State monitors health of Coastal Bend ecosystem

5/5/2013 8:30 AM
By Associated Press

CORPUS CHRISTI, Texas (AP) — The signs are all around us.

Brown grasses, brittle and hardened, choke vacant lots and highway medians. Lawns, now the subject of drought-level restrictions, crack open as soils constrict.

Drought conjures images of dead or dying plants and livestock, fields plowed under for lack of rain and wildfires burning out of control.

The local effects of drought are captured in the ecosystem of the Rincon Bayou, a natural area hidden in plain sight a short drive northwest from downtown Corpus Christi, where some organisms thrive in the hypersaline conditions produced by the drought while others suffer.

The bayou is a marshy area within the footprint of the larger Nueces Delta, formed where a freshwater river, the Nueces River, flows into a saltwater body, Nueces Bay. It is home to a network of strategically placed monitoring stations that gather data on salinity levels — the amount of salt in the water — as a way of mapping how freshwater, or a lack of it, affects the overall health of the delta.

Not all of the diversion is natural.

Through the years, freshwater diverted from the 5,529-square-mile Frio River watershed and the 11,235-square-mile Nueces River Basin into the manmade Choke Canyon and Lake Corpus Christi reservoirs has reduced the amount naturally flowing into the delta.

Though an agreement between the city of Corpus Christi and the state calls for monthly freshwater releases to the downstream ecosystem, the agreement is scalable based on the amount of water in the reservoirs.

The last time the bayou received a pass through of freshwater was a 1,981 acre-feet — about 646 million gallons — transfer in mid-October, said Jace Tunnell, a project manager with the Coastal Bend Bays & Estuaries Program.

The program is a nonprofit group dedicated to preserving and protecting a half-dozen bays in the Coastal Bend region, including the Nueces Bay system.

The last time the Rincon bayou received freshwater, at all, from the reservoirs was on Jan. 28, when about 17.6 million gallons was released either from maintenance pumping to keep the pumps operating properly or to keep water from running over the Calallen Dam.

Other than a smattering of rain here and there, it hasn't received a drop since.

Freshwater inflows into the entire system are the lowest on record, said Ray Allen, executive director of the program.

As freshwater has been diverted away from the bay, over the years, the bay itself has changed, said Larry McKinney, executive director of the Harte Research Institute of Gulf of Mexico Studies.

"It is not your daddy's bay anymore," he told the Corpus Christi Caller-Times (http://bit.ly/103Envb). "For example, reefs were at one time well developed in Nueces Bay and even supported an oyster population that was reported to be tolerant to higher salinities. That does not exist anymore as average salinity levels rose enough that disease and predators have all but wiped them out."

It's also not Capt. Jerry Tungate's bay anymore.

A 20-plus year shrimper who harvests Corpus Christi Bay's once-fertile crop of brown, white and hopper (pink) shrimp, from his trawler, the Reliant, Tungate remembered a time when more than two dozen shrimp trawlers called the Corpus Christi Marina home.

"Now there's four, maybe six," he said.

A die-hard member of a salty breed whose numbers have steadily declined in the past 20 years, Tungate acknowledged time is no longer on his side. He said when the reservoirs came, the shrimp mostly left. And then, the shrimpers.

"You couldn't even net a crab back then," he said.

"I'm not a farmer. I don't get a subsidy," he said while doing a checklist of maintenance work on his aging trawler during an April day otherwise lost to high winds. "We're going the way of the dinosaurs. We're stuck with what we have."

Allen said as drought increases, salinity levels in the bay will rise and increase bacteria compositions that affect the numbers of shrimp, clams and small fish in the water.

Global competition and low prices also have forced shrimpers out of the bay, Tungate said.

Salinity in one portion of the bayou clocked in at 40 parts per thousand, making it saltier than the Gulf of Mexico, according to a reading taken Thursday, Tunnell said.

A lack of freshwater stresses other creatures, too.

Thirsty javelina and wood rats have taken to gnawing on the many cactuses that abound in the delta, leaving brown furrow lines in the fleshy, thirst-quenching cactus arms.

Bees now live in the wood duck boxes because the ducks have gone elsewhere, looking for more water.

"This time of the year, they should be starting to nest," Allen said.

The drought places a strain on the youngest animals, survival rates will drop.

"You just hope it's not too severe," Allen said.

A culvert built to help water flow over a road splitting the bayou has seen only one heavy rain in the past year, Allen said.

In the distance, one of a pair of artesian springs lies surrounded by a phalanx of towering cat tails, an oasis of green in a vista carpeted with brown, parched grass.

The Bays & Estuaries Program has installed a couple of wildlife drips — faucets that drip raw, untreated water into a small pool for wildlife to drink.

Tunnell said the deer, normally elusive, are less willing to scatter from the small pools when humans are nearby.

"We've driven up on them before and they won't even move, they're so thirsty," Tunnell said.

The delta is a delicate mix of systems, all dependent upon natural inflows of water. After more than a half-century of reservoir development, natural inflows are about half of what they once were, Allen said.

The reservoir system, made up of Lake Corpus Christi and Lake Choke Canyon, that serves Corpus Christi and other towns now captures the water that once would have flowed into the Nueces Delta, which includes the bayou. The city is the managing operator of the system.

"When you talk about the bay and the delta, what you have is a natural system trying to work as a natural system but, because of the reservoirs, less water comes down," Allen said.

The same is happening worldwide.

In the four decades spanning 1960 and 2000, the volume of water in reservoirs quadrupled, and as of 2009, 60 percent of the earth's runoff water was captured, according to a report from a study led by Paul Montagna, one of several endowed chairs at the Harte Research Institute of Gulf of Mexico Studies at Texas A&M University-Corpus Christi.

The permit to create the Choke Canyon Reservoir, which in the early 1980s dammed up a portion of the Frio River where it feeds into the Nueces River near Three Rivers, included a requirement to allow about 151,000 acre-feet of freshwater and return flows — wastewater discharges — into the bay system, said Rocky Freund, deputy executive director of the Nueces River Authority. (An acre-foot is equal to the amount of water needed to cover an acre at a depth of 1 foot, or about 326,000 gallons.)

In the case of Choke Canyon, the entire amount was not needed all at once, but there was no schedule for when it was needed most, Freund said.

An interim operating order, set by the state in the 1990s, created a mandatory schedule each month when freshwater would leave the reservoir system and flow into the delta, Freund said. The amount of water released downstream each month is calculated based on how much flows into the reservoirs and is intended to reflect historic patterns, she said.

In 2001, the scheduled releases were further defined to allow for releases based on the natural order of things — higher inflows during historically wet months of May, June, September and October — and lower inflows in drier months. Salinity levels in the bay also are part of the equation.

This model, meant to mimic nature while serving man's need to provide freshwater to the city and industry, is known as the pass-through concept.

The order also allows the city of Corpus Christi to reduce freshwater inflows during periods of drought, Freund said.

It is meant to ensure as much freshwater flowing into the delta while maintaining enough in the reservoir yields for human use, Freund said.

It is a delicate, enormously complex system of checks and balances whose only substitute is a good, long rain, she said.

"If it doesn't rain in the watershed, even if the (reservoirs) weren't there, the bays would still get salty," Freund said.

When reservoirs drop below 40 percent of capacity, the target amount of pass-through dips to 1,200 acre-feet a month, or about 14,400 acre-feet a year. Credit is given for the amount of treated wastewater released into the bay each month. Freund said this usually is about 500 acre-feet.

Corpus Christi is now in Drought Stage 2, triggered when the reservoirs drop below 40 percent. . At 30 percent capacity, the pass-through requirements stop, regardless of the month, according to the terms of the agreed order.

Although the city can, and has, elected to initiate tighter restrictions on residents and businesses before the 30 percent capacity threshold, they will not cease pass-throughs to the delta until the combined capacity actually drops below the threshold, said Brent Clayton, the city's water planner.

McKinney said the main issue with high salinity levels in Rincon is in how it affects other, commercially harvested populations such as brown and white shrimp and crab. Saltier water is bad for the larvae, he said.

"The upper parts of a bay like Nueces should act as a nursery that eventually populates the estuary below at every trophic level," McKinney said. "At 40 parts per thousand plus, this will be significantly reduced, and the higher the salinity the more so."

If hypersalinity is hard on some organisms, it is not having a tangible effect on fish populations in the bays, said Art Morris, outreach specialist in the Coastal Fisheries Division of the Texas Parks & Wildlife Department.

"If salinity levels rise to 70 parts per thousand, the fish migrate to better conditions," Morris said.

Morris said the big question for an area with a salinity gradient as wide as the Nueces system is, what is normal?

"It's anything from completely fresh to hypersaline, for any of these systems," he said. "They are all subject to extremes. Everything that lives in these bays are survivors."

___

Information from: Corpus Christi Caller-Times, http://www.caller.com


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