Over two years from 2016 to 2017, water flow and phosphorus concentrations were measured in 12 tile drain systems in the Jewett Brook watershed, which drains to St. Albans Bay of Lake Champlain. Using a sampling approach that collected water in proportion to the water flow amount, this study was able to estimate the phosphorus load (mass of phosphorus per time) of phosphorus leaving each tile drainage system. The study also put these measurements into context to estimate how much of Jewett Brook’s phosphorus load can be attributed to agricultural tile drains.
Tile (subsurface) drainage on agricultural fields allows timely equipment access, reduced soil compaction, and increased crop yields on fields that would otherwise be too wet to efficiently farm. Tile drainage also significantly alters field hydrology by reducing surface runoff and increasing subsurface discharge. Reports in the scientific literature suggest that discharge from subsurface drainage systems can be a significant source of phosphorus to surface waters.
Although annual tile water flow was positively correlated with field size, phosphorus concentrations in tile drain water did not vary significantly with field size or water flow. This is contrary to reports from other areas found in the literature review. In addition, there was no clear seasonal pattern in the proportion of phosphorus in dissolved form when using data aggregated from all 12 sites.
This study confirms that tile drains are important contributors of phosphorus in the Jewett Brook watershed, and that particulate and dissolved phosphorus can both be significant fractions of phosphorus in tile drainage water. Tile drains are the focus of several Lake Champlain Basin Program funded research projects in recent years. More results from other studies will be posted on this blog soon.