18-Env-B6 Agricultural Waste Management · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, December 2019 — 18-Env-B6, Agricultural Waste Management (3 hours, open book, all 15 questions to be attempted, 100 marks total).
Reference texts: Rynk et al., On-Farm Composting Handbook (NRAES-54); OMAFRA, Nutrient Management Act, 2002 and O. Reg. 267/03 / Nutrient Management Protocol (NMAN); Metcalf & Eddy, Wastewater Engineering (anaerobic digestion chapter); ASABE Standards (manure storage, land application equipment); Environment and Climate Change Canada / Canada–Ontario Lake Erie Action Plan.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Lake Erie's water-quality concern is dominated by one mechanism: excess phosphorus loading driving recurring, sometimes toxic, harmful algal blooms (HABs) in the western basin, most visibly the annual Microcystis blooms that have on occasion shut down municipal drinking-water intakes (e.g., the 2014 Toledo water crisis). The main reasons manure application specifically contributes to this problem are:
1. Soluble reactive phosphorus (SRP) from surface-applied manure. Unlike particulate P, the soluble fraction is immediately bioavailable to algae once it reaches the lake, and surface-broadcast (unincorporated) manure leaves a P-rich film directly exposed to the next runoff event — a growing share of Lake Erie's P load is now SRP rather than particulate P, which is the opposite trend from what soil-erosion-control programs alone can fix.
2. Application to frozen, snow-covered or saturated ground. When the ground cannot infiltrate, manure and its P content sit on the surface until snowmelt or the next rain generates rapid overland flow with very little soil contact/adsorption — this is exactly the condition Ontario's winter-application restrictions (Question 7) are designed to prevent, and non-compliance or poorly-timed application is a direct driver of acute SRP loading events.
3. Tile-drainage short-circuiting (macropore flow). As in Question 4, manure and its dissolved P can bypass the soil profile entirely through cracks and biopores into subsurface tile drains, which discharge directly to field ditches and ultimately the Lake Erie tributary network (Maumee, Thames, Grand rivers) — tile drainage is now recognized as a major, historically under-appreciated SRP pathway across the basin's heavily tile-drained agricultural land.
4. The basin's own hydrology and morphology. Lake Erie is the shallowest and warmest of the Great Lakes with a relatively short water-residence time and a large, intensively farmed agricultural watershed feeding a comparatively small lake volume — the same nutrient load has a much larger per-litre impact here than it would in a deeper, larger-volume lake, and shallow warm water is itself more favourable to cyanobacterial bloom formation.
Canada and the U.S. jointly recognize this problem: the Great Lakes Water Quality Agreement (Annex 4) sets a binational target of a 40% reduction in total and soluble reactive phosphorus loading to the western and central basins, and the Canada–Ontario Lake Erie Action Plan directs agricultural nutrient-management measures (the same incorporation, timing and setback practices discussed in Questions 1, 4 and 7) specifically at this target.
