A new report uses landscape metrics in both the historical and contemporary Delta to help define, design, and evaluate functional, resilient landscapes for the estuary’s future
The state of California has set ambitious restoration goals for restoration of the Delta’s ecosystem as embodied in the Delta Plan; those goals include restoring large areas of interconnected habitats within the Delta and its watershed by 2100, establishing migratory corridors for fish, birds, and other animals along selected Delta river channels; and restoring, and where feasible, increasing migratory bird habitat. Other processes, such as the Bay Delta Conservation Plan, the biological opinions, and other regional planning processes also envision significant amounts of habitat restoration for the Delta.
But how can restoration of the Delta happen on such a large scale? The Delta in its pre-development days was a mosaic of a wide variety of different habitats, from the floodplains in the north to the tidal marshes in the central Delta to the distributary channel network in the south: restoration will involve creating multiple types of habitat in various patches across the Delta. Furthermore, the Delta is not a blank slate on to which restoration projects can be laid at will; existing land uses have to be considered as well as locations and physical characteristics of the available parcels.
The challenge is to create an ecologically functional resilient landscape out of these smaller projects that are built incrementally and dispersed across the Delta. This will require a master plan that can integrate large landscape-scale thinking with the smaller scale projects.
The San Francisco Estuary Institute-Aquatic Science Center is working on a project to provide that big picture thinking. The Delta Landscapes project is a multi-phase effort to develop a set of tools to facilitate large-scale restoration in the Delta that can be used by agencies, managers and restoration practitioners to design, implement, and evaluate projects that are effectively integrated with longer term landscape restoration strategies and are cost effective. These tools include landscape-scale conceptual models, design principles, and target metrics.
The basic challenge or goal of the Delta Landscapes project is to address the question of how to create that actual, functional landscape, began Robin Grossinger. “We have the challenge even more in the Delta than in the San Francisco Bay that available property for restoration is somewhat random in terms of willing sellers, it’s not of the ideal size or shape or location necessarily, and in and of itself, small pieces are not enough to make the larger system, so how do we create that framework that helps us feel like we actually are creating a system rather than some little projects?”
The idea of the Delta Landscape project is to create a framework that helps the smaller projects add up to the larger puzzle, he said. “The framework will provide guidance for what makes sense where, because these are different settings and we’re going to need different concepts,” he said. “Hopefully this helps us advance through projects quicker, because we have a sense of what we actually want to do in different parts of the Delta and we don’t have to debate that for quite as long as we do now.”
“The physical settings in the Delta do really vary,” he said. “There are still differences in tidal elevation, tidal range, and proximity to sediment supplies and despite the subsidence, there is a lot of residual complex topography around the edges that we should be working with and allowing to drive our projects rather than fighting against it.”
“Then there’s the challenge of species that need to cross this whole system in different ways and at a different times of their life cycle, and how do we think about that amongst the project’s stepping stones that we’re creating,” he added.
Building on the previous historical ecology investigative work completed two years ago, the Delta Landscapes project compares the present-day Delta to the historical Delta and analyzes how the historical and contemporary spatial habitat patterns and ecological functions that supported native species have changed.
“The historical ecology study created this data set about how the system used to work and how a healthy Delta ecosystem supported native species,” said Mr. Grossinger. “Now we’re analyzing and synthesizing that with all of the remarkable collective knowledge we have existing about species that use the system, what the species are looking for and what their needs are. We’re applying that knowledge to this system and trying to tease out what was important and useful about it.”
While the different types of habitats that once existed cannot be reestablished in the same places or in the same amounts, restoration projects do need to be designed to provide many of the same functions at suitable scales. “We’re not going to recreate the historical Delta, but we need to tease out what the elements are and the specifications that we want to achieve to guide us into what we’re trying to shape,” Mr. Grossinger said. “Presumably the native species are essentially looking for that system as that’s what they evolved with and that they are adapted to, so we can start to infer what they might be looking for from the specs of this system.”
In order to understand the landscape structure and how it has changed, landscape metrics are used. A metric is a type of measurement that is used to quantitatively assess a component of a process, system, or action. Landscape metrics are derived from satellite images, air photos, remotely sensed images, and GIS information that describes spatial patterns of landscapes. “It does limit it to some degree,” acknowledged Mr. Grossinger. “We can’t measure everything; we have to be able to map it, but if we can do that, then that means we can understand how it’s changed. We can also start to project into the future and use those as metrics for performance targets or guidelines as we see our projects adding up to systems.”
The first step to developing landscape metrics for the Delta was to define the ecological functions that the historical Delta provided. For the purposes of this project, ‘ecological functions’ were defined as those processes or manifestations of processes that support organisms. These functions were identified at both the wildlife population and the community level, and were then grouped into four themes: functions related to wildlife life-history support, functions related to wildlife adaptation potential, functions related to food webs, and functions related to biodiversity.
“A big part of the project is sort synthesizing contemporary knowledge with landscape mapping, both past and present, and that’s been essential to have a really awesome team of advisors, both biologists and physical scientists, who contributed a lot of time and intellectual thought shaping all the choices we’ve made,” he said. “What are the ecological functions that matter in the past and present Delta that we should be considering and how do we measure those? How do we prioritize which ones to do? What are the things that actually matter that we want to focus on? … Everyone contributing has really been a lot of help.”
“We went through a process evaluating what are the key life history needs and broader adaption biodiversity functions that we needed to focus on with the team,” he said. “This translates into more specific functions that we then track; those functions can each be linked to specific measurable mappable elements. Some of them support multiple functions.”
Once the functions were defined, eight key functions were identified to focus on for this phase of the project. Landscape metrics were chosen that could be correlated to ecological functions and were feasible with the available data; those metrics were developed using spatial datasets for both the historical Delta and the modern Delta, and the two compared to determine the nature and the extent of the changes to the Delta’s landscape.
Those changes have been significant. Mr. Grossinger then detailed just three of the many findings in the report.
There has been a 73-fold reversal in the ratio between marsh and open water in the Delta, affecting the character and quality of aquatic habitats.
“First one is that there’s been 73-fold reversal in the ratio between marsh and open water in the Delta which affects the character and quality of aquatic habitats,” Mr. Grossinger said. “Even with the loss of historical lakes and all of the channels, there’s a lot more open water in the Delta today – 63%. Then of course, marsh has decreased much more than in San Francisco Bay – 98%, a really extreme decline. The result of that is that where we used to have about 10 times as much marsh, now we have roughly ten times as much open water as marsh – 7 or 8 times.”
“One way I’m starting to look at it is that if the Delta was a pie, the pie has actually become much smaller – it’s almost ten times smaller – it’s like 6 or 7 times smaller, an order of magnitude smaller, and it’s a totally different pie,” he said. “It used to be a marsh pie and the crust was water, and now it’s a pie that is a lot smaller for everyone to work with, and it’s a totally different pie. It’s a water pie with a crust of marsh, if you will.”
Mr. Grossinger then put it a different way. “We used to have channels that were embedded in a giant marsh matrix, now we have little tiny marshes embedded in giant channels,” he said. “The overall shift is essentially two orders of magnitude, so it’s really remarkable inversion of the landscape. Then imagine native species still persisting there and trying to figure out what to do.”
“We know that many species use the marsh directly and even some fish species,” Mr. Grossinger said, noting that there’s been recent research that has found longfin smelt spawning on the marsh surface. “We think it’s likely that the marsh also has significant role in delivering organic matter and nutrients into the open water, although that’s less well documented because there’s so little marsh today to work with.”
There is twice as much shallow-water habitat (<2m) in the Delta today as there was historically.
Secondly, there’s actually twice as much shallow water habitat (less than 2 meters) in the Delta today as there was historically, he said. “Despite all of the changes, there’s actually more shallow water habitat, even though that’s something that we tend to focus on as something we need more of,” he said.
He explained that they used a 3D Digital Elevation Model to calculate and compare the historical mapping with contemporary elevations. “The shallow water in these smaller channels historically where as now it’s on the edge typically of very large channels, deep water, or large flooded islands,” he said. “So while there’s more area of shallow water habitat, there’s much less length of shallow water habitat, if you will, because there were thousands of kilometers of small and shallow channels, but now there’s are very few shallow channels, so that is where the dramatic change in shallow water habitat is.”
They also evaluated dendritic dead end slough networks and quantified those. “I am showing a page from the report so you can see how it’s laid out,” he said. “We can see that there used to be a tremendous amount of dendritic tidal channels, and we know from research from today that those tend to be associated with turbidity maxima, at least in some places; also some of the research from UC Davis says perhaps chlorophyll maxima and even sometimes less clams it seems in some of those areas. Those are probably important spots which have been greatly reduced today and replaced with the more connected channel network.”
“It looks like there was a lot of channels then and a lot of channels now, but they function completely differently because we’ve lost the ones that were dead end and had high residence time, and the characteristics associated with that, and we now have this relatively well mixed homogenous large channel system,” Mr. Grossinger said.
Most of the temporarily flooded habitat available to fish in the Delta has been lost.
Third, temporarily flooded habitat that was available has been greatly diminished, he said. “You can see that the deep water habitat, the open water and perennial waters, that’s somewhat increased,” he said.
“Then there’s the tidal areas and the area was then exposed as this massive expansion and contraction of habitat that many species could take advantage of. On tidal cycles, either daily or more towards the spring tide, weekly or monthly, a large area would be flooded and now there’s very little area that expands in that way now.”
They also looked at fluvial driven flooding, both the short-term seasonal flooding associated with rainfall events, and the longer-term flooding associated with snowmelt on the San Joaquin and the Sacramento, where areas would be flooded for months at a time.
“We have a little glimpse of the more temporary seasonal flooding in the Yolo Basin and also the Consumes, and we know from that from research by UC Davis and others that that is extremely high productivity for fish and that we’ve lost that in large part,” he said.
“We’ve also lost some of the other components of that flooding system. … We used to have this long duration flooding, which probably had benefits in addition to the short-term flooding in terms of delivering nutrients and fresh water into the tidal portions of the Delta throughout the summer.”
“We can think about this in terms of life stages of salmon runs and other species as we do in the report and see that we have some elements of that today, but such a reduced expression of that complexity,” Mr. Grossinger said. “The fish were adapted to find the spots that they needed and had a lot of different options in different water years and different seasons to adjust and find themselves where they wanted to be and there’s just very little of that today, compared to what there was historically.”
Mr. Grossinger noted that while his presentation focused on fish, the project is focused on the complete ecosystem. “We do talk about the riparian areas supporting birds and the marshes for marsh wildlife themselves, and all of these elements need to be brought together as well as the edge and all the species that are supported at the edge.”
A Delta Transformed: Ecological functions, spatial metrics and landscape change details the overall physical changes that have occurred in the Delta as it relates to ecological function, and analyzes different dimensions of the changes as it relates to different habitat-associated guilds, such as fish, marsh wildlife, and waterbirds. The report is full of maps, charts, and graphics and is available online as an eBook, downloadable as a pdf, or can be purchased in print.
The report is the first phase of a multi-phased project scheduled for completion in 2016. Future products include developing landscape-scale conceptual models, restoration principles, and target metrics. The Delta Landscapes project is funded by the Department of Fish and Wildlife and the Ecosystem Restoration Program.