DOI: 10.5061/dryad.nzs7h4526
title: Effects of riparian grazing on distinct phosphorus sources

description: Riparian areas play an important role in maintaining water quality in
 agricultural watersheds by buffering sediment, nutrients, and other
 pollutants. Recent studies have shown that in some cases riparian areas
 are a net source of phosphorus (P) in cold climates. This study assessed
 the impact of cattle grazing or harvesting of riparian areas on the
 spatial and vertical distribution of water-extractable phosphorus (WEP).
 This study measured the WEP in four distinctive sources: biomass, litter,
 organic layer, and Ah horizon in three riparian locations extending from
 the edge of the waterbody to the field edge. In addition to a control,
 three treatments were examined: 1) grazing; 2) high-density grazing; and
 3) mowing. Prior to implementing the treatments, the Ah (0-10cm) soil was
 the largest pool of WEP (42.5 mg m-2, ~44%); however, the biomass (i.e.,
 standing vegetation) was a considerable proportion of the total (26.3 mg
 m-2, ~25%) WEP pool. The litter and organic layer had median WEP areal
 densities of 11.1 and 17.7 mg m-2, respectively. Findings revealed
 significant reductions in biomass WEP with median reductions of 10.4 and
 18.7 mg m-2 for high-density grazing and mowing treatments, respectively.
 This reduction was more pronounced in the lower riparian locations where
 there was more biomass available to be grazed or mowed. There were no
 detectable changes in the other sources of WEP across all the treatments.
 Assessment of the control plots (pre- and post-treatment) clearly indicate
 that there is considerable small-scale spatial variability in P
 measurements in riparian areas. Overall, the results of this study suggest
 that management practices that target vegetation, including harvesting and
 autumn short-term grazing, may be mechanisms to reduce the potential P
 loss during the snowmelt period. To fully assess the risk of P loss,
 studies investigating other important riparian processes that also have a
 demonstrated impact on P mobility, including freeze-thaw cycles and
 flooding, are needed.
description: A randomized complete block experimental design was used to
 assess the sources of riparian WEP and investigate how it changes
 following cattle grazing or mowing treatments. In addition to a control,
 the three treatments included grazing, high-density grazing, and mowing.
 Each treatment, including a control, was replicated in riparian areas
 surrounding four prairie potholes (wetlands). Samples of biomass, litter,
 organic layer, and Ah horizon, were collected in three locations both pre-
 and post-treatment. Four types of samples were
 collected: 1) biomass, 2) litter, 3) organic layer, and 4) Ah horizon.
 Using a 0.25 m2 quadrate, biomass was collected by cutting the standing
 live vegetation and litter by raking the surface and picking up the
 previous year’s growth. Both the biomass and litter were dried at 40 deg
 C, weighed, and homogenized using a blade grinder (&lt;1cm). A
 composite of five soil samples was collected within the same quadrat as
 the biomass/litter using a 19 mm diameter soil probe and was divided into
 the organic layer (1 – 2 cm deep) and the top 10 cm of the Ah horizon. The
 organic layer and Ah soil were air-dried, disaggregated with a mortar and
 pestle, and passed through a 2-mm sieve. Water
 Extractable Phosphorus (WEP), an environmental soil and vegetation P test,
 was used to infer soil P release into runoff water. Dried and homogenized
 samples were extracted by shaking (150 RPM) with deionized water for one
 hour at a mass-to-volume ratio of 1:30 for the biomass and litter samples
 (1 g) and 1:15 for the organic and Ah samples (2 g). Extractions were
 gravity filtered through a Whatman 42 filter followed by syringe
 filtration with a 0.45 micron nylon filter. WEP in the extract was
 measured spectrophotometrically by the colorimetric molybdate–ascorbic
 acid method. The concentration of WEP (mg kg-1) was
 calculated for all sources of P. In addition, the areal density of WEP was
 calculated for biomass and litter by combining WEP concentration with the
 mass of material collected from the quadrat. The vertical profile of WEP
 within the riparian area assessed from samples collected before treatments
 were implemented across the 3-year study. For comparison, an approximate
 estimation of areal density WEP in the organic layer and Ah was calculated
 using the bulk density and depth measurements. For
 additional information see
 https://github.com/alex-koiter/riparian-grazing-manuscript
description: ## Effects of riparian grazing on distinct phosphorus sources Alexander J
 Koiter*1 and Tamaragh Y Malone2 *corresponding author 1Brandon University,
 Department of Geography & Environment 270 18th St, Brandon, MB Canada,
 R7A 6A9 email: [koitera@brandonu.ca](mailto:koitera@brandonu.ca) ORCID:
 0000-0002-9355-9561 2Brandon University, Department of Biology, 270 18th
 St, Brandon, MB Canada, R7A 6A9 ORCID: 0009-0002-5887-5574 This manuscript
 has been accepted for publication at the Journal of Environmental Quality.
 A preview of the manuscript, including notebooks for analysis, can be
 found at
 [https://alexkoiter.ca/riparian-grazing-manuscript](https://alexkoiter.ca/riparian-grazing-manuscript/) ## Data Overview The data sets and accompanying Quarto (.qmd) files used in this publication can be found in the [notebooks](https://github.com/alex-koiter/riparian-grazing-manuscript/tree/main/notebooks). 1. **P_concentration.csv** contains the Water Extractable P concentration for each sample. * sample_type - Samples of four distinctive sources of P were collected and characterized (Biomass, Litter, Organic Layer, Ah horizon) * site - Samples were collected in four separate riparian areas (1-4) * timing - Samples were collected before and after application of the treatment * plot - Each site was subdivided into four plots (a-d) * location - Samples were collected at three topographic positions within the riparian area (upper, mid, low) * p_content - Water Extractable P concentration (mg kg^-1) * year - Year in which samples were collected (2019 - 2021) * treatment - Project consisted of three treatments and a control (Control, graze, high graze, mow) 2. **mass.csv** contains the dry mass for the biomass and litter samples * sample_type - Samples of four distinctive sources of P were collected and characterized (Biomass, Litter, Organic Layer, Ah horizon) * site - Samples were collected in four separate riparian areas (1-4) * timing - Samples were collected before and after application of the treatment * plot - Each site was subdivided into four plots (a-d) * location - Samples were collected at three topographic positions within the riparian area (upper, mid, low) * dryweight - total mass collected from a 0.25 m^-2 quadrat (grams) * year - Year in which samples were collected (2019 - 2021) * treatment - Project consisted of three treatments and a control (Control, graze, high graze, mow) 3. **bulk density.csv** contains the bulk density measurements for the organic layer and Ah horizon samples (only measured in 2023) * sample_type - Samples of four distinctive sources of P were collected and characterized (Biomass, Litter, Organic Layer, Ah horizon) * site - Samples were collected in four separate riparian areas (1-4) * plot - Each site was subdivided into four plots (a-d) * location - Samples were collected at three topographic positions within the riparian area (upper, mid, low) * bd - Soil bulk density (kg^m-3) * treatment - Project consisted of three treatments and a control (Control, graze, high graze, mow) 4. **Forrest-Daily-TempRain.csv** contains weather data from the onsite weather station (located near Forrest, MB) operated by [MB Agriculture.](https://www.gov.mb.ca/agriculture/weather/manitoba-ag-weather.html) * Date (yyyy-mm-dd) * Temp - daily average (°C) * Rain - daily cumulative rainfall (mm) 5. **Foliar cover 2019.xlsx** contains all the plants species ID collected in 2019. Data collected by the [MB Beef and Forage Initiatives](https://www.mbfi.ca/) * Date - date collected (mm/dd/yyyy) * Site - Samples were collected in four separate riparian areas (1-4) * treatment - Project consisted of three treatments and a control (Control, Graze, High graze, Mow) * location - Samples were collected at three topographic positions within the riparian area (upper, mid, low) * All remaining columns are the percent (%) cover of plant species (Latin name) often found in the region. Empty cells can be considered NA's ## Funding This project was undertaken with the financial support of the Government of Canada through the federal Department of Environment and Climate Change and a Lake Winnipeg Basin Program grant awarded to the [Manitoba Association of Watersheds](https://manitobawatersheds.org/). Additional research funding was provided through a [Brandon University Research Committee](https://www.brandonu.ca/research/funding/internal-funding-information/burc/) grant awarded to AK.