Why study groundwater?
Water can be found (almost) anywhere. The most obvious places are oceans, rivers, lakes, glaciers, and clouds. If you, or someone you know, has a well, then maybe you would have also said groundwater. Groundwater is the water found underground, stored in the tiny pore spaces within soil, sand, and rock.
Hydrogeologists have studied groundwater for a long time because it’s an important source of public drinking water and irrigation for farming. It needs to be continually monitored in areas of human activities such as mining because it can be contaminated by different substances. But in more recent years, it has become clear that groundwater also plays a major role in the biogeochemistry of coastal ecosystems.
In some areas of the world, oceanographers have found that groundwater discharges more freshwater into coastal ecosystems than rivers, and this water flux is often enriched in nutrients, carbon, metals, and other chemicals. This is a key finding for a number of reasons: nutrient fluxes can support food webs that ensure strong fisheries and other aquaculture industries, carbon fluxes can alter the acidity of the water column, and fluxes of metals can increase water toxicity. In high-latitude coastal regions like those surrounding Alaska, ever-accelerating rates of glacial and permafrost melt will undoubtedly lead to increased volumes of groundwater entering our coastal waters, so it is especially important that we begin to understand the biogeochemical implications of current groundwater flow, and monitor changes over time.
What are we doing?
In the Burt Lab, we have started to identify the groundwater influxes in Kachemak Bay located in southeastern Alaska. This region has really strong tides, so it is likely that most of the groundwater is not fresh. Commonly, we think of groundwater as freshwater seeping through the earth and being discharged into the ocean. However, seawater can be injected into permeable sediments during the rising tide, where it mixes with sediment pore waters enriched in dissolved materials (like nutrients) before being drained back into the water column during the falling tide.
If the groundwater isn’t fresh, we can’t track it using salinity, so we use a oceanographic ‘tracer’ called radium. Radium is an element that diffuses off of rocks, which means it can be used to track groundwater inputs. It is especially useful because it does not interact with organisms so its concentration is only affected through physical and chemical interactions – which makes studying it so much easier!
We have just finished up our first field season in Kachemak Bay this September and are currently in the progress of analyzing our samples and trying to understand what our results mean.
If you have any questions about what we are doing, please feel free to reach out.