linking biological responses to river processes › ncer2009 › pptpdf... · linking biological...

Linking bioLogicaL responses to river processesA Focal Species Approach to Restoration and Management of the Sacramento River

Bruce K. Orr1, Clifford S. Riebe1,2, and Ryan A. Peek1,3

1Stillwater Sciences, 2855 Telegraph Avenue, Suite 400, Berkeley, CA 947052 Department of Geology and Geophysics, University of Wyoming, Laramie, WY 3 Department of Biology, University of San Francisco, San Francisco, CA

Copies of the Linkages Report and other reports from the Sacramento Ecological Flows Study can be found online at:

http://www.delta.dfg.ca.gov/erp/sacriverecoflows.asp

Identify critical management issues using a representative yet manageable subset of information

Suggest actions that are likely to produce desirable benefits for the ecosystem

Identify remaining uncertainties and inform development of study plans

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The Ecosystem Linkages Study was undertaken as part of the Sacramento River Ecological Flows Study, which was initiated by The Nature Conservancy (TNC) in collaboration with ESSA Technologies, Stillwater Sciences, UC Davis, and UC Berkeley to define how flow characteristics (e.g., the magnitude, timing, duration, and frequency) and associated management actions (such as gravel augmentation and changes in bank armoring) influence the creation and maintenance of habitats for a number of native species that occur in the Sacramento River corridor.

What are the effects of flow and other riverine processes on species

and habitats in the Sacramento River ecosystem?

Linkages Study Goals

Six focal species were selected to represent a wide range of habitats and riverine processes (see table below).

Species Selection

Introduction

cHaLLengeThe processes, habitats, and species of the Sacramento River have been the focus of much study, and the volume of available reports and datasets poses a challenge for synthesizing information and organizing a discussion of ecosystem components. Divergent conceptual models about process–habitat–biotic linkages complicate the process of summarizing what is known about the Sacramento River, and add to the challenge of evaluating alternative approaches for conserving and restoring the

river ecosystem.

soLUtionTo help overcome these challenges, the Linkages Report

discusses and analyzes the Sacramento River through the lens of six focal species. A focal species approach

facilitates the exploration of linkages among ecosystem processes, resultant habitats, and biotic needs.

AcknowledgementsWe thank the following for contributing data and results and photographs from recent or ongoing studies:

Barry Garrison, Ron Schlorff, Carolyn Rech (CDFG) Lisa Micheli (Sonoma Ecology Center)Koll Buer (GOOD Geotechnical Consultants)Tara Morgan and Adam Henderson (CDWR)Mike Roberts and Greg Golet (TNC)Steve Greco (UC Davis)Nadav Nur (PRBO Conservation Science)Joe Silveira (USFWS)

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And the following for serving as report reviewers:

Greg Golet, Ryan Luster, Mike Roberts, Campbell Ingram (and others at TNC)Numerous workshop and public review participants from CDWR, CDFG, USFWS and other agencies

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This study was funded by grants to The Nature Conservancy from the CALFED Ecosystem Restoration Program (# ERP-02D-P61) and the

Resources Legacy Fund Foundation.

Western Pond Turtle

FIGURE 1 Habitats associated with chute cutoffs.

ccurs

FLOWING SIDECHANNEL

(former main channel)

Lake Occurs

OXBOW SLOUGH

OXBOW LAKE

EMERGENT WETLANDOR SWAMP

RIPARIAN FOREST

Periodic Inundation byModerate to High Flows

WETLAOR S

Flows Above BankErosion Threshold


New Main Channel

Eventual Reset by Progressive

Migration or Chute Cutoff

OrganicDebris

Main Channel Meander Bend

Progressive Channel Migration

Occurs

Sinuosity/CurvatureThreshold Reached

Chute Cutoff Occurs

Upstream Sediment Plug Forms

Downstream Sediment Plug Forms

Sedimentation in Lake Occurs

Continued Sedimentation

Riparian Vegetation Dynamics/Succession


Flows Above Cutoff Threashold

Occurs


Variable Flow Hydrograph


Periodic Inundation by Moderate to High Flows


Inundation byHigh Flows

Interactions with RiverSediment

Load

with Geologic

Riparian

Interactions

Constraints and

Vegetation

ccurs

FLOWING SIDCHANNEL


FLOWING SIDCHANNEL


Lake Occurs

OXBOW SLOUGH

OXBOW LA

WETLAOR S

RIPARIAN FOREST

Periodic Inundation byModerate to High Flows

WETLAOR S


Flows Above BankErosion ThresholdFlows Above BankErosion Threshold


New Main Channel

Eventual Reset by Progressive

Migration or Chute Cutoff

OrganicDebris

OrganicDebris

Main Channel Meander Bend

Progressive Channel Migration

Occurs

Sinuosity/CurvatureThreshold Reached

Chute Cutoff Occurs

Upstream Sediment Plug Forms

Downstream Sediment Plug Forms

Sedimentation in Lake Occurs

Continued Sedimentation

Riparian Vegetation Dynamics/Succession



Occurs



Occurs


Variable Flow HydrographFlows Above BankErosion Threshold

Variable Flow Hydrograph










Load


Load

with Geologic

Riparian

Interactions

Constraints and

Vegetation

with Geologic

Riparian

Interactions

Constraints and

Vegetation

with Geologic

Riparian

Interactions

Constraints and

VegetationRiparian

Interactions

Constraints and

Vegetation

Interactions

Constraints and

Vegetation

DecnovoctseptaugJulyjuneMayaprMarFebJanlife stage

juvenile and adult overwintering

juvenile growth and adult activity

Hatchling overwintering

Hatchling emergence –northern pattern

Hatchling emergence –southern pattern

Egg incubation

nesting

Month

DecnovoctseptaugJulyjuneMayaprMarFebJanlife stage

juvenile and adult overwintering

juvenile growth and adult activity

Hatchling overwintering

Hatchling emergence –northern pattern

Hatchling emergence –southern pattern

Egg incubation

nesting

Month

TABLE 1 High flow timing is critical because eggs are sensitive to moisture.

Bank Swallow

species key HabitatsKey Processes and Characteristics of the Ecosystem

Chinook SalmonOncorhynchus tshawytscha

gravel deposits, pools, eddy/point-bar complexes, side channels and sloughs, inundated floodplains

coarse sediment transport and bed surface scourwater temperature regimeavailability of cover and/or slow water during high flowstiming and magnitude of flowfish passage barriers

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SteelheadOncorhynchus mykiss

gravel deposits, pools, eddy/point-bar complexes, side channels and sloughs, inundated floodplains

availability of cover and/or slow water during high flowswater temperature regimetiming and magnitude of flowfish passage barriers

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Green SturgeonAcipenser medirostros

deep pools, gravel deposits

water temperature regimetiming and magnitude of flowfish passage barriers

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Bank SwallowRiparia riparia

steep cutbanks bank erosionprogressive meander migrationmeander bend cutofftiming and magnitude of flow

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Western Pond TurtleClemmys marmorata

oxbow lakes, side channels and sloughs, pools, inundated floodplains

progressive meander migrationmeander bend cutofftiming and magnitude of flowterrestrialization of off-channel water bodies

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Fremont CottonwoodPopulus fremontii ssp. fremontii

point bars, side channels and sloughs, oxbow lakes, inundated floodplains

vegetation successiontiming and magnitude of flowmeander migrationterrestrialization of off-channel water bodies

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The Sacramento River and its tributaries provide important nesting locations for bank swallow, accounting for approximately 70% of the bank swallow nesting in California. Losses in habitat and declines in the number of individuals and colonies suggest Sacramento River population may be highly prone to extirpation.Implication: persistence of bank swallows in California is at risk.

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FIGURE 2 Average number of bank swallow burrows per kilometer of 1997 centerline channel plotted against average meander migration rates for the Sacramento River.

Natural processes of progressive meander migration and channel cutoffs create freshly eroded banks that are an essential component of bank swallow nesting habitat.This relationship is apparent in the distribution of bank swallow colonies and nesting burrows: most nesting occurs in the actively migrating reaches of the river (see Figure 2).

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Riverine Processes and Bank Swallow Habitat

LOW SUITABILITY• high risk of nest failure

due to inundation, bank slumping, or bank erosion

HYDROGEOMORPHICPROCESSES

PROGRESSIVE CHANNEL MIGRATION

CHUTE CUTOFF

UNSUITABLENear Vertical

Fresh (≤ 3 years old)Cutbanks available in March and April

Friable soils present

Bank Height >2 meters and

Bank Length >25 meters

Grasslands and Other Foraging Habitat <200 meters from Colony

No High Flows or Rapid draw-downs during nesting (April–June)

• high predation risk

• high ectoparasite loads (in old nests)

UNSUITABLE• soils do not support

burrow construction

LOW SUITABILITY• high predation risk• high risk of inundation or

other disturbances

LOW SUITABILITY• high energetic cost of

foraging for adults when feeding nestlings

NO

NO

NO

NO

NO

YES

YES

YES

YES

HIGH FLOWS

BANK EROSION

High habitat suitability

FIGURE 3 Conceptual model of the influences of hydrogeomorphic processes and physical and physical habitat conditions on habitat suitability for bank swallow nesting in riverine systems.

H A B i tAt S u i tA B i l i t y M o d E l

California’s only native freshwater turtle and a state Species of Special Concern In large alluvial systems like the Sacramento River, the western pond turtle appears to rely predominantly on off-channel water bodies, such as oxbow lakes and sloughs, as it’s primary habitat Historically, the Sacramento Valley provided huge tracts of riparian forests and floodplain wetlands: over 95% of these floodplain wetlands have been lost

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importance of off-channel Waterbodies

Bank eroding flows can be good or bad for bank swallows, depending on the tim-ing of such flows (see Figure 4).

i M P o R tA n C E o F H i g H F l o W t i M i n g

BEN

EFic

iAL

RENE

WAL O

F NESTiNG SiTES

DISRUPTION OF PAIR

BONDING AND

DELAYED NESTING

DISRUPTION OF NESTING AND NESTLING REARING WITH HIGH MORTALITY

Marc h

april

Ma y

juneJuly

Aug .

sept .

oct.

nov.

Dec. jan.

Feb.

March

april

Ma y

juneJuly

Aug .

sept .

oct.

nov.

Dec. jan.

Feb.

FIGURE 4 Timing of high flow impacts to nesting

bank swallows.

i M P o R tA n C E o F H i g H F l o W t i M i n g

Off-channel water bodies (e.g., sloughs and oxbow lakes) are created by meander migration and channel cutoff processes. Once formed, off-channel water bodies eventually vanish from the floodplain as they are colonized by vegetation and filled with sediment and organic detritus during overbank flow events (Figure 1). Quantifying how these processes have changed is important for under-standing the long-term evolution of remaining off-channel water bodies.

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A key potentially limiting factor for the western pond turtle is the rela-tionship between water level and flow in off-channel water bodies during the summer incubation sea-son (see Table 1). During incuba-tion, eggs are extremely sensitive to increased soil moisture, literally exploding in wet conditions from internal pressure caused by water absorption.

Effects of Flow on Seedling Establishment

Key Management ConsiderationsW E S t E R n P o n d t u R t l E

B A n K S WA l l o W F R E M o n t C o t to n W o o d

FIGURE 5 Nearly half of the channel from Red Bluff to Colusa (RM 243-143) is now covered by rip-rap on at least one side. This photograph, taken in December 2006, shows a recent bank armoring project near RM 182. (Photo courtesy of Joe Silveira, USFWS)

B A n K A R M o R i n g P R o j E C t S C A u S E d i R E C t l o S S o F H A B i tAt

Manage high flows to promote natural bank erosion in the middle Sacramento River before the beginning of the breeding season (late March) while maintaining stability throughout the summer during the nesting season.

Identify locations where levee setbacks are likely to create a larger meander zone and thus promote natural bank erosion processes and increase potential nesting habitat.

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Conserve cutbanks, remove riprap, and retire bank armoring, as appropriate, in locations where meanders are likely to migrate into soils that are suitable for nesting colonies.

Evaluate stage-discharge relationships at key bank swallow nesting sites.

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Period of peak ac�vity

Period of off-

Period of peak ac�vity

Period of moderate ac�vity

Period of off-peak/low-level ac�vity

Conduct basic surveys to assess the abun-dance and distribution of western pond turtle.

Manage flow regimes to promote the natural bank erosion, meander migration, and chan-nel cutoff in the middle Sacramento River.

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Implement opportunities to retire bank armoring and/or setback levees in the middle Sacramento River.

Manage flows during the summer nesting season to reduce risk of nest inundation.

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Manage the recession limb of spring high-flow events and summer base flows in wet water years to promote seedling es-tablishment of cottonwoods and willows.

Promote of channel migration to create new seedbeds for cottonwood recruit-ment through scour and fine sediment deposition.

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Promote strategic horticultural restoration on higher floodplains surfaces where passive recruitment is infeasible.

Prioritize actions to eradicate and control invasive plant species.

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Cottonwood seedlings require bare mineral sub-strates (typically found on recently formed point bar surfaces) and appro-priate soil moisture con-ditions for successful es-tablishment (Figure 6).

Altered flow regimes below large dams can substantially reduce the frequency and extent of successful establishment of new cohorts of cot-tonwood seedlings

Flow conditions during spring and summer are key factors affecting cot-tonwood seedling sur-vival.

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Fremont Cottonwood

Riparian vegetation dynamics are tightly coupled with riverine processes. Flooding, scour, and sediment deposition strongly influ-ence riparian plant species composition, distribution, and physical structure and are major drivers of riparian com-munity succession.

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L i n k i n g r i v e r i n e p r o c e s s e s A n d V E g E tAt i o n dy n A M i C S

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D = Disturbance RecurrenceInterval

R = Recovery Phase Dura�on

P = Persistence

Dura�on

Fluvial Geomorphic Processes

Infrequent Flood Disturbance (R<D)

Frequent Flood Disturbance (R>D)

D

PR

Bio

mas

s

Time

TimeD

R

Bio

mas

s

Hig

h

Low

Low

Freq

uenc

y of

Flo

odin

g R

elat

ive

Elev

atio

n

Dep

th to

Gro

undw

ater

Low

Hig

h

Hig

h

ErosionProgressive channel migra�on

Channel avulsion/cutoff

Late -Seral Communi�esValley oak riparian forest

Elderberry savanna

Recent Alluvial Deposi�onChannel bar deposits

•Abandoned channel/backwater depositsOverbank floodplain deposits

Pioneer Scrub Communi�esWillow scrub

Pioneer ForestCommuni�es

• Co�onwood forest

Mid Seral Communi�esMixed riparian forest

Fluvial Geomorphic Processes

Infrequent Flood Disturbance (R<D)

Frequent Flood Disturbance (R>D)

D

PR

Bio

mas

s

TimeD

PR

Bio

mas

s

Time

TimeD

R

Bio

mas

s

Hig

h

Low

Low

Freq

uenc

y of

Flo

odin

g R

elat

ive

Elev

atio

n

Dep

th to

Gro

undw

ater

Low

Hig

h

Hig

h

Hig

h

Low

Low

Freq

uenc

y of

Flo

odin

g R

elat

ive

Elev

atio

n

Dep

th to

Gro

undw

ater

Low

Hig

h

Hig

h

Phase

FIGURE 7 Conceptual model of the influence of flood disturbance and flu-vial geomorphic processes (sediment transport, ero-sion, deposition) on ripar-ian vegetation succession. Along geomorphically ac-tive meandering streams, riparian vegetation typically exhibits two distinct pat-terns or pathways of initial establishment: colonization on bare substrates associ-ated with point bars created by progressive channel mi-gration, and bare substrates associated with abandoned channels or oxbow lakes and sloughs created by me-ander cutoffs and channel avulsion.

F IGURE 6 This figure shows the generalized pattern of successful seedling recruitment observed for cotton-woods and willows along alluvial rivers. Seedlings that germinate too high on the bank cannot grow roots fast enough to keep up with the receding water table and soil moisture level during the hot summer months, while seedlings that initiate too low on the bank are removed by scour during high flow events during the subsequent winter or spring. Recent work at three point bars between RM 192–172 indicates that successful cottonwood recruitment occurs at relative elevations of 3–9 ft (1–3 m) above summer baseflow levels.

Water table decline too rapid for seedling survival

Seedlings killed by later floods

Successful recruitmentSand bar

Summer base flow

High Flood line

t

The Sacramento Valley has lost over 98% of its riparian forests since 1850.The greatest extent of cot-tonwood riparian forest remaining along the Sacra-mento River occurs in the 100 river miles between Red Bluff and Colusa.

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Fremont cottonwood is the dominant tree species of near-river forests where it provides ecological struc-ture to the riparian corridor by stabilizing substrates, fix-ing carbon, generating LWD, and creating habitat for wildlife species.

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Relatively modest changes in the managed flow regime of the Sacramento River, coupled with physical habitat restoration, could improve the extent, quality, and uti-lization of habitat for multiple species (see table 2).

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CONCLUSIONS

CHANGE FLOWS to promote off-channel rearing

Species affected

Remove Revetment

to promote plant succession

to enhance meander migra�on

in upper river

Fremont

co�onw

ood

western

pond turtle

bank sw

allow

green sturgeon

steelhead

Chinook

CHANGE FLOWS

Management ac�on

REMOVE REVETMENT

CHANGE FLOWS

ADD GRAVEL

Fremont

co�onw

ood

western

pond turtle

bank sw

allow

steelhead

Chinook

? ?

primary benefit to species

secondary benefit or poten�ally adverse impact

effects depend on �ming and magnitude of flows

?

TABLE 2 Examples of management actions that might benefit multiple species. Note that in same cases, actions beneficial to one species might have negative effects on other species. See Linkages Report and Final Report for more details.

Successful restoration of the Sacramento River eco-system will depend in large part on the preservation and enhancement of natural river migration processes, which are critical to the formation and preservation of off-channel habitats as well as to the healthy exchange of sediment from the mainstem to the floodplain.

The idea that active meander migration is critical to ecosystem health is at the heart of the “meander zone” concept. An assemblage of conservation partners has striven to assemble a coherent meander zone for the last 20 years by acquiring flood-prone lands from willing sell-ers within the floodway corridor. Some of the acquired lands have been actively restored by planting native veg-etation.

Considerable uncertainty remains regarding some “link-ages” between management actions and the ecological targets of restoration managers. Because these linkages are complex and interdependent, additional study is re-quired to identify and optimize flow management sce-narios that are consistent with a multiple benefit design strategy.

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