Lecture 29. Ecosystem “Health” and Biomonitoring

-variety of ways that human beings affect ecosystems and communities

-concern about how humans are changing the world has prompted efforts

to slow or reverse effects of human disturbance

-this effort falls into two related classes:

(1) work to assess the condition of ecosystems and to monitor changes through time,

(2) attempts to reverse or correct damaged ecosystems.

-first activity is called ecological monitoring or biomonitoring (subject of this lecture)

-second is called restoration ecology (next lecture)

Biological Monitoring

-also called biomonitoring

Definition: Measurements of populations, communities or ecosystem attributes

to assess the condition of an ecosystem and effects of disturbance

& Usually contrasted with chemical monitoring

(directly measuring pollutants)

& Originally conceived to monitor water quality (sewage effluents)

and air quality (smokestacks)

& Can theoretically be applied to any kind of human intervention

-idea grew out of work to assess condition of rivers receiving sewage wastes

-in development for nearly 100 years,

-though only practised routinely in the past 30

-basic assumption of biological monitoring is simple:

-organisms are closely adapted to their habitat,

-therefore, changes in environmental conditions should be reflected in

(1) changes in populations of organisms, (indicator organisms)

(2) changes in structure (species composition, diversity) of communities

(3) changes in ecosystem processes such as production, element cycling

-therefore, use biological survey data to flag deterioration in the environment

-from pollution, hunting, encroachment, habitat loss or other disturbances

1. Indicator organisms

- indicator is a single species used to monitor an entire group or ecosystem

-condition of the indicator is taken to imply condition of the whole

-“canary down a mineshaft” approach:

if indicator species falters, it tells us that something is wrong with the ecosystem

-this conclusion is a big leap, so indicator organisms must be carefully chosen

-often top predators, keystone species,

-or species particularly demanding about habitat quality

Examples: an understorey plant as indicator of forest health

-duck or frog populations as indicators of wetland habitat

-salmon or trout often used as indicators in stream restoration,

-because demanding of DO and temperature

-International Joint Commission (IJC) is charged with overseeing cleaning of lower Great Lakes

-IJC uses a burrowing mayfly, Ephemera, as indicator of the success of clean-up

-Ephemera burrows into bottom sediments

-deeply affected by low oxygen and sediment contamination

The mayfly Ephemera. Commonly knows as fishflies

because the adults bear a strong fishy odour.

-in 1940s and 1950s, Ephemera was fabulously abundant;

-adults emerging all at once would clog car radiators and pile up in windrows along beaches

-almost disappeared when the lakes were polluted in the 1960s

-now populations are bouncing back as organic pollution is abated (partly)

Extent of anoxic “dead zone” in Lake Erie. Anoxia in the central basin was largely cured by

1970 by banning phosphate detergents, and other measures that reduced P input to the lake. With

greater population pressure on both sides of the border, the dead zone has returned.

2. Community Structure

-more comprehensive approach is to use a group of related organisms,

-a taxocene or a functional group

-instead of one single species

-condition of ecosystem judged by number of species and their relative abundances

-more complicated indices, including diversity and various functional groups, also used

Examples: by far most widely used community is benthic invertebrates in rivers and streams

-benthos have been used for biomonitoring for almost 100 years

-excellent organisms for monitoring effects of degradation from untreated sewage

-have more recently been applied to many other kinds of aquatic degradation

-in Canada, benthos widely used for routine effluent monitoring

-around pulp and paper mills, sewage effluents, other industries

-also routinely used to assess environmental damage from spills, contamination, sedimentation

(interpreting benthic invertebrate data for environmental assessment was much of my

employment for 15 years before I became a prof)

-similar approach uses communities of benthic fauna in oceans,

-around oil wells, for example

-other examples: lichens are commonly used to monitor air pollution

-stream or lake fishes sometimes used for same purposes as benthos

-even benthic algae has been used for biomonitoring in rivers

-bird communities may be used for assessments of woodlands, meadows

-microbial diversity used to assess health of soil

-advantages: large number of species makes monitoring more sensitive than a single indicator

-and covers a greater range of conditions

-if one species doesn’t respond to a particular stress, another one may

-an indicator species may perfectly reflect habitat conditions;

-ideal habitat for the indicator may still be degraded for other organisms

-or indicator might not naturally occur in some habitats

-we can also derive more information from a group of species than from one

-perhaps can tell nature and degree of ecosystem change from community changes

-can quantify these changes using methods derived from population ecology

Drawbacks:

-much more work to follow many species instead of just one

-statistical methods for analysis can become tedious and confusing

-often difficult to tell real ecosystem changes from background noise

Lungwort (Lobaria pulmonaria), a foliose

lichen so named for its resemblance to lung

tissue. Appropriately, lichens are very

sensitive to air pollution and have proven to

be useful indicators of air quality.

3. Ecosystem Attributes

-if condition of the ecosystem is of interest, why not measure it directly?

-by measuring integrative attributes:

primary production,

decomposition rates,

rates of element transformation or cycling

-measurement of these ecosystem-level attributes has been greatly assisted by technology

-examples: laser analysers can detect trace gas emissions from entire grasslands and meadows

-satellite imagery can measure chlorophyll and photosynthetic rates of vast areas of ocean

-monitoring devices can measure rates of microbial activity such as nitrogen mineralization

-these approaches are limited to those that have the fancy equipment

-consequently tend to be more expensive than other methods

-and results can be difficult to interpret.

-if N mineralization rate declines by 20%, what exactly does that mean for ecosystem condition?

** biggest limitation of this approach is conceptual

-whole point of biomonitoring is to discover whether ecosystem function is declining

-useful to know that something like photosynthesis is changing,

-because that may indicate an ecosystem under stress

-more useful to know that the system is deteriorating before function declines

** recall discussion of diversity and ecosystem function

-diverse systems, especially those with great functional diversity, can maintain constant

ecosystem function because of inconstancy in individual populations

-as conditions change, some species prosper at the expense of others,

-but ecosystem functions do not vary greatly, because one species compensates for another

** similarly, if an ecosystem begins to deteriorate, through pollution or long-term disturbance,

many species can be lost before ecosystem function is compromised

-Example: because of functional redundancy, we may not see any decline in NPP,

-until species loss crosses a critical threshold and whole ecosystem collapses

-we know this sequence happens in response to chronic stresses like acid rain

-as more sulphur enters a lake and the pH drops, species of zooplankton disappear one by one

-but ecosystem appears to be functioning normally

-until too many species of too many kinds disappear

-suddenly, food chain for entire lake collapses, including fish populations

** by that time, it is too late to avoid collapse by restorative measures

-so what is the point of monitoring if you cannot predict future problems?

-we are merely “cataloguing catastrophe” instead of monitoring to prevent damage

-imagine medical advice that diagnosed a disease only as the patient lay dying

-in the lake example, monitoring function such as primary production is unrevealing

but if we monitor community structure, such as zooplankton community,

we may see the decline early enough to take action

Update: recent research in streams has eroded the above argument

-much interest lately in using leaf litter decomposition as an ecosystem attribute in streams

-small streams depend on litter as the main source of energy

-because they are too cold and shaded to produce their own NPP

-my argument, above, says benthic invertebrate populations are more sensible monitoring choice

**but researchers in France have shown that decomp rates across wide areas respond

to subtle gradients of contamination

-differences that are barely noticeable by chemical sampling

-and which produce no observable difference in benthos populations or decomposer fungi

-appears that the process does reflect changes that are not apparent at lower levels of organization

What makes a good indicator?

-organisms, communities or attributes measured are variously called

indicators or endpoints or metrics

-I’ll call them all indicators here, but this term is meant to apply to all three classes

-to be useful, species, pops or ecosystem attributes we measure must have several characteristics:

1. Relevant

-indicator must be directly linked to condition of the ecosystem

-otherwise, we are not measuring the right thing

-no point in measuring populations or communities that do not change

in tandem with rest of the ecosystem

-usually, we measure a range of different endpoints,

-because different variables may respond at different rates or to different stresses

-this approach also builds in redundancy:

-trends in one indicator are verified by checking against others

2. Reliable

-by this I mean the indicator has to be sensitive and trustworthy

-if indicator we choose is not sensitive enough, ecosystem could change profoundly

before our indicator shows any change

-remember, we want to know about impending damage to the ecosystem

-so we can take corrective action

-no value in an indicator that tells us the system is collapsing as it happens

-part of sensitivity comes from signal-to-noise ratio

-natural variation in all populations; that’s the noise

-signal is the systematic change in response to changes in external forces

**we want our indicator to have relatively low variance

-so the signal is easy to discern

-fast response is also essential:

-so we can track changes to the ecosystem as they happen,

-so we have time to respond

-organisms with short life spans are best

-or processes that respond quickly to the environment

3. Realistic

-remaining considerations are pragmatic

-if our indicator is an organism, it has to be

-easy to catch or sample,

-reasonably easy to identify,

-abundant in all seasons

-species that are cryptic, taxonomically difficult, dangerous, seasonal or physically large

are all poor choices for indicators

Ecosystem “Health” and Degradation

-what follows is a rant, but an important one

-notice throughout the discussion I have referred to condition of the ecosystem

-that term describes the ecosystem without judgement

-many practitioners of environmental monitoring refer to assessment of ecosystem “health”

-or its twin sister, “ecosystem integrity”

** ecologically, there are many difficulties here

-to be healthy, applied to an organism, implies (1) that it is free of disease,

-and (2) in the normal physiological state for that species

-normal state is easy to define for organisms

-because they have metabolic set-points, like constant body temperature,

-that are maintained in the absence of disease or malnutrition

** ecosystems do not have well-defined normal states,

-or if they do, we don’t know what they are

-while there are many feedback loops in an ecosystem, there is no good analogy of “health”

-many situations we think of as ecosystem degradation can be described as changes of state

Example: switch between macrophyte-dominated and algal-dominated productive lakes

-is one state more “healthy” than the other?

-no good evidence that an ecosystem has set-points that are analogous to metabolism

** consequently, ecosystem health usually refers to native condition of ecosystems

in the absence of human disturbance

-which would be better described as pristine

-or healthy may imply conditions of greatest diversity, productivity, aesthetic value,

or return of favoured species

-we think of clean streams and lakes as “healthy” compared with polluted ones

-that judgement may be valid,

** but it is a social-cultural decision, not a biological one

-this is not just my opinion

-majority of theoretical ecologists have grave reservations about concept of ecosystem health

-concept cannot be found in the mainstream scientific literature

** that hasn’t stopped governments and environmental groups from embracing it

-Environment Canada has developed elaborate mechanisms and programs to monitor

state of the environment,

-which they refer to constantly as ecosystem health

-partly because the idea has mass appeal, easier to sell to the common person

-I recall one seminal report that discussed and justified ecosystem health at great length, with refs

-when I checked, all the references were other government reports!

-no real literature at all!

-we even have a new Journal of Aquatic Ecosystem Health

-which, by its title, presumes validity of ecosystem health from the start

-this point is more than a quibble about accuracy

-this trend points to policy running far ahead of science, or even ignoring it

-we have one group of people vigorously measuring ecosystem health,

-while another group is not even convinced that it exists