project VII
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project VII: trends in acidification and eutrophication in the maritimes

The two most significant water quality issues related to inland waters in large parts of eastern Canada remain lake acidification and eutrophication. 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. Biogeochemical models offer a mechanistic understanding of the important processes involved that, once sufficiently understood, can be extrapolated to other systems.

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 lakeshore capacity model (LCM), which relates phosphorus inputs to trophic status characteristics (Dillon et al. 1994), has been used extensively in many regions of Canada and the US. 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). 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.

A process-based model (MAGIC) will also be used to estimate the pre-industrial chemistry of maritime lakes and to evaluate the rate and extent of acidification that occurred in these lakes based on biogeochemical processes.

Soil data required for model parameterization will be collected through an extensive field program, focussing on low-order lakes with relatively small catchments. The results, including the hindcasting of lake chemistries back to pre-1830, the estimation of the degree of acidification of the lakes, as well as the estimation of critical sulphur loads to these lakes, and predictions of future conditions based on scenarios describing proposed changes in deposition, will be compared with results generated through complementary paleolimnological work performed by researchers at Queen’s University.

In addition, the model provides the means of estimating future conditions based on deposition scenarios, and of estimating the critical deposition that cannot be exceeded without the lake passing pre-determined critical chemical thresholds. Because some of the characteristics of the investigated lakes are substantially different from others that MAGIC has been used for in the past, notably the high DOC, we will revise MAGIC by building an organic acid or DOC module that incorporates our current knowledge on the role of DOC in lakes. At present, the role of DOC in acid-base chemistry is represented in MAGIC in a very elementary way using simple dissociation constants, with no formation or loss of DOC within the system considered. A revised model with a detailed DOC module will be useful in other areas as well, and will almost certainly lead to better hindcasting and forecasting.

This portion of the project will seek to identify whether hypolimnetic oxygen levels have decreased significantly in Nova Scotia (NS) brook trout lakes, and if so, why and by how much? Over a 25-yr period, water quality measurements from 20 brook trout lakes distributed over a wide geographic area of NS indicated that the 11 lakes previously ranked as “good” with respect to brook trout habitat changed to “poor”, while the 9 others remained “poor”. The lack of historical data is hampering NS managers’ implementation of effective mitigation programs. A process-based approach can be employed to help establish the tools necessary for effective and ecologically sound management of these resources. A key feature of the LCM is its ability to estimate historical P levels in the absence of measured data. Specifically, the questions “have nutrient levels increased in these lakes?” and “if so, when (i.e. what were the cause(s)) and by how much?” will be addressed. The trophic status models use morphometric, hydrologic, land-use and geologic data, most of which typically are available from reference maps, to estimate historic lake nutrient levels and hypolimnetic oxygen concentrations. The model can also partition current nutrient levels between the contribution from anthropogenic activities and that which is natural, and can be used to estimate critical loads of nutrients that cannot be exceeded without trophic status degradation including unacceptable hypolimnetic oxygen loss. The most recent addition to the LCM has been a cold water fish habitat sub-model (Dillon et al. 2002), that will be used here to assess the impacts of the anthropogenic portion of the nutrient load on habitat size and quality. Additionally, biogeochemical modelling will be used to study eutrophication and land-use effects on lakes in Cape Breton Highlands National Park identified as potentially affected by eutrophication. As with the acidification component, the output from the eutrophication models will be compared with the results of the Queen’s group.