Report
Scarlett, P.M.; Old, G.H.; Rameshwaran, P. 2015. Monthly macrophyte
surveys of the CEH River Lambourn Observatory at Boxford.
NERC/Centre for Ecology & Hydrology. (Unpublished)
Copyright © 2015, NERC/Centre for Ecology & Hydrology
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Monthly Macrophyte Surveys of the CEH River
Lambourn Observatory at Boxford
Scarlett, P.M., Old, G.H., Rameshwaran, P.
Introduction
Chalk streams
Confined to areas of cretaceous upper chalk, chalk streams are not affected by the
hydrological influences of overlying substrates such as clays. This results in high base flows
with distinctive physical and chemical properties. They are internationally scarce and in
England have been subjected to varying degrees of management from their historic use to
power water mills to more recent exploitation as cress beds and game fisheries.
Macrophyte in chalk streams
The macrophyte communities of chalk streams are of great importance both for their
ecological value and the effect they have on hydraulic roughness. The relatively stable water
temperature, clear water and nutrient levels encourage growth over an extended growing
season which enhances the growth of macrophytes. The macrophytes help to trap silt and
provide varied habitats and food sources for invertebrates which in turn encourage fish
populations. However, in some chalk streams increased nutrient levels and the accumulation
of silt due to low flows, have reduced the abundance of macrophytes due to the growth of
epiphytic algae (Philips et. al, 1978). The most abundant aquatic macrophyte usually found in
chalk streams is Ranunuclus which may occur in great profusion. Therefore weed cutting is
sometimes carried out to reduce flood risk, lessen the influence of weed growth on flow
gauging stations and to enhance fisheries.
Research background
Scientific studies of chalk rivers have generally concentrated on invertebrate fauna (Wright
et. al., 1983), the growth and recession of macrophytes in shaded river sections (Ham et. al.,
1982;), the effects of marginal shading, (Dawson, 1978) and transport of sediment, weed
cutting (Old et. al., 2014) and vegetative material (Dawson, 1980). However, studies of
seasonal macrophyte growth are limited. The intention of this study was to address this by
monitoring seasonal changes in the growth patterns of the three most common macrophytes
in a representative chalk river. Results of this monitoring are presented in this report though
further analysis and interpretation will be presented elsewhere.
Study area
Macrophyte surveys were undertaken on the River Lambourn at Boxford. The river
Lambourn is a chalk stream situated in southern England. It is a designated SSSI and SAC
and is typical of other chalk streams in its clear, nutrient rich water and the associated
macrophyte and invertebrate communities. It is a tributary of the River Kennet which itself is
a tributary of the River Thames. Being relatively un-modified, the survey site (the CEH River
Lambourn Observatory at Boxford) is generally shallow and fast flowing, with accumulations
of fine sediments mostly limited to the margins.
Method
The surveys were designed to record both the cover and quantity of the three most common
aquatic macrophytes in the stream. These are Ranucnulus penicillatus ssp. Pseudofluitans
(with Ranucnulus penicillatus ssp. Pseudofluitans x Ranunculus peltatus hybrid), Calltiriche
platycarpa (with some Callitriche obtusanglia) and Berula erecta. The Ranunculus and
Callitriche species were not identified to species level as this is frequently impossible without
flowering material and because the study was more concerned with the quantitative behaviour
of aquatic macrophytes. Generally, cover of all macrophytes increases through spring and
peaks in the summer months, though this pattern is disrupted by weed cuts which usually
occurred twice a year in the summer months.
The surveys were conducted every month from March 2009 until October 2014 with one
occurrence of missing data due to high flow which prevented accurate (and safe) surveying.
When possible the surveys were timed to coincide with monthly hydraulic surveys reported
elsewhere.
The surveys were carried out at four points distributed along the length of the channel. These
were selected in order to represent a combination of shallow/fast flowing areas and
deeper/slower flowing areas, as well as shaded and unshaded reaches. At sites one to three
the channel width was approximately 10m, but at the downstream site the width is nearer
14m.
In order to ensure that the surveys were carried out at the same place, stakes were driven into
both sides of the bank on the first visit. On subsequent visits a tape was stretched between the
stakes and this was used as the centre of the survey.
Macrophyte cover (quadrat surveys)
These surveys were conducted using a 50cm x 50cm quadrat, divided into 25 10cm squares.
The quadrat was held over the channel at consecutive 50cm intervals and the number of
squares in which each macrophyte could be seen was recorded. This gave each macrophyte a
maximum count of 25 at each point, but the total count could be exceeded if vegetation
occurred at different heights, e.g. with trailing Ranunculus growing over submerged
Callitriche, in which case counts for both species were recorded. The process was repeated
from one side of the channel to the other. The sides of the channel were defined by the water
level when surveying was conducted, so the channel width varied according to the water level
at the time of survey. Terrestrial/amphibious vegetation at the channel edges such as
Glyceria, mentha and grass species was recorded as Overhanging Vegetation (OHV).
Macrophyte quantity
These surveys were conducted in order to provide more detailed information on the quantity
of vegetation. After the quadrat surveys had been completed, the dimension of each stand of
vegetation was measured along the centrepoint provided by the tape measure. Wherever any
aquatic macrophytes occurred, the water depth at that point and the height of the top and
bottom of the stand were recorded. These details were recorded at 30cm intervals until the
stand of vegetation ended, and re-started on the next stand. Only macrophytes directly below
the tape were recorded.
Biomass surveys
Biomass samples were taken for the first three years of the sampling (from March 2009 until
March 2012).
Three samples were taken from randomly selected stands of Ranunculus, Berula and
Callitriche using a 5cm quadrat. All of the plant material rooted within the quadrat was
included in the sample, including any trailing vegetation which extended beyond the border
of the quadrat. The volume, dry weight, wet weight, leaf area and stem length of the samples
were then recorded.
The survey techniques had little impact on the species recorded and the month long gap
between surveys allowed recovery from any disturbance. The only obvious damage was to
the marginal terrestrial/amphibious vegetation.
Water depths were taken at 50cm intervals across the channel to calculate the total wetted
channel area.
A photograph of the sites was taken at each visit.
Results
Key indices were produced to summarise the data and these are presented below.
Macrophyte cover (quadrat surveys) Ranunculus (Figures 1 and 2)
Maximum cover of Ranunculus usually occurred in August and quantities were noticeably
lower in the shaded site 3. Greater seasonal variation in the counts of Ranunculus was
apparent at site five, the deeper, slower flowing downstream site.
Macrophyte cover (quadrat surveys) Callitriche (Figures 3 and 4)
Counts of Callitriche were highest and seasonal variation most marked at the shaded site 3.
At site counts fell significantly after the first year of survey (2009).
Macrophyte cover (quadrat surveys) Berula (Figures 5 and 6)
Like Callitriche, counts of Berula were highest and seasonal variation most marked at the
shaded site 3, though there was a marked reduction in the number of counts after 2012.
Area of submerged macrophytes and wetted channel area (Figures 7-10)
Seasonal peaks are evident, especially at the deeper, slower flowing site 5 though allowance
should be made for the wider area of the channel (% of channel occupied shows a less
distinct trend).
1400
Site 2
Site 3
Site 4a
Site 5a
(
R
1200
a
n
u
n
1000
c
u
c
l
o 800
u
u
s
n
t
c
s
600
o
v
e
r
400
a
g
e
)
200
0
Month
July 2009
July 2010
July 2011
July 2012
July 2013
July 2014
Figure 1 Count of quadrat squares in which Ranunculus occurred at four sites (2009-2014
100.0
R
a
n
u
n
c
u
l
u
s
90.0
c
o
v
e
r
a
g
e
50.0
Site 2
Site 3
Site 4a
Site 5a
80.0
70.0
60.0
40.0
30.0
20.0
(
)
%
10.0
0.0
Month
July 2009
July 2010
July 2011
July 2012
July 2013
July 2014
Figure 2 Percentage cover of Ranunculus within the quadrats at four sites (2009-2014)
250
Site 3
Site 4a
Site 5a
200
150
(
C
a
l
l
i
t
r
i
c
h
e
Site 2
)
c
o
u
n
t 100
c s
o
v
e
r
50
a
g
e
0
Month
July 2009
July 2010
July 2011
July 2012
July 2013
July 2014
Figure 3 Count of quadrat squares in which Callitriche occurred at four sites (2009-2014)
25.0
C
a
l
l 20.0
i
t
r
i
c 15.0
h
e
Site 2
Site3
Site 4a
Site 5a
c
o 10.0
v
e
r
a
g
5.0
e
(
)
%
0.0
Month
July 2009
July 2010
July 2011
July 2012
July 2013
July 2014
Figure 4 Percentage cover of Callitriche within the quadrats at four sites (2009-2014)
450
B
e
r
u
l
a
400
Site 2
Site 3
Site 4a
Site 5a
350
300
c
o
v
e
r
a
g
e
250
200
(
150
c
o
u
n
t
s
100
)
50
0
Month
July 2009
July 2010
July 2011
July 2012
July 2013
July 2014
Figure 5 Count of quadrat squares in which Berula occurred at four sites (2009-2014)
40.0
Site 2
Site 3
Site 4a
Site 5a
B
e
r 30.0
u
l
a
c
o 20.0
v
e
r
g
a
e
10.0
(
)
%
0.0
Month
July 2009
July 2010
July 2011
July 2012
July 2013
Figure 6 Percentage cover of Berula within the quadrats at four sites (2009-2014)
July 2014
0.0
Figure 8 Area of all vegetation types 2009-2014
Month
Sep-14
Mar-13
Dec-12
Sep-12
Jun-12
Mar-12
Dec-11
Sep-11
Jun-11
Mar-11
Dec-10
Sep-10
Jun-10
Mar-10
Dec-09
Sep-09
Jun-09
Sep-14
1.0
Jun-14
2.0
Jun-14
3.0
Mar-14
4.0
Mar-14
Site 5a
Dec-13
Site 4a
Dec-13
Site 3
Sep-13
Site 2
Sep-13
Figure 7 Wetted channel area 2009-2014
Jun-13
Month
Jun-13
Mar-13
Dec-12
Sep-12
Jun-12
5.0
Mar-12
Dec-11
Sep-11
Jun-11
Mar-11
Dec-10
Sep-10
Jun-10
Mar-10
Dec-09
Sep-09
Jun-09
0.0
Mar-09
)
W
e
t
t a
e r
d e
a
c
h
m
a
2
n
n
e
l
Mar-09
(
Area of vegetation (m2)
12.0
Site 2
Site 3
Site 4a
Site 5a
10.0
8.0
6.0
4.0
2.0
Month
Figure 10 Channel cross section occupied by Ranunculus 2009-2014
Sep-14
Jun-14
Mar-14
Sep-14
Jun-14
Mar-14
Site 5a
Dec-13
Site 4a
Dec-13
4.5
Sep-13
Site 3
Sep-13
Jun-13
Mar-13
Dec-12
Sep-12
Jun-12
Mar-12
Dec-11
Sep-11
Jun-11
Mar-11
Dec-10
Sep-10
Jun-10
Mar-10
Dec-09
Sep-09
Jun-09
Cross section area (m2)
Site 2
Jun-13
Mar-13
Dec-12
Sep-12
Jun-12
Mar-12
Dec-11
Sep-11
Jun-11
Mar-11
Dec-10
Sep-10
Jun-10
Mar-10
)
0
Dec-09
(
a
c r
r e
o a
o s
f s
%
Sep-09
s
e
c
t
i
o
n
Jun-09
c
h
a
n
n
e
l
Mar-09
0.0
Mar-09
P
r
o
p
o
r
t
i
o
n
5.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Month
Figure 9 Cross section area occupied by Ranunculus 2009-2014
80
Site 2
Site 3
70
Site 4a
Site 5a
60
50
40
30
20
10
Concluding remarks
This study has resulted in the collection of a unique dataset of seasonal macrophyte growth
over a six year period, encompassing extreme levels of flow both high and low. Although not
analysed the results of the surveys are presented in this report. The data collected would
enable subsequent investigation of the impact of weed cuts on the composition, density, cover
and recovery time of these species and the relationship between macrophyte growth,
hydraulic roughness, flow regimes and sediment transport/deposition.
Acknowledgements
The authors would like to thank Mathew O’Hare for devising the field methodology used for part of
this survey, and the number of CEH staff and students who assisted with field work. This study
represents CEH core science that is funded by the Natural Environment Research Council.
References
Dawson F. H., and Kern-Hansen U. 1978. Aquatic weed management in natural streams: the
effect of shade by marginal vegetation. Verh. int. Verein. theor. angew. Limno 20, 1451-56
Dawson 1980. The origin, composition and downstream transport of plant material in a small
chalk stream. Freshwater Biology. 1, 419-435
Ham, S.F., Cooling D. A., Hiley, P. D., McLeish P. R., Scorgie, H. R. A., Berrie, A. D. 1982.
Growth and recession of aquatic macrophytes on a shaded section of the River Lambourn,
England, from 1971 to 1980, 12, 1-15
Phillips, G.L., Eminson, D., Moss, B., 1978. A mechanism to account for macrophyte decline
in progressively eutrophicated waters. Aquatic Botany, 4, 103-126.
Wright J. F., Hiley P. D., Cameron A. C., Wigham M. E, and Berrie A.D. 1983. A
quantitative study of five biotopes in the River Lambourn, Berkshire, England. Archiv fur
hydrobiology, 96 (3), 272-292
Old, G.H., Naden, P.S., Rameshwaran, P., Acreman, M.C., Baker, S., Edwards, F.K.,
Sorensen, J.P.R., Mountford, O., Gooddy, D.C., Stratford, C.J., Scarlett, P.M., Newman, J.R.,
Neal, M. (2014) Instream and riparian implications of weed cutting in a chalk river.
Ecological Engineering, 71. 290-300. 10.1016/j.ecoleng.2014.07.006