An inconvenient truth:  sketch shows prominence of highly acidic, calcium-deficient/high aluminum forest soils in Nova Scotia.  Sketch after Keys et al. (2016), Fig 3.

On Salmon and Soils, An Update

SUMMARY  As a result of the inherently poorly buffered soils that cover more than 60% of our landscape and acid rain, exacerbated by intensive logging and climate warming, Nova Scotia  has some of the most  acidic, high aluminum & low calcium surface waters and some of the poorest soils for forestry in North America.

Recovery of surface waters and soils following reductions in the acidifying components in fossil fuel emissions has been much slower than expected, but we are beginning to understand the mechanisms, thanks largely to aquatic scientists.

Impacts on aquatic life, particularly salmon, are well recognized and efforts are being made to address them, e.g. by raising salmon fry separately and releasing them into the acidified waters, and  by liming.

We have been slower to recognize  the impacts  on our forest ecosystems, and have not taken the  precautionary measures we could have  11 years ago or even earlier. However, some really good science has been conducted in the interim and finally the Forest Nutrient Budget Model published in 2016 has been  incorporated into manuals guiding forestry practices on Crown lands  and should be come functional in 2023.

Some significant  concerns remain, in particular that we will still push the forests too hard, especially  in the Ecological Matrix of Crown lands and on many private lands.

 I first wrote about this topic on NSFN in 2016 is a post titled “What’s good for salmon is good for trees in Nova Scotia…and v. versa“, and I wrote related pieces subsequently. I first raised concerns about the state of our soils in early hearings (2009-2010) related to the developing forest bioenergy industry. (View Posts etc.)

There have been  some  significant developments, in theory and in practice, in  the last two years especially, so here’s a lengthy,  updated version of the whole story.*   View Notes and subsections (Liming, Posts etc, SGEMnote, HPFnote)  for some of the scientific literature that was consulted in writing it.
*While I have some professional background in the related science and am doing my best to understand and explain some fairly complex science,  I am not the best writer and could well have misunderstood at least some of the details of this story, so I welcome feedback.  A major reason for writing about this topic is to put-some-pressure-on/encourage DNR/L&F/nowNRR, which has conducted some ‘world class’ research on the topic,  to incorporate more  about the issue in their own information/educational literature related to forestry practices; currently that is seriously lacking. I  acknowledge and appreciate that Kevin Keys and Ryan MacIntrye at NRR have been helpful recently by responding to  queries I have sent them about the Nutrient Budget Model. 

This is a long page and I hardly expect that it is going to be read through in detail by most readers of  NSFN. To make browsing it easier,  there is a Table of Contents, and I have subtitled and highlighted (in brown) much of the text.

I will be updating this page as new info is received and as my understanding of the science and the  issues (hopefully) get’s better.

– dp, feb 21, 2022


Atlantic salmon were the bell weather species
Emission controls reversed the trends but not in Nova Scotia
What about the forests?
More than trees and salmon are affected
Nova Scotia’s Forest Nutrient Budget Model
Soil Base Saturation
No wakeup call
July 2021: nutrient budgeting incorporated inSGEM and HPF docs
Liming and use of enhanced weathering materials
Concerns Remain

Atlantic salmon were the bell weather species 

The Map (from DFO, 2013) shows watersheds of the endangered Southern Upland salmon populations and the average pH of surface waters. Salmon populations in SW Nova Scotia have been the most severely impacted by acid rain. “Salmon populations in extremely acidified systems ([RED] pH <4.7) are thought to be extirpated (13 rivers), reduced by 90% in moderately impacted systems ([YELLOW] pH = 4.7-5.0; 20 rivers), reduced by about 10% in slightly impacted systems (pH = 5.1-5.4; 14 rivers), and apparently unaffected when pH >5.4 (13 rivers) based on research in the 1980s.”
Click on the image for a larger version and source.

The basics of the story were  elucidated by aquatic scientists studying the severe declines in salmon stocks in Nova Scotia in the 1980s and 90s.

Acid rain produced by sulphur and nitrogen compounds in emissions from the burning of fossil fuels and carried by winds over northeastern NA  had leached out  the ‘base cations‘, particularly calcium, from soils  of the mostly forested uplands.

At first the increased leaching of nutrient in the uplands  enriched  the surface waters (lakes, streams, rivers);  but with time, on poorly buffered landscapes,   the reservoirs of base cations in forest soils declined, and that was followed by declines in base cations, lowered ANC (acid-neutralzing capacity) and  increased  acidity (lower pH) in the surface waters.

The  result:  extreme acidification (low pH) and related mobilization of aluminum in surface waters on poorly buffered landscapes  impaired development of young salmon; in many streams of the Southern Uplands of NS, salmon were completely eliminated  or “extirpated”.  Brook trout were also impacted, but not as severely.

This publication provides a  widely cited overview of the status of acid rain issues more broadly in 2001, written for non-specialists:

ACID RAIN REVISITED Advances in scientific understanding since the passage of the 1970 and 1990 Clean Air Act
Driscoll, C.T et al., 2001 Hubbard Brook Research Foundation
“The absence of fish and the presence of aluminum in lakes provides important information about the condition of soils within a watershed. The release of aluminum from the soil into rivers and streams usually indicates that the available calcium in the soil is low and has been depleted. Furthermore, trees growing in such soils may experience greater nutritional stress.”

Sulphur dioxide emissions USA & Canada 1850-2005. Data from Smith et al., 2010, Anthropogenic sulfur dioxide emissions: 1850–2005. Atmos. Chem. Phys. Discuss., 10, 16111–16151,

Emission controls reversed the  trends of deterioration in water quality over much of the affected areas – but not in Nova Scotia

Beginning in the late 1970s, measures  were introduced to reduce the acidifying components – mainly sulphur-  in fossil fuels and in the  emissions from the burning of those fuels, and the levels of sulfur dioxide on emissions began to fall. In turn, by the early 2000s, there were signs that the trends of increasing surface water acidity (corresponding to falling pH) had begun to reverse. But not in Nova Scotia.

Reported Clair et al., 2011:

We analyzed chemistry trends for 66 Atlantic Canada lakes using data collected from 1983 to 2007, as well as from 1990 to 2007 and 2000 to 2007 for the original 66 and a further 25 lakes that were later added to the network. Though receiving the lowest acid deposition in eastern North America, the region’s waters are seriously affected by acid rain because of poorly buffering soils and bedrock. Earlier work had shown that despite large decreases in sulfate deposition, lake pH and calculated acid neutralization capacity (ANCc) had not increased as they had elsewhere in North America and Europe. Despite a 50% decrease in acid deposition, a further 10 years of lake chemistry data showed a regional increase in ANC only at the beginning of the sampling period but no increase since the early 1990s

Ten years later, the trend has remained the same, but is better understood, largely from  research conducted by aquatic scientists Shannon Sterling at Dalhousie University and colleagues.   It is a complex story chemically.  Here’s the short but I hope Ok version.

It’s not acid rain with its sulphuric and nitric acids  falling directly on surface water that causes the acidity – it’s the loss of the neutralizing ‘base cations” (Ca2+, Mg2+, K+ , Na+) and particularly the calcium (Ca2+) from soils of the mostly forested uplands.

It takes time to happen.  Initially acid-forming sulfur and nitrogen compounds  in the rain falling on forest soils cause  high levels of base cations to be washed out of soils and their concentration in surface water  actually increases.  So there is more available calcium and less acidity (higher pH).

With time, however, on poorly buffered landscapes*,  the reservoirs of these base cations in the soils decline and likewise they decline in the receiving waters, lowering the acid-neutralizing capacity of those waters. Then  those waters become more acidic as well as very low in available calcium needed by many aquatic organisms.
“Poorly buffered landscapes” are areas where there are relatively shallow soils over very hard, slowly weathering (slowly breaking down), nutrient-poor bedrock. Such conditions prevail  over much of Nova Scotia, in fact we have some of the most slowly weathering soils in all of North America and Europe (Whitfield et al., 2006). Those in SW Nova Scotia are most susceptible because that is also the area of highest acid rain deposition.

When on poorly buffered landscapes, the ‘Base Saturation’ of soils – a measure of the reservoirs of base cations held electrically on soil particles –  falls below 15-20%, ionic aluminum (represented here as simply Ali) is released into the soil solution and subsequently moves into surface waters.

At high levels, this aluminum (Ali) is toxic to many plants and animals, aquatic and terrestrial, including humans.  The negative impacts of “acid rain” on biota are generally due  to calcium deficiencies and/or aluminum toxicity rather than acidity (low pH, high H1+) per se.  Higher calcium levels can reduce aluminum toxicity, so the deleterious effects of low calcium might be related to calcium deficiency and/or increased aluminum toxicity.

There are complex  interactions of aluminum and dissolved organic matter (humic substances, DOC-Dissolved Organic Carbon), but overall the story developed that “there is generally more inorganic [Ali] and organic Al [Alo] as water pH decreases, and there is generally more organic Al as the concentration of DOM increases. In essence, DOM increases the solubility of Al, while decreasing Al toxicity” (Gessemer and Playle, 1999). Thus aluminum toxicity  was found to be reduced in in low pH waters with high levels of dissolved organic matter; in Nova Scotia for example, Kerekes, J., et al., 1989 commented ““Lakes in the study area appear to be sustaining fish populations at more acidic pHs than elsewhere. This may be due to the large concentration of dissolved organic matter in many lakes, which complexes and partially detoxifies metals such as aluminum.”

When the acidifying components of the emissions from burning fossil fuels were reduced beginning in the 1970s and through the 80s and 90s,  this process began to reverse itself in many areas;  the base saturation of soils increased, and in the surface waters, acidity decreased (pH went up), calcium increased, and aluminum decreased.

But not the  poorly buffered soils that are prominent in Nova Scotia and parts of Northern Europe. Again it is a complex story, but it is beginning to be explained though research by Shannon Sterling (at Dalhousie University) and colleagues, e.g. as cited in this paper:

Ionic aluminium concentrations exceed thresholds for aquatic health in Nova Scotian rivers, even during conditions of high dissolved organic carbon and low flow 
By S.M. Sterling. et al., 2020 Earth Syst. Sci., 24, 4763–4775

ABSTRACT Acid deposition released large amounts of aluminium into streams and lakes during the last century in northern Europe and eastern North America.

Elevated aluminium concentrations caused major environmental concern due to aluminium’s toxicity to terrestrial and aquatic organisms and led to the extirpation of wild Atlantic salmon populations.

Air pollution reduction legislation that began in the 1990s in North America and Europe successfully reduced acid deposition, and the aluminium problem was widely considered solved.

However, accumulating evidence indicates that freshwater systems still show delays in recovery from acidification, with poorly understood implications for aluminium concentrations.

Here, we investigate spatial and temporal patterns of labile cationic forms of aluminium (Ali) from 2015 to 2018 in 10 catchments in Nova Scotia, Canada; this region was one of the hardest hit by acid deposition, although it was not considered to have an aluminium problem due to its high dissolved organic carbon (DOC) concentrations that were expected to reduce Ali concentrations.

Surprisingly, our results show the widespread and frequent occurrences of Ali concentrations that exceed toxic thresholds in all sampled rivers despite high DOC concentrations.

Generalized linear mixed model results reveal that DOC, instead of being inversely related to Ali, is the strongest predictor (positive) of Ali concentrations, suggesting that the recruitment properties of DOC in soils outweigh its protective properties in streams.

Lastly, we find that, contrary to the common conceptualization that high Ali levels are associated with storm flow, high Ali concentrations are found during base flow.

[And from the Conclusions} The serious potential consequences of high Ali highlight the importance of actions to further reduce acid emissions and deposition, as critical loads are still exceeded across the province (Keys, 2015), and to adapt forest management practices to avoid base cation removal and depletion. The addition of base cations through liming and enhanced weathering of soils and freshwater may accelerate recovery from acidification.

“Enhanced weathering”: see this explanation

It should also be noted that this research has shown that in  some areas,  the levels of aluminum  have risen above those safe for human health and testing of well water is advised.

What about the forests?

The combined effects of acid rain and poorly buffered soils on forests and  forestry were not so immediate and stark as the extirpation of salmon from NS rivers and are taking longer to be well understood.

Forest Sensitivity to Atmospheric Acid
Deposition From: Miller, E. et al. 2007.

The overall pattern of base cation depletion in northeastern North America, a mostly forested area,  was revealed in the mid 2000s in the “the first scientific large-scale study of forest sensitivity to sulfur and nitrogen deposition in northeastern North America.” Nova Scotia (also parts of Newfoundland) were the most severely affected areas because of the prominence of hard, slowly weathering,  nutrient-poor   bedrock that covers more than 60% of the forested landscape.

Effects of these nutrient deficiencies/low pH/high aluminum  on trees  in our region were and still are not immediately obvious, e.g., rather than causing direct mortality they have effects such as slower growth, greater  susceptibility to disease, i,e, effects which are not readily detected and could be due to many causes. This  was the perspective in 1993 (bolding inserted):

The effects of acid deposition on aquatic ecosystems have been well documented and are understood at the large scale. Although many details at the fine  scale have yet to be elucidated, there is no longer any doubt that acid deposition can have devastating effects on aquatic communities in poorly-buffered waters that are susceptible to both episodic and chronic acidification.

Forest decline in a number of countries in Europe and North America has been attributed to acid deposition, although the evidence is not as strong as it is with respect to aquatic ecosystems. In Cechoslovakia, much of the forest in the Erzgebirge region has died and the remainder shows severe damage. In Germany, the Black Forest and forests in parts of Bavaria have undergone extensive dieback. In North America, forest dam­age appears to be confined  largely to high-elevation red spruce forests in the eastern and northeastern parts of the continent. The details of the extent of forest damage directly caused by acid deposition relative to gaseous air pollutants (e.g. 03, S02) is not clear; however all of these pollutants largely originate directly or indirectly from common sources. [From Acid Rain. O. Bricker and K. Rice. 1993 Annu. Rev. Earrh Planet. Sci. 1993. 21:151-74]

About the same time, the critical role of acid rain and low soil calcium in sugar maple decline began to be unravelled.  Now it’s  recognized that clearcutting on acidified soils can shift the balance in regenerating systems in favour of species like beech and birch over sugar maple. Effects (or lack of effects) on other tree species have not been  well documented, but Miller, E. et al. 2007 reported  that “preliminary results from the 30 sites of the Quebec Forest Monitoring Network (RESEF) show that forest sites in sensitive areas are growing 30% more slowly than sites located in tolerant areas.”

More than trees and salmon are affected

In addition to the well known effects of calcium loss and aquatic acidification on salmonids, many studies are finding that declines in calcium under forests are having diverse adverse effects either through calcium deficiency directly or indirectly through reduced pH, aluminum mobilization and enhanced mercury toxicity e.g., on , forest salamanders and snails, loon reproduction, zooplankton, forest herbs, invertebrates and song birds.

Nova Scotia’s Forest Nutrient Budget Model

In 2008, DNR (later to become L&F and now NRR), in a contract arrangement with Prof Paul Arp at UNB, began to develop a “Nutrient Budget Model” (acronym FNBM or just NBM) as  “a decision support model to assess site suitability for biomass harvest in NS”;  in a 2009 DNR slide presentation it was stated that this model would be “ready for use in mid-2010”. Harvesting trees for biomass energy was then  just getting geared up nationally and  in Nova Scotia  and concerns had been raised about the sustainability of intensive biomass removals, related to nutrient supply in particular. Arp is a recognized authority on nutrient budgeting and had been one of the authors of the 2007 forest sensitivity study.

There was keen interest in the topic  by people concerned about the possible impacts of harvesting our forests for biomass energy (myself amongst them). However 2010 passed and 2011…without a word about the model… In a report by Jamie Simpson/ECELAW published on Dec 15, 2015 titled Forest Biomass Energy Policy in the Maritime Provinces: Accounting for Science, Simpson wrote

In 2009, the Nova Scotia Department of Natural Resources (NSDNR) commissioned a more detailed study of the province’s soils to determine their resilience to productivity declineassociated with nutrient loss caused by whole-tree harvesting. The NSDNR received the report in 2012, but has yet to release the report.  The researcher who conducted the study published some of the results as a Master’s Thesis; NSDNR permitted him to release information only for federally-owned Kejimkujik National Park. The results, while geographically limited, suggest that biomass harvesting in Nova Scotia can result in decreased forest productivity.

The thesis referred to is this:

A mass balance, biogeochemical framework for assessing forest biomass harvest sustainability
Joshua Noseworthy. 2011. MSc thesis, Univ of New Brunswick

Noseworthy had come to some rather stark conclusions regarding the impacts of acid rain on the soils and forests of NS; further that forest harvesting – especially clearcutting – was having similar impacts. Noseworthy concluded that 73% of NS is  ‘in exceedance’ (way higher than a previous estimate of 39.9% by Jeffries & Ouimet 2004) meaning that even with no harvesting, soil fertility under 73% of our forests will continue to decline and toxic aluminum to increase because of acid rain.

More rattling perhaps was his estimate that that ‘stem-only’ clearcuts (whole-tree harvesting had been banned in NS) produce an average 52% increase in Base Cation Depletion over the background acid rain effect averaged for all of Nova Scotia. He noted also that “there are stands within the province which would be subject to harvest-induced nutrient losses, without the added strain of soil acidification,” but further details were not given. (Few detailed results are given in the thesis “due to confidentiality concerns with Nova Scotia forest inventory data”.)

The Noseworthy thesis was kept under wraps by DNR; it  was never  mentioned in any DNR/L&F/NRR literature and the thesis was unavailable publicly until it was posted on a UNB website (now defunct) and on Library and Archives Canada on or sometime after  March 7, 2013 (the date of creation  the pdf document). The reticence of DNR to even mention their on-going work on the NBM certainly made it appear that they could not deal with the implications of Noseworthy’s conclusions for the practice of forestry in NS. Questioned about it by journalist Robert Devet in 2014 , DNR spokesperson Bruce Nunn offered this explanation:

The Nutrient Budget Model is being calibrated for NS (Soil mapping information is being updated because the model version received had significant errors). The model is not in a state where we can share it, but we intend to do so once calibration for Nova Scotia is complete. The model remains under internal development at DNR but there are no final results to release.

DNR soil scientist Kevin Keys was indeed busy at work obtaining more and better soil data for the model and refining the model and he was very reticent about discussing it in public in the interim. Keys/DNR began to talk about it to select audiences in the spring of 2016 and in the fall of 2016 Keys and a host of co-authors (including Noseworthy as second author) published a  paper on the NBM in a peer reviewed journal. The full paper is available online:

A Simple Geospatial Nutrient Budget Model for Assessing Forest Harvest Sustainability across Nova Scotia, Canada
by Kevin Keys, Joshua D. Noseworthy, Jae Ogilvie, David L. Burton, Paul A. Arp. Open Journal of Forestry, 2016, Vol 6, pages 420-444.

The paper confirmed the patterns of nutrient depletion revealed in the 2007 map above, in fact  the degree and extent of depletion was much greater than previously estimated.

Keys et al., 2016 reported that

When they tested the model with site specific data for 25 plantations obtained in 2012, they found that “field-determined values for % BS and % N were lower than corresponding default data, with relative decreases ranging from −37% to −82% (% BS) and −19% to −71% (% N)”.  The ‘default data’  refers to the data used by Noseworthy (2011) which was based on soil surveys conducted 1934-1991, most  between 1934 and 1973. So the degree of base saturation was even lower than suggested by Noseworthy 2011).

Approximately 1/4 to 1/2 of the assessed plantation sites have non-sustainable MMAI yield expectations…Plantations with non-sustainable MMAI values are mainly associated with low soil weathering classes (especially Class 1) and/or tree species with high nutrient demands (e.g., Norway spruce).” Class 1 Gibralter soils cover much of SW Nova Scotia.

Keys et al., 2016 identified calcium and nitrogen as the most common limiting nutrients and noted that “Ca has long been considered a nutrient of concern in eastern North America…”, also concluding that “Nutrient assessments are even more important in areas that have been impacted by long-term acid deposition since harvest removals can exacerbate declines in base cation levels (especially Ca) in affected soils.”

The NBM  elaborated by Keys et al., 2016 is a “mass balance” or  “black box” model (see figure below). It looks simply at the major inputs of nutrients to forest soils and the major outputs, not at the processes the go on in between such as formation of humus and storage of nutrients in humus.

Diagram illustrates the major inputs (green arrows) and  outputs (red arrows)  of “base cations” ( calcium, magnesium and potassium) to and from  forest soils that are quantified in the  Nutrient Budget Model. The yellow arrows represent enhanced outputs from the soil caused  by acid rain. Click on image to enlarge it.

It’s like a bank account, you look at the inputs and the outputs, and figure what you can draw off in interest without affecting the capital – or what your options are for increasing the capital, which means taking out less of the interest. The model is simply the accounting for the bank account – it does not explain the decisions involved in maintaining it.

It is also assumed that other inputs (.e.g.  via nitrogen fixation) and outputs (e.g. losses by surface erosion and enhanced leaching after clearcutting) are small relative to the major inputs and to some extent cancel each other out.

The major inputs in the NBM model are (i) wet and dry deposition, and (ii) the release of nutrients associated with the “weathering” (breakdown) of rocks.

The major outputs are (iii) “deep drainage” or “leaching” which refers to the movement of some of the “soil solution” with its contained nutrients  to ground and surface-waters and (iv) the production of forest products which involves removing whole trees or parts of trees with their contained nutrients.

Keys et al. 2016 constructed a “geospatial, GIS-linked spreadsheet model”  that allows these balances to be estimated for each forest stand in NS – it is a stand based approach to nutrient management that required updating of our info. about soil characteristics at the stand level across NS, no small feat.

The NBM, combined with site specific geographic information, allows one to estimate for each stand a  “sustainable harvest rate expressed as the sustainable mean annual increment, i.e., SusMAI, in m3∙ha−1∙yr−1 of solid wood)” based on the nutrient supply and species composition. That value can then be compared with the “merchantable mean annual increment (MMAI)* by projected management regime” to determine if the projected (or desired) yields, as expressed by the MMAI are sustainable in regard to the nutrient supply –   to be sustainable, the harvest must not draw down the nutrient reserves for a particular stand over the  course of one rotation.
*From Wikipedia: “The mean annual increment (MAI) or mean annual growth refers to the average growth per year a tree or stand of trees has exhibited/experienced up to a specified age. For example, a 20-year-old tree that has a stem volume of 0.2 m3 has an MAI of 0.01 m3/year.” It is used to calculate how much wood can be harvested from a stand based on the observed or estimated growth rates of trees, i.e. so that what is harvested is balanced by new growth over the next rotation. It does not take into account needs of wildlife, or possible nutrient deficiencies – the latter issue is addressed by not harvesting more than indicated by the SusMAI. “SusMAI” is new terminology – at least it appears to be – introduced Keys and colleagues. Needs of wildlife are addressed by leaving unharvested patches, old trees etc. When foresters say “the harvest is sustainable” what they usually mean  is that the actual harvest is not removing more than than will be contributed by new growth over the next rotation – they are not saying that nutrient supply is also being maintained or increased and needs of wildlife are also being being met by XXX and YYYY.

So the criterion for nutrient sustainability is that SusMAI is equal to or less than the MMAI. If it is greater, then the soil nutrient reserves will be drawn down which is considered non-sustainable.

Soil Base Saturation 

Besides estimating the sustainable yields based on nutrient supply, the NBM is also used to determine how the pool of available soil nutrients* is affected over time by the balance between inputs and outputs. For the ‘base cations’  (calcium, magnesium and potassium),  a variable of concern is the “% Base Saturation” or Soil BS% a measure of ‘how filled up’ the soil is with available nutrients. In the bank account analogy cited above, it’s equivalent to the capital in the bank account.
“Available” means the nutrients are in a form that  can be readily taken up by plants.

For NS forest soils, BS% values vary between 5 and 35% (Fig 3 in Keys et al. 2016). Studies in the US cited by Keys et al. indicate that historical -pre acid rain values were above 20%, thus  BS20% is regarded as a threshold for recovery from acid rain.

Other studies suggest 15% BS as a threshold below which “aluminum stress” occurs in forest soils. At these low BS& values,  aluminum becomes mobilized and thereby potentially toxic,  and it also displaces base cations causing more of them to be flushed out of the soil. Acid rain, combined with inherently “poorly buffered soils” that cover more than 60% of NS,  is the major cause of forest soil BS% values falling below 15-20% in NS – the nitric and sulphuric acids cause aluminum to be mobilized, and the mobilized aluminum (Ali) in turn displaces the base cations. The condition is exacerbated by clearcutting.

Sketch shows prominence of low BS% forest soils in Nova Scotia.  After Keys et al. (2016), Fig 3.

As noted above, Noseworthy (2011) estimated that   73% of the forested area in Nova Scotia is in “exceedance of the critical load”, meaning that acid inputs on those landscapes are causing ongoing acidification and base cation depletion. i.e., even with no harvesting, soil fertility under 73% of our forests will continue to decline because of acid rain. Like acid rain, forest harvesting removes basic cations from forest soils and could be expected to exacerbate acid rain effects &/or lead to declines in nutrient reserves even in the absence of acid rain on some sites. For stem only-clearcuts, Noseworthy’s results indicated an average 52% increase in Base Cation Depletion over the background acid rain effect averaged for all of Nova Scotia.

Key’s et al. 2016, with their the more refined NBM, came to essentially the same conclusions but do not, as far as I can determine, give a specific figure for the % area of NS in exceedance or for the average increase caused by stem-only harvesting;  they do  give values for selected plantation sites. Keys et al., 2016  are clear that harvest removals can exacerbate declines in base cation levels (especially Ca) in areas that have been impacted by long-term acid deposition i.e., the areas with 5-15% BS% shown in the map above. 

Not a  wakeup call

The results should have been a wake-up call for DNR and the forest industry in NS but they weren’t. In 2013, the topic was not mentioned in a discussion paper on Revisions to Forests Act Regulations Affecting Forest and Wood Biomass Users (Report FOR 2013-3 Nova Scotia Department of Natural Resource), or in the 5 year Progress Report on the Natural Resources Strategy or in the Addendum on Forests (2016).  There was no mention  of this by-then-thoroughly-researched-by-DNR issue in   the 2016 State of the Forest Report, nor in a subsequent update, nor has it been elaborated on otherwise in documents produced by DNR/L&F/NRR, e.g., the  Field Guide to Forest Biodiversity Stewardship (2017).

Since 2014,  I have repeatedly  questioned  senior bureaucrats at DNR/L&F and  Keys himself   about  the NBM in  one-on-one conversations,  in a ‘stakeholder meeting’ related to the Lahey Report and in discussion following  a presentation by Keys to a select audience in the spring of 2016,  e.g., asking ‘when will it be ready for use’, ‘why are we not hearing about it’,  ‘why are we not taking precautionary measures in the interim?’   The responses before the paper was published were  ‘we are working to get better soil data and refine the model’;  asked after it was published ‘when will the model  actually be applied?’, the response has been  ‘we are working on it’ (or words to that effect.) View more in a NSFN post on Feb 3, 2019

In the meantime, intensive logging has continued on Crown lands without any reference to site nutrient conditions, even though it had been  clear since 2011  that clearcutting on highly acidified sites would  reduce the supply of critical nutrients and hence productivity of those sites over time (re: Noseworthy 2011).

The effects of clearcutting  on highly acidified landscapes on aquatic life are not discussed in Noseworthy 2011  or in Keys et al., 2016.  Regardless,  it must have been well known within DNR  that there  are significant  repercussions  for aquatic life as well as for tree growth.

Acid Rain issue is not well highlighted by any NS Government department

1999 Map posted on NSE page

It seems that the main source of public info. on the acid rain issue is a page under NS Environment – novascotia/nse/air/acidrain.asp. All it says about the effects of acid rain are this:

Damage to land and water ecosystems occurs when the land, water or plants like trees and crops cannot neutralize the acid being deposited by the rain. High levels of acidity can destroy life in our lakes and rivers and reduce forest growth. Nova Scotia has low tolerance for acid precipitation because of the low buffering capacity and neutralization abilities of water and land ecosystems in most of the province, especially in south-western Nova Scotia.

There is also a webpage on the “Lake Acidification Monitoring Program with links to an old paper, and one to a federal site not now viewable.

Under the Department of Fisheries & Aquaculture, there are many individual documents addressing or citing acid rain issues to be found using a search tool, but it seems no higher level webpage, and Acid Rain is NOT listed under Hot Topics on the home page.

Likewise, Under NRR (still cited as “natr’ in the website address), there there are many individual documents addressing or citing acid rain issues to be found using a search tool, but, it seems, no higher level webpage addressing the topic.

July 2021: nutrient budgeting is  incorporated into  SGEM and HPF procedures

SGEM: There is reference to  nutrient budgeting in the final (July 2021)  Silvicultural Guide for the Ecological Matrix). That guide  defines the decision-making processes that will be applied to managing all logging on the Ecological Matrix portion of the Crown land working forests. The guide  will be fully applied by 2023 under the new government’s schedule for ‘implementing Lahey’. Harvest levels will be adjusted so that nutrient removal does not exceed the sustainable nutrient supply, i.e.  so there is no change in the nutrient status.

The SGEM (2021) document is  vague on whether and how historical legacies of nutrient depletion will be addressed (view extracts). Recently, in response to  questions,  Kevin Keys told me that they (NRR foresters) recognize that the SGEM (July 2021) is vague on how  improvement of soils with very low base saturation values would be effected, but that  explicit processes to address this issue are in the works.

HPF: Likewise, there is reference to  nutrient budgeting in the HPF Phase 1 Final Report (July 2021). There is more discussion of nutrient issues in this document than in the SGEM, but exactly how they will be addressed is still being worked out.  The HPF sites sites will be mostly on  on Ecosites AC 10 and AC 11 on which “the majority of Acadian climax softwood and mixedwood forests are found” (SOURCE).  From FEC III: Ecosites

AC10: Occurring mainly on well drained slopes with medium textured glacial till deposits, this ecosite has fresh, nutrient medium soils which generally support late successional forests dominated by red spruce, hemlock and yellow birch. Earlier successional forests contain balsam fir, white birch, red maple and trembling aspen.

AC11: Occurring mainly on imperfectly drained lower slopes and level areas with medium textured glacial till deposits, this ecosite has moist, nutrient medium soils which generally support mixedwood climax communities dominated by red spruce, hemlock and yellow birch. Earlier successional forests contain balsam fir, aspen, white birch and red maple.

From HPF 2021:

By definition, HPF sites are expected to produce merchantable volumes at rates of 6 m3/ha/yr or more at time of final harvest. This type of production is nutrient-demanding and will likely match or exceed the natural long-term nutrient supply rates on many sites. Therefore, soil monitoring and development of nutrient management plans are necessary components of high production forestry.

Over the last several years, NSDLF has been directly involved with several soil and site productivity related projects including: (i) development of a forest soil classification system (Neily et al. 2013), (ii) development and calibration of a forest nutrient budget model (Keys et al. 2016), (iii) development of a forest soil and tree tissue sampling program, (iv) research on ground disturbance and soil damage assessment, (v) research on forest liming, and (vi) research on soil amendment use in spruce plantations (Keys et al. 2018). All this work, combined with ongoing research, will be used to develop science-based and effective soil monitoring and nutrient management regimes for HPF sites.

Read more under HPFnotes

There are two scientific papers by Kevin Keys & Co on fertilization of forest soils, one in 2018 and one in 2020. Kevin Keys’s PhD thesis (2018) – Impacts of surface applied alkaline-treated biosolids on spruce plantation soils and vegetation in Nova Scotia, Canada – includes a lot of background material that is discussed in more detail than in the related publications.

Liming and use of enhanced weathering materials

I am not aware of any publicity by NRR related to “forest liming”  but the department has been a sponsor of liming to improve habitat for salmonids and simultaneously improve forest soils e.g.  News Releases in 2016  and 2020

Lime is often applied to sugar maple stands elsewhere and probably also in NS. It is not without some risk, notably with regard to earthworm invasions (Jean-David Moore et al., 2015).

These observations and comments from Effects of Acidic Deposition on Aquatic Resources in the Central Appalachian Mountains by Rick Webb 2004 are pertinent:

.direct liming of tributaries of the Saint Mary’s River has resulted in increased numbers of both fish and aquatic macroinvertebrate taxa. Increased productivity of aquatic fauna has also been obtained for an additional small number of other western Virginia streams that are presently limed (Larry Mohn, Virginia Department of Game and Inland Fisheries, Verona, VA, pers. comm., 2003). In West Virginia, 26 streams and several lakes are limed with positive results for fish productivity (Mike Shingleton, West Virginia Division of Wildlife Resources, Elkins, WV, pers. comm., 2003). Liming programs have also been conducted in both Maryland (Price and Morgan, 1993) and Pennsylvania (Janicki and Greening, 1988). As summarized by Olem (1990), the majority of liming studies report successful reproduction and increased biomass of acid-sensitive fish species.

The extent of limestone treatment of impaired surface waters has been limited by the cost, although relatively low-cost methods have been developed (Downey et al., 1994). Other limitations include the probability that liming will not result in the restoration of the original preacidification biological communities (Olem, 1990). There have also been instances where liming has caused mortality due to increased aluminum toxicity (Rossland et al., 1992). In addition, limestone treatment of surface waters provides only a temporary solution; limestone must be continuously or periodically applied if reacidification is to be prevented. More importantly, adding limestone to surface waters only addresses the most obvious aspect of the acidification problem.

Although limestone treatment can improve chemical and biological conditions in a stream, the loss of base cations from watershed soils will continue as long as elevated acidic deposition continues.

Experiments on liming lakes and upper reaches of acid stressed watersheds have been going in NS since the 198os mostly in relation to salmon. A Terrestrial Liming Guidebook for South Western Nova Scotia  was produced by the Hydrology Research Group (Dalhousie University) and others in 2018. An indirect benefit of liming and use of enhanced weathering materials is reduced CO2 emissions from acidified rivers (Sterling et al., 2021)

Kevin Keys (Soil Scientist with NRR), Shannon Sterling (Dalhousie Hydrology group) and Edmund Halfyard (NS Salmon Association) are cited as supervisors of Upland Catchment Liming project in Mooseland, NS (2019); It was  hypothesized that liming of whole catchments will accelerate the long-term recovery of both soils and surface waters from acid deposition impacts. A 2021 conference report on the project concludes:  These early chemical results are promising and further support the use of helicopter liming as an effective tool to combat lingering effects from acid deposition in acidified forests.”

Concerns Remain, particularly at the watershed level

A criticism & a suggestion I have discussed with limnologists  and with Kevin Keys  and with a senior level bureaucrat at NRR, with Lloyd Hines when he was Minister of Forestry (a meeting arranged by Labi Kousoulis who was my MLA at the time) and with Stephen McNeil as premier (pre-announcement of the Independent Review) and in various submissions back to 2014 are these:

(a) DNR/L&F/NRR’s approach to addressing soil acidification/nutrient depletion issue is focussed pretty well solely at the stand level,i.e. decisions about modifying harvests levels are or will be made for a single stand without consideration of the status of and impacts on surrounding lands and the whole watershed.

(b) Even without the detailed refinements of the model and the soil info that Keys said was needed before they could release the model and then apply it, precautionary measures could be instituted. A simple one that I suggested would be to simply prohibit clearcutting in highly acid stressed watersheds as assessed by aquatic scientists. A slightly modified form of that suggestion made its way into the Addendum of the Independent Review (p.30) but went no further.

Now that the actual implementation of nutrient budgeting in Crown land forest management decisions is not far away, the matter of taking precautionary measures may be moot, but watershed level concerns remain.

A key issue is this: if, in an acid stressed watershed, harvests are focussed on the higher volume stands on above average fertility soils, e.g., on a drumlin, those harvests will lower reserves of key sources of calcium in the watershed as a whole, i.e. the harvest may be “sustainable” at the stand level, but the fact remains that reserves of calcium are being reduced in  an already calcium stressed watershed.

At the least, the watershed level impacts of forestry on soil quality and receiving waters should be modelled and formally considered as part of the forest management decisions. It is relevant that a recent paper by aquatic scientists on aquatic health of Nova Scotian rivers highlighted the need to both further reduce acid emissions AND manage firstly practices appropriately:

The serious potential consequences of high Ali highlight the importance of actions to further reduce acid emissions and deposition, as critical loads are still exceeded across the province (Keys, 2015), and to adapt forest management practices to avoid base cation removal and depletion. Sterling et al., 2020

Now finally, we will begin to explicitly address the uplands issue – on Crown lands at least – with ‘implementation of Lahey” by 2023 and specific requirements to apply the NBM.

I still have a general concern that that more than 50% of Nova Scotia’s forest soils are severely nutrient depleted (& have high levels of toxic aluminum), and that the implications of that state for forest productivity and aquatic and terrestrial life more broadly remain an ‘inconvenient truth’.

‘World class’ research on the acidity/low calcium/aluminum issue has been conducted in Nova Scotia, yet it’s not cited in NRR educational documents;  and although  NS Environment  and NS Fisheries and Aquaculture  support research on the issue, they don’t do much to highlight the issue in the public realm.

It has been mostly  Shannon Sterling and colleagues in academia and the NS Salmon Association and local watershed groups raising concerns about the aquatic side of the issue and connections to the whole watershed.

A strong argument can be made that there is no greater threat to productivity and health of our forests and surface waters than the ongoing acidification caused by acid rain and intensive forestry. Already there are  informal reports of clearcut land just not growing back well,  and of brook trout not being found following a lot of clearcutting on acidified landscape.

Remarkably, to me at least, in spite of all the hoopla about the Lahey Report, and the mantras about implementing Ecological Forestry, we see advertisements for senior level strategists in NRR* without mention of Ecological Forestry; and a whole campaign to attract and train workers in forestry in NS** without mention of Ecological Forestry – or of the challenges imposed by these serious limitations to future productivity and health of our forests.
*Vew Posts 13Feb2022 and 8Feb2022
**See for example, info provided by the Forestry Sector Council

The NBM and associated databases  is a long awaited tool that helps us understand the magnitude of nutrient deficiencies in our forest ecosystems on the poorly landscapes that cover 60+% of the province, and can help us evaluate indicate some options for addressing these deficiencies. Say Keys et al., 2016:

Although not perfect, models like NBM-NS (combined with necessary GIS data) allow forest managers to better evaluate planned management regimes with respect to regional and local nutrient inputs, and to make adjustments to accommodate predictable nutrient deficits. For example, species selection, percent removals, and rotation lengths can all be adjusted to varying degrees to reduce the amount and timing of nutrient outputs and related shortfalls. In some cases, as in intensive plantation management, soil amendments could also be applied to offset nutrient losses from harvesting and continued soil leaching.

I have some questions/concerns about the  options highlighted above:

It would seem that the logical species selection would favour softwoods over hardwoods because of the former’s much lower nutrient requirements. Could that lead to ongoing ‘borealization‘ of our forests? Is that process going on naturally now on the low base saturation soils?

If percent removals are reduced, will those be compensated for by harvesting more stands (essentially spreading out the damage)?

What are the implications of increasing rotation length? Will that be a book-keeping adjustment, with no actual requirement to follow it up in future?

Keys et al., 2016 are appropriately cautious about the use of fertilizers and Keys is approaching that issue as he has the NBM, with solid research. But will we then follow the same path that has been followed as the NBM was developed (2008-2016) and regularly applied (2023 on), and until there are definitive  guidelines, largely ignore the deficiencies rather than reduce intensity of logging as a precautionary measure?

Use of fertilizers or lime, or enhanced weathering materials is a legitimate  approach to addressing the the soil and water acidification/low calcium/high aluminum issue in restricted areas – e.g. in HPF sites, and around the headwaters where efforts are being made to restore habitat for salmonids –  but is not without risk and is impractical & risky on a broad scale.  

That leaves seeking legislative action to reduce emissions and reduced forest harvesting as the major tools to address the  issue on the Ecological matrix of Crown lands and likely over most of the private lands in Nova Scotia.