Abstract
BackgroundSoil-based on-site wastewater treatment systems (OWSs) are suspected to contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). However, along the flow path between the facilities and surface waters, different processes contribute to delay the transport of phosphorus through the ground. This may reduce the unwanted impact on receiving water bodies. However, the strength and significance of this so-called soil retention remains unclear.In Sweden, there are nearly one million OWSs. To protect surface waters, a high P removal rate (up to 90%) is often required by the local municipalities. However, since these requirements may have costly consequences to property owners, it is debated as to whether they are too strict. In this debate, it is often claimed that the retention of P occurring in natural environments may be underestimated by authorities. Accordingly, there is a need for a scrutiny of the available evidence related to soil retention of phosphorus from OWSs. This is the objective of the planned systematic map. Focus will be on boreal and temperate climate zones.MethodsSearches will be made for peer-reviewed articles and grey literature using bibliographic databases, search engines, specialist websites and stakeholder contacts. The references will be screened for relevance according to a predefined set of eligibility criteria. At stage one, after testing and clarifying the eligibility criteria, the references will be single-screened based on title and abstract. At stage two, potentially relevant references will be screened in full-text independently by two reviewers. We will compile a detailed database of the relevant studies. Moreover, a narrative report will be produced, describing the research landscape in general terms. This will be carried out with a conceptual model, describing the processes involved in P retention in natural environments, as a foundation. It will be discussed where the respective studies/study types fit into the conceptual model, and also evaluated how each study/study type can be related to the overarching question of eutrophication. Moreover, we will describe identified knowledge gaps that warrant further primary research effort, as well as identified knowledge clusters that could be suitable for systematic reviews.
Highlights
Soil-based on-site wastewater treatment systems (OWSs) are suspected to contribute to eutrophication of surface waters, due to the discharge of phosphorus (P)
On‐site wastewater treatment systems On-site wastewater treatment systems (OWSs) are facilities used for the disposal of wastewater from households that do not have access to a public wastewater treatment plant
An OWS consists of a septic tank in which sludge and pathogens are removed, and a subsequent soil treatment system, where the wastewater is further purified from e.g. phosphorus, nitrogen and pathogens
Summary
The systematic map will follow the Environmental Evidence Guidelines and conforms to the ROSES standards (see Additional file 1). The search strings used will be adapted to the specific syntax in each database Since this systematic map will include field studies as well as laboratory soil-column studies (for motivation, see under Eligibility criteria) we have developed two different search strings. Article screening and study eligibility criteria Screening process After removal of duplicates, the references will be screened for relevance based on title and abstract. Eligible study types We will include field studies (including surface water monitoring studies) and laboratory studies based on soil column experiments. Given the expected large amount of studies to be included in the systematic map, and given the large amount of different kinds of data suggested to be coded for each study, we will not be able to contact authors if any of these suggested data types is missing or unclear. Final prioritization of primary research questions as well as of systematic review questions needs thorough engagement with stakeholders and is beyond the scope of this systematic map
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