Catchment‐scale Phosphorus Export through Surface and Drainage Pathways

Abstract

The site‐specific nature of P fate and transport in drained areas exemplifies the need for additional data to guide implementation of conservation practices at the catchment scale. Total P (TP), dissolved reactive P (DRP), and total suspended solids (TSS) were monitored at five sites—two streams, two tile outlets, and a grassed waterway—in three agricultural subwatersheds (221.2–822.5 ha) draining to Black Hawk Lake in western Iowa. Median TP concentrations ranged from 0.034 to 1.490 and 0.008 to 0.055 mg P L−1 for event and baseflow samples, respectively. The majority of P and TSS export occurred during precipitation events and high‐flow conditions with greater than 75% of DRP, 66% of TP, and 59% of TSS export occurring during the top 25% of flows from all sites. In one subwatershed, a single event (annual recurrence interval < 1 yr) was responsible for 46.6, 84.0, and 81.0% of the annual export of TP, DRP, and TSS, respectively, indicating that frequent, small storms have the potential to result in extreme losses. Isolated monitoring of surface and drainage transport pathways indicated significant P and TSS losses occurring through drainage; over the 2‐yr study period, the drainage pathway was responsible for 69.8, 59.2, and 82.6% of the cumulative TP, DRP, and TSS export, respectively. Finally, the results provided evidence that particulate P losses in drainage were greater than dissolved P losses. Understanding relationships between flow, precipitation, transport pathway, and P fraction at the catchment scale is needed for effective conservation practice implementation. Core Ideas Single events accounted for the vast majority of annual P and total suspended solids export. Frequent, low‐depth events resulted in extreme P and total suspended solids losses. Particulate P losses in drainage waters can exceed dissolved P losses.

Catchment-scale export of antibiotic resistance genes and bacteria from an agricultural watershed in central Iowa

“…Catchment 15 has low mixed BMP coverage (21.4%) by at least one type of BMP and does not receive manure application, but drains effluent from the town of Breda, population 409, along with two AFOs that may contribute to bacteria inputs. Further hydrologic characterization can be found in [19].…”

“…Samples were collected at each site in 1 L high-density polyethylene (HDPE) bottles every two weeks in sampling year 2017 and every week in sampling year 2018. The following were the total number of samples collected at each site (2017 and 2018, respectively): S11 (16,33); ST12 (15,33); S15 (19,33); T8 (20, 33); EOC (0, 23). Surface water samples were collected at the mid-point of each stream channel in the highest velocity flow.…”

“…In the Great Lakes and Corn Belt states, 37% of cropland is artificially drained by tile drainage [17] to improve water infiltration, allowing machinery access to fields and improved root zone aeration for optimal crop growth among other benefits [18]. Although this has led to some of the most productive cropland in the world, tile-drainage has changed the natural hydrology of the region by increasing water flow to downstream catchments, consequently expediting the transport of pollutants to receiving waterbodies [19,20]. Tile-drainage may also facilitate the export of bacteria and AMR as found in previous studies [21,22,23].…”

Impact of stacked conservation practices on phosphorus and sediment export at the catchment scale

“…Harmel, Smith, King, and Slade (2009) estimated the median uncertainty in PO 4 -P concentrations to be ±19%, in TP to be ±23%, and in TSS to be ±18%; however, the uncertainty in dissolved constituents such as DRP receives much of the quality assurance focus due to holding times. Many other studies have reported similar challenges, including Brendel et al (2018), who conducted a study at this same location, although various DRP preservation and storage methods, such as acidification and refrigeration, have been used (Moore & Locke, 2013). Different lengths of holding time have also been reported in different studies (Royer, David, & Gentry, 2006;Sharpley et al, 2008;Stenberg et al, 2012).…”

Bioavailability of phosphorus of river sediments and its effect on growth of Selenastrum capricornutum

“…As algae may bind nitrogen, an increase in P-availability may trigger algal outbreaks. This has been observed in many cases to occur due to excessive fertilizer and manure applications For many aquatic systems, soil and particulate-P erosion together with runoff water are main sources of inputs of P to surface water (Brendel et al, 2019). Sediment pore water and desorption from its solid phase replenish P in overlying waters, and become available for consumption by aquatic organisms.…”