Keep Nutrients on the Land……..Not in the Lake

Alberta Agriculture and Forestry (AB Ag) research on nutrient transport has evolved over two decades is relevant to the situation in the Sylvan Lake watershed. About 67% of the land area within the watershed boundary is used for agriculture. Those uses are also diffuse sources of nitrogen (N) and phosphorus (P) nutrients as a result of the cycle of growth and decay of organic material on the land. During the growth phase plants extract needed elements from the soil, particularly from the inter-granular water in the root zone that contains soluble building-block species of N and P. Plant decay, promoted by organisms in the soil, is continuous and releases cell nutrients back to the soil inventory for re-use. Farmers know that and use soil test chemical analyses to determine how much fertilizer must be added to grow the next crop, without adding an excess. Growing and harvesting food crops also mines the soil and removes nutrients that must be replaced to maintain crop yields.

P in Cell Walls

Phosphorus is an important element in phospholipids that form cell walls that can decay and disperse.

P in DNA

Cell DNA contains phosphate groups that can also be recycled into the environment.

AB Ag has found that the concentration of nutrients in the top few centimetres of soil is also an important source of available N and P in runoff into streams and water bodies. So is manure that is stored for use or dispersed on the land as nutrient-rich fertilizer. Typically, nutrient levels are the highest in spring runoff, then drop as the ground warms up and plants grow, trap, and retain N and P. The next graph shows SLWSS results from water quality sampling of Golf Course Creek in 2014 that confirm the AB Ag finding. Data from other Sylvan Lake tributaries follow the same pattern. The lowest N and P concentrations in those streams have always been above those measured in Sylvan Lake and summarized by ALMS in Lakewatch reports. So the natural nutrient cycle on agricultural and forested watershed land loads the lake with nutrients on an annual cycle.

N and P in GCC

SLWSS water quality sampling results for Golf Course Creek in 2014. High levels of N and P were found in Spring runoff. Nutrient concentrations through the summer remained above those observed in the lake itself.

The element phosphorus is often the critical limiting factor that controls the trophic state of lakes. Sylvan Lake’s long term average Total Phosphorus analysis of 21 micrograms per litre keeps the lake in a meso-eutrophic state with typically low chlorophyll-a concentrations associated with suspended plant matter. Algal blooms have been rare. The watershed community counts on it staying that way. That is why AB Ag’s application of field research findings and modeling studies into practical best management practices are important. Phosphorus is better fertilizing plants on watershed land than algae and plants growing in Sylvan Lake.

Instead of presenting a technical review of the excellent experimental and modeling nutrient transport work of AB Ag, the department’s publications can speak for themselves. Here is an introduction to a few that illustrate the scope and caliber of that research. Reports on three field studies:

are complemented by a fact sheet, a link to the very important Soil Phosphorus Limits Project web page, and a Phosphorus Sources and Sinks analysis:

The latest AB Ag approach to analyzing nutrient transport in Alberta watersheds will soon be available in a series of reports that will be posted on an Alberta Agriculture and Forestry publications web page. This post will be updated when those documents are approved for release.

An important Sylvan Lake watershed question, not yet answered, is about the magnitude of annual N and P nutrient loading of the lake from the surrounding agricultural land. The AB Ag work provides the basis for addressing that lake nutrient loading issue. Attempts to estimate the phosphorus and nitrogen loads by measuring tributary water quality and cumulative flow have yielded unsatisfactory results. Consequently, knowledge of nutrient transport processes in the Sylvan Lake watershed are inadequate to allow due diligence predictions of the impact of urbanization on the scale imagined in municipal plans.

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