Spatial Variation in Water Quality in Rivers of the Boreal

8/12/2019 Spatial Variation in Water Quality in Rivers of the Boreal

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Manitoba Model Forest Report 05 2 - 63

Spatial Variation in Water Quality in Rivers ofthe Boreal Shield of Eastern Manitoba:

Influence of Soils, Disturbance History andBeaver Activity

Brian G. KotakMiette Environmental Consulting Inc.

October 2006

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ConservationWater Stewardship

Sustainable Development InnovationsFund

Black River First Nation

Citation:

This publication should be cited as:

Kotak, B.G. and A. Selinger. 2006. Spatial Variation in Water Quality in Rivers of the Boreal

Shield of Eastern Manitoba: Influence of Soils, Disturbance History and Beaver Activity. ManitobaModel Forest Report 05-2-63. 32 pp

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Table of Contents

1.0 Executive Summary .....................................................................................................................4

2.0 Acknowledgements.......................................................................................................................6

3.0 Introduction ..................................................................................................................................74.0 Methods .........................................................................................................................................8

5.0 Results and Discussion ...............................................................................................................115.1 Spatial Variation in Water Quality in the Three Rivers and General Relationship to Watershed

Features ..........................................................................................................................................15

5.2 Pair-wise Comparisons of the Effects of Soil and Disturbance on Water Quality...................215.3 Effects of Watershed Disturbance Level on Water Quality.....................................................26

5.3.1 Effects of Proportion of Watershed Harvested on Water Quality.....................................27

5.3.2 Effects of Proportion of Watershed Burned on Water Quality .........................................29

6.0 Literature Cited..........................................................................................................................32

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1.0 Executive Summary

A spatial survey of water quality was undertaken on September 12, 2005 along the length of the

OHanly, Black and Manigotagan rivers from the Ontario border, downstream to their near their

terminus near Lake Winnipeg. Due to the inaccessibility of the area, the water sampling was

conducted from a helicopter. Spatial trends in water quality observed along the rivers and their

main tributaries were then related to aspects of each watershed, including main soil types and the

amount of forest harvesting and fire disturbance through the use of GIS data.

Water quality varied along the length of each river, with lower concentrations of key parameters

(phosphorus, nitrogen, dissolved organic carbon [color], sulphate, cations such as calcium,

magnesium, potassium and sodium, as well as pH, alkalinity, conductivity and turbidity) in theirheadwaters near the Ontario border, and higher concentrations closer to Lake Winnipeg. The

Manigotagan River had the lowest concentration of ions and the smallest amount of variation in

water quality along its length, while the OHanly River had the highest concentrations and highest

spatial variability.

The spatial variability in water quality could be related to a number of watershed characteristics

including soil type and fire and forest harvesting disturbance. In addition, beaver activity,

particularly in the lower reaches of the OHanly and Black rivers near Lake Winnipeg, had a

significant impact on water quality, dwarfing the impacts observed for fire and forest harvesting.

Beaver impacts were caused by the construction of dams and the subsequent back-flooding of

riparian areas, as well as destabilization of stream banks and subsequent erosion. The effects of

beaver were so pronounced in certain areas that the impacts on turbidity and stream color were

noticeable from the air.

Sub-watersheds that had bedrock-dominated (BR) soils, and which had not experienced fire or

forest harvesting in the last 60 years, had rivers and tributaries with significantly lower

concentrations of cations, phosphorus, nitrogen, DOC and alkalinity than those located in

watersheds containing deep basin (DB) soils. This was expected, as thin and nutrient-poor BR soils

export less ions to receiving waters (rivers, streams) than do more well developed and relatively

nutrient-rich DB soils. A subset of the BR-dominated sub-watersheds had experienced forest

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harvesting over the last 60 years, but not fire. These sub-watersheds had rivers and tributaries with

elevated concentrations of many of the water quality parameters, including phosphorus, nitrogen,

color and turbidity. However, beaver activity was also significant in these sub-watersheds and it is

likely that the effects of beaver on water quality were more significant than that of harvesting. Fire

was a dominant feature in another subset of the sub-watershed, and because of the absence of forest

harvesting and beaver activity in these sub-watersheds, allowed for an evaluation of the impacts of

fire alone on water quality. Fire had the opposite effect on water quality than did harvesting and/or

beaver. Concentrations of phosphorus, nitrogen and color in fire-dominated sub-watersheds were

lower than in similar reference sub-watersheds.

The opposite effects of harvesting (or beaver) and fire found in this study, along with the effects of

soil type (from this and another closely related study in the region: Kotak et al., 2005) providesclues to the role of disturbance and soils type in regulating water quality in eastern Manitoba.

While fire in BR-dominated soils may result in a rapid pulse of nutrients and other dissolved

constituents from the land to water (as a result of the rapid mineralization effects of the fire)

immediately following the disturbance, a long-term decrease in dissolved constituents may follow.

Lower stream concentrations do not recover until the long process of re-developing soils has

completed on the burned landscape. In contrast, forest harvesting on BR-dominated soils may

cause a long-term elevation in stream concentration of many water quality parameters due to the

maintenance of soil processes (compared to fire) and the long-term release of ions (nutrients, DOC,

etc.) from decaying logging slash (tree tops, branches). Therefore, fundamentally, the effects of fire

and harvesting are different.

A different scenario may occur however in watersheds that are comprised of a mixture of BR soils

and organic soils (those found in peatlands). Under these circumstances, both fire and harvesting

may result in increased concentrations of nutrients and DOC as both disturbances increase water

flow from disturbed upland areas to lowland, organic sites. Increased water flow through these

organic soils will result in the sustained export of significant dissolved substances to receiving

waters. Therefore, the effects of disturbance on water quality not only depends on the type of

disturbance, but the composition of soils in the watershed.

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2.0 Acknowledgements

This project forms a component of a larger Manitoba Model Forest program examining the

influence of watershed features and disturbance agents on water quality in eastern Manitoba, with

the intent of developing simple watershed management tools for the forest industry. Specifically,

watershed management tools will be developed in 2007 to provide Tembec Inc. with a way of

incorporating water quality objectives into their forest management planning. The financial support

of the Manitoba Model Forest, Canadian Forest Service, Tembec Inc., Manitoba Hydro and the

Sustainable Development Innovations Fund is appreciated and acknowledged.

Field work (the helicopter survey) was carried out by Black River First Nation EnvironmentDepartment personnel, specifically, Brian Kotak and Allison Selinger. Hovering and spinning

around in tight circles, while looking straight down at the landscape below for 4.2 hours is enough

to upset anyones stomach. The fact that no one became sick is a testament to the dedication of the

field crew and the flying expertise of Paul Gibson (Provincial Helicopters, Lac du Bonnet)!

Tembec graciously provided all GIS data. Special thanks to Jennifer Lidgett for the refresher

course on GIS.

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3.0 Introduction

The eastern side of Lake Winnipeg contains a myriad of aquatic habitats including lakes, wetlands,

rivers, streams and creeks. Due to the inaccessibility, baseline data on water quality is very scarce

in eastern Manitoba, particularly north of the Winnipeg River. Where data does exist, information

on water quality is largely restricted to a few of the largest rivers (Poplar, Pigeon, Berens and

Bloodvein) and even in the more accessible and more developed southern portion of Ecoregion 90

(e.g., in Tembecs Forest Management License Area), surprisingly little water quality information

exists. Monitoring programs on some of the rivers (e.g., Manigotagan, Black) have been

discontinued many years ago. Lack of baseline information makes it impossible to gain insight into

whether water quality has changed over time and what factors may influence water quality.

Management decisions concerning land use practices are difficult in the absence of such vitalinformation.

In addition to a lack of baseline data, our understanding of what controls water quality in boreal

shield water bodies is rudimentary. Water quality in a water body is a direct reflection of the

characteristics of the watershed, both in terms of structure and processes. Watershed characteristics

such as soil type (e.g., thin bedrock-origin soils, deep basin soils, organic [peat] soils), and

disturbance regimes such as wildfire, forest harvesting and the activities of beaver may have a

profound effect on the water chemistry of a water body. Forested watersheds play a critical role in

controlling the hydrologic cycle, including water storage, flow and water quality in watersheds

(Hetherington, 1987). It is therefore important from a watershed management context that we

understand how these processes work.

This report summarizes the results of a spatial survey of water quality from several sites along each

of the Manigotagan, Black and OHanly rivers in eastern Manitoba. Due to the inaccessibility of

many of the sampling sites, water samples were collected from a helicopter. Sampling locations in

the three rivers and their main tributaries represented sub-watersheds within the larger watersheds

that contained combinations of different soil types, disturbance history (fire and forest harvesting)

and beaver activity. This work builds upon research and monitoring that was initiated in 2004 on

100 lakes and 24 rivers, streams and creeks in the same region in an attempt to understand the

factors influencing water quality in eastern Manitoba. The spatial survey of the three rivers also

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compliments seasonal monitoring of a subset of those water bodies that occurred in 2005. A

separate project report has been completed for the 2005/06 lakes study (Jacobs, 2006) as well as an

MSc thesis. The results of the 2004 monitoring of the rivers, streams and creeks are summarized in

Kotak et al. (2005). A technical report that summarizes all the seasonal data collected on the rivers,

streams and creeks from 2004, 2005 and 2006 will be available to project partners in March 2007.

Both the lake and rivers project were funded by SDIF, Manitoba Hydro, Tembec, the Manitoba

Model Forest, University of Manitoba and Black River First Nation, Natural Sciences and

Engineering Research Council (NSERC).

4.0 Methods

On September 12, 2005 a spatial aerial survey of the Black, OHanly and Manigotagan rivers wasconducted by helicopter (Figure 1). Each river and their major tributaries were sampled in several

locations along an east/west gradient from the Ontario border to close to Lake Winnipeg. All three

rivers flow from east to west, eventually emptying into Lake Winnipeg. Sampling was done by

lowering a sampling bucket on a rope over the side of a helicopter while hovering 50 100 feet

above the river. Care was taken to ensure that the rotors of the helicopter did not create significant

water disturbance and re-suspend bottom sediments. A total of 7 sites were sampled along the

OHanly River, 12 sites on the Black River and 10 sites on the Manigotagan River. The intent was

to study the spatial variability in water quality from the headwaters of each river to their terminus at

Lake Winnipeg. Prior to sampling, GIS analysis was used to identify sampling locations that

reflected parts of the watersheds with different soil type and disturbance history (fire, logging).

While not intentionally part of the study design, beaver activity (dam construction, back-flooding of

forested areas, disruption of riparian vegetation and erosion of bank soil) was observed in several

areas along the Black and OHanly rivers, particularly in sections of the rivers closer to their

terminus at Lake Winnipeg. In some cases, beaver activity caused a significant change in water

color and turbidity, noticeable from the air. Beaver activity was not prevalent along the main stem

of the Manigotagan River.

Water samples were kept chilled in a cooler and the samples were sent to Envirotest for water

chemistry analyses within one day of sampling. Water chemistry analyses include: total dissolved

phosphorus (TDP), total phosphorus (TP), ammonia (NH4), dissolved organic carbon (DOC),

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turbidity, pH, total dissolved solids (TDS), sulphate (SO4), nitrate (NO3), calcium (Ca), potassium

(K), magnesium (Mg), sodium (Na), conductivity, chloride (Cl), alkalinity, bicarbonate, carbonate

and hydroxide.

Prior to the statistical analysis that related changes in water quality along the length of the rivers to

watershed features (soil type) and disturbance history (fire, logging), each watershed was delineated

using topographic features on 1:50,000 topographic maps, supplemented with color infrared and

black and white ortho-photographs, provided by Tembec Inc. The photographs helped identify

potential direction of flow of water in peatlands that could not be determined from topographic

maps alone. Watersheds were digitized using ESRI ArcMap (v 8.3) software. The OHanly, Black

and Manigotagan River watersheds are 269.9, 715.0 and 1427.3 km2(26992, 71504 and 142734

hectares) in size (from the point of sampling near Lake Winnipeg). Watersheds were also brokenup into smaller sub-watersheds using the water quality sampling points as the locations of the

downstream extent for each sub-watershed. To determine the area of different soil types, fire events

and forest harvesting in the sub-watersheds, Tembec provided their GIS coverages for Enduring

Features (soils), forest fire history (including time since disturbance) and forest harvesting

(including time since disturbance). ESRI ArcView 3.1 software was used to create overlays and

intersections between each of the sub-watersheds and the soils and disturbance layers. A database

was then compiled based on the intersections. Based on a previous data analysis (Kotak et al.,

2005) of 24 rivers, streams and creeks in the same region, the time since disturbance aspect of the

fire and harvesting data were combined to create one category of fire (the amount [area] of fire

within each sub-watershed within the last 60 years) and one category of harvest disturbance (the

amount [area] of harvesting within each sub-watershed within the last 60 years).

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Figure 1. Location of study watersheds in eastern Manitoba. Red = Manigotagan River watershed,

Black = Black River watershed, Green = OHanly River watershed.

Analysis of the data occurred in several ways. Firstly, graphs were made for certain water quality

parameters in order to visualize trends in water quality at the sampling locations along the length of

each river. This provided an easy way to determine if water quality varied significantly from one

end of each river to the other. Secondly, to examine the effects of soil type and disturbance on

water quality, the data from all sub-watersheds were grouped into the following categories: Bedrock

dominated soil with no fire or harvesting (BR-Ref), Bedrock dominated soil with fire but no

harvesting (BR-Fire), Bedrock dominated soil with harvesting but no fire (BR-Harvest), Deep Basindominated soils with no harvesting or fire (DB-Ref) and Deep Basin dominated soils with fire and

harvesting (DB-Both). Not all combinations of soil types and disturbances were represented in the

watersheds. For example, deep organic [OD] soils were either absent or only a small component of

the sub-watersheds. The number of sub-watersheds in each soil/disturbance category varied from 1

to 8. The Manigotagan River watershed extends into Ontario, and due to a lack of GIS coverage for

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soils, fire and harvest for this area, most sub-watersheds of this river could not be included in the

statistical analysis. The only exception was the Ross River sub-watershed, which flows into

Manigotagan Lake, near its intersection with Quesnel (Caribou) Lake. Despite this, it was still

useful to sample the length of the Manigotagan River to assess if water quality did vary along the

river. Table 1 shows the specific characteristics of each sub-watershed category.

Table 1. Soil and disturbance characteristics of the various sub-watershed categories

Sub-WatershedCategory (# of

sub-watersheds)

Soil Type Harvest Disturbance Fire Disturbance

BR-Ref

(8)

Mean % BR: 99%

Range: 99-100%Mean %DB: 0%

Range: 0%

Mean % Harvested: 3.4%

Range: 0 13%

Mean % Burned: 4.2%

Range: 0.1 19%

BR-Fire

(6)

Mean % BR: 96.9%

Range: 91 100%

Mean % DB: 1.5%Range: 0 9%


Range: 0 8%

Mean % Burned: 54.3%

Range: 30 99%

BR-Harvest

(4)

Mean % BR: 81.8%

Range: 71 88%Mean % DB: 3.9%

Range: 0 16%


Range: 29 51%

Mean % Burned: 5.4%

Range: 0 19%

DB-Ref

(1)

BR: 46.5%

DB: 48.3%

% Harvested: 19% % Burned: 19%

DB-Both(1) BR: 24.5%DB: 57.7% % Harvested: 44.9% % Burned: 29.5%

Analysis of Variance was used to examine the differences between sub-watershed soil/disturbance

treatments certain water quality parameters. Correlation analysis was used to examine the

relationship between the proportion of watershed disturbed (by fire or harvesting) and various water

quality parameters.

5.0 Results and Discussion

In total, water quality was sampled at 7 sites along the OHanly River, 12 sites along the Black

River and 10 sites along the Manigotagan River. As mentioned previously, the water quality

sampling sites were used to define the lower (downstream) boundaries for the sub-watersheds.

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Figures 2, 3 and 4 show the sampling locations and sub-watersheds of the OHanly, Black and

Manigotagan rivers, respectively.

Figure 2. Water quality sampling locations (represented as the downstream boundary of each sub-

watershed) and sub-watersheds of the OHanly River.

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watershed) and sub-watersheds of the Black River.

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watershed) and sub-watersheds of the Manigotagan River.

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5.1 Spatial Variation in Water Quality in the Three Rivers and General Relationship to Watershed

Features

Overall, the Manigotagan River had the lowest concentrations of most dissolved ions, including

SO4, TP, TDP, NO3and NH4(Table 2). It also had the clearest water (i.e., has the lowest turbidity)

and was less colored (i.e., had lower DOC) than the other rivers. The slightly higher Ca, pH and

alkalinity of the Manigotagan River compared to the other two rivers reflects the greater proportion

of Deep Basin (DB) soils, which contribute Ca and alkalinity, and produces water with a higher pH

than Bedrock (BR) type soils. The range in values for any one water quality parameter was

generally much smaller than in the other two rivers. In contrast, the OHanly River had the highest

concentrations of nutrients (forms of phosphorus and nitrogen), conductivity, DOC and turbidity.

The Black River fell between the OHanly and Manigotagan Rivers with respect to many of the

water quality parameters. The slightly lower pH and alkalinity in both the OHanly and Black

rivers likely reflects the higher proportion of BR soils in these watersheds compared to the

Manigotagan. BR soils contribute little alkalinity to the water, and as a result, the pH is also

slightly lower.

Table 2. Summary of water quality characteristic of the three rivers. Mean values of all sampling

site (range in brackets). ND = not detected

Parameter OHanly Black Manigotagan

Ca (mg/L) 2.5 (3.7 7.1) 4.2 (1.9 9.3) 7.5 (4.4 8.9)

Mg (mg/L) 2.4 (1.5 3.5) 1.7 (0.9 4.4) 1.9 (1.2 2.9)

K (mg/L) 0.9 (0.7 1.1) 0.7 (0.3 1.4) 0.8 (0.7 0.9)

Na (mg/L) 1.1 (0.9 1.5) 0.9 (0.6 1.5) 0.9 (0.6 1.1)

SO4(mg/L) 79 (67 97) 43 (15 63) 32 (20 70)

TP (ug/L) 86 (49 118) 33 (12 82) 27 (14 42)

TDP(ug/L) 32 (27 40) 17 (4 36) 11 (7 19)

NO3(ug/L) 28 (ND 60) 23 (5 70) 15 (5 40)NH4(ug/L) 74 (30 110) 57 (30 170) 41 (30 70)

DOC (mg/L) 46 (38 64) 30 (13 61) 20 (15 37)

pH 6.48 (6.02 6.77) 6.57 (6.10 7.03) 7.25 (6.61 7.52)

Alkalinity (mg/L CaCO3) 16 (9 20) 13 (6 31) 25 (12 33)

Conductivity (uS/cm) 39 (28 49) 32 (18 62) 51 (45 64)

TDS (mg/L) 98 (83 120) 58 (23 98) 58 (46 85)

Turbidity (NTU) 27 (4 65) 5 (0.6 21) 3.7 (2 7)

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Water quality parameters varied considerably along the length of each river, and the changes

between sampling sites are illustrative of the influence of soil type, disturbance and beaver activity

on water quality.

O'Hanly River - pH and Alkalinity

0

5

10

15

20

25

O1 O2 O3 O4 O5 O6 O7

Site

Alkalinity(m

g/L

CaCO3),

pH

Figure 5. Changes in water quality along the OHanly River. Water quality parameters include pHand alkalinity, total and total dissolved phosphorus, dissolved organic carbon (DOC) and turbidity.

Figure 5 shows the changes in pH, alkalinity, phosphorus, DOC and turbidity along the length of the

OHanly River. Sites 1 and 2 were located in the headwaters of the OHanly River, while site 7 was

the furthest downstream location sampled, where the river crosses Highway 304. In the OHanly

River, alkalinity, TP, TDP, DOC and turbidity all increased when moving downstream from the

headwaters (sites 1 and 2). In particular, alkalinity, TP, TDP and DOC concentrations and turbidity

were much higher at the furthest downstream sites (sites 5, 6 and 7 Figure 5). The same trend was

observed for cations (Ca, K, Na, Mg), NO3, NH4and conductivity (data not shown). As there were

no differences in soil characteristics or fire history between all the OHanly sites, the differences in

water quality are likely due to two factors: forest harvesting and beaver activity. The amount of

pH

Alkalinity

O'Hanly River - Phospho rus

0

20

40

60

80

100

120

O1 O2 O3 O4 O5 O6 O7

Site

Phosphorus(ug/L)

TP

TDP

O'Hanly River - DOC

0

10

20

30

40

50

60

70

O1 O2 O3 O4 O5 O6 O7

Site

DOC

(mg/L)

O'Hanly River-Turbidity

0

10

20

30

40

50

60

70

O1 O2 O3 O4 O5 O6 O7

Site

Turbidity(NTU)

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forested area harvested in the last 60 years in these 3 sub-watersheds ranged from 34 to 50%. In

addition beaver activity was very evident in some of the OHanly River sub-watersheds. Beaver

dam building activity at sites 2, 3 and 4 caused back flooding of riparian vegetation, while even

more beaver activity occurred at sites 6 and 7. A change in water clarity (turbidity) and color was

easily seen from the helicopter between the more headwater sites (sites 1 4) and the last 2

downstream sites. In particular, beaver activity created significant bank erosion at sites 6 and 7

which was noticeable from the air, contributing not only suspended sediments (and therefore,

increased turbidity), but also color, phosphorus and alkalinity to the water. It is not possible to

completely determine the individual effects of the forest harvesting and beaver activity on the

OHanly River. However, a previous study (Kotak et al., 2005) on a much larger suite of rivers,

streams and creeks in the same region found that harvesting did not contribute to increased

turbidity, and only contributed to higher phosphorus concentrations and increased stream colorwhen harvesting occurred on more than 30-40% of the watershed area. For this reason, it is likely

that both forest harvesting and beaver activity were responsible for the change in water quality, with

beaver activity likely playing a more dominant role.

Figure 6. Changes in water quality along the Black River. Water quality parameters include pH and

alkalinity, total and total dissolved phosphorus, dissolved organic carbon (DOC) and turbidity.

Black River - pH and Alkalinity

0

5

10

15

2025

30

35

B1

B2

B3

B4

B5

B6

B7

B8

B9

B10

B11

B12

Site

Alkalinity(mg/L

CaCo3),

pH

pH

Alkalinity

Black River - Phosphorus

0

20

40

60

80

100

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12

Site

Phosphorus(ug/L)

TP

TDP

Black River - DOC

0

10

20

30

40

50

60

70

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12

Site

DOC(mg/L)

Black River - Turbidity

0

5

10

15

20

25

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12

SIte

Turbidity

(NTU)

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Changes in water quality along the length of the Black River (Figure 6) was equally as dramatic as

were

,

ther sites along the Black River are also illustrative of the effects of disturbance on water quality.

R

lso interesting to note is the lower color (DOC concentration) at certain sites along the Black

of

that observed in the OHanly River. Sites 1 3 were located in separate headwater sub-watersheds

near the Ontario border while site 12 was located downstream where the Black River crosses

highway 304. Higher alkalinity, higher TP, TDP and DOC concentrations and higher turbidityobserved at the downstream sites (particularly in sites 10 12 Figure 6) and again are illustrative

of the effects of watershed characteristics and disturbance history. Similar trends were observed for

cations (Ca, K, Na, Mg), NO3, NH4and conductivity (data not shown). For example, high values

for the previously-mentioned water quality variables at site 11, which is a tributary of the Black

River and not connected to the larger upstream watershed, may be due to a high proportion of DB

soils (58%), harvesting (45%) and fire (30%) history and the significant beaver activity (which was

noticeable from the air) in this small sub-watershed. The same can be noted for site 10, which 48%

of its watershed was dominated by DB soils, 19% of its watershed was harvested, and another 19%

of its watershed was burned. Beaver activity was also noticeable. Kotak et al. (2005) have shown

previously that DB soils, harvesting and fire all contribute to higher stream concentrations of TP,

TDP, color and higher alkalinity. Site 12 represents the whole Black River watershed. As a whole

the Black River watershed has only 15% DB soils, 29% has been harvested, and 19% has burned.

The elevated water quality values at this site was likely due mainly to beaver activity, which was

more noticeable than any other site.

O

For example, sites 1, 2 and 5 (Figure 6) represent the baseline water quality one can expect in BR-

dominated watersheds, in the absence of both fire and forest harvesting. Both harvesting and fire

were virtually absent in these sub-watersheds, and the sub-watersheds are dominated (>97%) by B

soils. Also, alkalinity, TP, TDP and DOC concentrations and turbidity were the lowest of all sites.

It is interesting to note that site 5, located downstream of the Black Lake campground, suggests that

the campground has no detectable impact on water quality of the Black River as it leaves the lake.

A

River, particularly sites 3 and 7 (Figure 6). Approximately 99% and 70% of the watershed area

sites 3 and 7, respectively, burned in the last 60 years. The lower DOC concentrations in the stream

water likely reflect the fact that color-producing compounds in the soils (which are limited even in

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the absence of fire due to the shallow, nutrient-poor nature of such soils) were destroyed during the

fire and thus, color export from the watersheds to the streams has decreased as a result. This idea

however is in contrast to what Kotak et al. (2005) has reported in a larger, regional stream water

quality study. In that study, fire caused a significant increase in several stream water quality

parameters, including DOC and forms of nitrogen and phosphorus. This apparent contradictio

be explained by the differences in soil types between sites 3 and 7, and the stream watersheds

studied in Kotak et al. (2005). The sub-watersheds of sites 3 and 7 were exclusively made up o

soils. Any movement of water from the watershed after the fires would result in a relatively short-

lived, and small increase in nutrients. These concentrations would quickly fall back to pre-

disturbance levels as BR-dominated soils contribute little nutrients. In contrast to phosphor

export of DOC after fire would likely decline immediately, as the organic color-producing

compounds are destroyed by the fire. In the watersheds studied by Kotak et al. (2005), thermuch higher percentage of soils in the DB and OD (organic) categories. In particular, OD soils

(which include peatlands) can contribute significant amounts of nutrients and color to receiving

water bodies (rivers, streams, creeks). Fires that occur in the upland areas of OD-dominated

watersheds, would produce runoff that would percolate through the peatlands, and result in ru

water bodies that contain high nitrogen, phosphorus and color. This would also elevate stream

concentrations of these substances for a much longer period of time. Based on this reasoning, it

not surprising that watersheds made up of exclusively of BR soils, even after significant fire events,

contribute little ions to receiving water bodies.

n can

f BR

us,

e were a

noff to

is

hanges in water quality along the length of the Manigotagan River were less dramatic than that

ith

f the

s

rshed.

C

observed in the other two rivers. While alkalinity, phosphorus, DOC and turbidity did increase w

increasing distance downstream from the headwaters of the river in Ontario (Figure 7), the

magnitude of the increase was much less than that observed in the OHanly and Black rivers

(Figures 5 and 6). Because soils, harvest and fire history information for the Ontario portion o

Manigotagan River watershed were not available, it is difficult to relate changes in water quality

along the length of the river to soils or disturbance history for almost all of sampling sites. Only

one sub-watershed (site 7, the Ross River watershed) was entirely contained in Manitoba, and thu

had soil, fire and harvest history data. This site has much lower alkalinity, higher TDP

concentration and higher color (DOC) than any other site in the Manigotagan River wate

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Manigotagan River - p H and Alkalinity

0

5

10

15

20

25

30

35

M1

M2

M3

M4

M5

M6

M7

M8

M9

M10

Site

Alkalinity(m

g/LCaCO3),

pH

ater quality parameters include

he reason for this is unclear. Approximately 30% of the watershed has burned in the last 60 years,

n

d

nt beaver

Figure 7. Changes in water quality along the Manigotagan River. WpH and alkalinity, total and total dissolved phosphorus, dissolved organic carbon (DOC) and

turbidity.

Tbut the contribution of phosphorus and DOC after such an event would be expected to be minimal

due to the high percentage (91%) of BR soil in the watershed. In addition, the fires occurred only i

the headwaters of the watershed. An alternate explanation, which may be more plausible, is that the

elevated TDP and DOC concentrations are due to extensive back-flooding of riparian areas along

the Ross River and its un-named tributaries as a result of beaver dam-building activity. This sub-

watershed contains a significant number of beaver dams. The lower pH of water from site 7 woul

also be consistent with the impacts of back-flooding, as increased decomposition of flooded riparian

vegetation and soils would lead to a lower water pH. Increased DOC and phosphorus

concentrations and lower pH were noted by Kotak et al. (2005) in creeks with significa

activity. Beaver activity was not observed anywhere else along the main part of the Manigotagan

River during the aerial survey.

pH

Alkalinity

Manigotagan River - Phosphorus

0

10

20

30

40

50

M1 M2 M3 M4 M5 M6 M7 M8 M9 M10

Site

Phosphorus(ug/L)

TP

TDP

Manigotagan River - DOC

0

10

20

30

40

M1 M2 M3 M4 M5 M6 M7 M8 M9 M10

Site

DOC

(mg/L)

Manigotagan River - Turb idity

0

1

2

3

4

5

6

7

8

M1 M2 M3 M4 M5 M6 M7 M8 M9 M10

Site

T

urbidity(NTU)

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The above section provides a descriptive summary of the possible effects of soil type, fire and

ers.

.2 Comparisons of the Effects of Soil and Disturbance on Water Quality

harvesting on the spatial variability in water quality of the OHanly, Black and Manigotagan riv

The following sections provide a more statistical approach to analyzing the data.

5

s mentioned in the methods section, sub-watersheds were grouped into one of five major

-

oils

A

categories based on soil type and disturbance (Table 1). These categories included Bedrock

dominated soils without fire or harvesting in the last 60 years (Br-Ref), Bedrock-dominated s

with fire (Br-Fire), Bedrock-dominated soils with harvesting (Br-Harvest), Deep Basin-dominated

soils without fire or harvesting in the last 60 years (DB-Ref) and Deep Basin-dominated soils with

fire and harvesting (DB-Both). Unfortunately, due to the nature of the sub-watersheds of the threerivers, not all soil and disturbance combinations were present.

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0

10

20

30

40

BR, reference BR, fire BR, harvest DB, reference DB, fire +harvest

Soil and Dist ur bance Type

Alkalinity(mg

/LasCaCO3)

0

2

4

6

8

10



Ca(mg/L)

Figure 8. Effects of soil and disturbance type on alkalinity (top) and Ca concentration (bottom) in

study streams located in sub-watersheds of the OHanly, Black and Manigotagan rivers.

While all sub-watersheds in the Black and OHanly river drainages could be used for this analysis,

only sub-watershed 7 in the Manigotagan River drainage could be used, as this was the one sub-

watershed which was completely encompassed in Manitoba, and for which GIS information on

soils, fire and harvesting history was available.

Soil type appeared to have a significant effect on the alkalinity of the rivers and their tributaries.

For example, in the absence of fire or harvesting (i.e., reference watersheds), water in sub-

watersheds that were dominated by DB soils had alkalinities that were 2.5 times higher on average

than in sub-watersheds that were dominated by BR soils (Figure 8, top). This is not surprising, as

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alkalinity (a measure of the ability to buffer acid) is generated by from the weathering and erosion

of rock. Soils developed over bedrock (BR) are typically thin, not well developed and lack a

significant clay component. In contrast DB soils are well developed and can contain a significant

proportion of clay. The alkalinity results are also supported by the trends seen in Ca concentration

in the water as well (Figure 8, bottom). Therefore, soil type can exert considerable influence on

water quality in the absence of disturbance.

Figure 8 also demonstrates the relative impacts of fire and harvest on water quality in watersheds

with the two main soil types. Fire appeared to have a much less impact on alkalinity and Ca than

did harvesting. In fact, alkalinity and Ca in BR-dominated sub-watersheds experiencing significant

fire (on average 54% of the watershed area was burned) was not very different than reference sub-

watersheds. In contrast, alkalinity and Ca in BR-dominated sub-watersheds where harvesting(average of 39% of the watershed area) occurred were approximately 2 times higher than in

reference sub-watersheds. While it is not possible to examine the impacts of fire and harvesting

separately in the DB-dominated sub-watersheds, both disturbances (30% fire, 45% harvest, 75%

total disturbance) resulted in an increase in alkalinity and Ca over reference conditions for that soil

type. These results are consistent with those obtained from a larger, regional water quality survey

of rivers, streams and creeks in eastern Manitoba, conducted in 2004 (Kotak et al. 2005).

Phosphorus, a key plant nutrient in aquatic ecosystems, also was influenced by soil type and

disturbance (Figure 9). However, in contrast to alkalinity and Ca, TP in the BR-dominated

reference sub-watersheds was only marginally lower than in the DB-dominated reference sub-

watersheds. Based on soil type and the results of Kotak et al. (2005), one would expect higher TP

concentrations in DB-dominated sub-watersheds. There was a considerable amount of variability in

TP concentration in the BR-dominated sub-watersheds (Figure 9). All of these sub-watersheds are

small, headwater drainages and are influenced by beaver activity, particularly by the resulting back-

flooding of riparian areas. The high variability in TP, and the higher TP concentrations than

expected likely reflect the influence of beaver activity.

Another interesting feature of the data is that TP in burned BR-dominated sub-watersheds was

lower than in reference watersheds (Figure 9). Kotak et al. (2005) found that fire increased TP

concentration. The lower TP concentrations in the present study may be due to the fact that all sub-

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watersheds had almost no OD (deep organic) soils, whereas the watersheds used by Kotak et al.

(2005) had higher proportions of OD soils. Without OD soils, a fire would likely result in a rapid

loss of phosphorus from the soils (and thus, a rapid increase in water TP concentrations). However,

the effects would be short-lived. OD soils tend to prolong the effects of the disturbance by acting as

a long-term reservoir for water and nutrients, which eventually are released to the rivers and

streams. The low TP concentrations in the BR-Fire watersheds therefore reflect the loss of TP

shortly after the fire events, phosphorus which has not accumulated appreciably in the soils since

the fires.

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0

20

40

60

80

100

120


Soil and Distur bance Type

TP

(ug/L)

0

20

40

60

80



NO3(ug/L)

0

20

40

60

80



DOC(

mg/L)

Figure 8. Effects of soil and disturbance type on TP (top), NO3(middle) and DOC concentration(bottom) in study streams located in sub-watersheds of the OHanly, Black and Manigotagan rivers.

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While it appears that harvesting in BR-dominated sub-watersheds had a significant impact on TP

(Figure 9), this must be interpreted with caution. All of the sites in this category (BR-Harvest) were

located at the downstream end of the Black and OHanly rivers, and as mentioned previously, had

significant stream bank erosion caused by beaver activity. While the amount of harvesting (39% of

the area on average) that did occur historically in these sub-watersheds would be expected to have a

minor effect on TP (Kotak et al., 2005), beaver activity likely played a much more prominent role.

As was mentioned previously, the impact of beaver on turbidity levels in these particular sub-

watersheds was very evident, even visually from the air. Kotak et al. (2005) found that forest

harvesting had no impact on stream turbidity. This may indicate that the higher TP, turbidity and

elevated levels of other parameters observed in the BR-Harvest category, are likely driven more by

beaver activity than harvesting history. Other parameters such as NO3and DOC follow an almost

identical trend to that of TP (Figure 9), reflecting the effects of soil type, harvesting history andespecially beaver activity, consistent with the results of Kotak et al. (2005).

5.3 Effects of Watershed Disturbance Level on Water Quality

An important aspect of the effects of disturbance on water quality is the relationship (if any)

between the proportion of the watershed area disturbed and various water quality parameters. One

would expect higher watershed disturbance rates to relate to more significant changes in water

quality relative to undisturbed (reference) conditions. This was indeed observed when the effects of

the proportion of watershed disturbed on water quality were examined for both harvesting and fire.

However, the relationships, particularly with respect to forest harvesting, must be interpreted with

caution as beaver activity in these sub-watersheds appears to have been an over-riding influence,

particularly at low watershed harvesting levels. Surprisingly, the relationships between disturbance

rates and water quality were opposite for harvesting and fire. Table 3 summarizes the correlations

between the % of watershed area disturbed and various water quality parameters.

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Table 3. Correlation coefficients between the % of watershed area disturbed (harvesting, fire) and

various water quality parameters.

Water Quality

Parameter

Harvested

Watersheds

Burned

Watersheds

Ca 0.86 -0.49

SO4 0.41 -0.55TP 0.88 -0.50

TDP 0.75 -0.51

NO3 0.84 -0.39

NH4 0.90 -0.45

DOC 0.90 -0.62

Conductivity 0.87 -0.46

Turbidity 0.95 -0.40

These trends will be explained in more detail.

5.3.1 Effects of Proportion of Watershed Harvested on Water Quality

At first glance, there appears to be a strong relationship between the proportion of watershed area

harvested and Ca concentration in the rivers and streams (Figure 9). While there is an increase in

Ca with only a small amount of watershed harvesting (


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It should be noted however, that the higher Ca concentrations at harvest levels above 30% are also

influenced by the greater proportion of DB soils (which naturally export more Ca to water) and

much higher bank erosion caused by beaver activity. The sub-watersheds with harvesting below

15% are all dominated (>99%) by BR soils but did have beaver activity in their drainages, and thus

reflect more the impacts of beaver than the impacts of harvesting on Ca. However, the effects of

harvesting and beaver activity on Ca is very small (1-2 mg/L). Indeed, the increase from 3-4 mg/L

in reference areas to 7 mg/L in the whole OHanly River watershed (represented by a harvest level

of 50%) is not biologically significant. While Ca more than doubles, this would not have any

discernable impact on water quality.

A similar relationship existed between % watershed harvest and TP concentration (Figure 10, top).

Watershed harvest rates between 3 and 13% were related to an approximate tripling of TP overreference conditions. Such dramatic effects on TP at very low watershed harvesting levels are not

consistent with the study of Kotak et al. (2005). Kotak et al. (2005) found no effects of harvesting

on stream water phosphorus below a harvesting level of approximately 30%. The high TP

concentrations at harvesting levels of 3 13% in Figure 10 likely reflect the impacts of back-

flooding of riparian areas by beaver activity than any sort of impact by such a low level of forest

harvesting. The higher TP concentrations above watershed harvesting levels of 35% (Figure 10)

likely represents a combination of the effects of harvesting, and especially beaver activity. The

three highest watershed harvesting rates in Figure 10 represent sampling locations 5, 6 and 7 on the

OHanly River, were beaver impacts were significant. An almost identical trend was observed for

DOC (Figure 10, bottom). In summary, there was a relationship between the proportion of sub-

watershed harvested and the concentrations of various water quality parameters, however, beaver

activity appeared to have more influence on water quality, particularly at low watershed harvest

levels.

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0

20

40

60

80

100

120

140

0 10 20 30 40 50 6

% of Watershed Are a Harvested

TP

(ug/L)

0

20

30

40

50

60

70

0 10 20 30 40 50 6

% of Watershed Area Harvested

DOC

(mg/L)

0

Figure 10. Relationship between proportion of watershed harvested and TP (top), and DOC(bottom) concentration.

5.3.2 Effects of Proportion of Watershed Burned on Water Quality

The relationships between the proportion of watershed burned and the various water quality

parameters were strikingly different that that observed for forest harvesting. Table 3 indicates that

the relationships were negative. That is, as the proportion of watershed area burned increased,

concentrations of dissolved ions decreased. Figure 11 shows this graphically for TP and DOC.

Other parameters followed a similar trend.

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10

20

30

40

50

60

70

80

0 20 40 60 80 100 12

% of Watershed Area Burned

TP(ug/L)

0

5

15

25

35

45

0 20 40 60 80 100 12

% of Watershed Area Burned

DOC

(mg/L)

0

Figure 11. Relationship between proportion of watershed burned and TP (top) and DOC (bottom)

concentration.

For both TP and DOC, as well as many other water quality parameters not shown, the rivers and

tributaries in sub-watersheds that represent reference conditions (no fire), had the highest

concentrations of TP and DOC (Figure 11). As the proportion of watershed that was burned

increased, concentrations of TP and DOC decreased. This is in sharp contrast to the trend observed

for harvesting (acknowledging the other impacts by beaver) and also in contrast to the results of

Kotak et al. (2005), who found no relationship between the proportion of watershed fire and

phosphorus (TP, TDP) and DOC.

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These apparent contradictions provide valuable insight into the dynamics of the effects of fire on

water quality and how soil type may alter the direction of the effects. The above rivers and streams

represented in Figure 11 are located in sub-watersheds comprised almost exclusively of BR soils.

When burned, these soils will readily export (release) phosphorus to receiving waters (rivers,

streams) rapidly after the disturbance. Concentrations will then likely decrease substantially and

take many decades to return to pre-disturbance levels. Because soil formation is such a slow

process, it may take many decades for enough soil to develop in order to contribute significant TP

to the water again, or to reach reference conditions. Because water color (DOC) is comprised of

organic material, fire will have the effect of destroying colored soil compounds immediately. Thus,

DOC concentrations in receiving waters will decrease dramatically in BR-dominated watersheds,

and not reach pre-disturbance levels until sufficient soil formation has occurred. All the above sub-

watersheds in Figure 11 burned in 1983, 22 years ago and thus have not had enough time yet tobuild up phosphorus and DOC in the soils (and thus a return to pre-disturbance levels of TP and

DOC in the streams) .

In the watersheds studied by Kotak et al. (2005), fire did not have this declining effect on TP and

DOC. This may be due to the fact that their watersheds contained OD soils, which tend to store and

be a source of TP and DOC to receiving waters. A conceptual model to explain the effects of fire in

watersheds comprised of BR and OD soils might be the following. After fire, DOC contributions

from BR soils would decrease immediately as DOC-containing compounds are destroyed by the

fire. TP export from the watershed may increase for a short period of time initially after the fire as

mineralized phosphorus is mobilized from the soil. The increased movement of water from these

topographically high areas to the lower lying OD soils (due to the lack of living trees and therefore,

reduced evapotranspiration), would facilitate either a flush or perhaps steady release of phosphorus

and DOC from the OD areas to the streams over time. Thus, the effects of fire in BR-dominated

areas on water quality should be expected to be different than that observed in OD-dominated areas.

This model would also explain why Kotak et al. (2005) and aspects of this study found that

harvesting had an opposite effect on water quality than did fire. Harvesting does not destroy

organic compounds that impart color (DOC) to water. In addition, mineralization of phosphorus

and subsequent movement phosphorus from the land to streams occurs much more slowly in

harvested areas than after fire. Soils remain relatively intact following harvesting, whereas fire may

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mineralize nutrients (phosphorus) immediately, making them more susceptible to leaching to water

bodies in the short term. Also, the retention of logging slash (tops of trees, branches, etc.) on

cutovers provide a long-term (at least longer term than fire) source of TP and DOC export to

streams due to decomposition of the slash, a commonly-noted phenomena observed after forest

harvesting. For this reason, harvesting may tend to provide a long-term input of nutrients and other

substances into streams, while fire may act quite the opposite by providing an initial pulse followed

by a long-term decline in certain water quality parameters (e.g., TP, Ca, etc.) or a immediate

reduction (e.g., DOC), that do not return to pre-disturbance levels until soil formation is sufficiently

advanced.

6.0 Literature Cited

Hetherington, E.D. 1987. The importance of forests in the hydrological regime. IN Canadian

Aquatic Resources (M.C. Healy and R.R. Wallace, eds.). Rawson Academy of Science. Canadian

Bulletin of Fisheries and Aquatic Sciences. 34 pp.

Kotak, B.G., A. Selinger and B. Johnston. 2005. Influence of watershed features and disturbance

history on water quality in Boreal Shield streams and rivers of eastern Manitoba. Manitoba Model

Forest Report 04 2 63. 161 pp.

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Spatial Variation in Water Quality in Rivers of the Boreal

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