18-Env-B6 Agricultural Waste Management · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, May 2018 — 04-Env-B6, Agricultural Waste Management (3 hours, open book, all 16 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); Ontario Environmental Protection Act and Ontario Water Resources Act; Canada–Ontario Lake Erie Action Plan / Great Lakes Water Quality Agreement Annex 4.
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 western and central basins have experienced recurring, large-scale harmful algal blooms (cyanobacteria, dominated by Microcystis) over the past two decades, driven primarily by excess phosphorus loading — and the basin's dense concentration of row-crop and livestock agriculture makes manure and fertilizer application the single largest controllable P source. Two features of the basin make manure application specifically, rather than agriculture in general, the focal concern:
Dominance of DISSOLVED reactive phosphorus (DRP), not just total P. Cyanobacteria preferentially use the immediately bioavailable dissolved fraction, and monitoring in the Maumee and other western-basin tributaries has shown DRP loads rising even where total P loads have been stable — the opposite of what soil-erosion-focused P control alone would predict. Manure applied to the SURFACE without incorporation, especially on the basin's extensive tile-drained clay soils, is disproportionately implicated because surface-applied nutrients are readily mobilized by the very next rain and travel to tile drains through preferential/macropore flow (Question 4) — a fast pathway that never lets the P sorb onto soil the way infiltrating, incorporated nutrients would.
Winter and freeze-thaw application on frozen or snow-covered ground. When manure is applied (or was historically applied) to frozen ground with no infiltration capacity, essentially the entire surface load is available to spring snowmelt runoff with minimal soil contact time, making this timing the single highest-risk manure-related loss pathway in the basin.
The combined effect is targeted specifically by the Canada–Ontario Lake Erie Action Plan (under the Great Lakes Water Quality Agreement, Annex 4), which sets a 40% phosphorus-load reduction target for the western basin and directs measures at exactly these two manure-application practices: incorporation/injection rather than surface broadcast, and prohibition or tight restriction of application on frozen/snow-covered/saturated ground.
