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The bioturbation activity of macroinvertebrates can affect the level of water exchange across the sediment–water interface. The impact of tubificid worm with different densities on the vertical water exchange at the sediment–water interface was investigated based on laboratory flume experiments. Vertical water fluxes, as well as physiochemical parameters, were measured at seven-day intervals, and the maximum penetration depths were obtained by dye injection before and after the tubificid bioturbation experiment, respectively. The bioturbation effects can be summarized in two aspects: (1) when the density was less than (or equal to) 20 individual/10 cm2, the volume of vertical water exchange positively correlated with the tubificid bioturbation. Once the density exceeded (or equaled) 25 individual/10 cm2, the vertical water flux decreased with increasing tubificid bioturbation. After 14 to 21 days, a negative correlation was identified between the bioturbation and the vertical water flux under all biological densities. (2) The maximum depth that the surface water can penetrate the sediment increased with increasing tubificid density. These results revealed that the vertical water was closely related to the biological density. The study has certain reference significance to understanding the spatiotemporal heterogeneity of hyporheic water exchange on a local scale.

The groundwater-dependent ecosystem in the Gnangara region is confronted with great threats due to the decline in groundwater level since the 1970s. The aim of this study is to apply multiple trend analysis methods at 351 monitoring bores to detect the trends in groundwater level using spatial, temporal and Hydrograph Analysis: Rainfall and Time Trend models, which were applied to evaluate the impacts of rainfall on the groundwater level in the Gnangara region, Western Australia. In the period of 1977–2017, the groundwater level decreased from the Gnangara’s edge to the central-north area, with a maximum trend magnitude of −0.28 m/year. The groundwater level in 1998–2017 exhibited an increasing trend in December–March and a decreasing trend in April–November with the exception of September when compared to 1978–1997. The rainfall + time model based on the cumulative annual residual rainfall technique with a one-month lag during 1990–2017 was determined as the best model. Rainfall had great impacts on the groundwater level in central Gnangara, with the highest impact coefficient being 0.00473, and the impacts reduced gradually from the central area to the boundary region. Other factors such as pine plantation, the topography and landforms, the Tamala Limestone formation, and aquifer groundwater abstraction also had important influences on the groundwater level.