Using the Provenance of Sediment and Bioavailable Phosphorus to Help Mitigate Water Quality Impact in an Agricultural Catchment

Abstract

The quality and health of surface waters can be impaired by sediment and sediment-bound phosphorus (P). The Waituna Lagoon catchment in southern New Zealand has undergone agricultural intensification that has been linked to increases in sediment and sediment-bound bioavailable P (BAP) in the lagoon. Time-integrated samplers trapped suspended sediment from the water column, and their geochemical signature was compared with likely sources (stream banks, stream beds, topsoil, and subsoil) in each of the lagoon's contributing streams and rivers. The proportion of BAP, but not necessarily total P, within trapped sediment was much greater in samples from the Moffat and Carran Creeks than from the Waituna Creek, probably due to the erosion of organic-rich soils that had little capacity to retain P compared with the more mineral soils of the Waituna Creek. Annually, most BAP and sediment came from bank erosion, and strategies such as fencing out stock should focus on minimizing this throughout the catchment. However, when considering losses in space and time relative to the impact on the Waituna Lagoon, strategies the Waituna Creek catchment should also minimize contributions from topsoil in winter-spring, whereas in the Carran and Moffat Creek catchments strategies need to decrease P inputs (e.g., effluent) to Organic soils likely to lose much BAP in summer-autumn when the impact on the Lagoon is quickest. This study highlighted the need to identify sources and timings of BAP and sediment loss before recommending mitigation practices, which without this information may be slow or not succeed.

Assessing the Yield and Load of Contaminants with Stream Order: Would Policy Requiring Livestock to Be Fenced Out of High‐Order Streams Decrease Catchment Contaminant Loads?

“…These strategies may also be beneficial and act as insurance against the failure of fencing to mitigate contaminant losses. For example, much anecdotal evidence highlights erosion of stream banks and SS loss where fencing is only temporary (McDowell et al, 2016b). Furthermore, contaminant losses can be exacerbated where significant deposition of excreta is associated with stock traffic (e.g., fenceline pacing by red deer) and ephemeral channels carry excreta to the stream (McDowell, 2009).…”

Dissolved Reactive Phosphorus Loads to Western Lake Erie: The Hidden Influence of Nanoparticles

“…The transport of both PP and dissolved P in rivers is complex and can be affected by numerous variables. Phosphorus can originate from various sources in a watershed (Grundtner et al, 2014; McDowell et al, 2016), and numerous studies have shown that P can transform between dissolved and particulate along the course of a river (Reddy et al, 1999; Withers and Jarvie, 2008). Furthermore, P may also be affected by legacies of land use management, which can affect retention and remobilization of P along the continuum from soils to rivers to lakes (Sharpley et al, 2013).…”

Soil phosphorus fractions in aggregate size classes in southwestern China

“…Soil erodibility is linked to aggregate stability that is considered an important indicator of soil physical quality. As the fine soil particles are susceptible to loss by erosion, bioavailable P attached to such particles is believed to have a negative impact on water quality (McDowell et al ., ; Salm et al ., ). The distribution and bioavailability of soil P associated with different aggregate size classes are strongly controlled by the form of P applied and soil texture (Geisseler et al ., ; Ahmed et al ., ).…”