During our Discovery Voyage program out of Redwood City, students study fish, invertebrates, plankton, and also the water that these organisms live in. The study of water, hydrology, is important to understanding the conditions in which certain plants and animals thrive. It can also help us to understand other connections and processes in the watershed and in the water cycle. Last Tuesday during a hydrology lesson aboard our ship, a student-steward asked a great question: “What is the term for water that has evaporated and is saltier than the ocean?”
The affix, hyper-, when added to the beginning of many words, indicates ‘more’ or ‘excess’. For example, when a person has excess energy, they are called “hyper” or “hyperactive”. The term hypersaline can be applied to waters that are saltier than ocean water (more than 35 ppt). Bodies of water can become hypersaline in a variety of ways.
In the San Francisco Bay Estuary, as in other estuaries, salinity changes throughout the year. There are a few factors that cause these patterns. The brackish, or mixed, water in the Bay come from salty water from the ocean mixing with fresh water from the watershed—most notably in our area, down the Sacramento/San Joaquin Rivers. During seasons and years of high precipitation, more fresh water runs down these rivers, plus more freshwater running down as snow begins to melt, typically during the spring. Conversely, when there is less fresh water flowing to the Bay, the ocean’s tides bring more salt water, which can encroach upstream. Add to this the semi-enclosed shape of the Bay that reduces flow and causes the water to mix, almost “trapping” it in the estuary. During the summer, a time of low precipitation and high temperatures, evaporation causes salinity to increase (water evaporates, leaving the salt behind). In fact, this is the first step in the process of producing salt!
Hypersaline conditions can also be found in lakes. These lakes are usually in basins with limited or no outflow, where the water coming in flows over rock formations with soluble salts. These lakes also typically experience a high amount of evaporation.
Deep Hypersaline Anoxic Basins are more recently discovered habitats of extreme salinity. These hypersaline “lakes” are found deep below the ocean’s surface, and are home to very unique lifeforms.
Life in these hypersaline habitats requires special adaptations. Diversity is typically low in hypersaline habitats, and the plants and animals that do live there are sometimes sensitive to dramatic or fast changes.
How do humans influence the salinity of the Bay? As you may have heard, there is a water shortage in California. Drought is a naturally occurring phenomenon, but human demands on available freshwater influence how much water is available for the environment under any conditions. In California, humans use over 50% of water from the Sacramento/San Joaquin watershed, leaving less than half of the regular amount to flow into the Bay. Less fresh water flowing to the Bay means salt water from the ocean can push farther into the Bay and up toward the Delta. Additionally, changes in climate that cause warmer weather and more sunny days contribute to more evaporation.
What can a steward do? As we have shared on Stewardship Monday, reducing your water use can help the Bay, the Ocean, and the local environment. Also, visit a salt pond! We can see them as we fly over the Bay to SFO—these briny, hypersaline ponds are home to interesting critters. Salt ponds can occur naturally, and have also created and managed by humans beginning with the native Ohlone tribes!