EVPP 550 Waterscape Ecology and Management – Lecture 11

EVPP 550Waterscape Ecology and Management – Lecture 11

Professor R. Christian

JonesFall 2007

http://www.artquotes.net/masters/monet-paintings.htm

Lake Biology – FishMajor Freshwater Groups

• Salmonidae– Trout and salmon– Distribution

• Clear, cool waters• Rivers & streams:

moderate to swift• Lakes: cool & well

oxygenated

– Food sources• Aquatic insects• Small fishes

Brook Trout – native to E. US

Rainbow Trout – native to W. US

Lake Whitefish – native to Gt. Lakes & other northern lakes


• Esocidae– Pikes, muskellunge– Distribution

• Shallow, weedy waters

• Large clear lakes & ponds

• Slow-moving rivers

– Food sources• Small fishes

Northern Pike – native to E. US

Muskellunge – largest pike – native to E. US

Chain Pickerel – native to E. US


• Cyprinidae– Minnows, chubs,

dace, shiners– Most are small– Distribution

• Widespread in both lakes and stream

– Food supply• Aquatic insects• Small crustacea• Oligochaetes

Blacknose dace – very common native

Common carp – native of Eurasia – can get large

Golden shiner – native forage fish

Creek chub – common creek forage fish


• Catostomadae– Suckers– Distribution

• Widespread in lakes and streams

– Food supply• Aquatic insects• Small crustacea• Oligochaetes• Periphyton

White sucker – common and tolerant creek fish

Northern hogsucker – creek fish that eats periphyton

Silver redhorse


• Ictaluridae– Catfish, bullheads– Distribution

• Slow-moving still waters often with muddy bottoms

– Food supply• Aquatic insects• Oligochaetes• Benthic items

Channel Catfish – native to S. US – can get 20 lb

Margined madtom – very small creek fish

Black bullhead – common in Potomac


• Centrarchidae– Sunfish, bass, crappie– Distribution

• Widespread, tendency to warmer waters

– Food supply• Aquatic insects• Crustacea• Molluscs• Fish (in large individuals)

Pumpkinseed sunfish –common in ponds and lakes

Bluegill sunfish

Largemouth bass – common piscivore in lakes and ponds


• Percidae– Perches, darters– Distribution

• Widespread

– Food supply• Aquatic insects• Crustacea• Molluscs• Fish in larger

individuals

Yellow perch – common early spring spawner

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Walleye – large lake and river species

Tesselated darter – small creek and lake species

Lake Biology – FishGlobal Distribution

Lake Biology – FishGlobal Distribution

Lake Biology – FishTrophic Roles

• Planktivores– Mostly zooplankton– Some (eg Tilapia) eat

phytoplankton– Some are filter

feeders, strain plankton through gill rakers (whitefish, gizzard shad)

– Others attack individual zooplankton (bluegill sunfish)


• Benthivores/ Detritivores– Some selectively feed

on individual prey (trout)

– Some consume bulk bottom material (catfish)

– Often looking for benthic inverts, but consume detritus and bacteria as well

– Some (suckers) feed on periphyton too


• Piscivores– Feed on other

fishes– Often will eat

young of their own species

– Largemouth & smallmouth bass

– Muskellunge

Lake Biology – FishLife History

• Most fish reproduce annually over a fairly short period producing a cohort

• Reproduction often occurs in spring or early summer in temperate areas

• Eggs hatch rapidly and larvae progress to juveniles over a few weeks

• Sexual maturity (adult status) may be reached in 1-3 year

Lake Biology – FishLife History

• Larvae are poor swimmers and if in the water column, they are considered plankton – ichthyoplankton

• Larvae feed on small zooplankton (rotifers, cladocera, nauplii)

• Some fish build nests & guard eggs and larvae

• Newly hatched larvae called “young-of-the-year”

Size structure of a fish population related to age classes (cohorts)

Note much lower numbers of 2 and 3 year olds: mortality or age class strength?

Lake Biology – FishFactors affecting growth

• Temperature– Has a strong effect

on growth rate and feeding rate

– Cold water species reach maximum growth rates at lower temperature


• Temperature– Also has an effect on spawning success– Warmer summer temperatures may allow young-of-the- year to

become large enough to avoid winter predation

Effect more consistent for pike


• Food Supply– White perch ate

large numbers of both zooplankton and benthos in spring

– Benthos (chironomid larvae) became more important in summer and fall White Perch feeding in

Gunston Cove


• Food Supply– Fish exercise selectivity– Gut contents have different contents than the environment

White perch in Gunston Cove

Much more scatter in environment (benthos and zooplankton) than in the fish stomachs

Fish stomach biased toward chironomid larvae, environment has a lot of oligochaetes and zooplankton too


• Food Supply– As they pass through

the larval stage, fish may exert strong pressure on larvae for a limited time and then move on to other food

– Zooplankton rebound both in numbers and size Oneida Lake: June through Oct

period shown

Strong pressure by age-0 yellow perch abates as their number decreases

Lake Biology – FishPatterns of Abundance & Production

• Resource & Habitat Partitioning– Partitioning is thought to have evolved to minimize

competition


• Habitat Selection– Many fish prefer vegetation and collections are often

greater at night


• Effect of variable year classes– Fish populations are often dominated by individuals from

particularly strong year classes (ex 1959, below)– Many years can have very low success– Can track successful years over time


• Effect of Bottom Up Processes– In Virginia reservoirs a

strong correlation was observed between total P (“base” of food web) and fish production (top of food web)

– Correlation also held when looking at a single lake (Smith Mountain Lake) over time


• Effect of Bottom Up Processes– The same trend but with

a different slope has been found in other systems


• Effect of Bottom Up Processes– A similar relationship

has been observed comparing fish production and primary production

– These all argue for bottom-up control of fish production


• Top Down Processes– The imporance of top-

down processes is emphasized by the Trophic Cascade model

Management of Freshwater Systems

• Freshwater is a valuable resource for:– Drinking water– Living resources– Food supplies– Irrigation– Transportation– Other

• It’s use may be impaired by pollutants– Decomposable organics

(BOD)– Excess nutrients– Acidification– Toxic chemicals– Hormones– Erosion and Sedimentation– Salinization– Other

Management – Decomposable

Organics

• Human and animal waste is very rich in partially decomposed organic matter and other substances

• When placed in a water body either directly or via a conveyance system (sewer) this can be very destructive

Managemenent – Decomposable Organics

• The input of raw or poorly treated sewage creates a whole chain reaction of problems downstream

• Immediately below the release, BOD (decomposable DOC) and ammonia are highly elevated which stimulates bacteria and causes rapid depletion of DO, often to 0

• As water moves farther downstream, the BOD is used up, but it takes longer to oxidize the ammonia (through nitrification)

• In zone II, algal blooms are rampant because P has not been removed and now other conditions are favorable

Management – Decomposable

Organics

• Sewage treatment facilities typically strive to remove BOD and solids through sedimentation (primary trt)and microbial breakdown (secondary trt)

• More advanced facilities try to remove N&P

• Basically, you try to move what would happen in nature into a controlled setting that doesn’t impact the natural environment

Excess Nutrients – N&PNatural Eutrophication

• Productivity of lakes are determined by a number of factors:– Geology and soils of

watershed– Water residence time– Lake morphometry– Water mixing regime

• Over thousands of years these factors gradually change resulting in lakes becoming more productive

Cultural Eutrophication• Human activities can alter

the balance of these factors, esp. when excess nutrients (P in freshwater) are introduced

• Untreated sewage for example has a TP conc of 5-15 mg/L

• Even conventionally treated sewage has about ½ that.

• Compare that with inlake concentrations of 0.03 mg/L that can cause eutrophic conditions

• So, even small amounts of sewage can cause problems

Cultural Eutrophication

• Problems associated with cultural eutrophication include– Anoxic hypolimnion

• Part of lake removed as habitat

• Some fish species eliminated• Chemical release from

sediments– Toxic and undesirable

phytoplankton• Blooms of toxic cyanobacteria• Phytoplankton dominated by

cyanobacteria and other algae that are poor food for consumers

– Fewer macrophytes• Elimination of habitat for

invertebrates and fish– Esthetics

Cultural Eutrophication - Management

• Source controls– Diversion

• One of the first methods tried

• Sewage captured and diverted outside lake to say large river or ocean

– Advanced wastewater treatment

• More desirable now that technology exists

Cultural Eutrophication –

Case Studies• Lake Washington

– Following WWII, pop’n increases in the Seattle area resulted in increases in sewage discharge (sec trted) to Lake Washington

– Secchi depth decreased from about 4 m to 1-2 m as algae bloomed from sewage P

– Diversion system was built and effluent was diverted to Puget Sound in mid 1960’s

– Algae subsided and water clarity increase

– Daphnia reestablished itself and further clarified the lake

Cultural Eutrophication –

Case Studies• Norfolk Broads, England• Shallow systems where

macrophytes dominated• Increased runoff of

nutrients, first from sewage and then from farming stimulated algae

• First periphyton bloomed and caused a shift from bottom macrophytes to canopy formers

• Then phytoplankton bloomed and cut off even the canopy macrophytes and their periphyton

Recovery of a Tidal Freshwater Embayment from Eutrophication:

A Long-Term Study

R. Christian JonesDepartment of Environmental Science and Policy

Potomac Environmental Research and Education CenterGeorge Mason University

Fairfax, Virginia, USA

Tidal Potomac River

• Part of the Chesapeake Bay tidal system

• Salinity zones– Tidal Freshwater

(tidal river) <0.5 ppt

– Oligohaline (transition zone) 0.5-6 ppt

– Mesohaline (estuary) 6-14 ppt

Tidal Freshwater Potomac

• Tidal freshwater Potomac consists of deep channel, shallower flanks, and much shallower embayments

• Being a heavily urbanized area (about 4 million people), numerous sewage treatment plants discharge effluent

• Note Blue Plains and Lower Potomac

• Study area is Gunston Cove located about 2/3 down the tidal fresh section of the river

Historic Distribution of Submersed

Macrophytes in the Tidal Potomac

• According to maps and early papers summarized by Carter et al. (1985), submersed macrophytes occupied virtually all shallow water habitat at the turn of the 20th century

• Gunston Cove was included

http://caliban.mpiz-koeln.mpg.de/~stueber/thome/band2/tafel_029_small.jpg

P Loading and Cyanobacterial Blooms• Fueled by nutrient inputs

from a burgeoning human population and resulting increases in P inputs, phytoplankton took over as dominant primary producers by about 1930.

• By the 1960’s large blooms of cyanobacteria were present over most of the tidal freshwater Potomac River during late summer months

Point Source P Loading to the Tidal Potomac

(kg/day)

1968 32,200

1978 7,700

1984 400

Macrophyte Distribution in 1980• Anecdotal records

indicate that by 1939, submersed macrophytes had declined strongly and disappeared from much of their original habitat

• An outbreak of water chestnut (floating macrophyte) was observed in the 1940’s

• Surveys done in 1978-81 indicate only very sparse and widely scattered beds

• Note no submersed macrophytes were found in Gunston Cove

Efforts to Clean up the River• A major national and

multistate effort was initiated to clean up the “nation’s river”

• This paper describes the response of one portion of the tidal Potomac – Gunston Cove to this major initiative

“The river, rich in history and memory, which flows by our Nation’s capital should serve as a model of scenic and recreational values for the entire country”President Lyndon B. Johnson - 1965

Point Source P Loading to the Tidal Potomac

(kg/day)

1968 32,200

1978 7,700

1984 400

Tributary Watershed of Gunston CoveWatershed Statistics

Population: 330,911

Pop’n Density: 1362/km2 or 5.5/acre

Area: 94 mi2 or 243 km2

39% developed

9% agriculture

42% forest

Noman Cole Pollution Control Plant

-Near the mouth of Pohick Creek

-42 MGD (2004 avg)

-began operation 1970

P Loading Factors - Gunston Cove Watershed

20000

40000

60000

80000

100000

120000

140000

160000

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

Year

Wa

ters

he

d H

ou

se

ho

lds

0

50

100

150

200

250

300

350

400

Da

ily

Po

int

So

urc

e P

Lo

ad

an

d F

low

Watershed Households

Point Source Flow (m3x103)

Point Source P Load (Kg)

Households in the Gunston Cove watershed have grown dramatically since the mid-1970’s. Since the study began in 1984 the number of households has grown by about 50%. All other things equal, an increase in households should produce an increase in nonpoint contributions.

The point source P load declined dramatically in the late 1970’s and early 1980’s.

Formal study initiated in 1983.

Since 1983/84, water quality, plankton, fish and benthos have been monitor-ed on a generally semimonthly basis at a number of sites in the Gunston Cove area.

Monitoring Site Key:

● water quality and plankton

▲fish trawl

■ fish seine

Water Quality and Submersed Macrophyte Variables

• Water Quality Variables– Temperature– Conductivity– Dissolved oxygen– pH– N: NO3

-, NH4+, organic N

– P: PO4-3, Part. P,Total P

– BOD– TSS, VSS– Chloride– Alkalinity– Chlorophyll a– Secchi depth

• Submersed Macrophytes– 1994-2006

• Areal coverage using aircraft remote sensing

• Data collected by Virginia Institute for Marine Studies for the Chesapeake Bay program

– Pre 1994• USGS field surveys:

• GMU field surveys:

Water Quality Data Analysis

• Summer data (June-September) utilized• Utilized one cove station (Station 7) that has been

sampled continuously over the period 1983-2006• Scatterplot by year over the study period• LOWESS smoothing function applied• Linear trends also tested over the study period• Regression coefficients determined for significant

linear trends• Pre-1983 data were examined to place current study

in context

Gunston Cove StationTotal Phosphorus

• P is limiting nutrient in this system

• Summer total phosphorus showed little change from 1983 through 1988

• Summer total phosphorus decreased consistently from 1989 through 2006

• Linear trend highly significant with a slope of -0.0044 mg/L per yr or 0.10 mg/L over the period of record.

• P load decrease was complete by early 1980s. Yet TP decrease doesn’t seem to start until 1990? Or was the 1983-88 period just a pause in a decline in TP that started earlier?

Station 7: June-Sept

1980 1990 2000 2010Year

0.10

1.00

Tota

l Ph

osp

ho

r us

(mg

/ L)

Gunston Cove StationChlorophyll a

• Chlorophyll a levels have decreased substantially over the period.

• In the mid to late 1980’s chlorophyll a frequently exceeded 100 ug/L.

• Decline started in 1990 and quickened after 2000

• By 2006 values were generally less than 30 ug/L with a median of about 20.

• Linear regression yielded a significant linear decline at a rate of -3.8 ug/L per year or 84 ug/L over the entire study

• Again, did the chlorophyll decline start in 1990 or was this only part of a longer chlorophyll decline?

Station 7: June - Sept

1980 1990 2000 2010Year

10

100

Chl

orop

hyl l

a, D

ept h

- int e

grat

ed (

ug/ L

)

Gunston Cove StationTP – Extended Record

• Limited data from 1969/70 indicates that TP was much higher at that time

• So, perhaps what appeared to be a lag or delayed response was actually just a pause in the loading-induced TP decline

• The pause was associated with high pH induced internal loading

• Total decline was from 0.8 mg/L to 0.06 mg/L over 36 yrs or 0.02 mg/L/yr

1960 1970 1980 1990 2000 2010YR

0.010

0.100

1.000

TP

Gunston Cove StationChlorophyll a – Extended Record

• In contrast to the TP and SRP, values of chlorophyll a from 1969/70 were not substantially higher than in the early 1980’s

• This suggests that P levels had to be drawn down to at least the early 1980’s levels (c. 0.15 mg/L) before nutrient limitation of phytoplankton could begin to be a factor

• By 2000, TP was at about 0.10 mg/L and as it dropped further it began to cause a clear drop in chlorophyll a

1960 1970 1980 1990 2000 2010YR

10

100

1000

CH

LA

TP response to decreased P Loading?

• Rate of TP decline was slow during 1980’s period of internal loading

• Rate quickened in 1990 with apparent cessation of internal loading

Chla response to decreased TP in water column?

• Adding in historic data shows that before P loading reductions, chlorophyll was not sensitive to P in water column

• Presumably it was saturated with P, but by 1983, P and Chl were pretty closely related.

• Even with reductions, TP had to drop below 0.2 mg/L, then Chl started to decline proportionately

Gunston Cove Light Environment

• Full restoration of Gunston Cove requires re-establishment of submersed macrophyte beds

• The primary requirement for this is light availability throughout the water column

• Light attenuation is due to algae, inorganic particles, and dissolved substances

Gunston Cove Station

• Secchi disk was fairly constant from 1984 through 1995 with the trend line at about 40 cm.

• Since 1995 there has been a steady increase in the trend line from 40 cm to nearly 80 cm in 2003.

• Linear regression was highly significant with a predicted increase of 1.51 cm per year or a total of 33 cm over the long term study period

Station 7: June - Sept

1980 1990 2000 2010Year

10

20

30

40

50

60

70

80

90

100

Sec

chi D

i sk

Dep

t h (

cm)

Gunston Cove Light Environment over time

• Using the two time series of Kd, maximum depth of macrophyte colonization was predicted using the 10% surface light criterion

• Predicted maximum macrophyte depth was well below 1 m during the 1980’s and 1990’s

• But beginning in about 2000 it started to rise consistently and passed 1 m by 2003/04

1980 1990 2000 2010Year

0.0

0.5

1.0

1.5

2.0

Pre

dic

ted

Ma

xim

um

Ma

cro

ph

y te

De

pt h

(m

)

ZSAV10PERKZSAV10PERKSDSecchi-disk approx. Measured Kd

Reemergence of Submersed Macrophytes in Gunston Cove

• 1987 Distribution



http://www.vims.edu/bio/sav/sav95/quads/fr039d.html



http://www.vims.edu/bio/sav/sav00/quads/fr039.html



http://www.vims.edu/bio/sav/sav05/quads/fr039.html

Summary of Phytoplankton, Light, Submersed Macrophyte Response

• Improvements in water clarity related to P-limitation and decline of phytoplankton were correlated with an increase in submersed macrophyte coverage in Gunston Cove

• Since 1 m colonization depth was achieved (2004), macrophyte coverage has increased strongly

Inner Cove SAV Coverage vs. Secchi and Chlorophyll

0

50

100

150

200

250

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

Inn

er C

ove

SA

V (

ha)

&

Ch

l a

(ug

/L)

at S

ta 7

0102030405060708090

Sec

chi

Dep

th (

cm)

at S

ta 7

SAV CoverageSecchi DepthChlorophyll a

We have documented the partial restoration of Gunston Cove to its pre-eutrophication conditions including:

-Decrease in P loading

-Decrease in TP and phytoplankton chlorophyll

-Increase in water clarity

-Reestablishment of submersed macrophyte beds to a substantial portion of the cove

EVPP 550 Waterscape Ecology and Management – Lecture 11

Documents

uslake whitefish native

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wellsome suckers feed