LAKE ECOLOGY Unit 1: Module 2/3 Part 4 – Spatial and Temporal variability January 2004.

LAKE ECOLOGY

Unit 1: Module 2/3 Part 4 – Spatial and Temporal variabilityJanuary 2004

Developed by: R.Axler and C. Hagley Draft Updated: January 14, 2004 U1-m2/3Part 4-s2

Modules 2/3 overview

Goal – Provide a practical introduction to limnology

Time required – Two weeks of lecture (6 lectures) and 2 laboratories

Extensions – Additional material could be used to expand to 3 weeks. We realize that there are far more slides than can possibly be used in two weeks and some topics are covered in more depth than others. Teachers are expected to view them all and use what best suits their purposes.


Modules 2/3 outline

1. Introduction2. Major groups of organisms; metabolism3. Basins and morphometry4. Spatial and temporal variability – basic

physical and chemical patchiness (habitats)5. Major ions and nutrients 6. Management – eutrophication and water

quality


4. Spatial & temporal variability – basic physical and chemical patchiness (habitats)


4. Spatial & temporal variability – basic physical and chemical patchiness (habitats)

Physical structure – morphometric features Physical properties – vertical patterns of light,

temperature and density Density stratification effects on chemistry

O2 pH, EC25 (specific conductivity/salinity) nutrients (in section 5)


The size and shape of the lake matter

Shoreline development Habitat Aquatic plants Water movement Erosion potential Privacy for people

Here’s 40 acre Ice Lake compared to 14,500 acre Lake Minnetonka


Lakes: spatial variability 1

How might water quality vary between site 1 and site 2?

How might their aquatic organism communities differ? Fish Zooplankton Algae Plants



How might water quality vary between sites 1, 2 and 3?

How might aquatic organism communities differ? Fish Zooplankton Algae Plants


How might water quality vary across this lake?

How might aquatic communities differ? Fish Zooplankton Algae Plants

Minnesota or Wisconsin bass-bluegill lake




Here’s a western US reality check

What are major sources of variation for this system ? Water Quality Fish Zooplankton Algae Plants

California bass-bluegill lakeZ-max ~ 4 mArea ~ 10 acres Watershed - ??

(urban runoff)Wind & water flow –

westerly


Riverlake, Sacramento, CA

Price: $798,000 (Sep ’03) Sq Ft: 3511 Year Built: 1990 Bedrooms: 4

“…Just minutes from downtown, you'll feel like you are living at a resort in the city! Dynamic architecture brings the lake view to all major rooms”.

… an upscale community … commenced development in 1987… Currently, it consists of 11 villages comprising approximately 1,000 home sites (incl. 150 lake front lots),…


Persistent seasonal and short-term longshore currents in Lake Superior

Upwelling and downwelling regions Sediment transport from shoreline erosion and deepwater

resuspension Where do you sample ? How might water quality and aquatic

communities vary spatially and temporally ? Where do stormwater and sewage overflows from Duluth go ?

•Duluth

Horizontal variations from physical factors


Water movements- currents and waves

Waves consist of the rise and fall of water particles, with some oscillation but no net flow

Currents consist of net unidirectional flows of water

•credit: www.aquatic.uoguelph.ca/lakes/waves


Surface waves

Surface waves are wind-driven. Regular patterns of smooth, rounded waves are called swells. Capillary waves have wavelengths less than 6 cm

and are restored to equilibrium due to the surface tension of the water

Gravity waves have wavelengths greater than 6 cm and fall due to the force of gravity


•Resuspension importantparticularily in shallow lakes but also in deep lakes

Resuspension of nutrients and sediments


Generated by steady wind Surface water driven downward Water piles up on the lee shore Water flows back due to gravity Standing wave rocks back and forth with

decreasing motion = "surface seiches" Sloshes at resonant frequencies based on

basin shape Can also result from landslides, air pressure,

and earthquakes

Standing waves - surface seiches


Standing waves - surface seiches cont.


www.northernimages.com

St. Louis River – Lake Superior seiches

The St. Louis River enters western L. Superior at the Duluth Aerial Lift Bridge

The site is influenced not only by river water flowing downstream but also occasionally by Lake Superior water flowing upstream due to the lake's seiche


St. Louis River – Duluth inlet data

Brown stripes are periods when water flows out into the lake

Blue indicates “negative” velocity when the lake is sloshing back into the bay

Which water body has higher EC ?

What factors influence the turbidity plot ?


Horizontal & vertical variability

• How do light, temperature, sediments vary across these zones ?

• How do plants, periphyton, invertebrates, fish and algae vary ?

LITTORAL ZONE LIMNETIC ZONE

Major Lake Zones


Littoral zone – usually shallow, nearshore region where sufficient light can penetrate to the bottom for plants to grow (~ 1% of midday surface light intensity)

Often estimated as that area of the lake’s surface either <10 ft (3m) or <15 ft (~5 m) deep

Where the majority of aquatic plants are found; a primary habitat for young fish

NRRI image

Littoral Zone


A "natural" shoreline

An altered shoreline

WI DNR

WI DNR

Shorelines


• Can you explain each seasonal pattern ?

• What might cause the mid-summer nutrient spikes ?

• Is this likely to be a stratified or unstratified lake and why ?

•Secchi depth

•Nutrients N or P

•Bottomwater- O2

winter

spring

summerfall

winter

Temporal variations - seasonality


Lake Ecology Module – light, temp, density, O2

The following slides represent the temperature, density, dissolved oxygen, and stratification portion of the Lake Ecology introductory lecture module 3+4, subtopic 4

Additional explanatory information is available by viewing the attached Notes for each slide


Density, Thermal and Oxygen Stratification

Temperature and oxygen levels are major factors regulating aquatic organisms

The layering of lake waters due to density differences is a major factor structuring the ecosystem and creating distinct habitats

The seasonal pattern of turbulent mixing is also a critical determinant of ecosystem function and community structure


A Review of Some Basic H2O Physics

DENSITY The warmer the water, the

better it floats, but ice floats too

Water becomes less dense as it warms

The difference in density per degree of warming increases as temperatures rise

SO ….


Density layering

Surface water is very buoyant because of the big density difference between it and cold bottom water (leading to stable thermal stratification)

Bottom water is colder than the surface in summer (and a bit warmer in winter)


Gas Solubility

Temp (o C)

Temp (o F)

O2- Sol(mg/L)

0 32 15

5 41 13

10 50 11

15 59 10

20 68 9

25 77 8

• Warmer water holds less gas (warm beer goes flat)

• As 100% air-saturated water warms, it loses O2


Dep

th

Lightx

x

x

x

Plotting profiles - light


Heat and Light

Light intensity decreases exponentially with depth in a lake

Which curve is the clear lake – blue or black ?

What shape would you expect for the profile of temperature ?


Vertical light extinction

Light intensity decreases exponentially with depth and is well described by the Beer-Bouguer-Lambert Law which states that:

I(z) = I(0) * [ e-kz ]

Where:

I(z) = intensity of light as a function of depth z

I(0) = intensity of light at the surface (0 m)

k = the vertical extinction or attenuation coefficient.


• The lake surface is exposed to the wind, which mixes the surface water, but the turbulent energy from the wind dissipates with depth, having less impact further down.

• The greater the density difference (mostly from temperature) between layers of water, the harder it is to mix them together.

Heat, as indicated by temperature would also be expected to decrease exponentially with depth, BUT ….

Wind: turbulent mixing


Wind mixing links

• Also see slides in Section 5 (Water Chemistry) of this module that discuss gases (O2, N2,CO2 and H2S)


Depth

Temperaturex

x

x

x

The Temperature profile would look just like the light profile – at least on a perfectly calm day

Temperature – calm day


Depth

Temperaturex

x

x

x

• But when the wind blows, it mixes the surface water with deeper water

• And its energy dissipates with depth

xx

Temperature – windy day


Depth

Temperature0oC


Depth

Temperature0oC 10oC


Depth

Temperature0oC 10oC 20oC


Bottom water colder than surface in summer

Surface water is very buoyant

BIG density difference between surface and cold bottom water = resistance to mixing

Mid-summer thermal stratification


Depth

Temperature0oC 10oC


Depth

Temperature0oC

Fall Turnover


Depth

Temperature0oC


Thermal stratification sequences

•Ice Lake, MN

•Apr 23 – Jun 3, 2003

•Shagawa Lake, MN

•May 7 – Jun 24, 2003

•Lake Independence, MN

•Apr 12 – Jun 29, 1999

•Temperature (o C)

time


Oxygen

What are the sources of oxygen to a lake?

What are the sinks for oxygen in a lake?


Wind energy

Photosynthesis

Two Major Sources of O2


Major Sinks (losses)

O2 O2O2

Diffusion

Water column respiration

Sediment respiration (bacteria and benthos)


Factors affecting dissolved oxygen levels

• How far down can light penetrate ?• Is the lake thermally stratified ?• How windy is it ?• Are there a lot of aquatic plants and algae ?• How warm is the lake ?• Is there a lot of organic “gunk” in the water ?• Are there sources of fertilizer, ag & urban runoff,

wastewater, etc. coming in ?• How much organic sediment area is there

relative to hypolimnetic volume ?


“Idealized” Stratification Curves

Un

pro

du

ctiv

eP

rod

uct

ive


Mid-summer thermal stratification - summary

Surface water is very buoyant – it floats on top of the thermocline

BIG density difference between surface and cold bottom water

It takes a lot of wind energy to push the surface water down long enough to mix with the water below

Bottom water is colder than the surface in summer


Annual cycle of thermal stratification - dimixis


Illustrations of Water on the Web lake data visualization tools (DVT’s):

Profile plotter (all parameters vs depth)

Color mapper (2 parameters vs depth)

DxT (depth vs time)

Reality – “real” data


Profile Plotter

West Upper Bay of Lake Minnetonka

8/31/2000

Temperature

Thermocline

Dissolved oxygen

Scales: oC and ppm O2

• Strong temperature and DO stratification

• No O2 below thermocline


Color Mapper

BackgroundBackground Scale

DO TempLine plotLine plot

Scale

Anoxic below

thermocline


Color Mapper - Shallow Lake

DO Temp


Seasonal Cycles of Temperature & Oxygen


Partial Mixing in Medicine Lake, MN

Temp

DO

8/31/2001

Is it totally mixed ?


Interpreting profiles – Ice Lake #1

Questions

1. Time of year ?

2. Explain profiles

• Temp

• DO

• pH

Temp

pH

DO


Interpreting profiles – Ice Lake #2

Questions

1. Time of year ?

2. Explain profiles

• Temp

• DO

• pH

Temp

pH

DO


Seasonal Cycles in Ice Lake, MN (Profile Plotter)

Temp

pH

DO

Here’s the full annual cycle on a monthly time step


Seasonal Cycles in Ice Lake, MN (Color Mapper)


Interesting Summer O2 Depth Profiles

Ice Lake Grindstone Lake

6/14/99 6/20/99


Compare with Three Nearby Lakes (June 1999)

Q1: Why is West Upper temperature so different?

Q2: What caused the strange West Upper O2 profile?

Halsted’s Bay, Minnetonka West Upper, L. M’tonka L. Independence


Onondaga midsummer – color mapper

• Set the color mapper for mid Aug 2003 (this profile is from Aug 22, 2003. Set EC to 1200-2200 uS/cm (in red), DO to % sat (black) and pH in blue

• DO > 150% from 0-3m and then <10% down to the bottom !

• pH drops >1 unit from 3 down to 5 m

• EC jumps up and down by 400 uS/cm !

Very dynamic data set


Depth versus Time Plotter (DxT)

Time of Year Location Parameter

Scale

Dep

th


Annual Temp & O2 in a Shallow, Productive Bay –

Halsteds Bay, L. Minnetonka

•Temp

•O2


Compare two bays of the same lake Halsteds and West Upper, Minnetonka, MN

Halsteds

West Upper


Medicine Lake - summer stratification


Ice Lake, MN - Interannual variation

Fall mixing

Fallmixing ?

Fall mixing

Fallmixing

spring mixing

rate of thermocline descent

No spring mixing

No spring mixing

No spring mixing

“rate of hypolimnetic O2 –depletion”


Ice Lake, MN: 1998-2003

Complete Mixing

Spring:

No-98,99,01

Yes- 00,02,03

Fall:

No-00 ??

Yes- 98,99,01,02


DO-Temperature squeeze on fish

Thermal stratification can be a challenge for coldwater & coolwater fish

Too little DO where the temperature is optimal

How would a warm water discharge from a new power plant affect the fish community ?

How would global climate change affect the fish ?


Case study of density layering - reservoirs

The influent water “seeks” its own density (and destiny)

Balance of temperature, dissolved salts and silt load

Varies seasonally

See movies in the WOW Lake Ecology Primer showing aquarium lake models at

http://wow.nrri.umn.edu/wow/under/primer/page5.html

Schematic from NALMS. 1990. The lake and reservoir restoration guidance manual. 2nd edition. North American Lake Management Society and USEPA Office of Water, Washington, D.C. EPA-440/4-90-006 August 1990.


USBR: http://www.hooverdam.usbr.gov/

Lake Mead, NV-AZ, USA


Mainstem Colorado R. Lifeblood of SW US Largest reservoir in US National Recreation Area

A: 158,000 acres V: ~ 21-26 million acre-feet z-max: ~ 150 m (main basins) z- max ~ 2-55 m (LV Bay )

• power for 500,000 homes

(2,074,000 kilowatts)

• drinking water ~20 million

• irrigation ~1 million acres

• wastewater ~ 153 mgd

• oligotrophic - main basins

• eutrophic Las Vegas Bay

• municipal sewage

• density plumes can combine

wastewater & drinking water

Lake Mead, NV-AZ, USA - features


DW intake

Las Vegas Bay

Boulder Basin- Sentinel I.

Hoover Dam

Lake Mead, Las Vegas Bay – images


Lake Mead – Boulder Basin images

Inner LV Bay

LV Bay

Sentinel I.

Effluent Inflow

About 120 million gallons of treated wastewater

flows into the inner Las Vegas Bay each day


April 1996

Density due to temperature vs salt load from sewage controls where the plume goes

EC

TEMP

DO

•pH

DE

PT

H (

m)

•Bottom scale: miles from LV Wash inlet

Salinity (EC25) overrides temp and the water mass sinks as it moves into bay

This is the approximate location of the Saddle I. drinking water intake

Warm over cool

Graphs from LaBounty, J.F. and M.J.Horn. 1997.


Density plumes – Outer Vegas Bay, L. Mead AZ

pH

DO

EC

TEMP

DE

PT

H

These graphs show how LV Bay water moves into the main lake in Boulder Basin

Drinking Water intake Hoover Dam– 10 miles out

Low salinity, narrow stratum of water is the “remains” of the Colorado River flowing down lake for over 70 miles

High salinity (EC25), low DO plume from wastewater

Graphs from LaBounty, J.F. and M.J.Horn. 1997.


Lake Mead – Las Vegas Bay RUSS DxT data

Data from ~ mid Bay for April – August 2003

T

DO

EC

pH

Explain the pattern for each parameter


Lake Mead – Las Vegas Bay DxT scaling

•An example of how playing with the scale adjustment on the DxT tool can highlight the behavior of a stratum of water


Lake Onondaga – also has a density layer

Corresponding DO (% saturation)

South Deep site

DxT: start 6/21/03 for 85 d

What’s causing the high salinity layer that is ~ 10 m thick ?

LAKE ECOLOGY Unit 1: Module 2/3 Part 4 – Spatial and Temporal variability January 2004.

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Transcript of LAKE ECOLOGY Unit 1: Module 2/3 Part 4 – Spatial and Temporal variability January 2004.