Stream Functional Responses to Metal-Enriched Leaf Material
Hazel Walling and Leah Bendell, Simon Fraser University, Burnaby, British Columbia
Methods
-
Figure 1. Proposed interactions of metals in aquatic foodwebs
Hypotheses
1. Leaves grown in metal-enriched soil will have higher
metal concentration and lower leaf quality.
2. Decomposition of metal-enriched leaves will be slower
than non-enriched leaves.
3. Invertebrate richness and diversity associated with
metal-enriched leaf packs will be lower.
Site Locations
West Vancouver
North Vancouver
Burrard Inlet
Figure 2. Six streams
of similar aspect (N-S),
size (>2m) and
elevation (250-300m)
were chosen in North
and West Vancouver,
British Columbia, and
sampled above the
major urban
development.
Cd
0.6
3.5
Cu
35.7
197
Zn
123
315
Figure 3. Red alder (Alnus rubra) saplings were grown in Cd, Cu and Zn enriched soils approximating the province of British Columbia’s
interim sediment quality guidelines (ISQG) and probable effect level (PEL) toxicity loads for metals in aquatic sediment. All metal
concentrations were measured using ICP and atomic absorption spectrophotometry. Leaves were harvested to construct leaf packs,
which were immersed in-stream to assess breakdown rate, and associated benthic invertebrate community.
Results
I. Metal uptake and leaf quality
a.
CTRL
ISQG
PEL
Treatment
%N
b.
% mass
Reduction in ecosystem
function (e.g. detrital
processing)
PEL (mg/
kg)
Leaf Pack Experiment
•  5g alder leaves/ pack
•  10mm mesh
•  3x 3 treatments/ 6
streams
•  21-day immersion
•  Oct. 18-Nov. 8, 2010
•  Inverts ID’d to family
Mean Zn (ppm)
-
Reduced growth
of aquatic
organisms
ISQG
(mg/kg)
Mean Cd (ppm)
Metal
loading in
riparian plants
Metal
contaminants
(traffic, industry)
Metal
c.
CTRL
ISQG
PEL
Treatment
d.
CTRL
ISQG
PEL
Treatment
%C
CTRL
ISQG
PEL
Treatment
Figure 4. Mean copper (a), cadmium (b) and zinc (c) uptake in ppm and % mass of carbon and nitrogen (d) in red alder leaves prior to
leaf pack construction. No significant difference in Cu uptake detected (Dunn’s method). Cadmium uptake between PEL and CTRL and
ISQG leaves was significantly different (p<0.05 1-way ANOVA; Holm-Sidak method). Zinc uptake between PEL and CTRL and ISQG
leaves was significantly different (p<0.05 1-way ANOVA; Holm-Sidak method). Initial %C differed between treatments (p=0.03),
whereas %N did not (p=0.2; Wilcoxon test).
II. Leaf decomposition rate
III. Invertebrate community
The following metrics were significantly
associated with stream site, but not
metal treatment:
•  Number of invertebrates
•  Number of orders
•  Number of EPT
% Mass remaining
Urbanization impairs structural and functional properties of
aquatic ecosystems. Vehicle exhaust, industrial activities,
manufacturing, landfills and waste disposal contribute metals
and other pollutants to stream ecosystems. In urban areas,
impervious surfaces (such as roads, buildings and compacted
soils) further expedite delivery of pollutants through degraded
riparian area and streams. While elevated concentrations of
toxic metals in stream reduce benthic invertebrate diversity
and thus, organic matter breakdown rates, few studies have
examined the functional dynamics of metal-enriched plant
material in stream ecosystems. We will address that
information deficit by asking whether metal enrichment of
leaves changes the way they are processed in-stream.
Mean Cu (ppm)
Background
CTRL
ISQG
PEL
Treatment
Figure 5. % mass remaining was different between
treatments (p> χ2: 0.0001; χ2 approximation of 1way ANOVA, blocked by stream).
Marginally significant relationship
between proportion EPT: Total
invertebrates and treatment
Discussion and future directions
•  Relationship between initial metal uptake and lower % carbon could influence decomposition rate and
carbon movement through stream ecosystem
•  Further identification of insects to lower taxonomic resolution and functional roles necessary
•  Further studies of how metals influence functional processes in aquatic ecosystems are important