No major changes in research directions have occurred and we continue to address the original
objective of characterizing, quantifying and modeling nutrient-foodweb dynamics of Hg
concentrations in sport fish communities of coastal BC lakes and reservoirs. However, we have
started to use two of our study lakes to link our results more directly to sport fishing
communities. In the original COMERN proposal to NSERC, we proposed to address the
following objectives:
Nutrient-foodweb processes determining Hg bioaccumulation in plankton and fish. Under this
objective we have been addressing the relative importance of energy content and sizes of
zooplankton;trophic status and community structure of zooplankton; and feeding and growth
characteristics of fish in determining the concentration MeHg and THg in major freshwater sport
fish species. However, our first task was to evaluate the level of Hg in fish of BC. We have
shown that Hg in fish (50-760 ng/g WW) is as much a health issue in BC as it has been shown
for central and eastern provinces. We have created a GIS based map for Hg concentrations in
major freshwater sport fish species from 63 lakes in BC and are currently working to develop a
fish consumption advisory for BC, which is currently not available. We are quantifying the
relative importance of ecosystem productivity, food web structure and feeding niches of different
trophic levels and along with the processes of loading, transformation and availability, it will
enhance the predictability of Hg levels in fish under variable physical, chemical, biological and
climatic conditions of lake ecosystems. Our project has been gathering data from 12
biogeochemically different coastal BC lakes including MeHg concentrations in rainbow,
cutthroat, dolly varden and small mouth bass. The following sections describe our progress to
date:
A. Relationship between MeHg dynamics and energy transfer efficiency in planktonic
foodwebs:. As MeHg in zooplankton is mainly derived from diet, it is likely that MeHg
accumulation is associated with seasonal dynamics of growth-enhancing energy transfer
processes in the planktonic food web. Therefore, identifying the role of the biochemical
composition of planktonic diet including diet specific lipid biomarkers is essential to our
knowledge about the energetic status of food webs. We examined the relationship between
MeHg concentrations and (1) plankton-size dependent dynamics of total lipid and fatty acid
concentrations ranging from seston (10-64 µm), micro- (100-200 µm), meso- (200-500 µm), to
macro- (>500 µm) zooplankton, and (2) the energetic role of sestonic total lipid and EFA
quantity for the energy composition within different zooplankton sizes on a seasonal basis of
pristine and used natural lakes as well as of drinking-water reservoirs and collaborate with Mike
Paterson’s ELA lakes. Eventually, we hypothesize that the seasonal development of the energetic
status and MeHg dynamics in planktonic food webs may predict the rate of MeHg accumulation
in fish.
On a biomolecular level, we observed significant positive relationships between the growthenhancing fatty acid eicosapentaenoic acid (EPA) and MeHg in zooplankton as well as between
arachidonic acid (AA) and MeHg (Figures below). This is the first time such relationships have
been observed, the implications of which for Hg in fish and consequently humans are not yet
clearly understood. The amount of MeHg indicates that somatic growth within the planktonic
food web is not restricted by the quantity of MeHg. Another finding that may link effects of
MeHg to physiological processes is that MeHg concentrations in the planktonic food web relate
significantly to the amount of AA, the precursor of eicosanoid synthesis. Eicosanoids regulate
many cell functions and play a crucial role in a variety of physiological processes including
regulation of various immune and inflammatory functions. The present dataset derived from field
analysis cannot undoubtedly identify the mechanisms or processes associated with higher
concentrations of MeHg on AA. More information on such dynamics are needed because (1) the
occurrence of AA concentrations is symptomatic of stress induced by levels of MeHg and that
(2) sufficient AA uptake may be suppressed at a certain, yet unknown, amount of MeHg in
zooplankton and consequently in fish. It should also be noted that EPA and AA also increases
significantly with zooplankton body size. Laboratory experiments with cultured zooplankton
(likely Daphnia) fed naturally containing AA algae with different levels of MeHg might provide
critical insight into MeHg dynamics and concentrations within the planktonic food web, the most
important link to Hg in fish. In addition, results of such experiment may also show relationship
between MeHg, somatic growth and on the frequency of reproduction. Because we principally
measure the effects of MeHg on the occurrence of fatty acids that are essential for good
physiological performance in zooplankton and fish, our research will be highly beneficial to the
overall COMERN objectives. However, these unique relationships have been observed only for
coastal BC lakes with warm monomictic conditions, which should be validated for cold dimictic
lakes in other Canadian regions.
B. Mercury in sport fish species under variable trophic status and food web structure: Based on
our last two years of total Hg analyses sport fish from 65 BC lakes, we found that the
concentrations of Hg in sport fish in BC lakes are highly variable among lakes (50-760 ng/gww).
These first ever systematic indication that Hg in sport fish species (mostly rainbow, cutthroat,
dolly varden and kokanee) show that Hg is as much variable among BC lakes as it has been
observed for other regions of Canada and that Hg should also be a concern for BC sport fishers.
We have been characterizing, quantifying and modeling the relative importance of 1) the energy
content and sizes of zooplankton; 2) the trophic status and community structure of zooplankton;
and 3) the feeding and growth characteristics of fish; in determining the high variability of Hg
concentrations in selected sport fish species. We are also testing how the patterns observed from
non-freezing and monomictic BC lakes compare to that from cold temperate dimictic lakes
through collaboration with other COMERN researchers at ELA and NB. Our research focus on
the role of nutrient-food web dynamics in determining Hg levels zooplankton and fish stemmed
from existing observation of higher MeHg in fish from oligotrophic lakes than in eutrophic lakes
may be due to a dilution effect of the algal blooms in eutrophic lakes. MeHg levels in toppredator fish are higher when the food chain is longer. It was showed that the presence of Mysis
or forage fish adds a trophic level that increases the MeHg accumulation in the top predators.
However, a significant amount of variability in MeHg in fish could not be explained with food
web length alone. Existing studies linking zooplankton to Hg in fish have used bulk zooplankton
communities as single trophic level, while research by our group has shown that composition of
zooplankton can vary substantially among lakes and there are at least two trophic levels within
zooplankton communities. More specifically, Daphnia and copepods are often considered to be in
the same trophic level; while the copepods are omnivorous, and Daphnia are herbivorous. We
have been using stable isotopes of N and C to develop a baseline correction model for temporal
and spatial variation in trophic positions among various zooplankton species and to demonstrate
show that copepods are almost one trophic level higher than Daphnia. Without this baseline
isotope corrections for trophic positions of zooplankton, it very likely to introduce errors in
predicting Hg in fish using stable isotope signatures as a surrogate for trophic level. Different
feeding regimes may affect the concentration of methylmercury in these groups and fish may
accumulate different concentrations of methylmercury depending on the dominance of
cladocerans versus copepods in the zooplankton community structure. In communities with
smaller bodied zooplankton, the food web is longer and less efficient, which may have significant
implications for Hg accumulation in fish. We have been quantifying the role of copepod versus
cladoceran dominance in determining the level of Hg in fish of given size, age and trophic
position. We will be collecting comparable samples from ELA and NB to test if the patterns
observed from warm monomictic lakes in BC are comparable to that observed from cold dimictic
lakes.
C. MeHg concentrations in fish as a function of growth and trophic position: Using new data
from otolith and scale samples of fish from 10 BC lakes and stable N isotopes we have been
testing how much of the variability in MeHg in fish is due to i) growth rate alone (in
collaboration with Reed Harris); ii) variability in diet composition and growth; and iii) trophic or
ontogenetic niche shift and growth.
D. Transfer of knowledge to fish-eating communities: We sampled sport-fishing lakes and have
access to fishing clubs and its registered members. We will develop a comprehensive database on
sport fishing, catch, fish consumption patterns from Shawnigan and Elk, the two of our most
popular sport fishing lakes.
E. Sediment biogeochemistry of Hg in coastal BC lakes. Our other collaborative research and
development with Dr. Kevin Telmer, included the setting up of analytical capabilities,
interlaboratory calibration and sediment biogeochemistry of Hg in our study lakes: 1)
Determination of the concentrations and masses of mercury being transported by major rivers in
the dissolved, particulate and adsorbed phases. 2) Determination of the concentrations of Hg in
west coast lake sediments through the Holocene (12,000 year record). Total and labile Hg have
been determined for the entire record. Total, labile, pore-water, as well as MeHg concentrations
have been determined for the upper 50 cm. 3) Determination of the total volume and mass of lake
sediment and Hg contained in the sediment package by sub-bottom seismic profiling. This work
also maps the distribution of methane in lake sediments – of probable importance for the
remobilization of Hg to the SWI. 4) Determination of lake sediment physical properties
important for the potential remobilization of Hg. Permeability and diffusion rate constants are
being determined by in-situ experiments using dialysis samplers and fluorescent tracers. 5) Initial
lab set-up and method development for the detection of Hg and MeHg by CVAFS-gold trap and
ICP-MS in several media including fish, zooplankton, sediments, and waters. 6) Initial lab setup
and method development for the detection of DOC, organic carbon, and inorganic carbon inn
waters and sediments. 7) Initial lab setup and method development for characterizing DOC
species and their associated Hg contents through a combination of HPLC, fraction collection,
stable isotope spiking, and ICPMS.