The hyporheic zone has been studied because of how important it is for stream dynamics, but only in the last few decades has it also been recognized as an influence on stream ecology, biogeochemistry, and water temperatures. Its importance can be seen in action when downwelling flows bring dissolved solutes into the riverbed and modify its concentrations by mixing surface water with the water in the sediments. 

A study conducted by Thomas Stuart (1953) showed that the stream’s downwelling flow introduces oxygen-rich water from the water column into the sediment, allowing salmon eggs to have available oxygen while underground (Figure 1. A). Without this downwelling flow, the eggs would not have enough oxygen beneath all that sediment, but because of this hyporheic-induced insertion of oxygen-rich stream water, they can survive and hatch into salmon fry! 

Another example would be how microbes reside in the riverbed sediment and like to take up nitrogen compounds and modify them (Master et al., 2005). So, let’s say we have reactive nitrogen form (i.e., ammonium) entering our stream, and through downwelling flow, this nitrogen will enter the riverbed sediment. The microbes will consume most of the reactive nitrogen from the water by a process called microbial denitrification. We can consider this process as a “nitrogen cleansing” process because after the nitrogen in the sediment is consumed, it will then come back to the stream with lower concentrations thanks to the upwelling flow (Figure 1. B). Some studies (i.e., Hill, et al., 1998 and Wagenschein & Rode, 2008) have shown that microbial denitrification in the hyporheic zone permanently removes between 30-70% of all the reactive nitrogen! 

Countless other biochemical cycles and interactions occur in our aquatic and terrestrial environments, and when we include the influence of human activities into the picture, things begin to get even more complex. Activities such as agriculture and energy production increase the reactive nitrogen concentrations in many aquatic ecosystems, which can cause the effects that were mentioned earlier. This is one of the main reasons hyporheic flow has been considered a focus for river restoration projects regarding nutrient cycling in the river systems. 

The importance of hyporheic exchange in surface water quality and riverine habitat for aquatic and terrestrial organisms has slowly been considered an important component of conserving, managing, and restoring river systems. However, there is still a long way to go when it comes to research, as it is a fairly new topic, and there is still so much we don’t know. 

How do we determine the physical extension of the hyporheic zone? How can we quantify the rate and magnitude of water being exchanged between surface water and sediment-water? How does it vary spatially within a river? These are all questions scientists have been trying to answer, but every river is so vastly different that there are still so many things yet to be explored and discovered!