Benthic fluxes refer to the exchange rates of nutrients and other compounds between the water column and the sediment bed in aquatic ecosystems. Their quantification contributes to our understanding of aquatic ecosystem functioning. Near-bed hydrodynamics plays an important role at the sediment-water interface, especially in shallow lakes, but it is poorly considered by traditional measuring techniques of flux quantification, such as sediment incubations. Thus, alternative sampling techniques are needed to characterize key benthic fluxes under hydrodynamic conditions. This study aimed to evaluate the performance of two promising methods: relaxed eddy accumulation (REA) and mass transfer coefficient (MTC). We applied them in a hyper-eutrophic shallow lake to measure the fluxes of ammonium, phosphate, iron, and manganese ions. For the first time, REA revealed hourly nutrient flux variations, indicating a strong lake biogeochemical dynamics at short time-scales. Daily average fluxes are of similar orders of magnitude for REA and MTC for ammonium (24 and 42 mmol m d), manganese (1.0 and 0.8), and iron (0.8 and 0.7) ions. They are one order of magnitude higher than fluxes estimated from sediment incubations, due to the difficulty in reproducing oxygen and hydrodynamic conditions in the laboratory. Although the accuracy of both techniques needs to be improved, the results revealed their potential: REA follows the short-term biogeochemical dynamics of sediments, while MTC could be widely used for lake monitoring because of its simpler implementation.

中文翻译：

---

评估浅湖湍流底栖通量的两种非侵入性测量技术


底栖通量是指水生生态系统中水柱和沉积床之间营养物质和其他化合物的交换率。它们的量化有助于我们了解水生生态系统的功能。近床流体动力学在沉积物-水界面上发挥着重要作用，特别是在浅湖中，但传统的通量定量测量技术（例如沉积物孵化）很少考虑这一点。因此，需要替代采样技术来表征水动力条件下的关键底栖通量。本研究旨在评估两种有前途的方法的性能：松弛涡流累积（REA）和传质系数（MTC）。我们将它们应用在一个超富营养化的浅湖中来测量铵离子、磷酸盐、铁离子和锰离子的通量。 REA 首次揭示了每小时的养分通量变化，表明在短时间内存在强烈的湖泊生物地球化学动态。对于铵（24 和 42 mmol m d）、锰（1.0 和 0.8）和铁（0.8 和 0.7）离子，REA 和 MTC 的日平均通量具有相似的数量级。由于实验室中难以再现氧气和水动力条件，它们比沉积物孵化估计的通量高一个数量级。尽管这两种技术的准确性还有待提高，但结果揭示了它们的潜力：REA 遵循沉积物的短期生物地球化学动力学，而 MTC 由于其更简单的实施而可以广泛用于湖泊监测。