in winter. These trends reflect the interaction between hydrological and biogeochemical processes, together with anthropogenic changes such as the use of phosphatic fertilizers. Time series indicate a decrease in the discharges of these compounds over time, except for PO₄³⁻ and TDS. Correlations between flow, nutrients and GHG highlight the influence of the hydrological regime on biogeochemical dynamics. Flow showed positive relationships with TDS and Si(OH)₄, but negative relationships with NO₃⁻ and PO₄³⁻, indicating a lag between their export and concentrations and indicating different mineralization, weathering and runoff processes. N₂O showed positive correlations with NO₃⁻ and NO₂⁻, reflecting its dependence on nitrogen cycle processes, while CH₄ had less interaction, except for a significant negative compensation with the flow rate and TDS. The land use analysis reveals an increase in forest plantations (+10%) at the expense of a decrease in agricultural land and natural vegetation in low and middle areas of the basin, critical areas for the contribution of nutrients to water bodies. Although land use changes between 2001 and 2021 were not statistically significant and an analysis of previous decades is required, they are related to significant decadal changes in nutrients and GHG, flow and precipitation, highlighting the potential impact of human activities on biogeochemical cycles. These findings underline the interaction between climatic and anthropogenic processes in the biogeochemical dynamics of the Itata River, highlighting the importance of integrated watershed management strategies to mitigate impacts on the quality of coastal ecosystems.
Description
Tesis presentada para optar al título de Biólogo/a Marino/a.
Keywords
Cuencas hidrográficas, Efecto invernadero, Costas, Sequías