David Walker PhD University of Arizona Compared to NorthTemperate Regions Increased drainage area size Flashy hydrology Watersheds prone to increased disturbance Elevation gradients ID: 271923
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Slide1
Reservoir Limnology of Arid Regions: Problems with Predictability.
David Walker Ph.D.
University of ArizonaSlide2
Compared to North-Temperate Regions.
Increased drainage
area size.
Flashy hydrology
.
Watersheds prone to increased disturbance.
Elevation gradients.
Wildland
Fire.
More productive with fewer bio-available nutrients. Slide3Slide4Slide5
More Prone to the Effects of Climate Change
Thinner
snowpacks
.
Relicts from last Pleistocene will dwindle.
Increased frequency and intensity of erosive events.
Increased nutrient loading in aging reservoirs. Slide6
From Meta- to Micro- Scale.
Phytoplankton assemblages are extraordinarily patchy.
Overall biomass is difficult enough to model!
Knowing what assemblage types to expect under any given set of conditions is extraordinarily difficult. Slide7Slide8
Large-Scale Models
Based on “mean-field” approaches.
Ecological patchiness is smoothed
Advantages:
Tractability
Few parameters
Clear interpretationSlide9
Disadvantages
Patchiness is smoothed out(!)
Micro-scale dynamics are impossible to ascertain.
Yet these are often the metrics we are most concerned about.
The effect of the multitude of possible disturbance types is difficult to determineSlide10
Commonly Used Lake/Reservoir Models for TMDL Development
Watershed Models
Loading Simulation Program in C++ (LSPC)
Watershed Assessment Model (
WAMview
)
Storm Water Management Model (SWMM)Slide11
Receiving Water Models
A Dynamic One-Dimensional Model of Hydrodynamics and Water Quality (EPDriv1)
Stream Water Quality Model (Qual2K)
Conservational Channel Evolution and Pollutant Transport System (CONCEPTS)
Environmental Fluid Dynamics Code (EFDC)
Water Quality Analysis Simulation Program (WASP)
EUTROMOD
BATHTUBSlide12
Problems with Quantification
“Examples
of indicators
for a
nutrient TMDL include total
phosphorus
concentration
, total
nitrogen
concentration,
chlorophyll
concentration
, algal biomass, and percent
macrophyte
coverage.”
Target values for indicators then need to be established.
“Although
such discrete impaired and unimpaired cutoffs do not exist in natural
systems, quantifiable goals nevertheless are a necessary component of TMDLs.”Slide13
Square Pegs and Round Holes
Often nebulous correlations between nutrient concentrations and both type and amount of phytoplankton…or any indicator for that matter.
We simply do not know all the environmental requirements for any given species of alga to grow and survive.
Let alone interactions between species. Slide14
Although models are able to predict pollutant concentrations and movement with decent accuracy, they often fail completely at determining the biological response. Slide15
Lake and Reservoir Characterization is Difficult
All are unique
Spatial and temporal variability
Biotic interactions the we cannot (yet) detect
Nebulous correlation between environmental change, disturbance, etc. and biotic response. Slide16
A Three-Pronged Approach
1)
Coordinated monitoring and sampling.
Taking spatial and temporal variability into account.
Covers the “uniqueness” of individual areas.
Helps to understand the biotic response to environmental conditions.
Needs to be on-going. Slide17Slide18
2) Field and Laboratory Studies
To determine specific lake/reservoir responses following manipulation.
Replication and control.
Based upon logical findings and observations.Slide19Slide20Slide21
INSERT CORING PICSlide22
Constant Model Calibration
Data collected during monitoring and field/laboratory studies used to determine individual reservoir response to a wide variety of environmental conditions.
Models individualized.
Model refinement should be on-going.
Heuristic. Slide23
A Narrative Approach
Square Pegs and Round Holes
We cannot quantify the, as of yet, un-quantifiable.
Defining reservoir condition should include a combination of quantitative, semi-quantitative, and qualitative approaches.
A
multi-tiered approach is the one most grounded in reality. Slide24
Questions