Eutrophication:
The second major water-quality problem is lake eutrophication. The export of nutrients into freshwaters from point (e.g., sewage) and diffuse (e.g., agricultural runoff) sources has had many deleterious effects on inland waters including increases in algal and aquatic macrophyte production, resulting taste and odour problems, and decreases in hypolimnetic oxygen levels that degrade and reduce the availability of cold-water fish habitat. Furthermore, there is growing evidence of interactions between nutrient inputs and acid deposition effects on lakes and catchments, such that these stressors cannot be considered in isolation. Consequently, managers require new tools and approaches to tackle these pressing environmental concerns.
This 5-year NSERC strategic program will address the major water-quality
issues facing the Maritime provinces of eastern Canada
(focusing on regions of NS and NB). We will develop a
novel hybrid approach to environmental assessment using the combined
techniques of state-of-the-art paleolimnology (Smol and Cumming) and
process-based biogeochemical models (Dillon). In close cooperation
with our users and partners, we will develop these models on a strategically
selected suite of east-coast lakes, so that these methods will be appropriate
for water-quality questions posed in this region. These issues revolve
around acidification and eutrophication, as well as associated water
quality interactions.
Pattern & Process-based Approaches To Environmental Assessment:
Water chemistry records that document pre-disturbance conditions
are unavailable for most aquatic systems, making it difficult to evaluate
the impact of human activities on water quality. Two complementary
approaches are available to estimate these missing data: 1) estimates
of past environmental conditions based on the information preserved in
sediment records (the paleolimnological approach); and 2) biogeochemical
process-based models. The paleolimnological (pattern-based) approach
offers empirical evidence of changes in water quality from all factors,
whereas biogeochemical models (process based, e.g. MAGIC, Cosby et al.
1985) offer a mechanistic understanding of the important processes involved
that, once sufficiently understood, can be extrapolated to other systems.
Both of these techniques are increasingly being used to obtain missing
historical data sets.
The Paleolimnological Approach
:
The central research focus at the Paleoecological Environmental Assessment and Research Lab (PEARL) is the development and application of paleolimnological techniques to provide an historical perspective to environmental change. From this information, we can generate and test hypotheses, define natural variability, and evaluate models. These studies have answered important questions that could not be addressed without this long-term perspective. As shown in many peer-reviewed scientific publications from PEARL, paleolimnological techniques have progressed to the point where they can be integrated into effective lake management strategies. Major advances have also been made in the areas of core collection and sectioning, data analysis, database management, quality assurance/quality control, variability, and error estimates.
The most widely used techniques are based on the analysis of
diatom and chrysophyte communities preserved in lake sediments.
Diatom assemblages are composed of a large number
of taxa that have quantifiable environmental requirements (e.g., pH, nutrient
levels, etc.), and hence provide considerable ecological information.
Statistically robust and ecologically sound models
(transfer functions) have been developed to infer these variables directly
from fossil diatom assemblages. Chrysophytes
are another widely distributed group that can provide models for important
limnological variables, have been especially useful in studies of lake acidification,
and are especially sensitive to episodic acidification events. Diatom and
chrysophyte microfossils provide an integrated overview (in space and time)
of the entire aquatic system because deep-water sediments integrate diatoms
and chrysophytes from various habitats.
Furthermore, they respond to changes in their environment quickly (weeks
to days) because of rapid immigration and replication rates.
Recent refinements in sediment sampling procedures
in conjunction with new inference models (e.g., direct-gradient and unimodal
statistical models based on weighted-averaging (WA) regression and calibration,
and partial-least-squares regression (PLS)) have made it possible to detect
changes in lake water quality that have occurred within the last few years.
These inference techniques are highly reproducible and
statistically robust.
Biogeochemical Process-Based Modeling Approach
:
The biogeochemical studies that are undertaken in Dillon’s lab focus on evaluating the effects and interactions of stressors including acid deposition, elevated nutrient levels, and climate change on lakes and their catchments. These studies include field and laboratory components measurement of long-term (25+ years) changes in lakes, streams and catchments (Eimers and Dillon 2002), measurement of elemental fluxes on an ecosystem scale (Dillon and Molot 1997), and evaluation of the effects of stressors on key biogeochemical processes. In addition, a modeling component that focuses on the development and use of predictive models that quantify the relationships between measures of the intensity of environmental stressors and the ecosystem’s response has been the principal means of integrating the various components of the studies.
Biogeochemical models related to acid deposition have served several purposes: they have been used to hindcast historical conditions in lakes and streams in the absence of measured data so that the degree and rate of acidification can be assessed, to predict future water quality as a function of changes (increases or decreases) in acid deposition rate resulting from emission variations, and to estimate critical loads of acidifying substances (S and N) below which harmful impacts of acidification will not occur, e.g. acid neutralizing capacity, exceeding critical threshold values. The most widely used model in acid deposition studies is MAGIC (Modelling Acidification of Groundwater In Catchments – Cosby 1985, 2001), which has been applied for all of the above-named purposes in many countries on at least 3 continents. Dillon has worked with Jack Cosby (U. Virginia), the principal developer of MAGIC, for almost 15 years, and has applied MAGIC to Ontario study sites. Recently, a new version of MAGIC (v.7.77), which includes a wetland module and the redox processes (e.g. sulphate reduction) that occur in wetlands, was initiated because of the observations from Dillon’s lab that drought-induced lowering of water tables in wetlands was leading to the release of previously-stored S in acid form, thus delaying and, in some cases reversing, recovery in Ontario lakes (Dillon et al. 1997). Although MAGIC has been used with a wide variety of lake types, there has been very limited use with dystrophic (high DOC, dissolved organic carbon) lakes; thus, part of this program will include modifications to the model so that it will be more applicable to the Maritimes.
Development of models related to nutrient enrichment has been
underway in Dillon’s lab for many years and the major output, the lakeshore
capacity model (LCM), which relates phosphorus inputs to trophic status
characteristics (Dillon et al. 1994), and has been used extensively in
many regions of Canada and the US, including some preliminary use in NS.
The model has been used to evaluate the potential
effects of new development and/or to ascertain development capacity,
given defined threshold water-quality criteria.
In recent years, new components have been added to the LCM, specifically
to address the response of hypolimnetic oxygen levels to nutrient inputs
(Clark et al. 2001), and to assess changes in cold-water fish habitat
(Dillon et al. 2002). The latter module
also considers loss of habitat through climate-change induced water
temperature changes. In some jurisdictions
(e.g. Ontario), the LCM is used to calculate historic nutrient levels,
in the absence of development, and allowable increases in nutrient inputs
are set as a proportional increase above the background level.
Because the LCM deals with a wide variety of land uses
and geological settings, lake morphometries, and variable hydrology, the model should be useful in eastern
Canada
after suitable modification.
Clark, B.J., P.J. Dillon et al. 2001.
Cosby, B.J. et al. 1985. Wat. Resourc. Res. 21: 51-63.
Cosby, B.J. et al. 2002. Hydrol. Earth Sys. Sci. (in press).
Dillon, P.J. et al. 1994.
Dillon, P.J. and
Dillon, P.J.,
Dillon, P.J. et al. in Management of Lake Trout Ecosystems.
J. Gunn (ed.) (in press).
Eimers, M.C. and P.J. Dillon 2002. Biogeochem. (in press).
Henriksen, A., J. Aherne and P.J. Dillon. 2002.
Jeffries, D. (ed). 1997. Canadian Acid Rain Assessment. Vol
3. Environment
Shaw, R.W. 1979. Envir. Sci. Tech. 13:407-411
Watmough, S.A. and P.J. Dillon. 2002. (in press).