TEAM - Trends in Eutrophication and Acidification in the Maritimes

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Objectives and Themes of Research

THEME 1: LAKE ACIDIFICATION:

A few paleolimnological studies related to water-quality issues were undertaken on New Brunswick (NB) and Nova Scotia (NS) lakes in the 1980s, but these were completed prior to development of the strong and robust inference tools as well as advancements in sediment-dating techniques. Similarly, biogeochemical modeling of lakes in this region is in its infancy.  Consequently, there is a need to determine whether these lakes have acidified since pre-industrial times, and if so, by how much.  It is also important to assess whether biological recovery has occurred since sulphate emissions have declined 30-40% since peak emissions in the early-1970s.

The Southern Upland region of NS is particularly sensitive to acidic precipitation and it has been estimated that NS has lost more fish habitat than any other province (DFO, 2000).  Furthermore, acidification and climate change have been identified as two major stressors that threaten the ecological integrity in Canada's National Parks, including both Kejimkujik (KNP) and Cape Breton Highlands (CBHNP).  Additionally, parts of NB, along the Fundy Coast, are believed to be sensitive to acidification and are of considerable concern for wildlife managers and other stakeholders (McNicol et al. 1996).  Due to the lack of long-term data, little is known about the pre-industrial water chemistry of this region, and so some of the basic questions (e.g. have these lakes acidified? if so, by how much?) have yet to be answered.  Such information is essential for predicting the minimum reductions in sulphate that will enable these lakes to recover.

We will determine how seriously NS and NB lakes have been affected by acidic deposition (magnitude and timing), as well as estimate the minimum critical load of sulphate that must be reached before these lakes begin to recover (Cumming et al., 1992, 1994).  In order to provide a comprehensive assessment of the impacts of acidification, we propose the following research program.  First, we will assess the relationship of diatom and chrysophyte communities to measured limnological variables in this region (Question 1, Task 1) to provide the basic data for developing appropriate inference models for pH and DOC).  We will then assess the magnitude of acidification that has occurred in these lakes since pre-industrial times (Question 1, Task 2).  A process-based model (MAGIC) will also be used to estimate the pre-industrial chemistry of the lakes and to evaluate the rate and extent of acidification that occurred in these lakes based on biogeochemical processes (Question 1, Task 3).  Empirical estimates of acidification (Task 2) and process-based models (Task 3) will then be compared.  Based on these results, we will have a clear idea of the impact that acidification has had on this region over the past century.

Next, we will assess the timing of acidification using detailed paleolimnological approaches in ~30 of the 98 lakes identified below, in categories stratified by region and their present-day pH values (Question 2, Task 1).  This analysis, in combination with results from the models (Question 2, Task 2), will allow us to estimate the load of sulphate under which these lakes became more acidic, as well as the minimum sulphate load necessary for these systems to recover (see Cumming et al. 1994).

Question 1: Have lakes in NS and NB acidified since 1850?

Many lakes in NS and NB are currently acidic, but may be naturally so (e.g. because of the high DOC content of many lakes, or as a result of the input of marine aerosols)Simple extrapolation of the possible damage from acidic deposition in other Atlantic regions (e.g. Maine ) is not possible due to local and regional differences in geology, soils, vegetation and climate.  As many NS lakes have high DOC, this natural acidity introduces complexity into the susceptibility of these lakes to acidic deposition.  Process-based models, such as MAGIC, have at least a basic capability of addressing these other sources of acidity, and recent modules also address interactions of acidification with other stressors (e.g. climate change).

The 72 LRTAP lakes in NS have been segregated into five study regions by Environment Canada (Env. Can.): Kejimkujik National Park, Yarmouth, Bridgewater, Eastern Shore of Halifax Co., and Cape Breton Highlands National Park .  None are more than 50 km from salt water, and, as such, all show evidence of marine influences.   In addition, catchments with large areas of wetlands provide substantial amounts of DOC to downstream lakes   (mean DOC is 5.3 mg/L, with a range of 1.0-14.7 mg/L).   In addition to acidification from these organic anions, some lakes may have been affected by the deposition of sulphate from industrial sources (deposition at Kejimkujik was 20 kg /ha (as SO4) in 1981). Deposition of nitrate (ca. 14.2 kg/ha in 1989) probably has had little effect on lake acidification in this region.  These lakes have nitrate levels below 20 g/L, indicating that the catchments are efficiently retaining nitrate and not allowing it to act as a mobile anion.

The 26 NB study lakes along the Fundy coast were studied by the Canadian Wildlife Service’s (CWS) monitoring program (McNicol et al., 1996). The pH of these lakes varies from 5 to 6.7, and sulphate concentrations range from 2.4 to 3.8 mg/L.  This region receives a similarly high level of sulphate deposition as Kejimkujik Park , but is exposed to less deposition of marine salts.

Task 1: Development of paleolimnological inference models for important limnological variables (e.g. pH, DOC, nutrients):  

Transfer functions to infer important limnological variables will be developed based on the present-day relationships between diatom and chrysophyte communities and limnological variables.  Sediment cores will be collected from each of the 72 NS LRTAP lakes and the 26 NB study lakes.   These cores will be sectioned at 0.25 cm intervals for later high-resolution analyses.   To ensure the accuracy of later inferences, 15 lakes, which cover the pH range encountered in this study, will be cored in triplicate.

Algae from the uppermost sediments (“tops”) will be used in conjunction with current water chemistry data (from Env. Can.’s monitoring program, with new measurements by this study for the NB lakes to update earlier measurements) to establish a modern surface sediment calibration set to estimate species’ environmental optima and tolerance ranges to important limnological variables, that then form the basis of the transfer functions for this region.   The predictive ability of these models will be statistically evaluated using jackknifing and bootstrapping techniques.  Furthermore, this dataset will be combined with the large NE USA lake diatom and chrysophyte datasets to assess the importance of regional vs extra-regional datasets on inferring historic changes in assemblages.  The predictive powers of these models are very high (r 2 = 0.8 – 0.9; 118).

Task 2: Assessment of the change in pH and DOC since pre-industrial times:

To determine acidification patterns on a regional scale, we will use the 72 NS LRTAP lakes and the 26 NB CWS lakes.  Based on the inference models developed above (Task 1), estimates of limnological conditions (e.g., pH and DOC) using present-day (surface) and pre-industrial (deposited before 1830’s) sediments will be made, from which estimates of change can be inferred and compared with the results based on process-based models (Task 3). This analysis is often referred to as the “top-bottom” approach, developed during the 1980’s acid rain work (Cumming et al. 1992) and since applied in a large number of applications.  Comparisons of the main direction of variation and inferred values will allow us to assess if factors other than those reconstructed are important in structuring the algal communities. Triplicate cores will be analysed for 20% of the lakes to assess variability (repeatedly shown to be low by our work).

Task 3: Biogeochemical models – MAGIC: 

An alternate method of assessing both pre-industrial conditions in lakes and the extent of changes in lake chemistry over time is the use of biogeochemical models such as MAGIC.  This model uses current lake and soil chemistry, current deposition rates (acid anions, base cations) and estimated historical deposition rates in pre-industrial times, along with hydrologic information to estimate lake chemistry circa 1830.   Historical (pre-industrial) deposition patterns have been constructed for many regions of eastern North America and Europe based on estimates of past emissions. In addition, a number of thermodynamic parameters are used in the model; these can be optimised to provide the best fit between current measured lake or stream chemical data and model predictions.  

Environment Canada is currently carrying out preliminary evaluations of the degree of acidification and potential recovery in some study lakes using MAGIC.   The chemistry data that are available for the NS LRTAP lakes are suitable for use with this model.  However, soil data for these lakes’ catchments are lacking, and current estimates of key parameters (e.g., cation exchange capacity, base saturation) are based on qualitative interpretation of generalized soil maps.   This will restrict the usefulness of these studies.   We plan, in consultation with Env. Canada, to select a subset of at least 20-30 LRTAP lakes, and to collect the required soil data so that MAGIC can be used.   These lakes will overlap with the subset chosen in Question 2, Task 1 to address the timing of acidification.   This will require an extensive field programme, because of the spatial heterogeneity in most catchments.  To minimize this problem, we will mainly study low-order lakes with relatively small catchments.   All subsequent modeling will be carried out in close collaboration with Clair, who will also assist by co-supervising the graduate student associated with this part of the project.   In addition, Dr. Jack Cosby (U. Virginia), who originally developed MAGIC, is also collaborating in this work.   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 from the paleo work.

The second part of this task will be the biogeochemical modeling of the NB lakes.  As less data are available for these lakes, this task will require a substantial field programme for the collection of both necessary lake and catchment (e.g., soil chemistry parameters) data for modeling and model testing. Again, the results of the modeling will be compared to those generated by the paleo studies.

Question 2: When did lakes in NS and NB acidify, by how much, and is there any recovery?  

Task 1: Assess the timing of acidification trajectories in a set of susceptible Maritime lakes:

We propose to assess the timing of acidification in 30 of the 98 lakes identified above, in pH categories stratified by region and present-day pH values.  This analysis, in combination with our biogeochemical models, will allow us to calculate the load of sulphate deposition under which these lakes acidified and consequently a minimum sulphate load that is required before pH recovery can be expected (Cumming et al. 1994).  

High-resolution sediment cores from these lakes will be sectioned at 0.25 cm intervals, and the chronologies using PEARL’s 3 gamma counters and established dating protocols. Six cores from each category will be selected for detailed analyses.  Fossil algal assemblages will be enumerated at ~ 5-year resolution over the past ~150 years.  Inferred changes in pH and DOC will be based on the models from Question 1 Task 3.  For each group of lakes, inferences of the sulphate load under which they acidified will then be determined based on comparisons of estimated levels of sulphate deposition over this period.  Ordination techniques will be used to assess the relationship between the inferred pH trajectories and measured lake/watershed characteristics.

Task 2: Biogeochemical models:

The modeling described under Question 1 will simultaneously address the question of the timing and rate of acidification in these lakes.   MAGIC provides, along with the estimate of pre-industrial conditions, a temporal sequence of acidification up to the present.   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 threshold values (largely based on biological requirements) for important parameters such as acid neutralizing capacity.  The ability to provide an accurate temporal sequence depends in part on the robustness of the model calibration, which, in turn, depends on the selection of key biogeochemical processes included in the model and how well they are represented.   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.  

THEME 2: LAKE EUTROPHICATION

Question 1. Have hypolimnetic oxygen levels decreased significantly in N.S. brook trout lakes? And if so, why and by how much?

The NS sport fishery is estimated to be worth ~$57 M a year in direct and indirect expenditures (Brylinsky, 2002).  The most important freshwater sport fish is the brook trout, which is stocked extensively in ~400 NS lakes.  Brook trout require cool, well-oxygenated water to survive, and are seldom found in waters with less than 5.0 mg/L dissolved oxygen.  A recent report (Brylinsky, 2002) presents potentially ominous predictions for the survival of this fishery.  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.  As nutrient concentrations, including total P, were not measured 25 years ago in these lakes, “…it is not possible to determine to what extent, if any, the trophic status of the lakes has changed” (Brylinsky, 2002).   We can, however, address this problem using paleolimnological tools, similar to those developed during Smol’s last strategic grant which reconstructed lake water nutrient levels from diatoms and hypolimnetic oxygen levels from chironomid assemblages.  Several factors may have caused the observed oxygen decreases in these lakes (e.g. eutrophication, climate change, natural changes).   Are deepwater oxygen levels in the brook trout lakes closely linked to land-use changes resulting in eutrophication? We can also address this using the trophic status modeling approach developed by Dillon in Ontario (Dillon et al. 1994).   A key feature of the lakeshore capacity model (LCM) is its ability to estimate historical P levels in the absence of measured data.

In collaboration with colleagues at the N.S. Dept Agriculture & Fisheries, we will collect duplicate cores from the 20 study lakes in the NS Hypolimnion Project (Brylinsky, 2002) with 6 deeper lakes added at request of our partners, and reconstruct past total P, hypolimnetic oxygen levels, and other water quality variables based on paleolimnological analyses.   We will address the questions “have nutrient levels increased in these lakes?” and “if so, when (i.e., what were the cause(s)) and by how much?”   We will also use trophic status models to address the same questions.   These 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.

Question 2. Eutrophication and model evaluation of Kings County lakes:

The municipal government in Kings County (NS) became concerned with local water quality during the early 1990's as a result of increased shoreline development.  Due to the absence of long-term water-quality data, planners and scientists undertook some preliminary monitoring and modeling programs (using early versions of Dillon’s Ont. LCM) on 10 lakes in the Gaspereau River watershed to determine if lake-water quality was deteriorating and to assess implications for future residential development.  Working with our partners in NS, who identified these lakes (and 1 control lake) as primary reference sites for developing suitable models and tools to establish provincial guidelines for lakeshore capacity planning, we will use our pattern- and process-based approaches to help establish the tools necessary for effective and ecologically sound management of these resources.  In addition, paleolimnological analyses of the 11 study lakes will determine past trajectories of water quality changes, and provide estimates of pre-impact limnological conditions (thus providing a key component of any paleo-LCM model comparison, as well as realistic mitigation targets).  Among the recommendations of the final consultants report (Horner Assoc., 1995) was the need for water-quality monitoring (which our NS partners have been doing, and which will provide a basis for this study); and the need to modify and refine these Ontario models for use in NS. Working with our partners, this collaborative project will fill these identified research needs.

Question 3. Eutrophication and land-use effects on lakes in Cape Breton Highlands National Park:

In addition to the LRTAP lakes, Park officials have identified 2 lakes that are potentially affected by eutrophication and other water-quality issues that can be addressed using our new techniques.

(1) Freshwater Lake: Water quality of this lake is of concern as it is subject to accelerated runoff, septic input, and other land use-related effects from the Park and local community.   Some monitoring data were collected in the late-1970s, but Park officials, although not certain if the lake’s water quality is deteriorating, want to understand the potential ramifications of increased Park and other activities.   We will conduct   paleolimnological and modeling studies of this lake to determine if there are trends in trophic status and a need for mitigation.

(2) French Lake: This lake lies immediately adjacent to a major highway, built in the late-1950s.  Have these land-use changes affected the limnology of this lake?  Has erosion in the catchment and into the lake increased?  Have lake nutrient levels increased?  Has the road salt used on the highway affected this lake?  All these questions can now be addressed with our paleolimnological and modeling techniques.  One aspect of the Park’s mandate is to preserve ecosystems, but it is not clear what is “natural” without this long-term perspective.

CONCLUSION:

Two major environmental issues presently affect lake-water quality in the Maritime provinces: acidification and eutrophication.  We will utilise two independent, yet complimentary approaches (paleolimnology and biogeochemical modeling) to identify the degree of change that has occurred as a consequence of these stressors, the timing of any changes that have taken place, and the requirements for restoration of lakes to pre-disturbance conditions.   This study will focus on a large region of Canada that has not been well-studied to date with respect to these concerns.   Our goal is both to refine existing methods and to develop new methods which will be of immediate practical value to our collaborators and end-users in this region.  We will also ensure that they be applicable to other locations and appropriate end-users in the country.

References Cited:

Brylinsky, M. 2002. Nova Scotia Hypolimnion Project.  NS Dept. Agriculture and Fisheries.  
Cumming, B.F., Smol, J.P. et al. 1992. Can. J. Fish. Aquat. Sci. 49:128-141.  
Cumming, B.F. et al. 1994. Can. J. Fish. Aquat. Sci. 51:1550-1568.
Dillon, P.J. et al. 1994. Lake Reserv. Man. 8:121-129.
Dillon, P.J. et al. in Managment of Lake Trout Ecosystems. J. Gunn (ed.) (in press)
DFO. 2000. The effects of acid rain on Atlantic Salmon of the Southern Uplands of Nova Scotia.
Horner and Associates. 1995. Lake carrying capacities and proposed shoreline development policies for the County of Kings. Consultants report to Kings Co.
McNicol , D.K. et al. 1996. The Can. Wildlife Serv. LRTAP Biomonitoring Program. Env. Can. Tech. Rep. 248.


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