EVPP 550Waterscape Ecology and Management – Lecture 11
Professor R. Christian
JonesFall 2007
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
Lake Biology – FishMajor Freshwater Groups
• 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
Lake Biology – FishMajor Freshwater Groups
• 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
Lake Biology – FishMajor Freshwater Groups
• 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
Lake Biology – FishMajor Freshwater Groups
• 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
Lake Biology – FishMajor Freshwater Groups
• 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
Lake Biology – FishMajor Freshwater Groups
• 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)
Lake Biology – FishTrophic Roles
• 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
Lake Biology – FishTrophic Roles
• 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
Lake Biology – FishFactors affecting growth
• 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
Lake Biology – FishFactors affecting growth
• 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
Lake Biology – FishFactors affecting growth
• 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
Lake Biology – FishFactors affecting growth
• 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
Lake Biology – FishPatterns of Abundance & Production
• Habitat Selection– Many fish prefer vegetation and collections are often
greater at night
Lake Biology – FishPatterns of Abundance & Production
• 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
Lake Biology – FishPatterns of Abundance & Production
• 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
Lake Biology – FishPatterns of Abundance & Production
• Effect of Bottom Up Processes– The same trend but with
a different slope has been found in other systems
Lake Biology – FishPatterns of Abundance & Production
• 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
Lake Biology – FishPatterns of Abundance & 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
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
Reemergence of Submersed Macrophytes in Gunston Cove
• 1995 Distribution
Reemergence of Submersed Macrophytes in Gunston Cove
• 2000 Distribution
Reemergence of Submersed Macrophytes in Gunston Cove
• 2005 Distribution
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