Phosphorus in aquatic ecosystems: chapter 3

Status and trends of phosphorus in water bodies across Canada

The following map presents the median levels of phosphorus found at the monitoring sites. It is important to keep in mind that some areas of Canada have naturally low levels of total phosphorus (e.g. oligotrophic) and others have naturally high levels (e.g. eutrophic). Thus, the impacts of excess nutrients, such as algal blooms, may be seen in all areas, including those described as oligo- or mesotrophic. These impacts may be particularly marking where the dissolved phosphorus portion is high relative to total phosphorus.

Concentration levels of total phosphorus (TP) and ratios of total dissolved phosphorus (TDP) to TP in rivers and the Great Lakes, Canada, 2004 to 2006. Based on median values. 

Notes: High TDP/TP ratios indicate a higher proportion of phosphorus which is readily available for uptake by plants (i.e. not bound in sediments). TDP was not available at sites identified by a square symbol (□), with the exception of 2 sites, Bow River at Lake Louise in AB and Callaghan Creek at Callaghan Lake in BC, where median phosphorus levels were below detection limits and a ratio could not be determined accurately.

Data source:Environment Canada water quality monitoring networks, including joint networks with British Columbia Environment, New Brunswick Department of Environment, Newfoundland and Labrador Department of Environment and Conservation, Prince Edward Island Department of Environment, Energy and Forestry, and Indian and Northern Affairs Canada.

Recent results for total phosphorus and total dissolved phosphorus (2004-2006) show that…

• Overall median concentrations for TP and TDP were 0.014 and 0.005 mg/L, respectively, but TP concentrations ranged between <0.0005 and 1.88 mg/L, while those for TDP varied from <0.0005 to 1.60 mg/L.
• 70% of the sites with high levels of TP (eutrophic and hypereutrophic) were located in the Arctic and Nelson River basins (i.e. Prairies and Northern watersheds)
• Intermediary concentrations were measured in Lakes Erie and Ontario, and, except for a few hotspots, in the Pacific and Atlantic drainage areas (both the Maritime Provinces and Newfoundland and Labrador)
• The lowest concentrations were found in mountain rivers of Yukon, Pacific and upper Nelson Drainage Areas and the upper Great Lakes (Superior, Huron and Georgian Bay)
• Higher phosphorus levels tend to be observed lower in the watershed, compared to upstream locations. This pattern was observed in the Fraser River, South Saskatchewan River, the Great Lakes and the St. Lawrence River and is due in part to the cumulative effect of human activities in lower portions of watersheds but also to natural changes in rivers which occur along their course.
• The ratio of TDP to TP at individual stations varied from 3% to nearly 90%. A ratio of 3% indicates that most of the phosphorus is bound to sediment in the water. A ratio of 90% indicates that most of the phosphorus is dissolved and easily available for take up by plants.
• The ratio of TDP to TP varies among rivers and lakes across the country and is not necessarily related to the total amount of P in the water body. Some sites with high TP have low TDP and some have a relatively high proportion of TDP, even within the same basin. Local river hydrology, point source inputs and land use likely contribute to these variations.

Trends in levels of total phosphorus and total dissolved phosphorus (1990 to 2006)

Data source:Environment Canada water quality monitoring networks, including joint networks with British Columbia Environment, New Brunswick Department of Environment, Newfoundland and Labrador Department of Environment and Conservation, Prince Edward Island Department of Environment, Energy and Forestry, and Indian and Northern Affairs Canada.

Results of the trend analysis show that…

• Of the 75 sites with total phosphorus (TP) data, 16 (or 21%) have increases, 23 (or 31%) have decreases and 36 (or 48%) have no change over the period 1990-2006.
• For half of the sites with increasing TP, the magnitude of the increase was great enough to change the trophic status category by at least one category (for e.g., oligotrophic to mesotrophic).
• Of the 39 sites with total dissolved phosphorus (TDP) data, 14 (or 36%) have increases, 9 (or 23%) have decreases and 16 (or 41%) have no change.
• Of the 39 sites with both forms of phosphorus, 30 have similar results including 9 with concurrent increases, 8 with concurrent decreases and 13 with concurrent no change. The nine remaining sites have trend results which differ between the phosphorus fractions, but only 2 have opposite trends - both are lake outlet sites (Lakes Ontario and Erie) and exhibited increasing TDP and decreasing TP. In both cases, this change in nutrient dynamics could be related to the presence of the invasive zebra mussel which filters algae and other suspended particles containing phosphorus and excretes dissolved phosphorus..