Ground water and surface water interactions are of fundamental importance for the biogeochemical processes governing phosphorus (P) dynamics in riparian buffers. The four most important conceptual hydrological pathways for P losses from and P retention in riparian buffers are reviewed in this paper: (i) The diffuse flow path with ground water flow through the riparian aquifer, (ii) the overland flow path across the riparian buffer with water coming from adjacent agricultural fields, (iii) irrigation of the riparian buffer with tile drainage water from agricultural fields where disconnected tile drains irrigate the riparian buffer, and (iv) inundation of the riparian buffer (floodplain) with river water during short or longer periods. We have examined how the different flow paths in the riparian buffer influence P retention mechanisms theoretically and from empirical evidence. The different hydrological flow paths determine where and how water-borne P compounds meet and interact with iron and aluminum oxides or other minerals in the geochemical cycling of P in the complex and dynamic environment that constitutes a riparian buffer. The main physical process in the riparian buffer-sedimentation-is active along several flow paths and may account for P retention rates of up to 128 kg P ha(-1) yr(-1), while plant uptake may temporarily immobilize up to 15 kg P ha(-1) yr(-1). Retention of dissolved P in riparian buffers is not as pronounced as retention of particulate P and is often below 0.5 kg P ha(-1) yr(-1). Several studies show significant release of dissolved P (i.e., up to 8 kg P ha(-1) yr(-1)).

Findings concerning P removal in buffer zones (BZs), constructed wetlands (CWs), and ponds in Finland, Norway, Sweden, and Denmark are presented in this paper because most such studies have been published only in Nordic languages. Retention of P was tested in 11 BZs, four CWs (less than 0.5‐m deep and vegetated with macrophytes), and seven ponds (deeper than 0.5 m). The grass buffer zone (GBZ) and vegetated buffer zone (VBZ) plots were compared with plots without a BZ; and P retention in CWs, ponds, and some BZs was estimated by subtracting total phosphorus (TP) mass in the outlet from TP mass in the inlet. Buffer zones decreased loads of TP from agricultural runoff water by 27 to 97% (0.24–0.67 kg ha−1 yr−1). The retention as a percentage increased with increasing BZ width. The BZ's upper part was, however, most effective in mitigating TP mass loads (1.6–4.4 g m−2), due to the importance of sedimentation as a retention process. The ponds and CWs reduced TP loads by 17 and 41%, respectively (2–116 g m−2 yr−1). The retention increased with the surface‐area/watershed‐area ratio. CWs were more effective in retaining TP than were ponds, possibly due to shallower depths and dense vegetation. The retention of dissolved reactive phosphorus (DRP) was inconsistent, both in BZs and in CWs. Vegetation should be harvested in BZs to decrease the DRP losses. Harvesting of vegetation is not recommended in CWs.

Background: Agriculture can have substantial negative impacts on the environment. The establishment and management of vegetated strips adjacent to farmed fields (including various field margins, buffer strips and hedgerows) are commonly advocated mitigation measures for these negative environmental impacts. However, it may be difficult to obtain reliable evidence on the effects of implementation and management of vegetated strips, even though a substantial body of evidence exists. We describe a systematic map of research relating to vegetated strips in boreotemperate farming systems to answer the question: What evidence exists regarding the effects of field margins on nutrients, pollutants, socioeconomics, biodiversity, and soil retention in boreo-temperate systems?Methods: We searched 13 bibliographic databases, 1 search engine and 37 websites of stakeholder organisations using a predefined and tested search string focusing on a comprehensive list of English language vegetated strip synonyms. Searches in Danish, Finnish, Spanish, and Swedish were also conducted using web searches. We screened search results at title, abstract and full text levels, recording the number of studies deemed non-relevant (with reasons at full text). A systematic map database of meta-data (i.e. descriptive summary information about the settings and methods) for relevant studies was produced following full text assessment. The systematic map database is provided as an evidence atlas: interactive, web-based geographical information system. Results:Over 31,000 search results were identified, resulting in a total of 1072 relevant primary research studies and 130 evidence reviews. Articles used a variety of terminology to describe vegetated strips, with 'field margin' , 'hedgerow' , 'shelterbelt' and 'riparian buffer' most common. The volume of primary research is increasing linearly year-by-year, whilst the increase in reviews has tailed off in the last 10 years. The USA and UK were most frequently studied and reviewed. Arable systems were investigated in c. 70% of primary research but 50% of reviews. Some 50% of primary research vegetated strips were field edge and 25% riparian, whilst riparian and field edge strips were roughly equally the focus of around a half of all described strips in reviews. Terrestrial biodiversity, nutrients (nitrogen and phosphorus) and soil/water loss or retention were the most commonly measured outcomes in primary studies and reviews, although some other outcomes were more common in reviews than research articles (e.g. pesticides). Conclusions:We identified substantial bodies of evidence on particular sets of related outcomes and ecosystem services, which constitute important knowledge clusters/synthesis gaps relating to: strip width, terrestrial biodiversity, nutrient retention, hydrological regimes, toxic substances, erosion protection, pests, carbon sequestration, and soil and biodiversity combined. We also identified key knowledge gaps relating to: climate regulation, freshwater biodiversity, stri...

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Buffer zones, established between agricultural fields and water bodies, are widely used as a measure to reduce N in surface runoff and groundwater. However, the literature indicates inconsistent results on the N removal efficiency of buffer zones between studies. We performed a weighed meta-analysis on the buffer zone effects on NO 3 -N and total N in surface runoff and groundwater by summarizing 46 studies published between 1980 and 2017. The overall effects of buffer zones were a 33 (−48 to −17%, n = 25) and 70% (−78 to −62%, n = 38) NO 3 -N reduction in surface runoff and in groundwater, respectively, compared with controls with no buffer zone. In addition, buffer zones reduced the total N in surface runoff by 57% (−68 to −43%, n = 16). The effects of buffer zones on N retention were consistent across continents and in different climates. Nitrogen retention increased with increasing initial N concentrations discharged from the source of pollution. According to a meta-regression, the N removal efficiency in surface runoff decreased in consort with increasing buffer zone age. Otherwise, the meta-analysis revealed no effects of buffer zone characteristics such as the width or species number (for grass buffer zones) on the N retention in surface runoff and groundwater. Unlike groundwater quality, which responded equally well regardless of the source of pollution, buffer zone type, or buffer zone age, surface water quality is more sensitive, and it might not be satisfactorily improved by tree buffer zones or aged buffer zones, or when the source of pollution originates from grass production fields.