Potomac Flow-by

Stated Management Objectives

• (1) estimate the amount and quality of biotic habitat available at different flow levels, particularly as it relates to the current minimum flow-by requirement

• (2) determine what instream flows are required to protect adequate habitat and to prevent a reduction of any representative important species beyond levels from which it cannot recover and re-colonize the area following a drought event.

Potomac Flow-byStated Management Objectives

• Many scientific issues to accomplish this objective.

• (1) estimate the amount and quality of biotic habitat available at different flow levels, particularly as it relates to the current minimum flow-by requirement

• (2) determine what instream flows are required to protect adequate habitat and to prevent a reduction of any representative important species beyond levels from which it cannot recover and re-colonize the area following a drought event.

Ecological Theory

• Disturbance = discrete event that causes mortality, alters resources, etc.

• Extreme event within natural range of variation (e.g., severe drought)

Systemstate Resistance and

Resilience

Time

Noise: - biological - sampling

Time

Systemstate

3 “parameters”

• System State• Time scale to measure system

state, recovery • Nature of disturbing force

• Management objectives direct how these 3 parameters are characterized and dictate data requirements.

Systemstate

Time

System State

• Ecological Scale– Single vs. many species

– Ecosystem process

• Ecological Grain– Fine: Abundance

– Coarse: Presence/Absence

Systemstate

Time

System State, 2 examples

• 1. Population Abundance– Population numbers recover after disturbance to “dynamic equilibrium”– Requires pre-disturbance population estimates– Population data naturally noisy, very dependent on ...

• Where samples taken• When samples taken (time since disturbance)• Spatial scale of “study area” relative to movement of individuals (metapopulation

dynamics)• Antecedent population dynamics• Life history of species, life stages affected

Time

Systemstate

System State, 2 examples

• 2. Community Persistence– All species persist within study

area (i.e., stay “in the game”)

– Data less noisy (coarser grain)

– Target most sensitive species for population estimates?

Time

Systemstate

Nature of Disturbance

• Specific components– Magnitude or intensity– Frequency (Once per year? Decade?)– Timing (Spring? Summer?)– Duration

• Characterize relative to ecological response variables• Data quality to characterize?

Time

Systemstate

Disturbance Frequency/Magnitude

• Natural “100 yr” drought?

Time (years)

Systemstate

Time (years)

Systemstate

• “Anthropogenic” droughts?

Management Objectives• (1) estimate the amount and quality of biotic habitat available at

different flow levels, particularly as it relates to the current minimum flow-by requirement

• (2) determine what instream flows are required to protect adequate habitat and to prevent a reduction of any representative important species beyond levels from which it cannot recover and re-colonize the area following a drought event.

• Is goal to provide a “high degree of protection” [risk assessment] or simply “quantify habitat at low flows?”

• CAVEAT: Reduction in “habitat area” per se does not necessarily translate directly into linear biological response. Must consider aspects of system that allow for resilience:– species behavior (movement) and tolerance– landscape scale (refugia, connectivity)

Points for Potomac• What is “System State” of interest?• Dynamic River System!

– Lots of natural flow variation, both intra-annually and inter-annually

– Lots of attendant biological variation (“noise”)– Ability to detect response and recovery to “drought”

depends on biological data (which appear to be limited)– Ecological Principle -- keep system within natural

range of variation and “system” will “persist”.