TEAM - Trends in Eutrophication and Acidification in the Maritimes

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Background and Rationale for Study

The environmental, ecological, economic, and social consequences of declining water-quality are of critical national and global importance.   The two most significant water-quality issues related to inland waters in large parts of eastern Canada remain lake acidification and eutrophication.

Acidification
:

In North America, about one billion dollars in research funding was dedicated to studying the problems related to acidification, prior to passing legislation that resulted in decreased sulphur emissions.  However, despite large declines in emissions, acidic precipitation is still falling at levels that may exceed the critical loads of many lakes and catchments (Henriksen et al. 2002, Watmough and Dillon 2000, 2002).

In the Maritimes, the principal acidifying agent is sulphate. 
Oxides of sulphur and nitrogen released by the combustion of fossil fuels (e.g. power generating stations, oil refineries, automobiles, etc.) or from metal smelters produce sulphuric and nitric acids which can be transported long distances in the atmosphere before fallout occurs.  Atlantic Canada is a critical area for which detailed studies on the effects of acidic deposition are required (Jeffries, 1997).  Nova Scotia (NS), with an estimated 9400 lakes, is extremely susceptible to acidic deposition because of its silicate bedrock and thin glacially-derived soils. It has been estimated that 90% of the anthropogenic pollutants responsible for acidic deposition in NS originate outside the region (Shaw, 1979).  Deposition of sulphate peaked in the early 1970s and reductions in the range of 30-40% have occurred since this time.  Naturally-reproducing Atlantic salmon populations are no longer present in many of the 65 rivers in the Southern Upland region of NS (DFO, 2000).  Likewise, the portion of New Brunswick (NB) along the Fundy Coast is an area of considerable concern for resource managers and other stakeholders (McNicol et al. 1996).

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.

References Cited:

Clark, B.J., P.J. Dillon et al. 2001. Lake Reserv . Man. (in press)
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.
Lake Reserv . Man. 8: 121-129.
Dillon, P.J. and
L.A. Molot. 1997.Biogeochem. 36: 29-42.
Dillon, P.J.,
L.A. Molot and M. Futter. 1997 Environ. Mon. Assess. 46: 105-111.
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.
Can. J. Fish. Aquat. Sci. (in press).
Jeffries, D. (ed). 1997. Canadian Acid Rain Assessment. Vol 3. Environment
Canada .
Shaw, R.W. 1979. Envir. Sci. Tech. 13:407-411

Watmough , S.A. and P. J. Dillon. 2001. Wat. Air Soil Pollut. Focus 1: 507-524.
Watmough, S.A. and P.J. Dillon. 2002. (in press).


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