The Scotian shelf: an atlas of human activities

Ocean disposal and marine environmental quality

Disposal of Material in the Ocean

A wide variety of material is deposited in the ocean both intentionally and accidentally, legally and illegally. Historically, the common practice of transporting and disposing dangerous wastes at sea prompted the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, referred to as the London Convention. In 1975, more than 50 countries, including Canada, ratified the convention. Canadian legislation on ocean dumping is found in the Canadian Environmental Protection Act (CEPA).

Under CEPA, disposal of approved substances at sea is permitted. Approved substances are limited to dredged material; fish waste and other organic matter resulting from fish processing operations; ships, aircraft, platforms or other structures from which all floating debris or other marine pollution has been removed to the maximum extent possible; inert, inorganic geological matter; uncontaminated organic matter of natural origin; and bulky substances that are primarily composed of iron, steel, concrete or similar matter that does not have a significant adverse effect on the sea or the seabed.

Various locations contain unexploded military ordinance, either through the regulated disposal of materials by the Department of National Defence in designated and charted munitions dump sites, or as a result of shipwrecks from the First and Second World Wars. During the Second World War, Canada and her Allies participated in a chemical and biological warfare program that included production, testing and training activities. At the end of the war, it was standard practice for Allied nations to dispose of their stockpiles of surplus materials in the ocean or through burial. Some of the surplus materials disposed of in Canadian waters contained chemical agents, like mustard gas, or biological warfare agents. A number of chemical and unexploded ordinance sites are being assessed to determine risks posed to the environment and other activities, such as fishing, and to identify potential mitigation needs.

In addition to the regulated introduction of material to the ocean, the marine environment receives a large amount of man-made material as a result of illegal spills and discharges, either accidental or deliberate. One of the most significant environmental concerns in the region is the chronic introduction of oil from vessel traffic, primarily as a result of bilge and oily water discharges. Other pollution issues include marine debris, various chemical contaminants from vessels and offshore hydrocarbon development activities, and the introduction of invasive species and pathogens through ballast water. The region has also experienced several large-scale environmental emergencies, including the wreck of the Arrow oil tanker and other vessel sinkings.

Introduction: Marine Environmental Quality and Heavy Metals in the Marine Environment

Heavy Metals in the Marine Environment

Heavy metals are introduced to the marine environment by both natural processes and human activities. Natural sources are predominantly from river runoff and atmospheric precipitation, but other sources such as hydrothermal vents can, in some locations, be important. Metal mining, metal processing and industrial and domestic uses of metals and metal-containing products add a human-made component to these natural inputs. Human activities can lead to direct discharges along the coastline, from offshore industrial developments such as oil and gas development, and from shipping activity. Metals can also be mobilized during other activities, for example the burning of coal or oil, because all natural materials contain varying amounts of heavy metals. Heavy metals will be removed from coastal waters either by deposition into coastal sediments or transport offshore. The pelagic ocean can represent another “source” of metals, returning metals to the shelf environment during onshore water transport.

Concentrations of heavy metals in water and sediments illustrate the impacts of chemical contamination on marine environmental quality. The observed distributions represent the exposure of biota to potentially toxic heavy metals in both water and sediments. The maps in this section show the observed distributions of dissolved cadmium and copper in surface water, and total chromium, copper, lead and zinc in surface sediments. The surface layer dissolved contaminant maps can be used to locate metal sources and the sediment maps to locate both sources and areas of metal deposition. For the Scotian Shelf, the main source of fresh water and of heavy metals is the discharge from the Gulf of St. Lawrence. Additional inputs of heavy metals would be anticipated from populated, industrialized areas such as Sydney and Halifax, as well as from offshore oil and gas activities. Metals will be deposited in the finer grained sediments in the deeper basins along the shelf or transported offshore with the currents.

Water and Sediment Quality

The impacts on environmental quality that result from inputs of metals can be assessed by comparing the observed distributions to water and sediment quality guidelines. Because heavy metals are naturally occurring components of the marine environment, natural background concentrations are another useful environmental quality threshold. In this analysis we have used a geochemical technique (Loring 1991) to account for the natural grain-size related variability in metal concentrations. The sediment maps in this section show sediment quality codes for each sampling location based on comparisons to natural levels and the Canadian marine sediment quality guidelines for protection of aquatic life (CCME 1999). Blue sites have levels below natural background concentrations; green sites are above background but less than the sediment quality guidelines threshold effects level (TEL); and yellow sites are above the TEL but less than the probable effects level (PEL). Sediments above the PEL would be red, but there have been no observations of concentrations above the PEL on the Scotian Shelf.

CCME. 1999. Canadian sediment quality guidelines for the protection of aquatic life. Canadian Council of Ministers of the Environment, Winnipeg.

Loring, D.H. 1991. Normalization of heavy metal data from estuarine and coastal sediments. ICES Journal of Marine Science 48: 101-115.

Dissolved Cadmium

Distributions of dissolved cadmium are governed by inputs from coastal areas that are related to salinity and by internal oceanic cycling that is driven by primary biological productivity and associated with phosphate dristributions. The concentrations of cadmium decrease with increasing salinity and increase with increasing phosphate concentration. The average cadmium distribution for surface waters (025 metres) in fall (September to December) is shown here. It is derived by first estimating cadmium concentrations from the relationship between cadmium and both salinity and phosphate determined from available data from the shelf. Optimal estimation techniques are then used to predict cadmium levels for the entire shelf.

The relationship between cadmium and salinity and phosphate is based on data collected on oceanographic cruises conducted since 1985. The on-going data collection is being conducted to investigate changes in cadmium concentrations over time. So far, no such temporal trends in concentration have been observed.

At the northeastern end of the shelf, the distribution shows the influence of the input of cadmium from the Gulf of St. Lawrence in the low-salinity Nova Scotia Current and the importance of the high tidal energies in the outer Bay of Fundy in mixing higher cadmium levels from subsurface waters into the surface layer. Offshore concentrations in the surface layer are very low because of the removal of phosphate and cadmium from oceanic surface waters by the growth and subsequent death and sinking of phytoplankton.

The Canadian marine environmental quality guideline for the protection of aquatic life is 0.11 nanomoles of cadmium per litre (a nanomole is one billionth of mole). The highest concentrations observed on the shelf are less than half of this guideline.

Dissolved Copper

Distributions of dissolved copper are governed by inputs from rivers and coastal communities that are related to salinity. The average copper distribution for surface waters in fall is shown here. It is derived by first estimating copper concentrations from the relationship between copper and salinity determined from available data for the shelf and then using optimal estimation techniques to predict copper levels for the entire shelf. Copper concentrations are high in fresh waters from both natural and anthropogenic sources and decrease in coastal waters with increasing salinity. The on-going shelf monitoring program has not detected any systematic temporal trends in copper concentration.

At the northeastern end of the shelf, the distribution shows the influence of the input of copper from the Gulf of St. Lawrence in the low-salinity Nova Scotia Current. Local discharges along the Nova Scotia coastline also contribute to this signal. Because of the magnitude of the Gulf of St. Lawrence freshwater discharge, concentrations on the eastern shelf are noticeably higher than those on the western shelf. Input of copper to the Bay of Fundy from rivers draining into the bay is also evident from this map. The copper concentrations in these rivers are relatively high, so this signal is stronger than would simply be indicated by salinity.

There is no Canadian marine environmental quality guideline for the protection of aquatic life for copper. Copper, however, is very toxic to many planktonic organisms and concentrations on the eastern shelf may be high enough to limit the growth of certain copper-sensitive species.

Chromium in Sediments

The background concentrations of chromium and most other heavy metals in marine sediments increase with decreasing grain size of the sediments, and can be estimated from the relationship between metal concentration and grain size. Concentrations are thus highest in the shelf basins and along the continental slope where finer sediments such as clays and silt are accumulating and lowest along the Nova Scotia coastline and on the offshore banks where coarser sediments such as sands and gravel are found.

The distribution shown on this map is based on all the data for surficial sediments collected by Fisheries and Oceans Canada from 1970 to the present. It also includes data from the first year of the Sable Offshore Energy Project environmental monitoring program and from an environmental survey carried out by EnCana. The samples are not very evenly distributed in space, being based almost entirely on geochemical studies of processes in the deep basins and surveying of environmental conditions in the vicinity of oil and gas exploration.

Sediments accumulate very slowly in continental shelf environments and physical and biological processes tend to mix the top few centimetres of sediment, so the entire data set can be seen as a snapshot of recent conditions. Temporal trends on decadal time frames would not be expected except near very large sources.

Two hundred and eighty-three of the 302 samples in the dataset are at background concentrations. Most of the 17 samples that are above background concentrations but below the Canadian marine sediment quality guidelines threshold effects level (TEL) are in the immediate vicinity of the Venture and South Venture offshore oil and gas platforms or in the vicinity of one of the exploratory drilling lease areas on the slope. However, most samples taken in the vicinity of these platforms are at background concentrations. The two samples that are above the TEL were collected in Emerald Basin, the largest depositional basin on the shelf. None of the samples are above the probable effects level.

Copper in Sediments

The concentrations of copper in marine sediments increase with decreasing grain size of the sediments, and can be estimated from the relationship between metal concentration and grain size. Concentrations are thus highest in the shelf basins and along the continental slope where finer sediments are accumulating and lowest along the coastline and on the offshore banks were coarser sediments are found.

The distribution shown on this map is based on all the data for surficial sediments collected by Fisheries and Oceans Canada from 1970 to the present. It also includes data from the first year of the Sable Offshore Energy Project environmental monitoring program and from an environmental survey carried out by EnCana. The samples are not very evenly distributed in space, being based almost entirely on geochemical studies of processes in the deep basins and surveying of environmental conditions in the vicinity of oil and gas exploration. Sediments accumulate very slowly in continental shelf environments and physical and biological processes tend to mix the top few centimetres of sediment, so the entire data set can be seen as a snapshot of recent conditions. Temporal trends on decadal time frames would not be expected except near very large sources.

Two hundred and ninety-seven of 314 samples in the dataset are at background concentrations, four are above background but below the Canadian sediment quality guidelines threshold effects level (TEL), and 13 are above the TEL. No samples are above the probable effects level. The samples that are above background concentrations are located in Emerald Basin, three smaller basins on the eastern shelf and along the continental slope. Natural processes that generate larger gradients in concentrations between continental shelf and pelagic sediments for copper than for chromium, lead or zinc are likely responsible for these observations. None of the samples with elevated concentrations were associated with the Sable Island Bank offshore oil and gas locations or the pipeline corridor.

Lead in Sediments

The concentrations of lead in marine sediments increase with decreasing grain size of the sediments and can be estimated from the relationship between metal concentrations and grain size. Concentrations are thus highest in the shelf basins and along the continental slope where finer sediments are accumulating and lowest along the coastline and on the offshore banks where coarser sediments are found.

The distribution shown on this map is based on all the data for surficial sediments collected by Fisheries and Oceans Canada from 1970 to the present. It also includes data from the first year of the Sable Offshore Energy Project environmental monitoring program and from an environmental survey carried out by EnCana. The samples are not very evenly distributed in space, being based almost entirely on geochemical studies of processes in the deep basins and surveying of environmental conditions in the vicinity of oil and gas exploration. Sediments accumulate very slowly in continental shelf environments and physical and biological processes tend to mix the top few centimetres of sediment, so the entire data set can be seen as a snapshot of recent conditions. Temporal trends on decadal time frames would not be expected except near very large sources.

Two hundred and sixty-five of 303 samples in the dataset are at background concentrations and 38 are above background. None are above the Canadian sediment quality guidelines threshold effects level. The observations of above-background concentrations are broadly distributed, including samples from Emerald Basin, the smaller basins on the eastern shelf, the pipeline corridor, the shelf break, and the immediate vicinity of the Sable Island Bank offshore gas production platforms.

Zinc in Sediments

The concentrations of zinc in marine sediments increase with decreasing grain size of the sediments and can be estimated from the relationship between metal concentrations and grain size. Concentrations are thus highest in the shelf basins and along the continental slope where finer sediments are accumulating and lowest along the coastline and on the offshore banks were coarser sediments are found.

The distribution shown on this map is based on all the data for surficial sediments collected by Fisheries and Oceans Canada from 1970 to the present. It also includes data from the first year of the Sable Offshore Energy Project environmental monitoring program and from an environmental survey carried out by EnCana. The samples are not very evenly distributed in space, being based almost entirely on geochemical studies of processes in the deep basins and surveying of environmental conditions in the vicinity of oil and gas exploration. Sediments accumulate very slowly in continental shelf environments and physical and biological processes tend to mix the top few centimetres of sediment, so the entire data set can be seen as a snapshot of recent conditions. Temporal trends on decadal time frames would not be expected except near very large sources.

Two hundred and ninety-nine of 312 samples are at background concentrations and 13 are above background. None are above the Canadian sediment quality guidelines threshold effects level. Concentrations are close to background everywhere with the few above-background samples showing no particular pattern.