Opportunity to enhance delta smelt science scrapped by Wanger compromise

The 2008 biological opinion prepared by U.S. Fish and Wildlife Service recommends a set of actions that should be taken to protect delta smelt while operating the federal and state projects.  USFWS will prepare yet another version of this BiOp by an order of Judge Wanger, or else be relieved of the need to do so by a favorable result on appeal — but until that is resolved there continue to be skirmishes debating specific actions in the current BiOp.

One action, the “Fall X2” action, is triggered when the preceding year’s precipitation levels are classified as wet or above normal.  The Fall X2 action requires that enough water be allowed to flow out of the Delta in September and October so that X2, the location of the 2 psu isohaline, is either 74 kilometers (in a wet year) or 81 km (in an above normal year) upstream of the Golden Gate Bridge along the estuary’s axis.  Those two locations fall at Chipps Island and Collinsville, respectively.

When more water is allowed to flow out to the Pacific Ocean, whether by decreasing exports or by increasing inflow released from upstream reservoirs in the Sacramento Basin, the 0.5 to 6 psu “low salinity zone” (LSZ) where freshwater outflow meets salt water is pushed toward Suisun Marsh and away from the area upstream of the Sacramento-San Joaquin river confluence.  The LSZ salinity range is suitable for delta smelt, and the LSZ’s placement in the estuary in a given year influences the geographic range of delta smelt habitat in that year such that smelt are approximately centered on the 2 psu isohaline.  An underlying goal of the Fall X2 action is to increase outflow and push the 2 psu isohaline seaward, thereby increasing the area of suitable delta smelt habitat within the estuary.

The BiOp’s rationale is basically that in years when X2 is located too far upstream of the confluence, the area of suitable habitat is confined to narrower river channels.  When X2 is located further west, however, the area of suitable habitat can include the broader territory of Suisun Bay, Suisun Marsh, and Grizzly Bay:

Darker shades of gray indicate more suitable habitat, for X2 = 71, 85 km. Habitat for X2 = 71 km appears both larger and more productive than habitat for X2 = 85 km. Courtesy of USFWS, USBR.

If younger delta smelt can gain access to this comparatively more expansive area — as a result of salinity there being maintained at a level that well-suited to their physiology — then they have more space in which to prey on zooplankton while growing and maturing into adults that will later migrate upstream to spawn.  This observation suggests an association between Fall X2 and smelt abundance in the subsequent year.

This curve, which shows how outflow and X2 location can increase habitat area, is largely a function of estuary geometry. For X2 < 74 km, comparatively less habitat is provided at greater water supply cost. Further upstream, even relatively small upstream shifts of X2 decrease habitat area. Courtesy of USFWS, USBR.

Moreover, even though water clarity is largely a function of non-flow factors — for example, the invasion of submerged aquatic vegetation like the Brazilian waterweed, Egeria densa — the higher turbidity of the expanded seaward habitat also better protects delta smelt from predators.  In short, the goal of the Fall X2 action is to influence salinity through outflow so that delta smelt can be directed to the parts of the estuary that will provide them with superior habitat in this pre-adult life stage.

The future of delta smelt is not certain, but the trend of the past ten years suggests a fragile population that is propelling toward extinction:

The arrows, directed chronologically from 2000 to 2009, outline a path collapsing toward the origin. Courtesy of USFWS, USBR.

2011 is the first wet year since the 2008 BiOp was issued, which means that this September was to be the first occasion to test the Fall X2 action.  As exports have increased, Delta outflows in wet years have been reduced.  The system variability that delta smelt is naturally accustomed to has been largely eliminated, so that outflow in wet years resembles outflow in dry years.  Likewise, fall salinity levels are more stable as wet years resemble drought years, and the LSZ now shifts landward for longer periods of time.  In short, the geographic span of X2 locations attained over all water year types has narrowed over time as the outflow regime has stabilized, and the wet year location of X2 has trended upstream over time, thereby directing more of the delta smelt population toward inferior habitat.

This autumn, following the 2011 wet year, thus presents a tremendous opportunity to study how delta smelt responds to higher outflows and the more expansive habitat provided thereby, establishing valuable data points that could lead to a refined approach in future wet years and inform Delta planning generally.  It offers an excellent chance to advance the state of delta smelt science, and it’s not clear when a similar opportunity will present itself in the future.

But the Fall X2 action, like other action measures contained in the biological opinions, was challenged by water contractors, and two weeks ago Judge Wanger granted an injunction to stop the Fall X2 action (PDF of decision).  To summarize the 140-page decision in one sentence, Wanger determined that the biological justification for Fall X2 was not sound enough to justify the water supply loss, which he estimated to be 300,000 acre-feet.  The Fall X2 action would not impact immediate water supply, but rather would reduce exports and prevent recharge of groundwater for use in future dry years.  NRDC disputes Judge Wanger’s water supply conclusions (PDF), suggesting that 300,000 acre-feet of State Water Project carryover storage may be lost in 2012 if Fall X2 is enjoined and San Luis Reservoir fills too quickly — water better “lost” to the Pacific Ocean this autumn where it could provide an environmental benefit.

Although Wanger did not completely reject the X2 framework — indeed, he formulated his order in terms of X2 — he rejected the claim that X2 must be placed at 74 km this fall.  His order required that X2 be located no further west than 79 km, forging a compromise that provides some outflow while reducing potential impact to water supply.

This discussion continues in the next post.

Thanks to Brandon Middleton at PLF, as well as KMTG, for making various court documents available for public consumption.