Sunday, August 31, 2008

Delta in distress

The Sacramento San Joaquin River Delta (Delta) is dying. It has really been dying since 1849, when that historically highly invasive and destructive race of homo sapiens - the white man - discovered gold and started invading the state in large numbers. To be fair, white women started arriving, too.

This particular delta is a fairly rare example of an inverted river delta. Map from the 1995 Sacramento-San Joaquin Delta Atlas. Click to enlarge

An inverted delta comes to a point where the river leaves a wide, flat area rather than where it enters. In fact, if you look up inverted river delta on the internet, the Sacramento-San Joaquin Delta very often used as an illustration. Historically, the Sacramento and the San Joaquin rivers dropped much of their sediment loads in the valley before converging and flowing out to the Pacific Ocean through a gap in the Coast Range, forming a huge inland tidal marsh. If you look at a relief map of California, you'll see a large valley down the middle. This is the Sacramento-San Joaquin Valley, otherwise known as the Central Valley.
This entire area used to drain through the Delta, the Carquinez Straights, and out to the Pacific through San Pablo and San Francisco bays.

The Delta is important for many species, including: anadromous species (e.g. sturgeon, lamprey, salmon), the endemic Delta smelt, and the non-endemic humans. The anadromous species migrate out through the Delta as juveniles, and then back in again as adults. Half the waterfowl migrating along the Pacific Flyway use it as a stop over.

Gold Rush
One of the first major negative impacts to the Delta was the California Gold Rush.

The gold rush brought hundreds of thousands of people into California very suddenly. This many people meant that within a short time, most of the easily accessible gold had been collected, and the miners resorted to more destructive means of collection. Hydraulic mining - using high pressure jets to wash all alluvial sediment, often entire hillsides, down where the miners could then extract the gold - was the most destructive. Photo of hydraulic placer mining at the Malakoff Diggings, circa 1860.

This created millions of tons of sediment that washed down into the Central Valley, aggrading the stream and rivers beds, burying farmland, and causing widespread flooding. Farmers sued, and the practice was largely stopped in 1884, but much of the environmental damage is still being felt today.

Thousands of pounds of liquid mercury were used in the placer mining process. The very dense mercury amalgamates with gold, making it heavier and easier to separate from sand and gravel. The U.S. Geological Survey indicates that potentially over 10,000,000 lbs. of mercury were lost to the environment in California due to placer mining. This mercury is very slowly making it's way down the river systems and out to the Pacific - via the Delta. In addition, other watersheds that drain into the Sacramento River have naturally high concentrations of cinnabar (mercury ore).

Over about the last 7000 to 10,000 years (since the last ice age), peat had built up in the Delta, and formed very low islands surrounded by meandering waterways. This peat is extremely fertile. Farmers arrived along with the Forty-niners, and started building levees around the edges of the islands to barricade their houses and crops against the natural yearly flooding - and then unnatural flooding due to mining.

Once peat is dried out and disturbed, it starts to oxidize and subside. This, wind, and compaction have caused some of these islands to subside by more than 20 feet in the last 150 years. Rather than many small islands with gently sloping banks covered with emergent vegetation, the Delta is now enormous leveed "bowls" surrounded by dredged and riprapped channels.From a 2000 USGS pamphlet about Delta subsidence.

Although most of these levees have been raised, strengthened, and riprapped over the years, many are original and getting very old. Built on soft peat soils, and made mostly of peat and dredge material, they are highly susceptible to erosion and external pressure during flood events, and rodent burrowing. Note the water surface elevation compared to the island interior. The more the interior of the islands subside, the higher the pressure from the water.

There are also numerous faults in the area, and a moderate earthquake could cause several levees to break at once. When a levee breaks, it can "suck" salt water from San Francisco Bay into the Delta. Breaches in the levees of several islands at once could disrupt the water supply of millions of Californians (see below).

A levee around the Jones Tract island broke on a clear morning in June of 2004 when water levels were normal for that time of year.Photo from the California Department of Water Resources website.

The California Department of Water Resources spent months and millions of dollars fixing the break and then pumping out all the water.

The Delta farmers pump water from the channels. This map from the California Delta Atlas shows thousands of pumps - many of which are unscreened. Map from the 1995 Sacramento-San Joaquin Delta Atlas. Click to enlarge

Fish are sucked in and pumped out onto fields ending up as very expensive fertilizer (or cheap, depending on how you look at it).

The conversion of seasonally inundated wetlands and floodplains due to urbanization and agricultural land conversion also results in a reduction in overall primary productivity.

Historically, salinities in the Delta fluctuated greatly. Salt water would ebb and flow with the tide, and how far upstream it "intruded" depended on the Sacramento and San Joaquin river outflows.

As the area became more populated, a constant source of fresh water became much more important. The California legislature authorized the Central Valley Project (CVP) in 1933, and the project was reauthorized by the federal Rivers and Harbors Act of 1937. Construction began on Shasta Dam on the Sacramento River in 1938. Shasta Dam alone dramatically reduced the Delta salinity fluctuations, but numerous large dams have been built on most of the major and many minor rivers in the system. The State Water Project (SWP) was authorized in 1960, and the tallest dam in the United States, Oroville Dam, was finished in 1968.Photo of Oroville Dam from the California Department of Water Resources website.

The dams affect the system in several ways:
1. They block the upstream migration of anadromous fish.
2. They act as sediment traps, leaving the rivers below with "hungry" water, which tends to erode steep, incised banks. Some were built as sediment traps due to the huge volumes of sediment still moving down from the hydraulic mining.
3. They are operated to keep the summer river flows artificially high and constant for irrigation and Delta water export purposes.

Another component of the CVP and SWP are the delta pumps. Each project has huge pumps at the south end of the Delta which pump millions of gallons down through the Central Valley in enormous aqueducts; irrigating California agriculture, supplying drinking water, and helping keep California between the 7th and 10th largest economy in the world. Much of the water coming out of taps in Los Angeles comes from the Delta, 444 miles away.

When the Delta pumps are operating, they are pumping enough water to reverse the flow in many delta channels. This confuses fish who are trying to swim downstream and end up swimming back up into the Delta. The pumps have enormous screens to filter out (most of the) fish and divert them into tanks rather than into the canals. The fish are then pumped into trucks and taken to be released back into the Delta. Not surprisingly, many fish do not survive this process. Predatory fish also learn where the release points are, and hang out in the area waiting for confused and stunned prey to be dropped in front of their noses. The federally threatened Delta smelt (Hypomesus transpacificus) are particularly delicate, and rarely survive the ordeal.

Invasive Species
The Delta is rife with introduced species which directly compete with or eat native species. Additionally, some have the ability to change the environment. When the tiny estuarine Asian or overbite clam (Corbula amurensis) was introduced in the 1980's, probably via bilgewater from one of the many ships docking in the San Francisco Bay Area, it rapidly spread up through the estuarine system, and now coats the bottom in many places. There are enough of them to filter out huge amounts of phytoplankton - the basis of the food web. The future freshwater parts of the Delta will likely include quagga and zebra mussels, as I pointed out in a previous post. These have a history of, among other things, filtering out phytoplankton and reducing primary productivity.

Another species which has changed the Delta environment is Brazilian elodea (Egeria densa). This was probably introduced via people dumping fishtank water, as it is a common aquarium plant, and it forms dense mats in many of the shallower freshwater areas, crowding out many of the native aquatic plants. It also slows water flow, allowing fine sediments to drop out, and increasing clarity in a naturally turbid environment. The pelagic and nearly translucent Delta smelt evolved in this environment and relies on turbidity to hide from predators.Photo from the California Department of Fish and Game Bay-Delta Region website.

Introduced plankton are changing the base of the Delta food web. The cyclopoid copepod Limnoithona tetraspina has made up a large part of the copepod biomass for about the last 15 years, but it apparently is not a good food source for native species.

Purposefully introduced species include: Striped bass, large mouth and small mouth bass, bullhead and channel catfish, American shad, threadfin shad, wagasaki...the list goes on.

Toxins that occur in the Delta are many and various. Almost the entire Central Valley drains through the Delta, and any pesticides, municipal, industrial, or agricultural effluent, mercury and arsenic from mining, and other toxins that get into the water supply, eventually make it through there. In addition, since it was first detected in 1999, there have been more frequent, and more widespread blooms of the toxic cyanobacteria, Microcystis aeruginosa.

Threatened and Endangered Species
Here is a short list of native species in trouble in the Delta:

Delta Smelt
Central Valley Spring-run Chinook salmon (Oncorhynchus tschawytscha)
Sacramento River Winter-run Chinook salmon,
Apparently Fall-run Chinook are also having trouble, now
California Central Valley steelhead (Oncorhynchus mykiss)
longfin smelt (Spirinchus thaleichthys)
green sturgeon (Acipenser medirostris)
river lamprey (Lampetra ayresii)

Hopefully we can avoid what happened to the thicktail chub - once one of the most common fish in the Delta, which was extinct by about 1953.

I am an aquatic ecologist, so I tend to be biased toward the aquatic species, but Tule Elk, once the predominant deer in California, - thousands of which lived in the Delta - were nearly extinct by the 1860s. There are now 22 small herds left, scattered throughout California. The California state animal, the California Grizzly, was hunted to extinction by 1922. There are numerous threatened and endangered amphibians, reptiles, birds, and plants in California. The historic range of many of these includes or once included the Delta.

Threats to the Delta are multiple and synergistic. One of my former university professors, Peter B. Moyle, calls this "the heavy hand of humans."


RAT GiRL! said...

Giggle is a tart over at my place!
Ya might wanna bring a bucket because you'll probably puke!!!

P.S Me T-shirt looks flamin great on ya sidebar!

Kia said...

Very well written post, but it makes me reconsider writing my proposed book "1001 Reasons to be Depressed". To those of us in the environmental field, it seems like there are way more problems than there are resources to fix them.

Laurie said...

RAT GiRL! - She was a bit of a tart. Reminded me of Betty Boop for some reason...It was kinda sappy, but kinda cute, too. I just want to know what happens to Rocco and Jaxon!

I think I accidentally shrank your shirt, but I do that with all the laundry. Sorry!

Kia - I didn't mean to depress you! Why reconsider? Just add more. 2001 Reasons...

That sounds like the book my friend and I were going to write: Tales of the Light Rail; Interesting Things that Could Happen to You Too on Sacramento Public Transportation

artificialhabitat said...

Really interesting, and detailed post, thanks. I would have commented sooner, but I wanted to wait until I had the chance to read it properly.

And I just noticed it was part of 'Tangled Bank #113'. Cool.

Human influences are driving so many ecological changes it is staggering. We certainly live in interesting times....