Can the Morphological Quality Index (MQI) be used to determine the ecological status of lowland rivers?

Abstract

Stream assessment indices have become increasingly important in quantifying the overall status of river networks to define specific targets for restoration initiatives. Such an assessment is particularly needed in degraded environments, such as agricultural streams. Some of these evaluation tools, for instance the Qualitative Habitat Evaluation Index (QHEI), are resource intensive because they are field based. Indices that are less dependent on detailed field observations, such as the Morphological Quality Index (MQI), can provide a greater spatial coverage at a lower cost. The objectives of this study are to (1) verify whether a river's morphological quality, quantified using the MQI, can predict the fish habitat quality of a stream determined with the QHEI for eastern Canadian lowland streams, (2) compare the morphological quality, estimated solely from remotely sensed data (RMQI), to the standard MQI, (3) test whether a modified MQI (MMQI) is more appropriate than the original index for the eastern Canadian landscape when comparing with the QHEI fish habitat assessment, and (4) considering the near absence of dams in lowland eastern Canadian streams, compare an MQI where dam-related indicators are optional (MQI-OD) with the QHEI. The hydrogeomorphological and ecological conditions of 118 stream reaches, including 97 in agricultural areas, were assessed across Quebec and southern Ontario using the MQI and QHEI. Each stream was initially evaluated using remotely sensed data: 1-m LiDAR (Quebec) and 5-m DEMs (Ontario), historical aerial photography (1964–2010), and orthophotos. Field assessments were conducted to validate fish habitat and morphological data for both indices. A strong correlation was observed at the reach scale between the MQI and QHEI (r = 0.81) and MQI and RMQI (r = 0.95). Both modified MQI (MMQI and MQI-OD) showed stronger correlation than the standard MQI with the QHEI (r = 0.87), likely because the standard MQI slightly overestimates the current quality status at the habitat scale in the case of small agricultural catchments where main pressures are not always represented by artificial structures. However, because the standard MQI performs generally well in the study area, we suggest using it to ensure consistency and facilitate comparison with other regions. The results from this study demonstrate that the MQI can be used to provide an assessment of ecological (fish habitat) quality. In addition, our results indicate that a remote hydrogeomorphological assessment can be conducted to estimate the overall status of stream networks.