Estuaries are complex systems where environmental fluctuations occur over distinct timescales due to local meteorological and large-scale climatic factors. Consequently, studies with low temporal resolution and taxonomic coverage may fail to detect isotopic variations in basal sources, providing biased interpretations of isotope mixing models. We investigated the seasonal and El Nino Southern Oscillation (ENSO)-driven interannual variations in δ13C, δ15N and C:N values among distinct basal sources and their implications for mixing models interpretation in a subtropical estuary. δ13C variations among sources differed in their magnitude and timescales, being large enough to confound source-specific values. Macroalgae and POM δ13C varied seasonally, whereas ENSO effects prevailed for C3 and C4 salt marsh plants, highlighting the contrasting influence of local versus remote environmental drivers on short- and long-lived primary producers, respectively. Peaks of δ15N were detected for all sources during short-term anthropogenic nutrient inputs. Isotope mixing model comparisons showed that overlooking isotopic variations in basal sources under distinct ENSO conditions can cause misinterpretation of local trophic interactions and nutrient cycling. The present study contributes to design appropriate sampling delineations in highly variable aquatic environments, emphasizing the importance of comprehensive, long-term monitoring of estuarine primary producers to encompass environmental drivers of stable isotopic variations.

中文翻译：

---

季节性和厄尔尼诺南方涛动导致河口初级生产者同位素和元素模式的变化：对生态研究的影响

河口是复杂的系统，由于当地气象和大尺度气候因素，环境波动会在不同的时间尺度上发生。因此，具有低时间分辨率和分类学覆盖率的研究可能无法检测基础源中的同位素变化，从而提供对同位素混合模型的有偏见的解释。我们研究了季节性和厄尔尼诺南方涛动 (ENSO) 驱动的 δ13C、δ15N 和 C:N 值在不同基础源中的年际变化及其对亚热带河口混合模型解释的影响。来源之间的 δ13C 变化在幅度和时间尺度上不同，大到足以混淆特定来源的值。大型藻类和 POM δ13C 随季节变化，而 ENSO 效应对 C3 和 C4 盐沼植物占优势，强调本地和偏远环境驱动因素分别对短期和长期初级生产者的不同影响。在短期人为营养输入期间，所有来源都检测到 δ15N 的峰值。同位素混合模型比较表明，忽略不同 ENSO 条件下基础源的同位素变化会导致对局部营养相互作用和养分循环的误解。本研究有助于在高度可变的水生环境中设计适当的采样划定，强调对河口初级生产者进行全面、长期监测以涵盖稳定同位素变化的环境驱动因素的重要性。在短期人为营养输入期间，所有来源都检测到 δ15N 的峰值。同位素混合模型比较表明，忽略不同 ENSO 条件下基础源的同位素变化会导致对局部营养相互作用和养分循环的误解。本研究有助于在高度可变的水生环境中设计适当的采样划定，强调对河口初级生产者进行全面、长期监测以涵盖稳定同位素变化的环境驱动因素的重要性。在短期人为营养输入期间，所有来源都检测到 δ15N 的峰值。同位素混合模型比较表明，忽略不同 ENSO 条件下基础源的同位素变化会导致对局部营养相互作用和养分循环的误解。本研究有助于在高度可变的水生环境中设计适当的采样划定，强调对河口初级生产者进行全面、长期监测以涵盖稳定同位素变化的环境驱动因素的重要性。