The effects of cattle exclusion on stream structure and function

April H. Hughes

Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of

Master of Science In

Biological Sciences

E.F. Benfield, chair J.R. Webster W.M. Aust

July 8, 2008 Blacksburg, Virginia

Keywords: Cattle, stream, riparian vegetation, leaf breakdown, shredding

macroinvertebrates, fungal biomass, microbial respiration, sediment, nutrients

The resilience of stream ecosystem function as indicated by leaf processing following

cattle exclusion

April H. Hughes

ABSTRACT

Stream ecosystems can be influenced by cattle grazing in the riparian zone due to

sediment input, nutrient loading, and soil compaction, which lead to alterations of

macroinvertebrate and microbial activity. Recently government programs, such as the

Conservation Reserve Enhancement Program (CREP), have provided funding for farmers

to exclude cattle from streams and riparian zones. Funding for CREP is limited and does

not allow for post exclusion assessment. The objectives for this study were; 1) to explore

whether CREP and other cattle exclusion initiatives help restore functional integrity to

streams; 2) and if they do, to evaluate the time required for integrity to be restored. I

predicted leaf processing (a fundamental ecosystem level function) in streams would be

influenced by excluding cattle from the riparian zone due to changes in nutrient

availability, sediment abundance, shredding macroinvertebrates, and microbial activity. I

tested this prediction by measuring leaf processing at sites that had cattle excluded for <1

to 15 years. Breakdown rates did not correspond linearly to time since cattle exclusion.

This was probably due to the opposing effects of elevated sediment versus nutrients on

leaf breakdown at recently grazed sites. Leaf breakdown and shredder density were

strongly correlated with riparian vegetation density. This study suggests that in addition

to cattle exclusion, reforestation of woody riparian vegetation may be essential to restore

functional integrity to agricultural streams.

iii

Table of Contents

Contents:

Introduction……………………………………………………………………... 1

Methods………………………………………………………………………….

6

Results…………………………………………………………………………... 16

Discussion………………………………………………………………………. 43

Conclusions……………………………………………………………………... 49

References………………………………………………………………………. 50

Appendices……………………………………………………………………… 57

iv

List of Tables

Table 1. GPS coordinates for each site…………………………………………. 8

Table 2: Total watershed area and percentage area of total watershed cleared for development, agriculture, and other anthropogenic uses……………………

8

Table 3: Physical characteristics of study sites…………………………………. 10

Table 4: Summary of breakdown coefficients (k) and correlation coefficients (r2) of box elder leaves…………………………………………………………..

17

Table 5: Summary of breakdown coefficients (k) and correlation coefficients (r2) of sycamore leaves…………………………………………………………..

18

Table 6: pH and alkalinity at each site on day 32 of leaf breakdown study……. 28

Table 7: Physical characteristics of each site as predicted by the WEPP model.. 31

Table 8: Loading values for principle component one for PCA analysis of water chemistry………………………………………………………………….

41

v

List of Figures

Figure 1: Common effects of cattle exclusion on leaf breakdown in stream ecosystems……………………………………………………………………..

4

Figure 2: Study sites were headwater streams located in Floyd County, VA, USA……………………………………………………………………………

7

Figure 3: Bedrock geology in Floyd County, Virginia (VDMR, 1993). Study sites are indicated by red dots…………………………………………………

9

Figure 4: Boxelder (dots) and sycamore (solid) breakdown rates at each site...

17

Figure 5: Boxelder %AFDM remaining over the course of the study at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●). Error bars represent the means (+/- 1 SE) of three replicate samples…………………….

18

Figure 6: Sycamore %AFDM remaining over time at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●). Error bars represent the means (+/- 1 SE) of three replicate samples…………………………………...

19

Figure 7: Sycamore breakdown rate at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) was related to riparian woody vegetation density (r2=0.81, p= 0.01)……………………………………………………………...

21

Figure 8: Boxelder breakdown rate at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) was not significantly related to riparian woody vegetation density (r2= 0.34, p=0.23)………………………………………….

21

Figure 9: Wetted width to depth ratio was significantly related to riparian woody vegetation density at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) (r2=0.87, p=0.006)…………………………………

22

Figure 10: Wetted width to depth ratio was significantly related to stand basal area at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) (r2=0.94, p=0.001)…………………………………………………………

22

vi

Figure 11: Breakdown rate of sycamore leaves was weakly related to wetted width: depth of stream (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) (r2=0.63, p=0.06)………………………………………………...

23

Figure 12: Riparian woody vegetation density at each study site……………..

23

Figure 13: Stand basal area at each study site…………………………………

24

Figure 14: Mean nitrate-N concentrations at each site over the duration of the study. Nitrate concentrations were significantly different among sites (p< 0.05). Different letters represent statistically significant differences among site means. Error bars represent the 95% confidence interval for the mean…..

27

Figure 15: Mean ammonium concentrations at each site over the duration of the study. Nitrate-N concentrations were significantly different among sites (p< 0.05). Different letters represent statistically significant differences among site means. Error bars represent the 95 % confidence interval for the mean…………………………………………………………………………...

27

Figure 16: Mean phosphate concentrations at each site over the duration of the study. Phosphate concentrations were significantly different among sites (p< 0.05). Different letters represent statistically significant differences among site means. Error bars represent 95 % confidence interval for the means…………………………………………………………………………...

28

Figure 17: Temperature at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) over the duration of the study……………………….

29

Figure 18: Mean (± SE) monthly fine sediment accumulation on Boxelder (dots) and sycamore (solid) leaf packs…………………………………………

29

Figure 19: Mean (± SE) monthly coarse sediment accumulation on Boxelder (dots) and sycamore (solid) leaf packs…………………………………………

30

Figure 20: Mean annual sediment yield at each site as predicted by the water erosion prediction project (WEPP) model……………………………………

30

Figure 21: Shredder density on sycamore leaves at each site (5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●) throughout sampling season…………….

33

vii

Figure 22: Shredder density on boxelder leaves at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) throughout sampling season…………...

34

Figure 23: Shredder density on sycamore leaves was significantly related to wetted stream width to depth ratio (r2=0.81, p=0.014). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●…………………………………………

35

Figure 24. Shdr richness on sycamore leaves at each site (5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●) throughout sampling season was related to total sediment accumulation (r2=0.81, p=0.015)…………………………….

36

Figure 25: Fungal biomass on boxelder leaves throughout the duration of the study (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●)………………..

38

Figure 26: Fungal biomass of sycamore leaves throughout the duration of the study. (5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●)………………..

38

Figure 27: Sycamore fungal biomass is negatively related to stream ammonium concentration (r2= 0.17, p= 0.021). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●…………………………………………………….

39

Figure 28: Microbial respiration was inversely related to water chemistry (r2=0.65, p= 0.05). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●. Chemistry values are alkalinity, pH, phosphate, nitrate-N, and ammonium as indicated by principle component 1 in PCA…………………………………...

41

Figure 29: Microbial ition on sycamore leaves was positively related to coarse sediment accumulation (r2= 0.29, p=0.004). 5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●………………………………………………………...

42

Figure 30: Microbial respiration on boxelder leaves was significantly related coarse sediment accumulation (r2=0.19, p=0.049). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●…………………………………………..

42

viii

Acknowledgements

I would like to thank Dr. E.F. Benfield for his guidance throughout my career as a

graduate student. He gave me the perfect balance of freedom and guidance to allow me

to learn to develop ideas, manage time, and explore the field yet keeping me focused on

the task at hand. In addition I would like to thank Dr. Jackson Webster for his guidance

throughout this project and Dr. W. Michael Aust for his advice and for helping with the

topographical analysis. Funding for this project was provided by grants from the

National Science Foundation (DEB-0218001 and DEB-9236854) and the Virginia Tech

Graduate Research and Development Program.

I would also like to thank Bobbie Niederlehner for all of her technical support and

Eric Sokole for statistical guidance. Many thanks to all of the undergraduates, especially

Zach Minter and Laurel Ackison, who helped out with this project. I would like to thank

the landowners who so graciously allowed me to conduct this research on their

properties. This research could not have been done without your willingness to allow me

to use your land. Finally, I would like to thank all of my family for their encouragement

and support throughout my academic career. Special thanks to my husband, Caleb

Hughes; my grandmother, Nancy Harrison; and my parents, Paul and Tambra Eilers.

1

Introduction Livestock production is a substantial source of income to residents of the southern

Appalachian region of Virginia. Cattle in the Blue Ridge Mountains are often raised in

pastures drained by first and second order streams (Braccia and Voshell, 2006). In their

search for shade, water, and forage, livestock trample and overgraze the streambank

vegetation and diminish streambank stability and water quality (Belsky et al., 1999).

Approximately 80 % of stream and riparian ecosystems in the western United

States have been damaged by livestock grazing (Belsky et al., 1999). Annual levels of

stream bank erosion have been observed to be significantly more severe in areas where

livestock are present than in ungrazed regions (Kauffman et al., 1983). Sediment loading

from eroded stream banks is a significant source of stress to stream macroinvertebrates

(Braccia and Voshell, 2006). Nutrients from cattle urine and feces are readily

transported from riparian zones to open channels and can cause local stimulation of

primary productivity in streams (Valett et al., 1994).

Overgrazing and trampling by cattle and the subsequent reduction of riparian

vegetation can have serious implications for stream channels. Impacts include increased

water temperature and light availability, which can lead to excessive algal production and

toxic conditions (Swanson et al., 1982).

The Importance of riparian vegetation Riparian zones are the regions of land along both stream banks that act as an

ecotone between streams and their watersheds (Minshall, 1988). Riparian zones have

great influence on the microclimate, physical structure, and food resources of streams

(Gregory et al., 1991). Autumnal leaf-fall is the primary source of energy to forested

headwater streams where photosynthesis is limited by low light (Vannote et al., 1980).

According to Leopold et al. (1964) headwater streams comprise approximately 85 % of

the total stream length in the U.S.. These streams interact with the surrounding

environment by transporting outputs from the surrounding landscape to larger water

bodies downstream (Likens, 1985).

2

A common management practice used to protect streams is to maintain riparian

buffer zones. These zones are defined regions where certain land use activities such as

agricultural practices are prohibited (Naiman and Decamps, 1997).

Line et al. (2000) demonstrated that the exclusion of livestock and the

establishment of riparian buffer strips are efficient at reducing weekly stream nitrogen,

phosphorous, and sediment loads. Watersheds differ in that they have varying channel

morphology, soils, climate, riparian species, geology, and hydrology (Elmore and

Beschta, 1987; Myers and Swanson,1991; Trimble and Mendel, 1995). Therefore,

ecosystem responses vary drastically among streams and thus streams should be treated

individually in terms of management options (Kauffman et al., 1983). Much of the

research on riparian grazing in the United States has been conducted in the arid West.

There is a paucity of research on the topic in more humid climates such as the eastern

United States. Grazing may be especially damaging in humid environments due to moist

soils being more easily compacted and disturbed than dry soils (Trimble and Mendel,

1995).

Cattle exclusion programs: The conservation reserve enhancement program (CREP) is a relatively new

program developed by the United States Department of Agriculture-Natural Resources

Conservation Service (USDA-NRCS). The goal of CREP is to encourage farmers,

through monetary incentives, to sign contracts agreeing to halt agricultural production on

environmentally sensitive land. This is achieved by constructing fences to keep cattle out

of riparian zones and wetted stream channels and by providing off stream watering

sources (VDCR, 2006).

Complete recovery of streams after being fenced may take hundreds to thousands

of years (Fleischner, 1994). Certain aspects of ecosystems such as the return of woody

and herbaceous vegetation in riparian zones may begin immediately. However, other

aspects such as geomorphic changes to stream channels may lag behind vegetative

recovery due to the time required to deposit sediment back along the banks (Kondolf,

1993). Harding et al. (1998) found that agriculture may result in long term changes to

and reductions in aquatic biodiversity even after reforestation of riparian zones. To this

3

point there has not been sufficient funding to enable CREP authorities to conduct post

exclusion studies in order to analyze the success of the program.

Leaf breakdown:

Leaf breakdown studies are a valuable tool for stream ecologists. They are used

to study mechanisms involved in organic matter processing and they provide a means by

which to compare stream responses to altered environmental conditions (Webster et al.,

2001). Many factors affect breakdown rates of leaves (Fig. 1). Physical properties of

streams can directly affect leaf breakdown through physical abrasion or characteristics

such as high levels of suspended sediment may indirectly affect leaf breakdown by

influencing macroinvertebrate or microbial colonization of leaves (Allan, 2007). When

leaves fall into stream channels, breakdown begins with leaching of soluble materials.

Leaves are quickly colonized by fungi and bacteria, which both directly and indirectly

affect leaf breakdown by improving the nutritional value of leaves for consumers (Tank

et al., 1993; Gessner and Chauvet, 1994; Allan, 2007). Shredding macroinvertebrates are

also important in leaf breakdown by feeding on decaying leaf matter, assimilating some

as biomass and breaking some down into fine particulate organic matter (FPOM), which

becomes an energy source for other biota (Hieber and Gessner, 2002).

Brooks et al. (2002) suggested that measures of ecosystem function are more

appropriate than measures of structure for evaluating stream recovery following

restoration. Many studies have attempted to evaluate stream recovery from

anthropogenic stressors by measuring only structural attributes and failing to recognize

the importance of functional attributes (Gessner and Chauvet, 2002). Though leaf

breakdown can serve as a functional measure of ecosystem condition in streams, caution

must be exercised in studies of agricultural streams when confounding factors may

influence outcomes (Niyogi et al., 2003; Hagan et al., 2006).

4

Figure 1: Common effects of cattle exclusion on leaf breakdown in stream ecosystems.

Cattle Exclusion

Sediment Nutrients

Shredding Macroinvertebrates

Stream Temperature

Leaf Breakdown

Riparian Vegetation

Light

Bacteria

Fungi

5

For example, in New Zealand agricultural streams Niyogi et al. (2003) found that the

positive effects of nutrients on litter breakdown outweighed the negative effects of

sedimentation. In contrast, Lee and Bukaveckas (2002) found that breakdown rates of

leaf litter were not affected by surface water nitrogen concentration. However, sediment

and water column phosphorous and C:N ratios were major predictors of breakdown rates.

There is a gap in the literature regarding the effects of cattle exclusion on the

functional recovery of streams. The objectives of this study were; 1) to explore whether

CREP and other cattle exclusion initiatives help restore functional integrity to streams; 2)

and if they do, to evaluate the time required for integrity to be restored. I predicted leaf

breakdown (a fundamental ecosystem level function) in streams would be influenced by

cattle exclusion from the riparian zone because of changes in nutrient availability,

sediment abundance, and leaf shredding macroinvertebrates, and microbial activity (Fig.

1).

6

Methods Site Description:

Study streams were located in Floyd County, VA, in the southern Appalachian Mountains

(Fig. 2, Table 1, Appendix A). Sites were chosen based on a gradient of time since cattle

exclusion from the reach. Sites were characterized as currently grazed, rotationally

grazed, <1 year since cattle exclusion, 5 years since cattle exclusion, 15 years since cattle

exclusion, and forested. The forested site was chosen to represent long term absence of

cattle. All sites were headwater streams with bedrock geology consisting of biotite gneiss

(Fig. 3). Watershed area of sites ranged from 6.27 ha at the <1 year exclusion site to

117.60 ha at the long term meadow site (Table 2). Average gradient in the watersheds

ranged from 16 to 20 % and all stream sites were sinuous (Table 3, Equation 1: SI =

stream length/direct straight length). Mean watershed slope was calculated by averaging

the hillslopes to the right and left of the bottom of each reach (Equation 2: Watershed

slope = elevation of hillslope/horizontal distance from point at the bottom of the reach to

top of hillslope). Average annual precipitation in the watersheds was 107.7 cm (WEPP,

2006).

The currently grazed site had areas of intact riparian vegetation as well as areas of

pasture land. Tree and shrub species of greatest importance were northern spice bush

(Lindera benzoin), sycamore (Platanus occidentalis), and flowering dogwood (Cornus

florida). The cattle had open access to the stream channel at all times throughout the

year. The banks were severely degraded in places.

7

Figure 2: Study sites were headwater streams located in Floyd County, VA, USA.

Long Term Meadow

<1yr Exclusion

Currently Grazed Rotationally Grazed

Forested

5yr Exclusion

8

Table 1. GPS coordinates for each site.

Site Longitude Latitude Elevation (m) Notes

Long Term Meadow -80.4047 36.9175 764.7 Off Huckleberry Rd. 5 year Exclusion -80.3856 36.8454 831.8 Off Black Ridge Rd.

Forested -80.3539 36.8103 1102.5 Off B.R.P. near Rocky Knob

Rotationally Grazed

-80.3552 36.8186 880.9

Off Patrick Rd. which is on Fairview Church Rd.

Currently Grazed -80.3345 36.8696 767.2 Off Rt. 8

<1 year Exclusion -80.3133 36.9900 737.0 Off Huckleberry Ridge Rd.

Table 2: Total watershed area and percentage area of total watershed cleared for development, agriculture, and other anthropogenic uses.

Site

Total Area in

Watershed

(ha)

Cleared Area

in Watershed

(%)

<1 year Exclusion 6.27 71.03

Long Term Meadow 117.60 5.37

5 year Exclusion 23.27 46.26

Currently Grazed 129.34 56.32

Forested 39.75 4.68

Rotationally Grazed 60.01 7.42

9

Figure 3: Bedrock geology in Floyd County, Virginia (VDMR, 1993). Study sites are indicated by red dots.

10

Table 3: Physical characteristics of study sites.

Site

Stream

Order

Stream

Type

Sinuosity

Index

(SI)

Stream

Slope

(%)

Average

Watershed

Slope

(%)

<1 year Exclusion 1 Perennial 1.14 12.5 18.5 Long Term Meadow 1 Perennial 1.11 5.1 20.0 5 year Exclusion 1 Perennial 1.20 6.6 18.3 Currently Grazed 2 Perennial 1.49 3.6 16.0 Forested 1 Perennial 1.15 6.0 16.0 Rotationally Grazed 1 Perennial 1.09 5.4 16.0

11

The rotationally grazed site ran through an open pasture with no woody riparian

vegetation. Cattle had access to the stream for six months of each year from

approximately June to December. Banks were severely degraded.

The <1 year and 5 year cattle exclusion sites had been fenced in accordance with

the CREP program (USDA-NRCS, 2005). They had intact riparian vegetation including

saplings planted in accordance with the program and mature trees. Riparian trees and

shrubs of greatest importance were alder (Alnus serrulata), red maple (Acer rubrum), and

white pine (Pinus strobus) at the <1 year exclusion site and white pine (Pinus strobus),

red maple (Acer rubrum), and winterberry (Ilex verticillata) at the 5 year exclusion site.

The long term meadow site had cattle excluded for 15 years and ran through a

currently farmed hay field with no significant woody vegetation.

The forested site was on the Blue Ridge Parkway property and was relatively

undisturbed. The riparian woody vegetation species of greatest importance consisted of

rhododendron (Rhododendron maximum), tulip poplar (Liriodendron tulipifera), and

yellow birch (Betula alleghaniensis).

Leaf litter breakdown: The leaf pack method was used to measure litter breakdown in streams (Benfield,

2006). Packs of recently senesced sycamore leaves (5 g dry wt) or recently senesced

boxelder leaves (7 g dry wt) were placed in mesh bags (7x7 mm mesh size). Boxelder

leaves were used to represent a common native “fast” riparian species whereas sycamore

leaves were used to represent common native “slow” riparian species (Peterson and

Cummins, 1974). Leaf packs tied to nylon strings were placed randomly in the stream

channels. Three packs of each species were returned to the laboratory from each stream

once per month, from December 2006 through June 2007, for determination of mass loss

versus time. Exponential breakdown rates were calculated by regressing loge % AFDM

remaining against incubation time (Webster and Benfield, 1986).

12

Microbial Respiration:

Prior to the first retrieval date, water was collected from each stream and filtered

in the lab through 125 mm glass fiber filters (GFF). The filtered water was stored at

approximately 7 ºC. Disks (1.5 cm dia.) were cut from leaves with a cork borer and

placed with filtered stream water in 40 ml vials that were capped with gas tight septum

sealed caps. 5 replicates were used for each leaf type from each site and 5 replicates for

abiotic controls as filtered stream water from each site. Vials were incubated for 24

hours in the dark at approximately stream temperature. An OI Analytical Model 1010

carbon analyzer was used to measure the carbon dioxide (CO2) evolution over time. The

respiration rates were calculated by taking the difference of the sample dissolved

inorganic carbon (DIC) and the corresponding abiotic control DIC. It was assumed that

CO2 would be the only component of DIC that changed between abiotic controls and

samples during incubation. The method was similar to that used by Davis et al. (1993)

except a headspace in the vial was not included in an effort to minimize the influence of

atmospheric pressure.

Ergosterol:

Fungal biomass was quantified as ergosterol. Ten disks (1.5 cm dia.), from

sycamore and boxelder leaf packs from each site, respectively, were cut with a cork borer

in the lab immediately after collection and stored in the dark at -20 °C in 10 mL of

methanol. Once leaves were too degraded to be cut with a cork borer, they were cut with

a surface area similar to those cut with the cork borer. Ergosterol was extracted using an

adapted version of the methods outlined by Gulis and Suberkropp (2006). Ergosterol was

extracted into methane by refluxing samples containing saponification fluid (KOH) in a

dry bath for an hour and a half at 70 °C. Samples were centrifuged and the pellet

discarded. Ergosterol was extracted from the methane into pentane by adding two ml of

pentane to the samples, vortexing, and decanting the methanol layer. This process was

13

repeated thrice. The sample was dried, re-dissolved in methanol, and the ergosterol was

quantified with a high performance liquid chromatograph (HPLC).

Shredder Abundance:

Macroinvertebrates associated with leaf packs used for leaf breakdown study

were collected on a 600 µm sieve and preserved in 85 % ethanol until further processing.

Invertebrates were sorted under a dissecting microscope and shredders were identified to

genus. Shredder presence was expressed as abundance (number of shredders per leaf

pack) and density (number of shredders per gram AFDM leaf litter) (Webster and

Benfield, 1986).

Sedimentation and Bed Stability:

Sedimentation was estimated by quantifying both the coarse and fine fractions of

sediment that settled on leaf packs. Coarse fraction sediments (those that could pass

through a 600 µm pore size sieve but were trapped by a 250 µm sieve) were collected and

the dry mass was determined. Fine fraction sediments (those that could pass through a

250 µm pore size sieve) were collected in 5 L of water and three 125 mL subsamples

were taken for filtration to determine the dry mass from each leaf pack. In addition,

pebble counts were performed in the field at each site following the methods of Statzner

et al. (1988) and Wolman (1954).

Physicochemical variables: Water samples were collected at each leaf pack sampling date and frozen for

future analysis for nitrate-N, phosphate, and ammonium. A LaChat QuickChem 8500

Flow injection Analyzer was used to measure ammonium and phosphate colorimetrically

and a Dionex DX500 ion chromatograph was used to measure nitrate-N by reading

absorbance (USEPA, 1993). In addition, pH of filtered stream water was measured in the

lab with an Orion portable pH meter and alkalinity was calculated by titration with

14

sulfuric acid. Conductivity and temperature were measured once per month at each site

with a handheld YSI 30 conductivity, salinity, and temperature meter.

Riparian Vegetation:

Two 50 m by 10 m plots were established on each stream bank at each site.

Woody vegetation ≥ 2 cm diameter at breast height (DBH) was identified and counted in

each plot. Importance values, riparian woody vegetation density, and stand basal area

were calculated for each site.

Topographic analysis:

Watersheds were hand delineated with Terrain Navigator Pro (Maptech, inc.,

Amesbury, MA) (Appendix B-G). Stream slope, watershed slope, and sinuosity index

were calculated by hand. The water erosion prediction project (WEPP) model (United

States Department of Agriculture) was used to estimate average annual precipitation,

runoff, sediment yield, and erosion.

Statistical Analyses:

Differences between boxelder and sycamore breakdown rate were analyzed by

Wilcoxon Signed Ranks test. Linear regression was used to assess the relationships

among riparian vegetation, temperature, water chemistry (alkalinity, pH, phosphate,

nitrate-N, and ammonium), sediment (coarse and fine), macroinvertebrate density, fungal

biomass, microbial respiration, incubation time, and leaf breakdown. R2 (coefficient of

determination) values represent the proportion of the variability in the data explained by

the regression fit. Differences in response variables among sites were assessed using

Friedman’s test with site as a treatment and blocked by days of incubation followed by

Wilcoxon Signed Ranks multiple comparison tests (Dythan, 2003; Sharrer and

15

Summerfelt, 2007). Results were considered significant if p < 0.05. Principle

components analysis (PCA) was used to simplify relationships among chemical

parameters.

16

Results Leaf breakdown among sites

Boxelder breakdown rates were faster than sycamore at all sites except for the 5

year exclusion site where sycamore broke down faster (Fig. 4). Boxelder breakdown

rates ranged from 0.0061 d-1 at the 5 year exclusion site to 0.0194 d-1 at the forested site

(Table 4). Sycamore breakdown rates ranged from 0.0033 d-1 at the rotationally grazed

site to 0.0150 d-1 at the forested site (Table 5). There was no statistically significant

difference between boxelder and sycamore breakdown rates (p = 0.16). Percent AFDM

remaining of boxelder leaves rapidly declined over the first two months in the streams

and then more slowly at all sites except for the forested site which declined rapidly for

the first three months (Fig. 5). Percent AFDM remaining of sycamore leaves declined

slowly over the first month and then sped up in subsequent months

(Fig. 6).

17

Table 4: Summary of breakdown coefficients (k) and coefficients of determination (r2) of box elder leaves.

Figure 4: Boxelder (dots) and sycamore (solid) breakdown rates at each site.

Site k (d-1) r2 <1 year Exclusion 0.0143 0.8144

Long Term Meadow 0.0138 0.6004

5 year Exclusion 0.0061 0.7467

Forested 0.0194 0.7058

Currently Grazed 0.0118 0.6475

Rototationally Grazed 0.0110 0.2418

0.0000.0050.0100.0150.0200.025

<1yr

Exclus

ion

Foreste

d

Currentl

y Graz

ed

Rotatio

nally

Graz

ed

5yr E

xclus

ion

15yr

Exclus

ion

<1yr

Exc

lusio

n

Fore

sted

Cur

rent

ly G

raze

d

Rot

atio

nally

Gra

zed

5yr

Exc

lusio

n

Lon

g T

erm

Mea

dow

18

Table 5: Summary of breakdown coefficients (k) and coefficients of determination (r2) of sycamore leaves.

Site k (d-1) r2 <1 year Exclusion 0.0111 0.6916

Long Term Meadow 0.0044 0.3859

5 year Exclusion 0.0099 0.9094

Forested 0.0150 0.8633

Currently Grazed 0.0098 0.5531

Rototationally Grazed 0.0033 0.4882

Figure 5: Boxelder %AFDM remaining over the course of the study at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●). Error bars represent the means (+/- 1 SE) of three replicate samples.

Days

0

20

40

60

80

100

120

0 32 60 89 117 152 201Days

19

Figure 6: Sycamore %AFDM remaining over time at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●). Error bars represent the means (+/- 1 SE) of three replicate samples.

Days

0

20

40

60

80

100

120

0 32 60 89 117 152 201

20

Riparian vegetation among sites

Sycamore breakdown rate was directly related to riparian woody vegetation density

(r2=0.81, p= 0.01) (Fig. 7) but boxelder breakdown rate was not related to density (r2=

0.34, p=0.23) (Fig. 8). Wetted width:depth of channel was significantly related to riparian

woody vegetation density and stand basal area at each site (r2=0.87, p=0.006) (Fig. 9, Fig.

10). Sycamore leaf breakdown rate appeared to be weakly related to wetted width:depth

though the relationship was not significant (r2=0.63, p=0.06) (Fig. 11). This relationship

was not significant for box elder leaf breakdown (p>0.05).

A complete list of riparian species basal area and density at each site appears in

Appendix H. Riparian woody vegetation density ranged from 0 trees and shrubs/ha at the

rotationally grazed and long term meadow sites to 2,875 trees and shrubs/ha at the

forested site (Fig. 12). Stand basal area ranged from 0m2/ha at the rotationally grazed

and long term meadow site to 34 m2/ha at the forested site (Fig. 13). Riparian woody

vegetation density and stand basal area were not related to duration of cattle exclusion in

this study.

The forested site had the greatest species richness in riparian vegetation. Woody

vegetation of greatest importance at the forested site were rhododendron, tulip poplar,

and yellow birch. White pine, yellow birch, and alder were the most important species at

5 year and <1 year exclusion sites. Northern spicebush, sycamore, and flowering

dogwood had the highest importance values at the currently grazed site (Appendix I).

21

Figure 7: Sycamore breakdown rate at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) was related to riparian woody vegetation density (r2=0.81, p= 0.01).

Figure 8: Boxelder breakdown rate at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) was not significantly related to riparian woody vegetation density (r2= 0.34, p=0.23).

R ip arian W o o d y V e g e ta tio n D e n s it y ( # /h a)

k

3 0 0 02 5 0 02 0 0 01 5 0 01 0 0 05 0 00

0 .0 1 7 5

0 .0 1 5 0

0 .0 1 2 5

0 .0 1 0 0

0 .0 0 7 5

0 .0 0 5 0

Riparian Woody Vegetation Density (#/ha)

Riparian Woody Vegetation Density (#/ha)

k

300025002000150010005000

0.0200

0.0175

0.0150

0.0125

0.0100

0.0075

0.0050

Riparian Woody Vegetation Density (#/ha)

22

Figure 9: Wetted width to depth ratio was significantly related to riparian woody vegetation density

at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X,

Currently grazed = , Rotationally grazed = ●) (r2=0.87, p=0.006).

Figure 10: Wetted width to depth ratio was significantly related to stand basal area at each site (5

year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed =

, Rotationally grazed = ●) (r2=0.94, p=0.001).

Riparian Woody Vegetation Density (#/ha)

w:d

300025002000150010005000

100

80

60

40

20

0

Stand Basal Area (m2/ha)

Stand Basal Area (m2/ha)

w:d

35302520151050

100

80

60

40

20

0

23

Figure 11: Breakdown rate of sycamore leaves was weakly related to wetted width: depth of stream

(5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed

= , Rotationally grazed = ●) (r2=0.63, p=0.06).

Figure 12: Riparian woody vegetation density at each study site.

w:d

k (d

-1)

100908070605040302010

0.0175

0.0150

0.0125

0.0100

0.0075

0.0050

w:d

0

500

1000

15002000

2500

3000

3500

Forested

<1 ye

ar Exc

lusion

5 yea

r Exc

lusion

Currently

Graz

edRotatio

nally G

razed

15 ye

ar Exc

lusion

24

Figure 13: Stand basal area at each study site.

05

10152025303540

Forested

<1 ye

ar Exc

lusion

5 yea

r Exc

lusion

Currently

Graz

ed

Rotationall

y Graz

ed

15 ye

ar Exc

lusion

(m/h

a)

25

Physicochemical variables

Nitrate-N and ammonium levels were significantly higher at the <1 year exclusion

site than other sites (Fig. 14; Fig.15). Nitrate-N concentrations ranged from 15 ppb at the

long term meadow site in December to 1,294 ppb at the <1 year exclusion site in January.

Ammonium concentrations ranged from <1.5 ppb at the forested site, rotationally grazed,

and 15 year and 5 year exclusion sites to 65.7 ppb at the <1 year exclusion site.

Phosphate concentrations were statistically significantly higher at the <1 year and 5 year

exclusion sites than other sites (Fig. 16). Phosphate concentrations ranged from <1.5 at

the rotationally grazed and long term meadow sites to 18.6 ppb at the <1 year exclusion

site in January. pH was circumneutral at each site and alkalinity was low at all sites

ranging from 4 mg/L CaCO3 at the long term meadow site to 20 mg/L CaCO3 at the <1

year exclusion site (Table 6). Leaf breakdown rates were not statistically significantly

related to physicochemical variables.

Average stream temperature at all sites was 11.8 °C. Stream temperature ranged

from 2.5 °C at the long term meadow site in February to 18.2 °C at the <1 year exclusion

site in May. Average stream temperature throughout the study at the <1 year exclusion

site was 4 °C warmer than the forested site. The forested site was slower to cool down in

the winter than other sites and slower to warm up in the spring (Fig. 17).

Average substrate size ranged from 41.3 mm to 67.9 mm. Sites ranged from

pebble to cobble bed streams (Wentworth, 1922) or very coarse gravel to small cobble

(Wolman, 1954). Fine sediment accumulation on boxelder leaves was greater than that

on sycamore leaves at all sites but the currently grazed site. Fine sediment accumulation

was greatest at the <1 year exclusion site and currently grazed site on boxelder and

sycamore leaves, respectively (Fig. 18). Fine sediment accumulation was lowest at the

forested site. Coarse sediment was greatest at the long term meadow site and lowest at

the forested site (Fig. 19). Mean annual sediment yield to each site, as estimated by the

water erosion prediction project (WEPP) model ranged from 2.0 tons/ha/yr at the forested

and currently grazed sites to 15.3 tons/ha/yr at the <1 year exclusion site (Fig. 20).

Measured discharge ranged from 0.89 L/s at the 5 year exclusion site to 14.06 L/s

at the currently grazed site. Average annual surface runoff ranged from 3.0 cm at the

26

currently grazed site to 8.6 cm at the 5 year exclusion site as predicted by the WEPP

model (Table 7).

27

.

Figure 15: Mean ammonium concentrations at each site over the duration of the study. Nitrate-N concentrations were significantly different among sites (p< 0.05). Different letters represent statistically significant differences among site means. Error bars represent the 95 % confidence interval for the mean.

a c, d b, c, d d

b b, c

a d

b

c

b, c, d

b

Figure 14: Mean nitrate-N concentrations at each site over the duration of the study. Nitrate concentrations were significantly different among sites (p< 0.05). Different letters represent statistically significant differences among site means. Error bars represent the 95% confidence interval for the mean.

<1yr

Exc

lusi

on

Long

Ter

m M

eado

w

5yr

Excl

usio

n

Cur

rent

ly G

raze

d

Fore

sted

Rot

atio

nally

Gra

zed

<1yr

Exc

lusi

on

Long

Ter

m M

eado

w

5yr

Excl

usio

n

Cur

rent

ly G

raze

d

Fore

sted

Rot

atio

nally

Gra

zed

28

Table 6: pH and alkalinity at each site on day 32 of leaf breakdown study. Site pH Alkalinity (mg/L CaCO3)

Currently Grazed 6.4 14

Rotationally Grazed 6.2 6

Forested 6.3 6

5 year Exclusion 6.5 6

Long Term Meadow 6.4 4

<1 year Exclusion 6.9 20

Figure 16: Mean phosphate concentrations at each site over the duration of the study. Phosphate concentrations were significantly different among sites (p< 0.05). Different letters represent statistically significant differences among site means. Error bars represent 95 % confidence interval for the means

a d a

b b, c

c, d

<1yr

Exc

lusi

on

Long

Ter

m M

eado

w

5yr

Excl

usio

n

Cur

rent

ly G

raze

d

Fore

sted

Rot

atio

nally

Gra

zed

29

Figure 17: Temperature at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) over the duration of the study.

Figure 18: Mean (± SE) monthly fine sediment accumulation on Boxelder (dots) and sycamore (solid) leaf packs.

02468

101214161820

32 89 117 152 180 201

Day

Tem

pera

ture

(C)

<1yr

Exc

lusio

n

Cur

rent

ly G

raze

d

Long

Ter

m M

eado

w

5yr

Excl

usio

n

Rot

atio

nally

Gra

zed

Fore

sted

30

Figure 19: Mean (± SE) monthly coarse sediment accumulation on Boxelder (dots) and sycamore (solid) leaf packs.

Figure 20: Mean annual sediment yield at each site as predicted by the water erosion prediction project (WEPP) model.

Long

Ter

m M

eado

w

5yr

Excl

usio

n

<1yr

Exc

lusio

n

Cur

rent

ly G

raze

d

Rot

atio

nally

Gra

zed

Fore

sted

<1yr

Exc

lusi

on

Long

Ter

m M

eado

w

5yr

Excl

usio

n

Cur

rent

ly G

raze

d

Fore

sted

Rot

atio

nally

Gra

zed

31

Table 7: Physical characteristics of each site as predicted by the WEPP model.

Site

Avg. Annual

Precipitation

(cm)

Avg. Annual

Surface

Runoff

(cm)

Avg. Annual

Erosion

(ton/ha/yr)

Mean

Annual

Sediment

Yield

(ton/ha/yr)

<1yr Exclusion 107.7 4.1 15.3 15.3

Long Term Meadow 107.7 5.1 4.4 3.0

5yr Exclusion 107.7 8.6 13.6 13.6

Currently Grazed 107.7 3.0 5.4 2.0

Forested 107.7 4.8 4.0 2.0

Rotationally Grazed 107.7 4.3 4.3 4.3

32

Shredders among sites

Average shredder density on leaf packs ranged from none at the <1year exclusion

site to 0.84 shredders/gAFDM at the forested site. Shredders colonized leaf packs over

the first month of incubation. Shredder density was fairly consistent from day 32 through

the end of the study except in the forested site in which shredder density increased

monthly until all leaves were gone (Fig. 21; Fig. 22). Shredder density on sycamore

leaves was highest in May at sites with leaves remaining (Fig. 21).

Shredder density was not significantly related to box elder or sycamore

breakdown rate (p>0.05). Shredder density was not related to microbial respiration or

fungal biomass (p>0.05). Shredder density on sycamore leaves was significantly related

to wetted stream width to depth ratio (r2=0.81, p=0.014) (Fig. 23). Shredder density on

boxelder leaves was not significantly related to wetted stream width to depth ratio

(p>0.05).

Mean shredder abundance on sycamore leaves ranged from 1.06 at the <1 year

exclusion site to 7.46 at the the forested site. Mean shredder abundance on boxelder

leaves ranged from 0.31 at the <1 year exclusion site to 5.61 at the rotationally grazed

site. Tallaperla was the most abundant shredder on sycamore and boxelder leaf packs at

the forested site and on boxelder packs at the rotationally grazed site. Lepidostoma was

the most abundant shredder on sycamore leaf packs at rotationally grazed and long term

meadow sites. Shredder abundance at the 5 year exclusion site was comprised mostly of

Pychnopsyche. Tipula was the only shredder found at the <1 year exclusion site.

Shredders at the currently grazed site were mostly Taeniopteryx (Appendix J).

The rotationally grazed, long term meadow, and 5 year exclusion sites had the

highest shredder richness (4, 3, and 3 respectively on sycamore and 5, 4, and 4 on

boxelder) and the <1year and currently grazed sites had the lowest (1 and 2 respectively

on sycamore and 1 and 1 on boxelder). Shredder richness at the forested site was

intermediate (3 on boxelder and sycamore). Shredder richness was inversely related to

total sediment accumulation (r2=0.81, p=0.015) (Fig. 24).

33

Figure 21: Shredder density on sycamore leaves at each site (5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●) throughout sampling season.

Time (d)

0 32 60 89 117 152 201-5

0

5

10

15

20

34

Figure 22: Shredder density on boxelder leaves at each site (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●) throughout sampling season.

0 32 60 89 117 152 201-2

0

2

4

6

8

10

12

14

16

18

Time (d)

35

Figure 23: Shredder density on sycamore leaves was significantly related to wetted stream width to depth ratio (r2=0.81, p=0.014). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●.

w:d

Den

sity

(#/g

AFD

M)

100908070605040302010

4

3

2

1

0

36

Figure 24. Shredder richness on sycamore leaves at each site (5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = •, Rotationally grazed = ●) throughout study was related to total sediment accumulation (r2=0.81, p=0.015).

Shredder Richness

Tot

al S

edim

ent/g

AFD

M

4.03.53.02.52.01.51.0

20

15

10

5

0

37

Fungal biomass among sites

There were no significant differences in fungal biomass among sites (p>0.05).

Fungal biomass on boxelder leaves was highest during the first month of incubation

except at the long term meadow site where it was highest during the second month (Fig.

25). Fungal biomass on sycamore leaves peaked during the third month of incubation at

the forested, <1 year exclusion, and long term meadow sites and later for the currently

grazed and 5 year exclusion sites (Fig. 26).

Mean fungal biomass on boxelder leaves ranged from 30.5 mg/gAFDM at the

15year exclusion site to 71.0 mg/gAFDM at the forested site. Mean fungal biomass on

sycamore leaves ranged from 28.7 mg/gAFDM at the <1 year exclusion site to 47.8

mg/gAFDM at the forested site. Averaged over all sites fungal biomass was 10 % higher

on boxelder than sycamore leaves.

Fungal biomass was significantly related to ammonium concentration in the

stream (r2= 0.17, p= 0.021) (Fig. 27). This relationship was driven by the ammonium

concentrations and fungal biomass at the <1yr exclusion site. Fungal biomass was not

related to nitrate-N or phosphate concentration, sediment accumulation, riparian woody

vegetation density, or leaf breakdown (p>0.05).

38

Figure 25: Fungal biomass on boxelder leaves throughout the duration of the study (5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●).

Day

32 60 89 117 152 201

Fung

al B

iom

ass (

mg/

g le

af A

FDM

)

0

20

40

60

80

100

120

140

160

Day

32 60 89 117 152 201

Fung

al B

iom

ass (

mg/

g le

af A

FDM

)

0

20

40

60

80

100

120

140

160

Figure 26: Fung biomass sycamore leaves throughout the duration of the study. (5 year exclusion = ♦, long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●).

39

Figure 27: Sycamore fungal biomass is negatively related to stream ammonium concentration (r2= 0.17, p= 0.021). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●.

Ammonium (ppb)

Fung

al B

iom

ass

(mg/

gAFD

M)

706050403020100

80

70

60

50

40

30

20

10

40

Microbial respiration among sites

There were no significant differences in microbial respiration among sites

(p>0.05). Mean microbial respiration was 39 % higher on boxelder than sycamore

leaves. Microbial respiration on sycamore leaves ranged from 0.01 mgO2/gAFDM/hr at

the long term meadow site to 0.26 mgO2/gAFDM/hr at the currently grazed site.

Respiration on boxelder leaves ranged from 0.04 mgO2/gAFDM/hr at the <1 year

exclusion site to 0.49 mgO2/gAFDM/hr at the long term meadow site.

Microbial respiration was significantly related to water chemistry (r2=0.65, p=

0.05) (Fig. 28, Table 8). Microbial respiration was highest at low levels of alkalinity, pH,

phosphate, nitrate-N, and ammonium. Respiration was significantly related to coarse

sediment accumulation on sycamore (r2= 0.29, p=0.004) and boxelder leaves (r2=0.19,

p=0.049) (Fig. 29) (Fig. 30) but was not significantly related to fine sediment

accumulation (p>0.05). Microbial respiration was not significantly related to leaf

breakdown rate (p>0.05).

41

Table 8: Loading values for principle component one for PCA analysis of water chemistry.

Figure 28: Microbial respiration was inversely related to water chemistry (r2=0.65, p= 0.05). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●. Chemistry values are alkalinity, pH, phosphate, nitrate-N, and ammonium as indicated by principle component 1 in PCA.

Water Chemistry

PCA Loading Values

(PC1)

pH 0.47

NH4+ 0.46

PO4- 0.40

NO3- 0.46

Alkalinity 0.44

Chemistry (PC1) Chemistry (PC1)

Mic

robi

al R

espi

rati

on (

mgO

2/g

AFD

M/h

r)

43210-1-2

0.250

0.225

0.200

0.175

0.150

42

Figure 30: Microbial respiration on boxelder leaves was significantly related coarse sediment accumulation (r2=0.19, p=0.049). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●.

Figure 29: Microbial nn sycamore leaves was positively related to coarse sediment accumulation (r2= 0.29, p=0.004). 5 year exclusion = ♦, Long term meadow = ■, <1 year exclusion = ▲, Forested = X, Currently grazed = , Rotationally grazed = ●.

Coarse sediment (g)

Mic

robi

al r

espi

rati

on (

mg0

2/gA

FDM

/hr)

50403020100

0.4

0.3

0.2

0.1

0.0

Coarse Sediment (g)

Coarse Sediment (g) 181614121086420

0.20

0.15

0.10

0.05

0.00

43

Discussion Leaf breakdown as an indicator of ecosystem function

Sycamore breakdown rates were within the range commonly observed in the

literature from 0.0018-0.0193 d-1 (Webster and Benfield, 1986; Swan and Palmer, 2004;

Swan and Palmer, 2006). Sycamore leaves broke down fast at the forested and <1yr

exclusion sites, medium at the currently grazed and 5yr exclusion sites, and slow at the

long term meadow and rotationally grazed sites (Petersen and Cummins, 1974).

Boxelder breakdown rates were also within commonly observed ranges.

Literature values of boxelder leaf breakdown in streams ranged from 0.0140- 0.0414 d-1

(Webster and Benfield, 1986; McArthur and Barnes, 1988; Swan and Palmer, 2004;

Swan and Palmer, 2006). Box elder broke down fast at the <1yr exclusion, long term

meadow, forested, currently grazed, and rotationally grazed sites. Box elder broke down

medium at the 5yr exclusion site (Petersen and Cummins, 1974). Box elder broke down

faster than sycamore at all sites except for the 5 year exclusion site.

Paul et al. (2006) observed faster leaf breakdown rates in agricultural and urban

streams than in forested and suburban streams. They attributed this finding to higher

nutrient concentration and biological activity in agricultural streams and higher storm

runoff and mechanical fragmentation in urban streams. In this study, breakdown rates did

not correspond linearly to time since cattle exclusion. This is probably due to the

opposing effects of elevated sediment versus nutrients on leaf breakdown (Harding et al.,

1999; Huryn et al., 2002; Hagan et al., 2006). High sediment levels reduce oxygen

content and the heterogeneity of macroinvertebrate habitat leading to declines in shredder

abundance, whereas high nutrient concentrations tend to stimulate microbial activity,

which may encourage shredding by macroinvertebrates (Cummins et al., 1980; Hagan et

al., 2006). In this study the negative effects of sediment on leaf breakdown masked the

positive effects of excess nutrients at more recently grazed sites.

44

Alteration of physicochemical parameters with cattle exclusion

There was high sediment accumulation on leaves at the currently grazed and <1

year exclusion sites, intermediate sediment accumulation at the 5 year exclusion, long

term meadow, and rotationally grazed sites, and low sediment accumulation at the

forested site. Mean nitrate-N concentrations were significantly higher at the <1year

exclusion site than the forested site. Mean phosphate concentrations were significantly

higher at the <1 year and 5 year exclusion sites than at the forested site. Mean

ammonium concentrations were high at the <1 year exclusion site, intermediate at the

currently grazed and 5 year exclusion sites and low at the long term meadow, rotationally

grazed, and forested sites. These results provide strong support for the contention that

cattle exclusion leads to stream bank stability and limited support that it decreases

nutrient loading to streams. A before and after cattle exclusion study by Line et al.

(2000) demonstrated reductions in weekly nitrate, total phosphorous, and sediment loads

following cattle exclusion and riparian reforestation. Similarly, McKergow, et al. (2003)

found decreased sedimentation following cattle exclusion and revegetation but no

significant reduction in nitrogen and phosphorous.

An abundance of alder in the riparian zone at the <1yr exclusion site may have

acted in concert with the agricultural influence in the watershed to enhance nitrate-N

concentrations. Nitrogen fixing alder trees produce leaves high in NO3-N and low in

lignin. Leaching can initiate transfer of nutrients and secondary chemicals among leaf

litter types and enhance soil nitrogen in terrestrial ecosystems (Fyles and Fyles, 1993;

Gartner and Cardon, 2004). Riparian zones dominated by alder have been shown to have

positive effects on stream and wetland nitrate concentration (Gregory et al. 1991; Hurd

and Raynal, 2001). High concentrations of ammonium at the <1 year exclusion site and

phosphate at the <1 year and 5 year exclusion sites may be attributable to high

agricultural intensity in the watersheds.

Average stream temperatures in this study were highest at the <1 year exclusion

and currently grazed sites, intermediate at 5 year exclusion and rotationally grazed sites,

and lowest at the long term meadow and forested sites. These thermal characteristics

correspond to the amount of cleared area in the watersheds. Stream temperature was

45

likely affected by advection through groundwater discharge, alterations in stream width,

and changes in riparian vegetation associated with development in the watershed

(Leblanc et al., 1997).

Influence of cattle exclusion on biological parameters

Line (2003) saw reductions in bacterial abundance in streams following cattle

exclusion. Fungi and bacteria involved in leaf breakdown obtain a significant amount of

their required nitrogen and phosphorous from the water column and hence fungal

biomass accumulation and microbial respiration rates are often high in water bodies with

high concentrations of these nutrients (Suberkropp, 1995; Carter and Suberkropp, 2004;

Pascoal and Cassio, 2004; Suberkropp, 2005). The <1yr exclusion site was significantly

higher in nitrate-N, phosphate, and ammonium than other sites but lower in fungal

biomass accumulation and microbial respiration. Fungal biomass was significantly

negatively related to water ammonium concentrations and, though not significant, fungal

biomass appeared to be negatively related to phosphate and nitrate-N concentrations.

These trends seem to be driven by the high nutrient concentrations at the <1 year

exclusion site. In addition to having high nutrient concentrations, the <1year site has the

highest alkalinity. Carter and Suberkropp (2004) found that hardwater streams have

significantly more fungal biomass accumulation than softwater streams. The unexpected

results found in my study may be due to the confounding influences of sediment

accumulation on the leaves and burial causing anaerobic conditions, mechanical

fragmentation, and decreased palatability and accessibility of the leaves to microbes and

shredders (Herbst, 1980; Benfield et al., 2001). Similarly, Pascoal and Cassio (2004)

observed suppression of fungal biomass accumulation at a nutrient polluted stream and

attributed this result to slow current velocity and low dissolved oxygen.

Fungal biomass on box elder leaves in this study ranged from 30.5 mg/gAFDM at

the 15year exclusion site to 71.0 mg/gAFDM at the forested site. Mean fungal biomass

on sycamore leaves ranged from 28.7 mg/gAFDM at the <1 year exclusion site to 47.8

mg/gAFDM at the forested site. Fungal biomass measured in this study was consistent

with values reported in the literature. Suberkropp (1997) demonstrated a range in fungal

46

biomass accumulation on beech, oak, yellow poplar, red maple, dogwood and hickory

leaves from 40 mg/gAFDM to 90 mg/gAFDM in a woodland stream. Carter and

Suberkropp (2004) found a mean fungal biomass accumulation of 53.9 mg/gAFDM on

maple leaves in a softwater stream. Fungal biomass on sycamore leaves in a French

Pyrenees stream ranged from 74.6 mg/gAFDM to 91.8 mg/gAFDM and peaked at 8

weeks with a gradual decline thereafter (Gessner and Chauvet, 1994).

Microbial respiration on sycamore leaves in this study ranged from 0.01

mgO2/gAFDM/hr to 0.26 mgO2/gAFDM/hr. Respiration on boxelder leaves ranged from

0.04 mgO2/gAFDM/ to 0.49 mgO2/gAFDM/hr. Respiration rates measured in this study

were consistent with those reported in the literature. Carter and Suberkropp (2004)

measured microbial respiration rates on maple leaves ranging from 0.02

mgO2/gAFDM/hr to 0.6 mgO2/gAFDM/hr in a softwater stream. Tank et al. (1993)

measured microbial respiration rates ranging from 0.07 mgO2/gAFDM/hr on

rhododendron leaves to 0.14 mgO2/gAFDM/hr on birch leaves in 2nd to 4th order

Appalachian streams and saw a strong positive correlation between microbial respiration

rates and stream temperature.

Fine sediment accumulation on leaves was high at recently grazed sites with

continuous grazing, moderate at sites where cattle had been excluded for longer or where

grazing was rotational and low at the forested site. Sediment loading from eroded stream

banks is a significant source of stress to stream macroinvertebrates (Braccia and Voshell,

2006). In my study shredder richness was negatively related to sediment accumulation

on sycamore leaves. Only pollution tolerant organisms, such as tipulids, were present in

streams with recent cattle grazing and high sedimentation. Angradi (1999) showed that

fine sediment negatively influenced macroinvertebrate taxa richness in Appalachian

streams.

Importance of riparian vegetation to stream ecosystem function

Sites with the fastest leaf breakdown rates were associated with the highest

density of riparian vegetation and sites with the slowest breakdown rates were associated

with the lowest density of riparian vegetation. The forested site had the most dense

47

riparian vegetation and fastest sycamore breakdown rate while the long term meadow and

rotationally grazed sites had the slowest breakdown rates and no woody riparian

vegetation.

The presence or absence of riparian vegetation causes variability in the energy

source of the stream from allochthonous to autochthonous, respectively. Shredders have

been shown to be more abundant in streams with more riparian vegetation as this

provides the basis of their food source (Vannote et al., 1980; Stone and Wallace, 1998).

In this study, shredder density on box elder leaves was significantly positively correlated

with riparian vegetation density but, shredder density on sycamore leaves was only

weakly correlated with riparian vegetation density. This weak correlation may be

accounted for by a low density of shredders at the <1 year exclusion site. However, the

shredders present at the <1 year exclusion site were purely tipulids, which have larger

biomass than the other shredders present in this study. Tipulids have been observed to

generate up to 5.2 times as much dissolved organic carbon (DOC) as peltoperlids and up

to 6.6 times as much DOC as pteronarcids (Meyer and O’Hop, 1983). My results support

the contention that shredder biomass may be a better indicator of leaf processing ability

than abundance or density alone.

My study demonstrated a significant positive relationship between woody riparian

vegetation density and wetted width to depth ratio. Sweeney et al. (2004) showed that

riparian deforestation causes significant stream narrowing in first through fourth order

streams. Furthermore, if all woody riparian vegetation were removed from a channel,

greater than 50 % of the benthic stream habitat would be lost along with its ecosystem

services due to this narrowing effect. McTammany et al. (2007) demonstrated that

stream metabolism in agricultural streams can be restored to reference levels if riparian

zones are reforested. Though riparian grasses can be effective at reducing sediment and

nutrient input and increasing macroinvertebrate density (Osborne and Kovacac, 1993;

Lyons et al., 2000; Carline and Walsh, 2007), there is substantial evidence that riparian

forests are more effective at reducing erosion, balancing temperature regimes, and

providing heterogeneous habitat and food sources for biota (Allan, 1995; Sweeney and

Blaine, 2007). My study suggests that in addition to cattle exclusion, reforestation of

48

woody riparian vegetation may be essential to restore functional integrity to agricultural

streams.

49

Conclusions:

Complete recovery of stream ecosystem function following cattle exclusion may take >15 years.

Woody riparian vegetation should be replanted in addition to

cattle exclusion. Leaf breakdown studies may not be the best indicator of stream

ecosystem function in assessing recovery of agriculturally impacted streams due to the confounding influences of sediment and nutrients.

Stream incision, due to diminished riparian vegetation

diminishes benthic habitat available to macroinvertebrates and thus slows leaf shredding by macroinvertebrates

Sediment reductions associated with cattle exclusion may allow

for increased shredder biodiversity. Shredder biomass may be a better indicator of leaf processing

potential than abundance or density alone.

50

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57

Appendices Appendix A: Directions to sites heading southbound at the intersection of U.S. 221 and Va-8 in Floyd, Va.

Site Directions

Long term meadow Go west on US-221 (1.2 mi). Turn right onto Laurel Branch Rd (3.7 mi). Turn left onto Huckleberry Rd. Site is a couple miles up on the right.

5 year exclusion

Continue south on Rt. 8 (6.0 mi). Turn left onto VA-716 (0.1 mi). Turn right onto Blue Ridge Pkwy (6.6 mi). Turn right onto Black Ridge Rd. Several miles up on the left there is a gate and a dirt farm road (Shelor property). Take that dirt road to the second gate and the site is on the left.

Forested

Continue south on Rt. 8 (6.0 mi). Turn left onto VA-716 (0.1 mi). Turn right onto Blue Ridge Pkwy (about 5.0 mi). At the Rocky Knob picnic area turn right into the parking lot. Hike down hill to the site (about 0.5 mi).

Rotationally Grazed Continue south on Rt. 8 (about 5.0 mi). Turn right onto Fairview Church Rd. Continue for several miles. Turn left on Patrick Rd. Drive about a mile and the site is on the left.

Currently Grazed Continue south on Rt. 8. Pull off the road just after passing Canning Factory Rd. Site is on the right.

<1 year exclusion

Go east on US-221 (0.7 mi). Take a slight left onto Christiansburg Pike NE (5.2 mi). Turn right onto Huckleberry Ridge Rd. (about 1.3 mi). Turn right onto gravel rd. Site is on the right.

58

Appendix B. Watershed delineation for the <1yr exclusion site.

59

Appendix C. Watershed delineation for 5yr exclusion site.

60

Appendix D. Watershed delineation for forested site.

61

Appendix E. Watershed delineation for rotationally grazed site.

62

Appendix F. Watershed delineation for currently grazed site.

63

Appendix G. Watershed delineation for long term meadow site.

64

Appendix H. Stand basal area (Ba: m2/ha) and density (d: # of trees and shrubs/ha) of woody riparian vegetation species at each site.

Vegetation species

Forested RotationallyGrazed Long Term Meadow

5yr Exclusion <1yr Exclusion Currently Grazed

Ba d Ba d Ba d Ba d Ba d Ba d red maple Acer rubrum 0.24 50 2.50 145 2.73 90 0.14 5 alder Alnus serrulata 0.11 30 3.78 1110 yellow birch Betula

alleghaniensis 7.20

260

pignut hickory Carya glabra 0.09 5 flowering dogwood

Cornus florida 0.25 20 0.63 30

white ash Fraxinus americana 0.66 20 1.20 85 american witchhazel

Hamamelis virginiana

0.04 10

mountain holly Ilex montana 0.10 35 winterberry Ilex verticillata 0.57 205 northern spicebush

Lindera benzoin 0.13 50 0.60

120 0.14 55 1.27

230

tulip poplar Liriodendron tulipifera

11.25

185 0.19 20 0.40 5

cucumber tree Magnolia acuminata 0.01 5 black tupelo Nyssa sylvatica 0.60 55 0.13 5 white pine Pinus strobus 6.94 260 1.91 110 sycamore Platanus

occidentalis 1.12 15

black cherry Prunus serotina 1.33 50 0.21 15 0.24 5 black oak Quercus velutina 0.27 20 rhododendron Rhododendron

maximum 12.71

2120

black locust Robinia pseudoacacia

0.21 5 1.04

55 0.16 25

eastern hemlock

Tsuga canadensis 1.19 115

apple Malus domestica 0.66 35 0.34 5 Total 34.01 2875 15.79 1060 8.96 1400 3.79 295

65

Appendix I. Riparian woody vegetation importance values for trees and shrubs >2cm DBH. Importance values were calculated by summing relative basal area and relative density of each tree and shrub species.

Vegetation species

Forested Rotationally Grazed

Long Term Meadow

5yr Exclusion

<1yr Exclusion

Current Grazing

red maple Acer rubrum 2.4 29.5 36.9 5.5 alder Alnus serrulata 3.5 121.5 yellow birch Betula alleghaniensis 30.2 pignut hickory Carya glabra 4.2 flowering dogwood

Cornus florida 3.4 26.8

white ash Fraxinus americana 2.6 15.6 american witchhazel

Hamamelis virginiana 0.5

mountain holly Ilex montana 1.5 winterberry Ilex verticillata 22.9 northern spicebush Lindera benzoin 2.1 15.1 5.5 111.6 tulip poplar Liriodendron tulipifera 39.5 3.5 12.1 cucumber tree Magnolia acuminata 0.2 black tupelo Nyssa sylvatica 9.0 5.0 white pine Pinus strobus 68.5 29.2 sycamore Platanus occidentalis 34.8 black cherry Prunus serotina 13.1 3.5 8.0 black oak Quercus velutina 1.5 rhododendron Rhododendron

maximum 111.1

black locust Robinia pseudoacacia 0.8 11.8 12.8 eastern hemlock Tsuga canadensis 7.5

apple Malus domestica 7.5 4.1

66

Appendix J. Composition of shredders colonizing Sycamore (S) and Boxelder (BE) leaf packs. Values are mean numbers of

shredders/leaf pack from January 2006 to June 2006 at each study site.

Forested Rotationally

Grazed

Long Term

Meadow

5yr

Exclusion

<1yr

Exclusion

Currently

Grazed

Taxa

S BE S BE S BE S BE S BE S BE

PLECOPTERA

Peltoperlidae Tallaperla 4.69 3.04 0.66 2.51 0.86 0.83 0.42 0.28

Taeniopterygidae Taeniopteryx 0.34 3.48 1.24

TRICHOPTERA

Lepidostomatidae Lepidostoma 2.15 1.04 3.60 0.31 1.76 0.23 0.59

Limnephilidae Pychnopsyche 0.62 0.69 0.46 0.32 0.48 0.65 1.17 0.70 0.53

DIPTERA

Tipulidae Tipula 0.32 2.13 0.37 0.38 0.38 1.08 0.35

Totals: 7.46 4.77 5.04 5.61 3.10 2.08 1.97 1.95 1.08 0.35 4.01 1.24