Environmental effects of maintenance dredging works in a highly modified estuary: A short-term approach

Dredging operations present significant environmental risks in estuaries, which can potentially result in alterations to the physicochemical parameters of water and sediment, as well as the biota of the ecosystem. The assessment of environmental impacts in estuaries is challenging due to the dynamic nature of these systems. Furthermore, the inconsistent findings in studies examining these impacts emphasize the necessity of a case-by-case approach for evaluating the environmental consequences. It is crucial to employ various temporal and methodological approaches to evaluate environmental impacts, draw valid conclusions, and propose suitable management measures. However, there is a limited availability of studies that investigate short-term ecological processes. Therefore, the objective of this study is to characterize the short-term responses of physicochemical characteristics in the water column and sediment, particularly focusing on the content of heavy metals, as well as the impacts on community structure. Additionally, the study aims to assess the suitability of stable isotope analysis in two species as bioindicators of nutrient enrichment. The findings of this research indicated no discernible impact from dredging activities on any of the evaluated physicochemical parameters in the water column, sediment, or biological communities. However, the nitrogen stable isotope signals of the goby Pomatoschistus sp. exhibited an effect associated with an increase in certain nutrient levels suggesting its suitability as a bioindicator of nutrient enrichment in human activities. Interestingly, a flood event prior to the latest survey had a more significant influence on all measured parameters compared to the dredging operation. Changes in salinity and other factors related to freshwater management in the Guadalquivir estuary may have a more substantial impact on soft-bottom communities than other pressures. Consequently, management efforts should be directed towards mitigating these pressures to foster more stable communities.