The Delta of the early 1800s was spatially and temporally complex, and that complexity expressed itself in distinct patterns across the vast physical space of the Delta. Patterns occurred at many scales. At a regional scale, the Delta can be discussed in terms of three primary landscapes: the tidal islands landscape of the central Delta (blue area), the flood basins landscape of the north Delta (green area), and the distributary rivers landscape of the south Delta (orange area).
Central Delta tidal islands (middle diagram), on the order of 10,000 acres, supported a matrix of emergent vegetation (primarily tule), willows, grasses, sedges, shrubs, and ferns and were surrounded by broad and deep tidal channels. Channel banks were low and numerous small branching tidal channels wove through the wetland plain, allowing high tides to regularly inundate most of the area.
Flood basins of the north Delta (top diagram) were greatly influenced by the flooding regime of the Sacramento River as well as other streams that regularly overflowed into the low-lying basins running parallel to the rivers. Large lakes occupied the lowest and most isolated positions, and few channels penetrated far into the dense emergent vegetation wetland plain as it transitioned gradually away from tidal influence upstream. The basins were bounded by riparian forest along natural levees and seasonal wetlands of the upland margin.
In the south Delta (bottom diagram), the three distributary branches of the San Joaquin River influenced the general pattern of the landscape. These branches put off numerous secondary overflow channels that serviced the floodplain, which broadened quickly downstream and merged gradually into tidal wetlands. Patches of different habitat types were interspersed within the emergent wetland, including willow thickets, seasonal wetlands, grasslands, as well as perennial and seasonal ponds and lakes.
These historical Delta landscapes were governed by many of the same physical processes and shared many of the same habitat types. However, many characteristics differed, including the relative proportion of habitat types, size features and habitats, vegetation community, hydrologic and habitat connectivity, and landscape position. Boundaries between the landscapes were indistinct and varied depending upon the characteristic examined. Thinking about these landscapes in a conceptual manner, removed from their exact geographical location, can help support a flexible landscape framework to guide sustainable restoration strategies in the contemporary and projected future Delta.
With the rapid conversion of the lush freshwater wetlands with winding tidal channels and adjoining riparian forest to a predominantly agricultural landscape, it is difficult to imagine what the Sacramento-San Joaquin Delta was once like.
A recent collaboration with KQED QUEST and Stanford’s Bill Lane Center for the American West brings the historical landscapes of the Delta to life through an online interactive map. The effort drew from the draft report and accompanying map of the early 1800s Delta developed as part of the Delta Historical Ecology Study. Within the context of the interactive map, historical maps, texts, photographs and land surveys used to interpret the diversity and productivity of the past Delta are explored in vignettes.
The online interactive map,"Envisioning California’s Delta As it Was,” accompanies a KQED QUEST radio report by Lauren Sommer: “California’s Deadlocked Delta: Can We Bring Back What We’ve Lost?”.
These target questions have been developed through conversations with project partners and local stakeholders, review of current scientific research questions in the Delta, and previous experience in systems with similar concerns. We expect questions will continue to evolve through future conversations with technical advisors and project partners.
This study aims to document the pre-modification habitat characteristics of the Delta at a spatial scale and level of detail relevant to restoration planning and conservation efforts. The target questions provide the guiding framework from which to assemble key scientific information towards this goal.
It will likely not be possible to answer all questions with the same certainty or thoroughness. Consequently, technical questions will be re-evaluated after data collection and compilation to decide which are worth pursuing or should be de-emphasized. This process shall include review by technical advisors to reach consensus on the approach and associated level of certainty with which questions can be answered. Key criteria for this re-evaluation shall include consideration of data availability and cost, as well as relevance to Delta restoration and conservation planning.
The fundamental goal of the Delta Historical Ecology Study is to document, to the extent possible, the pre-modification extent and character of different wetland, riparian, and terrestrial ecotonal habitats. This description of spatial patterns will help us better understand ecosystem support functions and controlling physical processes within the landscape context. Such information will
provide a basis for identifying target locations and physical conditions necessary to restore functional habitat mosaics within the projected future Delta landscape that are capable of providing multiple ecological services.
Extent and Density
What was the density of tidal channels in the Delta? Did that vary significantly along ecological gradients?
Were there large "undrained" occasionally tidal areas with no channel network -- such as along the eastern margin?
Were the channels along this edge seasonal?
Were they dominated by fluvial or tidal processes?
Order, size and sinuosity
What was the historical extent of channels of different sizes?
How wide were second and third order channels?
How does this compare to more saline systems?
How much marsh area was associated with 2nd, 3rd, and 4th order systems?
What was channel sinuosity relative to location within the Delta (e.g. relative to tidal and salinity gradient)?
What was the extent of "dead-end" versus connected channels and how did that (and associated residence time) vary across the Delta?
Tidal and salinity gradient
What was the extent of tidal influence upstream along main channels?
Can we define historical X2?
Tidal marsh extent
What were the historical boundaries of tidal marsh within the Delta?
What was the character and extent of the transition between fully tidal, occasionally tidal, and nontidal marsh habitats?
What was the extent of brackish versus freshwater tidal marsh?
What was the proportion of low versus high elevation marsh?
Inorganic v. organic input: To what extent did inorganic inputs affect the form and function of the tidal marshes?
How did marsh types vary regionally within the Delta and what were the physical drivers of these differences?
What were characteristic features (e.g. size, mudflats, species, plant height) within the freshwater marshes?
Were marsh interiors characterized predominantly by expansive homogenous tule stands or were there significant variations in interior marsh vegetation?
How common were features associated with microtopography, such as swales on the margin, old channel levees, etc?
How extensive were perennial freshwater marshes along the tidal margin?
How did they vary from South to North?
Were these always associated with basins or sinks (e.g. Yolo Basin, Cosumnes Sink)?
Were adjacent non-tidal marshes primarily supplied by groundwater or surface water?
How wet were these features -- did they discharge significant freshwater to the tidal margin during summer months?
With what frequency did these basins fill?
How persistent were they?
How was water routed within them -- sheet flow, sloughs?
What positions and configurations did surface waters occupy within the marsh landscape?
Did that vary significantly along ecological gradients (tidal, freshwater inflow, climate)?
How common were terminal ponds at the ends of channels?
What size channels were these associated with?
How common were "chains of sloughs and ponds"?
Are variations in form associated with identifiable physical controls (e.g. fluvial controls, tidal prism)?
How big were they and did size vary depending on location?
How does this compare to more saline conditions?
How persistent or well defined were open water bodies?
What were their mechanisms of formation and how does this differ from the mechanisms governing terminal ponds?
In what ways can they be distinguished from the form and function of the larger floodplain basins?
How did riparian forest habitat vary regionally within the Delta (differences in tree type, relative stand density, etc.)?
How far downstream did riparian forest extend from different river mouths into the Delta?
How wide were riparian corridors, and how did this vary among rivers?
What habitats characterized the upland margin (e.g., oak savanna, grassland, alkali meadow, vernal pools, freshwater marsh)?
What was the relative extent of these different ecotone types?
How did the characteristics of the upland ecotone vary along the Delta margin?
What physical factors/gradients controlled these differences?
Are upland ecotone variations correlated with adjacent soil types or other persistent physical characteristics?
How did fluvial input affect the upland habitat characteristics?
What evidence is there for habitat use and distribution of fauna of particular interest (e.g., Greater Sandhill Crane, Least Bell's Vireo, Western Yellow-billed Cuckoo, Giant garter snake, Sacramento splittail, Delta smelt, Green sturgeon, Chinook salmon, Steelhead, tule elk, antelope)?
|Delta Historical Ecology Target Questions||57.42 KB|