From the Tuolumne to the Sea

By Maya Akkaraju

The world’s water systems — from lakes to rivers to the open ocean to the clouds — are deeply interconnected. The Tuolumne River is no different, and these connections only strengthen the case for preserving our beautiful waterway.

The Tuolumne begins in the Sierra Nevada and winds its way down to the Central Valley where it meets the San Joaquin River. From there, the San Joaquin River and the Sacramento River come together to form the Sacramento-San Joaquin Delta, where they feed into the San Francisco Bay and out to the Pacific Ocean. These connections are crucial, and life in the watershed — including us — relies on river-to-ocean networks. The nature of this network means that protecting the Tuolumne has a bigger impact than on the river alone — it helps protect the health of the river’s wildlife and the ocean. 

The Sacramento-San Joaquin Delta is rich with wildlife. According to The Nature Conservancy, over 750 species of plants and animals rely on the habitats in and surrounding the estuary, including the Tuolumne’s fall-run Chinook salmon. 

After hatching in the river’s gravel beds, where the water is shallow and oxygen-rich, these salmon spend around half a year growing in floodplains (like the ones we’re helping restore at Dos Rios Ranch in Modesto). Once they become smolt, the salmon are ready to migrate out to sea. As a part of their migration, the fish utilize the brackish Sacramento-San Joaquin Delta water to acclimate to a saltwater environment before moving through the bay and out to the Pacific Ocean. 

During their life cycle, Chinook salmon play an important role in the flow of nutrients between the ocean and river. While in the ocean, salmon are a critical food source for important species, such as Orca whales. Salmon spend about two and a half years maturing in the ocean before returning to the river to breed. After making the long journey back upstream — and spawning in the Tuolumne in the fall, the male and female fish both die.

The death of adult salmon is an essential part of what makes them a keystone species in this ecosystem — they fuel the food web, supporting a multitude of species and distributing nutrients they brought back to the river from the ocean. 

When Chinook salmon die, some act as an important food source for bears and scavengers. Others are eaten by aquatic insects, which ultimately become food for the baby salmon once hatched. In this way, the lifecycle of fall-run Chinook salmon is set up in the most beneficial way possible for the propagation of their species and to continue the flow of nutrients between oceans and rivers.

Although salmon aid in nutrient flows from the ocean to the river, in many water systems nutrients primarily flow the opposite way. The nutrients that rivers deliver to oceans include nitrogen and phosphorous, both of which are commonly limited in oceanic surface waters but are necessary for the growth of phytoplankton, or microalgae. This means that when delivering nitrogen and phosphorous to the ocean, rivers are fueling the growth of microorganisms, which are the base of the ocean’s food web. Through photosynthesis, microalgae play an imperative role in sequestering carbon dioxide from the atmosphere. 

The delivery system of nitrogen and phosphorus from the rivers to the ocean is important. But this also means that how we treat our rivers directly impacts the health of estuaries and the sea. 

Excessive amounts of nitrogen and phosphorus, or eutrophication, in our water system, can lead to the overgrowth of algae. When the algae dies, it’s broken down by decomposers. The excessive amount of algae requires more decomposers to break down, who use the ocean’s oxygen in the process. This leads to low-oxygen conditions that can suffocate fish, and create “dead zones.”  

This problem is the result of an upset in the balance of the world’s natural cycles. The issue extends from the poor treatment of our rivers that happens when we allow excessive amounts of nutrients to be carried into our waterways, from sources like agricultural fertilizer runoff and wastewater treatment facilities. While the nutrients that are naturally carried to the ocean are important, the human inputs exceed natural levels to a dangerous point.

When we opt to protect our rivers, the impacts are not isolated. Our actions towards the river ripple and spread to the ocean, and affect the entire water system and the life it supports, including yours and mine. The Tuolumne River provides our drinking water, supports wild salmon fisheries, and supports our agricultural system. In addition to all of this, it plays a role in keeping the Pacific Ocean healthy, which is why it is so important to keep it flowing. Join us in protecting our river and our ocean.

 

 

Sources:

https://www.nature.org/en-us/get-involved/how-to-help/places-we-protect/delta/

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GB005483

https://www.ncbi.nlm.nih.gov/pubmed/28586682

https://oceanservice.noaa.gov/facts/phyto.html

https://oceanservice.noaa.gov/facts/eutrophication.html

https://oceanservice.noaa.gov/facts/nutpollution.html