Busting through

At 07:40 on Tuesday 5 January 2016, the sandbar at the mouth of Younger Lagoon broke open for the first time this rainy season. The Younger Lagoon Reserve (YLR) is located directly west (or "up the coast," as we say; the terminology gets a little weird because the coastline runs east-west in Santa Cruz) of the Marine Science campus of UC Santa Cruz. The actual lagoon is Y-shaped, and while it receives run-off from land, including from the adjacent agricultural fields, for most of the year it is cut off from the Pacific Ocean by a thick sand bar.

Map of UC Santa Cruz's Marine Science campus and adjacent Younger Lagoon Reserve.
Map of UC Santa Cruz's Marine Science campus and adjacent Younger Lagoon Reserve.

This week California has been glorying in the might of El Niño, which has been bringing heavy rain to most of the state and lots of snow in the Sierra Nevada. As the first new moon of the year tomorrow creates the usual extreme high and low tides, we've been treated to some spectacualr waves on the coast. However, it's not the incoming tidal surge that causes the lagoon to break through; if that were the case, then the sand bar would be broken open, or at least seriously eroded, more often than it is. Rather, it's the surge of fresh water, the accumulation of heavy rain and run-off, coming from the top of the lagoon that breaches the sand bar from the upstream side.

This photo was taken on Tuesday by staff of the Younger Lagoon Reserve:

Temporary channel through the sand bar at the mouth of Younger Lagoon. 5 January 2016 © Younger Lagoon Reserve
Temporary channel through the sand bar at the mouth of Younger Lagoon.
5 January 2016
© Younger Lagoon Reserve

You can see that the ocean is rushing through the channel and mixing with the brown stagnant water from the lagoon. Those two tiny white dots on the far side of the channel are snowy egrets. The same egrets also appear in this video that I shot from the overlook which is the closest I can get to the lagoon itself without trespassing on the Reserve:

The break through the sand bar is a temporary thing. This photo and my video were taken around mid-day on Tuesday. Later in the afternoon I looked down on the lagoon from a more distant vantage point and already the sand had begun to accumulate again. Today the lagoon broke through again, and the YLR staff took another great photo from down in the reserve:

Channel through the sand bar at the mouth of Younger Lagoon. 7 January 2016 © Younger Lagoon Reserve
Channel through the sand bar at the mouth of Younger Lagoon.
7 January 2016
© Younger Lagoon Reserve

This being the first break-through of the sand bar this season, the water running out was pretty stagnant and nasty. In fact, as I drove in Tuesday morning I noticed a strong smell of H2S permeating the entire lab complex, and wondered if the construction workers had hit a sewer line. Obviously, the first breach of the sand bar releases all of that gunky, H2S-laden water into the ocean, where it flows right past our seawater intake.

I've long wondered what nutrient levels are in the lagoon at different times of the year, and whether or not conditions in the lagoon affect our seawater quality at the marine lab. I used to think that there might be a correlation between nutrient input from the lagoon and the occasional gunky algal bloom that clouds our seawater and makes life difficult for animals and aquarists alike. However, seeing for myself how little actual water exchange there is between the lagoon and the ocean when the sand bar breaks open, I'm pretty certain now that any nutrients from the lagoon would be quickly diluted to the point of having no effect on productivity in the ocean. Besides, those pesky algal blooms are a regional phenomenon, occurring over large swaths of coastline. Still, it would be interesting to study how nutrient levels within the lagoon fluctuate throughout the year. Maybe I can get a student to take this on as a senior thesis project.

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