Quiz 11 Flashcards
(21 cards)
What is biomanipulation? (4)
A type of food web manipulation that has been used to improve water quality in several lakes
Relies on phytoplankton filtering capability of large zooplankton populations (eg. daphnia)
Daphnia can be increased by:
Reducing planktivorous fish populations either by removal or by increasing predation on planktivores through stocking of piscivorous fish
What does biomanipulation require? (2)
Ongoing monitoring of the ratio between planktivorous and piscivorous fish
Is more effective in lakes which have already undergone reductions in P loading
What was the experiment in New Zealand? (2)
Silver carp were introduced to control the growth of floating aquatic plants known as phytoplankton
They are herbivores and so cleaned the water by filtering phytoplankton out
Where is biomanipulation most often considered? (2)
Shallow lakes where nutrient sources cannot be controlled (ie. non-point source or internal loading)
In lakes with centrachid plankitivores (eg. Crappie, pumpkinseed) and top predators such as pike and/or walleye
Wahleach Reservoir (3)
First ever to experience biomanipulation and nutrient enrichment at the same time
Biomanipulation has rarely been attempted in a lake with salmonid species
Site of an experience to determine 5 possibilities
What are the five possibilities for the Wahleach Reservoir experiment?
- Restore productivity to an ultra-oligotrophic montane reservoir
- Re-establish extirpated Kokanee population
- reduce/eliminate introduced planktivores (sticklebacks)
- use sterile cutthroat trout as introduced top predator
- rebuild resident stocks of rainbow trout and cutthroat trout
Wahleach hydroelectric system (3)
Opened in 1952
Used to supply 13.5% of required electric power but now only 1% (population growth?)
Important for lower mainland
“High head, high value” installation
Estimation of hydroelectric power
P = m x g x Hnet x n
p = power in watts m = mass flow rate kg/s g = gravitational constant 9.81m/s2 Hnet = net head m n = product of all the component efficiencies (the turbine, drive system, and generator)
What led to the improvements undertaken at the dam and what were they? (3)
Engineering investigation by BC Hydro in the 1980s showed several modifications were required to enhance the safety of the dam and associated works
Improvements were undertaken within the tunnel, at the spillway, and at the dam between 1990 and 1994
Bc hydro also completed a partial debris clearing operation within the Jones lake reservoir
The collapse of Kokanee in the wahleach reservoir (4)
The lake was flooded in the 1950s and is now well past the period of trophic upsurge and into the long term dormant state of cultural oligotrophy
In addition to cultural oligotrophication caused by impoundment, 3 spine sticklebacks were illegally introduced sometime in the 1980s to early 1990
They occupied both pelagic and littoral areas and competed with Kokanee and rainbow trout for food
Because 3 spine stickleback are planktivores and Kokanee are obligate planktivores, they were extirpated from the lake in 1995 (rainbow could eat other things)
Food web biomanipulation dates (3)
Pre-treatment years: 1993-1994
Nutrient treatment: 1995 onwards
Fish stocking: 1997-2000
What fish was the Wahleach Reservoir stocked with? (3)
Kokanee
Cutthroat trout
Anadromous cutthroat trout
What happened after biomanipulation and nutrient treatment? (8)
- Nutrient treatment increased phosphorus
- epilimnetic chlorophyll a
- And decreased secchi depth
- Which are indicators of the lake moving from ultra oligotrophic to oligomesotrophy
- Daphnia appeared for the first time in 1997, with biomass increasing by 100 times by 2000
- Total zooplankton biomass increased
- Sticklebacks increased initially up until 1997, but decreased by 94% after coastal cutthroat trout introduction
- there were older rainbow trout found (used to be just 2 year olds)
What was the problem with the Wahleach Reservoir experiment? (3)
Monitoring was not done by the ministry of environment
In 2009 there were reports of had odours caused by Cyanobacteria, and the hypolimnion became anoxic
In 2010 fertilization ceased and monitoring of oxygen-temperature, secchi depth, and phytoplankton resumed
What was the innovative use of nutrients example? (4)
Onondaga Lake cleanup
Lake was a dumping ground for industry for decades but is sacred to onondaga nation
Riparian and wetland Restoration
Adding nitrate to the bottom of the lake to reduce mercury levels
What is the issues with methylmercury? (6)
MeHg bioaccumulates strongly in aquatic food webs
Results in toxic effects at upper trophies levels when concentrations are high
Sulfate reducing bacteria at the sediment interface “methylates” mercury (Hg+2) so more MeHg is produced
MeHg is produced by iron-reducers as well
And by anaerobic conditions and the supply of Hg, sulfate (SO4), and labile organic carbon
This MeHg is taken up by phytoplankton from the water column during summer anoxia and fall turnover, which introduce mercury into the food web
What are the three potential mechanisms for NO3 control on MeHg accumulation?
Suppression of the activity of sulfate reducing bacteria
decrease in the methylation ratio
Increase sorption to Fe and Mn oxyhydroxides in surficial sediments
What did they do in Onondaga Lake to control MeHg mobilization?
Added whole-lake NO3 (nitrate) through a calcium-nitrate solution (CaNO3)2) injection to the hypolimnion 3 times a week during summer stratification (during stratification to avoid release of MeHg from pelagic sediments into the hypolimnion with mixing)
What was the outcome of the Onondaga Lake nitrate addition? (5)
Before nitrate addition:
No nitrogen in the water because NO2 is being replaced by NH3 (bad = mercury being methylated)
DO decreased, temperature decreased (as DO decreases we get Mercury because of reduced state)
From 2007-2011
Methylmercury in the water column decreased and Nitrate increased
Reactive phosphorus decreased
Methylmercury in zooplankton decreased
What is the best way to use NO3 control on hypolimnetic accumulation of MeHg? (3)
A combination of
- suppressing the activity of sulfate reducing bacteria (so sulfate isn’t reduced at the interface)
- increasing the sorption to Fe and Mn oxyhydroxides in surficial sediments
Adding NO3 results in a shift in electron flow from established methylators of Hg to denitrifying bacteria so NO3 can be broken into N2 instead of MeHg being produced
What was the choice they had to make in the Onondaga Lake nitrate additions? (2)
Had to choose between having less mercury or having fish
This was because adding NO3 inhibited sulfate bacteria at the interface, but anoxic conditions and don’t want to oxygenate lake because this would increase bacteria which would break the sediment surface and increase mercury
